Skip to main content

Full text of "Foundations of psychology"

See other formats



Digitized by the Internet Archive 

in 2010 with funding from 

Lyrasis Members and Sloan Foundation 




By Edwin G. Boring, Herbert S. Langfeld, and Harry P. Weld 

By Edwin G. Boring, Herbert S. Langfeld, and Hakky P. Weld 

By Daniel Katz and Richard L. Schanck 

By S. Smith Stevens and Hallowell Davis 

By Aaron J. Rosanoff 
OGY. Fourth Edition 

By C. B. Davenport and Merle P. Ekas 

By P. T. Young 

By Edwin G. Boring, Herbert S. Langfeld, and Hakry P. Weld 

By John G. Jenkins 

Advisory Editor 


By Alphonse Chapanis, W. R. Garner, and C. T. Morgan 

By Ernest Glen Wever 

By QuiNN McNemar 

T. G. Andrews, Editor 

By MuzAFER Sherif and Hadley Cantril 

Leonard Carmichael, Editor 

By P. T. Y'oung 


By James Grier Miller 

By Fred McKinney 

By Hadley Cantril 




Edwin Garrigues Boring 


Herbert Sidney Langfeld 


Harry Porter Weld 




Copyright, 1948 


John Wiley & Sons, Inc. 

All Rights Reserved 

i?his book or any part thereof must noi 
be reproduced in any Jorm wiil.oui 
'he. vtrilten permission of the publisher. 





Fordham University 


Yale University 




Cornell University 

Harvard University 

Princeton University 



Tufts College 

Princeton University 

U. S. Naval Medical Research Laboratory 
at New London 


University of Virginia 


Cornell University 


Northwestern University 


University of California 


The Johns Hopkins University 




Harvard University 

Brown University 

Cornell University 


Teachers College, Columbia University 


Ohio State University 


Harvard University 

THE strongest evidence of the rapid advance of psychology is the need of 
frequent revisions of textbooks. It is nine years since our last book, Intro- 
duction to Psychology, was published. In the meantime we have had a long war 
and a victory which psychological research helped attain. In this wartime re- 
search much new and valuable knowledge came into being. In addition there 
has been the more normal acquisition of facts as well as a clearly distinguishable 
change in point of view. This advance in our science had to be covered in a 
revision, but we soon found that instead of a revision we were going to have a 
book so nearly new that it needed a new title. And so we present here the third 
book that has appeared under our combined editorship. 

To describe in detail the changes in this book over the last would be to tie- 
scribe a large part of its contents. We must confine ourselves to indicating a 
few of the more significant differences. It is about twice as large as the 
Introduction of 1939. Approximately 80 per cent of the material is either new 
or freshly described. What has been taken from the previous book has been 
re-edited. There are eighteen contributors, of whom fifteen are new. A num- 
ber of new chapters have been added, two of which introduce the student to 
problems of personal adjustment. Some of the material of the old chapters has 
been differently distributed among the chapters of this book. Some of the 
topics have been given more detailed treatment; no material of importance 
has been omitted. There are also a large number of new illustrations, and 
many of the old ones have been redrawn. In selecting the illustrations we 
have intended to include only those which we feel would help the student 
to understand the text. 

The order of the chapters is completely changed. In our first book ^ve hcUl 
to the conventional arrangement of sensation at the beginning and thought ami 
personality at the end. In the second book \\'e reversed this order. \\'e had a 
principle in mind with each book: synthesis in the first order, analysis in the 
second; but we must confess to a certain dependence on trial and error. Now. 
with the trials and, we hope, the errors past, and giving attention to the opnuons 
expressed by some teachers of introductory courses, we present Avhat is partly a 
compromise between the two orders and partly a reflection of psychology's 


changed orientation. In 1948 the important thing about the organism is not 
that it is conscious, btit that it reacts to stimuhition. So .we are having the book 
start with response— its nature, its mechanics, its maturation, its dependence on 
moti\e. After that the student is prepared to study learning as change in the 
organism's response repertoire, and then perception as a form of the organism's 
adjustment to its physical environment. Such an approach leads on naturally 
to the study of the facts of individual difference, to the problems of human 
efficiency and personal adjustment, and finally to the understanding of attitudes 
and social relations. 

The amount of necessary editing has varied considerably. Some chapters 
remain very much as they were presented by the collaborator. Some had to be 
rewritten. In several instances we transferred material from one chapter to 
another. Some material was deleted, some new material added. For the sake 
of unity and style all chapters had to undergo at least some changes by the 
editorial pen. 

From this explanation the reader will see the reason for the wording of our 
acknowledgment of the authorship of each of the chapters. We as editors must 
assume responsibility for any errors that may have occurred in the text. We wish, 
on the other hand, to give full credit to the collaborators for their contributions 
to this book and to thank them for their generous cooperation, which we realize 
was motivated by their loyalty to their science. 

We are also grateful to our former collaborators, all of whom helped to make 
this book possible. They are C. W. Bray, J. G. Beebe-Center, "Warner Brown, 
D. W. Chapman, K. M. Dallenbach, H. B. DeSilva, S. Feldman, Norman Fred- 
eriksen, George Humphrey, Daniel Katz, Carney Landis, R. B. MacLeod, J. A. 
McGeoch, C. C. Miles, D. McL. Purdy, M. A. Tinker, E. G. Wever and M. J. 
Zigler. We note a special debt to Dr. Wever for his continued advice. 

We acknowledge an especial debt of gratitude to the secretarial staff of the 
Harvard Psychological Laboratories, who retyped entirely the much-edited manu- 
script; to Elizabeth MacLeod, who administered the retyping and its proofing; 
to Robert S. Harper of Harvard University, who, with some assistance from 
Mabel Mills, prepared the figures for our publisher's artist; and to Helen Orr 
of Princeton University, who lent us her very considerable editorial experience 
in reading both manuscript and proofs. 

E. G. B. 
H. S. L. 
H. P. W. 

January 11, 19-lS 

N T E N 

1. The Nature of Psychology 1 

Behavior and Consciousness: Behavior; Consciousness. Origins of 
Scientific Psychology. Schools of Psychology: Introspective Psy- 
chology; Functional Psychology; Behaviorism; Gestalt Psychology; 
Modern Psychology. Fields of Psychology. Scientific Method: Ex- 
periment; Control; Hypothesis. Definitions. References. 

2. The Response Mechanism 19 

Differentiation of the Response Mechanism: The Stimulus; Evolu- 
tion of the Response Mechanism; The Effectors; Endocrine Ef- 
fectors; The Receptors; The Adjusters. Structure and Function 
of Neurons: Stimulation; Mechanisms of Intensity; Synaptic Con- 
nections. Structure of the Nervous System: The Efferent Peripheral 
Nervous System; The Autonomic Nervous System. Functions of 
the Brain: Localization in the Brain. References. 

3. Response ^^ 

Varieties of Behavior: Locomotion and Manipulation; Tropisms 
and Reflexes; Conditioned Response; The Reflex Circle; Condi- 
tioned Voluntary Responses. Motivated Behavior: Instinct; Needs 
and Activity; Problem-Solving Behavior; Covert Behavior; Set and 
Readiness. Voluntary and Automatic Behavior: The Will; Volun- 
tary Control of Movement; Reflexes, Conditioned Responses and 
Voluntary Acts; Voluntary Acts and Learning. Acts and Ideas: 
Ideomotor Action; Empathy; Suggestion; Hypnotism. Reaction: 
Reaction Time; Simple Reactions; Sensory and Motor Reactions; 
Discrimination and Choice Reactions; Word Reactions; Practical 
Use of Reaction Experiments. References. 

4. Growth and Development 64 

Growth, Development and Maturation: Conditions of Growth; 
Integration and Maturation; The Nervous System as Integrator. 
Growth and Development before Birth: The Beginning of Human 
Growth; Rates of Prenatal Growth. Growth after Birth: Types of 
Growth; Maturity. Maturation at Birth: The Neonate in a New 
Environment; Reflexes in the Neonate; Maturation of the Recep- 
tors; Maturation of Emotion. Maturation after Birth: The Matura- 


tion of Adaptive Behavior; Norms of Early Development; Matura- 
tion of Ability to Learn; Maturation of Speech and Language. 
Adolescence, Adulthood and Old Age: Puberty and Adolescence; 
Adulthood; Old Age; The Trajectory of Life. References. 

5. Feeling and Emotion 90 

Pleasantness and Unpleasantness: Affective Value of Stimuli; The 
Relativity of Hedonic Tone; Dependence of Learning upon He- 
donic Tone; Hedonism. Emotion: Visceral Reactions and the 
Autonomic Nervous System; Direct Action of the Nervous System; 
Peripheral Response and Expressive Behavior; Facial Expression in 
Emotion; The Startle Pattern; The Emotional Consciousness; Emo- 
tion and Learning; The Genetic Development of Emotion. Specific 
Emotions: Smiling, Laughing and Crying; Fear; Anger. The Meas- 
urement of Emotion: The Galvanic Skin Response; Blood Pressure 
Changes; Rating Scales; Observational and Psychoanalytic Tech- 
niques; Questionnaire Methods. Disorders of Emotion: Patho- 
logical Conditions; Functional Disorders; Psychosomatic Medicine. 
Hygiene of Emotion. References. 

6. Motivation 112 

Needs: Distinction among Needs; Needs, Structure and Environ- 
ment. The Physiological Basis of Behavior: Hunger Drive; Sex 
Drive; Other Drives; Behavior and Structure; Needs for Particular 
Foods; Derived Needs. Behavior as Dependent on the Environ- 
ment: Relation of Environment to Needs; Incentives; Cultural 
Determination of Needs. Definition of Need. Measurement of 
Needs: Obstruction Method; Learning Method. Some Effects of 
Need: Effect on Perception and Imagination; Effect on Sensitivity; 
Effect on Persistence; Frustration Tolerance. Individual Differ- 
ences in Respect of Needs. References. 

7. Learning 138 

Associative Learning: Conditioning; Factors Affecting Condition- 
ing; Conditioned Emotional Responses; Anticipatory Function 
of Conditioned Responses; The Law of Contiguity. Trial-and- 
Error Learning: The Law of Effect. The Role of Motivation in 
Learning. The Effect of Practice: Plateaus; Insight; Physiological 
Limits; The Law of Frequency. Other Factors Affecting the Effi- 
ciency of Learning: The Learner; Kind of Material; Distribution 
of Practice; Whole or Part Learning; Verbalization; Active Partici- 
pation; Recitation. Acquisition of Skills: Basic Principles in the 
Acquisition of Skills. References. 


8. Retention and Transfer of Learning 167 

Retention and Forgetting: How Retention Is Measured; Individual 
Dirtercnces in Retention; The Exceptional Memori/xr; Retention of 
Different i ypes of Material; Retention as Affected fjy Original 
Learning; Reminiscence. Cause of Forgetting: Retroactive Inhi- 
bition; Alteration of Stimulating Conditions; Change of Set. Un- 
learning: Overcoming Fears; Breaking Habits. Transfer of Learn- 
ing: Formal Discipline; A Transfer Experiment; Transfer within 
the Same Class; Bilateral Transfer; Fransier from One Class to 
Another; Positive versus Negative Fransier. Efficient Study: Moti- 
vation; Planning; Reading Habits; Meaningfulness; Active Par- 
ticipation. References. 

9. Recollecting, Imagining and Thinking 185 

Recollecting: Eidetic Images; Recollection and Perception. Re- 
liability of Recollection: Reliability of Testimony; Changes in 
Recollection with Lapse of Time; Nature of Errors in Recollec- 
tion; Failures of Recollection. Types of Recollection. Imagining: 
Imagination and Perception. Thinking: Important Tools of 
Thinking; Language; Reading; The Problem and the Set; Trial- 
and-Error and Insight. Incorrect Thinking: Fallacies; Wishful 
Thinking; Hunches; Word Fallacies; Motivation; Tacit Assump- 
tions; Atmosphere Effect; Habitual Methods of Attack; Faulty 
Transfer of Method; Individual Differences. How to Think. Ref- 

10. Perception 215 

The Definition of Perception. Change Is the Basis of Perception. 
Perception Is Selective. Perceiving Is Organized. What Is It That 
We Perceive? The Simplest Perception— Figure on a Ground. Ob- 
jects Are Our Commonest Perceptions. The Constancy of Objects: 
Size Constancy; Whiteness Constancy; General Explanation of Con- 
stancy. The Framework of Perception— Space. The Framework of 
Perception— Time. Temporal Patterns: Short Intervals; Rhythm. 
Orientation in Time. References. 

11. Sensation and Psychological Measurement 250 

Sensation Is the Core of Perception. Stimulus and Attributes: 
Stimulus; Attributes of Sensation; Quality; Intensity. Psycho- 
physics: Psychophysical Problems and Methods. Scales of Meas- 
urement. Statistics and Measurement: Central Tendency: \'aria- 
bility. Thresholds. The Weber Fraction. References. 

xii Contents 

12. Color 

Characteristics of Colors: Color Names; Unique Colors; The Color 
Equation; The Color Pyramid; Chromatic and Achromatic Colors. 
The Stimulus to Color: Nature of the Stimulus; Dependence of 
Color on Its Stimulus; Purity and Saturation; Sensation versus 
Stimulus. Color Mixture: Laws of Mixture; Methods of Mixture; 
Colorimetry. Color Phenomena: Adaptation; Afterimages; Con- 
trast; Indirect Vision; Color Blindness; Night Vision. Physiology 
of Color Vision: Duplexity of Retinal Function. References. 


13. Visual Space Perception 

Visual Perception of the Third Dimension: Implicit Clues; Motor 
Context; Retinal Disparity; Stereoscopy. Visual Perception of Size: 
Perceived Size and Perceived Distance; Perceived Size and Sur- 
rounding Objects; Visual Acuity. Visual Perception of Movement: 
General Conditions for Perceived Movement; Afterimages of Move- 
ment; Perceived Movement with a Moving Stimulus; Perceived 
Movement with Stationary Stimuli. References. 


14. Hearing 

Stimulus for Hearing: Sound Waves; Simple Waves and Complex 
Waves; Fourier Analysis; Analysis by Resonance; Sine Waves; Har- 
monics. Sounds— What We Hear. Pitch: Pitch and the Sound 
Wave; Pitch Thresholds; The Scale of Pitch. Loudness: Loudness 
Thresholds; The Scale of Loudness. Interaction of Stimuli: Beats 
and Combination Tones; Masking. How the Ear Works: The 
Outer Ear; The Middle Ear; The Inner Ear; How the Cochlea 
Works. Localization of Sounds: Binaural Clues; Secondary Clues. 
Deafness. Music. Communication: Speech Sounds; Sound Pattern 
in Speech; Perception and Speech. References. 


15. Taste and Smell 

Taste, Smell and the Common Chemical Sense. Taste: Primary 
Tastes; Sensitivity; Adaptation; Physiological Effects. Smell: Pri- 
mary Odors; Sensitivity; Adaptation; Physiological Effects; Odor 
Mixtures and Blends. References. 


16. Somesthesis 

Cutaneous Sensibilities: The Skin and Its Receptors; Exploration 
of the Skin Surface. Pressure Sensitivity: Perception of Vibration; 
Pressure Adaptation; Localization of Pressures; Receptors for Pres- 


Contents xiii 

sure. Pain Sensitivity: Pain Adaptation; Pathways for Pain; Pain 
Receptors. Temperature Sensitivity: Skin Temperature: Physio- 
logical Zero and Adaptation; Paradoxical Cold and 'Heat'; Recep- 
tors for Temperature. Kinesthesis: Kinesthetic Receptors. Organic 
Sensibility: Hunger and Appetite; Thirst. Ecjuilibrium: The Semi- 
circular Canals; Receptors in the Sacs; Adaptation and Habituation. 

17. Topographical Orientation 380 

The Topographical Schema: Components of the Schema; Graphic 
Representation of the Schema; Extension of the Schema to New 
Territory; Nonvisual Clues. Sensory Basis of Orientation: Orienta- 
tion by the Blind; Auditory Perception of Obstacles; Auditory 
Orientation by Bats; Echolocation; Other Problems of Animal 
Orientation. Migration and Homing: The Sensory Basis of Mi- 
gration. References. 

18. Individual Differences 393 

Measurement of Individual Differences: Characteristics of a Psycho- 
logical Test; Standardization; Norms; Reliability; Validity; The 
Correlation Coefficient. Intelligence Testing: The Binet Tests; 
Group Testing; Performance and Nonlanguage Tests; Testing In- 
fants and Preschool Children; Evaluation of Intelligence Tests. 
Measurement of Special Aptitudes: Trait Variability; Factor Analy- 
sis; Dynamic Organization of Mental Traits. Measurement of 
Personality Characteristics: What Are Personality Tests?; Construc- 
tion of Personality Tests; Evaluation of Personality Tests. Distribu- 
tion of Individual Differences: Frequency Distributions; Types; 
Constitutional Types; The Subnormal Person; The Genius. Group 
Differences: Sampling; Psychological Sex Differences; Are There 
Racial Differences? References. 

19. Heredity and Environment 436 

Fundamental Concepts: What Is Heredity?; Popular Misconcep- 
tions Regarding Heredity; Environment; Structure and Function. 
The Study of Hereditary and Environmental Influences: Selective 
Breeding; Family Resemblances; Foster Family Relationships: Evi- 
dence from Maturation; Effect of an Unusual Environment; Effect 
of Parents' Socio-economic and Occupational Status; Urban, Rural 
and Regional Influences; Cross-comparisons of Cultural and Bio- 
logical Groups. The Heredity-Environment Question— Present 
Status. References. 

xiv Contents 

20. Efficiency 459 

Measurement ol Human Efficiency: Output— Evaluation of Per- 
formance; Input— Expenditure of Bodily Resources; Physiological 
Indicators of Effort and Fatigue; Measuring Efficiency and Fatigue 
by Performance; Laboratory Tests of Efficiency; Work Decrement; 
Summary. Methods of Working: The 'Natural' Way versus the 
'One Best' Way; Motion Study; Time Study; Evaluation of Motion 
and Time Study. The Working Environment: Atmospheric Condi- 
tions: Respiration; Temperature Regulation; Illumination; Noise. 
Rest and Sleep: Hours of Work; Rest Periods; Sleep. Effects of 
Common Drugs: Alcohol; Tobacco; Caffeine. Job Satisfaction. 
Accident Control: General Causes of Accidents; Accident Prone- 
ness. References. 

21. Personality 487 

Psychological Concepts of Personality: Definitions of Personality; 
Personality Types; Personality Traits. Measurement of Person- 
ality: Informal Diagnosis; Rating Methods; Questionnaires; Per- 
formance Tests; Projective Methods. The Origins of Personality. 
Biological Factors in Personality: Body Chemistry and the Endo- 
crine Glands; Physique and Physical Health; The Nervous System. 
Influence of Culture on Personality. Development of Personality: 
Infancy; Childhood; Adolescence; Personality in Maturity. Ref- 

22. Personal Adjustment 51 1 

The Adjustment Process: Motives in Adjustment; Thwarting; Ad- 
justment by Trial and Error; Adjustive Solutions. Responses to 
Thwarting: Constructive Adjustments; Substitute Adjustments; 
Consciousness in Adjustment. Typical Adjustment Mechanisms: 
Compensation; Rationalization; Identification; Seclusiveness; Fan- 
tasy; Repression; Projection; Regression; Sublimation. Conflict: 
An Analysis of Conflicts; Approach-Approach Conflicts; Avoidance- 
Avoidance Conflicts; Approach-Avoidance Conflicts. Experiments 
on Conflict: Conflicts in Cats; Experimental Neurosis; Effects of 
Conflict. Common Sources of Conflict: Family Conflicts; Sex Con- 
flicts; Other Cultural Conflicts. Psychoneuroses: Anxiety; Phobias; 
Compulsions and Obsessions; Ailment Adjustments. Psychoses: 
Organic Psychoses; Functional Psychoses; The Treatment of the 
Psychoses. Techniques for Readjustment: Counseling and Psycho- 
therapy; Interpretation of Psychotherapy. Mental Hygiene: Mental 
Hygiene in Childhood; Mental Hygiene for Adults. References. 

Contents xv 

23. Vocational Selection 546 

Criteria: Criteria of Vocational Success; Choice of Criterion. Job 
Analysis. Nature of Occupations: Dictionary of Occupations; 
Census Classification; Characteristics of Occupations. Trade 
Knowledge and Performance: Oral Trade Tests; Performance 
Tests. Vocational Potentiality: Intelligence; Interests; Other 
Measures. Basic Factors in Occupational Skills. References. 

24. Attitudes and Opinions 560 

Social Norms. The Process of Socialization: Acceptance of Social 
Norms; Suggestion; Formation of Attitudes; Emotional Origin of 
Attitudes. Effects of Attitudes. Development of the Ego: Effects of 
Ego Involvement; The Ego and Group Loyalty. Attitudes and 
Social Change: The Effects of Technology on Thought and Be- 
havior; Propaganda; Techniques of Propaganda; Receptivity to 
Propaganda; Social Bias of Propaganda. Measurement of Atti- 
tudes and Opinions: Sampling; Accuracy; Setting the Problems 
and Questions; Analysis of Results; How to Poll. References. 

25. Social Relations of the Individual 589 

Primary Social Relations: General Functions of the Family; The 
Family in Relation to Social Control; Imitation; Suggestion; Iden- 
tification; Language; Semantics. The Individual in Relation to 
the Assembled Group: Social Facilitation and Social Inhibition; 
Crowds and Mobs. The Individual in Relation to the Dispersed 
Group: Group Attachment; Group Conception. Leadership. Re- 
lations between Groups: Socio-economic Interest Groups; Social 
Participation Groups. Social Prejudice: Nature of Prejudice; 
Origin of Prejudice; Motivations for Prejudice; Rationalizations 
about Prejudice; Individual Differences in Prejudice; Elimination 
of Prejudice. References. 

Index 615 




The Nature of Psychology 

PSYCHOLOGY is the study of human 
nature. It is the study of man, man as a 
living being, acting in an ever-changing 
world, responding to things and events and 
other people. If you know what man is, if 
you know the full answer to the question 
about the nature of man, then you know 
what himian nature is and what psychology 

The single person is the psychological 
unit. He acts more or less consistently 
with himself, although often differently 
from other persons. There is, moreover, 
a great deal of interaction among persons. 
They act together in groups: families, so- 
cieties, parties, nations. They communi- 
cate with one another by language. They 
talk as man to man, and also as author to 
his readers or statesman to his radio audi- 
ence. With language they incite each 
other to action. The mother incites her 
son to be good. The propagandist incites 
a nation to accept or reject a government. 
There is always a good deal of conflict 
between persons and between groups, for 
the same people get incited in different 
directions simultaneously. Sometimes they 
actually get pushed around or made to go 
where they do not want to go, but mostly 
the forces of social interaction are ex- 
pressed by words. The first thing we note 
abotit a man is that he is a unit in a com- 

This chapter was prepared by Edwin 


plex field of social relations. It is the 
psychology of these social functions that 
supplies the details as to just how man 
fits into the social structure and how he 
adjusts to it or resists it. 

The ftmdamental nature of man does 
not appear, however, merely in his rela- 
tion to his fellows. We have also to con- 
sider him as a single individual. \Vhile 
chemically he seems to be only an active 
mass of protoplasm, he turns out to have 
many consistencies of behavior Avhich make 
up what is called his personality. His par- 
ticular pattern of behavior may, ho^\e\er, 
vary greatly from the patterns of other 
men. He may be introverted or extraverted 
in his relation to his ^vorld, ascendant or 
submissive in his relation to his felloA\-s. 
persistent or volatile in his activities, a 
radical or a conservative in his thought. 
He may have a high or low level of aspira- 
tion in his motivation. The ntimber of 
traits and attitudes which would describe 
these consistencies of mind and conduct is 
enormous. If we ask why men differ in these 
various respects, we learn that it is because 
of their differences in inheritance, in edu- 
cation, in physiological constitution, in 
past emotional experience, in the secre- 
tions of their endocrine glands and in a 
myriad of other properties of this acti\e 

G. Borine of Hai-vard University. 

The Nature of Psychology 

mass of protoplasm, which is a man, and 
^vhich psychologists call the organism. 

To understand why man acts as he does 
in different circumstances, psychology has 
to study all the properties of this organism. 
Just what, we may ask, is an organism? An 
organism is a mass of protoplasm that re- 
sponds to excitation. It has certain neces- 
sities for response, and they are called its 
needs. Man has a need for food, and, if 
we keep a man from food, he will be 
driven to seek it until he gets it. In this 
way a need unsupplied creates a drive. 
Every need leads to a drive which is ter- 
minated by the satisfaction of the need. 
Man has a great capacity for needs. His 
primary needs become differentiated, and 
in that way he acquires many new needs. A 
child may need not only food, but candy; 
a youth not only love, but good clothes. 
Around man's needs and drives centers the 
psychology of his motixmtion. 

Man's emotions are closely related to his 
needs. In his need for self-preservation 
may arise his emotion of fear. In his sex- 
ual need may arise his emotion of love. 
Like his needs, his emotions become dif- 
ferentiated and specific. The fear of in- 
sult and the love of music are important, 
useful, acquired emotions, whereas the fear 
of mice and the love of liquor are acquired 
but less useful. 

Since man is a doer, he satisfies his needs 
by doing something about them. He acts. 
His action is, however, never fortuitous or 
spontaneous, for it occurs always as a re- 
sponse to excitation. Why? Because of 
the nenious system. To understand man, 
the doer, we must understand his nervous 
system, which activates his muscles and his 

The nervous system connects stimulus 
with response, making excitation effective. 
It has simple levels for reflex action, levels 

that may not even involve the brain. It 
has complex, levels, where action depends 
on elaborate connections in the brain. Be- 
cause no animal that does not respond to 
stimulation can be said to have a mind, 
the nervous system is often said to be the 
organ of man's mind. 

Responses develop as the individual 
grows up. The embryo can squirm as a 
whole. The infant can clench his fist. 
The adult can trill a note or say a tongue- 
twister. Some responses are primitive and 
automatic, like winking, whereas others 
are complex and voluntary in the sense 
that they are excited by ideas, like going 
shopping. Still others are complex and 
learned, like walking. The essential cause 
of a response may be social pressure, emo- 
tion, need, thought, learning, idea or sim- 
ple stimulation. To understand thor- 
oughly the causes of the organism's re- 
sponses would be to understand man him- 

Next in importance to the fact that man 
can respond with movement to excitation 
is his characteristic of being able to alter 
his modes of response. He can learn. 
Learning is the establishment of new rela- 
tions between stimulus and response. Food 
in a man's mouth makes his saliva flow; 
that is an inherited relationship. Man can. 
however, learn what food looks like so 
that his saliva flows at the mere -sight of 
food. His mouth may even learn to water 
at the soimd of a dinner bell. 

It often happens that a complex response 
seems entirely new because it is a brand 
new combination of old response elements, 
as in the learning of a poem or of a stroke 
at tennis. Man makes these new integra- 
tions of responses under the pressure of 
some need, primitive or sophisticated. He 
learns to recognize food, because he needs 
to eat to live; and he learns to recognize 

The Subject Maffer of Psychology 

musical intervals because he needs to play 
the violin in order to enjoy the life in 
which he lives. Sometimes he perceives a 
new relationship suddenly, and ever after- 
ward acts differently about what he has 
perceived. That is insight. More often 
he learns slowly, with many repetitions, a 
little at a time. Learning accounts for 
most of the differences between the 
adult and the infant. It is so important 
that some animal psychologists have said 
that without learning there can be no 
mind, although it is probably more accu- 
rate to say that mind exists wherever re- 
sponse exists. 

It turns out that learning is not perma- 
nent in man. He forgets. In general his 
forgetting goes on continually. His recent 
memories are more numerous than his old 
ones. One cause of his forgetting is his 
limited capacity for the acquisition of re- 
sponse relationships. He cannot learn 
more than so much at a time and thus gen- 
erally for complete learning he requires 
many repetitions. What he succeeds in 
learning, however, interferes with what he 
has already learned, so that the new ac- 
quisitions cancel out some of the old. Per- 
haps if a man could sleep without thinking 
or learning at all for a hundred years, he 
would, like the sleeping beauty, wake up 
with no forgetfulness and go on just where 
he had left off. 

Next in importance to learning is man's 
capacity for representation. He can re- 
spond to an absent object because he can 
learn to let a present object represent it, 
or because he creates within himself a rep- 
resentative. These internal representatives 
have been called images. Out of sight is 
not out of mind for man. In terms of his 
imagery he can recollect and he can think; 
he can imagine and dream the bizarre 
dreams of sleep or the wise dreams of crea- 

tive genius, liy images he can solve prob- 
lems in thought. Similarly he ran um; 
words, either imaged or spoken, to repre- 
sent absent objects or abstract generaliza- 
tions. With them he can think, and create, 
and solve jjroblems. This great capacity 
to utilize the symbolic power of words and 
images is the chief distinction between man 
and the animals. 

Inhere is also the question as to how man 
learns about the world in which he lives, 
how he finds out what is there. That is 
the problem of perception. Man does not 
perceive his environment exactly as it is, 
but alters what he perceives in accordance 
with his needs, for the outside world is too 
complicated and variable for him to be 
able to perceive it in all its chaotic change- 
fulness. Needing to simplify his environ- 
ment for his own purposes, the first thing 
man does is to divide it up into objects. 
Objects are thus man-made. Perception 
pulls many items of experience together 
into an object and puts other items off on 
the outside, so that man, when he sees the 
world as a collection of objects, has done 
something to the world in perceiving it. 
An object must have a certain amount of 
stability in order that it may always seem 
to be itself and not to be forever becom- 
ing something else. Thus we find man 
equipped with a set of laws of perceptual 
constancy: seen objects tend to stay the 
same size, even when thev vary in distance: 
they tend to stay the same shape. e\en 
when viewed at different angles; they tend 
to stay the saqie color, even Avhen tlie in- 
tensity and hue of the illumination cliange. 
Since man needs to kno^v where he is and 
where other things are, Ase find that he can 
perceive the locations and distances of 
many objects, as well as tlieir shapes and 
sizes. From various clues tliat come to him 

The Nature of Psychology 

he correctly reconstructs some of the data 
of his environment— or rather his nervous 
system is such that it makes these 'infer- 
ences' about the outer world for him and 
presents them to him as his perceptions. 
Man is so built that he gets in this way the 
picture of the world that he needs. 

It is via the five senses that the nervous 
system gets the data which it works over 
into perceptions of objects. Psychology 
had a great deal to say about the senses 
because they constitute its oldest field of 
research, and much is now known about it. 
It is an historical accident that we know 
more about tones than about needs, more 
about colors than about prejudices, but 
there will not always be this discrepancy. 
Eventually, as research continues, the laws 
of thinking and wishing will become fully 
as explicit as the laws of seeing and hear- 
ing are now. 

So this is what psychology is about— man, 
the organism: man's capacity (1) for per- 
ceiving, (2) for response, (3) for learning 
and (4) for symbolization. The organ- 
ism has these various properties, man has 
these various capacities, and man uses them 
all in a world filled with things, which 
have been created by his own perceiving, 
and with other people, who themselves 
have comparable capacities and whose re- 
lations and responses to one another are 
of the utmost importance to all. 


Psychology deals with both the beliavior 
of man as it appears in his responses and 
with consciousness as he finds it in his im- 
mediate experience. "We need now to con- 
sider a few matters about each of these two 
kinds of data. 


If beha\ior is just movement of the or- 
ganism, why does it come into psychology? 
Is not physiolog)' the field where bodily 
moxement is studied? People are always 
asking that question, asking where the line 
between physiology and psychology comes, 
where one science leaves off and the other 
begins; but there is no line. Sciences never 
have sharp boundaries. 

Think, for instance, about the behavior 
of the stomach. You put food into it and 
then study how it contracts while the gas- 
tric juice flows in rapidly. In doing that 
you are being a physiologist, studying di- 
gestion. But suppose you keep food out 
of the stomach and then see how, after sev- 
eral hours, it starts its long slow contrac- 
tions that make men restless and make 
them say, "Oh, how hungry I am!" Then 
you are being a psychologist, studying 
hunger as motivation. Or you start find- 
ing out how continued worry makes the 
stomach keep contracting too much and 
the gastric juice flow too much, forming 
presently a stomach ulcer, and then you 
are— what? A psychologist. A physiolo- 
gist. A physiological psychologist. A sci- 
entist interested in what is now called psy- 
chosomatic medicine. The terms do not 
really matter. 

Actually a psychologist ought to know, 
besides psychology, a great deal of physi- 
ology, physics and sociology, and have some 
acquaintance with the history of science 
and enough knowledge of philosophy to 
prevent him from trying to make too rig- 
orous a definition of psychology for stu- 
dents to learn. Actually he has to be con- 
tent with less. 


Psychology studies consciousness as well 
as behavior. Only a hundred years ago 


you would have been told that jjsyrhoirjgy 
is the study of consciousness, that men have 
minds and bodies, and that psychology 
studies the minds and physiology the bod- 
ies. That is really how this distinction be- 
tween physiology and psychology devel- 
oped, the one group of men studying the 
workings of the body and the other con- 
sciousness—sensations, perceptions, feelings, 
emotions, imaginations, memories, thoughts 
and volitions. The two sciences would 
never have overlapped had it not been 
for the fact that consciousness depends on 
the body and its nervous system. No scien- 
tist has ever been able to observe a dis- 
embodied consciousness. There is always 
a body around, and the body is behaving— 
talking or acting in some way. So, al- 
though it is true that psychology studies 
both consciousness and behavior, you never 
find consciousness in anyone but yourself 
except by observing his behavior. The 
basic rule is: no behavior, no conscious- 
ness. It is for this reason that the psy- 
chologists, who began with the study of 
consciousness, got to studying behavior, so 
that after a time the sharp line between 
physiology and psychology disappeared. 

The fact that consciousness can be known 
only through behavior reduces to the 
simple statement that there are three kinds 
of behavior which psychologists study. 

(1) First, there is the behavior which gives 
information about consciousness:, like 
laughing or crying or saying the words, 
"It's pink," or telling abovit a dream. 

(2) Then there is the behavior which gives 
information about unconscioiisness~ior 
psychologists believe in the paradox of an 
unconscious kind of consciousness. This 
is the behavior that implies that you are 
acting on wishes which you do not know 
about and would, perhaps, deny having, 
like wishful forgetting when you remain 

li;ipjjily uruoriscious of something you 
ought to remember and do not want lo 
remember. Rebuking a person you know 
well and do not like by forgetting his name 
is a good instance. (.S) And then there is 
just plain behavior, like putting the .5014th 
candy neatly in a box in a candy factory 
because you have learned to do it and it 
is now a habit which you carry on, hour 
after hour, while you occupy your con- 
sciousness with memories of last night's 
date. It all gels back to behavior in this 
way, even if you start with consciousness. 

On the other hand, even though you 
have to study the behavior of other people 
to know about their consciousnesses, your 
own consciousness always seems to be 
known to you yourself immediately. You 
do not need a mirror to find out that vou 
are angry. A science of psychology cannot, 
of course, be built up on any one man's 
experience, so most of consciousness for 
every psychologist is the experience of 
others. Nevertheless it is interesting to 
pause to consider just what sort of stuff 
your own experience is and how it differs 
from what you know exists in the world 
about you. 

Begin with an experiment. Look at Fig. 
1. See the spirals. Find the letter A at the 
top of the figure on one of the spirals. 
Follow that spiral with your eyes or your 
pencil around the figure until you come 
back to the top again. There you are, back 
at the letter A. W^hat vou ^vere folloAving 
was not a spiral after all, but a circle— in 
fact a perfect circle, as you could discover 
if you had a compass. Nevertheless \\hat 
you see is a spiral, even though Avhat you 
follow is a circle. Therein lies die distinc- 
tion which we are considering. The spiral 
is your consciousness. The circle, A\hich is 
there and which you cannot see. is the 
physical stimulus for your perception of 

The Nature of Psychology 


The conscious data are the spirals, which are seen immediately and persist in spite of sophistication. 
The stimuli for the spirals are perfect circles. Start at A at the top and follow all the way around; you 
come back to A again. [Adapted from J. Fraser, Brit. J. Psychol., 1908, 2, 307, Fig. 3.] 

the spiral. This is an illusion, a percep- 
tion in which consciousness and its stimu- 
lus coexist in a lawful, scientifically under- 
stood disagreement. 

In others words, consciousness is what 
you experience immediately. Physical ob- 

jects, unless you have already learned about 
them, have to be figured out. It takes a 
compass to discover the circularity of the 
spiral's stimulus. One of the commonest 
illusions is seeing a single object as single 
Avith two eyes. You can find out that that 

Origins of Scientific Psychology 

sort of stimulation is double only by fiisi 
shutting one eye, then opening it and shut- 
ting the other. Consciousness, on the 
other hand, is the sort ot experience which 
you can describe immediately without hesi- 
tation or reasoning. 

Unconsciousness has to be figured out— 
by yourseir, your friends, your psychiatrist 
or someone else. Maybe / am wise enough 
to know more about your motives than 
you yourself when you address the letter 
meant for Boston to Baltimore where lives 
the girl you met last night. Motives are 
very likely not to be directly conscious. 


Psychology has had a long history, and 
we had better have some words about how 
it came to be the way it is. 

The first name to mention is that of the 
philosopher-physiologist Descartes (1596- 
1650), whose effect upon psychological 
thinking is still felt. Descartes made these 
two important contributions. (1) He ar- 
gued that animals are automata, that they 
act like machines, and that men do too in 
their irrational conduct. Based on this 
view is the modern notion that, if you 
knew enough about the nervous system, 
you could make a mechanical or electronic 
robot who could act and think like a man. 
(2) Descartes also argued that soul and 
body, consciousness and nervous system are 
quite separate, forming different worlds, 
which nevertheless interact, each affecting 
the other, at a specific point in the brain. 
Consciousness is in the body but it occu- 
pies no space within it— is, as Descartes put 
it, "unextended substance." This view of 
quite different body substance and mind 
stuff is called dualism. It is responsible for 
the modern common-sense notion that the 

mind is soiixtliiiig within the head, taking 
up no separate space oi its own, yet work- 
ing there to perceive the oiitsifle world, lo 
do its own thinking and to (ontrol the 
actions of the body— a little extra person 
immured in the skull, perpetually busy, as 
news comes in along one set of nerves, 
sending out orders along another set. 

Next we must jnit in our record the long 
tradition of liritish psychology thai began 
in 1690 with the philosopher John Locke 
(1632-1704) and continued up into mod- 
ern psychology two centuries later. 'I "his 
school is sometimes called British cinpirt- 
cisrn and sometimes British associationisrn. 
It was empiricism first when Locke argued 
—he was trying to refute Descartes in this 
matter— that all content of the mind conies 
from experience. The infant's mind, he 
said, is just a piece of white paper on which 
experience Avrites. Actually he had hold 
of half the truth, for there is nothing in a 
man's consciousness or behavior that is not 
partly learned, although heredity also plays 
its role. Having made learning so im- 
portant, Locke then had to say how learn- 
ing works. He suggested that association 
is the principle. Ideas that belong to- 
gether tend to stay together in the mind: 
that is what association is. Locke's view 
led eventually to a kind of mental chem- 
istry, in which perceptions and ideas were 
thought of as complex molecules made up 
of atoms of sensations and images held to- 
gether by association. 

Dualism remained the rule in psychology 
pretty much up to the end of the nine- 
teenth century. You had mind and you 
had body. There were many guesses as to 
how the two were related, but, in the 
middle of the nineteenth century, the gen- 
eral acceptance of the notion of the con- 
servation of energy led psychologists to 
accept, for the most part, the conception 


The Nature of Psychology 

of parallelism. That view is that man is 
a machine in which all conduct is to be 
explained by the action of the sensory 
nerves, the spinal cord, the brain and the 
motor nerves, and that certain of these 
events— some of those that occur in the 
brain— are paralleled by the occurrences in 

Against this parallclistic-dualistic view 
of the relation of the mind to the body 
were put forward various kinds of monism, 
the A'icw that mind and body are the same 
kind of stuff or at most different aspects 
of the same basic e^'ents. These views of 
the relation of mind to body matter to us 
only in respect of what they led to. Paral- 
lelistic dualism led to introspectionism. 
Monism has realized itself in modern times 
in behaviorism. These two schools of psy- 
chology we shall consider presently, but 
first we must get- back to the nineteenth 

When physiology' -vvas growing into a 
science, some of the physiologists became 
interested in what are really psychological 
problems. There was, for instance, Jo- 
hannes Miiller (1801-1858), called the 
father of experimental physiology, who in 
1826 laid down the theory that the nature 
of sensory quality depends on which par- 
ticular nerve is excited. Press on your eye- 
ball, and you see colors; get your ears 
boxed, and they will ring. Miiller was a 
dualist. He was supposing that the mind, 
within the brain, would be noting: "This 
is something that can be seen, a sight not 
a sound, because it is the optic nerve that 
is being stimulated." There was also E. H. 
Weber (1795-1878), who gave us AVeber's 
law in 1834, the law which asserts that the 
just perceivable difference between two 
stimuli gets larger as the stimuli get larger. 
Two men shoiuing make more noise than 

one man, but, if you add only one extra 
shouter to fifty shouters, you will never 
hear the difference. In such ways it was 
getting quite clear toward the middle of 
the nineteenth century that you could ex- 
periment with the mind— at least with sen- 
sations—as well as with the brain. 

At that point experimental psychology 
began. Three men contributed to its 
founding. There was Hermann von Helm- 
holtz (1821-1894), perhaps the ablest scien- 
tist who has as yet touched psychology, the 
man who set the physiologists by the ears 
in 1850 by measuring the velocity of the 
nerve impulse and who wrote and pub- 
lished what are still the gieat classical vol- 
umes on visual and auditory sensation in 
the decade following 1856. There was also 
G. T. Fechner (1801-1887), who worked 
out the methods for measuring sensation 
and published them in 1860. And then 
there was AVilhelm AVundt (1832-1920), 
■who coined the phrase physiological psy- 
chology to stand for the kind of work 
Miiller and Weber and Helmholtz and 
Fechner had been doing. He wrote in 1874 
the first systematic handbook of physiologi- 
cal or experimental psychology (the classic 
up to its sixth edition in 1911), he founded 
the first important laboratory of experi- 
mental psychology at Leipzig in 1879 
(William James had a little laboratory at 
Harvard a few years earlier) and he really 
got the new experimental psychology im- 
der way as a separate social institution. 
■Wundt was a dualist and parallelist in his 
theory of mind and body. Fie took over 
the notion of association from British em- 
piricism. He was a mental chemist, and 
he believed that we can, by introspection, 
analyze consciousness into the mental ele- 
ments of which it is composed. Introspec- 
tion is the ha\ ing of experience and de- 

Schools of Psychology 

scribinj^ il. VVlicii wc note iIkil tlic cuivcs 
in Fig. 1 are spirals, we arc introspecting. 
Introspcrlion is llie way to gel at conscious- 

As late as 1910 most psychologists re- 
garded introspection as the basic method 
or psychology, that is to say, most psycholo- 
gists were dualists: they believed that phys- 
iology studied the body, that psychology 
studied consciousness and that introspec- 

cliological expeiimcnls on animal intelli- 
gence. He studied how cats can learn to 
get out of puz/le boxes. 

From this point it will be easy for us to 
follow the main developments in the hiv 
tory of scientific psychology by noting how 
the four most important schools of mod 
ern psychology waxed and waned from the 
end of the nineteenth century until the 
present. We turn to them now. 


Diatjram shows the relationship of four schools of psychology to each other and to the theory of eyolii- 
tion. Modern psychology tends to ignore schools but to deal with both consciousness and behayior in in- 
teurated wholes. 

tion was the direct way of getting at con- 

Meanwhile, in 1859, Darwin had con- 
tributed the theory of evolution to science. 
It created a revolution in scientific think- 
ing and cast some doubt upon dualism. 
Before that time consciousness liad been 
thought of as practically the same stuff as 
the soul. Now Darwin suggested that men- 
tal characteristics— especially emotional be- 
havior—might be inherited by man from 
his animal ancestors. Consciousness was 
thus being biologized. Darwin's famous 
cousin, Francis Galton (1822-1911), pub- 
lished in 1869 a study of British genius, in 
which he sought to show that genius is 
inherited. Several investigators in England 
and America became interested in mental 
evolution and so in animal psychology, and 
in 1898 Thorndike in America published 
what were almost the first systematic psy- 


There have, then, been these four schools 
of psychology. They are of different ages, 
but the last two were contemporaneous. 
See Fig. 2 for a diagram of their relation- 

(1) Introspective Psychology 

That is the school which regards con- 
sciousness as the important object of study. 
It was the school of Wundt and for the 
most part it used some kind of introspec- 
tive analysis of consciousness, a kind of 
mental chemistry. In America it was most 
strongly defended by Titchener (1867-1927) 
at Cornell. The school was at its gieatest 
power about 1910. No one noAvadays calls 
himself an introspectionist. but everyone 
has to know about this oldest of the schools 
in order to understand the others. 


The Nature of Psychology 

(2) Functional Psychology 

The theory of evohition was marvelovisly 
well fitted to thrive in the American atmos- 
phere, where competition and the struggle 
tor success resembled Darwin's principle of 
the survival of the fittest. It was natural 
for American psychology to be functional, 
to consider mind in terms of its uses to 
tiie organism in its effort to succeed. 
William James (1842-1910) at Harvard was 
the first American to react against intro- 
spectionism, and most of the other Ameri- 
can psychologists in the period 1890-1910 
believed that psychology should deal pri- 
marily with human abilities and capacities. 
The school that was called the functional 
school was established by John Dewey 
(1859- ) at the University of Chicago 
about 1896 and was carried on there later 
by James R. Angell (1869- ). This 
school was dualistic, interpreting conscious- 
ness in terms of its use, and. because it was 
(oncerned primarily with himian abilities, 
it provided a friendly background for both 
(he mental tests and animal psychology, 
neither of which is primarily concerned 
about consciousness. The school of func- 
tional psychology may be said to have 
evaporated when behaviorism became well 
established, but the spirit of the school is 
still the dominating force in American 
psychology. Mental testing and applied 
psychology have thrived in America be- 
cause they are useful psychologies and ac- 
cord well with tlie spirit of competition 
liiat marks the American culture. 

(3) Behaviorism 

The next step in functionalistic progress 
in America was the founding of behavior- 
ism about 1913 by John B. Watson (1878- 
). Watson had been working with rats 
at Chicago under Angell. His early inter- 
ests were in animal psychology, and the 

conventions of his day held that animals, 
in learning, to solve puzzles, to find food 
in mazes and to discriminate the correct 
food box, were displaying consciousness 
and that the psychologist ought, therefore, 
to assess their consciousnesses. Watson ar- 
gued that you never know much about the 
consciousness of a rat, although you can 
study his abilities and capacities, and that 
such study is properly to be regarded as 
psychology. He laid down the law that 
psychology should deal only with behavior. 
Introspection he ruled out, and conscious- 
ness he ignored. His behaviorism proved 
practicable for the very reason that you 
never learn about the consciousness of any 
organism, human or animal, unless the or- 
ganism behaves somehow in its introspec- 
tion. Thus Watson could really keep in- 
trospection in behaviorism by calling intro- 
spection "verbal behavior." Nevertheless, 
interest in consciousness was diminishing 
and interest in behavior increasing. Be- 
haviorism was consistent with mental test- 
ing and animal psychology. The study of 
consciousness was still fmther depreciated 
about the turn of the century when the 
psychoanalytic doctrine of Sigmund Freud 
(1856-1939) began to direct the thinking 
of the psychologists toward imconscious- 
ness. Partly on this accoiuit and partly 
because of the outcome of experiments on 
thought and action, they came to realize 
that a great deal of motivation is luicon- 
scious and quite tmavailable to introspec- 
tion. By 1930 introspection had become 
only a secondary method of psychology, ex- 
cept as it was used in simple sensory dis- 
criminations or employed loosely in social 
psychology and psychotherapy. 

(4) Gestalt Psychology 

1 he success of behaviorism was some- 
what diminished by the appearance of Ges- 

Schools of Psychology 


tak psychology in (iermany about 1912. 
The new movement had caught American 
interest by the 1920's, and then in the 
I930's its leaders migrated to America when 
the Nazi power destroyed German treedom. 
(ieslall means form, and the name was de- 
rived from rcr(ain studies of visual percep- 
tion of spatial form, it is better trans- 
lated, however, as structure, for the thesis 
of the school, which was founded by Max 
Wertheimer (1880-1943), is that psycholo- 
gists nnist deal with total structures and the 
system of their internal forces, eschewing 
the mental chemistry and the analysis that 
both introspectionism and behaviorism 
favored. The Gestalt psychologists say 
that, in looking at a square, it is the total 
figure that makes the square look square, 
not the parts. A square is more than four 
black lines. It is four black lines in a par- 
ticular relation to one another, and square- 
ness really depends on the relation and not 
the lines. Four dots will also make a 
square, as will four red lines. The mental 
chemists were always talking about the 
sensations, the parts that made up the 
s(|uare, as if the squareness of a red square 
were different from the squareness of a blue 
square. By the late 1930's this school had 
accomplished its main purpose of getting 
the attention of psychologists directed to 
larger systems of interrelated facts. The 
movement did not revive American inter- 
est in consciousness, though for a while it 
delayed the general shift of the Americans 
toward behaviorism. Meanwhile the Nazi 
power had destroyed German psychology, 
and America took the lead in the new 

(5) Modern Psychology 

During the 1930's the isms pretty well 
dropped out of psychology. The func- 
tionalists first gave place to the behavior- 

ists, but nowadays yon never hear a jnaii 
call himself a behaviorisi, although you 
may still hear about behaviorism. It has 
fjeen even longer since anyone liked to 
label himself an inlrospectionist. There 
are, jjerhaps, still a few Creslallisls, but 
that is only because Germans like istns 
ijetter than Americans do. 

What has actually happenerl is iliat con- 
sciousness, inherited from inlrospec tionism, 
is used in psychophysics (for example, in 
discrimination of colors, tones, visual div 
tances and all the other sensory capacities 
for which perceptual accuracy must be de- 
termined) and, at the other extreme, in 
psychotherapy where experiences from 
waking life or dreams need to be recorded 
and studied. The spirit of functional 
psychology pervades the modern American 
scene which studies mind in use for the 
organism as a matter of course. Behavior- 
ism has contributed behavior and the mod- 
ern stimidus-response psychology. This 
kind of psychology also claims to be study- 
ing consciousness, because consciousness is 
revealed to scientific observation only 
through behavior of some kind. Gestalt 
psychology disappeared as an ism because, 
after a battle, nearly everyone had accepted 
its basic tenet that too much analysis gives 
false residts, that wholes are safer objects 
of study than their parts, that you must 
always take into consideration enough of 
the interrelated forces to make you fairh 
safe about not having omitted any essential. 

From here we can go on to the fields of 
modern psychology. The only reason for 
mentioning these four schools in this book 
is that the student hears about behaviorism 
and Gestalt psychology and has a right to 
be told what they are and that they are no 
longer important as scliools. AN'hat was 
good in all the schools is now simph pare 
of psychology. 


The Nature of Psychology 


The way in which modern psychology 
has become further complicated appears if 
we pick out and define eleven of its more 
important fields. Let us do it. 

(1) General psychology includes the fun- 
damental principles of all psychology. It 
also deals particularly with the normal 
human adult, leaving other matters to spe- 
cial fields. It is sometimes divided into the 
smaller fields of (a) sensation and perce|> 
lion, (b) feeling and emotion, (r) learning 
and motivation and (d) the higher proc- 
esses, including thought. 

(2) Physiological psychology studies the 
functions of the nervous system which con- 
trol behavior and consciousness and of 
other similar mechanisms like the endo- 
crine glands. It often uses operative tech- 
niques, investigating the functions of ani- 
mal brains, for instance, by removing por- 
tions of the brain tissue and noting the 
effect upon behavior. This kind of experi- 
ment is older than experimental psychol- 
ogy, going back to the early nineteenth 

(3) Comparative psychology is the name 
given to the study of the comparison of 
the behaviors of different animal species. 
It is the natural history of animal conduct. 
Most of the psychological work with ani- 
mals is now in the hands of physiological 
psychologists, but there are still some com- 
parative psychologists left. 

(4) Psychology of individual differences 
is the name given to the measurement and 
assessment of human abilities, largely by 
the employment of mental tests. The use 
of mental tests for this purpose goes back 
to Francis Galton in England in 1883, but 
the development of the tests has been great- 
est in America in the last forty years. Both 
the World Wars greatly stimulated research 

in these modes of the appraisal of human 

(5) Industrial psychology includes all the 
means of personnel selection by the use of 
tests, inter\iews and other devices, and all 
the means of training on the job and of 
measuring efficiency of work. It is not 
new, but it has been accelerated by the suc- 
cess of these procedures in the Second 
^^'orld ^Var. 

(6) Child psycliology studies the develop- 
ment of the child, assesses his abilities by 
the use of tests, seeks evidence on the prob- 
lem of the relative effects of heredity and 
environment upon ability, and also con- 
siders the adjustment of the child, a form 
of clinical psychology (vide infra). 

(7) Educational psychology examines the 
educational process in terms of child psy- 
chology, clinical psychology' and the dy- 
namic psychology of learning and moti^'a- 
tion (vide infra). 

(8) Abnormal psychology has to do with 
the deviation of the human adult from the 
normal. It is allied to psychiatry, the 
medical field for the treatment of psycho- 
logical disorders and maladjustments. 
Since about 1930 this field has been greatly 
influenced by psychoanalysis, and the psy- 
choanalytic conceptions of unconsciotis mo- 
ti\ation are now used by all. 

(9) Dynamic psychology is the result of 
this interpenetration of abnormal psychol- 
ogy by psychoanalysis and of other re- 
searches tliat have indicated how often 
motivation is unconscious. Dynamic psy- 
chology can be defined, therefore, as the 
psychology of normal moli\ation. While 
its origins can be traced far back into the 
French abnormal psycholog)' of the nine- 
teenth century, its important development 
lies entirely in the present century. 

(10) Clinical psychology is the practical 
application of dynamic and abnormal psy- 

Scientific Method 


(liology to ihc problems of fiuinan adjiist- 
incnl. It has been stimulalcd by the de- 
mand for psychological assistance for the 
many veterans of the Second World War 
who suffer from psychoneurosis. 

(11) Social psycholoiry is the study of the 
individual in the group and the relations 
of groups to one another. Thus social psy- 
chology considers the psychological inter- 
relations of people forming families, 
crowds, societies and mobs, and of the 
leader with his followers. It includes the 
study of the formation of group attitudes 
and opinions and of the assessment of so- 
cial attitudes and public opinions. It is 
thus forced into a consideration of social 
and national conflict, of race prejudice and 
similar manifestations of the interrelations 
of the conflicting needs of many individ- 
uals. Social psychology is as old as sociol- 
ogy and cultural anthropology, but its 
specific development along psychological 
lines is visually traced from the writing of 
William McDougall in 1908. 

The present book has something to say 
about these kinds of psychology: general, 
physiological, individual differences, indus- 
trial, dynamic and social. The other five 
fields enter only incidentally, often by way 
of illustration. In general this book limits 
itself to the scientific core of psychology. 
The other fields are more specialized or are 
fields of application. 


We ought now to say something about 
how the scientist works. He does not fol- 
low rigid rules. Usually he has a hunch 
that something might be true and tries it 
out in an experiment. If his hunch proves 
wrong, he does not, as a rule, publish that 
fact; so perhaps someone else will make the 
same guess and try it out again, and find 

again iliat the guess is wrong. The scien- 
tist is sometimes motivated by intellectual 
curiosity, .sometimes by that esthetic feeling 
which makes a man want to make concrete 
a good idea and sometimes by the desire 
to advance civilization or to solve a par- 
ticularly pressing practical problem; but all 
the other human competitive motives work 
too— the need for money, the need for pres- 
tige, the need to prove yourself right and 
the other man wrong. The rules for re- 
search have been worked out, not to con- 
strict scientific imagination and constrain 
drive, but to stimulate men into what are 
usually the more profitable avenues of 


The basic scientific method is experi- 
ment. Experiment is the observation of 
concomitant variation and the interpreta- 
tion of the concomitances as causes and 
effects. You change x, and )' happens. So 
y is observed as a function of x. You prick 
a man's finger with a pin, and he quicklv 
withdraws his finger. The prick is .v, the 
independent variable, which the experi- 
menter controls. The withdrawal, )', is 
the dependent variable, which the experi- 
menter observes as a result of x, the prick. 

Sometimes you have to wait for nature 
to do the independent ^arying for you. 
The astronomer does. His independent 
observation is often a date and a moment 
at which he makes the observations whicli 
his hypothesis (or hunch) requires. It is 
also impossible for the psychologist to cre- 
ate individual differences in intelligence, 
but he can choose persons who ha^e differ- 
ent scores on an intelligence test (inde- 
pendent variable) and then see whether 
they do differentlv as clerks or salesmen 
(dependent variable). 

It is fair to define the scientist as the 


The Nature of Psychology 

man who is always after generalizations, 
and the engineer or applied scientist as the 
man who is solving particular problems. A 
generalization would be the statement: All 
dreams arc pariially concealed expressions 
of unconscious wishes. A particular prob- 
lem of psychiatric 'human engineering' 
would be tlie use of John's dreams to show 
why he had had a nervous breakdown. 
John is an immediate problem for 'human 
engineering,' but he is interesting to sci- 
ence only if he serves to represent some 
larger class of objects— like all men, or all 
the dreamers with psychoneuroses. Usu- 
ally 'pure' and applied science go ahead 
together. Work in the one contributes to 
the advance of the other, but it is impor- 
tant to remember about generalization. 
The whole value of science is that it re- 
duces the complexities of the world to gen- 
eral rules, which, once established, enable 
you to explain or predict many, many in- 
dividual cases. 

You cannot generalize without repeti- 
tion. If y changes when .v is changed, that 
may be chance. Try it again. If it hap- 
pens ten times, perhaps it is 'right,' that is 
to say, perhaps the general rule can be ac- 
cepted. More cases make you more sure. 
Yet you are never entirely certain; the fu- 
ture may still reveal some discrepancy. 


You also need control if you are to gen- 
eralize. That means ordinarily that you 
must keep all the conditions constant when 
you repeat or you may not get the same 
result. If conditions are going to be al- 
lowed to change, you had better change 
them at will and then you may learn some- 
thing extra. If you withdraw your finger 
when it is pricked and you are awake, what 
will you do when you are asleep? But the 
experimenter must not let you sleep and 

wake at random. He must control yoiu 
sleeping, keeping it constant or varying it 
at his will. 

On the other hand, hunch comes into 
this business too. No one can keep all the 
conditions constant, and the experimenter 
has to guess which conditions are the most 
important. Suppose you discovered on a 
Tuesday that a certain percentage of auto- 
mobile drivers cannot tell a red traffic light 
from a green, except by knowing that the 
red is on top. (You could do it by inter- 
changing the red and green in one signal, 
provided you prevented accidents in some 
other way.) Well, that was Tuesday. 
Would you have to repeat the experiment 
on Wednesday and all the other days? No, 
you assiune that the day of the week makes 
no difference, that eyes see the same on 
Tuesdays and on Wednesdays. Nor does 
the phase of the moon matter, nor the 
last name of the driver. It is by hunch that 
)ou leave these matters out of control. 
You hope they make no difference. Some- 
times, when a long-accepted generalization 
turns out later to be wrong, it is because 
some such essential condition was not con- 
trolled when the original generalization 
was formed. For instance, most people 
w^ould expect sex to make no difference in 
observing traffic lights, biu it does. Very 
few women are color-blind. 

In reading about experiments you often 
see the phrase control series or control 
group or you meet the criticism that an 
experiment was uncontrolled. What do 
those statements mean? This. The ex- 
periment consists of seeing whether y varies 
when .V varies. The control consists in 
seeing whether y does not vary when x does 
not vary. You want to see whether men 
can do better on an intelligence test when 
you give them some of the drug benzedrine 
sulphate. So you divide the men into two 

Scientific Methods 


groups. To ihe experimental group you 
give the benzedrine in capsules without 
telling them what it is. I'o the control 
group you give sugar in capsules without 
telling them what it is. If the experimen- 
tal group does better or worse than the 
control group, maybe benzedrine has some 
effect. If both groups do as much better 
with the capsules as without, perhaps the 
improvement is due merely to the confi- 
dence of the men that a psychologist's cap- 
side will make them more efficient. If you 
do not have two groups, but only one, you 
must have control series with the sugar, and 
experimental series with the benzedrine, 
both for the same people. 

There is a great deal of pseudoscience 
which fails to get reliable results just be- 
cause it has no controls. Colleges, for in- 
stance, keep changing their course require- 
ments in order to manufacture better A.B.'s. 
How do they know when the A.B.'s arc 
better unless they keep half the students as 
a control on the old plan and put the 
other half on the new plan and also know 
how to compare the two finished products 
after Commencement? 


Now one word about the use of hypoth- 
eses in science. If a psychologist gets a 
hunch that blond women are more placid 
than brimettes, he is privileged to try to 
pro\'e his hypothesis by experiment if he 
has the time and facilities for such research. 
The safe rule for research, however, is to 
use it to test plausible hypotheses which 
grow out of other research. That is, by 
and large, the way science has progressed. 
Here, then, is the best way, which has been 
burdened with the name hypothetico- 
deductixie method. 

(I) On the basis of general knowledge, 
previous research and insight into the re- 

lationships of the available facts, you form 
an hypothesis. It had fjctter be a sensible 
one, but you arc the judge of its plausibil- 
ity. If you are trying to serve science, you 
choose an hypothesis the proof or disprrxjf 
of which would advance scientific knowl- 

(2) The hypothesis is a generality, the 
sort of proposition that makes a law when 
it is proved. So you deduce from it some 
jjarticular consequence that ought to fol- 
low, one that can be subjected to experi- 
mental lest. 

(3) Then you set up the test experirnenl 
and see whether the deductive prediction is 
verified or not. 

(4) If the prediction is verified, you may 
assume tentatively that the hypothesis is 
strengthened. You may even decide to 
accept it, always subject, of course, to the 
possibility that it may be overthrown later. 

(5) If the experiment gives negative re- 
sults, does not justify the hypothesis, then, 
if you arc very anxious to understand the 
phenomena being investigated, you Avill 
have to use your wits to find another plaus- 
ible hypothesis to test out. 

(6) When an hypotliesis is verified, you 
are very likely to find that it sets you ne^v 
problems. So now you think up new finer 
hypotheses to direct you toward finding out 
?('/?}' the hypothesis just verified is true, and 
that process of refinement can go on prac- 
tically forever. 

The study of the moon illusion shows 
this process operating. It was early ob- 
served that the full moon looks larger on 
the horizon than up in the heavens. Many 
hypotheses were advanced— that the differ- 
ence is due to refraction at the horizon, or 
due to the atmospheric haze at the horizon, 
or due to the fact that the moon looks 
farther a\va\ at the hori/on and tlius would 


The Nature of Psychology 

have to be big in order to give the normal- 
sized image on the retina. The first tAvo 
hypotheses fail when tested by the camera. 
A photograph of the horizon moon is as 
small as the photograph of the moon in 
elevation. The third hypothesis fails be- 
cause the horizon moon no longer looks 
large when you bend over and \ie\v it be- 
tween your legs. The next hypothesis is 
that the illusion depends on looking up, 
and that hypothesis has been proved. It 
holds even for experimental moons only 
thirty meters away. So now you know; the 
phenomenon is an illusion and not an 
astronomical change, and it depends on 
looking up. But why, you ask at once. 
That needs another hypothesis. Perhaps 
what shrinks the moon is raising the eyes, 
or perhaps it is bending the neck. That 
question has been answered. The raised- 
eyes hypothesis is right, the bent-neck hy- 
pothesis is wrong. So, by forming and 
testing new hypotheses, you have refined 
your knowledge. Now you want to know 
why raising the eyes shrinks the moon, but 
no one has yet been clever enough to for- 
mulate for test the crucial hypothesis that 
will answer that question. Sometime it 
will be done. 


Nearlv all the definitions of terms come 
up in their proper places in this book. 'We 
may, however, examine here a very few 
special words that we need to use at the 

Stimulus. A stimulus is any change in 
external energy that gives rise to such an 
excitation of the nervous system as arouses 
a response. (See pp. 20, 217, 251.) A 
stimulus cannot exist without a response 
because it is defined as producing a re- 

sponse, but in this sense a conscious event 
must be regarded as a response. 

Stimulus object. An object, like a col- 
ored paper that is seen or a sweet substance 
that is tasted, is often called a stimulus, but 
it is more correct to call it a stimulus object, 
since it determines a change of energy but 
is not the change. 

Situatio77. "When a stimulus object is ex- 
tremely complex or has special meaning to 
the obser\'er, it is often loosely called a 
situation. A red light may be a stimulus, 
but an enemy is a situation. 

Proximal stimulus. Since energv changes 
progress serially from a stimulus object to 
the organism, it is plain that stimuli can 
be more or less proximal (near the nervous 
system). "When the pistol shot makes you 
jump, the pistol is the stimulus object, the 
sound in the air is a stimulus, the motion 
of your eardrmn is a more proximal stim- 
ulus, and motion of the hair cells where 
the sensory nerve fibers are in your inner 
ear is a still more proximal stimulus. The 
stimulus does not exist, for there is always 
a series of more and more proximal energy 
changes when stimulation occurs. 

Response. A response is the second and 
later event in a stimulus-response pair. In 
man it is usually a muscular movement or 
the secretion of a gland. AVhen a psychol- 
ogist is dealing with consciousness, he 
thinks of a sensation as a response. Re- 
sponse exists only in relation to a stimidus, 
and in man it is always an end result of 
the action of the nervous system. Re- 
sponses, like stimuli, can be more or less 
proximal. The contraction of a muscle is 
more proximal than the finger movement 
which the muscle's contraction causes. 

Behavior. "When the responses are Aery 
complicated, it is better to call them bc- 
hax'ior. Behavior has the same relation to 
a situation that a response has to a stimulus. 



Suhjrci and ohserxx^r. 7'hc psychologist 
docs Ills research with the stimulated re- 
sponses of men and lower animals. These 
organisms on which he works are his sub- 
jects— \\\c subjects of his experiment. The 
psychologist performing an experiment is 
the experimenter. Sometimes, when a hu- 
man subject is asked to observe his own 
consciousness, he is called an obserxier. 
That means that the human subject has 
been able to take over a part of the experi- 
menter's responsibility for the accuracy of 
observation. In an experiment with ani- 
mal subjects, it is always the experimenter 
who is the observer, for animals cannot be 
trusted with responsibility for scientific 

With all these matters out of the way, we 
can now turn to the real business of this 
book, and we shall begin with the mecha- 
nism of response, which is, in man, the 
nervous system. 


1. Boring, E. G. A history of experimental psy- 
chology. New York: Appleton-Century, 1929. 
A thorough-going history, from 1690 to about 
1920, of psychologists and their schools within 
the scientific tradition in psychology. 

J. Boring, E. G. Setisatio?i and perception in the 
history of experimental psychology. New 
York: Appleton-Century, 1942. 

The history of research and ideas in the field 
of sensation and perception from the seven- 
teenth century down to about 1930. 

3. Cohen, M. R., and Nagel, E. An introduction 
to logic and scientific method. New York: Har- 
court. Brace, 1936. Chaps. 10-16. Or abridged 
ed. London: Rutledge, 1939. Chaps. 5-10. 

Discussion of experimental method, classifica- 
tion, use of hypotheses, probability, induction, 
measurement and statistical method by two 

4. Dennis, "\V., ct al. Current trends in psrcliol- 

ogy. i'iilsljuigl), I'a.: University of l'illf>l>ur^!i 
Press, 1917. 

Eight lectures by eight disiiriguishcd fMvchol- 
ogists showing hoiv the .Sccontl World War al- 
tered the scientific picture in eight of the m'»M 
important fields of scientific and applied psy- 

5. F.llis, W. I). A source book of Cje\lall psy- 
chology. London: K. Paul, Trench, Trubiier, 

Thirty-lour silcdious from (he writings of 
seventeen Gesialt psuliologisis translated into 

6. I'ciiriiig, r. Urftf'x action: a sluity in the his- 
tory of physioloniial psychology. Baltimore: 
'Williams and Wilkins, 1930. 

A good and quite detailed survey of the 
history of physiological psychology from 
Descartes to about 1930. 

7. Flugel, J. C. A hundred \ears of psychology. 
New York: Macmillan, 1933. 

A picture of modern psycholog\- from 1K33 
to 1933 with especial emphasis upon the psy- 
chology of Great Britain and psvchoanalvsis. 

8. Guilford, J. P. (Ed.) Fields of psychology. 
New York: Van Nostrand, 1940. 

Twenty-t^vo chapters by thirteen authors on 
the content of ph)sioIogical, animal, differen- 
tial, child, educational, industrial, abnormal, 
clinical and social psychology. 

9. Hartmann, G. W. Gestalt psychology. Xew 
York: Ronald Press, 1935. 

A good interpretation and summarv of the 
theories and researches that belong to the 
school of Gestalt psychology and other closeh 
allied schools. 

10. Heidbreder, E. Seven psxcliologies. Xew York: 
Appleton-Century. 1933. 

A clear summarv of the psvchologv of the 
schools of introspective, functional, behavioris- 
tic, d)namic and Gestalt psvcholog\. 

11. Keller, F. S. The definition of psychology. 
New York: Appleton-Century, 1937. 

Brief discussions of the principles involved in 
introspective, functional, behavioristic and Ge- 
stalt psychologies. 

12. Kohler, "W. Gestalt psychology. (2nd ed.) 
New York: Liveria;ht, 1947. 


The Nafure of Psychology 

A clear, readable exposition of Gestalt psy- 
cliology by one of its leading exponents, some- 
what revised since the 1929 edition. 

13. Moore, J. S., and Gurnee, H. The foiinda- 
lions of psychology. (2nd ed.) Piinceion: 
Princeton University Press, 1933. 

A good. aUhough not recent, discussion of 
tlie fimdamental concepts and principles of 

11. Minphv, G. Ati historical inlroduction to 
modem psychology. New York: Harcourt, 
Brace, 1929. 

An excellent detailed and accurate history of 
modern psychology, not limited to the experi- 
mental tradition. 

15. Petermann, B. The Gestalt theory and the 
problem of configuration. New York: Har- 
court, Brace, 1932. 

A straightforward exposition and evaluation 
of the Gestalt psychology of the three leading 
exponents, of the school. 

16. \Vatson, J. B. Behaviorism. (2nd ed.) New 
York: Norton. 1930. 

.\ readalile and elementary presentation of 
tliis school of psychological thought, by the 
founder of the school long after the founding. 

17. Woodworth, R. S. Contemporary schools of 
psychology. New York: Ronald Press, 1931. 

Clear chapters on introspective, behavioristic, 
Gestalt, dynamic and purposive psychologies. 

18. Zilboorg, G., and Henry, G. ^V. A hisloy of 
medical psychology. New York: Norton, 1941. 

.\ vividly written history of psychopathologv 
from the Greeks to the present with especial 
emphasis on the psychoneuroses and t! eir ante- 


The Response Mechanism 

Now that we have seen what psychol- 
ogy in its essentials is, and how it 
came to be what it is, we are prepared to 
go ahead with the study of psychology's 
actual facts. We start with the topic of the 
nervous system. Psychology is not physiol- 
ogy, but it has constantly to consider that 
part of physiology which explains the 
mechanisms of human action. Psychology 
studies man, the doer. Man's doings are 
res23onses— responses to stimulations, to sit- 
uations, to his own needs and ideas. The 
nervous system, considered together with 
the system of endocrine glands, is the prin- 
cipal response mechanism. These two sys- 
tems are basic to all human behavior. 

This chapter sketches the machinery of 
the body which enables man to perceive 
and to respond to his environment in intel- 
ligent fashion. 

As a matter of fact, nearly every part of 
the human body is involved either directly 
or indirectly in behavior, for each part 
plays some role in the smooth functioning 
of the whole body. The digestive tract is 
the portal of entry for food and water 
without which other tissues of the body 
cannot survive or carry on their functions 
normally. The liver stores food materials 
which the brain uses. The heart pumps 
blood which carries these materials to the 
sense organs, the brain and the muscles. 

The lungs provide oxygen for the use ol 
the food materials in tissues of the body, 
and they carry away carbon dioxide result- 
ing from such use. The kidneys, similarly, 
rid the body of the poisonous products 
which are generated in the activities of 
the body's tissues. These are but a few of 
the interrelations of organs of the body; the 
list could be greatly enlarged. 

The response mechanism in man and in 
the higher animals includes (1) the sense 
organs or receptors, which react to stimula- 
tion and set in operation the processes of 
excitation in the living individual, (2) the 
nervous system, which transmits and con- 
ducts excitation, and (3) the muscles and 
glands, or effectors, which make actual re- 
sponse possible. Combined in a highly 
complex mechanism, these three principal 
parts give the living organism means of 
responding in an organized fashion to the^ 
physical energies of the environment -^vhich 
stimidate him. The immediate analog)- is 
a system of push-buttons and buzzers. Eacii 
button (receptor) is connected (ner\ous 
system) to its own buzzer (effector). A pai- 
ticular buzz is a response. Actually this 
analogy is much too simple. Different pat- 
terns of pushes should produce different 
patterns of buzzes, and the system of con- 
nections should change from time to time 

This chapter was prepared by Clifford T. Morgan of The Johns Hopkins University. 



The Response Mechanism 

as situations change. We must, howe\er, 
understand the simplest things first. 


All around tis, all the time, energy 
changes are going on. Light is emitted by 
tlie sun, stars, fires and man-made light 
bidbs; it is reflected by the moon, the walls 
ot our rooms, the plants, our clothes and 
the earth. Heat is given off in the absorp- 
tion of light, in chemical process in our 
bodies, from machinery and from hot ob- 
jects; it is absorbed by the cold objects in 
our environment. Electromagnetic waves 
are sent out by our radio and radar trans- 
mitters and picked up by sensitive receivers. 
Sounds are made by the whirling of the 
wind, the boiling of the water or, generally, 
whenever one object strikes or rubs against 
another. Changes in chemical energy oc- 
cur in food as it is being cooked, in the 
barnyard, in the brewery, in the plants 
around us and in the tissues of our bodies. 

The Stimulus 

Many, but not all, of these energ)' changes 
afl^ect living tissues. Radio and magnetic 
waves do not, some frequencies of light and 
sound do not and some chemical substances 
are relatively inactive. On the other hand. 
X-rays can destroy living tissue, infrared 
rays heat it up, ultraviolet rays assist in 
the synthesis of vitamin B in the body. 
Heat causes changes in chemical reactions 
in our tissues and, if extreme enough, can 
destroy them. Sounds set tissues into vibra- 
tion, causing mechanical changes in them 
and, at certain frequencies and intensities, 
destroying them. Chemical reactions are 
necessary for the growth and maintenance 
of living cells but, if of the wrong kind, can 
kill them. 

Ot those energy changes which affect 
living tissues, some produce responses in 
the organism, others simply affect the tis- 
sues directly. Those energy changes which 
produce responses are defined, for the pur- 
poses of scientific psychology, as stimuli. 
Thus, in man, who is equipped with recep- 
tors and effectors for responding, the word 
stimulus is used to describe any change in 
the energies outside a receptor which is 
responsible for altering the physical-chemi- 


(a) Just stimulated by glass rod, S; (b) change of 
flow of protoplasm and response of amoeba to such 

cal state of the receptor in such a way that 
excitation is initiated. The essential char- 
acteristics of a stimidus, we may note, are 
described in the same quantitative units as 
are employed in the sciences of physics and 

Man's response mechanism is very com- 
plex. We may, however, more easily un- 
derstand it by seeing how it got to be the 
way it is, how the response mechanism 
evolved from the simple to the complex. 

Look at a simple unicellular animal, the 
amoeba. It has no specialized receptors, 
no organs for the reception of stimuli, for 
the transmission of excitation or for the 
effecting of response. Yet the amoeba is a 
self-contained, living system, which may be 
acted upon and changed by many of the 
same physical stimuli which are significant 
in complex animal behavior and, indeed, 
in the whole psychological life of man. 
Radiant energ)', \ibrations in its surround- 
ing medium, chemical and other energies 

Differentiation of the Response Mechanism 


;h t upon (lie ;iitio('h;i ;<ik1 initiate processes 
in the single cell. If strong light or heat, 
for example, is projected upon one side of 
an amoeba, the creature contracts its body 
on the stimulated side in such a way as to 
effect its withdrawal from the stimulus. As 
the result of processes so initiated the 
orientation of the organism in relation to 
its environment may be changed. The 
amoeba, like man, responds to the stimuli 
in its environment. 

Evolution of the Response Mechanism 

Between the amoeba and man, there is 
obviously a vast difference, not only in the 
complexity of the organism as a whole, but 
also in the response mechanism. It is a 
difference in the number of cells involved 
and in the specialization of their functions. 
Above the amoeba in the evolutionary 
scale are the simple multicellular organisms 
like the sponge and the jellyfish. In them 
we see the first steps in the differentiation 
which finally residts in the complex re- 
sponse mechanism of man. The very first 
step, the most primitive differentiation, 
consists in the appearance of the independ- 
ent muscle-effector cell, as seen in the 
sponge. These independent effectors of 
the sponge are more sensitive to external 
physical stimuli than primitive undifferen- 
tiated cells like amoebae. Tliey contract 
more readily and vigorously than primitive 
cells, thus featuring response to external 

After the specialization of cells for re- 
sponse had begun in the evolutionary de- 
velopment, there came the differentiation 
of special cells for excitation by stimuli, the 
receptor cells. In such primitive animals 
as the sea anemone, these receptor cells 
took the form of diffuse nerve nets which 
are excited by external stimuli and dis- 
tribute the excitation to effector cells. It 

was in this way that the: rereptor-efjff lor 
mechanism first appeared (¥i^. 4, /I). 

Finally, in somewhat higher animaS 
forms, specialized nerve or ganglion cells 
(adjustors) came to he interposed between 
the receptors and effectors to make up a 
true nervous system for conducting excita- 
tion from receptors to effectors (Fig. 4, B). 
Such a ganglionic nervous system, or recep- 
lor-adjustor-elfector mechanism, is seen in 


(A) A simple receptor-effector mechanism; <B) a 
receptor-adjustor-effector mechanism. [From G. H. 
Parker, The elementary nervous system, Lippincott, 
1919, pp. 201 f.] 

worms. Thereafter, this mechanism in- 
creases in complexity and also in effective- 
ness in the series of vertebrate and mam- 
malian animals to reach its highest devel- 
opment in man. 

The Effectors 

To the muscle cells, which were the first 
effectors to appear in evolution, ^vas later 
added another class of effectors, the glands, 
so that, in man, we must distinguish two 
main classes of effectors, the muscles and 
glands. The glands secrete chemical sub- 
stances, needed in the bodv"s functions, and 
deliver them into the blood stream for 
general circulation or into special cavities 
of the body like the moudi or stomach. 


The Response Mechanism 

The muscles are of three kinds, varying 
according to the amount and kind of dif- 
ferentiation which they have undergone 
(Fig. 5). (1) Most primitive, or least differ- 
entiated, of the muscle effectors is the un- 
striped. or smooth, muscle cell (D). It is 




(A, B) Striped muscle fibers: (C) heart muscle 
fibers; and (£)) smooth muscle fibers. [From M. F. 
Guyer, Animal biology (3rd ed.), Harper, 1941, p. 

foiuid, for example, in the walls of the 
intestine. Typically a spindle-shaped cell, 
it contains within it a special substance, the 
fibrillae, upon which its contractual prop- 
erties depend. (2) More elaborate in form, 
however, is a second class of muscle cells, 
the striped muscle cells {A, B), which are 
typical of arm and leg muscles. They are 
much more elongated than smooth muscle 
cells and are enclosed in a special elastic 
membrane, the sarcolemma. In them the 
contractile fibrillae are differentiated into 
two substances, one darker than the other, 
the regular alternation of which through- 
out the length of the fiber gives the muscle 
cell its striped appearance. (3) A third type 
of muscle, the cardiac muscle of the heart 
(C), is actually a special kind of striped 
muscle. Its chief distinction is that its 
fibers are not arranged parallel or enclosed 
in a membrane as are the striped muscle 
cells, but branch and unite with each other 
in a network. 

All muscle— be it smooth, striped or car- 
diac—is specialized for but one function, 
contraction. The excitation transmitted 
through the adjustors of the nervous system 
initiates the essential physical and chemi- 
cal events in the muscle, events which lead 
to the release of the muscle's stored energy 
in the form of a contraction. Contraction 
is the final step which determines the be- 
havior of the stimulated organism. 

Because glandular cells, in most instances 
at least, are connected with the cells of the 
nervous system and respond, like muscle 
cells, to excitation transmitted by the ad- 
justors, they too are called effector cells. 
The differentiation by which glands have 
developed their secretory function is not 

(a) (b) 


(a) Glatid composed of irregular sacs (heavy bhisk 
lines) surrounded by tissue and blood vessels (e.g., 
thyroid and ovary); (b) gland simply consisting of 
epithelium (black) penetrated by networks of blood 
\essels (white). Most endocrine glands belong to 
this type (adrenals, pancreas, parathyroids, hypoph- 
ysis). [From A. A. Maximow and W. Bloom, 
A textbook of histology (4th ed.), Saunders, 1941, 
p. 291.] 

particularly prominent in their structure, 
for they look very much like simple cells 
of the skin. They differ, however, in their 
chemical function and in the way in which 
they deliver their secretions into the body. 
In fact, glands may be classified into two 

Endocrine Effectors 


principal groups: (1) duel or exocrine 
glands, like the salivary and the tear 
glands, which pour the product of secretion 
through a tube into a cavity o£ the body or 
out upon the body surface, and (2) endo- 
crine glands, as shown in Fig. 6, of which 
the thyroid and the adrenal glands are 
typical, and which have no ducts but pour 
their secretions directly into the blood 
stream. Such endocrine secretions, called 
hortnones, must be taken into consideration 
for a complete imderstanding of the re- 
sponse mechanism. We, therefore, must 
consider them in more detail. 

Endocrine Effectors 

The adrenal glands, for exampfe, are 
known to be directly involved in the physi- 
ological expression of emotion. Two forms 
of secretion, both of which are circulated 
in the blood stream, are produced by these 
glands: the hormone from the medulla of 
the gland, which is called adrenalin (some- 
times epinephrine), and the hormone of 
die cortex of the gland, which is called 
cortin. Cortin is made up of several chemi- 
cally distinct hormones, active in several 
bodily functions. Thus cortin has a slight 
effect on the sugar content of the blood and 
tissues, but more significant is its role in 
controlling sodium and water content. If 
cortin is withdrawn by removal of the 
adrenal cortex, sodium is excreted through 
the kidneys, and the sodium level falls in 
the blood stream and tissues of the body. 
Sodium, in turn, is necessary for the reten- 
tion of water in the body, and lack of cortin 
therefore causes dehydration. Sodium is 
also necessary for nervous excitability, and 
without it animal organisms become in- 
active and may eventually go into a coma 
and die. This condition occurs with a 
severe deficiency of cortin, but it may be 
partially remedied by feeding large 

amounts of sodium chloride (common salt; 
to make up for the large amounts lost from 
the body. 

liesides cortin, the adrenal cortex secretes 
in small amounts some of the so-called 
androgenic hormones, hormones having the 
same physiological effects as the hormones 
secreted by the glands of sex (see below;. 



[From R. G. Hoskins. Tides of life. Norton. 1933. 
p. 19.] 

Cortin is itself closeh' related chemically 
to these hormones and is derived from the 
same tissues in embryological dexelopment. 
In many of the commonlv observed fea- 
tures of emotion we can see the physiologi- 
cal effects of the hormone adrenalin which 
is poured into the blood stream in times of 
emotional reaction. An increase in the 
amount of adrenalin in the blood has the 
following effects upon physiological activ- 
ity: (1) it increases the tremor in striped 
(voluntary) muscles; (2) it causes relaxation 
of smooth (involuntary) muscle; (3) it 
counteracts fatigue in striped muscle. b\ 
facilitating the transmission between the 


The Response Mechanism 

adjustor and the muscle effector; (4) it 
alters distribution of the blood in the body, 
sending more blood to the Aoluntary mus- 
cles, less to the digestive tract; (5) it in- 
creases blood pressure; (6) it hastens clot- 
ting of blood; (7) it relaxes the bronchioles 
in the hmgs: (8) it causes the liver to re- 
lease sugar into the blood stream; and (9) 
it causes the spleen to secrete or release red 
corpuscles into the blood stream. All these 
physiological changes brought about by 
adrenalin may be considered emergency 
reactions which prepare an organism to 
meet situations calling for quick and prob- 
ably prolonged discharge of energ)'. (See 
pp. 95 f.) 

The thyroid gland is directly related to 
the metabolism of the body, that is to say, 
to the destructive and constructive changes 
in the body tissues. Its hormone, thyroxin, 
acts as an agent which facilitates the break- 
ing do^vn of waste products so that they can 
be readily eliminated from the body. If 
the thyroid gland is underactive, partially 
decomposed proteins are retained in the 
tissues, oxidation is lessened, blood pres- 
sure falls and metabolic processes are gen- 
erally slo^ved up. If the thyroid gland is 
overactive, on the other hand, metabolism 
is increased and body tissues are overstimu- 

Situated just behind the stomach, the 
pancreatic gland is attached to the intes- 
tinal tract by a duct. Through this duct, 
the pancreas deli\ers secretion to the di- 
gestive tract, thereby aiding digestion; in 
addition, it manufactures a hormone, in- 
sulin, which it pours directly into the 
blood. This hormone is concerned pri- 
marily in the utilization of sugar by the 
tissues of the body. AVhen insulin concen- 
tration is low, as in diabetes, blood sugar 
does not get into the tissues to be used but 

remains in the blood at abnormally high 
levels. "When insulin concentration is ex- 
cessively high, the opposite process occurs, 
and sugar leaves the blood to be deposited 
in the liver, the muscles and the brain. 
Sugar in the blood is utilized as fuel by the 
brain and muscles. It is especially impor- 
tant for the brain, which uses sugar almost 

The gonadal glands are important in the 
development of secondary sex characteris- 
tics and also, to a considerable extent, in 
sexual motivation. (See pp. 1 16-1 18.) The 
adult's secondary sex characteristics, which 
are determined in great part by the gonadal 
hormones, include height, weight, the dis- 
tribution of hair over the body, subcu- 
taneous fat and the development of the 
mammary glands, all of which are features 
distinguishing the two sexes. In animals. 
moreo\'er, these hormones are important as 
determiners of sexual beha\'ior, and they 
are undoubtedly of significance too in the 
sexual behavior of man, although it has 
been shown that man's sexual conduct is 
also influenced greatly bv his ctistoms and 
moral codes. 

The pituitary gland, sometimes called 
the master gland and located deep within 
the skull at the base of the brain, manu- 
factures many different hormones. Among 
them are many whose principal function is 
to stimulate or regidate other glands of the 
body. There is also the growth hormone 
which comes from the pituitary gland and 
is important in regulating body growth. 
Deficiency of the growth hormone in child- 
hood creates a dwarf; excess may produce 
a giant, a very tall person with a long 
spindly frame. In general, impairment of 
pituitary function in childhood results in 
a deficient body structin^e, weakened striped 
muscles and tniderde\eloped sex organs. 

The Receptors 


The Receptors 

Receptor cells are cells upon which the 
physical stimuli ol' the. environment act 
and which start in motion tlie processes by 
which the organism makes adjustment to 
stimulation. It is instructive to observe 
how receptors have been differentiated in 
evolution, changing their structures, their 
positions in the body and their chemical 
make-up so as to respond to different types 
of physical energy. The first primitive 
step (noted above) in the differentiation of 
receptors is the relative increase in excita- 
bility of receptor cells as compared with 
other tissues. Further evolution has car- 
ried this trend forward by specializing cer- 
tain receptors to respond to one kind of 
stimulation and other receptors to be ex- 
cited by other kinds. (See Fig. 8.) 

As a result of this differentiation, in man, 
receptors may be divided into four classes: 
thermal (warmth and cold), mechanical, 
chemical and light receptors. The fourth 
class, the light receptors, differs from the 
others, in that it has arisen through the 
differentiation of special chemical mate- 
rials in the cell which are responsive to 
light. In none of these specializations, 
however, does a receptor completely lose 
sensitivity to other kinds of energy change; 
its development results only in a special in- 
crease in one type of sensitivity. Thus the 
thermal receptors are more sensitiAC to 
changes in temperature than other recep- 
tors, but they can be chemically stimu- 
lated. For the mechanical receptors a me- 
chanical stimulus is more effective than 
other kinds of stimuli, yet thermal stimu- 
lation may affect them. 

The kind of stimulus to which a receptor 
is most sensitive because of its specializa- 
tion is known as the adequate stitymliis; 
other kinds of energy changes which will 

excite the receptor if presented in unusual 
amounts are sometimes called inadequate 
stimuli, being inappropriate and therefore 
less adequate. As a result of this differen- 
tiation with respect to stimuli, we have the 
following specific types of receptors in man: 
photic receptors— the eyes; mechanical re- 
ceptors—the ears and the pressure receptors 
in the skin; chemical receptors— taste, smell, 
and the common cheinical receptors in the 

Specialized nerve cell 



Unspecialized receptor Q 

Specialized epithelial cell y 



[After G. H. Parker: from C. T. Morgan, Phyfio- 

loglcal psychology, McGraw-Hill, 1943, p. 25.] 

mouth and nose; and thermal receptors— 
the receptors in the skin responsi\'e to 
changes in temj^erature and giving rise to 
the sensations of warmth and of cold. 

Along with this functional differentia- 
tion of the receptors ha\e gone changes in 
their structure— from simple to complex. 
Those chemical receptors, which are acti- 
vated only by high concentrations of cliem- 
ical substances, are very simple in structure 
and not highly differentiated in function. 
Tlie receptors for taste are chemical organs 
which have become much more complex in 
structure and precise in disaimination. 
The receptors for smell are die most highlv 
developed of the chemical receptors. They 
are nerve ceils with different chemical com- 
positions. The same differences occur for 
mechanical stimulation. The receptors for 


The Response Mechanism 

touch are relatively simple, for hearing (a 
mechanical sense) extremely complex. 

We may note also how receptors have 
taken different positions in the body in 
order to be available for the different kinds 






A diagram to show the relationship of exterocep- 
tors, proprioceptors and interoceptors to the periph- 
eral, central and autonomic nervous systems, and 
to the muscular and glandular effectors of the body. 
[Adapted from various sources.] 

of Stimulation which come to act at the dif- 
ferent positions. Some of the receptors are 
at the surface of the body, so located that 
they may easily be affected by external en- 
vironmental forces. These, called extero- 
ceptors, are exemplified by the receptor 
cells of the eye. Some receptors, on the 
other hand, are embedded in the bodily 

substance itself. Typical of such receptor 
cells are the sensory cells of the muscles, 
which are stimulated by the movement of 
the muscle substance. Such receptors are 
called proprioceptors. Proprio means self, 
and these receptors inform the organism 
about itself. There are also receptors asso- 
ciated with the lining of the digestive tract, 
sometimes called interoceptors. (See Fig. 

The Adjusters 

The central nervous system— the adjustor 
mechanism— makes possible the different 
connections between receptors and effectors 
and consequently between the impulses 
coming in from receptors and going out 
to effectors. The possibility of this switch- 
board-like action is due in part to the fact 
that the continuity of the nervous system, 
as it was seen in the old nerve-net stage, 
has given place in the receptor-adjustor- 
effector system to relatively independent 
nerve cells or neurons. In understanding 
the function of the human nervous system, 
a clear knowledge of the structure, function 
and interdependence of neurons is impor- 
tant. (See Fig. 10.) 


First we need to establish the meanings 
of a few terms. The central nervous system 
consists of the brain and the spinal cord. 
In it lie all the adjustor mechanisms. The 
peripheral nei-uous system is the totality of 
the nerves which connect the central nerv- 
ous system with the receptors and effectors. 
The afferent nervous system is the totality 
of nerve fibers which connect receptors with 
the spinal cord and the brain. It is the in- 
put or sensory half of the peripheral nerv 
ous system. The efferent nervous system 




(A) A typical efferent (motor) neuron. (B) A typ- 
ical afferent (sensory) neuron (in less detail than A). 
(C) Typical central (connector) neurons (in less detail 
than A). Abbreviations: D = dendrites, N = nu- 
cleus, CB = cell body, CO = collateral, A = axon, 
NE = neurilemma sheath, M = myelin (medullary 
sheath), MU = muscle, EN = motor end plate, 
TE = terminal arborization or end brush. 

is the totality of nerve fibers whicfi lead 
from the spinal cord and brain to the effec- 
tors. It is the output or motor half of the 
peripheral nervous system. 

The basic unit of the nervous system is 
the neuron, which is a nerve cell having a 
cell body and nerve fibers leading to it and 
away from it. Impulses are ordinarily ad- 
mitted to a neuron by fibers called 
dendrites and are passed on to the next neu- 
rons by the fibers called axons. Within the 
single neuron, therefore, impulses are nor- 
mally transmitted from dendrite to axon. 

In the simplest cases in the liuman body, 
a receptor is merely a free ending of an af- 
ferent neuron of the peripheral nervous 
system. More often, however, as we have 
just seen, a receptor is a specialized cell 
associated with such a neuron. The af- 
ferent peripheral neuron itself is typically 
a continuous thread of protoplasm connect- 
ing a receptor with the neurons of the cen- 
tral nervous system. The peripheral fiber 
of a single neuron may thus be several feet 
long, for it is unbroken from receptor to 
central nervous system, although it is micro- 
scopic in diameter. In most cases each neu- 
ron fiber is insulated by special sheaths. A 
great many insulated fibers are ordinarily 
held together by other tissue to form a 
cable called a peripheral nerve. Such 
nerves usually contain, at least for certain 
distances, many independent fibers of 
which some may be efferent and others af- 


The energy changes which make up the 
world's stimuli act upon receptors or af- 
ferent neurons to cause physical and chem- 
ical changes in the fibers of the neurons. 
These disturbances travel— propagate them- 
selves—along the fibers and cause similar 
disturbances, in turn, in neurons of the cen- 
tral nervous system, and eventually in the 
effectors. Stimulation in an animal thus 
initiates processes which usually lead in the 
course of time to effector response and a 
change of the individual in relation to its 

Stimulation is in some respects analo- 
gous to the finger pressure on the trigger 
which initiates the release of energy in the 
gunpowder of a cartridge, and thus leads to 
the expulsion of a bullet from a gun. Ob- 
viously, in the cartridge, the explosion of 
the stored energy, not the mo\ement of the 


The Response Mechanism 

finger, is what drives the bullet. In the 
same way, the release by stimvilation of 
energy stored in the receptor or neuron is 
what starts the nervous impulse off. Un- 
like the bullet, however, the impulse is not 
a thing which moves along a fiber. It is 
merely a progressive release of energy; that 
is to say, the physical energy of the stimulus 
does not itself go through the receptor but 
releases certain energies of the organism 

Direction of impulse 

Positive ions 
Membrane -[- -|- .f 


The semipermeable membrane is shown in black 
with the positive ions on the outside and the nega- 
tive ions on the inside. A local current flows when 
the polarization of the membrane breaks down. 
That part of the membrane which is being restored 
after the passage of the impulse is shaded. Thus 
the diagram also shows the refractory periods. 
[Adapted from E. G. Boring.] 

located in the receptor, whereupon other 
progressive releases of energy follow all the 
way along the excited fiber. Movement is 
analogous to the movement of fire along a 
train of gunpowder in which each bit of 
powder is ignited by a preceding bit and in 
turn ignites still another bit. 

Recent research has shown that there are 
complex chemical and electrical events oc- 
cuning in a receptor, neuron or effector 
when it is excited by a stimulus. The place 
of these events, it is now known, is in the 
membranes, not in the interior, of the 
microscopic neuron fiber. Across this mem- 

brane, in the normal resting neuron, there 
is always a difference of electrical potential, 
represented in Fig. 11, created between the 
positive ions accumulated on the outside 
and the negative ions accumulated on the 
inside of the membrane. This electrical 
difference, because of the arrangement of 
chemical ions on the two sides of the mem- 
brane, is known as polarization of the inem- 

The effect of the trigger-like action of a 
stimulus applied to the membrane is to set 
off a series of chemical reactions in the 
membrane. The most important result of 
these reactions is a release of energy conse- 
quent upon a sudden depolarization of the 
membrane and a rapid change in the rest- 
ing potential across the membrane. This 
sudden and progressive electrical change is 
the nervous impulse. 

If a single neuron is excited by a stimu- 
lus which sets up a nervous impulse, the 
neuron is always excited to its maximum 
extent. This principle is known as the 
all-or-none laxu. The law may be stated 
formally as follows: The magnitude of the 
activity in any single neural functional 
unit is as great as it can be in that unit at 
that time and is independent of the magni- 
tude of the energy exciting it, provided 
only that the stimulating energy is suffi- 
ciently strong to excite the neuron at all. 
This law follows from the more general 
principle that the characteristics of the im- 
pulse at any point depend upon the state 
and properties of the fiber at that point and 
not upon the nature of preceding events. 

The nervous impulse arises at any point 
on the neuron at which the stimulus is ap- 
plied. Once initiated, it in turn becomes a 
stimulus to adjacent points on the mem- 
brane and thus the impulse propagates it- 
self along the neuron fiber, like a burning 
train of gunpowder or a burning string. 



except for the lact that burning is chemical, 
whereas the neural impulse is an electrical 
depolarization which is set off by an im- 
mediately preceding depolarization. It is 
important to remember that the energy of 
the nervous impulse depends upon the 
energy released in the neuron, not upon 
the energy of the original stimulus. 

The progress of a nervous impulse along 
a fiber may be recorded on a galvanometer 
(as represented in Fig. 12). On this instru- 
ment, the active region of the neuron fiber 
is seen to be electrically negative in relation 
to the unexcited portion of the same fiber, 
because, in nervous excitation, the normal 
polarization of the membrane with positive 
ions on the outside is destroyed and the re- 
gion of depolarization (the region of the 
impulse) is therefore less positive and thus 
more negative than it was before the im- 
pulse arrived. This region of negativity, 
which is the measure of the impulse, travels 
on down the neuron. Though the impulse 
travels in mammalian neurons at varying 
speeds, a speed of approximately one hun- 
dred meters a second, or two hundred miles 
an hour, may be taken as typical. Such a 
speed, though relatively fast, is, of course, 
in no way comparable to the speed of light 
or the speed of an electrical impulse in a 
wire. It is only about a quarter as fast as 
the speed of sound. 

Returning for a moment to the analogue 
of the burning trail of gunpowder, Ave may 
note that, once a gunpowder trail has been 
burned, it cannot be ignited again until 
new energy in the form of a new trail of 
powder has once more been laid down. In 
the nerve, there is a similar effect. Im- 
mediately following the peak of the nerv- 
ous impulse, there is a period during which 
the nerve fiber cannot be activated again, 
no matter how strong the stimulus. The 
potential difference has been used up. This 

time inicrval is known technically as the 
absolute refractory period. Then, follow- 
ing this period, there is an interval of con- 
tinuous recovery during which the neuron 
may lie stimulated again, provided the 
stimulus is stronger than the minimal stim- 
ulus which ordinarily is effective. This 

_Kr__ ^1^ 











I, II, III, IV show successive time intenals as 
the impulse passes from left to right. The gal- 
vanometer deflection is indicated in each case. It 
will be noticed that the impulse is marked by a 
negative deflection. Abbreviations: S = stimulus, 
NI = nerve impulse, G = galvanometer. 

second interval is called the relative re- 
fractory period. At the end of the relati\e 
refractory period, the excitability of the 
neuron has completely reco\ered and die 
neuron is again ready for activation by a 
stimulus of normal degree. In certain neu- 
rons, especially in the larger sensory neu- 
rons and Avhen the neurons are not greatly 
fatigued, it has been demonsu-ated diat 
there may be a brief period, immediately 
following the relative refractory period, 


The Response Mechanism 

during which a stimulus of an intensity less 
than that normally required to excite the 
resting nerve may be effective. The time 
during which this phenomenon is possible 
has been called the supernormal period. A 
diagram of the relation of these various 
periods is given in Fig. 1 3. 

Time in thousandths of seconds 


Graph shows schematically the absolute and rela- 
tive refractory periods and the supernormal period. 

Mechanisms of Intensity 

Because animals and human beings are 
quite capable of appreciating differences in 
the intensity of various stimuli, it is inter- 
esting to see how nervous impulses may rep- 
resent these differences in the intensity of 
stimulation. Increasing the intensity of 
stimulation may affect nervous impulses in 
two ways: (1) it may increase the frequency 
of successive nerve impulses in a particular 
neuron fiber and (2) it may increase the 
number of fibers in which there are nervous 

Laboratory experiments show how in- 
creasing the intensity of the stimulus may 
increase the number of nerve impulses in a 

single neuron fiber. If a stimulus is ap 
plied continuously to a fiber, a strong stimu- 
lus will reexcite the fiber at an earlier stage 
of the refractory period than a weak one. 
Consequently, an intense continued stimu- 
lus produces a relatively rapid series of suc- 
cessive impulses, whereas a weak stimulus 
may produce a less rapid series. The rate 
of discharge in a peripheral nerve fiber thus 
tends to become greater the more intense 
the physical energy of the stimulus applied 
to it. The total limits of this frequency 
are, as can be seen (Fig. 13), always deter- 
mined by the time limits of the relative 
and absolute refractory periods of the neti- 
rons in question. 

The second neural mechanism of in- 
tensity is an increase in the number of 
neurons being excited. To understand this 
mechanism, it should not be forgotten that, 
in many of the sense organs, as well as in 
centers of the nervous system, there are 
many receptors or neurons exposed at the 
same time to every strong stimulus. The 
neurons and receptors differ among them- 
selves with respect to their excitabilities, 
so that a stimulus of a particular physical 
intensity may call into action some, but not 
all, of the neurons being stimulated. 

From this description it can be seen that, 
when the intensity of the stimulus applied 
to a group of neurons increases, an increas- 
ing number of individual neurons is acti- 
vated as each neuron reacts in an all-or- 
none manner. It thus appears that an in- 
crease in the intensity of a stimulus may be 
associated in the peripheral nervous system 
with an increase in number of units af- 
fected as well as with an increase in the 
number of impulses per second in each 
fiber involved. These two factors jointh 
determine the intensity of sensation. 

Synapfic Connections 


Synaptic Connections 

In order to come to an understanding of 
the response mechanism, we have dealt 
with tlie structure and properties of indi- 
vidual neurons. Not single neurons, how- 
ever, but myriads of them, connected with 
each other in many diverse ways, make up 
the central nervous system. Someone has 
calculated that there are approximately 
twelve billion neurons in the central nerv- 
ous system. At first, this inconceivable 
complexity might seem to balk any hope of 
understanding the mechanisms of the nerv- 
ous system. It is well to remember, how- 
ever, that, no matter what the complica- 
tions of this system may be, it is possible 
to look at it as basically organized for the 
purpose of making connections between in- 
coming and outgoing nerve impulses. 

Neurons, according to most observers, 
are not actually connected one with an- 
other, for each is an individual cell with its 
own membrane. Nevertheless, the fibers of 
the neurons interlace to form functionally 
effective junctures, which are known as 
synapses. Nowadays a general understand- 
ing of the nervous system requires a knowl- 
edge not only of the properties of the indi- 
vidual neurons but also of the special ana- 
tomical and functional characteristics of 

Three of these synaptic characteristics 
are worthy of special attention. (1) In the 
synapse, fibers tend to divide many times 
into small terminals which come in contact 
with the terminals of other neurons or, in 
some cases, with the body of another neu- 
ron. (2) By virtue of the fact that each 
neuron has, usually, several collaterals or 
branches of its fibers, one neuron usually 
makes connections with many other neu- 
rons, both afferent and efferent. Thus, 
synapses may be regarded as 'choice points' 

from which nervous activity may be trans- 
mitted along different neurons. (3) The 
synapse acts as a valve, permitting passage 
of the impulse only from axon to dendrite. 
It is the synapses that liriu't the nerve fibers 
to one-way traffic. 

For many years psychologists have 
thought of the synapses as having resist- 
ance, just as water in a large main meets 
resistance when it comes to a small outlet, 
or as an electrical current is resisted when 
it is conducted through a very small wire. 
The notion of synaptic resistance should 
be regarded only as an analogy, but there 
are conditions at the synapse which give it 
resistive characteristics. For one thing, we 
know from the all-or-none law that the size 
of the nervous impulse is reduced when it 
comes to the very small terminals which are 
common at the synapses. For another 
thing conduction across a synapse' means, 
of course, that the nei-ve impulse at the 
terminals of the fibers of one neuron must 
initiate an impulse in a second neuron, in 
spite of the discontinuity of the mem- 
branes. For this reason one would expect 
transmission of the nerve impulse to be 
more easily blocked at a synapse than along 
a neuron fiber. 

Out of these anatomical and functional 
characteristics of the synapses arise some 
properties of the central nervous system 
which are not ordinarily seen in peripheral 
nerves. One of these properties is spatial 
surnmation. In many cases an impulse 
coming along a fiber to a synapse is not suf- 
ficiently strong to excite, by itself, the ner^■e 
fiber on the other side of the synapse. In- 
stead, it is necessary that two, three or even 
more impulses arrive along different fibers 
and stimidate the same region aaoss the 
synapse simultaneously. In this Asay the 
effect of impulses arriving at the cenual 
nervous system over afferent neurons is 


The Response Mechanism 

summative. Such spatial summation is en- 
countered in sensory phenomena and re- 
flex behavior. For instance, a tiny spot 
of hght, too faint to be perceived, may be- 
come visible if its size is doubled, simply 
because more adjacent fibers are activated 
simultaneously and their impulses are sum- 
mated at some synaptic point. 

Another important characteristic of activ- 
ity in the central nervous system is reverter- 







The circles represent cell bodies; the lines repre- 
sent the axons and dendrites. Direction o£ the 
nerve impulse is indicated by the arrows. [From 
C. T. Morgan, Physiological psychology, McGraw- 
Hill, 1943, p. 64.] 

ation. By tracing, with electrical record- 
ing, the impulses in groups of neurons in 
certain centers of the nervous system, it has 
been possible to demonstrate that neurons 
are frequently arranged in circuits in which 
the fiber of one neuron comes back and 
ends on the neuron whose fiber stimulated 
the first neuron. A typical arrangement of 
neurons in such a recurrent nervous circuit 
is shown diagrammatically in Fig. 14. 
Such an arrangement of neurons means 
that in the central nervous system activity 
may be set up by a stimulus and, unlike 
the situation in peripheral neurons, may 
continue for some time after the stimulus 
has disappeared. This principle of rever- 
beration has many important applications 
in understanding the response mechanism 

and human psychological capacities. It ac- 
counts in some instances for the persistence 
of sensory motivation. A pang of hunger 
or surge of fear, for example, may start 
activity. Often the activity persists, even 
though the hunger or fear subsides. The 
nervous system seems often to hang on to 
such motives, and reverberation may well 
be the mechanism. 

A third characteristic of central nervous 
function is recruitment. This term refers 
to a progiessive increase in the number of 
nerve fibers giving nervous impulses as the 
exciting impulse is repeated. The phe- 
nomenon of recruitment is based on the 
fact that the excitability of a neuron varies 
from time to time and that, on repeated 
stimulation, the fiber that fails to respond 
on the first or second try may be activated 
on the third or fourth because by that time 
it has, in the random variation of its sensi- 
tivity, become more excitable. Once ex- 
cited, there is a tendency for a nerve fiber 
to continue giving nervous impulses be- 
cause of the chance of stimulation during 
the supernormal phase. 

Recruitment has also been demonstrated 
in peripheral nerves, but it is a more im- 
jjortant phenomenon in the central nerv- 
ous system. Recruitment, especially when 
taken in connection with reverberation, ex- 
plains many cases in which persistent activ- 
ity becomes more vigorous as it persists. 
Reverberation and recruitment are sta- 
bilizing factors in the lives of the higher 
vertebrates. They keep the organism from 
mirroring in its behavior every casual 
change in its stimulating environment. 


It is now time, after being introduced tc 
neurons and synaptic functions, to take up 

Sirucfure of the Nervous Sysfem 


the nervous syslcin as a whole and lo con- 
sider its general structure and functions. 
This system, in man, is made up of the 
brain, the spinal cord, the autonomic nerv- 
ous system, the afferent peripheral nervous 
system, the receptors, the efferent periph- 
eral nervous system and the effectors (Fig. 

The spinal cord is the part of the nerv- 
ous system that is enclosed in the jointed 
iDony case of the vertebral column. It is 
connected with receptors and effectors by 
more than thirty pairs of spinal peripheral 
nerves. The spinal cord is primarily to be 
thought of as a cable of insulated fibers, 
by means of which impulses initiated at 
the receptors may be transmitted to and 
from the higher centers of the brain. Yet 
the cord is also in its own right a center 
for the connection of afferent and efferent 
neurons taking part in the action of rela- 
tively simple reflexes. 

Continuous with the spinal cord and 
protected by the bony case of the skull is 
a very complex system of nerve centers and 
communication tracks known as the brain. 
Immediately above the cord and in con- 
tinuity with it is located the medulla 
oblongata. Like the cord, the medulla is 
an important adjustment center in its own 
right, but it is primarily— again like the 
cord— to be regarded as a great cable of 
fibers connecting the spinal system below 
with the higher brain centers above. In 
addition, however, it plays a vital role in 
the control of certain bodily functions, 
such as breathing, heart rate and circula- 
tion of the blood. 

Situated above the medulla, and, as it 
were, off the main track of the central 
nervous system, are the two hemispheres of 
the cerebellum, which functions in the co- 
ordination of bodily movements. In front 
of the cerebellum, there is a large structure. 

the pons, made up (jI fiber tracks and sjjc- 
cialized adjustment centers. Above the 
cerebellum and pons is an elaborate scries 
of special connecting centers, all of which 
f)iay an important part in the adjustment 

Base of frontal lobe _ 
of cerebral hemisphere 

Base of temporal lobe fX 
of cerebral hemisphere 

Cerebellum ^. 

Base of occipital lobe^--^ 
of cerebral hemisphere 

Chain of ganglia of 
autonomic nervous system 

Longitudinal fissure 

( between cerebral 


Olfactory bulb 

Cut end o( 
one optjc nerve 

Optic chiasma 


Cut ends of other 
typical cranial nerves 

I Cervical spinal nerve 

I Thoracic spinal nerve 

ts" Lumbar spinal nerve 

Sacral spinal nerve 


Heavy black structure at left of cord indicates 
part of autonomic nervous svstera. [Adapted from 
C. J. Herrick, An introduction to neurology, 1931: 
by permission of the W. B. Saimders Co.] 

of imptilses and in the adaptation of the 
organism to its environment. Much is 
known concerning these centers, and much 
is still to be discovered. It is impossible 
to review here their anatomical relation- 
ships. It is important to note, nevertheless, 
that, before we reach the cerebral cortex, 
the upper le\el of the central nervous svs- 
tem, ^ve pass through a complex group of 


The Response Mechanism 

amplifying and contributing centers known 
as the thalamus, or thalamic region. The 
thalamus proper is concerned mainly with 
rela)ing afferent impulses on their way 
from the sense organs to the cerebral cor- 
tex, but the parts known as the subthala- 

Receptor Effector 


Schematic diagram showing alternative loops at 
various levels of the central nervous system. Many 
other schemes of levels in the nervous system have 
been proposed. The diagram given here does not 
represent an accepted view of the hierarchy of gov- 
erning centers but is given to emphasize the fact 
that there are levels in the brain and that they in- 
fluence each other. [Adapted from W. M. Bayliss, 
Principles of general physiology, 1927; by permis- 
sion of Longmans, Green.] 

mus and hypothalamus are concerned with 
the control and coordination of bodily 
functions involved in metabolism, and the 
hypothalamus has also a special role in 
the expression of emotion. More will be 
said elsewhere (see p. 100) concerning this 
function of the hypothalamic region. 

In man, by far the largest part of the 
brain is the great cerebrum, which is di- 

vided into two cerebral hemispheres. 
Large, closely organized masses of neurons, 
these structures almost fit the skull. The 
surface of the hemispheres is the cerebral 
cortex. It is convoluted and deeply fis- 
sured, and in it lie the cell bodies of the 
cerebral neurons, the gray matter of the 
brain. The cerebruin is constructed both 
to receive impulses from and to send im- 
pulses back to the lower levels of the cen- 
tral nervous system. It thus forms an ad- 
justment center for recircuiting and pat- 
terning impulses, a center superimposed, as 
it were, upon the lower, more immediate, 
connecting centers of the central nervous 
system. Sometimes the activities of the 
cerebral hemispheres facilitate processes al- 
ready in progress in lower centers; some- 
times, on the contrary, they inhibit such 

The Efferent Peripheral 
Nervous System 

We have seen how sensory activity tends 
to spread out over many paths, ultimately 
involving many regions of the central nerv- 
ous system. Often it is this total complex 
of excitation that determines just which ef- 
fectors shall be activated and how. Dis- 
tributed excitation must be brought to- 
gether to act along particular efferent paths 
upon specific effectors if response is to be 
adequate to the needs of the organism. We 
may think then of the efferent system as the 
place where excitation converges upon final 
common neural paths to produce response. 

The final common path is the name ap- 
plied to the avenue along which all im- 
pulses, no matter whence they come, must 
travel, if they are to act on particular mus- 
cle fibers or glands and bring about the 
corresponding response. Thus activities in 
various parts of the brain and spinal cord, 
which have resulted, it may be, from ex- 

The Autonomic Nervous System and the Bram 


leroceptive stimulation, can be brought 
into relation with impulses from other 
parts of the central nervous system which 
have themselves originated, for example, in 
the proprioceptors of certain muscles. 
Some of these impulses may mutually 
strengthen or facilitate one another; some 
may act in such a way as to lead to mutual 
extinction or inhibition. In the normal 
individual the oiucome of such complex 
adjustment is the finely graded and pre- 
cisely timed effector response. In this way 
activities occur which make up adaptive, 
intelligent behavior. 

The Autonomic Nervous System 

In a complete consideration of the motor 
aspects of the response mechanism, it is 
necessary to deal with the so-called auto- 
nomic nervous system, a motor nervous sys- 
tem which enjoys a measure of independ- 
ence from the great peripheral and central 
systems already considered. This system, 
together with the secretions of the endo- 
crine glands, constitutes a neurohumoral 
system which, to a large degree, controls 
the organic functions of the body— the di- 
gestive functions, the circulatory functions 
and others that are connected with efficient 

The autonomic nervous system is essen- 
tially a nerve net of interconnections. 
Anatomically, it is divided into the sympa- 
thetic and parasympathetic divisions. The 
parasympathetic division is composed of 
the cranial and sacral sections. Figure 17 
is a schematic diagram of the interrelations 
of these divisions and their relationship to 
the various bodily organs. 

Generally speaking, the activity of the 
sympathetic division is antagonistic to that 
of the parasympathetic; for example, the 
heart rate is inhibited by nervous excita- 
tion reaching it over the parasympathetic. 

while it is actelerated by excitation from 
the sympathetic. On the whole, the action 
of the autonomic nervous system, which 
serves involuntary muscles and glands, is 
diffuse and relatively slow in effect com- 
pared with that of the central nervous sys- 


[Reprinted from Bodily Changes in Pain. Hun- 
ger, Fear and Rage by ^Valter B. Cannon, bv per- 
mission of W. ^V. Norton & Company, Inc. Copv- 
right 1915, 1920 bv D. Appleton-Centurv Co.. copy- 
right 1929 b) \Valter B. Cannon.] 

tem. (See the further discussion of the uses 
of this system in emotion, pp. 94 i.) 


There are certain general problems of 
the central nervous system in ^vhich the 
student of mental phenomena is keenlv in- 

One of these, abotit v.'hich there has been 
much speculation, is the relationship be- 
tween brain ^veight and intellectual abilitv. 
\Vhen a formula is used Avhicli makes pos- 


The Response Mechanism 

sible the comparison between the ratios of 
brain weight to body weight, it is found 
that there is some positive relationship be- 
tween the relative brain weight and adapt- 
ability, as far as the various species of ani- 
mals in the evolutionary series are con- 
cerned. Animals with brains that are large 
in proportion to the size of their bodies 
tend to be more adaptable, more clever. 
It has not been demonstrated, however, 
that this relationship also holds true statis- 
tically in comparing human beings of dif- 
ferent intellectual abilities. 

Localization in the Brain 

Another problem of interest in the fimc- 
tioning of the central nervous system is the 

r Frontal 

■^y^^ Body 
/ ^ association 



^ Auditory 

/^ association 


if \ 



^ 1 Visual 
^ / area i 

f/ 7 


s^ jC^^\ Cerebellum / 


Diagram oE side-view of cortex. [From C. T. Mor- 
gan, Physiological psychology, McGraw-Hill, 1943, 
p. 16.] ■ 

localization of various psychological func- 
tions in the brain. This problem has been 
extensively investigated in recent years by a 
variety of techniques: by observing the ef- 
fects of accidental destruction of brain tis- 
sue in human individuals, by experimental 
removal of parts of the brain in animals 
preceded and followed by tests of behavior 

of various sorts, by directly stimulating 
with electrical stimuli centers of the brain 
in animals and in human beings to get ob- 
servations or verbal reports of the effects 
and by using various methods of the elec- 
trical recording of activity in the nervous 

We know now that there is a consider- 
able amount of localization of psycholog- 
ical functions in the brain; on the other 
hand, there is also a considerable independ- 
ence of the various parts of the brain, such 
that many mental functions depend on sev- 
eral different areas of the brain or even, in 
some cases, it would seem, on the brain as 
a whole. 

The simplest aspects of perceiving and 
acting are well localized. In rats and other 
aniinals below man these functions are lo- 
calized in part at subcortical levels; but in 
man, though the subcortical centers still 
exist, they are concerned mainly with sim- 
ple reflex reactions to stimuli, and the pri- 
mary centers for perceiving and acting are 

In the occipital region at the extreme 
back of the head is the area for seeing. De- 
struction of this area causes almost com- 
plete blindness in man, leaving him with 
only the crudest appreciation of light and 
dark but depriving him of ability to see ob- 
jects and to perceive color. In the tem- 
poral lobes at the side of the head are the 
primary cortical areas for hearing. We 
know less about them than the visual areas, 
but their loss, by destruction or operation, 
causes 'cortical deafness' which is consider- 
able, if not complete. Along and behind 
the central fissure in the cerebrum, a fissure 
which lies under the skull on a line run- 
ning roughly from the center and top of 
the head toward the ear, is the area repre- 
senting the sensations of the body— pres- 
sure, pain and temperature as well as pro- 

Localization in the Brain 


prioceptive sensations Ironi liic imisclcs. It 
is interesting to note that when this area is 
exposed under local anesthesia and stimu- 
lated by electricity, it is possible to obtain 
reports from the patient of the occurrence 
of the proper sensory experiences. 

Just in front of, but also running along, 
the central fissure is the motor area of the 
brain. It is not so well defined in lower 
animals, but in monkeys and in man it is 
the area through which 'voluntary' acts of 
behavior are controlled. By direct electri- 
cal stimulation of different parts of the mo- 
tor area one may produce movement of the 
fingers, the legs or the moiuh, depending 
upon just which spot is stimulated. By ex- 
citing the right spot it is possible to get 
'forced' vocalization, voiced sounds from 
the larynx. Extirpation or destruction of 
this area causes paralysis of muscles in vol- 
untary acts. This is what we see in a per- 
son who has suffered a 'stroke' or apoplectic 

Both the motor area and the bodily sen- 
sation area lying near it are laid out like a 
map of the body, with those spots near the 
top of the head representing the feet and 
legs, those along the sides the hands and 
arms, and those farther to the sides the face 
and movith. 

Although simple perceiving and acting 
depend on specific areas, more complex per- 
ception, learning and memory are not so 
well localized. There is, however, good 
reason to believe that there are sensory as- 
sociation areas, situated immediately ad- 
jacent to the primary areas for sensation 
and concerned in the more complex per- 
ceptions of the respective senses. Thus the 
visual association area seems to be neces- 
sary for coordinated responses to seen ob- 
jects and may well play a role in visual re- 
membering. The auditory association area 
is needed in auditory space perception, the 

otientiiig of ilic body in iclaiion to the di- 
rection of the source of sound. It is 
thought also to be essential to auditory re- 
call. These functions, however, are not 
fully established, and much more research 
is needed before this chapter of brain psy- 
chology can be written. 

For the majority of complex memories 
and intellectual activities in man there is 
only a rough localization of functions. It 
is possible to distinguish between receptive 
memory functions, involving the recogni- 
tion and naming of objects and the mean- 
ing of experiences, and expressive func- 
tions, consisting of memories for skills and 
ways of doing things. In general, recep- 
tive types of memories, as in simple percep- 
tion, reside in the back portion of the cere- 
bral cortex, particularly in the areas not 
directly concerned with sensation, whereas 
expressive types of memory are dependent 
on the frontal areas of the cortex lying 
ahead of the motor area. 

Worthy of particular mention is recent 
research concerning the function of the ex- 
treme frontal association areas. Although 
the whole cerebral cortex seems to be con- 
cerned in reasoning and thinking, a man's 
ability to order his behavior and direct it 
toward a goal depends especially on tiiese 
areas. In certain standard tests with mon- 
keys, for example, in which it is necessary 
to use tools or rakes in a certain order— first 
a short rake is used to obtain a longer rake, 
and then that rake in turn is used to obtain 
a longer rake, in order eventually to obtain 
food— in these tests monkeys deprived of 
their frontal association areas are unable 
to solve the problem. In man, similarly, 
destruction of the frontal areas interferes 
with ability to svnthesize acts into a com- 
plete pattern and, in particular-, to plan 
and administer daily activities. 

This function of the frontal areas of the 


The Response Mechanism 

cortex has been recognized in the surgical 
treatment of mental disorders. Certain 
types of patients, who suffer from such an 
excess of anxiety and planning of their 
lives that they are depressed or are ob- 
sessed with complex, compulsive rituals of 
behavior, have been treated by partial re- 
moval of the frontal areas (prefrontal lo- 
bectomy) or by interrupting the fibers 
which go to and from these areas (pre- 
frontal lobotomy). This treatment has had 
some success in relieving patients. Along 
with the good results there has been some 
loss in their ability to plan their behavior; 
yet, all in all, the results have been good. 


1. Adrian, E. D. The mechanism of nervous ac- 
tion: electrical studies of the neuron. Phila- 
delphia: University of Pennsylvania Press, 1932. 

A short seiies of lectures outlining the meth- 
ods of electro-physiology and the nature of ac- 
tion potentials in various types of nerves. 

2. Boring, E. G. Sensation and perception iri the 
history of experimental psychology. New York: 
D. Appleton-Century, 1942. Chap. 2. 

Chapter 2 gives a brief history of experiments 
in nerve conduction. 

3. Cannon, W. B., and Rosenblueth, A. Auto- 
nomic neuro-effector systems. New York: Mac- 
millan, 1937. 

A monograph summarizing a great deal of 
research on the functions of the autonomic 
nervous system and particularly on the role of 
chemical messengers in synaptic conduction. 

4. Creed, R. S., Denny-Brown, D., Eccles, J. C, 
Liddell, E. G. T., and Sherrington, C. S. 
Reflex activity of the spinal cord. Oxford: 
Clarendon Press, 1932. 

A summary of experiments on reflex action 
and synaptic functions in the nervous system. 

5. Erlanger, J., and Gasser, H. S. Electrical signs 
of nervous activity. Philadelphia: University of 
Pennsylvania Press, 1937. 

A monograph covering experiments on ac- 
tion-potentials. It illustrates especially well the 

methods by which one can determine the func- 
tions of different groups of fibers in different 

6. Forbes, A. The mechanism of reaction. In C. 
Murchison (Ed.), A handbook of general ex- 
perimental psychology. Worcester, Mass.: Clark 
University Press, 1934. Chap. 3. 

A comprehensive review of the functions of 
the nervous system forming the background of 
behavior. It is now a little out of date. 

7. Freeman, W. J., and Watts, J. W. Psycho- 
surgery. Springfield, 111.: C. C. Thomas, 1942. 

An account of use of brain operations in hu- 
man patients performed to alleviate or cure 
certain types of mental disorder. 

8. Fulton, J. F. Selected readings in the history 
of physiology. Springfield, 111.: C. C. Thomas. 
1930. Chaps. 6 and 7. 

Excerpts from the classical writings on the 
action of the nervous system and of muscles by 
thirty-two physiologists from the second century 
down to 1926. A third of the excerpts belong 
to the twentieth century. 

9. Fulton, J. F. Physiology of the nervous -system. 

(Rev. ed.) New York: Oxford University 
Press, 1943. 

A comprehensive, up-to-date textbook on the 
functions of the nervous system. 

10. Gardner, E. Fundamentals of neurology. 
Philadelphia: Saunders, 1947. 

Contains excellent illustrations of the nervous 

11. Herrick, C. J. Brains of rats and men. Chi- 
cago: University of Chicago Press, 1926. 

An elementary description of brain anatomy 
and functions. 

12. Hill, A. V. Muscular actixnty. Baltimore: Wil- 
liams and Wilkins, 1926. 

A summary of classical researches on muscle 
contraction, the nervous excitation of muscles 
and muscular work. 

13. Lillie, R. S. Protoplasmic action and nervous 
action. (2nd ed.) Chicago: University of Chi- 
cago Press, 1932. 

A discussion and summary of biochemical 
problems of propagation and integration of 
nervous impulses. 



14. Marquis, D. G. The neurology of IcarniiiK. In 
F. A. Moss (F,(l.), Coniparalive psychology. 
New York: Prentice-Hall, 1912. Chap. 7. 

An excellent summary,- not too technical, of 
what is known of brain functions in learning 
and memory. 

15. Papez, J. W. Comparative neiirnln^y. New 
York: Thomas Y. Crowell, 1929. 

An olf! hut iiscfnl introduclioii lo neurology 
in animals and man. 

10. I'arkfi, (i. II. '/'he clcmenlary nervou.% system. 
Philadelphia: J. B. Lippintott, 1919. 

A classical description of the evojuiion ol 
the nervous system in simple invcnchraic ani- 

17. Weisenburg, 'I., aiirl McIJride, K. Aphasia. 
New York: The C>)inmonwealth Fund, I9.?.5. 

An advanced but readable treatment of the 
localizal ion of psychologiral rnnctions, jiarticn 
larl) langinigc liint.lioiis, in llic human f^rain 



MAN is seldom, if ever, quiet in his wak- 
ing moments, nor is he very tranquil 
in sleep. In response to stimulation he is 
constantly making movements, though 
often they are hardly noticeable. There are 
the incipient niovements of his vocal organs 
and other muscles while he is thinking, the 
ever-recurring eyewink, the shifting of his 
limbs, the restless movement of his body, 
the frequent turning of his head, as well as 
the more coordinated activities like walk- 
ing, talking, piano playing and tennis. All 
such behavior is directed primarily toward 
a manipulation and understanding of 
things of the external world. It is this be- 
havior with which the psychologist is chiefly 
concerned. Such movements are depend- 
ent, for the most part, on the striped mus- 
cles. There are, in addition, the actions of 
the smooth muscles, like those connected 
with the functions of nutrition and of re- 
production, but these movements are 
mainly of interest to the physiologist. 

The importance of the behavior which 
the psychologist studies need hardly be em- 
phasized. If we may judge from the lower 
forms of life, such as the sponge whose 
muscles are stimulated by direct contact 
only, behavior was present in the evolution 
of life even before the development of a 
nervous system. It is the means by which 

the organism, in order to survive, becomes 
adapted to the ever-changing external situa- 
tion. We have seen in the previous chapter 
what are the physiological mechanisms 
which affect the behavior of the organism. 
Our present task is to survey the kinds and 
characteristics of the various responses 
which make up this behavior. 


There are many ways to classify human 
and animal behavior. We may inquire 
whether an act has been learned through 
experience or whether it is an innate char- 
acteristic of the organism, whether it is 
evoked by external stimuli or whether it 
arises from a need within the organism, 
whether it is automatic or conscious and 
voluntary, and whether it is a movement of 
the body as a whole or of a part or limb 
in particular. All these distinctions have 
their place in helping us to understand 
man's behavior, and we shall employ them 
in a description of the varieties of behavior. 

Locomotion and Manipulation 

Since the maintenance of life is depend- 
ent upon the physical environment— the 
supply of food, water, oxygen and sunshine, 
and protection from extremes of tempera- 

This chapter was prepared by Clifford 

T. Morgan of The Johns Hopkins University. 

Tropisms and Ref}exes 


Lure— living things cillicr iiiiist use vvIkii is 
available as plants do, or ilicy iriiist try to 
change their environment as animals do. 
Most behavior may be tlassihetl in terms of 
whether the individual changes its environ- 
ment by moving about, or by manipulating 
or altering it to suit his needs. For ex- 
ample, in the auttunn many ol: the birds mi- 
grate from north to south to obtain a 
warmer climate and a more abundant food 
supply. Man, on the other hand, can build 
and heat a shelter, and can grow, preserve 
and store food for the winter months. The 
former action we call locomotor behavior, 
the latter manipulatory behavior. 

Locomotor behavior is the more primi- 
tive. It is interesting to note that in lower 
invertebrate forms, such as the worm, and 
also in the lower vertebrates, such as fishes, 
organisms must adjust to their environment 
merely by swallowing some of it or by mov- 
ing to and fro within it. The higher in- 
vertebrate and vertebrate forms, however— 
insects, most of the mammals, monkeys and 
man— have evolved appendages with which 
they can manipulate objects in their en- 
vironment, and in this way they adjust 
themselves to it or adjust it to themselves. 
Thus the worm or the fish can avoid light 
only by moving away from it, but man can 
turn the light out. The fish procures its 
food by swimming to it and grabbing it in 
its mouth, but the monkey can use its hands 
to pick bananas from the tree, and man 
can eat by manipvdating a fork and a spoon. 
A worm gets a home by burrowing in the 
ground, but man, by handling a hannner 
and saw, builds himself a house. 

As we look at evolutionary history, we see 
that the development of appendages, an 
important aid to locomotion, accompanied 
change of the animal's habitat from the 
water to the land. An earlier step was 
taken, however, when animals began to use 

their iiK>utiis ir< i/iaiiipulate the enviion- 
ment. This is the only way in which man\ 
animals can alter their environments. The 
insects, for example, carry food to their 
nests by clasping it in their rnanfliblcs. 
Birds construct nests with their beaks. Tlic 
dog retrieves a stick by carrying it in his 

It was late in evolution that animals be- 
gan to use their limbs for manipulation. 
A rat can, under appropriate circumstances, 
learn to pull a string with its foreleet in 
order to obtain food. Monkeys are skillful 
with their hands, and chimpanzees can 
handle tools to solve many problems. Man, 
however, represents a tremendous refine- 
ment in manipulative ability: in the precise 
movements of his hands and fingers and in 
the extremely delicate coordination of his 
vocal apparatus and of his eyes. It is his 
use of a very small part of himself to alter 
his environment that has made man capable 
of his mechanical and engineering achie\e- 

Tropisms and Reflexes 

The distinction between the use of the 
whole body or some part of it in an act of 
behavior is also useful in understanding 
two other varieties of behavior, the tropism 
and the reflex. Both types of behavior, 
unlike any others, are relatively stereo- 
typed immediate reactions to stimuli. The 
tropism, however, is an orientation or 
movement of the ^vhole body ^vith respect 
to a stimulus, whereas the reflex is the 
movement of a specific part, such as a leg 
or an e\'elid, in response to a stimulus. 

AVe get the concept of the tropism from 
observation of the behavior of plants, such 
as the sunflo^ver's turning its face to^vard 
the sun in die daytime and drooping it to- 
ward the ground in the night. Orientatior 
toward the siui is a lieliotropism, and orien- 



lation toward light in general is a photo- 
tropism. Many of the lower animals, espe- 
cially the insects, also show phototropic be- 
havior. Some, like the night bugs which 
seek the light on a summer evening, are 
positively j^hototropic; others, like the cock- 
roach which scurries out of the light into 
the dark corner, are negatively phototropic. 
There are many other kinds of tropism. 
The larval salamander, for example, dis- 

FIOtlRE U). 


(A) Wlieii light from abo%e illuminales dittusely 
the suiiate. llie bug wanders around randomly until 
it accidenially finds the dark corner (D). (B) When 
light is directed from one side, the bug mo\es di- 
rectly away from it to the dark corner. [From 
N. R. I". Maier and T. C. Schneirla, Principles of 
animal psVcholog)', McGraw-Hill, 1935, p. 131.] 

plays a galvanolropism to electrical stimu- 
lation. It lowers its head and tail, arching 
the body concavely, when the positive elec- 
trode is near the head and the negative one 
near the tail; it raises its head and tail, 
arching its body convexly, when the di- 
rection of electrical stimulation is reversed. 
Many animals which live in the water show 
a rheolropism, an orientation and a swim- 
ming movement opposite to the current. 
^Ve may see such a rheotropism in fish 
swimming upstream or attempting to jump 
a falls. There is also geolropism, a re- 
sponse elicited by the force of gravity (the 
(at lands on its feet), and stereolropism, 
elicited by the stirfaces with which the body 
makes contact (the mouse hugs the wall as 

it runs). These are but a few of the tropis- 
tic responses. All of them have the charac- 
teristics that (1) they are not learned, (2) 
they are controlled by external stiinuli 
rather than by volition, (3) they are orient- 
ing responses involving approach to stimu- 
lation or withdrawal from it, and (4) they 
invohe the entire organism rather than 
some part of it. 

We see little that can be called tropistic 
behavior in man and the higher animals. 
Just as specific manipulative responses have 
in large part displaced locomotion as a 
means of adjusting to the environment, so 
reflex responses of parts of the organism 
have, in man and the higher animals, taken 
the place of the gross orienting movements 
in the tropistic behavior of the lower ani- 

The reflexes may be defined as iinolun- 
tary and prompt responses of the striped 
or the smooth muscles of the body. In the 
human repertoire of beha\ior there is a 
great \'ariety of such reflex acts. If licjuid 
gets into the throat of an infant, its mus- 
cles immediately respond and the liquid is 
swallowed; if there is too much liquid, the 
infant chokes. It begins breathing at birth 
as a reflex response to lack of oxygen and 
accumulation of carbon dioxide in its 
blood. Its eyelids close automatically at a 
lotid noise or wheii something moves rap- 
idly toward its eyes. These are a few early 
examples of man's many reflexes. 

It will aid our understanding of the re- 
flex to consider briefly its physiological 
mechanism. The simplest form of reflex 
would require a receptor, a sensory neuron, 
a motor neuron and an effector. Such a 
simple reflex arc, however, is not found iso- 
lated functionally from all other parts of 
the nervous system in a mature human or- 
ganism. Take, for example, the following 
illustration of a spinal reflex. If we jjinch 

Conditioned Response 


ihe paw oi a clog whose spinal coid has been 
cut just below the brain, we can still ob- 
tain a withdrawal or flexion oi the one paw 
accompanied by a forward thrust of the 
other paw. A relatixely simple neural arc 
is involved in the flexion of the paw, but 
even here more than one motoi neuron is 
necessary lo bend the leg: and, besides, 
there must be a (onnection in the spinal 
(oixl between the sensory neuron and the 
motor neuron going to the opposite leg to 
produce the thrust of that leg. There are 
also connections between these arcs and 
many more remote reflexes, which, if stim- 
ulated at the same time, may exert either 
an inhibitory or facilitating effect upon the 
first reflex. Furthermore, when the central 
nervous system is intact, the legs may be 
moved voluntarily— a fact which means that 
there are connections between the spinal 
reflex arc and the cerebrum. This brief 
sketch of the physiology of the reflex arc is 
given to emphasize once more the fact that 
even the simplest form of response involves 
a complicated neural and muscular pattern. 
By obser^ ing reflex acts in young infants, 
or e\'en in human and animal fetuses before 
birth, one can see that the maturing of cer- 
tain parts of the response mechanism is nec- 
essary for the appearance of reflexes. 
There may be, in addition, some stimula- 
tion necessary for their appearance (see 
below), but in the broad sense of the term 
reflexes are unlearned acts. Once firmly 
established, they remain stable and predict- 
able, many of them being common to all 
organisms of the same species. 

Conditioned Response 

Pavlov, a famous Russian physiologist, 
was the first to demonstrate experimentally 
that there are learned reflexes, and that 
they appear through the conditioning of 
unlearned reflexes. Pavlov stimulated a 

dog with the sound of a bell lor a brief 
period, then gave it food and measured the 
resulting flow of .saliva. After a consider- 
able number of such pairings of fjeil with 







Air puff^^ j \^ 

t 1 

yu-- 1 







^ \ 

Air pun 1 


(A) Reaction of the eyelid (Unc R) lo a putt of 
air before conditioning. (B. C) The beginnings of 
conditioning (CR), in which the closure of tlie eve- 
lid anticipates somewhat the puff of air. (D) Full 
conditioned response to light. Rj^ is the light re- 
flex. [From E. R. Hilgard and D. G. .Ntarquis. 
Conditioning and learning, Appleton-Century, 1940, 
p. 38.] 

food, the sound of the bell alone ^vould 
call forth the saliva in somewhat the same 
manner as had the food, diat is to say. the 
bell had taken the place of the food as a 
stimulus to saliAation. Pavlov called diis 
fact a conditioned reflex. 



Later work, however, has shown that 
many responses other than simple reflexes 
can be conditioned. For instance, a man 
places his hand on a grid of electric wires, 
a bell is rung, and then, a second later, the 
man recei\es a shock in his hand. Quickly 
he withdraws his hand. After this sequence 
of events has happened often enough, the 
man begins to withdraw his hand at the 
sound of the bell, thus escaping the shock. 
Since the conditioned withdrawal was a 
learned response and not a simple reflex, it 
seems better in general for us not to speak 
at all of a conditioned reflex, but to call it a 
conditioried response. (For a further de- 
scription of conditioned responses, see pp. 

The Reflex Circle 

There are several situations in human 
behavior, particularly at the early stages of 
infancy and childhood, when a reflex pat- 
tern of behavior may be strengthened or 
perpetuated through conditioning. Con- 
sider, for example, the grasping reflex. If 
a stick is placed on the palm of an infant's 
hand, its fingers will curl about the stick 
and hold on with considerable strength. 
Indeed, shortly after birth an infant can be 
raised from the ground by its hold on the 
stick. Although this reflex is present at 
birth, it is probable that the grasping re- 
sponse is not due entirely to inherited fac- 
tors, but involves the formation of a reflex 
circle through conditioning. It is easy to 
see that, in this case of grasping, when a 
movement occurs, the resulting stimulation 
of the proprioceptors— the receptors in mus- 
cles, tendons and joints— produces a sensory 
impulse which goes into the central nerv- 
ous system and that this impulse may then 
become connected by conditioning to the 
motor response of the original movement, 
so that it acts to continue the original 

movement. The gi-asping is strengthened 
because it becomes conditioned upon itself 
by way of proprioception. This type of 
reflex circle which involves proprioceptors 
is called a circular response. 

It is through the mechanism of a reflex 
circle that various other responses are sus- 
tained and perpetuated, often by means of 
exteroceptors. For example, if an infant 
utters the sound ah, this sound stimulus af- 
fects its ear, and impulses travel along the 
auditory nerve to the brain. Since the 
muscles of the vocal organs are the ones 
that have just moved, this motor path tends 
to be reactivated by the impulses from the 
auditory nerve, and the infant says ah 
again. It is clear that until there is a break 
in this circle, the infant would continue to 
say ah, but the reiteration always gets termi- 
nated presently by some other stronger 
stimulation from outside the circle. 

Even in older children this circular phe- 
nomenon is frequently observed. They de- 
light in repeating sounds— to the annoyance 
of their parents, who may think the chil- 
dren do it purposely to irritate them. One 
boy of eight would bleat like a sheep and 
keep on until, only with difficulty, he was 
made to stop. There was a mental de- 
fective who sat in a corner, day in and day 
out, hitting his two index fingers together 
and murmuring "Beelzebub." The normal 
adult also has many such continuous cir- 
cular responses— like chewing gum, twisting 
a lock of hair, turning a coat button while 

Conditioned Voluntary Responses 

Other complex aspects ol liimian behav- 
ior may be understood, at least in part, in 
terms of the method and phenomenon of 
conditioning. It is even possible to obtain 
voluntary control of what is for most per- 
sons an involuntary reflex. 

Condition and Moiivafed Behavior 


In one experiment of tliis nature, liic 
pupil of a man's eye was trained to contract 
at command. In the first stage of training, 
a bell was rung immediately before a light 
was shone in his eyes. After some trials, 
ihe sound of the bell alone would cause his 
pupil to contract. Then the man was in- 
structed to close and open the circuit for 
both bell and light by closing and opening 
his hand at the verbal command of the ex- 
perimenter. In this way verbal commantl 
became connected through the iiand move- 
ment and the sound of the bell to the 
pupilary reflex. The next step in the ex- 
periment was to eliminate both the hand 
movement and the bell. This left only the 
vocal instruction of the experimenter as the 
conditioned stimidus, and the man's pupil 
now contracted to it alone. The last stage 
of the experiment consisted in having the 
subject himself repeat the verbal instruc- 
tions, first aloud, then in a whisper and 
finally subvocally. Each of these forms of 
stimulation, it was found, could become the 
condition for the contraction of the pupil. 
So the man could, at the end of the experi- 
ment, effectively command his own pu- 
pilary reflex, and this ability was still pres- 
ent fifteen days later, without practice in 
the meantime. 


Thus far we have been dealing with the 
kinds of behavior which are directly and 
immediately controlled by stimulation. 
Tropisms are orientations of the whole or- 
ganism with respect to external stimuli. 
Reflexes are responses of specific parts of 
the organism to stimuli. Conditioned re- 
sponses are reflexes, which, through learn- 
ing, have come under the control of new 
stimidi. In addition to these stimidus-con- 
trolled responses, however, there are many 

varieties ol behavior which arise from needs 
located within the organism. .Such behav- 
ior, although it may use various stimuli as 
cues or signals, depends in its character and 
manifestation primarily on the motive of 
the organism. Now we shall consider such 


It is common among laymen to call reflex 
action instinctive, because both reflexive 
and instinctive behavior are, in the first 
instance, unlearned responses which de- 
jaend upon innate connections in the nerv- 
ous system. In the vocabulary of the psy- 
chologist, however, the instinct differs from 
the reflex because it is in part activated bv 
internal needs of the organism. Responses 
are called instinctive when they involve not 
only innate reflexes in their response pat- 
terns, but also organic needs or drives as 
their immediate causes. Complicated re- 
sponses, however, often owe their develop- 
ment to experience as well as to innate con- 
nections, and it is to the interest of the psy- 
chologist to determine by observation and 
experimentation how much may rightly be 
classed as instinctive or innate and how 
much is acquired. 

An interesting form of beha\ior, which is 
in part instinctive, is the pecking response 
of chicks. Shortly before the chick is 
hatched, its ^vhole body moves violently in 
the shell. The movements of its head take 
on the form essential to pecking, and its 
legs dirust upward against die shell. It is 
during one of diese agitated movements 
that the shell cracks open and the chick 
emerges. The chick's action in breaking 
out of the shell is instincti\e in die sense 
that it is caused by the internal develop- 
ment of the organism. It is not instinctive 
in the popular but incorrect sense that the 



idea of getting out of the shell at the right 
time was inherited by the chick. 

After the chick is thus released, it uses its 
pecking response for eating, but it has to 
learn to peck effectively. At first the chick 
often misses the grain of corn that it strikes 
at. It may strike the com but not seize it, 
or it may seize the giain but not swallow it. 
Only after some days does the chick peck 
accurately and eat with the proficiency of 
the adult hen. If some of the chicks are 
fed artificially for several days and not al- 
lowed to peck during that time, they will 
nevertheless very soon learn to peck as ac- 
curately as the chicks who had been 'prac- 
ticing' earlier. Thus we see, even in this 
relatively simple response of pecking, that 
both instinctive response and learning play 
a part. 

Many animals build nests according to a 
pattern which varies little within the spe- 
cies. In some instances, the offspring have 
had no opportunity to learn from their pro- 
genitors. There must, therefore, be at least 
some innate tendency controlling the activ- 
ity. That such behavior, however, cannot 
possibly be an instinct in the sense in which 
an instinct is sometimes defined (that is to 
say, a series of chain reflexes whose con- 
nections are innate and fixed) is evident 
from the fact that the animal must change 
the nature and sequence of its responses in 
order to fit its behavior to the particular 
siuToundings in which it finds itself and to 
the kind of material immediately available 
for the purpose. 

In other cases, so-called instincts, both in 
animals and in man, are learned behavior. 
Naturalists frequently have reported, for 
example, that some wild animals they have 
encountered were not 'instinctively' either 
afraid of man or inclined to attack him 
imtil they had had unpleasant experiences 
with him. Hunters in Africa have fre- 

quently been able to approach by automo- 
bile within a few yards of a lion without 
the lion's paying particular attention to 
them. There are many other confusions of 
instincts with learned behavior, and it is a 
wise and prudent principle, when explain- 
ing a particular response, to endeavor first 
to determine all the factors of experience 
that could possibly have been operative in 
the development of the behavior in ques- 
tion before concluding that it is instinctive. 
It may safely be stated, however, that 
there are many aspects of behavior which 
are primarily instinctive. Many fishes 
carry out long and comjalex cycles of mi- 
gration and spawning. The salmon, for 
example, spawns in fresh water streams, 
and the young swim downstream to the sea. 
Later and at the proper time in their ma- 
turity, they swim back up the rivers and 
tributaries from which they came, there to 
spawn again. Some species of birds mi- 
grate back and forth between particular 
areas in the north in the summertime and 
in the south in the wintertime. (See Fig. 
195.) Birds too not only build complex 
nests characteristic of their species but also 
display well-patterned activity in procuring 
food and feeding their young. The ma- 
ternal behavior of many animals is largely 
instinctive; they deliver their young, clean 
them, construct nesting places, retrieve the 
young when they venture from the nest anil 
suckle them. The complex sequences of 
sexual behavior— courting and strutting, 
billing and cooing, the male's pursuit of the 
female and finally the complex responses in 
copulation— are all largely innate and in- 
stinctive. Vestiges of these instinctive ac- 
tivities may often be seen in man's behax- 
ior, but learning, habit, intelligence and 
culture have so overridden them that it is 
seldom proper to speak of instinctive be- 
havior in man. 

Needs and Problem Solving 


Needs and Activity 

Tropisms, reflexes and inslinctivc acts are 
all relatively definite, invariable and stereo- 
typed kinds of behavior. li' we knov^' the 
stimulus conditions in the environment and, 
in the case of instinctive acts, the needs ol 
the organism, we can predict with relative 
accuracy the kinds of acts which will Occur. 
There is, however, much behavior in man 
and animals that is not so predictable; it is 
simply a pacing to and fro, or running 
through the wilds or exploring hither and 
yon. Such behavior may appear to be ran- 
dom, because we cannot see a stimulus or 
any other immediate cause for it, nor can 
we see any definite, repeated pattern in it. 

We therefore often call such behavior 
general activity or general exploratory be- 
liaxnor. This kind of activity is important 
to the psychologist, for it is from general, 
exploratory and apparently aimless move- 
ment that patterns of learned behavior, and 
eventually of thinking, arise. Upon close 
observation, it is possible to conclude that 
most general exploratory behavior is the 
result of primitive needs or tensions within 
the organism. (See p. 114.) The organism 
is cold or hot, it is hungry, it is in need of 
water, or it is suffering sexual deprivation. 
Many experiments in which general activ- 
ity has been measured in various animals 
show that large increases in activity and 
exploration occur when one or another of 
these needs is present. 

Problem-Solving Behavior 

It is no accident that general exploratory 
behavior accompanies the presence of needs 
in the organism. In the evolution of the 
response mechanism and in the adjustment 
of the organism to its environment, general 
activity becomes the first step in insuring 
that the organism has an opportunity to 

obtain the satisfaction of its needs. By for- 
aging around the wild animal ha.s a good 
chance to come upon food; by exploring a 
maze a rat finally, if .somewhat randomly, 
finds the food at the end of it; and, sinn- 
larly, the thirsty deer by roaming about 
comes to a stream and finds water. I lius 









' Entrance 


[After C. p. Stone; from F. A. Moss (Ed.). Com- 
parative psychology (2nd ed.). Prentice-Hall. 1942, 
p. 221.] 

general activity has use. It is instrumental 
in satisfying needs. 

Although, in a new and unfamiliar situ- 
ation, general exploration is the onlv avail- 
able means for finding the satisfaction of a 
need, when the need arises again and again 
in the same situation, learning has an op- 
portunity to take place. Activity tlien be- 
comes less random and more stereotyped, 
and specific learned patterns of beha\ior 
emerge. Thus, the first time a hungry rat 
is placed in a maze, it wanders randomly 
in and out of tnany of the blind alleys, but 
after it has been placed in the maze manv 
times, each time finding food at the end, it 



gradually eliminates its random behavior 
and, instead, runs rapidly through the maze 
along the shortest true path. Such learn- 
ing behavior is called problem-solving be- 

Problem-solving behavior as thus de- 
scribed involves a need which at first gives 
rise to general activity. It also may involve 
conditioning. Just as, in conditioning, the 
bell comes to elicit the salivary response 
originally evoked only by the sight of food, 
so, in establishing habits for problem-solv- 
ing, stimuli like odors, shadows, cracks and 
soimds come to serve as signals for the cor- 
rect responses which were originally only a 
part of general random activity. In this 
way conditioning establishes behavior pat- 
terns for solving problems. (Figure 21 shows 
a maze used in problem-solving studies.) 

Covert Behavior 

In animals and in children we can usu- 
ally see many random movements in the 
cotu'se of their solving of a problem, but 
adult human individuals do not display so 
many random movements. In solving a 
puzzle, for example, an adult is likely to 
study the parts, not making any trial solu- 
tions, but putting two pieces together only 
when he has 'decided' that they will fit. He 
seems to think the solution out rather than 
to attain it by trial-and-error. Many ex- 
periments indicate, however, that the prob- 
lem-solving behavior is there, even though 
it is not seen, that it is simply reduced in 
magnitude to very small muscular contrac- 
tions. Even in the problem solving of ani- 
mals, it may be shown that, when random 
responses seem to drop out, actually they 
ai-e simply reduced in magnitude to the 
point where the eye cannot see them. 

Such covert behavior, sometimes called 
implicit behavior, has been measured by 
mechanical and electrical methods of re- 

cording activity in muscles. In some ex- 
periments, for example, an apparatus was 
constructed for showing slight movements 
of the tongue. Subjects were then in- 
structed to think of certain words, and, 
while they were thinking, the movements 
of their tongues were recorded. The think- 
ing was found to be accompanied by defi- 
nite movements of the tongue. In other 
cases, electrical voltages arising in various 
muscles were recorded while subjects ^vere 
engaged in 'mental' problem sohing, for 
example, the solution of arithmetical prob- 
lems. In such subjects, muscle contractions 
almost always appeared in the course of 
problem solving, even though they coidd 
not be seen by the eye, and the electrical 
records showed that these contractions were 
similar in pattern to the responses obtained 
Avhen the subjects were solving the prob- 
lem 'out loud' or with observable move- 
ments. Thus it is important to realize that 
covert movements may be going on, and, in 
fact, that a person may be behaving all the 
time, even when no behavior is observable 
by the casual observer. 

In the following experiment covert be- 
havior is clearly demonstrated. If a record- 
ing instrument is placed on a person's head 
so that a graphic record of his head move- 
ments can be obtained, it is found that 
when, with his eyes closed, he merely thinks 
of his head's moving to the right, the rec- 
ords show that his head actually makes a 
slight movement to the right. AVhen he 
thinks of moving his head to the left, the 
record indicates that such a movement to 
the left is made. Yet the person himself is 
unlikely at any time during the experi- 
ment to realize that he has made an actual 

The feat of muscle reading, a form of 
'mind reading,' is based on this fact of cov- 

Set and Readiness 


ert behavior. II (lie iiulividual, wliosc 
hand is held by the perlonner, (liiiiks ol 
going toward the window, his hand will 
make a slight movement "in that direction, 
which the performer, who is especially sen- 
sitive to such weak muscular responses, 
will immediately i'ecl and use as a clue. 
Animals are particularly acute in noticing 
such involuntary movement. A trained 
dog may be able to pick out the correct 
one of a series of playing cards spread on 
the floor if persons who know the correct 
card are near by. In thinking of the card, 
these onlookers are likely to turn their 
heads involuntarily for a fraction of a sec- 
ond toward the card in question, a hint 
which is not lost on the dog. 

Set and Readiness 

There is another aspect to the behavior 
of problem solving and conditioning, which 
is known as set or readiness to respond. An 
odor at a particular point in the pathway 
of a maze may be a signal to a rat to turn 
right, but it may be more than that. It 
may not only tell him to turn right but may 
also prepare him for making a second right 
turn after that. A pianist in learning to 
play the piano must learn not only to play 
one note at a time from the score but also 
to read ahead and to be ready to strike 
other notes at the appropriate time. He 
must let himself be 'set' for the particular 
key in which the piece is written and must 
not have to be constantly reminding him- 
self about the sharps or the flats. 

A more detailed example of set may be 
taken from laboratory experiments in 
which a subject is asked to push a key with 
his right hand when a red light appears 
and to jDUsh another key with his left hand 
when a green light appears. In this situa- 
tion the subject of the experiment may at 

(iisl icjjcai I lie instriiriions to liirfiscll. He 
may also consciously associate his right 
hand with the red light and his left hand 
with the green light. He will probably, in 
addition, feel some tension in his arms. In 
such terms as these the task or problem is 
represented in the subject's mind before a 
reaction takes place. This attitude of the 
subje<:t is called the set toward the task. 
The set will, however, become increasingly 
less conscious, so that eventually the 
movement will occur immediately and au- 
tomatically upon the appearance of the 
stimulus without any intervening mental 
state at all. Such a set may be either posi- 
tive or negative. In the experiment with 
the red and green lights, the set for the 
right hand is positive for the red light and 
negative or inhibitory for the green light. 
The subject is set not to move his right 
hand for the green light. It Avoidd be 
much harder to reverse the meanings for 
red and green now for the t^vo hands than 
to set up new sets for yellow and blue. 

An experiment can be arranged to in\cs- 
tigate a motor set by jjlacing a rubber ball 
on the reaction key in order to measure the 
amount of pressure of the finger. By such 
means it has been found that the finger fre- 
quently makes an actual anticipatory move- 
ment of downward pressure on the key be- 
fore the real movement is carried out. An- 
other good example of motor set is that of 
the football player who has in mind ju^t 
what to do in answer to the play of his 
opponent. As soon as he sees the i^lay. his 
intended response follo\\s immediately 
without further diought. Off-side play is 
frequently due to an overintensified set. 
The player is so ready to act, that he re- 
sponds to the A\-rong stimulus or even to an 
imaginary stimidus. (For the relation of 
set to )ieed and attitude, see p. 126.) 




AVe arc now ready to consider briefl) 
more complex forms of behavior, including 
voluntary behavior. A person decides to 
go to town. He walks down the stairs, puts 
on his coat and hat, opens the door, gets 
into his car and starts the engine. Com- 
mon sense says that he has willed to do 
lliese various acts. Or again someone is 
trying to read a difficult passage in a text- 
ijook. His mind continues to wander from 
the book to irrelevant matters, until finally 
with great effort he succeeds in concen- 
trating on the work at hand. It is usual 
to say that he has had to use his will power. 
No fault can be found with such an ex- 
pression in ordinary speech, but the psy- 
chologist desires to know what is the gen- 
eral process that one calls 'will.' 

The Will 

In a voluntary act there is no special 
force that can be called the 'will.' Most 
important is the preliminary set or attitude 
already described. In addition, what is felt 
in an experience of 'will power' is the mus- 
cular tension involved— tension in the arms, 
for instance, in acts where arm movement 
is involved, or tension in the muscles of the 
forehead when the brow is wrinkled in an 
effort to concentrate on a mental task. It 
has been argued that, since a person para- 
lyzed in one leg experiences an effort of will 
when he tries to move the inert limb and 
yet does not move it, the will experienced 
obviously cannot come from these muscles. 
What actually happens is that, unknow- 
ingly, he moves some other member. It is 
these other muscular sensations, imagined 
bv their owner as coming from the missing 
ineinbcr, that give him the impression of 
will power. 

The will, then, so far as experience is 
concerned, turns out to be tlie preliminary 
set ph/s the experience of movement plus 
the knowledge that the movement follows 
directly on the set and has not been caused 
by any external force. We know that we 
have made the movement. It is unfortu- 
nate that xi'ill is a noim, as if it were an 
agent, a faculty or a special kind of energy. 
There is 'willing' but not a 'will.' Willing 
is a process which one calls a vohinlary act. 

Voluntary Control of Movement 

What do we have to do in order to gain 
voluntary control of a response? It was at 
one time supposed that, if we could call to 
mind how the muscles would feel when 
moved in a certain way— in other words, if 
we had a clear memory of the propriocep- 
tive sensations produced by the movement 
—we could then move those muscles appro- 
priately. It was even sometimes supposed 
that such a memory of a movement must 
necessarily precede the movement which we 
desire to make. That this assumption is 
not true was demonstrated in the experi- 
ment already described, the one showing 
that voluntary control of a reflex can be 
obtained by the method of conditioning 
(pp. 44f.). 

Not only, however, is this anticipatory 
proprioception not necessary, but research 
has also shown that proprioception alone— 
or even when combined with a visual image 
of what the movement should be— is not a 
sufficient preliminary process to produce 'at 
will' a movement never before voluntarily 

In certain experiments, persons who 
could not move their ears voluntarily had 
their ear muscles stimulated electrically so 
as to produce the mo\ement. These per- 
sons felt the movement and saw it in a 
mirror. Still they could not move their 

Voluntary and Auiomafic Behavior 


ears voliiiilarily. In allciiij^tiiig lo iikjvc 
them, they had the same sense o£ helpless- 
ness which they had experienced before the 
electrical stimulation. In their attempts, 
however, they moved the volimtarily con- 
trolled muscles of the brow, jaw and cheek, 
in such a way that the nuiscles of the ear 
were accidentally moved with them. Thus 
the ear muscles were brought into the re- 
action pattern, with the result that there 
occurred both afferent impidses lo liie mus- 
cles and proprioception irom their contrac- 
tion. It was only then that the proprio- 
ception, by becoming a link in a reHex cir- 
cle, helped to develop fidl voluntary con- 
trol of the ears. 

These facts give us a picture of the ori- 
gin and development of voluntary move- 
ment. It is clear from them that the first 
movement of our muscle groups are un- 
conscious and involuntary, and that they 
come under conscious voluntary control 
only later, after the muscles have been 'ac- 
cidentally' innervated. 

Reflexes, Conditioned Responses 
and Voluntary Acts 

In many instances of human behavior 
there is no difficulty in distinguishing a 
simple reflex from the more complicated 
conditioned response or from a voluntary 
response. Simply by observing the ante- 
cedents to the movement, we can tell, for 
example, whether an eyewink has occurred 
voluntarily or has been caused by some 
stimulus. In the case of the conditioned 
knee jerk, however, an investigator may not 
always be able to tell whether the move- 
ment of the leg in response to a bell as a 
conditioning stimulus is an involuntary 
conditioned response or whether the sub- 
ject is 'faking' results by voluntarily mov- 
ing his leg when he hears the bell. 

Numerous experiments have been de- 

vised (o oblaiii some, oljjctlive crilcrion for 
llie dillereiitiatirjii ol these three forms of 
response. It has been found that the reflex 
is, on the average, more rapid than either 
the conditioned response or the voluntary 
response. Experiments in which the pupi- 
lary light reflex was conditioned showed 
that the average latency (the time jet ween 
the presentation of the stimulus and the 
onset of the response) of the conditioned 
dilation of the pupil was 1.56 seconds and 
of the conditioned (onlraction 2.29 seconds, 
whereas the simple reflex to light is gen- 
erally 0.2 lo 0.5 second. The average 
duration of the conditioned dilation re- 
sponse was 8.24 seconds and of the condi- 
tioned contraction response 10.93 seconds, 
whereas the duration of the simple reflex 
to light is usually 1 to 4 seconds. 

There may be overlapping, however, in 
the speed of these different forms of re- 
sponse. In the case of the eyelid response, 
it was found that, through practice in open- 
ing the eyes as quickly as possible immedi- 
ately after the eyes had closed, the speed of 
such voluntary opening increased above the 
speed of the reflex. Yet this result does not 
mean that the voluntary response has de- 
veloped into a reflex. 

The conditioneci response, moreo\er, usu- 
ally differs qualitatively from the uncondi- 
tioned. The conditioned knee jerk is not 
quite the same as the reflex knee jerk, nor 
is the conditioned wink response identical 
with the reflex eyewink. Under most ex- 
perimental conditions the conditioned re- 
sponse is seldom as great in magnitude as 
the unconditioned. 

Another objective difference bet^veen tlie 
reflex and the voluntary response appears 
in an analysis of the total time of the wink. 
If this time is analyzed into the time of 
opening and the time of closing the eye, it 
is found for the reflex that, as the time of 



dosing decreases, the time of opening also 
decreases. In voluntary response this rela- 
tionship is changed. 

A further difference is that voluntary re- 
sponse is more readily modified by instruc- 
tion than the reflex. At times the change 
of tlie reflex is found to be opposite in di- 
rection from the change in voluntary re- 
sponse. For example, subjects were told 
to relax as much as possible during both 
voluntary and reflex action. When the 
records of the eyelid movements were ana- 
lyzed, it was found that the latency of re- 
sponse was generally slightly decreased for 
the reflex, whereas the latency of the volun- 
tary response increased under relaxation. 
These last results are readily understood. 
The football player has to be 'keyed up' 
to start immediately upon the snapping of 
the ball. If he relaxes for a moment, he 
may be caught off his guard. The reflex, 
on the other hand, seems to work best when 
we are caught off guard. If our attention 
is concentrated on the appearance of the 
stimulus for, let us say, the knee jerk, there 
is likely to be a slight inhibitory effect on 
the reflex. 

Experiments have also been made to de- 
termine whether any differences between 
reflex and voluntary activity can be discov- 
ered in the electrical potentials as the im- 
pulses pass along the nerves involved. The 
results indicate that the pattern of these 
potentials is more stereotyped in the reflex, 
a discovery which is in accord with the con- 
ception of a reflex as a fixed form of re- 
sponse as compared with the variability of 
voluntary response. 

Voluntary Acts and Learning 

The fact that voluntary acts have been 
so highly developed in man gives him a 
considerable advantage in learning various 

sorts of behavior, for he employs volun- 
tary acts in his initial solutions. When, 
for example, a man starts to learn some 
difficult movement, like a new kind of dive, 
he has an idea of the form of movements 
that he wishes to make and then vohmtarily 
attempts to carry out the movements. Dur- 
ing the dive he will be aware to a certain 
extent of the position of his limbs, and 
after the completion of the dive he will 
have a memory of what he has done. On 
the next occasion, he may make use of this 
experience by voluntarily attempting to 
alter the form of his dive. By successively 
and voluntarily altering his behavior on 
subsequent occasions, he is able to learn 
much more rapidly and to achieve a higher 
degree of proficiency than if learning had 
to take place through random trials or con- 

After a great deal of practice, acts which 
were originally voluntary become more and 
more involuntary and finally result in auto- 
matic acts or habits. Thus, in learning to 
operate a typewriter, each pressing of a key 
is at first a voluntary act, but, after a rea- 
sonable degree of proficiency has been at- 
tained, the typist thinks no more of indi- 
vidual finger movements and may type au- 
tomatically, while thinking about some- 
thing else. By practice, the component vol- 
untary acts become integrated into a 
smooth sequence of movements which do 
not, for the most part, enter consciousness. 
In fact, if the person becomes aware of the 
acts and attempts voluntarily to carry them 
out, his performance is usually impaired. 
Let a person suddenly become fidly con- 
scious of what he is doing, while he is per- 
forming some well-coordinated response, 
and there is likely to be an interference in 
the smoothness of the response. When he 
is very eager not to make a mistake in the 

Voluntary Acts and Learning 


letter he is typing, lie is almost suie to do 
something wrong. If he thinks of volun- 
tarily moving his legs when going rapidly 
upstairs, he is likely to trip. This change 
from an automatic response to a voluntary 
act throws the individual back to tlie initial 
stages in the development of his habit. 

There arc many examples in everyday 
life of the way in which acts which were 
originally voluntary become automatic. A 
pitcher, when he throws a ball, docs not 
have to think of the movement he is going 
to make. The act is voluntary in the sense 
that he intends to pitch the ball, but, as he 
starts the swing of his arm, he is likely to be 
looking at the plate, his mind occupied 
with little else than the corner of the plate 
he wishes to 'cut.' Seldom are you con- 
scious of the movements of your vocal or- 
gans while you are talking, nor are you 
often conscious of how you are going to 
move them before you start. For the most 
part, you are occupied with the direction 
of your thought and the effect you are 
achieving. You hear your own voice 
vaguely. If you want to know what words 
you are actually using to express your ideas, 
you have got to listen to yourself talking. 
In rapid conversation there is no feasible 
way of being aware of your own words be- 
fore they are uttered. Conversation is only 
one example of habituated automatic ac- 
tion. A day is replete with such semivol- 
untary acts, acts that hardly touch the con- 
scious level at all. 

There are examples of voluntary acts 
which have become even more automatic. 
We curl a strand of hair, bite our pencil 
tip, tap on the floor, lattle our keys, en- 
tirely unaware that we are doing anything. 
While walking with a friend, we engage in 
animated conversation, completely uncon- 
scious of the action of our legs. Such auto- 

matic acts can be as complex and can in- 
volve as highly an iruegrated set of reac- 
tions as any fully voluntary response. This 
fact is well demonstrated by instances of 
automatic writing, where a person writes 
the answers to (juestions put to him with- 
out the least ability to say what it is he 
has written. Since it seems evident in such 
cases that ilie hand has been guided by 'un- 
conscious' processes, the method is often 
used to discover what lies below the level 
of conciously controlled behavior. 

The examples which we have examined 
in these last paragraphs illustrate the vari- 
ous forms of action, from wholly voluntary 
to unconscious automatic acts. Such a 
classification, however, is by no means clear- 
cut. We can have acts that are entirely 
automatic and unconscious, and acts that 
are entirely voluntary, but almost all volun- 
tary acts contain some automatic process. 
In fact, such acts as piano playing, when 
performed by a proficient player, contain 
so much automatic response that it is cus- 
tomary to use the word automatic rather 
than voluntary in regard to them. Here 
action has become so well established a 
habit that correct response follows immedi- 
ately upon stimulus, whether the musician 
is using the score or playing from memorv, 
that is to say, whether the stimuli are the 
printed musical notations and the preced- 
ing finger movements or the latter alone. 
It is, indeed, frequently difficult to say 
whether an action is entirely automatic or 
not, as when the musician plays softlv over 
the keys while conversing with a friend, or 
when a telegraph operator taps SOS on 
the desk with his finger while he is reading 
an engrossing detective stor). The impor- 
tant point is that most of om^ responses ai-e 
a mixture of the t^\o types, being both 
automatic and voluntary. 




Closely related to the complex \oluntary 
and automatic acts which we considered in 
the last section are the forms of behavior 
which are controlled by ideas rather than 
by external stimuli, needs or volition. Al- 
though some animals can solve elementary 
problems involving reasoning and ideas, 
only man's behavior can be controlled in 
any considerable way by ideas. The fact 
that ideas may cause acts of behavior is 
called suggestion. Sometimes such sugges- 
tion comes from within the individual, 
sometimes from external events which he is 
observing and sometimes from the actions 
or words of other individuals. We shall 
now consider these forms in turn. 

Ideomotor Action 

If the idea of an act impels a person to 
carry out the act, we speak of ideomotor ac- 
tion. This form of action may be illus- 
trated by the dislike of some persons for 
high places. The idea of jumping comes 
so strongly to them that they fear it will 
break over into action. Nearly everyone 
has had at some time so vivid an idea of the 
act of jumping out of the window at which 
he was standing that he has wished to with- 
draw from the spot in order to avoid the 
danger. Another example is the desire to 
knock off the top hat of a fellow traveler, 
an idea which, once brought to mind, may 
prove almost irresistible. Advertising has 
made good use of the principle of ideo- 
motor action. The tired tennis player is 
portrayed in the act of smoking a certain 
brand of cigarette, so that the reader may 
be induced by the idea to do likewise. In- 
numerable examples of a similar natuie 
could be taken from daily life, for ideo- 
motor action is a very common experience. 


Still more frequent, however, are the in- 
cipient movements, sometimes too slight to 
be readily detected, at other times quite 
noticeable, which are aroused in us by 
movements in our environment. An ob- 
vious example may be observed at a foot- 
ball game where the home team, let us say, 
is holding on the one-yard line. An en- 
thusiastic and partisan spectator may push 
actively and urgently with the players, until 
suddenly he realizes that he is actually push- 
ing his neighbor. Or again, when spec- 
tators watch an acrobat climb to the top 
of a pole balanced on the head of a col- 
league and swing back and forth with the 
tottering pole, the whole crowd sways in 

In looking at statues and buildings and 
pictures, or in listening to music, this sort 
of movement likewise occurs. We may feel 
the thrust of the foot or the tension of the 
outstretched hand of a statue, the weight 
of the arch on its columns or the rise of the 
cohmins themselves, and the direction of 
the lines and weight of the represented 
mass in the picture. Listening to music, 
we often find ourselves following the rhythm 
with some part of our bodies. Even the 
rhythmical click of the car wheel over the 
lail may arouse a motor response. Since wc 
are occupied with the perception of the ob- 
ject, we are for the most part not conscious 
of these movements in ourselves. Neverthe- 
less our responses, though unconscious as 
such, give dynamic quality to these percep- 
tions. The lines of the picture become 
lines of force, the represented mass has 
weight, the rhythm of the music seems to 
flow smoothly, the curves of the architec- 
ture appear to have the grace of a moving 
object. It is as if we had projected our 
own unconscious movements into the ob- 

Acts and Ideas 


ject ot our perception. Because ol iliis 
'projection' the experience has been termed 
empathy, a feeling of oneself into the ob- 
ject of regard. 

An example of empathy is presented in 
Fig. 22. It is assumed that the trainer is 
unconscious of the movement of his leg; he 

(IrawaJ of the hand. The sight ol a half- 
read book suggests continuing the story; 
without any intervening thought the stu- 
dent picks it up, when he had fully in- 
tended to settle down to study. The 
sleight-of-hand performer, by a movement 
of the other hand, suggests a shift of the 









Blind Bill Kelley clearing the pole, with his trainer, Peter Bennett, watching. Notice the cmpatliic re- 
sponse ot the trainer. [By permission of Pictures, Inc.] 

is only aware, through projection of his 
own movements, of the effort being made 
by the jumper, that is to say, of the dynamic 
quality of the perception. Without this 
assumption of projection the illustration 
would be merely an example of imitation 
and not of empathy. 


In the broad sense of the term, sugges- 
tion plays a large role in our lives of ac- 
tion. The immediate perception of an ob- 
ject most frequently leads to some response 
which depends upoii previous experience 
with the object. The flame suggests with- 

attention of the audience away from the 
hand that is doing the trick. In the em- 
pathic perception of lines and mass there 
is the direct suggestion of some motor re- 
sponse. The individuals of a mob are ex- 
tremely suggestible to the action of one or 
more of their companions. Although the 
term suggestion is used legitimately in all 
these instances, it is usually restricted to 
that action which is brought about by a 
verbal instruction. \Ve act through sug- 
gestion when we respond to the written or 
spoken word uncritically. In most in- 
stances such a response is immediate, but it 
may on occasions be delayed. 



Children, being obviously less critical 
than adults, are more suggestible. As a 
consequence their testimony is particularly 
imtrustworthy. This trait may be easily 
demonstrated. The child is asked to place 
his hand on an electric heater and told to 
say when he feels the warmth. After the 
experimenter has made the motion of turn- 
ing on the current (^vithout actually throw- 
ing the switch), the child will soon report 
that he feels the heat. 

On occasion, however, adults can be just 
as suggestible as children. Given the 
proper emotional setting, they will imagine 
the impossible. An excellent example is 
what occurred in the autumn of 1938 when 
the story of the Martians came over the 
radio. Many persons 'actually' smelt the 
poisoned fumes which the men from Mars 
were supposed to have spread on Earth. 

A person is said to be highly suggestible 
when he lacks firm convictions of his own. 
Though most of us can act through sug- 
gestion a thousand times a day without 
losing individuality, there are the extreme 
cases where a person has so few firm con- 
victions of his own that no counter argu- 
ment enters his mind when he is presented 
with an important course of action. Con- 
versely, there is the negatively suggestible 
person. He almost invariably has some 
reason for not doing what is desired of him. 
The first type cuts out the coupon of the 
advertisement at once and mails it. The 
second type immediately throws the adver- 
tisement in the wastebasket. It is thus that 
attitudes toward suggestion determine ac- 
tion in the large as well as the small affairs 
of life. Degree of suggestibility is an essen- 
tial feature of personality. 


The hypnotic trance and its manifesta- 
tions are the result of an extreme state of 

suggestibility. It is a state which may be 
induced in varying degrees in most normal 
persons who are willing to cooperate with 
the hypnotist. Except that he can respond 
adequately to external stimulation when 
the hypnotist suggests it, the person who 
has been hypnotized is in a condition re- 
sembling sleep. If the subject's mind is 
free from the ordinary inhibitions and re- 
sistance, he readily carries out the instruc- 
tions given him by the hypnotist, provided 
that the task does not conflict with his most 
fundamental convictions. He will commit 
an artificially arranged crime but, contrary 
to popular belief, he cannot easily be in- 
duced to commit an offense if it really con- 
travenes strong tendencies of ethical con- 
duct, as we shall see presently. 

It has been supposed that under hyp- 
nosis a person's senses are keener and his 
strength greater than normal. Experi- 
ments, however, have shown that this is not 
the case. There is little if any difference 
in his sensitivity, and the feats of strength 
he performs under hypnosis he can also do 
in his normal state if he is willing to make 
great effort. It has also been found experi- 
mentally that persons who acted through 
hypnotic suggestion as if they could not see, 
actually had normal vision. 

The state of hypnosis is characterized by 
its contradictory phenomena. The hypno- 
tized person behaves as if he were enthusi- 
astically acting out a big lie in order to 
please the hypnotist, acting it out and be- 
lieving it as he acts. Sometimes he has to 
perceive something in order to know that 
it is something he is supposed not to per- 
ceive. For instance, the subject may be 
told that he is now blind in his left eye, can 
see only with his right. Immediately he be- 
gins to act consistently as if he were blind 
in his left eye. The hypnotist then shows 
him a little box into which he can look 

Hypnosis and Reaction 


with both eyes. First the hypnotist lets the 
subject see that a red disk is inserted at 
the back o£ the box at the left and a green 
disk at the back at the right. Then he tells 
the subject to look into the box with both 
eyes and asks him what he sees. The sub- 
ject reports that he sees a green disk, be- 
cause the red disk is at the left and he is 
simulating blindness with his left eye. Ac- 
tually the box, by the use of prisms, reverses 
the images of the disks left for right, so that 
the reported green disk is really seen with 
the left eye. Thus it appears that the sub- 
ject really can see with his left eye when it 
helps him to play the game of being blind 
in his left eye. 

Experiments of this sort make hypnosis 
resemble faking, but it is a very insistent 
and enthusiastic kind of faking. For in- 
stance, it is easy to suggest successfully to 
a subject that he is insensitive to pain in 
some part of his body and then to burn or 
cut him in that region while he carries on a 
gay conversation with the hypnotist. In 
fact, hypnosis was used successfully in many 
cases for surgical anesthesia just before the 
discovery of ether in 1846. It certainly 
takes a good deal of enthusiastic coopera- 
tion to fail to notice the pain when your 
leg is being amputated, with no anesthesia 
but with the hypnotic suggestion that you 
are not to feel anything in the leg. 

This desire to please the hypnotist has 
to take its chances along with all the other 
desires that fight for dominance. Will a 
subject under hypnosis stab a man with a 
dagger? He will stab a friend with a card- 
board dagger if he knows the dagger is 
cardboard. An habitual stabber might be 
persuaded to stab an enemy with a real 
dagger. A college student was once in- 
dviced under hypnosis to throw what he 
knew certainly to be strong nitric acid at 
the face of a very good friend. The acid 

never reached its goal because invisible 
glass was interposed, but the student did 
not know about the glass. Still he did 
know that he was in a psychological labora- 
tory wiiere strange things may happen with- 
out permanent liarm to any one, and he 
may have been trusting the hypnotist to 
jjrotect him from the apparent consequences 
of his act. Hypnotic suggestion is only 
one among many motives that act upon the 
hypnotized subject. 

Suggestion may also operate after a sui)- 
ject has been awakened from the hypnotic 
state. That phenomenon is called posl- 
hypnotic suggestion. For instance, the sub- 
ject may be told: "After you awaken and 
before you leave the room, you will take 
that chair and stand it on the table." Then 
the subject awakens, looks at the chair, and 
puts it on the table. He gives all sorts of 
excuses. It is in the way on the floor. It 
looks better on the table. He was thinkini; 
he would like to sit way up there on the 
top of the table. One such subject looked 
at the chair and exclaimed: "I want to put 
that chair on the table. I bet it is because 
you told me to in hypnosis. I am not going 
to do it!" He left the room, banging the 
door. In five hours he was back, a little 
sheepish. He looked at the chair and the 
table. "Well," he said, "I may as well get 
it over w^ith!" And he lifted the chair and 
put it on the table. Then he heaved a 
sigh of relief for a dut)' at last accomplished. 


The preceding sections ha\ e dealt princi- 
pally with the qualitative aspects of voli- 
tional acts. 

Reaction Time 

We turn no^v• to the speed of response ami 
the conditions ^vhich determine the speed. 



The problem o£ the reaction time arose in 
1796, when a certain astronomer at the 
Greenwich Obser\atory in England dis- 
missed his assistant because the latter's ob- 
servations of the time at which stars cross 
a cross-hair in the field of the telescope were 
almost a second later than his own. 
Twenty vears later it was disco\ered bv 

One of the most accurate arrangement- 
for the measurement of human response is 
illustrated in Fig. 23. Its main feature is 
a chronoscope or timing device, consisting 
of a synchronous motor and a dial whose 
hand is attached to a magnetic clutch. Two 
telegraph keys are wired to the instrument 
in such a ^\ay that ^vhen one key is pressed 


(A) Bulb for response kev; {IS) voice keys; (C) light stimulus; (D) relay for touch stimulus; (E) chron- 
oscope; (F) relay for sound stimulus; (G) tuning fork for time control; (H) stimulus keys. [Courtesy of 
the C. H. Stoelting Company of Chicago.] 

checking the observations of different 
astronomers that the discrepancies were due 
to more fundamental differences in the 
manner of reaction than would be produced 
by mere carelessness. The conclusion was 
reached that these measurements, which de- 
pend upon the speed of reaction of the ob- 
server, were affected by what was then 
called Ure personal equation, that is to say, 
constant individual differences in reaction 
time. When the first psychological labora- 
tory was established in Leipzig in 1879, ex- 
periments on reaction times were under- 
taken. Ever since, the determination of 
reaction times has represented an impor- 
tant technique in experimental psycholog)'. 

the clutch engages with the motor and 
when the other key is pressed the motor is 
released. In the simplest experiment the 
subject is seated at one key and the experi- 
menter at the other, and the motor is 
started. The experimenter presses his key, 
ivhich gi\es the desired stimulus to the sub- 
ject and engages the cltuch so that the hand 
on the dial revolves. As quickly as possible 
upon perceiving the appropriate signal, the 
subject presses his key, thereby releasing the 
clutch, so that the hand on the dial stops. 
The revolutions of the hand are recorded 
on the dial. As the speed of revolution is 
already known, the time that elapsed be- 
tween the pressing of the two keys— in 

Simple Reactions 


short, between stimulus and response— may 
be read from the dial in milliseconds. 

Various stimuli and types of response 
may be used. For example, the experi- 
menter may signal by means of a clicking 
sound produced by a relay, or he may give 
a tactual stimulus by means of a magnetic 
contrivance that presses on the subject's 
hand. He may flash an electric lamp as a 
visual stimulus; or, if a discrimination re- 
action is desired, he may illuminate in hap- 
hazard order a green and a red lamp, re- 
quiring the subject to react to one color 
and avoid reaction to the other. For word 
reactions he uses a voice key containing a 
thin diaphragm which vibrates when 
spoken against, thus temporarily breaking 
the electric circuit. The experimenter may 
speak into one voice key, starting the clock, 
and the subject may speak into the other 
key, stopping it. There are other possible 
arrangements and other forms of electric 
clocks, but in each of them the clock is 
started and stopped automatically and re- 
action times are obtained which are accu- 
rate within a few milliseconds. 

Simple Reactions 

In the siinple reaction experiment, the 
subject is generally instructed to respond 
by pressing a telegraph key as quickly as 
possible after the signal is given by the ex- 
perimenter. Not only do individuals vary 
among themselves in speed of reaction, but 
also the reaction time of the same individ- 
ual varies according to the sense organ 
stimulated. The following table will give 
an idea of the approximate range of the re- 
action times in seconds for the different 

The reaction times to painful stimuli are 
especially long, owing in part to the fact 
that there is a considerable lag between the 
application of a stimulus and the conscious- 

Reaction Times 

Kind of Stimulation 



0.150 to 0.225 


0.120 to 0.185 


0.115 to 0.190 


0.200 to 0.800 


0.305 to 1.080 


0.400 to 1.000 





ness of pain. The reaction times for 
warmth and cold vary according to the 
manner of application of the stimuli. Tiie 
reaction to taste varies with the pan of the 
tongue stimulated and the kind of stimu- 
lus; the time is shortest for salt and longest 
for bitter. The time for touch varies ac- 
cording to the part of body stimulated and 
to the limb making the response. The re- 
action time for a stimulus applied to the 
forehead is longer than for one applied to 
the hand, although the forehead is nearer 
the brain. The reaction of one hand to a 
tactual stimulus applied to the same hand 
is quicker than to a stimulus applied to the 
opposite hand. The reaction to light is 
faster when the light falls on the fovea (tlie 
area of clearest vision near the center of the 
retina of the eye) than when it falls on an 
eccentric part of the retina, the time in- 
creasing continuously with the distance ol 
stimulation from the fovea. Reaction is 
more rapid to binocular than to monocidar 

In most experiments upon reaction time. 
a preparatory signal is given before the 
presentation of the stimulus. It is found 
that the reaction time varies Avith the 
length of the intewal between the prepara- 
tory signal and reaction signal. Constant 
intervals between 2 and 4 seconds give the 
shortest times. If the preparatory^ signal is 
varied wathin a series, so that the subject 
never knows exactly how long he will have 
to wait for the reaction signal, the optimal 



interval ranges between 12 and 16 seconds. 
The act of preparation seems to be the 
chief factor involved in these results. If 
the interval is too short, the subject has 
not sufficient time to 'get set' and the stimu- 
lus may come before he is quite ready. If 
he has to wait more than 4 seconds, the in- 
terval becomes too monotonous for him to 
hold his attention entirely on the task. If 
the interval is varied, he is unable to as- 
sume a constant attitude of expectation and 
therefore requires a longer interval for his 
quickest reaction than when the interval is 

Distraction usually lengthens reaction 
time, but sometimes the supposedly dis- 
tracting stimulus acts as a spur and de- 
creases the time. This paradoxical effect, 
which has been found in other experiments 
where concentration is necessary, is ex- 
plained by the fact that some persons use 
more effort to concentrate when there is an 
obstacle to o\ercome. City dwellers be- 
come so accustomed to concentration 'in 
spite of the noise of the street that they 
often have difficulty at first in working ef- 
ficiently when they go into the country. 
Students, studying with the radio turned 
on, may be more alert to their work because 
they are fighting the radio as a potential 
distractor— more alert than they would have 
been in the quiet without the radio's chal- 
lenge. (For fiuther description of the ef- 
fects of distraction, see pp. 477 f.) 

Reaction times to all kinds of stimuli de- 
crease with an increase in the intensity of 
the stimulus. This decrease in time is most 
marked in the range of weak intensities. 

Although an individual's reaction time 
varies according to the nature of the stimu- 
lus, the question arises whether, if he is 
quicker than his fellows in his response to 
visual stimuli, he will also respond more 
quickly to auditory and tactual stimuli. In 

other words, is there a speed characteristic 
of response that runs through all a person's 
motor reactions? In a series of experiments 
it was found that the correlation of simple 
visual, auditory and tactual reaction times 
is really quite high. Thus if a person ex- 
cels in speed of reaction to one kind of 
stimulus, there is a good chance that he will 
also be quick in his reactions to other kincis. 

Sensory and Motor Reactions 

If a runner starts sooner than his rival at 
the crack of the pistol, it is owing in part to 
the difference in set of the contestants. It 
has been shown in the laboratory that there 
are two types of reaction, sensory and 
motor. In the sensory type, the subject's 
attention is directed by die initial set to the 
stimulus, and in the motor type to the re- 
sponse which he is to make. In the ex- 
treme form of sensory reaction, the expecta- 
tion of the subject is directed almost ex- 
clusively to the coming stimulus, often 
with a steady fixation in the direction of its 
appearance. In the extreme motor reac- 
tion the idea of the mo^•ement to be per- 
formed in terms of proprioception is domi- 
nant. If the subject is allowed to react 
'naturally,' there is usually an attitude mid- 
way between these two forms, or an alterna- 
tion of the two. 

These differences in set cause differences 
in reaction time. "When the reaction tends 
toward the sensory type, the time is longer 
than when it tends toward the motor type. 
In the table on reaction times (p. 59) vis- 
ual reactions range from 0.150 second to 
0.225 second. It is probable that the time 
0.150 second was obtained under a motor 
set and the 0.225 second under a sensory 
set. With practice one tends to become in- 
creasingly motor until the reaction becomes 
practically automatic; then the finger move- 
ments occur with little conscious intention 

Simple and Complex Reactions 


as soon ;is a signal is given. With this ex 
treme niolor set, however, premature re- 
actions are not infrequent, as we find not 
only in the laboratory but also in such sit- 
uations as racing. A runner who is of the 
extreme motor type often makes a false 
start. Some runners, however, prefer to be 
sure of the signal, even though they are a 
little late. These different types are found 
among people in general; there are those 
who are slow, safe and sure, and those who 
go off 'half-cocked.' 

Discrimination and Choice Reactions 

Most of oiu- reactions in life are not like 
the simple reaction experiments. It is sel- 
dom in everyday life that we can be so sure 
of what is going to happen as to set our- 
selves to react automatically at maximum 
speed. The runner who is not alert may, 
for example, start at the soimd of an auto- 
mobile backfiring instead of at the pistol 
shot. Consequently some discrimination is 
generally necessary for a correct response. 

In the laboratory this more complicated 
situation is produced by varying the stim- 
uli. The stibject may be instructed to re- 
act only to a red light, when both red and 
green signals are used in haphazard order. 
This is a discrimination reaction. It is ob- 
vious that this problem is similar to that 
confronting the locomotive engineer and 
the automobile driver. The necessity of 
recognizing the correct signal increases the 
average reaction time above the time of the 
simple reaction; and, the more motor the 
set of the subject is, the more likely he is 
to react to the wrong light. The discrimi- 
nation situation may be further compli- 
cated by requiring a choice between two or 
more reactions as well as a discrimination 
between stimuli. The subject may, for ex- 
ample, be instructed to respond with die 
right hand if the light is red and witli the 

left hand it the light is green, or with the 
right hand if the red light appears on the 
right of the green and with the left hand if 
the stimuli are reversed. The greater the 
complications in such choice reactions, the 
longer the reaction time. 

In the discrimination reaction it is found 
that the more the stimuli resemble each 
other, the longer are the reaction times. If 
black and white are used as stimuli, the 
reactions are quickest. Red and green 
come next, then red and blue, followed bv 
red and yellow, and finally red and orange. 
If tones are used, the reaction to tones dif- 
fering by 16 cycles per second is quicker 
than to tones differing by 12 cycles, and 
much quicker than to tones only 4 cycles 
apart. When lines differing in length are 
the stimuli, the less the difference between 
the lines, the longer are the reactions. The 
reaction time is, for example, shorter for 
discrimination between lines of 10 and 13 
millimeters than for 10 and 12 millimeters. 

Word Reactions 

The commonest reactions in life are 
verbal. To determine the nature and speed 
of such responses numerous experiments 
have been devised. The usual method is 
to present a word visually or vocally, the 
subject being told to respond as quicklv as 
possible with the word that is suggested by 
the stimtdus word. The time, -which may 
be taken by a stop watch or by means of 
voice keys and a chronoscope, indicates the 
speed of the association of ideas for the 
person tested. 

If the subject is told to respond ^\•idl die 
first Avord that occurs to him, the associa- 
tion is termed 'free.' Frequently, however, 
the instructions are more limited. For ex- 
ample, a general term indicating a class, 
such as animal, is given and the subject is 
requiied to repl) widi tlie name of a mem- 



ber of this class, such as bear; or he is in- 
structed to respond with a word opposite 
in meaning to the stimulus word. Many 
other varia'^ions in instruction may be 
given. These associations, being partially 
determined from the start, are called con 
trolled associations. Experiments of this 
nature have been extensively employed in 
investigations of the nature of the thought 

Practical Use of Reaction Experiments 

An individual's ability in practical affairs 
depends in part upon his speed of reaction. 
It is, therefore, frequently of value to know 
both his speed of reaction in a given situa- 
tion and how he compares with other indi- 
\iduals under similar circumstances. It is 
also of interest to know how much he may 
improve his speed and accuracy by practice 
as well as under the incentive of increased 
interest in the task. 

Reaction time is an important factor 
both in vocational selection and in deter- 
mining the individual's aptitudes as a basis 
for vocational advice. For example, in the 
selection of telephone switchboard oper- 
ators, speed of response and relative free- 
dom from errors are essential requirements. 
A consideration of the same characteristics 
is necessary in the selection of chauffeurs 
and machine operators. According to the 
results of tests of taxicab drivers, those men 
with the greatest number of accidents have 
the slowest reaction times. Those who 
have the fastest reaction times have also 
many accidents, perhaps because they are 
overconfident and take chances. It is 
therefore desirable to select drivers whose 
reaction times are neither very fast nor very 

The association-reaction experiinents 
have been used with some success to deter- 
mine guilt. Words which are related to the 

crime are interspersed with 'neutral' words. 
The words of this combined list are read 
to the subject, who must answer as rapidly 
as possible to each one with any word he 
can think of. Anyone knows from his own 
experience that when he is faced with an 
embarrassing situation— one that is emo- 
tionally toned— he is likely to hesitate and 
often to reply foolishly or irrelevantly. In 
the 'crime' experiment there is exactly 
such an embarrassing situation for the 
guilty person. Therefore the tendency is 
for the reaction time to the relevant words 
to be unusually long, or at least to vary 
more than the reaction times to the neutral 
words. In addition, the meaningful refer- 
ence of the words is often different in the 
cases of guilt and of innocence. 

This same method is used to discover sup- 
pressed complexes— the memory of painful 
experiences which, held in an unconscious 
state, often give rise to abnormal mental 
conditions. Because such complexes are, 
like the concealed knowledge of the guilty 
subject, highly emotional in nature, the two 
test situations are very similar. 


1. Crafts. L. W., Schneirla, T. C, Robinson, E. E., 
and Gilbert, R. S. Recent experiments in psy- 
chology. New York: McGraw-Hill, 1938. 
Chaps. I to 3. 

These chapters deal with 'instincts' (cats 
and mice, migration of birds and salmon) and 
with the behavior of newborn babies. 

2. Estabrooks, G. H. Hypnotism. New York: 
Dutton, 1943. 

An up-to-date survey of hypnosis and sugges- 
tion in man. 

3. Hilgard, E. R., and Marquis, D. G. Condition- 
ing and learning. New York: Appleton-Cen- 
tury, 1940. Chaps. 2 and 13. 

A text and reference book which surveys con- 
ditioning and learning in both animals and 



man. Chapter 13 deals vviili physiological 
mechanisms in conditioning. 

4. Hull, C. L. Hypnosis and suggestibility. New 
York: Appleton-Century, "1933. 

An old but useful summary of experiments 
and unsolved problems in the understanding 
of hypnosis and suggestion. 

5. Morgan, C. T. Physiological psychology. New 
York: McGraw-Hill, 1913. Chaps. 1.5, 18, 19, 
l-'O, 21. 

An up-to-date textbook in physiological psy- 
chology. These chapters deal with reflexes, 
sleep and activity, instinctive behavior, mating 
behavior and bodily needs. 

6. Shaffer, L. F. The psychology of adjustment. 
Boston: Houghton Mifflin, 1936. Chaps. 2, 3, 4. 
An elementary text on mechanisms of human 
adjustment approached from a biological point 
of view. These chapters consider the origin 
and modification of behavior and the role of 

7. Tomkins, S. S. CKd.) Contemporary psycho- 
pathology. Cambridge: Harvard University 
Press, 1943. Chaps. 34, 36. 

Selected readings from experiments and dis- 
cussions dealing with abnormal behavior. 
Chapter 34, by H. .S. Liddell, treats of the 
modification of instinct by conditioning. Chap- 
ter 35, by R. W. White, considers the nature of 

8. Woodworlh, R. S. Experimental psychology. 
New York: Holt, 193H. Chaps. 5, 13. II. 

A comprehensive textbook of experimcMtal 
psychology. These chapters deal with ihe 
conditioned response, the galvanic skin response 
and reaction time. 

9. Young, P. T. Motivation of behai'ior. New 
York: Wiley, 1936. Chap. 5. 

The only text and reference book dealing 
entirely with motivation in relation to response 
Chapter 5 deals specifically with set. 


Growth and Development 

MAN is an organism, as the preceding 
chapters have shown, a mass of proto- 
jjlasm moving about on the lace of the 
earth. His movements are lawful. They 
depend on his properties as an organism, on 
his bodily structure and on his capacities 
for response to stimulation which in turn 
depend upon inherited and acquired char- 
acteristics of his nervous system. 

This organism that is man has a life to 
U\e. It begins at the moment of concep- 
tion when two parent cells unite to form a 
new individual. Then at once the new 
organism begins to grow and develop, at 
first as an embryo, then into a fetus, and 
then, being born, into an infant, a child, a 
youth, an adult and finally, if he lives, 
into an old person. Since growth and de- 
velopment are such important characteris- 
tics of man, it is proper that we should 
begin our detailed study of man's proper- 
ties by seeing what happens to an individ- 
ual organism as it grows and develops from 
conception to extreme old age. 


It will simplify our account of the proc- 
esses of growth and development if, at the 
outset, we carefully distinguish between 
them. We shall use the term growth, as 

the biologists do, to mean merely increase 
in size, and it will apply not only to the 
overall dimensions of the body in terms of 
height (or length) and weight, but also to 
the parts of the body as, for example, the 
head, arms and trunk— the heart, brain, 
skeleton, muscles, etc. By the term devel- 
opment we shall mean the changes in the 
shape of the parts of the body and the inte- 
gration of the various parts into functional 
units as growth goes on. Growth can be 
measured. Development can be observed 
by noting changes in shape as they occiu^ 
and in modes of behavior as their matura- 
tion is completed. 

We shall use the term maturation to 
mean the growth and development that is 
necessary either before any unlearned be- 
havior can occur, or before the learning of 
any particular behavior can take place. For 
example, one of the first coordinated move- 
ments that any baby makes, is to raise its 
head, and to hold its head upright without 
support while sitting. The child could not 
perform this act earlier because its matura- 
tion was not complete, that is to say, the 
muscles at the back of its head and neck 
had not gi-own sufficiently, and the con- 
nections of nerve fibers and synapses lead- 
ing from the muscles to the cerebral cortex 
and back again had not developed enough 
to activate the muscles. The maturation 

This chapter was prepared by Leonard Carmichael of Tufts College. 


Conditions of Growth 


ol' this bit ol bcliavior is, llicicloie, (oin- 
jDlcte as soon as the f^rowth and integration 
of the parts have progressed sufficiently. 
The child does not learn "to raise its head; 
maturation is all that is needed. But, laicr 
in life, it does learn to raise its head in 
order to see something, for that behavior 
means attaching the newly available move- 
ment to some stimulus. Similarly the child 
cannot learn to write until the growth of 
the small muscles in the fingers and their 
neural connections have developed suffi- 
ciently. It can learn to write only after it 
has developed the brain capacity for learn- 
ing and the mviscular capacity for fine 

Conditions of Growth 

The first essential condition for growth 
is food. For a few days the newly fertilized 
cell finds its food in the cell itself. Then, 
as embryo and fetus, it derives its food 
from the mother and will continue to get it 
in this way throughout the prenatal period. 
If growing is to be normal, the mother must 
supply her child with a well-balanced diet, 
for the growing cells require proteins, car- 
bohydrates, fats, vitamins and a variety of 
mineral salts. After birth the neonate, as 
the newborn infant is called, gets its food 
by mouth and must digest it himself. If 
he cannot digest his food properly, or if 
his mother's milk lacks needed elements 
for his diet, his growth will suffer. 

A second important condition for human 
growth is the supply of the secretions called 
hormones from some of the endocrine 
glands. (See pp. 23 f.) Chief of these 
are hormones from various lobes of the 
pituitary body, a small gland situated at 
the base of the brain. One hormone af- 
fects the growth of the body as a whole— 
particularly the skeleton. If the amount of 
the secretion is too great, growth is abnor- 

mal and rcsidls in gigantism; if not eiiougii, 
it results in dwarfism. Anotlier hormone, 
called thyroxin and produced by the 
thyroid gland, influences the consumption 
of oxygen in the tissues and thereby in- 
fluences metabolism and growth. An ab- 
sence of this hormone in early childhood 
stops the growth of the brain, inhibits 
growth in stature— particularly of the arms 
and legs— and results in producing the kind 
of dwarf known as a cretin. 1 he intersti- 
tial cells of the sex glands furnish a hor- 
mone that stimulates the growth of the 
secondary sex characters— the rapid growth 
and changes in figure, hair and voice that 
occur in early adolescence. A less dramatic 
but equally important part is played by 
hormones from still other glands in the as- 
similation of food and the removal of 
waste products which are necessary for 

A third condition of growth is heredity, 
which, of course, also determines the two 
2:)revious conditions— food assimilation and 
the hormones. However, heredity also de- 
termines whether the fertilized cell, when 
gi'own and developed, will be a human be- 
ing or some other animal and, if human, 
to what race it will belong; ^vhether it will 
be a boy or a girl; Avhether, other tilings 
being equal, it will eventually be large, 
medium or small in size; whether the shape 
and size of many of its features (for ex- 
ample, eyes, nose, mouth, lo'^ver ja^v, hands 
and fingers) will be like those of its father 
or mother or one of its grandparents or a 
more remote ancestor. 

A detailed account of the la^\'s of hered- 
ity would take us too far afield. "We may 
say, however, that the basic factors for die 
transmission of characters from one gener- 
ation to others are called genes. No two 
germinal cells have tlie same genes. Be- 
fore fertilization there is usually onlv one 


Growth and Development 

ovum (female cell) but there are millions 
of sperms (male cells), only one of which 
joins the ovum. The newly fertilized cell 
has, therefore, an almost certainly unique 
combination of genes. If some other sperm 
had fertilized the ovum, the combination 
would have been different. If conception 
should take place a month later, the ovum 
woidcl have a different set of genes and the 
fertilized cell would have quite another 
combination. These facts help us to un- 
derstand why, for example, in a family con- 
sisting of a large number of children of the 
same parents, no two children (identical 
twins excepted) are of the same size and 
bodily contour. You can always tell one 
child from another (except, of course, with 
the identical twins). 

Finally, a fourth condition of growth is 
use or exercise. General exercise, such as 
walking, gymnastics and sports, increases 
heart rate and blood pressure and the rate 
and depth of respiration. As a result, the 
blood, carrying an increased supply of oxy- 
gen and food, passes with new force into 
the smallest of the capillaries and thus 
reaches all the cells of the body. During 
the growing years the development of all 
parts of the body is thus quickened. In 
continuous and violent exercise the muscles 
particularly involved grow larger. The 
sprinter develops his leg muscles, the oars- 
man his arm, trunk and leg muscles, and, 
since the heart has an additional burden 
laid upon it, it is frequently permanently 

Integration and Maturation 

Thus far we have regarded growth as if 
it were an end in itself, as if, for example, 
all that the brain does is to grow until it 
stops at maturity. Growth, however, is only 
one aspect— though a very important one— 
of a larger process of development. The 

end of development is the production of a 
living organism prepared to do all the 
things that man does. Development, there- 
fore, requires not only the growth and for- 
mation of the structural parts but also, as 
we have seen, their integration into a func- 
tioning whole. 

We may illustrate this process by a crude 
analogy. The structural parts of a gas en- 
gine—the cylinders and pistons, the battery, 
wire^ and timer, the carbureter and spark 
plugs— must be assembled, fastened into 
place, carefully adjusted and provided with 
fuel before the engine as an integrated 
whole is ready to run. The integration 
both of the engine and of the developing 
organism consists in uniting and coordi- 
nating the parts. 

There are, however, two important dif- 
ferences between man and a gas engine. 
First, in man, under the guidance of the 
genes inherited from his ancestors, develop- 
ment takes place automatically. Second, 
when the gas engine leaves the assembly 
line its development ends. It can then do 
all the things it can ever do; it can start 
and stop, run at various speeds, and pro- 
duce various amounts of horsepower. Ex- 
cept for limbering up and the effects of 
subsequent wear, its basic behaviors are all 
matured at once. In man, on the other 
hand, maturation of various forms of be- 
havior goes on for a long time. Although 
at birth maturation of the functions neces- 
sary for the maintenance of life has been 
reached, it will be many months before the 
child has complete control of its muscles 
and years before it can reproduce its kind. 

The Nervous System as Integrator 

The great integrator and coordinator of 
the organism is the functioning nervous 
system. Its fibers pass into almost every 

The Nervous System as Integrator 


structure of the body, few of which can 
function without nerve direction. 

The rate of development of the nervous 
system is not, however, uniform through- 
out. The spinal cord is formed and devel- 
oping throughout its entire length by the 
middle of the second month of the pre- 
natal period. The lower parts of the brain 
—the medulla, midbrain and other parts 
necessary for automatic control— also de- 
velop early. Last of all the cortex develops. 

We may illustrate the course of develop- 
ment in the lower centers by experiments 
that have been made with the larva of the 
salamander, Amblystoma. This salaman- 
der develops quickly under water from a 
fertilized egg which has its own rich supply 
of yolk. It becomes a free-swimming ani- 
mal before it must seek for food. Thus it 
is an ideal animal in which to study the 
maturation of nerve and muscle coordina- 
tion at the automatic level. The develop- 
ment which leads up to swimming behav- 
ior in this embryo (see Fig. 24) may be de- 
scribed in five typical stages, as follows: (1) 
a nonmotile stage, in which the direct mus- 
cle stimulation by electrical or mechanical 
means leads to muscular contractions which 
occur without bodily movement; (2) an early 
C-flexure stage, in which a light touch on 
the skin of any portion of the body leads 
to a bending of the head to one side; (3) a 
tight-coil stage, in which the contractions 
noted in stage (2) extend toward the tail 
to make a coil; (4) the S-reaction, which is 
characterized by a reversal of flexure before 
the previous C-flexure has been completely 
executed, thus leading to the sinuous be- 
havior of the organism; and (5) the speed- 
ing up of this S-reaction so as to produce 
the typical swimming movement of the am- 
phibian larva. 

Studies were also made of the neural or- 
ganization of the central nervous system at 

every one of these stages. It was found that 
development in specific chains of neurons 
in the central nervous system arc necessary 
before the alterations of behavior from 
stage to stage can take place. These studies 
showed clearly that a particular set of con- 
nections must be produced by growth be- 
fore particular responses occur. In gen- 


(A) Stage before neuromuscular activity has be- 
gun. In this stage muscles may be directly stimu- 
lated. (5) Beginning of C or reverse-C movement. 
(C) S-shaped swimming movement. The first re- 
verse-C-flexure progresses toward the tail while an- 
other C-flexure begins at the head. Muscle con- 
tractions shown black at flexures. [After G. E. 
Coghill, Anatomy and the problem of behavior, 
Cambridge University Press, 1929, pp. 7 f.] 

eral, it is found that the earliest movement 
is the bending of the head to one side. A 
little later the bending progresses down- 
ward toward the tail. The development of 
the swimming behavior is, therefore, in a 
head to tail, or cephalocaudal direction. 
This is a pattern of an orderly develop- 
ment of neuromuscular function which is 
also found in the maturation of bodily 
movements in die child. 

The development in the central ner\ous 


Growth and Developmenf 

system begins with the spinal cord and 
continues to higher and higher centers of 
the brain. As higher centers become ef- 
fective, the lower centers, without ceasing 
to act, begin to be influenced by the higher 
in new ways. This development from 
lower to higher centers is spoken of as the 
encephalization of junction. The word 
rncephalon means brain, and encephaliza- 
tion occurs when the control of functions 
migi^ates in the developing child or in the 
evolution of animal species from the spinal 
cord to the brain. After encephalization 
has taken place, the same, process of devel- 
opment is continued as corticalizalion of 
function, the migration in individual or 
evolutionary development of functional 
control from the lower centers of the brain 
to the cerebral cortex, where the highest 
centers lie. Thus, as development of the 
individual continues, the higher centers 
come to play a more and more important 
role in what the organism does. In man 
all volimtary movement and all learning 
are largely dependent upon the develop- 
ment of these higher centers. 


We turn now to follow the course of 
growth and development of a human being 
from a fertilized cell to his birth. 

The Beginning of Human Growth 

The growth of a human being starts first 
^\'ith the enlargement of the fertilized cell. 
Then, when the cell has reached a certain 
size, it divides into two smaller cells, each 
with a nucleus and surrounding proto- 
plasm. These cells grow and again divide. 
The process continues, the number of cells 
increasing in geometrical proportion. 
Meanwhile the tiny individual is migrating 

from the o\iduct, where fertilization took 
place, to the wall of the uterus, where it 
soon becomes attached. Here growth con- 
tinues more rapidly until, two weeks after 
fertilization, the first period, called the 
germinal period, comes to an end. (See 
Fig. 25.) 

The next fi\'e weeks of the life of the 
prenate (as tlie organism is called before 

Uterine blood vessel 

blood - 

Fetal villi 


[After L. Carmichael, A handbook of child psy- 
chology (2nd ed.), Clark University Press, 1933, p. 


birth) constitute the embryonic period. 
Growth goes on as before by cell enlarge- 
ment and division, but differentiation also 
begins. These changes are tlie start of a 
long process, and some of the new struc- 
tures do not become recognizable for sev- 
eral weeks. Others develop rapidly. By 
the end of the first week of the period 
(three weeks after fertilization) there occurs 
the first independent activity of the grow- 
ing human embr)o, namely, the beating of 
the cells which later de\elop into the adult 
human heart. 

It may be remarked that at all times in 
the uterine life of the prenate, the circula- 
tory system is completely separated from 
the maternal blood s)stem by cell walls. A 
highly complex structure called the 

rfie Beginning of Human Growth 


placenta develops to provide a iiuaiis 
whereby the independent blood systems o£ 
the mother and child can communicate. 
(See Fig. 26.) Through the walls of this 
structure oxygen and food substances pass 
from the mother's blood to the independ- 
ent blood stream of the embryo and fetus. 
Carbon dioxide and the other waste prod- 
ucts from cell activity pass back into the 
maternal blood through the placenta. Fur- 
thermore, there is no neural connection at 
any time between the mother and the 
growing fetus. Contrary to superstitious 
belief, no transfer of ideas can take place 
between the mother and the fetus. Some 
drugs taken by the mother may, it is true, 
affect the fetus. It may be also that some 
strong emotions of the mother, which are 
related to changes in the chemical make-up 
of her blood, have some effect on the tni- 
born child. If, however, the future mother 
wants a certain big strawberry and does not 
get it, this act does not produce a 'straw- 
berry mark' on the unborn child which she 
is carrying, no matter what superstition 
may say. 

By the end of the second month, the 
embryo begins to look like a human being, 
and thereafter until birth seven months 
later it is called a fetus. The fetal period, 
regarded as a whole, is first merely a con- 
tinuation of the growth and development 
already begun. The external parts of the 
body— the features of the face, the arms and 
fingers, the legs and toes— become more 
clearly defined. There is also at this time 
a rapid increase in size. Beginning with 
the fourth month the cerebral cortex de- 
\elops rapidly. Development of functional 
connections in the nervous system thus far 
has been restricted for the most part to the 
spinal cord and the lo^\'er parts of the brain 
—those parts which have the involuntary 
controls of the organs and muscles of the 

body. Now the cortex, man's most distin- 
guishing feature, starts its rapid functional 
development. Presently, the fetus begins 
a wide variety of movements which, as its 
development proceeds, become more and 
more individualized. The first recorded 
movement, as the result of experimental 

Intervillous Amnion 


■J r:^'^/^} 1^, - 


vein artery 


In the placenta the fetal blood stream (umbilical 
artery and vein) and the maternal blood stream 
(uterine artery and vein) do not join. [From 
Human Physiology by Winton and Bayliss, by per- 
mission of J. & A. Churchill, Ltd., London.] 

stimulation of fetuses that were born pre- 
maturely or removed from the mother by 
surgical means, occtured Avhen die fetus 
was about eight and one-half weeks old. 
(See Fig. 27.) The stimulus Avas a light 
touch on the cheek near die moudi and it 
induced a contraction of die long muscles 
of the body and neck whicli resulted in a 
flexion of the body and accompanying 
movements of the arms. A week later a 


Growth and Development 


Photographs of response of fetus to touch stimulation at about eight weeks of age. [After D. Hooker 
A preliminary Alias of early humafi fetal activity, 1939, p. 15.] 

Rates of Prenatal Growth 


similar stimulation produced a rotation of 
the pelvis in addition to a flexion of the 
body. By the twelfth week local move- 
ments resulted from stimulation of the 
arms and legs of the fetus. About the 
same time stimulation of the palm resulted 
in a partial closure of the fingers; this is 
the response which will later develop into 
the grasping reflex. These instances are 
perhaps enough to indicate the course of 
development of motor responses. 

sponse does not succeed in removing the 
stimulus, the guinea pig rotates its whole 
trunk in such a way as to favor removal 
of the touched spot from the noxious stim- 
ulus. If the stimulus still continues to be 
effective, it may be that the guinea pig's 
limbs begin to beat out a rhythmic swim- 
ming pattern which effectively moves the 
whole organism away from the stimulus 
save in so far as it is held fast by the um- 
bilical cord. No one can watch such be- 


Tracings of outline posture of the localizing paw movement of a guinea pig fetus a few days before the 
period of natural birth. Note the accuracy of this unlearned behavior. [After L. Carmichael and M. F. 
Smith, /. genet. Psychol., 1939, 54, 432.] 

The responses of the prenate become 
more and more versatile and more and 
more effective as growth continues. In 
some mammals, such as the guinea pig, in 
which the development of behavior before 
birth has been studied in great detail, this 
sequence can be seen clearly. It is possible 
in the few weeks of prenatal development 
to observe how a first slight twitch of the 
forelimb develops into behavior which in- 
volves the effective use of almost every 
group of body muscles. Some of these late 
fetal sequences of response are marvelously 
well adjusted. In experimental work on 
still unborn guinea pigs it has been shown, 
for example, that the animals can localize 
and brush away with an appropriate paw a 
stimulus applied to almost any area of the 
skin. (See Fig. 28.) If this brushing re- 

havior in a fetus that has been prepared for 
experimental observation without recog- 
nizing the subtle perfection of the develop- 
ment for future activity that is begun be- 
fore birth. 

Rates of Prenatal Growth 

Growth before birth is exceedingly rapid. 
The fertilized cell has a diameter of 0.013 
millimeter or ^2000 inch. By the end of 
the two weeks of the germinal period the 
prenate has a length of 6.0 millimeters or 
y^ inch, an increase 5 hundredfold in 
length (more than 100 millionfold in vol- 
ume). During die eighth week die fetus is 
about an inch long and has increased its 
length 2 thousandfold since tlie beginning. 
At birth an average neonate has a length of 
20 inches. That makes it about 40,000 


Growth and Developmeni 

times longer than the ovmn from which it 
sprang, several thousand million times its 
original volume. The average rate per 
week for the 40 weeks of the uterine period 
is one-half inch. The growth per week at 
first increases rapidly and then after birth 
slows down. If the rate at birth were 
maintained until maturity, a grown man 
would be 45 feet tall. 

the prenatal period, however, the brain 
reaches about two-thirds of its adult size. 

Before birth growth of the brain by the 
cell division of its neurons comes to an 
end. There are approximately twelve 
thousand million neurons in a normal 
brain at birth and there is no increase in 
this number dining any part of postnatal 

£ mo. (fetal) 5 mo. Ncvx/bom 


Changes in relative form and proportion of human bodv in fetal life, childhood, \oiith and adult life. 
[After C. M. Jackson; in W. J. Robbins, S. Brody, A. G. Hogan, C. M. Jackson and C. ^V. Green, Growth, 
Yale University Press, 1928, p. 118.] 

The structures within the body also grow 
rapidly during the entire prenatal period. 
From about the third month until birth 
the weight of most of these structures in- 
creases at about the same rate; the small 
structures groAv, in a gi\en period, as much 
as the larger ones. 

In the early days of the embryonic 
period, however, the heart and brain grow 
much more rapidh than other parts of the 
body. At about the fourth week, because 
of the large brain, the head constitutes 
nearly half the length of the embryo. Even 
at birth the size of the head is much larger 
in proportion to its body length than it 
will be at maturity. (See Fig. 29.) During 


Although, as we have seen, during most 
of the fetal period the structures of the 
body gi'ow at about the same relative rate, 
after birth their rates and increments vary 
widely. Despite this variability, it has been 
found that the rates of many structures fall 
into groups for each of which the incre- 
ments of gi'owth through a number of years 
are so similar as to suggest types of growth. 

Types of Growth 

Four of these types widi their typical 
growth curves are shown in Fig. 30. They 
represent only the growth that occurs be- 

Types of Growth 


twecn birth and Llic iwentieth year. Ihc 
increments shown in the figure are percent- 
ages of the total growth chiring that period. 
The topmost curve is of the Lymphoid 
Type. It represents tlie growth of the ihy- 


years, and (inalJy it neaily slops lor the 
remainder of the period. 

Below this in the figure is the curve of 
the General Type. It represents the growth 
of the body as a whole (excepting ihe head, 

Lymphoid Type 

Thymus, lymph nodes, 
intestinal lymphoid masses. 

Neural Type 

Brain and its parts, dura 
spinal cord, optic apparatus, 
many head dimensions. 

General Type 

Body as a whole, external dimensions 
(with exception of head and neck), 
respiratory and digestive organs, 
kidneys, aorta and pulmonary trunks, 
spleen, musculature as a whole, 
skeleton as a whole, blood volume. 

Genital Type 

Testis, ovary, epididymis, 

uterine tube, prostate, prostatic urethra, 

seminal vesicles. 


The several curves are drawn to a common scale by computing their values at successi\e ages in terms 
ot their total postnatal increments (to twenty years). [From J. A. Harris, C. M. Jackson. D. G. Paterson 
and R. E. Scammon, The measuremetit of man, University of Minnesota Press, 1930. p. 193.1 

inus gland and a few lymphoid tissues. The 
curve rises sharply for eleven years and 
then falls until the end of the period of 
twenty years is reached. 

The next curve is of the Neural Type. 
It includes the brain, the spinal cord and 
the eye. The ciuve of the pineal gland is 
similar but does not rise quite so rapidly. 
In this type, growth is rapid for the first 
six years, then slower for the next two 

neck and chest) in its external dimensions, 
the respiratory and digestive organs, the 
kidneys, the spleen, the muscles, the skele- 
ton and blood volume. The cur\e rises 
rapidly until about the fourth year, much 
more slowly until about the twelfth year, 
rapidly again until the eighteenth year and 
slowly again until the end of tlie period. 

The last curve is of the Genital Type. 
It shows the trend of groAvth for tlie testes. 


Growth and Development 

ovaries, uterine lube, prostate gland and 
the seminal vesicles. There is first a slight 
growth for four years, then no growth at 
all until the twelfth year, after which there 
is a rapid growth until the end of adoles- 

Two things should be said abovu these 
typical curves. One is that they do not in- 
clude all curves of growth. There are a few 
—those, for instance, of head, neck and 
chest circumference, of the weight of the 
suprarenal glands, the human uterus and 
the thyroid gland— that do not fit into any 
type. Second, it should be emphasized that 
the typical curves are merely graphic repre- 
sentations of trends of growth. As such 
they are exceedingly useful in aiding the 
luiderstanding of the growth and develop- 
ment of the individual. 


Maturity means cessation of growth. A 
time is ultimately reached beyond which, 
normally, there is no further increase in 
size. Structures belonging to the neural 
type reach that stage, as we have seen, at 
about ten years after birth; those of the 
lymphoid type at twelve years; those of the 
general and genital types may continue to 
grow until at least the twenty-fifth year. 

Increase in weight of the body may, of 
course, occur as a result of deposits of fat. 
When growth ceases, its curve either be- 
comes a straight horizontal line and may 
so continue for thirty-five or forty years or 
even until death in extreme old age, or the 
curve turns downward representing a de- 
crease in size, the regression of senescence. 


The newborn infant is called a neonate. 
We turn now to the appraisal of its mat- 

The Neonate in a New Environment 

Development after birth is a continua- 
tion of prenatal development. At the mo- 
ment of birth the neonate comes into a 
different world. For months he has been 
living as a prenate in a fluid medium of a 
constant temperature; he has been shielded 
by his liquid environment from all external 
stimuli and has derived his oxygen and 
food from his mother without breathing 
and without digestion. In a short interval 
he becomes an air-dwelling animal living 
in a variable temperature. He is now sub- 
ject to a wide variety of external stimula- 
tion and must obtain his oxygen by his 
own breathing and his food by his own 
digestion. These new needs require that 
the great physiological functions— circula- 
tion, respiration and digestion— be matu- 
rated if the infant is to survive. Prema- 
ture births show that the maturation of 
these functions is fairly well established as 
early as 220 days after fertilization, 60 days 
before normal birth. A baby born 180 days 
after fertilization rarely survives, princi- 
pally because its digestive system is not at 
that time sufficiently developed. 

We shall subsequently see that a num- 
ber of other forms of behavior reach matu- 
ration at birth. The muscles of the trunk, 
legs and arms, however, have not yet 
reached sufficient development for their 
proper effective functioning in air. The 
liquid prenatal environment, because it is 
so nearly of the same specific gravity as 
the fetus, allows a complexity and preci- 
sion of prenatal muscular response that the 
neonate cannot again achieve until some 
time after its birth. At birth the cortex of 
the brain, despite the fact that it has been 
developing since the latter half of the fetal 
period, is still immature. 

Maturation at Birth 


Reflexes in the Neonate 

During the firsi lew days the (:om{)lc;x 
feeding reactions, involving head orienta- 
t'on, lip reflexes, sucking and swallowing, 
mature. Soon after birth many infants can 
also grasp a rod and support their own 
weight if the rod is lifted. This involun- 
lory grasping reflex ordinarily disappears 
during the first half year of life. Another 
reflex which soon disappears is the Babinski 
reflex m which the infant extends its toes 
when the bottom of the foot is tickled. 
(See Fig. 31.) This reflex is later replaced 

!>y tlie plantar reflex which consists of a 
( urling up of the toes when the sole of the 
loot is stimulated. The plantar reflex de- 
pends ujjon certain motor tracts that lead 
from the brain to the spinal cord and ap- 
pears when these fibers mature after birth. 
An infant a few hours old, when held 
vertically in such a way as to support his 
head and trunk, and with the soles of his 
feet touching the floor, often makes pranc- 
ing movements. These movements con- 
sist in alternately raising the legs and flex- 
ing them at the knee— behavior which is 





I^^^^N* l^^^l 





^^/!i-~ """ JH 



~ ^ty^g^--^ 


- — '_ .••,„™. 


^^ — 

- -^ 


{A) Defensive reflex with left foot to slight pinch on inner surface of right knee. [B) Stimulation for 
Babinski reflex. The blunt end of a match is rubbed across the sole of the foot. The result is shown in 
(C). The great toe shows extension, whereas the small toes shown "fanning' or flexion. This is a variable 
reflex as far as the pattern is concerned. (D) The grasping reflex (infant 12 days old). [After J. B. AVat- 
son. Psychology from, the statidpoint of a behaviorist, Lippincott, 1919. p. 239.] 


Growth and Development 

part o£ tlie leg movement in walking. (See 
Fig. 32.) 

There are many other specific reflexes 
\\hich develop in normal human individ- 
uals at various periods. 


Infants a few hours old sometimes show prancing 
steps when they are supported under the arms, as 
shown in diagram. The patterns basic to this be- 
havior are probably related to walking responses 
which will appear much later. [Sketch of photo- 
graph from M. B. McGraw, Child dex'elopment, 
1932. 3, 295; by permission of Williams and Wilkins 

Maturation of the Receptors 

The skin sense for pressure develops 
first. We have already seen that a human 
fetus eight and a half weeks old responded 
to pressure stimulation near the mouth. 
The mouth is the first area that can be 
activated by pressure stimuli. Later, ef- 
fective areas for pressure stimulation spread 
over the entire skin surface. Such sensory 
development, like the development of move- 
ment, proceeds in a general cephalocaudal 

Responses to the stimulation of tem- 
perature and pain receptors can also be 
elicited during fetal life. The pain sense 
is, howe\er, not well developed in the 
prenate. A needle prick or even a lacera- 
tion of deep tissues in a fetus may not cause 
any more vigorous response than would a 
light touch with a soft hair. This late de- 
velopment of pain may have important 
value, for it may minimize the shock of the 
mechanical pulling and squeezing that arc 
incident to birth. 

It has long been known that at birth the 
receptors for smell, taste, vision and hear- 
ing (as soon as the liquid has drained from 
the middle ear) respond to their appropri- 
ate stimuli. The responses are movements 
usually of some part of the face like blink- 
ing, frowning or opening the eyes wide. 
The neonate does not distinguish objects 
until the higher levels of the brain have 
developed. Recently systematic obsen'a- 
tions have been made of a number of in- 
fants, some of whom were prematurely 
born babies that are called fetal infants 
because, except for the accident of birth, 
they would still be fetuses. They ranged 
in age from twenty-eight to forty weeks. 
It was found that they not only respond to 
both auditory and visual stimuli during the 
seventh month, but also that their re- 
sponses inay change in kind at a later 
time. For example, the first response of 
fetal infants to a bell may be a slight frown 
with a blink of the eyes, but during the 
ninth month its response changes to an 
opening of the eyes. Furthermore, the 
earliest movements are feeble and spas- 
modic, and, as a general rule, they cease 
entirely if the stimultis is frequently re- 
peated. Later, they become stronger and 
more continuous. These facts mean that, 
■with the earliest responses, de\elopment 
is not quite complete; a little more tinre 

Maturation at Birth 


or, it may be, some practice is necessary 
before it is complete. 

Eye movements, which are later so im- 
portant for visual perception, may also be 
observed in course of development in the 
fetal infant. During the seventh month 
the two eyes may move together in both 
horizontal and vertical directions, even be- 
fore there is any definite response to a 
visual stimulus. During the eighth month 
the eyes may follow, with brief movements 
Ijut without fixation, any object that moves 
slowly across the visual field. During the 
next month the eyes may definitely follow 
a moving object through an arc of forty- 
five degrees. All these eye movements ma- 
ture quickly shortly after the time of nor- 
mal birth. 

There are located in each inner ear of a 
mammal, not only the complex sense or- 
gans which make hearing possible, but also 
stabilizing mechanisms, the static or vestib- 
ular receptors, which assist the organism 
in maintaining body balance. (See pp. 374- 
378.) There is good reason to believe that 
these inner-ear receptors are effective in 
fetal life. Before the eyes of the fetus have 
moved in response to stimulation by light, 
they can be made to move by changing the 
position of the fetus with respect to grav- 
ity in such a way as to stimulate the re- 
ceptors in the inner ear. The maturation 
of such adjustments makes it possible for 
an infant, as he later develops, not only to 
maintain his posture but also to keep his 
eyes focused upon objects even when his 
own head and bodv move. 

tion which results from certain sf>-called 
emotion-arousing situations such as undue 
restraint, sudden noises or being dropjxrd 
onto a pillow. It is almost certain that 
the component movements of the behavior 
patterns of emotions are a result of matu- 
ration in the part of the brain called the 

The hypothalamus thus tends to induce 
certain emotional patterns, and tiie cerebral 
cortex tends to inhibit or limit this action 
of the hypothalamus. (See p. 100.) For 
instance, rage is natural to cats and dogs 
—the snarling, hissing attack of the cat, the 
growling, snapping attack of the dog. 
These behavior patterns are activated bv 
the hypothalamus, but inhibited by the 
action of the cortex. The surgical removal 
of the cortex releases the thalamic action, 
and these animals, when disturbed, snarl 
and snap quickly and automatically in a 
manner so closely resembling a reflex that 
their behavior is called sJiam rage. 

Thus it comes about that the develop- 
ment of the cortex makes possible the de- 
velopment of emotional restraint in man, 
as well as in the cat and dog. A child, 
using his cortex, gradually learns what 
emotional expressions are approved by the 
social groups to which he belongs, modify- 
ing his inborn behavior patterns accord- 
ingly. It follows that emotional maturity, 
the control of emotion, depends on the 
maturation of the cortex and learning— 
when the individual has a cortex with 
which to learn. 

Maturation of Emotion 

It is doubtful that the prenate and the 
neonate show clearly differentiated emo- 
tional responses, such as fear, joy and rage. 
Rather it appears that very young infants 


Between the neonatal and adolescent 
levels of development comes cliildhood. In 
it adapti^•e behavior appears, the ability to 

experience onlv a state of general excita- learn develops and language is acquired. 


Growth and Development 

The Maturation of Adaptive Behavior 

As the child develops he progressively 
makes a large number of movements com- 
mon to all human beings, which are un- 
learned and have only awaited maturation 
to be performed. These movements require 
the action of the higher brain centers and 
so are instances of the encephalization or 
corticalization of function. They are, in a 
sense, controlled movements and may be 
classified as \oluntary. Examples of these 
forms of behavior are grasping, creeping, 
standing erect, walking, running. ^Ve may 
take the maturation of the act of walking 
as an illustration of their development. 

The alternate innervation of the two 
legs in the prancing movement already de- 
scribed shows that a highly complex neuro- 
muscular organization is well along at 
birth. Before the child can walk, how- 
ever, he must first be able to hold up his 
head, then to hold his trunk erect with- 
out support while sitting. The matura- 
tion of erect sitting must await the stiffen- 
ing of the spine. Next he must be able 
to stand erect, an act which he cannot do 
until the bones and muscles of his legs 
are strong enough to bear his weight. The 
order of these maturations, it will be no- 
ticed, follow the cephalocaudal rule. The 
child still cannot maintain his equilibrium 
until maturation effects the coordination 
of the sensory nerves from his muscles, the 
sensory nerves from his semicircidar canals 
(see p. 378) and the motor tracts leading 
to his muscles. Only then can he trans- 
form the prancing into a walking move- 
ment by thrusting his flexed leg forward 
imtil it rests on the floor, at the same time 
letting his center of gravity also go for- 
ward. He must then maintain his balance 
on the one foot until the other is brought 
up and thrust forward. The repetition of 

this sequence is walking. Walking is the 
end product of a series of maturations 
which it takes the prancing infant about 
twelve to fourteen months to complete. 

Norms of Early Development 

There are tables and charts showing the 
general sequences of behavior which may 
be expected to take place during the first 

Sociality . Kindergarten 

^ Concepts : Number, form 

Speech : Sentences ■ 
^^ _^ Sptiincters : Bladder and bowel control 
_^ Larynx: Words, ptirases. Walks 
-^ Legs, feet: Stands, cruises 
_» Trunk, fingers : Sits, creeps, pokes 
. Hands: Grasp and manipulate 
Head: Balance 

Autonomic system: Physicochemical control 

, ' , / ^ Tonic -neck -reflex: Quickening 

,'///_^ Hand closure and grip 
"./_^ Prerespiratory movements 
^ Swallow, sneer, Babinski 
„ Trunk extension 

. Fetal stage (trunk flexion, oral sensitivity) 
/_^ Embryonic stage (preneural organization) 
. Conception (germinal organization) 


Diagram to sho\\' gradual development of behav 
ior in early life. [After A. Gesell and C. S. .Ama- 
truda, Dex'elopmental diagnosis: normal and abnor- 
mal child development, Hoeber, 1941, p. 9.] 

five years. (See Fig. 33.) In the first year, 
the child gains control of his basic muscles 
so as to be able to grasp objects and stand 
erect and to do many other acts in his new 
nonaquatic environment. In his second 
year, typically^ he walks and runs and 
articulates words and phrases. At this 
time he may acquire bladder and bowel 
control. In his third year, he speaks sen- 
tences and begins to comply with the de- 
mands of his home. In his fourth year, 
he asks many questions and becomes self- 

Maturafion Afier Birth 


dependent in the routines of the house. 
At five he hops and skips, can tell a long 
story and is "a self-assured conforming citi- 
zen of his small world." 

There are, nevertheless, great differences 
in the sequence of development in differ- 
ent children. No doubt some of these dif- 
ferences are due to differences in inherited 
rates of maturation. Some differences are 
also due to differences in environmental 
opportunity, as the studies of twins sug- 
gest. (See pp. 448 f.) It is also likely that 
there is a basis in maturation for the ap- 
pearance of certain aptitudes, like musical 

Maturation of Ability to Learn 

Thus far our discussion has been limited 
almost entirely to development in general 
and the maturation of unlearned behavior 
in particular. We can now turn to some 
of the relations between maturation and 
learning. It is, of course, impossible to say 
just when maturation ceases and learning 
begins. It may be that the fetal infant, 
by exercise or practice, 'learns' something 
from the feeble, spasmodic and discontinu- 
ous movements that he makes before the 
maturation of his eye movements is com- 
plete. It may be that the child can be said 
to learn from his successes and failures 
when he— as some of them do while taking 
their first steps— totters, staggers, falls down, 
gets up and tries again. The question of 
the effectiveness of such learning— assuming 
that it takes place— has been the subject of 
a number of investigations. 

Experiments have been carried out on 
animals, birds and mammals to determine 
the effect of withholding exercise from 
certain young of a brood or litter, while 
allowing the others to exercise as they 
de\'eloped. Chicks, for instance, have been 
hooded or otherwise kept from visual ex- 

perience after they hatch, to keep them 
from using the seeing-pecking behavior for 
food. Birds have also been prevented from 
flying until other birds of the same age 
were flying well. Figure M shows the re- 
sult of some experiments in this field. 

T 5 

t; 3 

1 — r 

Group A 

\>— Group B 

\ y- Group C 

\ \ 
\ ^ y-'Group D 
\^\ \ ^Group£_ 

J \ I ^^^^^ 

12 3 4 5 6 7 

Daily test series 


Errors of chicks given opportunity to peck foi 
first time when 1 day old (Group A) up to when 5 
days old (Group E). Curves show greater initial ac- 
curacy in older chicks, but learning is alwavs needed 
to supplement maturation. Note speed of learning 
in 4-day groups. [From W. W. Cruze. J. cnnip. 
Psychol, 1935, 19, 391, Williams and Wilkins Co.] 

In experiments with amphibians it has 
proved possible to raise experimental 
groups of larval Amblystoma (salamanders) 
in water containing a drug ^\hidi kept 
the larvae from making any mo%ements. 
At a later time, when a control group de- 
veloped from eggs of the same age and 
raised in undrugged water were freely 
swimming, the experimental animals were 
placed in fresh water. In a few minutes 
the preA'iously anesthetized animals swam 
in a way hardly to be distinguished from 


Growth and Development 

that of the animals that had been freely 
'practicing' for some days. 

All these experiments seem to show that 
the animal who was backward for want of 
exercise may overtake the animal who has 
had exercise all alon^ after thev have been 

given equal opportunity. Does this result 
hold also for the human organism? This 
question too has been put to experiment. 
A detailed study has been inade of a pair 
of twin boys from the age of twent)-onc 
days to the age of twenty-two months. 




Johnny (left), who had been given a great deal of active exercise, tackles the problem of getting him- 
self down from the pedestal with ease, whereas Jimmy (ri_^ht), who had been given a minimum of active 
play, sits perched on top, unable to solve his problem, [.\ftcr M. B. McGraw, Growlh: a sliidy of Johnny 
and /jHiwi)', .Appleton-Century, 1935, pp. 156-157.] 

Maturation of Ability to Learn 


Johnny, one of the twins, was regularly 
exercised in motor abilities, while his twin, 
Jimmy, was kept in a crib in the laboratory 
during the day. The two were compared 
with each other and with sixty-eight other 
children. This study showed that the be- 
havior which every child must ac(|uire in 
order to act as a biologically normal hu- 
man being is not markedly modified by op- 
portunity for practice. Maturation alone 
seems to take care of such responses. Spe- 
cialized skills, on the other hand, are de- 
pendent on practice. Actually, Johnny, 
the exercised twin, continued all the way 
up to ten years of age to show greater mus- 
cular skill than his brother who received 
relatively little practice during the first two 
years of life. (See Fig. 35.) Human skills, 
unlike swimming of salamander larvae, 
depend on much more than inheritance. 
A good coach is an important factor in the 
success of a team. 

This experiment, taken with the others, 
seems to show that the exercise of a be- 
havior before its maturation is finished 
does no more than hasten the maturation. 
It can act in one or both of two ways. 
Exercise increases the growth and thus the 
strength of the muscles involved. That is 
one way in which exercise could hurry 
maturation. It is also conceivable that 
exercise hastens the integration of a neuro- 
muscular pattern. In either case exercise 
woidd be doing little more than time alone 
would accomplish in completing the nia- 
turation. Furthermore it seems clear that, 
if there is any learning as a result of exer- 
cise, it affords little profit in so far as man's 
basic and fundamental acts of behavior are 
concerned. In the acquisition of special- 
ized skills, on the other hand, learning is 
necessary, and what Johnny, the exercised 
twin, had learned, together with his greater 

strength, txjjjains his superiority over his 

Since learning itself dejjeiids upon matu- 
ration, individual differences in the rate 
of maturation create individual difierences 
in the capacity to learn. Children who 
matuie earlier (an learn specific skills 
earlier. Some infrahuman animals of a 
given age can learn more cjuickjy than 


For two and a half years this chimpanzee lived in 
a human family with two children, one of them 
about its own age. (See also Fig. 216, p. 451.) 
[From R. M. Yerkes, Chimpanzees: a laboratory 
colony, Yale University Press, 1943, p. 191.1 

human children of the same age those 
forms of behavior that are common to both, 
simply because the child matures more 

There is an interesting example of this 
difference. A human infant and a cliim- 
panzee infant of about the same age were 
brought together in the human child's 
home. (See Fig. 36.) Both ^vere treated 
exactly alike. Each was fondled, kissed as 
he went to sleep and pimished in the same 
way. Because tlie chimpanzee matured 
more rapidly, he outdistanced his human 
companion in many ways. At Iwehc 


Growth and Devehpmenf 

months the chimpanzee could respond to 
twenty verbal commands such as "Open the 
door" and "Shake hands," but the human 
child could respond to only three. In con- 
trol of bowels and bladder and in other 
skills the chimpanzee was superior to the 
child. The chimpanzee learned better to 
use a spoon and to drink from a glass. In 
general, at one year of age the chimpanzee 
could do better with a problem of learn- 
ing than the child. This finding means 
simply that the physiological basis for 
learning had matured earlier in the ape 
than in the child. No ape, however, reared 
in human or other environment, has ever 
acquired the advanced use of language or 
of the other symbols that are basic to man's 
mental life. When the centers of the hu- 
man brain, which are essential in the use 
of language and other symbolic processes, 
finally mature, a new kind of learning, not 
possessed by any organism other than man, 
becomes available. At this stage of matura- 
tion the human child soon outdistances 
all his animal competitors. (For other de- 
tails of this experiment, see p. 451.) 

Maturation of Speech and Language 

Speech implies both vocalization and 
symbolization— the production of sounds 
and their use as symbols. Both functions 
depend on learning, and both recjuirc the 
development of the higher brain centers 
before progress with respect to them can 
be made. 

Vocalization consists in the coordination 
of the nerves and muscles which control 
movements of the throat, palate, tongue, 
lips and the lower jaw. Separately, as re- 
flexes, all these movements are present at 
birth, and all are at least partially coordi- 
nated in the infant's first cry. The birth 
cry of the human infant has siipcrstitiously 
been regarded from early times as having 

symbolic significance. It is, however, only 
a reflex which results from a stimulation 
of receptors and a coordination of groups 
of motor nerves in the medulla of the 
brain. For example, when the contraction 
of the walls of the empty stomach stimu- 
lates the receptors there, the baby cries. 
The cry has no symbolic significance what- 
ever to the baby although to its nurse it 
means "the baby is hungry." Crying is 
not necessarily speech. 

The coordination of the motor nerves 
necessary for speech occurs in the cortex of 
the brain in an area that is called the 
speech center. This coordination, the in- 
tegration of the nerves to the various mus- 
cles of the throat and mouth, is sufficiently 
matured by the sixth or seventh month 
after birth to make possible the beginning 
of learning to talk. At this time the child 
begins to babble. Babbling consists in the 
automatic production of meaningless syl- 
lables; they are variable in sound, but 
generally the same syllable is repeated a 
number of times. The child hears, of 
course, the sounds of its own voice and 
apparently finds the experience pleasur- 
able. Babbling is a period of practice in 
enunciation, particularly in the use of the 
tongue and lips. It has been said that 
before the period ends all the sounds are 
produced which occur in any language. 
This statement docs not mean that the 
child can at will enunciate any speech sound 
that he hears and wislies to imitate. He 
needs much practice before he can com- 
mand the sounds of his mother tongue. 

When vocalization has become possible, 
then symbolization can follow. The 
sounds can acquire meanings. Symboliza- 
tion is created by learning and the build- 
ing up of conditioned responses. Since this 
process is discussed in a later cliaplcr (pp. 
51H f.), we need not consider it here. 

Adolescence, Adulthood and Old Age 


When a vocalized sound has acquired a 
meaning, it has become a word. A reper- 
toire of words is a -(incnbulary. At first the 
child accjuires a vocabulary but slowly. 
When twelve months old he can usually 
respond to his own name and to two or 
three other words. At fifteen months he 
may know half a dozen more words; at 
eighteen months, twenty to (ilty words. 
When he discovers that all objects have 
names, an event which occurs during his 
second year, his progress becomes much 
more rapid. By the beginning of his third 
year he will have learned some three hun- 
dred words. There can be no doubt that 
every one of these advances in his learn- 
ing is preceded by a new stage of matura- 
tion, some new coordination or integration 
that occurs in the cerebral cortex. 


The period from adolescence to old age 
may be four times as long as the period 
from conception to adolescence, but it does 
not include nearly so much change. The 
adult reaches the height of his powers I)ut 
slowly, and thereafter declines but slowly. 

Puberty and Adolescence 

Adolescence is the period of some eight 
or ten years dining which the human in- 
dividual develops from childhood to adult- 
hood. The period is characterized by pu- 
bescence, the beginning of the procreative 
functions. It is the maturation of a com- 
plex mechanism which includes the sex 
glands, the external sexual organs and parts 
of the nervous system. The chronological 
age at which puberty begins is variable; it 
may, however, be expected dining the thir- 
teenth year in girls, and the following year 
in boys, and is generally regarded as estab- 

lished at the first menstruation in girls and 
at the appearance of pubic hair in fwys. 
The common belief that puberty is reached 
early in tropical countries is not borne out 
by careful study. Ciirls in the United 
States reach sexual maturity on the aver- 
age as early as any group that has ijcen 
scientifically studied. 

A second characteristic of adolescence is 
the rapid increase in the growth and de- 
velopment of the individual. As we have 
seen in the curve of the general type of 
growth in Fig. 30 (p. 73), the period be- 
gins during the eleventh year and the curve 
begins to flatten out about the sixteenth 
year, although it will continue to rise bv 
smaller increments beyond the twentieth 
year. The change thus begins before pu- 
berty, and it commences earlier in girls 
than in boys, with the result that, although 
tliroughout childhood the boy has on the 
average been taller and heavier than the 
girl of the same age, from the eleven tli 
to the fourteenth year this relation is re- 
versed. Thereafter the boy will resume 
his superiority in this respect. We have 
also seen that the sex glands and all the 
internal and external sexual organs begin 
a period of rapid growth at about the 
twelfth year, starting at least a year earlier 
in girls than in boys. 

This growth results not only in an in- 
crease in height, weight and the maturation 
of the sexual organs, but also in changes 
in the relative proportions of the head, the 
legs and arms, the trunk and the features 
of the face. Other changes are the second- 
ary sexual characters noted previously. In 
a boy these changes are the starting of the 
beard and hair on odier parts of the bodv 
and a lowering of the pitch of the voice, 
which sometimes amounts to as much as an 
octave. In a girl, the voice drops onlv 
slightly in pitch and she develops pubic 


Growth and Development 

hair and the soft downy hair on her face. 
There is also a widening of the pelvis and 
a consequent broadening of the hips and 
the development of the breasts. 

A third characteristic of adolescence is 
the appearance of an increased emphasis 
upon certain previously existing interests 
and attitudes. The adolescent begins to 
be concerned about the other sex, and in 
romance and sexual matters. He feels a 
heightened self-consciousness, realizes more 
fully his position in the social group in 
which he moves. He gains a greater de- 
sire for independence and a tendency to 
resist parental direction. The girl, in par- 
ticular, may become critical of her mother's 
dress and the way she does her hair. Both 
boys and girls acquire new attitudes toward 
social, economic and religious ideas which 
they formerly accepted without thought, 
but which now they question, at times 
with intolerance. Because he is still in- 
experienced the adolescent often says and 
does many things that he will later regard 
as radical or ill advised. 

For many individuals this period is diffi- 
cult. The adolescent has so many new 
adjustments to make. He yearns for action, 
but his goals are not yet clear. Nor does 
he yet know that his problems are char- 
acteristic of the period through which he is 
passing and that time alone will bring 
their solution. 


There are wide individual differences in 
the chronological age at which the adoles- 
cent period ends. It ends earlier in women 
than in men, and within a sex it happens 
earlier in some persons than in others. It 
may be said to be all over by the age of 
twenty-five. By that time, as we have seen, 
the organism has practically completed its 
growth— only the skin, the nails and the 

hair continue to grow. Repair, however, 
will still go on. 

When all matmation has come to an end, 
the normal individual does everything that 
all normal members of the human race do. 
His neuromuscidar growth and develop- 
ment, however, are now such that he may 
learn to do many other things. His rate 
of metabolism is high; he has great stores 
of energy; he fatigues slowly and recuper- 
ates quickly. For this reason he is able 
to do more and harder work with fewer 
ill effects than at any other time in his 
life. He has presumably decided on his 
life's work— his trade, business or profes- 
sion. His formal education is finished, and 
his apprenticeship or professional training 
is nearly completed. The end of matura- 
tion is, therefore, the beginning of another 
period, the period of adulthood, which 
may last for thirty-five or forty years, while 
the individual rears a family, masters a 
trade or profession and otherwise plays 
the part of a mature person in the culture 
to which he belongs. 

The first twenty years of adulthood are, 
however, the most productive. A study 
of the recorded achievements of one thou- 
sand historically eminent persons showed 
that about a third of their best work was 
done between the ages of thirty and forty, 
and seventy per cent of it before the forty- 
fifth year. The causes for this difference 
must be very complex. The younger adult 
has more endiuance; he can work harder 
and longer. He has higher motivation tc 
work, not only because of his need to make 
a living for himself and his family, but also 
because he feels competition with his fel- 
lows more keenly when he is at the thresh- 
old of his career. It is not clear whether 
besides endurance and motivation there 
is something else that makes young animals 
and young people and younger adults more 



active, more aggressive, iriore ciithusiasiic, 
more 'energetic' than they will be later in 
life. It is certainly true that younger ani- 
mals and persons expend effort more read- 
ily than older ones. What happens seems 
to be that this 'energy' diminishes with age 
while wisdom and skill increase, with the 
result that maximal effectiveness occurs 

I I I I ' I I I ' I I I I 
-Pursuit reaction 

eg CO ^ in i£> 

Age in semidecades 


Many other human functions follow similar 
curves. See also Fig. 30. [After W. R. Miles, Proc. 
Nat. Acad. Sci., 1931, 17, 631.] 

for human beings in an intermediate dec- 
ade around forty. There is possibly also a 
third effective factor: creative work in 
older adults becomes more difficult because 
society makes more demands upon older 
responsible people and seeks oftener to de- 
termine their activities. For instance, great- 
ness, once achieved, may bring about its 
own limitation, for it takes time and is 
fatiguing to play the role of a famous 

The high tide of muscular strength, en- 
durance and speed of action at first re- 
cedes slowly and then, as the years go on, 
more rapidly. The professional baseball 
player, particularly the in-fielder, is fre- 
quently said to be an old man at thirty to 

tliirty-seven years of age. He no longer 
lias the blinding speed necessary to play 
his position with his former skill. Experi- 
ments also show that the speed ol various 
movements of the hand, fingers and fool 
reaches its peak just before or soon after 
the twentieth year, and within the next 
decade begins a decline which continues for 
the remainder of life. The curves of some 
of these results are shown in Figs. 37 and 

After the forty-fifth year other decre- 
ments which at first were so small as to be 
unnoticed begin to be bothersome. The 
individual finds that his hearing is not so 
good as it was; he can no longer hear very 
high tones like the chirp of the cricket, and 
he frequently misses a word in a conversa- 
tion. He discovers also that, although he 

Digital extension -flexion speed 

in vD 
Age in semidecades 


See also Fig. 37. [.After AV. R. Miles. Pioc. Xiit. 
Acad. Sci., 1931, 17, 629.] 

can still see distant objects, he cannot fo- 
cus his eyes to near objects as \\ell as for- 
merly. His memory too is often bother- 
some. At times he cannot recall proper and 
place names that are perfectly familiar. His 
immediate memory is bad. For example, lie 
may look up a telephone niunber and dien 
forget it before he puts in his call. He 


Growth and Development 

has trouble also in renicinbering tacts that 
belong to a field which is unfamiliar. On 
the other hand, he may recall with fidelity 
the details of events that happened many 
years earlier, as well as new facts in a 
familiar field. 

As a man grows older there is a decided 
shift in his interests and attitudes. He 
cares less for physical activity, and he gradu- 
ally gives up those forms of sport that rc- 
(juire strength, speed and endurance. If 
he continues to play tennis, he no longer 
tries to cover the coiut; instead he tries 
to win by strategy and gieater accuracy. 
If he plays golf, he is satisfied with nine or 
l^erhaps six holes; and, if he defeats his 
younger opponent, it is through accuracy 
rather than distance. As observer, how- 
ever, his interest in sports increases. He 
does not care so much for dancing or the 
cinema as younger persons do. The statis- 
tical studies show also that he has an in- 
creased interest in his home, in art gal- 
leries, in his chinch and in his clubs. 

The least diminution with advancing 
years occurs in those human activities that 
depend less upon muscle and more upon 
brain. For example, tests of the kind of 
imagination which sees objects in the 
clouds or in ink blots show that there is 
little decline with age. Moreover, tests of 
comparison and judgment in which speed, 
inmiediate memory or recall of unfamiliar 
material are not involved, reveal that the 
older person does just about as well as the 
yoimger. On the whole, skill in verbal 
association, interpretation of meaning, 
generalization and the finding of relations 
resists the influence of age. Thus it comes 
about that the older man, provided he has 
escaped the hardening efi^ect of habit, be- 
comes a valued counselor; his long and 
varied experience renders his judgments 
more objective and impartial and gives his 

opinions greater breadth and perspective. 
Thus he finds compensation for the physi- 
cal disabilities that overtake him. 

Old Age 

The period of old age is called senes- 
cence. There is no particidar time at 
which senescence can be said to begin. 
Ihe process of aging, like the process of 
maturing, is continuous and the two kinds 
of change are often just the obverse and 
re\'erse of the same process. Actually aging 
begins as soon as the ovimi is fertilized. 
When the prenate, two weeks after devel- 
opment has started, passes from the germi- 
nal period to the embryonic period, its 
cells undergo a change. At first they are 
what is called iotipolent: any cell could 
develop into a whole individual or into 
any of the kinds of tissue of which the in- 
dividual is composed. Then the cells 
change, acquiring special fimctions, and it 
is no longer possible, for example, to get a 
nerve cell from a cell destined to be mus- 
cle. This specialization is a stage of ma- 
turation, but it is also a stage of prenatal 
aging. For the gain in special potency 
there had to be a loss in general potency. 
Senescence can be regarded simply as the 
ultimate maturity when the losses have be- 
come more noticeable than the gains. 

Man does not grow old at the same rate 
all over. His vital organs, his glands, his 
bones and muscles, his senses and his psy- 
chological abilities age at different rates. 
It is only after a long time, somewhere be- 
tween the ages of fifty and seventy-five, that 
all these symptoms combine to make up the 
picture of true old age. It may be even 
later before we find the extreme picture of 
age— the tottering step, the trembling 
hands, the filmed and watery eyes, the flut- 
tering heart, the wrinkled skin, the extreme 
forgetfulness. Even then the old man has 

The Trajectory of Life 


not lost his usefulness to society if liis diIikI 
remains clear. He needs to resist the tend- 
ency to withdraw into himself, to nurse his 
growing infirmities, and thus lo becoinc 

Postmortem studies show tliat all the 
structuies of the body have degenerated in 
old age. Nearly all (he inlernal organs 
and glands are alropliicd and decreased in 
si/e. The niusdcs are slioi ilirougii wiili 

itstif, and whidi, il ii progresses far enough, 
may result in senile dementia, a form of 
irunlal disorder which sometimes occurs in 
the very old. Personality changes at vari- 
ous ages of the individual are discussed in a 
later chapter (pp. 505-509). 

The Trajectory of Life 

The course of Inirn.iii life througlioul 
lis ages has been likened lo the trajectorv 


(n) Small segment of the cerehial cortex Avith co\eiiug membranes removed. The deep wide fissures 
result from atrophy of the brain, common in senility. This brain weighed only 1000 grams, whereas 
the average normal braiir weighs al)out 1300 grams, (h) Cross-section of one hemisphere of brain, show- 
ing in the center a large hemorrhage, such as often occurs in older people as a result of arteriosclerosis. 

fibrous tissue losing their elasticity and 
contractility. The cartilages are stiffened 
with deposits of lime. The arteries are 
hard and inelastic, a condition (arterio- 
sclerosis) which results from a cellular 
change in the walls of the arteries, mak- 
ing it more difficult for the heart to force 
idood into the small capillaries of the brain, 
and thus depriving the brain of the needed 
food and oxygen. (See Fig. 39.) Some- 
times, under high blood pressure, the blood 
vessels in some region of the brain burst, 
resulting in a 'stroke' (apoplexy), a partial 
paralysis. There is another kind of sclero- 
sis which is a degeneration within the brain 

of a bullet fired from a gun. The bullet 
first shoots upward and forward after leav- 
ing the gun, then le\els off and eventually 
drops again to the earth. It is eas) to see 
the analogy. From the moment of the 
fertilization of the egg until the end of 
adolescence there is an increase in size, in 
jDhysical strength and encUirance, in motor 
responses, in sensory capacity, in 'intelli- 
gence.' Ultimately a peak is reached at 
which the individual is at his best average 
in these respects. Then decline begins, 
at first very slowly and then more rapidly 
until death is reached in extreme old age. 
This picture of the course of human 


Growth and Development 

life is useful because it brings into bold 
relief an important triuh. Notwithstand- 
ing the complexity of the comse of growth 
and development Avhich has been re- 
counted in this chapter— the fact that every 
structure of the body has its own rate of 
growth and dexelopment, the fact that the 
maturation of the various structures and 
forms of behavior occurs at different times 
and yet all are about at their best when 
life is at its peak, the fact that the decline 
of the various psychological abilities is not 
imiform— notwithstanding these complexi- 
ties, the course of life, regarded as a whole, 
is first an evolution, then a continuation 
and then an involution This is the basic 
life pattern of other living things, and, 
since man also conforms to it, the plan of 
his life course must surely have been laid 
down in heredity and directed by his genes. 
The wide individual variation in the chron- 
ological ages at which the several life pe- 
riods are reached is not surprising. The 
mar\elous timing of the genes is not done 
with respect to any astronomical calendar. 
The calendar of the genes is physiological, 
and some racial strains are longer lived 
than others. 

Finally, it may be said that the task of 
heredity is finished only when it brings the 
organism to the peak of its powers and has 
enabled it to reproduce and rear its kind. 
What, in addition, man makes of his life, 
he does on his own initiative in relation 
to the social and other environmental 
forces which bear in upon him. What his 
resources are and what means he employs 
are set forth in subsequent chapters of this 


1. Brooks, F. D.. and Shaffer, L. F. Child psy- 
chology. Boston: Hoiighloh Mifflin, 1937. 
Ctiap. 7. 

A student tcxtlioolc whicli reviews and in- 
terprets tlic scientific literattne in its field. 

2. Cannicliaei. L. (Ed.) Manual of child ps\- 
choloffy. New York: Wiley, 1946. 

An ad\anced-level book on developmental 
psycliologv' by nineteen experts. Excellent bib- 

3. Cowdry, E. V. (Ed.) Problems of ageing. (2nd 
ed.) Baltimore: Williams and ^Vilkins, 1942. 
Especially Chap. 28. 

A general book in a new field, including an 
excellent chapter on psychological aspects by 
Walter R. MHes. 

4. Dewey, E. Behavior development in infants: a 
survey of the literature on prenatal and post- 
natal activity, 1920-1934. New York: Columbia 
University Press, 1935. 

A source book which gives a summarv of 
scientific literature, some of which was previ- 
ously available only in obscure journals. 

5. Gerard, R. W. The body functions: physi- 
ology. New York: Wiley, 1941. Chap. 11. 

An excellent general summary which in- 
cludes consideration of the phvsiology of de- 

6. Gesell, A., and Amatruda, C. S. Developmen- 
tal diagnosis: normal and abnormal child de- 
velopment. New York: Hoeber, 1941. 

A basic description, trait by trait, of typical 
and atypical early human development. 

7. Gesell, A., and Amatruda, C. S. The embry- 
ology of behavior. New York: Harper, 1945. 

A general consideration of the growth of be- 
havior discussed as the anatomist considers the 
growth of structure. 

8. Gilbert, M. S. Biography of the unborn. 
Baltimore: Williams and Wilkins, 1939. 

A somewhat popular description of some as- 
pects of prenatal life. 

9. Hollingworth, L. S. The psychology of the 
adolescent. New York: Appleton-Century, 1928. 

A wise treatment of a difficult period of 
human development bv a scientifically minded 
woman psychologist. 
10. Kellogg, W. N., and Kellogg, L. A. The ape 
and the child: a study of environmental in- 
fluence upon early behavior. New ^'ork: Mc- 
Graw-Hill, 1933. 



A detailed study of a cliimpanzce :ind a liu- 
man infant reared together in a liiiiiiaii home. 

11. McGraw, M. B. Growth: a sludy of Johnny 
and Jimmy. New York: A|j|jlcloii-Ceiitury, 

An elaborate experiment on twins, one of 
whom was given much exercise while the other 
was kept relatively quiet. 

12. Miles, W. R. Age and human society. In C. 
Murchison (Ed.) , A handbook of social psy- 
chology. Worcester, Mass.: Clark University 
Press, 1935. Chap. 15. 

An excellent summary of the psychological 
factors that are important in human aging. 

13. Munn, N. L. Psychological development: an 
introduction to genetic psychology. Boston: 
Houghton Mifflin, 1938. 

A sinnmary of the psychology of develop- 

jr)(iii uiih due reference to relevant liiolo^ical 

H. Scammon, R. E. The measurement of the IxmK 
in childhood. The measurement of man. .Min- 
neapolis: University of .Minnesota I'rc-ss, 1930. 
Chap. 4. 

Facts and generalizations concerning the 
measurement of human growth in childhof>d. 

15. Warthin, A. S. Old age: the major involution. 
New York: I'aul B. Hoeher, 1929. 

A general book wiili special reference to 
medical problems. 

16. Windle, W. !•'. Physiology of the fetus: origin 
and extent of function iii prenatal life. Phila- 
delphia: Saunders, 1940. 

An excellent summary of the physiological 
functions of the mammalian and human fetuses 
before birth. 


Feeling and Emotion 

FEW areas of human experience and be- 
havior are as vital and interesting to the 
individual as his feelings and emotions. 
They occur in situations of special impor- 
tance to him, when his interest is aroused, 
his attention held, and his energy increased 
and directed toward a definite goal. They 
range from the milder feelings which we 
call pleasantness and unpleasantness to 
stronger emotions like fear and anger. We 
do not know what the exact relationship 
may be between the affective states, as 
pleasantness and unpleasantness are called, 
and the stronger emotions, but this we do 
know: they both involve general reaction 
attittides of the organism toward something 
in its environment. 


Pleasantness and unpleasantness, referred 
to either as afjeclive stales or as Jiedonic 
tone, correspond to broad attitudes of ac- 
ceptance or rejection that the organism 
assumes toward various aspects of its en- 
vironment. Pleasant things are the things 
that we like, that we desire and seek to ob- 
tain. Pleasant situations are ones that we 
attempt to maintain and prolong. Un- 
pleasant things arc not liked. We strive 

to avoid them. Unpleasantness is a condi 
tion which we try to terminate. 

In one sense, pleasantness and unpleas- 
antness may be said to be indicators of the 
organism's normal reaction tendencies to- 
ward stimulus objects. This interpretation 
is supported by laboratory experiments 
which show that under conditions where 
movement by the subject is not possible, 
pleasant stimuli lead to muscidar relaxa- 
tion, and unpleasant ones to musciUar ten- 
sion. Where movement by the stibject is 
possible, where he sits unrestrained and the 
stimulus moves past him, pleasant stimuli 
prodtice movements of his approach to the 
stimulus, and unpleasant ones movements 
of his withdrawal. The actual behaviors 
involved in such acceptance or rejection 
vary from situation to situation, and from 
individual to individual, and resemble one 
another only in this one common charac- 
teristic, that they are designed to continue 
or to remove the source of stimulation. 

Affective Value of Stimuli 

Because pleasantness and unpleasantness 
serve as indicators of the direction an in- 
dividual's behavior will take, it is impor- 
tant to know which stimuli are normally 
pleasant and which unpleasant. This 
knowledge should help us in predicting 
and controlling liuman behavior. 

lliis tliaplcr was jncparcd by William A. Hunt of Nortliwcstcni Uni\ersity. 


Pleasantness and Unpleasantness 


There is some indication that pleasant 
stimuli tend to be those which are of posi- 
tive biological value to the individual, and 
that unpleasant stimuli are in general bio- 
logically harmful. Thus the alkalies, which 
are often poisonous, are bitter and usually 
unpleasant; whereas the sugars, which have 
food value, are sweet and nearly always 
pleasant. Pain, which accompanies tissue 
damage or physiological disorganization, is 
notoriously unpleasant. The relationship 
is not exact, for many harmful stimuli are 
pleasant and many beneficial ones unpleas- 
ant. Few people relish the flavor of cod 
liver oil although its biological effect may 
be desirable; and diabetics continue to 
crave the sugar which has become bad for 

This biological interpretation is sup- 
ported by the relationship which exists 
between affectivity and the intensity of the 
stimulus. In general, pleasantness and un- 
pleasantness vary in direct relation to the 
intensity of the stimulus, both the pleas- 
antness and unpleasantness becoming 
greater as the intensity of the appropriate 
stimulus increases. In most cases, however, 
there comes a point beyond which an in- 
crease in intensity causes the pleasant 
stimulus to become unpleasant. Thus, as 
the concentration of salt in a solution is 
increased, the solution is at first indiffer- 
ent, then it becomes pleasant as more salt 
is added, and finally, when the concentra- 
tion is increased beyond a certain point, the 
solution becomes definitely distasteful and 
unpleasant. (See p. 356.) The biological 
importance of this general rule of intensity 
seems obvious— intense stimuli tend to be 
dangerous, and unpleasantness acts as a 

Whatever the biological significance of 
the affective states, it is possible to plot 
certain general relationships between pleas- 

antness and unpleasantness, on the one 
hand, and their specific stimulus condi- 
tions, on the other. Human beings show 
broad resemblances in their preferences. 
For instance, they tend to prefer saturated 
colors to unsaturated. Primitive peoples 
and young children seem to prefer the 
'warmer' colors like red, whereas our adult 
culture prefers the 'cooler' colors like blue. 
Certain combinations of tones have differ- 
ent hedonic value. The musical interval 
of the major third is usually considered 
most pleasant and the minor second least 
pleasant by musically sophisticated persons. 
Sweet is usually pleasant, and fjitter im- 

Although there is no doubt that these 
general tendencies exist, we must remem- 
ber that they are only tendencies, broad 
generalizations concealing a great amount 
of individual variation among the members 
of the groups studied. Not only do pleas- 
antness and unpleasantness change with 
learning, but they also depend on manv 
other conditions. The breakfast food that 
is so pleasant today, through monotony 
may become vmpleasant a few months from 
now. The favorite dress of ten years ago, 
discovered and put on today, niav now 
look ridiculous. 

The Relativity of Hedonic Tone 

Not only are pleasantness and unpleas- 
antness dependent on individual stimuli, 
but they also are affected by the relation- 
ships within a group of stimuli. If a less 
pleasant stimulus is presented as one of a 
group of more pleasant stimuli, its affec- 
tive value may be enhanced by its inclu- 
sion, as belonging, within tlie group of 
more pleasant stimuli. This change is 
called assimilation. AVhen vou really like 
a person, you may find yourself liking even 
his (or her) faults. On the other hand, if 


Feeling and Emotion 

the less pleasant stimulus is not assimilated 
into the group, it may seem even less pleas- 
ant or definitely unpleasant by contrast 
with the more pleasant stimuli present. 
This is called afjeciive contrast. How 
much worse it is to spend an hour with 
the chap you do not like right after you 
have spent an hour with the chap you do 
like very much. 

The affective value of a stimulus also is 
conditioned by the range of stimulus values 
presented to an individual. If we give a 
subject a series of odors which covers a wide 
range of hedonic tones, we can establish 
which odors are pleasant, indifferent or 
unpleasant to him. If we now remove the 
unpleasant odors, and continue to present 
to him over and over again the indifferent 
and the pleasant ones, some of the indif- 
ferent ones gradually become unpleasant 
and some of those previously less pleasant 
are presently judged to be indifferent. In 
other words, the subject rearranges his re- 
sponses, spreading them over the present 
range of his olfactory experience. This 
phenomenon, known as affective equilib- 
rium, is an example of the general prin- 
ciple of relativity of judgment with which 
we are all familiar. 

Suppose, for example, a man found the 
food at a given restaurant so extremely un- 
pleasant that he declared it the worst food 
he had ever eaten. Subsequently, if he has 
changed to a cheap boarding house where 
the food is even worse, it now seems to 
him that his present fare is really the worst 
food he has ever eaten. Should he then 
return to the original restaurant, the food 
there would seem much better, just as long 
as he keeps remembering about the food 
at the boarding house. If, however, he 
forgets all about the boarding house, the 
food at the restaurant is going to become 
worse aa;ain. To the Children of Israel in 

the wilderness the taste of the flesh pots of 
Egypt would .have been very pleasant. 

The same relationships work out at the 
other end of the scale. Our present pleas- 
ures fade before still greater ones; nor do 
the still greater ones long remain 'still 
greater.' This ride provides one of the 
reasons why wealth does not assure happi- 
ness. There seem, nevertheless, to be limits 
to such relativity. Some stimuli show 
great constancy in pleasantness or unpleas- 
antness. Within a wide range, however, 
human beings do adjust their affective 
values to fit the experiences available to 
them, and this relativity has important 
consequences for man's contentment im- 
der varied environmental circumstances. 

Dependence of Learning 
upon Hedonic Tone 

Hedonic tone depends upon learning 
and, conversely, learning in part upon 
hedonic tone. This relationship between 
the two has received much attention in 
educational psychology. A child who likes 
candy learns to like the aimt who gives 
him candy; hedonic tone depends upon 
learning. Similarly, the child learns the 
multiplication table because the aunt, 
whom he now likes, teaches it to him and 
gives him the pleasiu'e of her approval as 
a reward; learning depends upon hedonic 
tone. By such transfers of hedonic value, 
it might be possible to make a lover of 
candy into a mathematician, provided cer- 
tain other capacities were available. 

Pleasantness reinforces learning, and im- 
pleasantness hinders it. For this reason 
either reward or punishment may be used 
to establish a learned response. Experi- 
ments with animals show that the task 
which is followed by the greater reward or 
by lesser punishment is the task that is 
learned most rapidly and effectively. Fur- 



thcniiore, reward or |nniislinicnl is more 
effective the more immediate it is. 


Because of the apparent importance of 
affectivity, or hedonic tone, in human mo- 
tivation and behavior, it has frequently oc- 
cupied a prominent part in some philo- 
sophical systems. These theories have as- 
sumed that hedonic tone determines ac- 
tion, a doctrine which is called hedonism. 
In its various forms hedonism reduces hu- 
man motivation to a desire to seek pleasure 
and to avoid unpleasantness. Some of the 
theories base all present action on the part 
played by hedonic tone in the past when 
the action was learned; others hold that 
action is in direct accordance with present 
hedonic tone; still others maintain that 
action is determined by the anticipated 
pleasantness of the future. 

These theories are too naive to explain 
adequately the complicated facts of human 
behavior. Hedonic tone is really not so 
much a determiner of human behavior as 
it is an accompaniment and indicator. 
Pleasantness indicates the existence of an 
attitude of acceptance and unpleasantness 
of an attitude of rejection. 

Objection is often made to this state- 
ment because it implies that all positive 
action is pleasant, whereas it is obvious that 
man often 'chooses' unpleasant action or 
action with unpleasant consequences. Mo- 
rality seems to depend on his capacity so 
to choose. Does the martyr like his mar- 
tyrdom? Is it jaleasant? That is the he- 
donic paradox. 

This paradox arises because we tend to 
think of conflict situations in simple terms 
as if they were completely pleasant or com- 
pletely unpleasant. If the martyr experi- 
ences no conflict, perhaps he can march 
to the lions with joy at this opportunity to 

glorily his laiili, and soitiicrs similarly 
have been known to go into almost certain 
death with enthusiasm and without hesi- 
tation. Such instances are, however, rare. 
Expectation of death or pain normally 
leads to unpleasantness and the attitude of 
rejection, or, if opposed by some other mo- 
tive, to a conflict and vacillation of accept- 
ance and rejection. The stronger motive- 
courage or fear— is what wins out, but 
meanwhile there has almost always been a 
fluctuation of pleasantness and unpleasant- 

This matter, however, requires two fur- 
ther qualifications. (1) Often the only 
choice lies between two unequally unpleas- 
ant alternatives, courage with danger versus 
cowardice with shame. The hero may then 
choose unpleasant courage because it is less 
unpleasant than very unpleasant shame, 
may choose it without affective' equilib- 
rium's getting a chance to turn the less 
unpleasant courage into positive pleasant- 
ness. (2) Habit, moreover, enters into these 
equations. For instance, the purpose of 
military discipline is, in part, to substitute 
habit for choice when simple hedonistic 
preference would lead to the wrong action. 
Undoubtedly habituated action patterns 
have also lent support to martyrs. 


Classed with pleasantness and unpleas- 
antness under the general heading of 
feelings are such emotions as fear, anger, 
sorrow, love, joy, laughter. The emotions 
resemble the affective responses in diat 
both represent general reaction attitudes of 
the organism and seem to have special bio- 
logical significance for the organism. It is, 
moreover, an affective state that usually 
ushers in an emotion. As a rule you feel 
unpleasantness as a prelude to feai- or 


Feeling and Emotion 

anger, pleasantness as a prelude to joy or 
elation. In fact, all the emotions them- 
selves may be roughly classified as either 
pleasant or unpleasant experiences. A£- 
fectivity is thus intimately connected with 

The differences between the emotions 
and the affective responses are also marked, 
in some respects more marked than the re- 
semblances. The reaction attitudes are 
more specific in the emotions than in the 
affective states. The general rejection that 
belongs to unpleasantness may be differen- 
tiated into actual flight in fear or actual 
attack in anger. The emotional behaviors 
themselves are more forceful, more ex- 
treme; they involve more of the body and 
involve it in a greater intensity of response. 
Attended by great feelings of excitement, 
they disorganize and disrupt other behav- 
ior patterns of the moment. We speak of 
being 'engulfed,' 'overwhelmed' or 'swept 
away' by emotion. We have only to re- 
member the difference between disliking a 
person and being angry at him for the dis- 
tinction between feeling and emotion to be 

The biological significance of emotional 
stimuli lies back of this intensitive differ- 
ence. Emotions arise in situations which 
the individual feels are emergencies. We 
dislike things that are bad for us, but it is 
not until they become actually threatening, 
until an emergency arises, that we become 
emotional and respond with fear or with 
the aggressive attack that is typical of 
anger. We like pleasant things, strive to 
attain them and to keep them, but it is 
only the particularly desirable object or 
goal, the much-wanted or much-desired, 
whose attainment produces the excited re- 
sponse of elation or joy. Emotion accom- 
panies an emergency, be it real or fancied. 
Emotion is typical of crisis. 

Visceral Reactions and the 
Autonomic Nervous System 

Emotions involve generalized reaction at- 
titudes of the organism. Thus anger is al- 
ways marked by some aggressive response, 
some kind of attack on the object that 
makes us angry; yet the specific behavior of 
attack varies from person to person and 
from situation to situation. We may at- 
tempt to dispose of an enemy by blacken- 
ing his eye with a blow, by woiniding his 
self-esteem with an epithet or by imdcr- 
mining his social reputation through derog- 
atory remarks about his character. All 
strong emotion, however, does involve one 
common behavioral element: it is accom- 
panied by increased visceral action, height- 
ened response in the vital organs. 

The importance of visceral response in 
emotion has been recognized since the ear- 
liest times. We speak of love as an affair 
of the heart, compassion as residing in the 
bowels and fear as striking in the pit of the 
stomach. Modern physiology has con- 
firmed the general correctness of this liter- 
ary usage. We know that the viscera are 
controlled by a special section of the nerv- 
ous system, the autonomic nertio^is system, 
which is intimately involved in emotion. 

The autonomic nervous system is a group 
of nerve centers or ganglia lying just out- 
side the spinal cord. It controls those in- 
ternal vital processes which have to do 
with metabolism and the vasomotor and 
glandular responses. Heart rate, blood 
pressure, salivation, digestion, elimination 
are a few of these involuntary functions 
that operate under the control of the auto- 
nomic nervous system. 

This nervous system is divided into two 
parts (see Fig. 17, p. 35): the parasympa- 
thetic (craniosacral) and the sympathetic 
(thoracico-lumbar). The actions of these 

Visceral Reactions and the Autonomic Nervous System 


two branches are opposed; sympallictic 
stimulation, for example, increases the pulse 
rate, parasympathetic stimulation decreases 
it. These functions may be seen in Table I. 



OF THF. Autonomic 

Nf.rvous Systkm 







speeded up 

slowed down 

Surface arteries 

dilated; more blood 

constricted; less blood 

Visceral arteries 

constricted; less blood 

dilated; more blood 

Pupil of eye 

dilated; more light 

contracted; less light 

Sweat glands 

sweat secreted 

Hair on skin 

hairs erected 

Adrenal glands 

adrenalin secreted 


sugar liberated into 

insulin liberated; blood 


sugar reduced 

Salivary glands 

salivation stopped 

salivation increased 


contraction and secre- 

contraction and secre- 

tion stopped 

tion increased 


contraction and secre- 

contraction and secre- 

tion stopped 

tion Increased 


defecation inhibited 

feces expelled 


urination inhibited 

urine expelled 

(Jenilal organs 

seminal vesicles con- 

erection induced 

The parasympathetic system governs 
those vegetative functions which are con- 
cerned with the normal metabolic activities 
of the organism, the functions which main- 
tain the organism in everyday living; 
whereas the sympathetic system has an 
emergency function. It comes into action at 
times of crisis when normal metabolic func- 
tion must be suspended and energy must be 
marshaled to counteract some threat. 

In contrast to the parasympathetic sys- 
tem, the parts of which may act separately 
in activating specific individual organs, the 
sympathetic system tends to discharge it- 
self as a whole, furnishing a general dif- 
fused excitation to all the organs under its 
control. It is this diffuse sympathetic ac- 
tion which provides the visceral response 
typical of all strong emotion. When you 
are angry or afraid and you feel as though 
the bottom of your stomach had 'dropped 
out,' feel yourself shaking and trembling. 

feel your heart rating and your blood 
pounding in your throat, it is a sign that 
your sympathetic nervous system has gone 
into action. 

The parasymjjathctic system is also active 
in emotion, and its differential activation 
of various organs may account for some of 
the difference between such unpleasant 
emotional states as anger and fear; but this 
parasympathetic adion usually is masked 
by the violent, generalized response of the 
sympathetic system. It is the sympathetic 
system that is primarily responsible for the 
bodily state of excitement common to all 
strong emotion. 

Walter B. Cannon, in his emergency 
theory of emotion, has made the point that 
sympathetic action not only occurs com- 
monly in all the emergencies which tall 
forth emotion, but that tiie bodily results 
of such action place the individual in a 
state of physiological preparedness or effi- 
ciency to meet the threat of such emergen- 
cies. Sympathetic action occurs because it 
is useful in an emergency. Digesti\e func- 
tions are stopped, and the blood supply of 
the body is directed to the voluntary mus- 
cles—the attack muscles, the flight muscles. 
The heart beats more rapidly supplying 
more blood to these muscles. At the same 
time, blood sugar is liberated from the 
liver to furnish extra fuel for heavy muscu- 
lar activity. The bronchioles to the lungs 
dilate, making it easier to breathe and in- 
suring a greater supply of oxvgen. The 
sympathetic innervation of the adrenal 
glands results in the secretion into the 
blood stream of a hormone, adrenalin, 
which acts directly upon the viscera in the 
same manner as direct sympathetic stimu- 
lation. Adrenalin thus becomes a sustain- 
ing or reinforcing agent, building up the 
sympathetic response. Because of this ac- 
tion it is called a sympathomimetic chem- 


Feeling and Emotion 

ical agent, for it duplicates the effects of the 
sympathetic system. 

Adrenalin also has some particular prop- 
erties of its own which it contributes to the 
general bodily picture of efficiency for ac- 
tion during an emergency. It hastens the 
coagulation time of the blood, helping to 
counteract hemorrhage in a surface wound; 
and it is thought also to have some direct 
action in counteracting the effects of fa- 

The actual efficiency of such an emer- 
gency response in the complicated condi- 
tions of present-day civilized living is du- 
bious. We no longer fight wild beasts in 
hand-to-hand combat, but there are many 
social relations, ranging from an argument 
between two persons to war between na- 
tions, where perceived aggression begets ag- 
gression in the perceiver by way of these 
automatic reaction mechanisms of the sym- 
pathetic nervous system. Usually civilized 
man avoids fight with his muscles, using 
words or the police as his agents. Yet the 
visceral response of emotion is still present, 
and the effort to suppress emotion in civili- 
zation is often costly to him who is moved. 
Later we shall return to a consideration of 
this matter, when we come to the discussion 
of the measurement of emotion, and also 
when we deal with some of the harmful ef- 
fects of emotion upon the body, a subject 
of great importance today in the medical 
specialty called psychosomatic medicine. 

Direct Action of the Nervous System 

The pattern of sympathetic excitation 
just described results in energizing the or- 
ganism. The person experiencing emotion 
is ready for action; he is 'rarin' to go.' This 
fact has been shown in experiments where 
the visceral pattern of emotion has been 
artificially produced by the injection of 
adrenalin, whose action, as we have just 

learned, duplicates that of sympathetic 
stimulation. . Few subjects report feeling a 
genuine emotion imdcr these circum- 
stances, but most of them report feeling 
tense, excited and moved to action. This 
state has sometimes been called a 'cold 
emotion.' Subjects say: "I want to have 
an emotion and get it over with" and "I 
feel all wrought up and want to get it off 
my chest." 

When the emotional stimulation is par- 
ticularly strong or when the usual channels 
of emotional expression are blocked, the 
excitation initiated may overflow into 
other nervous pathways to result in confus- 
ing, extraneous responses which are not 
part of the usual pattern. Thus an impa- 
tient man may relieve his tension by tap- 
ping his foot; an angry man attempting to 
control his rage may giind his teeth. In 
one experiment of infants' reactions to a 
sudden loud noise (revolver shot), it was 
found that many of the male infants, in 
addition to being startled, crying, etc., also 
showed a sexual response with genital 
tumescence. In 1872 Charles Darwin de- 
scribed the behavioral overflow of emotion 
in his classic work on the expression of 
emotion. The phenomenon illustrates the 
dynamic, energizing nature of emotion. 

Peripheral Response and 
Expressive Behavior 

Emotion is not limited to visceral reac- 
tions, but also involves the peripheral mus- 
culature under the control of the central 
nervous system. It is these easily observed 
peripheral responses which, as indicating 
certain internal or central events, are usu- 
ally spoken of as expressive behavior in 
emotion. The attempt to find specific and 
predictable patterns of expressive behavior 
has attracted the research efforts of many 

Expression in Emotion 


Unfortunately, the results of liieir inv<-s- 
cigations have been bf)(ii eoiif using and 
controversial. No clear .and univotal ex- 
pressive patterns have been found for the 
different emotions. Anger, it is true, seems 
to involve a general attitude of aggressive 
attack by the organism, but the specific be- 
haviors by which such an attack is carried 
out are infinitely varied and change from 
situation to situation. 

fn part this variability arises from the 
fact that the peripheral musculature, un- 
like the visceral, is subject to voluntary 
control involving fewer reflexes. Thus a 
man can often inhibit and suppress his 
expressive behavior during emotion, and in 
different civilizations sang froid is culti- 
vated in different degrees. When you are 
angry you cannot control your rapid pulse, 
nor your rising blood pressure; but you can 
repress hostile movement and you may 
even force a pleasant, disarming smile. 
The expressive peripheral behavior in emo- 
tion thus is not an immediate, involuntary, 
primitive reaction like the visceral re- 
sponse. It is complicated by voluntary con- 
trol, the acquisition of learned modifica- 
tions and the effects of social and cultural 
standards. No wonder that few clear, 
identifiable patterns of emotional expres- 
sion have been discovered. Even those 
which are almost universal in meaning, like 
the smile, can, being voluntary, be used 
to deceive. 

Facial Expression in Emotion 

The difficulties of investigation and the 
conflicting findings of such research are 
seen most typically in the studies of facial 
expression. Most of the early work was 
undertaken under the assumption that spe- 
cific facial expressions exist for the various 
emotions. Actors or other persons trained 
in mimicry were asked to pose, assuming 

the expressions representative of such emo- 
tions as anger, fear, surprise and disgust. 
Their faces were then photographed or 
drawn by an artist, and the pictures were 
presented to subjects who were asked to 
name the emotion portrayed. 

That roughly typical facial expressions 
for certain emotions exist is demonstrated 
by the fact that subjects can identify these 
expressions when they are posed. The 
older and less subtle emotions are most 
consistently interpreted, whereas in other 
posed expressions there is a wide range of 
diverse interpretations. The ability of per- 
sons to interpret these expressions correctly 
improves with training, with increasing age 
and with increasing intelligence. \\'hat 
have we got in these uniformities: behavior 
that is instinctive and biologically deter- 
mined, or behavior that is learned and ad- 
justed to certain cultural conventions? 

Since the pictures used in these experi- 
ments were deliberately posed and did not 
represent the features of an individual ac- 
tually experiencing an emotion, they can 
only demonstrate the existence of stereo- 
typed, socially accepted patterns of facial 
expression which can be assumed volun- 
tarily by a man when he wishes to com- 
municate his feelings to others about him. 
The behavior need not be instinctive but 
merely a culturally acquired means of so- 
cial communication. Thus 'looking sur- 
prised' is not an immediate, necessary mus- 
cular response to certain stimulus situa- 
tions, but rather a learned means of telling 
people how you feel under certain condi- 
tions. Facial expression substitutes for 
verbal expression in the communication of 
feeling. There are manv anthropological 
findings on the differences of expressive 
movement in different cultures. For in- 
stance, in our culture round, wide-open 


Feeling and Emotion 

eyes suggest surprise, but to the Chinese 
they mean anger. 

One experimenter substituted for posed 
expressions photographs of the faces of 
people who ^vere having actual laboratory- 
induced emotions. When the stimuli were 
weak, the classical expressions appeared as 
expected, but when strong stimuli were 
used to arouse strong emotions, the con- 
ventional facial patterns did not appear. 
The emotional situations were genuinely 
upsetting and included plunging the hand 
into a bucket of live frogs, decapitating a 
rat, looking at pornographic pictures and 
being suddenly given ammonia while smell- 
ing a pleasant perfume. 

Instead of the conventional patterns 
there appeared a diverse mass of nuiscidar 
response whicii varied from person to per- 
son. Each subject seemed to have his own 
characteristic pattern and there was little 
agreement among them. Nevertheless the 
amount of facial response varied signifi- 
cantly. Pain showed the most movement, 
anger less, disgust still less and revolting 
experiences very little. 

This finding confirms the view that typ- 
ical facial expressions exist as a tradition 
in our culture, and that people learn to 
use them as a means of social communica- 
tion. In mild emotional situations where 
the reaction is largely intellectual, these 
cultural patterns predominate, biu in 
strong emotion the social language is for- 
gotten and varied expressions appear that 
have little relation to the classical pat- 

This interpretation is still further ad- 
vanced by experiments which show that, 
in judging the feelings of people in actual 
emotional situations, observers rely more 
upon their knowledge of the stimulus con- 
ditions than upon the subjects' facial ex- 
pression. A group of medical students 

were shown moA'ing pictures of the re 
spouses of infants who were hungry, were 
dropped, were restrained by having their 
heads held and were stuck with a pin. 
AV^ith no knowledge of the stimulus condi- 
tions, the students had little success in 
identifying the emotions. With knowledge 
of the stimuli, the students could spec- 
ify the proper emotions. But when the 
stimidi were associated with the wrong pic- 
tures of expressive behavior, the students 
became at once confused about the signifi- 
cance of the behavior. 

The Startle Pattern 

The one consistent exception to the gen- 
eral statement that there has been found 
no fixed, innate pattern of facial or bodily 
emotional reaction is sudden surprise or 
the startle pattern. If a per^on is suddenly 
stimulated by a loud soiuid or a flash of 
light, a very rapid response pattern occurs 
in him. 

By means of high-speed motion-picture 
photography, the response to the sound of 
a pistol shot has been studied. Cameras 
rimning as fast as three thousand exposures 
per second have permitted the very exact 
analysis of this pattern. Figures 40 and 41 
are schematic drawings showing the ele- 
ments of this pattern in both the infant 
and the adidt. The startle response con- 
sists of a sudden movement of the head, 
blinking of the eyes, a characteristic facial 
expression, raising and drawing forward of 
the shoidders, turning inward of the upper 
arms, bending of the elbows, turning down- 
ward of the forearms, flexion of the fingers, 
forward movement of the trunk, contrac- 
tion of the abdomen and bending of the 
knees. Not all these elements occur in 
every person every time he is stimulated. 
Elements in the response which are op- 
posed to any of these reactions, however, 

The Startle Pattern and the James-Lar^ge Theory 


rarely if ever occur. Present cvidentc leads I'he startle pattern is usually tornpkted 

us to believe that, witiiin limits, complete- in less than half a second. Hence it tan- 
ness of appearance of the pattern is closely not be adcfpiatcly oljserved except by the 

related to the intensity of the stimulus; 

mild simuli may give only the eyeblink, 

but intense stimuli give the complete pat- 


[From C. Landis and W. A. Hunt, The startle 
pattern. Farrar and Rinehart, 1939. p. 22.] 

It has also been shown that with repeti- 
tion certain parts of the startle response 
die out— rapidly in some individuals and 
slowly in others. After a long series of 
stimuli, the eyeblink and certain elements 
of the facial contortion persist in practi- 
cally everyone, although most other ele- 
ments of the pattern will have dropped 
out. After a sufficient period of time, how- 
ever, the appropriate stimulus will again 
elicit the total pattern. 

The pattern, which can be evolved in 
very early infancy, does not change in its 
form throughout life. It appears in all the 
higher animals. In certain diseases it is 
exaggerated, whereas in epilepsy it is totally 
absent in about one-fifth of the patients. 

temporal magnification of ultra-rapid pho- 
tography. Few people are even aware that 
it has occurred in them. 

The Emotional Consciousness 

"I'he c|uestifjn of whether or not the vari- 
ous emotions are accompanied by some 
.sort of imique and specific conscious crjn- 
tent has long bothered psychologists. 
While we would presume that the logical 
answer to this question would be found in 
a direct appeal to introspection (asking sub- 
jects undergoing emotion to report di- 


{A) resting posture. (B) startle pattern. [From 
C. Landis and W. A. Himt, The startle patient, 
Farrar and Rinehart, 1939. p. 61.] 

rectly on how they feel), this method has 
not been used to any gieat extent. Most 
of the classical studies have assumed the 
existence of such distinguishing feelings 
and then proceeded to make hypotheses 
concerning their origin. 

In 1884 William James, the American 


Feeling and Emotion 

psychologist, and in 1885 C. G. Lange, the 
Danish physiologist, proposed independ- 
ently what came presently to be called the 
James-Lange theory of emotion. This the- 
ory states that the conscious emotion consists 
of a man's awareness of his bodily changes 
as they occur in his emotion. There is a 
stimulus to emotion, the organism responds 


The James-Lange theory states that emotional ex- 
perience in the cortex arises from autonomic re- 
actions to the emotional stimulus. The impulses 
from the receptors go through the thalamus to the 
effectors and travel back through the thalamus to 
the cortex, giving rise to the consciousness of the 
emotion. The Cannon-Bard theory holds that both 
emotional experience and autonomic effects arise 
from the stimulus. The impulses from the recep- 
tors go to the thalamus and then both to the cortex 
and to the effectors. The responses of the effectors 
are an accompaniment of the emotional experience. 
[From C. T. Morgan. Physiological psychology, 
McGraw-Hill, 1943, p. 3,'i6.] 

reflcxly, and then the conscious awareness 
of these reflex changes gives the man his 
feeling of emotion. James said "the bodily 
changes follow directly the perception of 
the exciting fact, and . . . our feeling of 
the same changes as they occur is the emo- 
tion." We do not cry because we feel 
sorry, but feel sorry because we cry. 

In some neurological disorders when the 
patient cannot feel these bodily changes, 
he may, nevertheless, report feeling an emo- 

tion. In other disorders, like pathological 
laughing or weeping, bodily responses typ- 
ical of einotions take place and yet the pa- 
tient may be without any experience that 
he would call an emotion. These facts 
and others have cast doubt upon any literal 
acceptance of the James-Lange theory. 

The fact that the hypothalamus, a lower 
brain center, acts in mediating the reflex 
responses typical of emotion has led Can- 
non and Bard to posit this part of the 
brain as the seat of emotional conscious- 
ness. According to this theory, the action 
of this center adds the quale or distin- 
guishing element of consciousness which 
gives emotion its typical characteristic feel. 
(See Fig. 42.) 

All these interpretations, however, seem 
to rest upon an oversimplification of emo- 
tional behavior. There is little evidence 
that a peculiar, unique type of conscious- 
ness accompanies and identifies the differ- 
ent emotions. Different persons describe 
their emotional feelings in different ways. 
To one man conscious emotion may be his 
awareness of the bodily responses taking 
place; he may report that fear is typified 
by "an awful feeling in my stomach, and 
cold, clammy hands." Another man, how- 
ever, may concentrate upon the cognitive, 
relational aspects of experience. He feels 
fear as the awareness of a threatening situa- 
tion. "Something is present which I would 
like to avoid." We can only conclude that 
the conscious experiences in emotion arc as 
complex and multiform as the behavioral 
items and that the existence of specific, 
unique, distinguishing conscious content in 
the various emotions has not been dem- 

Emotion and Learning 

Emotional behavior, like much other be- 
havior, is subject to learning. New re- 

The Development of Emofion 


sponses may be attached Lo old stimuli, ;ni(l 
new stimuli may be attached to old re- 
sponses. Such learning^ resuks in a rapid 
comph'cation ol wliatevcr slimuhis-responsc 
patterns may be present innately in the 
human infant. Any universal patterns that 
may exist then are rapidly altered by learn- 
ing in accordance with the unique life ex- 
periences of each individual. 

A classic, early experiment in this field 
was performed in 1920 by John B. Watson. 
A nine months' infant showed no fear of 
a white rat, but showed evidence of fear 
when a loud sound was made by striking an 
iron bar. Striking the bar when the infant 
was reaching for the white rat resulted in 
fear behavior which later appeared when 
the rat was presented alone without the 
loud sound. The infant had now learned 
to be afraid of the white rat because of its 
association with the fearsome noise. 

An important result of this experiment 
was the demonstration that the fear be- 
havior not only became attached to the 
white rat as a new stimulus, but also spon- 
taneously became attached to other stimuli 
resembling the rat, although these had not 
been present in the original learning situa- 
tion. The infant now feared other furry 
animals, as well as fur coats and a teddy 
bear, which had never been associated with 
the loud noise. This generalization of 
learning shows how complicated our emo- 
tional behavior may become on the basis 
of a single emotional experience. 

Such learning may explain the genesis 
of abnormally strong fears which become 
attached to specific stimuli or situations. 
During the war, an examination of Naval 
recruits who could not swim showed that 
many of them were nonswimmers because 
of a fear of water attributable to some emo- 
tional shock experienced during boyhood. 
One recruit had dived into a swimming 

hole shortly alu-r a boy had been drowned 
there, lie hit the corpse on ilje bottom 
and came up with it entangled in his arms. 
Since that one gruesome experience, he has 
been unable to force himself to enter the 

Not only can emotions be altered by 
learning, but emotion itself may inter- 
fere with learning. Subjects attempting 
to solve prcjblems under emotional stress 
do not do well. Their reasoning is in- 
ferior, and they tend to forget more re- 
cently learned responses and to fall back 
upon older habits which may no longer 
be applicable. Whether the emotional be- 
havior directly affects the learning process 
or merely acts as a distraction to the indi- 
vidual attempting to learn is not clear, but 
the interference of emotion during learn- 
ing has been demonstrated amply. It is 
hard to study when you are excited. It is 
also hard to think clearly when you are 
excited. The emergency aspect of emotion 
is right for running away or fighting or 
even for primitive love making, but civili- 
zation brings emotions and emergencies 
which need more brain than brawn. Man's 
emotions are still useful to him, but he is 
nowadays well advised to keep a cool head 
when emergencies arise. 

The Genetic Development of Emotion 

The preceding discussion has sho^vn that, 
apart from the common element of visceral 
excitement attributable to the excitation 
of the sympathetic branch of the auto- 
nomic nervous system, there is very little 
vniiformity and agreement in the specific 
behavior of different individuals during 
emotion with the exception of die startle 
response. To some scientists this finding 
means that no inherent emotional re- 
sponses are provided for in the nervous 
system of the human being. Others believe 


Feeling and Emotion 

that instinctive emotional patterns exist but 
that learning enters at so early an age as 
to confuse and complicate the original pic- 

The appeal, to studies of infant behavior 
has not clarified the problem. Smiling, 
laughing and crying, as we shall see later, 
seem to be fairly uni\ersal and predictable 
in infants, but even these behaviors are 
rapidly altered by learning and social pres- 
sme. Recent studies of these patterns show 
their occurrence in blind children in the 
same manner and under the same circum- 
stances as in seeing children. In the seeing 
children, however, mimicry and social pres- 
sure produce beha\ioral changes which in- 
crease with age. 

Watson, in an early study of the emo- 
tional behavior of infants, claimed to have 
loimd three basic patterns of response— 
fear, anger and lox'e. The stimuli for fear 
were sudden loud sounds and the sudden 
loss of support (dropping the child and 
catching it); for anger, restraint of move- 
ment; and for love, cuddling and the stimvi- 
lation of the erogenous zones. On this sim- 
ple basis, through the various combinations 
obtainable by learning, he proposed to ex- 
plain the entire complicated picture ol 
adult emotion. Thus a student who fears 
loss of social prestige by dismissal from the 
football squad is afraid because, through 
learning and generalization, he has associ- 
ated loss of social prestige with the loss of 
physical support which was the original 
fear stimulus in his infant environment. 
Fear of the dark, Watson thought, may 
also spring from a fear of loss of support, 
since in the darkness all the familiar orient- 
ing visual clues by whicli we habitually 
guide and steady ourselves in space are 

Later work has demonstrated that Wat- 
son's findings do not present the complete 

picture of infant emotion. Loud sounds, 
loss of support and restraint of movement 
are common and potent, but not universal, 
determiners of emotion. Not all infants 
cry when they are startled by a revolver 
shot. If they are already crying when the 
gun is fired, some ma) stop crying instead of 
crying harder. The triuh is not so simple 
as \Vatson had believed. 

The emotional response of the infant at 
birth, like all his other behavior, is limited 
by the relatively primitive state of his nerv- 
ous system. As his nervous system de\'el- 
ops, more complicated behavior becomes 
possible for him. Whether these changes 
are learned or not, it is hard to say. For 
instance, it was found that children under 
two had no fear of snakes. After two, cau- 
tion in approach to snakes became e\ident 
in the children's behavior. Definite fear of 
snakes did not appear with any frequency 
until the age of four. Is this progressive 
development of the fear of snakes related 
to some innate reaction pattern which be- 
comes operative as the nervous system ma- 
tures, or is it a learned response acquired 
as the child becomes socialized? The com- 
plex nature of any emotional behavior 
shows that it must derive from both sources. 

The emotional development of the child 
is characterized by a decreasing frequency 
of intense emotional response, by a pro- 
gressive transfer of emotion to socially ap- 
proved and experientially determined situ- 
ations and by a change in the patterns of 
emotional behavior to accord with cultural 


Most of our consideration of emotion so 
far has been about the general characteris- 
tics common to all emotions. Now it is 
time to be more specific, to deal with indi 

Smiling, Laughing and Crying 


vidual chanittciistics associated with the 
different emotions. 

Smiling, Laughing and Crying 

Well-defined examjjies ol emotional ex- 
jiression are smiling, laughing and crying. 
We habitually accept the occurrence of this 
sort of behavior as indicative of emotional 
experience. Although it is true that these 
behaviors may occur without attendant 
emotional experience, yet in the ordinary 
conduct of everyday life smiling, laughing 
and crying are by common consent re- 
garded as truly emotional expressions. 

The development of these patterns of 
response in the infant has long been a 
matter of interest to child psychologists. 
Smiling is exhibited at a very early age by 
most children. In the very yoimg infant it 
is almost invariably brought about by spe- 
cific stimulation, the response usually being 
evoked by other people, or at least exhib- 
ited only in their presence. Study of the 
development of smiling and laughing 
shows that originally several varieties of 
respiratory reactions or compensatory mo- 
tor mechanisms are elicited by certain situ- 
ations whicfi the child lias not met before 
and for which, consequently, he has ready 
no immediate appropriate pattern of re- 
sponse. On such occasions a response in- 
volving smiling or laughing is appro\ed 
by the infant's mother or nurse, whereas 
other respiratory mechanisms may be dis- 
approved. Smiling and laughing are thus 
quickly foiuid to be socially acceptable and 
to lead to reward or comfort. They be- 
come learned reactions, selected as socially 
appropriate. Once incorporated in the re- 
action repertoire of the child, this original 
usage becomes widely generalized, blending 
into all the patterns of response which din- 
ing most of our lives we call amusement. 
Already by the end of the first )'ear of life, 

smiling has become a learned response to 
such an extent that the smile must be re- 
garded as a communicative, adaptive, social 
reaction rather than a modified respiratory 

Laughing appears much later in die 
child's life than smiling, usually not until 
after the twentieth week. During the first 
year of life it remains a stereotyped form of 
behavior. More differences between chil- 
dren occur in the frec|uency of smiling or 
laughing than in the actual form of these 
two behaviors. 

Laughter presents us with more than one 
problem. We have laughter of joy, laugh- 
ter of comedy, laughter as a form of social 
response, laughter as a release from tension 
and laughter under pathological, organic 
or mental conditions. All these laughters 
involve different psychological elements. 
The joyfid laugh, a bubbling over of good 
humor, occurs in children or adults in a 
state of well-being. The comic laugh is di- 
rected at some joke or ludicrous situation. 
Laughter as a social response invoh es many 
principles of social psychology. AVe laugh 
more easily in a group tlian alone, for 
laughter is a \ariety of gesture language. 
The act of laughing may be used at times 
for a commimication of good will and a 
spirit of fun, at others of pme jov and, at 
still other times, of embarrassment. 

The laughter which is associated with a 
relief of tension has been explained on an 
evolutionary basis. Since the facial nius- 
cidature is not primarilv necessary to the 
active energetic preservation of life, it has 
been suggested that the excess energy, set 
up by emotional stimulation, is drained off 
by the activity of the facial and respiratory 
muscles in a way which does not interfere 
with any activity of the body essential to 
the emergency which induces the emotion. 
Ihis drainage theory must not be taken 


Feeling and Emotion 

loo literally. The nervous system does not 
accumulate energy which has to be released 
by one channel, if not by another. Never- 
theless, it is true that individuals often find 
themselves in slates of emotional tension 
which can be relieved only by action— al- 
most any relevant action. It is a problem 
of motivation, however, not of physics. 

The behavior of infants during crying 
has been observed experimentally in a se- 
ries of standard situations. Crying induced 
by the perception of strangers increases in 
frequency up to about ten months of age. 
Crying caused by fear or strange situations 
can, however, be distinguished from other 
types of the response. In the adult, crying, 
like laughing and smiling, is so bound up 
with the social reactions of the individual 
that it is impossible to be certain in a ma- 
jority of cases whether the response is truly 
emotional, only partly so or an habituated 
response, devoid of emotion. 

The observation of adults in situations 
which produce tears (funerals, for example) 
shows that tears are usually indicative of a 
mixed emotional state. Sorrow, dejection, 
joy and elation, when occurring alone, have 
but little effect in producing tears. Adult 
crying occurs in the main only when an 
otherwise depressing or unpleasant situa- 
tion is partially redeemed by some pleasant 
or alleviating stimulation, or when there is 
a conflict in extreme frustration. 


The most jDrominent feelings associated 
with fear are the bodily sensations at- 
tributable to the activation of the auto- 
nomic nervous system. Pounding of the 
blood, a sinking feeling in the stomach, 
trembling and shaking, weakness, faintness 
and tension all are common and promi- 

Present witJi these ieelint!,s is an insistent 

desire to get away from some threatening 
situation with which the individual does 
not feel able to deal adequately. Some 
form of withdrawal behavior usually re- 
sults. Once the threatening stimulus has 
been removed or the threatening situation 
has been controlled, and the real or imag- 
ined danger has passed, fear disappears. If 
the danger increases rapidly, or if the fear 
strikes suddenly and severely, terror may 
result with a complete disintegration of 
the individual's behavior. Typical of ter- 
ror are both the blind flight of panic and 
the occasional complete inhibition of activ- 
ity with its attendant immobility and paral- 
ysis of volition. When fear is anticipatory, 
when it is aroused by something foreseen 
in the future rather than existing in the 
present, we may call it anxiety or appre- 

The stimuli for fear are many and varied 
but they all involve some sudden change in 
the environment, some change which the 
individual regards as threatening and to 
which he is either unprepared or unable to 
respond. This fact has led one psycholo- 
gist to speak of such situations as cata- 
strophic, and fear behavior as catastrophic 
behavior. Once an adequate course of ac- 
tion develops, once the individual feels he 
is in control of the situation and doing 
something about it, fear disappears. 

It is not the man who is successfidly run- 
ning away from a bear who is afraid. Fear 
comes when he realizes that the gap be- 
tween him and the bear is decreasing in- 
stead of growing larger, or when he realizes 
that he is becoming exhausted and cannot 
run much farther. It is the soldier about 
to go into combat who most often experi- 
ences fear, rather than the one who is ac- 
tually in combat, fighting desperately for 
his life. 

Ade(iuaic action seems to be llic antidote 

Fear and Anger 


for fear. Such action is more possible when 
the individual has full knowicdf^e of the 
threatening situation. Ihe existence of 
well-established habit patlerns also helps. 
It is not the experienced big-game hunter 
who feels fear when faced by a lion. He 
has met the situation before, knows what to 
do and acts habitually and smoothly. It is 
the neophyte, hunting for the first time, 
who becomes frightened. 

Knowing what to do and doing it is the 
best way to handle fear. As we have seen, 
it is possible that all the complicated re- 
sponse of the autonomic nervous system in 
emotion may be the body's way of organ- 
izing its reserves for action. To fight fear, 
use what the autonomic system has pro- 
vided, the capacity for effective action. 

Our understanding of fear has been con- 
firmed by exhaustive questioning of men 
who have returned from battle. One study 
of 4504 flyers who had returned to this 
country after extensive tours of combat is 
particularly enlightening. These flyers re- 
ported the usual signs of fear when flying a 
combat mission. They experienced a rapid 
pulse rate, muscle tension, irritability, dry- 
ness of the mouth, sweating, stomach sensa- 
tions and a feeling of unreality. Delayed 
symptoms which appeared later included 
fatigue, restlessness, depression, over-reac- 
tion to stimuli, loss of appetite, loss of zeal 
and even obsessive thoughts. 

Their fear was greatest in danger when 
they were idle or unable to take counter- 
action. Fear was reduced by confidence in 
equipment and leadership, goal-directed ac- 
tivity and social stimulation. Organiza- 
tional morale, sense of duty, hope of sur- 
vival and personal pride were motivating 
factors which were much more successful in 
reducing fear than citations for bravery, 
pay, self-advancement and hatred of the 


Anger is the normal response to frustra- 
lion. When some situation or another per- 
son unduly limits the freedom of action of 
an individual, the restrained individual is 
likely to become angry. He may then at- 
tack the obstacle which is inhibiting his 

I'hus, the condition which arouses anger 
in young children is a situation which, in- 
stead of being a sudden call for action, is 
often a more or less sudden stoppage or 
interference with action. Interference with 
activity, especially activity motivated by 
the common urges or drives, is an essen- 
tial characteristic of the anger-producing 

The anger responses in the child are out- 
bursts of impulsive activity— kicking, stamp- 
ing, slashing about with the arms and often 
a prolonged holding of the breath. With 
increasing age, the anger becomes more 
overtly focused upon a given end. Along 
with a decrease in the proportion of out- 
bursts consisting of mere displays of undi- 
rected energy comes an increase in the fre- 
quency of retaliative behavior. The per- 
centage of observable after-reactions, such 
as resentfulness and sulkiness, increases 
steadily with advancing age, perhaps in 
part because retaliation is not always prac- 
ticable or carries with it its own penalties. 

Mild anger, directed toward the legiti- 
mate removal of some barrier obstructing 
individual action, may well become an im- 
portant moti\ator of beha^ ior. Anger, 
however, is difficult to control and easily 
develops into disorganized rage. It may, 
moreover, call forth the same type of re- 
sponse from tlie object against which it is 
directed. In human affairs aggression 
tends to be met by aggression, and the re- 
sults are disastrous for social intercourse. 


Feeling and Emotion 

Anger, like fear, is a primitive emergency 
response which energizes the individual. 
We may seriously question the general 
serviceability of such primitive responses 
in tlie complex social organization of con- 
temporary life, in spite of the occasional 
good uses for righteous anger and moral 

Anger can be misdirected. If the aggres- 
sion aroused by frustration cannot be di- 
rected against the frustrating situation it- 
self, it may be displaced and vented upon 
a substitute. If you are publicly embar- 
rassed by some incident about which you 
can do nothing, you may suddenly become 
angry with an innocent witness of the af- 
fair. Majority groups may thus take out 
their aggressions against a minority group, 
and within the minority group aggression 
in turn may be directed against some poor 
individual selected as a scapegoat. Beyond 
the fact that such substitute reactions may 
offer emotional relief to the individual 
aroused, misdirected anger, being false, 
cannot be said to have any social value. 


The importance of emotion, both as be- 
havior itself and secondarily as an indi- 
cator of the conscious and unconscious 
vital concerns of the individual, has led to 
gieat interest in its measurement. The 
participation of the autonomic nervous 
system, with its attendant changes in pulse 
rate, blood pressure, breathing, etc., has 
held out to psychologists the hope that 
measures of such bodily changes might 
give a clear measure of emotion. Such 
hopes have not been fully realized. The 
autonomic nervous system is not exclusively 
concerned with emotion, and its complex 
organization adds further to the difficulty; 

still, measures of bodily processes are our 
best indicators of emotion. 

The Galvanic Skin Response 

In 1888 the French scientists, Vigouroux 
and Fere, called attention to the fact that, 
when electrodes are placed on the skin and 
attached to the proper electrical measuring 
instruments, variations in the electrical 
properties of the skin appear from time to 
time. During emotional excitement, they 
found, there is an increase in these electii- 
tal variations. The occiurence of these 
changes has been named the galiianic skin 
response or the psychogalvanic reflex, a phe- 
nomenon which has been extensively stud- 
ied by many investigators. The response 
was first called prominently to the attention 
of psvchoiogists by the work of C. G. fimg 
and his pupils, who came to tiie general con- 
clusion that the galvanic skin response is as- 
sociated with repressed emotional com- 
plexes. \Vhether this electrical response is 
associated with physiological and psycholog- 
ical occurrences other than emotion, they 
did not particularly consider. Their claim 
to have a measure of emotion was accepted 
more or less uncritically by many psychol- 
ogists. More recent investigations show, 
however, that these electrical responses 
occur not only during emotional experience 
btit also to some extent with practically 
every other variety of psychological experi- 
ence. Furthermore, it appears that the de- 
gree of electrical change does not measure 
accurately the amount of emotion experi- 
enced by the individual. 

Blood Pressure Changes 

The amount of inciease, decrease or 
variability in blood pressure has been used 
as a measure of emotionality. Perhaps the 
most extensive use of this type of measure- 
ment has been in the detection of false- 

Measurement of Emotion 


hood, the so-called lie deleclor being an in- 
sirunient lo record changes in blood pres- 
sure. (Some lie detectors record the gal- 
vanic skin response and changes in lespira- 
tion as well.) Under certain conditions it 
seems possible on the basis o£ the changes 
in the record of blood pressure to deter- 
mine whether or not a person has told the 
truth or has lied, provided always that he 
is more moved when lying than when tell- 
ing the truth. It has not been jxjssible lo 
standardize this procedure, since it depends 
upon so many variables and there are so 
many different factors which must be con- 
sidered in the interpretation of the record. 
For instance, an habitual liar may be cjuite 
unmoved about his lies. There are, more- 
over, people who can convince themselves 
by their own lies to become sincere liars. 

In a study of blood pressure, made on 
persons who had suffered severe injmy in 
automobile accidents and upon friends and 
relatives who were called to the hospital to 
see them, interesting results were obtained. 
It was found that the injined individuals 
themselves, who had undoubtedly gone 
through profoimd physical and emotional 
shock, did not show very much alteration 
in blood pressure. Their friends or rela- 
tives, on the other hand, waiting to find 
out how severely the patients had been in- 
jured, showed a tremendous variability. 
Evidently, then, the rise in blood pressure 
frequently accompanies the apprehensive 
state preceding some possible emergency. 

Rating Scales 

The failure to establish good physiolog- 
ical measures of emotion has led to the 
development of new techniques. A com- 
mon one is the rating scale. In this pro- 
cedure, we ask the friends and acquaint- 
ances of some person to rate his emotion- 
ality or emotional expressiveness. By sta- 

tistical manipulation of tlic data it is j>ov 
sible (o obtain some idea ol the probable 
emotional reactivity of an individual in 
comparison with that of his friends and 

Observational and 
Psychoanalytic Techniques 

Several investigations ol emotional re- 
actions, jjarticularly with children, have 
been made by the observational method. 
One observer watched a large group (j| 
children on the playground, following their 
behavior over a period of several months. 
All instances of anger, fighting, fear or 
other emotional reactions were noted. On 
the basis of such observational studies, we 
can obtain very good descriptions of ac- 
tual emotional behavior, the stimuli or 
situations which produced the behavior 
and the results of the reactions. Although 
it has been foimd possible in this way to 
predict rather acciu-ately the sort of situa- 
tion which will evoke an emotional reac- 
tion in a particular individual, the e\i- 
dence shows that the same situation is not 
luiiformly effective in producing the same 
reaction in all indi\iduals or even in the 
same individual every time. 

Psychoanalysis provides a special situa- 
tion under which emotion can often be ob- 
served in adults. In such an analysis, 
which consists essentially of talking in a 
free and uninhibited fashion about any- 
thing that comes into the mind, \ery 
marked emotional reactions sometimes take 
place. The subject may respond in an in- 
tense emotional fashion to his OA\n descrip- 
tions of events long past and previously be- 
lieved forgotten. By such methods we can 
acquire much knowledge concerning the 
emotional history of the person being ana- 


Feeling and Emotion 

Questionnaire Methods 

An entirely different method of meas- 
urement and test makes use of tlie ques- 
tionnaire, as, for example, the Pressey X-O 
test. Form B. This test consists of three 
lists of words. In the first, the individual 
is told to cross out everything he thinks is 
Avrong; in the second list, everything about 
Avhich he has ever worried; and in the 
third, everything he likes or is interested 
in. He is also told to encircle the crossed- 
out word in each line which he considers, 
respectively, to be the worst, the most wor- 
risome or the most interesting. The total 
niunber of words crossed out is called the 
score of emotionality, since, theoretically, 
the more things a person dislikes, worries 
about or likes, the more generally emo- 
tional he is. The encircled words having 
been compared with a standard list that 
giAes the most frequently encircled word 
for each line, the number of encircled 
words which deviate from this standard list 
is the score of idiosyncrasy. Various inves- 
tigators have reported that students who 
obtain high scores of emotionality and 
idiosyncrasy tend to have more than the 
usual nuinber of emotional conflicts in 


Like the other bodily processes the emo- 
tional mechanisms sometimes fail to func- 
tion correctly. The trouble may be some 
physiological or organic disorder, such as 
a wrong functioning of a gland or a dis- 
order of the nervous system. Such disturb- 
ances can be classified as the pathology of 
emotion. On the other hand, if the cause 
is not organic but arises from faulty learn- 
ing or poor habits of adjustment, we call 
the disturbances functional disorders. 

Often both functional and organic dis- 
abilities occur together in relation to each 
other, as in the problems of psychosomatic 
medic itJe. 

Pathological Conditions 

Since emotional behavior is mediated by 
the nervous system, it can be ujjset by any 
injury or disease which affects the pertinent 
parts of the nervous system. Tumorous 
growths in the thalamic or hypothalamic 
regions of the brain may produce uncon- 
trollable weeping or laughing. The re- 
moval of large areas of cortical brain tissue 
has been known to result in an apparent 
lessening of social inhibitions with result- 
ing inappropriate and embarrassing emo- 
tional behavior of a sort previously inhib- 
ited by the individual. Glandular dis- 
functions may also unbalance the emo- 
tional behavior. Feelings of anxiety, 
which may be accompanied by terror night- 
mares, are often found in advanced cases 
of hyperthyroidism. 

Extreme emotional states are also promi- 
nent in the symptoms of the major mental 
disorders. Extreme euphoria, an abnor- 
mally strong sense of well-being, happiness, 
and exaggerated self-confidence, is found in 
the manic patient, and sometimes in gen- 
eral paresis. Both the depressive phases of 
manic-depressive psychosis and of involti- 
tional melancholia include persistent deep 
depressions which are accompanied by tn> 
happiness, anxiety, apprehension and oc- 
casional thoughts of self-destruction. 

In schizophrenia, or dementia praecox, 
we may find apathy, a relative dulling of 
emotional response. The patient does not 
show a normal emotional interest in and 
response to his environment. Such a pa- 
tient might commit a crime, even murder, 
%v'ithout the emotional conflict ^s'hich stich 
beha\'ior would cause in the normal indi- 

Disorders of Emotion 


vidua]. Wc describe such emotional apa- 
tliy as a blunting of affect. 

Functional Disorders 

Some emotional disorders are not due 
to physiological disorder but must be con- 
sidered as inappropriate behavior produced 
by unusual experiences in the individual's 
past. Phobias, or unusually strong, per- 
sistent fear reactions, are an example. As 
we have already noted, the examination of 
Naval recruits who were nonswimmers 
showed that many of them had developed 
a phobia for water because of soine trau- 
niatic experience with swimming or water 
in the past. 

Phobias may appear to occur without 
reason and remain inexplicable to the in- 
dividual suffering from them. They handi- 
cap his adjustment and limit his activities. 
They are often found in exaggerated form 
in the psychoneuroses. 

Anxiety, which, as we have already noted, 
normally functions as a forerunner of some 
anticipated dangerous situation, may also 
get out of hand and may so dorninate the 
individual's behavior that he is vmable to 
take any logical action concerning the situ- 
ation which produces the anxiety. Thus 
the student who is anxious and worried 
about an examination may become so up- 
set as to be unable to study. His inability 
to study increases his feeling of unpre- 
paredness which in turn increases his anx- 
iety, and he is caught in a viciotis circle. 
Next time he had better schedule his work 
so that he does not get caught so unpre- 
pared or he might make some other intelli- 
gent administrative changes in his life of 
study. In general, the best way to handle 
anxiety is by a frontal attack upon the 
problem causing it. 

In many maladjusted individuals, how- 
ever, the basic reasons for the anxiety may 

be repressed and unconscious. The pers<^jn 
is then faced with a persistent worry or 
apprehension which colors all his emo- 
tional life and about which he is unable to 
do anything since he cannot unflerstand its 
origin. In such cases, psychiatric counsel- 
ing may be necessary to uncover the source 
of the basic insecurity or inferiority caus- 
ing the anxiety. 

Anxiety very frecjuently has a profound 
effect ujjon the physiological functions of 
the individual. Persistent respiratory, cir- 
culatory, digestive or muscular disturb- 
ances may occur. Chronic fatigue accom- 
panied by insomnia is also common. 

The effect of anxiety on psychological 
functions is to lower the general acuity and 
completeness of response. Although the 
individual still reacts, he does so either in a 
preoccupied fashion, paying attention to 
only part of what is going on around him, 
or inadequately, as though he were fa- 
tigued or had instifficient energy to meet 
the demands of the situation. Since anxiety 
is a rather common human experience, a 
great deal of medical work has been done 
in the attempt to control or alleviate it. 
Generally speaking, if in one way or an- 
other the anxious person can be made to 
discover the original connection between 
his anxiety and its primary or original 
cause, he will be able either to free him- 
self of the anxiety or to control it in a 
satisfactory fashion. (For more on phobias 
and anxieties, see pp. 531-534.) 

Psychosomatic Medicine 

We have already seen that emotion in- 
volves activity of the autonomic ner^•ous 
system and hence a profound change in 
the activity of the vital organs. Inaeased 
pulse rate, increased blood pressure, irregu- 
larities in respiration and interference witli 
dia;estion may all result. Wliere the emo- 


Feeling and Emotion 

tion perse\'eres o\er a period of time, as 
it does in chronic worry or anxiety, it may 
result in a persistent disturbance of vital 
function. Modern medicine has finally 
realized that many disorders of digestion, 
respiration and heart function are at- 
tributable, not to organic difficulties, but 
to emotional disorders. They must be 
treated by treating the individual's prob- 
lems of psychological adjustment which 
are causing the emotional disturbance re- 
sponsible for the physical symptoms. Thus 
a wliole new branch of medicine, psychu- 
somntic medicine, has arisen to handle 
these problems. 

It must be remembered, however, that if 
such finictional disorders continue they may 
in time result in organic damage to the 
ijodily system involved. A chronic fear 
may produce the persistent diarrhea known 
as colitis, and, if such diarrhea persists, 
ulceration of the colon may residt. After 
the ulcer has formed, psychological treat- 
ment alone has become insufficient. 


In the preceding pages emotion has been 
pictured both as a helpful reinforcing agent 
which energizes and motivates man when 
he is faced with some threatening emer- 
gency and as a disrupting force which dis- 
organizes his behavior and confuses his 
thinking at a moment of crisis. Actually 
it is both. The answer to whether emo- 
tion is helpful or harmful depends on 
whether the emotion is appropriate to the 
situation in which the individual finds 

The question of the appropriateness or 
inappropriateness of a specific emotional 
response must be settled by the individual 
himself after a consideration of all the 
important circumstances entering into the 

specific stimidus situation of the moment. 
Psychology can only offer us broad truths, 
but every man must apply them to his own 
particular needs at any specific time. The 
description of emotion which this chapter 
contains has in it much of value to govern 
us in imderstanding and controlling our 
emotions. We want to be able to have 
appropriate emotions, to dispense with the 
inappropriate ones. How can we tell the 
two apart; decide about appropriateness? 
Here are three principles which may help. 

(1) Emotion is inappropriate if it is 
harmful to the biology of the indixndual. 
No intelligent person should allow himself 
the luxiuy of flying into a severe rage im- 
mediately after eating a full meal. Nor 
can fear or anxiety be considered desirable 
in an individual who is suffering from 
stomach ulcers, high blood pressine or a 
colitis of functional origin. 

(2) Emotion is inappropriate if it arouses 
conflicting motivations within the individ- 
ual. If we allow ourselves to become angry 
with those we love, we are plunged into a 
bitter and disrupting conflict within our- 
selves. The soldier who is possessed of an 
overwhelming fear of death while being 
driven at the same time by an equally 
strong desire not to let his comrades down 
may succumb to a mental breakdown din- 
ing combat. 

(3) Emotion is inappropriate if it brings 
the individual in conflict ivith society. 
There are innmnerable social codes that 
control emotional behavior and they must 
be respected if the individual is to live in 
harmony with his neighbors. A frank ex- 
pression of fear at an inappropriate time 
may result in a man's being branded a 
coward and subjected to the ridicule of his 
comrades. However strong the provoca- 
tion, the enlisted man who strikes an offi- 
cer must face severe disciplinary measures. 

Hygiene of Emotion 


The overt dcnionstralioii ol allcction may 
not be considered proper in public. 

Unfortunately, these principles do not 
always coincide. Anger in response to an 
insult may be considered socially accejH- 
able, and the failure to exhibit it may re- 
sult in the person's feeling he has lost caste 
and in being plunged into an unhappy 
personal conflict within himself. Never- 
theless, such justifiable anger may be lethal 
to an individual afflicted with a severe heart 
disorder. The answer to such dilemmas is 
not an easy one, but on it rests the deci- 
sion as to whether our emotions are bene- 
ficial or liarmful, and on it rests in large 
part our cliances for happiness. 


1. Bard, P. liniolion: I. The ncino-luimoral Iiasis 
of emotional reactions. In C. Mmxhison (Ed.), 
A handbook of general cxpcriinenlal psy- 
chology. Worcester, Mass.: Clark University 
Press, 1934. Chap. 6. 

In need of revision but still a standard icih 
nical reference on the ncuro-lunnoral basis of 

2. Beebe-Centev, J. G. The psychology of pleas- 
antness and unpleasantness. New York: D. Van 
Nostrand, 1932. 

I he only adc(jiialc vjukc \><x>i for the cx- 
|)( riiri<nl;il lilciiil iiic in rhis field. 

3. (Gannon, W. 15. liodily chiuiges in pain, hun- 
ger, fear anil rage. (2nd cd.; .New Vork: 
Applcton, 1929. 

An historical classic still very iriiicli woith 
reading as the basis of the emergency theory 
ol emotion. 

I. jersild, A. T. Kmotional development. Jn L. 
Carniichael (Ed.), Manual of 'child psycholo^-. 
New \ork: Wiley, 1946. 

An excellent survey of the lileialiirc on the 
development of emotion in the child. 

5. Landis, C. Emotion: If. The expressions of 
emotion, fn C. iVfurchison (Ed.) , A handbook 
of general experimental psychology. Worcester, 
Mass.: Clark University Press, 1931. Chap. 7. 
An excellent survey of the experimental find- 
ings on cmolion up to 1931. 

G. Landis, C, and Hunt, W. A. The startle pat- 
tern. New 'iork: I'arrar and Hi'iehart, 1939. 
An intensive study of the reflex response in 
startle based upon the use of ultra-rapid pho- 

7. Ruckmick, C. .\. The psychology of feeling 
and emotion. New York: McGraw-Hill, 1936. 

Somewhat outmoded as a survey of emotion, 
but valuable for its historical material. 

8. Yoting, P. T. Emotion in man and animal. 
New York: Wiley, 1943. 

A treatment of emotion with particidar stres: 
on its relations to drive and motivation. 



THIS chapter is concerned with what the 
layman usually considers the most impor- 
tant problem of psychology. The question 
which, above all others, he wants psychol- 
ogy to answer for him is, "Why do people 
act as they do?" Not satisfied with a mere 
description of man's behavior, he wants to 
know the motives back of it. The problem 
of motivation, narrowly conceived, is the 
problem of discovering the motives of hu- 
man beings; but, broadly viewed, it is the 
problem of determining the forces which 
impel or incite all living organisms to 


We cannot long study the behavior of 
living organisms without observing that 
they need things; and it is their wants, 
lacks or needs which have to be investi- 
gated if the reasons for their behavior are 
to be discovered. The things which they 
need, however, vary greatly, not only from 
species to species, but also from individual 
to individual within the same species. 
Oysters do not need automobiles and men 
do not need shells; but, if they are to con- 
tinue to live, oysters and men, like all other 
living organisms, need to get from their 
environments a continuous supply of 
energy and materials. The needs of the 
amoeba arc limited to these vital ones, 
'lliis cliiiplcr \\:is |)r(']);ii((l h\ Donald \V. 

The needs of man, on the other hand, are 
ever so much more numerous. He, too, has 
vital needs. He needs to breathe oxygen, 
to eat food, to drink water, to eliminate 
wastes from his body, to maintain a rela- 
tively constant body temperature. But, in 
addition to these, he has other needs which 
cannot be considered so vital or so uni- 
versal. He may need to have more money 
than anyone else in his town, he may need 
to be loved by a particular person, he may 
need to be constantly praised and ap- 

Distinction among Needs 

There are important respects in which 
xiital and nonvital needs are different, 
though in other respects they have much 
in common. 

The vital needs are primary and innate 
in the sense that they are the first needs 
of the organism. If they remain unsatis- 
fied, the organism does not live to develop 
nonvital needs as a result of experience. 
In this sense, nonvital needs are secondary 
and acquired. This distinction does not 
mean, however, that secondary needs are 
necessarily weaker or less important than 
primary ones. The terms primary and sec- 
ondary apply only to the origins of needs 
and imply nothing about their relative 
strengths. The need to possess great wealth 

MacKinnon of llic University ol California. 



may be so iiuidi slroiif^cr in a man than 
his needs lor lood and rest and exercise 
that, even though he succeeds in amassing 
great wealth, he may so break his health as 
to die. In such a case the secondary need 
lor possessions is obviously stronger than 
the primary vital needs which are frus- 
trated. Furthermore, the distinction be- 
tween primary and secondary needs does 
not imply that the latter are always in the 
service of the former. The example just 
cited shows that such is not the case. The 
amassing of great wealth (a secondary need) 
may be an end in itself and not necessarily 
a means to the certain and more adecjuate 
satisfaction of the need for food or of any 
other primary need. 

lliere is a sense, then, in which a sec- 
ondary need may be more vital for the 
continued existence of an individual than 
a primary need. It is, for example, not 
uncommon for a man to commit suicide 
because he has lost his fortune in a crash 
of the stock market or because he has lost 
his honor through becoming involved in a 
public scandal. For such persons life with- 
out money or life without honor is impos- 
sible. In a A'ery real sense their secondary 
needs have become vital ones. 

The primary needs are sometimes called 
physiological needs and the secondary ones, 
psychological needs. This does not mean 
that the secondary psychological needs lack 
the physiological basis in the body which 
the primary physiological needs have, but 
merely that, in general, we know more 
about the specific physiological basis of pri- 
mary than of secondary needs. We know, 
for example, that the physiological basis 
of the need for food is a matter, in part, of 
a reduction of the sugar concentration of 
the blood and consequent contractions of 
the smooth muscle of the stomach: and we 
know at least something about the physio- 

logical basis (A ilic oilier so-called physio- 
logical needs, liut what the physiological 
basis of a man's need for superiority may 
be, or of any other of his socalled psycho- 
logical needs, we do not know. We as- 
sume, however, that they have a physio- 
logical basis even though we cannot demon- 
strate it. 

On the other hand, the distinction be- 
tween physiological and psychological needs 
does not mean that the psychological needs 
have a representation in consciousness 
which is absent in physiological needs. We 
may be just as much aware of our need for 
food as we are aware of our need to pass 
a crucial examination; and we may, at an- 
other time, be just as unaware of our need 
to get even with a person for a slight which 
he has given us as we are una\\are of our 
need for vitamin B. Physiological and 
psychological needs are alike in that both 
may be at certain times known but at other 
times unrecognized. 

The primary needs are sometimes re- 
ferred to as biological needs because they 
have biological origins. The secondary 
needs are sometimes called, in contrast, 
social needs because they are the products 
of social life. Though this is a valid dis- 
tinction among needs, we must not over- 
look the fact that social needs are also bio- 
logical in the sense that they are needs of 
biological organisms and that biological 
needs are also social in that the expres- 
sions of these needs are to a large extent 
socially determined. All men need food, 
but the particular objects Avhich -svill satisfy 
this need vary widely from one society or 
culture to another. Religious taboos and 
cultural prohibitions limit greatly tJie num- 
ber of objects whicli will satisfv an indi- 
vidual's need for food. 

W^e have seen that needs are of twc 
kinds: first, needs which are primary, vital 



physiological and biological and, second, 
needs which arc secondary, nonvital, psy- 
chological and social. But we have seen 
also that, valid as these distinctions be- 
tween the two classes of needs are, they are 
not rigid. All needs have much in com- 
mon. It is this fact which makes it pos- 
sible for psychologists to seek the general 
laws of need regardless of the particidar 
need studied. 

Needs, Structure and Environment 

All organisms have the primary need for 
oxygen, but, although they have this need 
in common, they satisfy it in different ways. 
The hsh supplied with gills and living in 
water gets oxygen in one way; man sup- 
plied with lungs and living on land gets 
his in a different manner. The ways in 
which an organism's needs may be satis- 
fied are determined by its structure as well 
as by the nature of its environment. This 
relationship is no less valid for secondary 
needs. A common need in a highly com- 
petitive society is the need to be or to feel 
superior to others, but it may be satisfied 
in very different ways. A person skillful in 
athletics may gain his superiority by ex- 
celling in sports; a man of puny body but 
keen intellect may gain his feeling of supe- 
riority by scholastic excellence. 

Behavior which is motivated by need de- 
pends then upon the following three fac- 

(1) The need itself, conceived of as a 
want or lack in the organism, involving 
always a physiological disequilibrium or a 
tension which tends to discharge in beha- 
vior in such a way as to bring about a 
restoration of the equilibrium which was 
disturbed by the need. (See pp. 511-514 
on tension reduction.) Su(h physiological 
disc(juili!)ria are to be (onsidered llic 

sources of the stinudation which drive the 
organism to action. 

(2) The structure of the organism, which 
determines to an important degree not only 
the needs of the organism but also the man- 
ner in which they will be satisfied. Here 
are to be considered certain mechanisms- 
gills as against hmgs, the claw of the lobster 
as against the hand of a man— as well as 
the sensory organs and nervous system 
which mediate the perception of needed 
objects and the muscles and glands which 
are organized into systems of response. 

(3) The enviromneni of the organism 
and the objects, present in the environment 
or absent from it, which are retjuired for 
the satisfaction of any need. Here both the 
social and the physical environment have 
to be considered. 

Any concrete case of behavior is deter- 
mined by the interrelated fimctioning of 
all three of these factors; it is only by 
adopting an analytical attitude that they 
can be discussed separately. Later we shall 
consider them in their interrelation. 


The psychologist has long considered 
that one of his problems is the determina- 
tion of the conditions in bodily tissues 
which release energy so as to stimulate the 
organism to overt activity. He has sotight 
to determine the precise correlation be- 
tween these known conditions and activity, 
both general and specific, and having found 
such correlations he has developed the con- 
cept of drive, which he defines as an intra- 
organic activity or condition of tissue sup- 
plying sliiuulation for a particular type o' 

Hunger Drive 


Hunger Drive 

riic lollowing Ijicts arc known iiIkhH ilic 
pliysiology ol the Imnger dritic. When 
the sugar (onccnlration ol the blood is re- 
duced below a (crtaui level, vigorous con- 
tractions ot the stomach ensue. These con- 
tractions of the smooth muscles ot the 
stomach wall are the physiological con- 
comitants of tlie conscious pangs of hunger. 
This latter fact has been demonstrated by 
having subjects swallow a tube to the end 
of which a rubber balloon is attached. 
Wlien the balloon is in the stomach, it is 
inflated and the tube connected to a record- 
ing apparatus so as to give a graphic record 
of the stomacli contractions, f f under these 
conditions subjects are instructed to press 
a signal key whenever a pang of hunger 
is experienced, it is found that their stom- 
ach contractions and liunger pangs coin- 
cide. These experiments have been car- 
ried further to determine the relation be- 
tween stomacli contractions and general 
bodily activity. Subjects were asked to re- 
cline on a bed so constructed as to yield a 
graphic record of their movements— even 
so slight a movement as that of a single 
finger. By taking simultaneous records of 
bodily activity and stomach contractions 
both when ttie subjects were asleep and 
when quietly reading, a very close correla- 
tion between the rhythmic contractions of 
the smooth muscle of the stomach and bod- 
ily activity was demonstrated. 

Just as the altered chemical state of the 
blood consequent upon the reduction of its 
sugar concentration affects the stomach, 
setting up the vigorous contractions of the 
smooth muscle, so these contractions in 
turn set up nervous impulses which make 
for an increase of bodily activity. Hungry 
persons are restless. 

I'.odily (ondiiions such as those just de- 
scribed are correlated, however, not only 
with ;in in(reasc in general bodily activity 
but ;dso uiih specific activity directed to- 
ward the satisfaction of the momentary 
need. J he hungry jjerson seeks food and 
eats it when he finds it. The thirsty one 
seeks water and drinks it if he gets it. 

Although this activity, both general and 
specific, has been found to be associated 
with sudi specific: internal conditicjns as 
stcjmach contracticjns, there are a number 
of experiments which have demonstrated 
that the activity may likewise occur in the 
absence of the usually associated physio- 
logical state. Rats in which practically all 
the contractile tissue of the stomach has 
been removed or in which the nerves be- 
tween the stomach and the brain have been 
severed are still motivated, when deprived 
of food, to seek food and ingest it. A 
hungry hen placed before a heap of giain 
will eat a certain amount and stop, though 
there is still more food before her. Never- 
theless, the hen can be motivated to eat 
again— this time in the absence of anv 
stomach contractions— if the remaining food 
is removed and immediately replaced. 
With some hens this process can be i^epeated 
as many as eight times. In the light of 
such- evidence we cannot assume that stom- 
ach contractions are always and necessarih 
the source of stimulation which motivates 
the hen to eat. In this case the percep 
tion of the food presented is alone sufficient 
to stimulate eating. 

In another experiment the amoimt of 
grain that a hen will eat spontaneoush 
after a twenty-four-hour fast Avas deter- 
mined. The hen was then presented after 
a similar fast with a heap of grain larger 
than before. If ordinarily the hen eats 
fifty gi-ains from a heap of one hundred 



grains of wheat, from a larger heap she -will 
eat thirty-five to fifty grains more. Since 
presumably the chemical state of the blood 
and the condition of the tissues of the 
stomach are about the same under both 
conditions, the increase in eating must be 
determined by neither of these factors but 
by the increase in the size of the heap and 
by whatever physiological changes result 
from the perception of this fact. 

Or again, if a hen eats until satisfied and 
remains motionless in front of a pile of 
grain, she will begin to eat once more if a 
hungry hen introduced into the situation 
starts to eat. And like hens we, too, will 
start to eat again if, having eaten our fill, 
we are joined by hungry friends. 

Such observations as these indicate how 
necessary it is to consider, in addition to 
the internal sources of stimulation in the 
stomach wall, the environmental factors 
which may also stimulate the organism to 
eat. Objects which in the past have been 
present when physiological hunger has 
driven the organism to eat, or situations in 
which eating has occurred, may, because of 
their connection with previous eating, be- 
come adequate in their own right to stimu- 
late the same behavior on later occasions. 
Thus, we eat when we see others eating; 
we eat more when more food is presented 
to us; and we eat, in everyday life, long be- 
fore we are driven to do so by the goading 
pangs of hunger. Once we develop habits 
of eating certain things at certain times and 
in certain places, the appearance of these 
things, at these times and in these places, 
alone suffices to make us eat. 

Sex Drive 

Sexual desire waxes and wanes in cycles. 
There are life cycles: the specific desire for 
the sexual act does not characteristically 
arise until the animal is sexually mature 

or in man imtil puberty, and in old age the 
desire weakens. There are seasonal cycles 
for many animals: some mate only in the 
spring, others in the spring and fall. And 
there is also the estrus cycle in female mam- 
mals, the period of recmrent 'heat' when 
females are receptive to the advances of 
males. This sexual receptivity occurs at 
the time when the o\a or female germ cells 
become matiue and seems, indeed, to be 
dependent upon the process of their growth 
and development. The period of heat is 
also a period of increased activity. Female 
rats have been placed in cages with 'activity 
wheels,' like those provided for the exer- 
cise of squirrels, and the activity of the 
animals has been measm-ed by the num- 
ber of revolutions of the wheels per unit 
of time. Mechanical counters keep the 
record. Although a female rat ordinarily 
rims about a mile a day, it is not imusual 
for her, every fourth or fifth day at the 
peak of the estrus cycle, to run as much as 
fifteen miles in a day. Sexual drive, like 
the hunger drive, gives rise to general acti^•- 
ity as well as specific. 

In the absence of certain hormones- 
hormones secreted by the gonads or sex 
glands and by the pituitary gland— there 
is little sexual drive in the higher animals. 
The testes of the male, in addition to form- 
ing the male germ cells, the sperms, secrete 
hormones called androgens, and the ovaries 
of the female, besides producing the fe- 
male germ cells or ova, secrete hormones 
that are known as estrogens. These hor- 
mones are most immediately responsible for 
sexual desire, but hormones secreted by the 
pituitary gland located at the base of the 
brain also determine the strength of the 
sex drive, since they in turn stimidate the 
secretion of the androgens and estrogens. 
In fact, the pituitary gland and the gonads 
act reciprocally. Pituitiiry secretion stimu- 

Sex Drive 


lilies f^(jii;i(l;il secretion, which in luin acis 
lo (h'lninish pituitary secretion, a process 
(ailed honicuslasis, by which the proper 
i)alance of the sex hormones is maintained 
in the body. 

The role of the pituitary gland and the 
gonads in the sexual need and behavior of 
higher animals can be demonstrated in a 
lumiber of ways. In female rats, for ex- 
ample, the increased activity at the time 
of the estrus cycle appears at puberty and 
disappears at menopause. Removal of the 
ovaries reduces general activity and abol- 
ishes the activity cycle. Injection of estro- 
gens will, on the other hand, restore the 
cyclical behavior as will also replacement 
of the ovaries by grafting. Similarly, the 
removal from an animal of that part of the 
pituitary gland which secretes the gonad- 
stimulating hormones results in a loss of 
sexual drive unless gonadal hormones are 
artificially introduced into the animal's 
blood by injection. When the testes are 
removed from male rats and ovaries sub- 
stitiUed for them, typically female cycles 
and le\'els of activity appear in the male. 

The sex drive of the male rat, as well as 
that of other male mammals, does not ap- 
pear vmtil puberty. Castration after pu- 
berty reduces sexual desire as well as gen- 
eral activity and, although sexual behavior 
may not immediately cease, it is presently 
^\'eakened and in most cases eventually 
disappears entirely. Injection of andro- 
gens into the blood stream of castrated rats 
not only revives their specifically sexual 
behavior but increases as well the amount 
of their general activity. 

There is, then, no doubt that the sex 
drive of higher animals is in large measure 
dependent upon the presence of hormones 
in their blood. The hormonal origin of 
the sexual need of man is also clear. 
Though an infant or child may seek to 

gain lliroiigli stimulation ol certain eroge- 
nous /ones of the body (for example, by 
masturbation of the genitals) a kind of 
pleasure which later would normally be 
gained in the act of sexual intercourse, a 
specific and strong sex drive is not observed 
in children prior to puberty. In fact, if 
ovaries are removed from a female child 
or fail to develop, she will never become 
pubescent; adult female characteristics will 
not appear and there will be a complete 
absence of sex drive. Similarly, early cas- 
tration of a male child results in a person 
of neutral sex, lacking both sex drive and 
the male secondary sexual characteristics. 

The mere fact that a person has reached 
or passed bc)ond the stage of puberty does 
not necessarily mean, however, that his 
sexual drive will find a normal and healthy 
outlet. Sexual maturation gives no guar- 
antee of adequate psychosexual develop- 
ment. Unfortunate early experiences may 
so warp a man's attitudes toward sex that, 
although he may have a fully de\eloped 
sexual mechanism and an adequate secre- 
tion of hormones in his blood, he may, 
nevertheless, find himself imable to per- 
form the sexual act (impotency). A 
woman who has been made to fear her 
sexual impulses or has been led to think of 
sex as something dirty or sinful may find 
herself unable to experience any pleasure 
in the sexual act (frigidity). e\en though 
she is fiUly equipped physiologically and 
anatomically for such experience. 

The hormonal basis of the sex drive can 
vary tremendously, but sexual need and 
behavior are not related in any simple 
manner to the amount of this variation. 
Just as frigidity is not alwa\s caused by a 
deficiency of. hormones, so an abnormally 
strong sexual desire in ■women (nympho- 
mania) is not always the result of an ex- 
cessive secretion of hormones. In fact. 



nymphomania is o[ten an attempt of a 
woman to compensate for a real or an im- 
agined sexual inadequacy. Impotence in 
males, and its opposite, satyriasis, though 
sometimes correlated respectively -vvith low 
and high Levels of hormonal secretion, are 
in other cases entirely unrelated to physi- 
cal and structural factors. 

Man's sexual need and behavior arc, 
ihen, no more completely determined by 
the level of hormones in his blood than is 
his eating determined solely by his stom- 
ach's hunger contractions. Both appetite 
and sexual desire also depend upon habits 
and attitudes that are learned and become, 
as derived needs, part of the personal ad- 
justment of the individual. Herein lies 
the reason why love in man, with a better 
cerebral cortex than any other animal, can 
persist and even arise in the absence of ade- 
quate hormonal secretions. 

The menstrual cycle in women is an 
estrus cycle, biu a woman's sexual desire is 
not completely determined by the cycle. 
The peak of her desire has no fixed relation 
to the time of ovulation; it is usually re- 
jiorted to be gieatest just before and jtist 
after menstruation, but it is often reached 
at other times. The fact that women do 
not lose their sextial desire or their ability 
to enjoN the sexual act after menopause is 
further evidence that sexual need and be- 
havior are not entirely determined by hor- 
monal secretions, once women have learned 
to enjoy sexual relations. 

Androgens in men constitute an impor- 
tant basis for their sex drive, but the andro- 
gens do not alone explain the drive. Re- 
moval of the male gonads in mature indi- 
viduals may have little effect upon sexual 
behavior, and old men who are impotent 
may still experience desire. This is not 
to say that androgens have no effect; they 

are important in the first stirring of de- 
sire, and beyond this they contribute to a 
man's energy and general efficiency. There 
is no doubt that castration impairs bodily 
vigor, and probably also intellectual verve 
and the power of creati\e thinking, but 
it does not necessarily destroy sexual desire 
or eliminate sexual behavior. 

Jt can, then, be said of sex, as of hunger, 
that objects and situations associated with 
the arousal of the sex drive may, because 
of this association, become in themselves 
adequate to stimulate sexual behavior. 
Once an individual has developed habits 
of sexual behavior with a certain person or 
kind of person or at certain times and in 
certain places, the appearance of these 
established 'stimidi' alone may suffice to 
e\oke again sexual need and beha\ior. 

Other Drives 

Many experiments have confirmed the 
drive character of other endocrine or duct- 
less gland secretions. The remo\al of the 
jjituitary, adrenal or thyroid glands in rats, 
as well as in other animals including men, 
has been shown to be followed by a reduc- 
tion in general activity. 

Other bodily conditions ser\'ing as dri\es 
to action are dryness of the mucous lining 
of the throat in thirst, distention of the 
bladder or large intestine, injury to the 
skin. Such examjales could be many times 
multiplied, but these will suffice. 

It is important to point out again, hoAV- 
evev, that while such physiological condi- 
tions as have just been described may be the 
primary drives to action, nevertheless, the 
environmental situation in which such ac- 
tion occurs may in itself become the effec- 
tive stimulus for a similar form of be- 
havior thereafter when the primary stimu- 
lus is lackins;. 

Needs for Particular Foods 


Behavior and Structure 

As wc liave already seen, the way in whidi 
organisms satisfy their needs depends in 
part upon their striittures. We cannot 
understand how an engine runs if we know 
only that there is steam in the boiler; we 
must also know the structure of the whole 
and the relationships among its parts. We 
have to know as much about living or- 
ganisms if we are to understand their l)e- 
havior. Needs and structures are related. 
Tiie needs of a blind man are not the same 
as those of a man who sees, or those of a 
Ijed-ridden cripple the same as those of an 
athlete. Such individuals may and do 
have some needs in common, but they will 
iiave, in addition, unic]ue needs. 

One important respect in which organ- 
isms difler is in ihe extent to wliich they are 
able at birth to satisfy their needs. "Hie 
luniian infant is absolutely dependent upon 
others for the gratification of many of his 
needs; not until years have passed is he 
able to care for himself alone. He must 
first learn how to get most of the things 
he recjuires. Many animals, such as spiders 
and the lower insects, on the other hand, 
are from the very first as capable of satis- 
fying their needs as the adults of the same 
species. They do not have to learn how 
to take care of themselves, for they are born 
with mature structures organized for pat- 
terns of action adequate to meet all their 
needs. Such inborn patterns of response 
have been called instincts, and the be- 
liavior resulting from the activation of such 
patterns, instinctive. A fuller account of 
instinctive beha\'ior has already been gi\en 
(pp. 45-47). Here it is important only 
to note that, whereas man has to learn 
through years of exj^erience how he may 
satisfy his needs, other animals start with 

beliavior all ready to take care of most ol 
their tjasic needs. 

Needs for Particular Foods 

Most animals are superior to man in the 
degree to which patterns of response acti- 
vated by bodily needs operate unconsciously 
in the satisfaction of these needs. In one 
experiment hens were fed a diet almost en- 
tirely deficieni in calcium carbonate. The 
omission oi this imp(jrlant material from 
the diet soon residted in a marked thinning 
of the shells of their eggs and, after lour 
days, in a complete cessation of laying. 
After nine days of this diet deficient in 
calcium, the investigator divided the hens 
into two groups. To one group on one 
occasion he gave short pieces of macarf)ni 
within which shell had been jjlacetl. with 
the ends of the macaroni so closed that the 
shell could neither Ije seen nor tasted. 
These hens ate at that time an average of 
seventeen grains of shell. AVhen he pre- 
sented them plain shell a few hours later, 
each of these hens ate an average of only 
five grains more, making twent)-two grains 
of shell eaten in all. The other gioup he 
first gave plain macaroni, but. when later 
lie presented them with plain shell, thev 
ate on the average nineteen grains of shell. 
On the two occasions taken together the 
hens of the two sets ate approximately the 
same amount of shell, but that was because 
the hens who needed the calciimi more on 
the second occasion ate more shell then. 
They were guided, it would seem, b\ phvsio- 
chemical processes within their bodit-s. Be- 
ing calcium hungrv thev kept on t-ating 
calcium when they got it. 

In a similar experiment hens ^vere of- 
fered a choice between three kinds of but- 
ter, one high in \ itamins A and D, a sec- 
ond high in A but low in D, the third \o\v 
in both A and D. They ate more of the 



first butter, the one most adequate for the 
satisfaction of niitrilional needs, than of 
the others. 

Rats have been shown to have the same 
ability to choose between suitable and un- 
suitable diets when presented with a variety 
of foods in so-called 'rat cafeterias.' Pre- 
sented with two kinds of food, one con- 
taining sufficient and the other insufficient 
protein for normal growth, the rats ate 
both foods, but enough more of the former 
to maintain normal growtli. Given foods 
varying in vitamin B content, they chose 
the foods with the richer vitamin content. 
The same resiUts have been obtained with 
pigs and cows; these animals have demon- 
strated under controlled conditions their 
ability to select a diet adequate to their 
bodily needs. 

These experiments have also demon- 
strated that hunger is not just an indis- 
criminate demand for any kind of food, 
but a complex of specific himgers or appe- 
tites, each for a particular nutritive sub- 
stance, like protein, fat, carbohydrate, 
water, sodium, phosphorus, or calcium. 
(The desire for salt due to the removal or 
a disease of the adrenal glands is discussed 
on pp. 355 f.) 

This discovery does not mean, however, 
that animals limit their eating to food- 
stuffs that satisfy specific nutritive needs. 
Like human beings, they may be tempted 
to eat whatever is appetizing to them rather 
than what is needed by their bodies. 

In one experiment rats were allowed to 
choose between two different foods, a pro- 
tein (casein) and a carbohydrate (sucrose), 
but they were required to make the choice 
in two different ways. In the first kind of 
choice, the protein and the carbohydrate 
had no fixed positions, but were shifted 
at random between the left and the right. 
The rats could see, smell and taste both 

these foods and made their choices on this 
immediate sensory basis. In the othei 
kind of choice, the positions of the pro- 
tein and carbohydrate were fixed, and the 
rat was required to make his choice in ad- 
vance, after he had had enough experi- 
ence to remember which food was where. 
When the rats had been deprived of pro- 
tein for thirty days, they were allowed to 
select food under these two conditions. 
Their bodies then needed protein much 
more than carbohydrate. Were they wise? 
They were wise in advance, that is to say, 
when they had only the memories of the 
foods and their awareness of their own 
bodies in mind, they chose protein; but 
when they were close to the foods so that 
they could see, smell and taste them, they 
tended to take the carbohydrate, even 
though it was not so good for them. 

This experiment was repeated with dis- 
tilled water and powdered dog chow as 
the substances between which choice had to 
be made. The rats were deprived of both 
chow and water. When they had to choose 
in advance they all chose water, but, faced 
immediately with tasteless, odorless water 
versus smelly, tasty chow, they chose the 

The himian analogy is apt. Motivation 
in rat or man is altered by immediate 
perception The lure of the senses is 
strongest when sensation is actual and not 
merely remembered. In the days of the 
saloon and the drunkard, it was always a 
(question as to whether the drunkard coidd 
get home with his pay without squander- 
ing it on drink. Starting home with high 
resolve, he could succeed if he did not pass 
the saloon, if he avoided the visual-olfac- 
tory perception that could so easily shift 
his motivation. The dinner table is replete 
with similar dilemmas. Do you eat what 
is good for you or what tastes good to you? 

Derived Needs 


Since lumiaii ;i(liills so ric(|ii(iuly cal an 
improper diet, it is interesting to note that 
newly weaned infants, ii presented with a 
variety of simply prepared, natural foods 
(includino all kinds necessary to pTodnce a 
good state of nutrition, but excluding all 
food mixtures, refined cereals and sugar) 
and if then allowed complete freedom of 
choice, select their food so that they have 
an adetjuate and balanced diet in terms of 
protein, carbohydrate, fat, calories, acidity 
and alkalinity. They gain in weight more 
than the average for this growth period. 
Jn view of the above limitations these find- 
ings evidently do not imply that free choice 
at the family table would produce the 
same satisfactory results. 

Experiments of this sort, however, 
hardly justify the conclusion that infants 
and children should be allowed complete 
freedom in the choice of their food in the 
situations of everyday life. If a complete 
and adequate range of foods were always 
available to children— something which 
would be most uneconomical— and if the 
feeding habits of adults were unknown to 
them, and if, in addition, they were left 
absolutely free to choose, perhaps they 
would do as well. In the absence of such 
conditions, however, they seem to develop 
specific food preferences and habits of eat- 
ing which make it difl&cult, if not impos- 
sible, for the infant to get along if such 
unconscious regulation of diet continues 

Derived Needs 

The greater plasticity of man means that 
he, more than any other animal, has to 
learn hoiv to satisfy his needs. It also 
means that he learns to need more things 
than any other animal. 

Learned skills and abilities and habits 

arc imjjortant in the study ol motivation 
not only because they enable the individ- 
ual to satisfy his needs, but also because 
they may themselves become drives to ac- 
tion, constituting needs in their own right. 
The boy who learns boxing in sclf-delense 
may find that he wants to box, no longer 
in self-defense, but just for the fun of box- 
ing; or the girl who learns to sew in order 
that she may have clothes as attractive as 
her friends may discover that she wants 
to sew, even though she needs no more 
clothes for her few social engagements. It 
might be argued that the boy who con- 
tinues to box does so in order to feel supe- 
rior instead of merely to protect himself, 
and that the girl who continues to sew does 
so in order to feel superior in the exercise 
of her skill rather than merely to be attrac- 
tive. But even so it is in such ways that 
the number of our specific needs is multi- 
plied niany times over in the course of oiu" 
lives. In general, the greater the pattern- 
ing of the nervous processes underlying our 
actions, the greater will be the number of 
needs which we shall experience. 

Such needs, resulting from mechanisms 
and Iiabits which have become drives in 
their own right, are called derived needs. 
They are the clearest examples of what at 
the beginning of this chapter we called sec- 
ondary needs. Their importance for every- 
day life lies in the fact that, through their 
development, objects and activities which 
earlier were means to an end now become 
ends in themselves. Their importance for 
any theory of motivation lies in the fact 
that they indicate the complexity of the 
physiological basis of the behavior which 
results from need and they re\"eal die in- 
adequacy of conceiving of drive as simply 
a matter of a specific condition of the tis- 
sue in an organ or other restricted part of 
the bod\-. 



Because these secondary needs result 
from the patterning of the response mecha- 
nism, it follows that their physiological 
basis must be in large measure these neural 
patterns. Since even primary needs are 
satisfied only when the appropriate pat- 
terns of response are activated, and since, 
as we ha\e seen, these primary needs may 
be aroused in the absence of the usually 
associated organic condition, it would seem 
no less true that their physiological basis 
is also in large part a matter of patterns in 
the nervous system. In other words, we arc 
forced to conceive of the physiological basis 
of all needs, both primary and secondary, 
as being a matter both of certain organic 
stimulating conditions (for example, stom- 
ach contractions) and of certain neural 
states (for example, neinal patterns). 


So important is the role of the environ- 
ment in eliciting and determining behav- 
ior that it has been impossible not to men- 
tion it in connection with the other factors 
already discussed. 

A rat confined in an activity cage shows 
an increase of activity as the time for feed- 
ing approaches. In that environment it is 
all he can do when driven by himger. But 
if we take him from his cage and put food 
before him, he will no longer rvui; he will 
eat. If, on the other hand, we place him 
in a maze which he has learned, he will 
run directly to the food box and eat. We 
may assume in all three cases the existence 
of the same internal state of physiological 
disequilibriimi or drive, so that the differ- 
ences in behavior appear to be determined 
i)y differences in the rat's environment in 
the three situations. 

Let lus observe the same rat iusi nfter hr 

has eaten to satiety. A satiated rat re- 
mains relatively quiet in his activity cage. 
If there is food before him, he ignores it. 
If placed in a maze, provided it is not a 
strange one, he shows no active seeking 
after food. Here, in the same three situa- 
tions as described above and all quite dif- 
ferent from each other, the behavior of the 
rat is practically identical— a quiet indif- 
ference to his environment. Are we, then, 
to draw from observation of a satiated rat 
a different conclusion from that we reached 
by observation of a hungry rat, namely, 
that the similarity of behavior in different 
environments is determined by the similar 
internal state of the rat in all three situa- 

Relation of Environment to Needs 

Neither conclusion is wholly right nor 
^\■holly wrong, and the conflict between 
them can be resolved if, instead of consider- 
ing the internal and external factors sep- 
arately, we see them in relation to each 
other. The point is that any situation as 
it exists psychologically for the organism— 
that is to say, as it is perceived and reacted 
to— is in large measure dependent upon the 
needs of the organism; and, since the needs 
of any organism are constantly changing, 
this fact means that the same physical en- 
vironment and objects in it ha\e at differ- 
ent times quite different meanings. When 
a child is hungry, an apple is something 
to eat; but when he is angry, it is some- 
thing to throw at the provoking person. 
Similarly, a hungry rat is an alert rat, 
actively seeking in its environment any- 
thing that may serve as a means to the 
satisfaction of its need; but a satiated rat 
is a sleepy rat, indifferent to many aspects 
of its environment. Whether food is pres- 
ent or absent is a matter of no conse- 
(juence to it. Environments physically im- 

Environmenfal Determinafion of Needs 


like may all be the same psychologically, 
in that they are reacted to as though they 
were alike. 

It is helpful in distinguishing the physi- 
cal and psychological environment to call 
the former the silualion and the latter the 
field. The physical situation is the en- 
vironment considered as having independ- 
ent real existence, whereas the psycholog- 
ical field is the situation as it exists psycho- 
logically for the individual. The psycho- 
logical field is not to be equated merely to 
what is consciously perceived or known but 
rather to everything that at the moment 
determines the behavior of an individual. 

Food in the situation may or may not be 
food in the field. If there is a need for it, 
food in the situation is likely to be per- 
ceived and reacted to. It then exists as 
food in the field and has a positive, at- 
tractive value, exciting the hungry person 
to eat. But the need for nourishment hav- 
ing been satisfied, the same food may be 
ignored. Although it may be perceived, it 
will not excite the individual to activity, 
for it now has a neutral quality, neither at- 
tracting nor repelling him. The presence 
of others who are hungry and eating may 
make the food seem slightly attractive so 
that it is nibbled at. An unpleasant story 
told at the table may make the food seem 
unpleasant so that it is pushed away. If, 
however, for any reason food has been 
eaten to the point of satiation, especially if 
this overeating has resulted in any degree 
of discomfort, the sight and smell of food 
cease to be neutral and acquire a negative 
character. The individual experiences a 
need to push the food out of sight or to 
remove himself from it. 


The existence of objects or activities in 
a person's field is thus seen to depend to 

an iiriportanl dcgicc upon his needs. Jt is 
for this reason that objects and artivities 
in the field so often have to be described 
psychologically as having an attracting, re- 
pelling, exhorting, summoning, inviting or 
demanding character. Things f>ossessing 
such characteristics are called incentives. 
An incentixie may be defined as an object, 
a situation or an actit)ity which excites, 
maintains and directs behavior. It must be 
clear, however, that a thing which is an 
incentive at one moment may not be an 
incentive at tlie next moment, or that a 
thing which is at one time a positive in- 
centive attracting a person may subse- 
quently be a negative incentive repelling 
the same individual. 

Objects or activities offered to an indi- 
vidual may act as incentives to arouse his 
needs and stir him to action, ^\'hen a 
need is very strong, he will actively seek 
objects to satisfy it if they are not present 
in his environment. But, under condi- 
tions of a lesser need, an individual mav 
be relatively quiet and contented until 
something brought into his environment 
acts as an incentive to arouse that need 
more actively. A person may not be con- 
sciously hungry until he smells the pleas- 
ant aroma of food, or he may be little in- 
terested in stamp collecting until he hears 
a lecture on the fascinations of philately. 
As the advertiser knows, it is possible, 
within limits, to motivate people to action 
through a manipulation of their environ- 
ments; but, if this activation is to be 
wholly successful, it is necessary to know 
something about the latent needs of those 
whom one seeks to influence. Otherwise 
what may seem the most attractive of in- 
centives to the one ^vho offers them may 
turn out to be no incentives at all for those 
to whom thev are offered. 

The social environment, no less than the 



physical, influences the activities of indi- 
\'iduals, causing things to lose or to acquire 
incentive value for them. It has already 
been pointed out that a hen which has 
eaten to satiation will begin to eat again 
if a hungry second hen is introduced into 
the situation; and she will eat more if two 
hungry hens, and still more if three, are 
brought in. This result occurs, however, 
only when the hungry hens have been ac- 
customed to tyrannize over the satiated 
hen in other situations. If, instead, the 
satiated hen has habitually tyrannized over 
the hungry hens, she will attempt to keep 
them from eating by pecking at them or 
chasing them away. The converse experi- 
ment has likewise been performed, in 
which three hens eat to satiation and then 
are joined by a single hungry hen. Under 
these conditions the hungry hen begins to 
peck the grain, but her behavior has no 
effect upon the group of three, who re- 
main passive or peck only a little. Evi- 
dently the satiated hens support one an- 
other in their indifference. 

Other experiments have demonstrated 
comparable effects of social situations on 
eating in fishes, rats and monkeys, and the 
same effect is noticeable among persons. 
The child who does not want his oatmeal 
may nevertheless eat it eagerly ^vhen he 
sees his brother eating his with relish, just 
as, in the same way, the eating to excess at 
an old-fashioned Thanksgiving dinner is a 
function not only of the increased quantity 
of food (tlie same effect as seen in hens) 
but also of the social facilitation supplied 
b) the sight of others eating. The presence 
of others may, of course, just as well cause 
objects or activities to become negative in- 
centives as positive, as when, for example, 
the work we are doing ceases to be inter- 
esting because others gather lor an evening 
of fun. (See also pp. 596 f.) 

Cultural Determination of Needs 

The importance of the environment in 
the behavior that is dependent on needs is, 
however, most clearly seen in the cultural 
determination of needs. The infant is 
born into a society in which there are cer- 
tain social norms of behavior, certain cus- 
toms which determine to a large extent not 
only the needs which the members of that 
society experience but also the particular 
means by which these needs may be satis- 
fied. What the norms of his society are is 
one of the things the infant has to learn. 
The process of socialization in the devel- 
oping child is in large measure the incor- 
poration of these norms within himself in 
order that his general patterns of behavior 
may coincide wuth those of his gioup. In 
short, he learns that certain ends may be 
sought, but not others. 

The specific nature of the means of sat- 
isfying primary needs no less than sec- 
ondary ones is determined by social norms. 
The kind of food eaten by people of differ- 
ent cultures varies greatly. In many so- 
cieties individuals are not permitted to eat 
the flesh of certain animals which are be- 
lieved to be related to them, a relationship 
which thus renders the idea of eating such 
flesh abhorrent. In other societies fruits 
or plants are prohibited. There is no so- 
ciety in which the entire range of edible 
objects is included in the diet. Having 
learned to eat certain things and not cith- 
ers, and having learned to eat them only 
when prepared in certain ways, we find it 
difficult, if not impossible, to change our 
eatmg habits. It is known, for instance, 
that immigrants frequently find it easier to 
learn a new language than to learn to like 
the dishes of their new counti-y. ^\n Amer- 
ican may demand a soft mattress and pil- 

Cultural Determination of Needs 


low ii his need lor rest is to be satisdcd, ;i 
Japanese may demand a hard mat and jjil- 
low of wood and the African native may 
be able to rest only if he tan lie upon the 
ground. Such differences as these are not 
racially determined but are rather the ef- 
fect of social pressure on the needs of in- 
dividuals in different cultures. 

The young of the human species must 
be cared for if the species is to survive. 
This fact has led many persons to assume 
the existence in every mother of a need to 
care for her offspring, a need so fixed in its 
expression as to constitute a malernal in- 
stinct. Yet, actually, there is to be found 
among different peoples a wide range of 
norms of behavior in regard to the care and 
protection of infants. Among the Arapesh 
of the South Seas an infant is the object 
of great warmth and affection. Suckled 
whenever it cries, sleeping in close contact 
with its mother and carried by her wher- 
ever she goes, the Arapesh infant is almost 
continuously fondled and caressed. In 
contrast to the Arapesh, the Mundugumor 
treat their children with little love. The 
infant is kept in a hard uncomfortable 
basket, is not suckled unless clearly in need 
of milk, is not fondled or caressed, is made 
early to fend for itself and in general is 
so harshly treated that only the strongest 
survive. Among the Andaman Islanders 
adoption of children is so customary that 
it is rare to find a child of more than six or 
seven years of age living with its parents, 
for to adopt the child of a friend is an 
accepted form of expressing friendship and 
regard. On the Island of Mota, on the 
other hand, an infant may be sold at birth 
to the man who pays the midwife. Al- 
though this person is usually the father, it 
sometimes happens that, in the absence of 
the father or in the event that he lacks the 

ii((cssai) lunds, another man bu)s the 
(hild and Ijccomes its 'lather.' In otiicr 
societies infanticide, at least under certain 
conditions, is an accepted practice; and th," 
Aztecs sold their children into slavery. 

y\nother form of human behavior which 
has sometimes been regarded as instinctive 
is the aggressiiie reaction to frustration. 
Nevertheless conflict between individuals 
does not invariably or universally result 
in the same behavior. Instead of fighting 
with his fists, the Kwakiutl Indian fights 
with property in the institution of the 
"potlatch," in which the more property he 
can give away or destroy, the more superior 
he is to his opponent. Eskimos settle their 
conflicts in a public contest in which each 
sings abusive songs about the other. ^Vhen 
two Indians of Santa Marta quanel, in- 
stead of striking each other, they strike a 
tree or a rock with sticks, and the one first 
breaking his stick is considered the braver 
and hence the victor. In other societies 
aggression is expressed in still other Avays; 
even within the same society there may be a 
wide range of different socially approved 
expressions of aggression. 

It is noiv possible to demonstrate a wide 
range of behavior for any need. In the ab- 
sence of crucial anthropological kno^vl- 
edge, it was formerly assumed diat the 
needs were in all societies the same as in 
ours, and therefore instinctive. The fixed- 
ness and universality of forms of human 
beha\ior, ho^vever, turn out to be a myth. 
Instead, we find that the needs of die indi- 
vidual, as well as the ways in A\hich he is 
jjermitted to satisfy them, are determined 
to a large extent by the social and cultural 
environment into which he is born and in 
■which he is reared, (^\'e shall learn more 
about social norms on pp. 560-562.) 




The iacts reviewed in the preceding sec- 
tions of this chapter suggest the following 
definition of need. A need is a tension 
within an organism which tends to orgaji- 
ize the field of the organism with respect 
to certain incentives or goals and to incite 
actixnty directed toivard their attainment. 
For each need there are certain objects or 
activities— terminal situations— which, if 
they are obtained, satisfy the need, thus re- 
leasing the tension. It is for this reason 
that the fullest meaning of any behavior is 
described only when the final situation to- 
ward which it is leading is discovered. 

At this point we must pause to note that 
a 7ieed, a set and an attitude are psycho- 
logically the same thing. The terms are 
merely being used in different contexts. 
When a subject is given pairs of digits and 
told to write down their sums, he is put in 
the adding attitude and is operating under 
a set for addition. Actually it would be 
just as reasonable to say that he has tempo- 
rarily acquired a need for sums, a need 
which is derived from his need to do what 
the experimenter asks him to do and to do 
it well, which in turn is a phase of his need 
for approbation, which, of course, be- 
longs properly to all gregarious animals 
like man. Need, set, attitude— these are 
all dynamic psychological concepts which 
express the fact that the organism can be 
set to pursue a given end or purpose con- 
sistently and without being put off the 
main track by every casual stimulation that 
comes along. 

Needs have a qualitative aspect which 
makes it possible for us to distinguish such 
primary needs as those for food, sex, ther- 
mal constancy and elimination, and such 
secondary needs as those for superiority, 
submission, affiliation, freedom and invio- 

lacy. Such terms as these are, of course, 
generalizations from the specific situations 
in which the concrete activities of needs 
end. We do not have a general need to 
be superior, but rather a need to be su- 
perior in a particular way in a specific sit- 
uation, for example, to win this race, to get 
the highest mark on this examination, to 
know more about a certain field of study 
than any other person. Yet it is often help- 
ful in the study of certain problems of per- 
sonality and in the comparison of individ- 
uals to conceptualize general needs of 
which any given behavior or trait is but a 
specific and concrete expression. 


Needs also have a quantitative aspect 
which makes it possible by the use of cer- 
tain techniques to measure their strength. 
Although, of course, a need cannot be 
measured directly, an indirect estimate can 
be obtained by measuring its effect upon 
consciousness and behavior. Thus, by de- 
termining the work which the need will 
do, we get an indication of its intensity. 

Obstruction Method 

One technique for the measurement of 
needs is the obstruction method, by which 
the strength of a need is measured in terms 
of the magnitude of an obstacle or the 
number of times an obstacle of a given 
magnitude will be overcome in order to 
obtain a needed object. The obstruction 
method has been employed most often in 
the measurement of animal drive, rats hav- 
ing been the subjects most frequently stud- 

A diagram of an obstruction box used in 
such investigations is shown in Fig. 43. To 
measure the sex need a female rat is placed 

Measurement of Needs 


in compartment A, a male rat (the in- 
centive) in compartment 1). In order to 
reach the incentive, the female rat must 
pass through the alley B. The floor of 
this section is covered with an electric grid 
which enables the experimenter to give the 
animal a shock. If she crosses the grid, she 
steps on E which releases door ^21 liber- 
ating the male from D. It has been found 
that when a female rat is in heat she 

order to get the food; and, presumably, the 
stronger the first need, the more often will 
the grid be crossed in a given period of 
time. Since every need is unstable, the 
measurement of one against another can- 
not be exact. In evaluating these results 
we must remember that the animal tends to 
become accustomed to the electric shock, 
so that the negative incentive of the physi- 
cally constant shock decreases in time. 




1 a — 





(A) Entrance compartment; (B) obstruction compartment (electric grid): (C, D) divided inceiiiive com- 
partment; (£) release plate; (d^) manually operated door between entrance compartment .-/ and grid li: 
((I2) automatic door operated by animal's stepping on release plate E. [From T. N. Jenkins, L. H. Warner 
and C. J. Warden, /. conip. Psychol., 1926, 6, 366; reprinted by permission of the Williams and ^VilkiIls 

crosses the charged grid frequently and 
with little hesitation, though at other 
times she scarcely ever crosses it. 

Similar investigations of hunger, thirst 
and inaternal need have demonstrated that 
a rat does not repeatedly cross the grid and 
take a shock in the absence either of a 
motivating need or of the appropriate in- 

In the obstruction inethod not one need 
is measured, but two which are in conflict. 
There is the need for food, or water, or 
whatever other need is being investigated, 
but there is also the need for avoidance of 
pain, so that what is actually being meas- 
ured is the relative strength of the two 
needs. If, for example, the need for food 
is stronger than the need for avoidance of 
pain, the animal will take the shock in 

With the use of this method of obstruc- 
tion attempts have been made to determine 
the relative strengths of various animal 
needs. In the most extensive investiga- 
tions so far recorded, the maternal need 
has been found to be the strongest. The 
others in rank order of strength are thirst, 
hunger, sex and the exploratory need. 
This order depends, howe\'er, upon the de- 
gree of deprivation of the animal and upon 
the particular apparatus used as well as 
upon the comparison of one need at a time 
with the need for avoidance of pain. 

Needs, hoAvever, are all interrelated. It 
has been shown that prolonged hunger 
both in man and in animals is accompa- 
nied by a lessening of sexual diive; that 
prolonged deprivation of water reduces ma- 
terially the intake of food in rats; that the 



brooding of a hen reduces greatly the 
amount of food she eats: that an increase 
in the hunger of rats is accompanied by an 
increase in their need for exploration; and 
that, when sex need is strongest (at the time 
of estrus in the female rat), the need for 
food as measured by its intake is greatly 
reduced. A similar interrelation can be 
observed in persons. The need to get good 
grades may become much less when the 
student falls in love, the need for food may 
become secondary to the desire to have a 
slim figure, and the need of the mother to 
dress attractively may become negligible 
when the need to care for her child is 

Learning Method 

A second technique for the measurement 
of needs is the learning method, by which 
the strength of need is measured in terms 
of the readiness with which a task is learned 
under different conditions of motivation. 
It has long been known that for an organ- 
ism to learn it must be motivated. This 
fact makes it possible to vary the factor of 
motivation and to measure its effect upon 
the rate of learning. Here again, because 
animal experimentation is simpler than hu- 
man, most of the studies have been made 
with animals, but an analogue of the ex- 
perimental findings can usually be found 
in the realm of human behavior. 

It has been shown that, within limits, 
the stronger the motivation the faster the 
learning. In one experiment which dem- 
onstrated this relation, the rate of maze 
learning by three groups of rats differing 
only in their motivation was investigated. 
The first group was very hungry and very 
thirsty, the second was very hungry but 
only slightly thirsty and the third was very 
thirsty but only slightly hungry. During 
the first nine days of the experiment the 

rats were rewarded with bran mash; during 
the last nine days they were rewarded with 
water. In the first half of the experiment 
the rats motivated both by hunger and 
thirst learned slightly faster than the ani- 
mals of the other two groups, a fact which 
indicates the superiority of two needs over 
one in motivating learning. In the second 
half of the experiment, with the shift to 
water as the reward, the very hungry and 
thirsty animals were temporarily disturbed 
by the change. They showed at first an in- 
crease in the number of their errors, but at 
the end of the experiment they were again 
superior to the other two groups. The ef- 
fect of the shift in reward upon the other 
two groups, which had learned at the same 
rate during the first nine days, was striking. 
Now rewarded with Avater, the very thirsty 
animals speeded up their learning, whereas 
the very hungry rats showed very little im- 
provement with the inappropriate reward. 
The second half of the experiment not 
only confirmed the finding of the first in 
demonstrating that two needs constitute a 
more effective condition for learning than 
one, but it also showed that learning is 
faster when the need serving as motive is 
appropriately rewarded. 

The needs motivating children for their 
school work are numerous and varied. 
The arousing of more needs by presenting 
additional incentives has been shown to in- 
crease their accomplishment. In one in- 
vestigation, the offer of a reward of a choco- 
late bar raised the performance fifty-two 
per cent above the usual level, whereas the 
introduction of a number of incentives, 
like candy, a definite goal, rivalry and 
praise, increased the performance sixty-five 
per cent. In human motivation, then, as 
in animal, it is easy to demonstrate that an 
increase in motivation leads to an increase 
of performance. 

Effecfs of Need 


1 1 has also been shown that the amount 
ol reward offered inHuences the rate of 
learning. For instance, chicks who find six 
grains of boiled rice in the reward box at 
the end of a simple maze learn the maze 
more effectively than chicks who are re- 
warded with only one grain. That the 
amount of reward offered human beings is 
not without its effect upon performance is 
also clear. We work harder and better for 
more rather than for less pay. The stu- 
dent works harder for a large scholarship 
than for a small one. 

Not only is the amount of reward impor- 
tant in determining the rate of learning 
but also the kind of reward. It has been 
shown, for example, that of two groups of 
rats learning a maze, the group rewarded 
with bran mash will learn the maze more 
rapidly than the group rewarded with less- 
preferred sunflower seeds. This finding 
also has its analogue in human behavior. 


Sensitivity, perception, imagination, 
thought, activity and persistence all depend 
on need and are affected by needs. Frus- 
tration often arises from a conflict of needs. 
To these effects we now turn. 

Effect on Perception and Imagination 

The investigations just reviewed have 
demonstrated the role of need in learning. 
They have also shown the effect of need on 
perception, for all learning involves a re- 
organization of a field. The maze which a 
rat has learned is psychologically quite dif- 
ferent from what it was when first encoun- 
tered. The keyboard of a typewriter is for 
the skilled typist quite a different field 
from what it is for the novice. 

A simple example will illustrate that 
learning involves a reorganization of a 

field as a result of need. Let us lake the 
case of a young child separated from an 
apple by a lerKC, as indicated in Fig. 44(a). 
If the child is not hungry, and is content- 
edly playing wiiii some toys in the blind 
alley, he may not even sec the apple; or, 
if lie does, he will not be interested in it. 
If, on. the other hand, he is restless, either 
because he is hungry or because he is tired 
of playing with his toys, the likelihood is 
greatly increased that he will see the apple. 



+ -K^ 






(fc) (c) 


-|- = apple. O = child. -^ = path taken bv child. 

Under two different conditions of need the 
field of the child is differently organized. 
Thus, whether the apple will become a 
positive incentive depends upon whether it 
can serve in any way to satisfy a need. 

If it does become a positive incentive, 
the very young child will try to get it in 
the simplest and most direct manner, as 
indicated in Fig. 44(6). Since he cannot 
reach it, or crawl through the fence to it, 
his need is blocked and his field reorgan- 
ized until ^vhat was previously for him a 
fence or a row of sticks no^v looms as a 
barrier. He may push against this barrier, 
try to crawl under or over it or reach 
through it as far as he can, all because the 
way to the apple is a straight line towaid 
it. Then, blocked and frustrated, he may 
look around, see the opening and suddenly 
run to tlie apple in the roundabout direc- 
tion indicated in Fig. 44(c). Again his 
field has been reorganized. \\'hat was pre- 
viously either nonexistent as a way to the 



goal, or else a path away from the goal, 
now becomes the first phase of the path to 
the goal. If the child is again put back 
into the blind alley, he will at once take 
the roundabout way to obtain the apple. 
He has, in other words, learned the solu- 
tion of what is called a detour problem. 
In this case it is clear that learning is the 
result of a need which reorganizes a field. 
When there is no possible solution of a 
problem, the role of need in reorganizing 
the field may be even more marked. In 
an investigation of anger, subjects were 
given a task for which three different solu- 
tions were demanded, although there were 
only two possible ones. The subject was 
asked to step within a square outlined by 
long sticks laid upon the floor and, with- 
out leaving this area, to obtain a flower 
which was placed upon a sawhorse four 
feet outside the square. The two possible 
soltitions were: (1) to place a chair which 
stood within the square between the square 
and the horse and, leaning with one hand 
on the chair, reach the flower with the 
other hand; and (2) to kneel down (keep- 
ing the feet within the square) and reach 
the flower. Both these solutions were pos- 
sible only if the subject had perceived the 
field reorganized in these two ways. After 
the subjects had arrived at these two solu- 
tions, they were asked to demonstrate a 
third. Since there was no third solution 
and since the subjects were kept for hours 
at the task, the mounting tension result- 
ing from the blocking of their need was 
expressed not only in anger but also in 
many new perceptual organizations of the 
field. As the experiment continued, all ob- 
jects came to be seen in relation to the goal 
—as baniers, disturbances, tools, etc. The 
greater the tension, the more did objects 
offer themselves as possible means to the 
solution. Some rings which had been 

placed along the side of the square were 
seen again and again as having something 
to do with getting die flower. Although 
they were of no use, they were picked up 
repeatedly and juggled about in a vain at- 
tempt at use. Then they became disturb- 
ing factors which the subjects wanted to 
forget but could not. The subjects were 
also disturbed by the fact that the back of 
the square was made of two sticks rather 
than one, as though this, too, had some- 
thing to do with the solution. 

Such behavior clearly indicates that 
while a certain degree of need is necessary 
for that reorganization of a field which con- 
stitutes insight and learning, a need in ex- 
cess of such an optimum may come so to 
distort the field that it no longer bears any 
resemblance to the situation. In this ex- 
periment, some of the subjects after long 
periods of frustration revealed momentary 
fantastic distortions of the field. One per- 
son began to act as though she had hyp- 
notic power to draw the flower to her, 
while another, yielding to fantasy, saw the 
room filled with water and the horse and 
flower floating in her direction. Both sub- 
jects in their momentary fantasies forgot 
the harsh realities of their situation. Such 
a denial of the frustrating realities of a 
situation is, of course, characteristic of all 
fantasy and wishful thinking. 

The behavior of these subjects was simi- 
lar to that of a student who, having en- 
dured one frustration after another in his 
boyhood, was still in college being frus- 
trated both in his scholastic work and in 
his social relations. Yet, if in reality his 
needs were frustrated, in fantasy his wishes 
were fulfilled. He confided that when he 
sat in a classroom he paid little attention to 
the lecture, for he found it easier and pleas- 
anter to indulge in the fantasy that he was 
the head of a large office and that all the 

Effect on Perception and Imagination 


other members of the class (so industri- 
ously taking notes) were his secretaries and 
stenographers busily working for him. 
When he walked from one building to an- 
other on the campus, he thought of each 
as a separate city or town. To his mind 
he was not merely passing buildings on a 
campus; he was speeding over the highways 
from one city to another in a high-powered 
car. And when, one night, he was, in 
reality, walking along a country road with 
two of his friends, it seemed to him in his 
fantasy that they were a couple of the 
enemy whom he had captured in a lone 
raid into no man's land and whom he now 
was escorting back to his own lines— for 
which brave action he was soon to be deco- 

The fields of this student deviated far 
from the objective realities of his everyday 
situations. Since he found in them a 
pleasant, vicarious satisfaction of the needs 
which were in reality frustrated, his fan- 
tasies constituted escapes from this reality. 
We all indulge in such flights from reality 
from time to time, when our needs are ex- 
cessively frustrated. We return from them 
frequently with renewed vigor and strength 
to force the satisfaction of our needs on 
the level of reality. As a matter of fact, 
the very distortion that our fields undergo 
at such times may suggest to us the way 
in which we can in reality satisfy our needs. 
There is always the danger, however, that 
such flights from reality will cease to be 
momentary or of relatively short duration 
and will become instead permanent. It is 
in this sense that the delusions characteris- 
tic of certain mental disorders are merely 
extreme and lasting distortions of the pa- 
tients' fields by their needs. The poor man 
whose need for material things has been 
enduringly frustrated may end by living in 
a fantastically distorted field in which he is 

fabulously wealthy, although in leality he 
is an inmate of a mental hospital. 

Less marked and less pathological exam- 
ples of the organization of a field by a need 
can be seen in everyday life. When two 
persons behave differently in the same ob- 
jective situation, they do so because the sit- 
uation is for each a different field. 
Whereas one individual's need for atten- 
tion may make him see a group of indif- 
ferent strangers as an appreciative audi- 
ence before whom he must show off, an- 
other's need for inviolacy may cause him 
to perceive the members of the same group 
as hostile critics from whom he must shrink 
and withdraw. That Napoleon's need for 
superiority often determined the structure 
of his fields is revealed in his remark to an 
attendant prior to the meeting of an Aus- 
trian conference. "Carry that chair away 
before we begin. I have never been able 
to see a raised chair without wanting to 
sit in it." 

Explorers who have been forced to live 
on short rations or whose food supplies 
have become exhausted have often reported 
their preoccupations at such times with 
thoughts of food. During the day their 
conversations have been mostly about the 
preparation of food; at night their dreams 
have been of sumptuous feasts. 

In one investigation of the effects of ab- 
stinence from food upon imaginal proc- 
esses, subjects were given, at various inter- 
vals after eating, a series of tests in which 
ambiguous or incomplete material had to 
be interpreted or completed. \Vith all the 
tests it was found that, as the incenal of 
time since the last meal ina'eased, the num- 
ber of interpretations or completions which 
referred to food also increased. ^Vhen, for 
example, the subjects ^vei'e given a word- 
association test in which they had to re- 
spond to a given word ^vitli die first ^vord 



Avhich came to mind, hungry subjects, more 
often than others, thought of such words 
as spoon, fork, eat and food. In another 
test the subjects were asked to tell what 
was going on in a series of pictures, parts 
of which had been cut away. In the case 
of one picture of a child pointing, subjects 
who were not hungry were likely to inter- 
pret this as a child about to strike a key 
of a typewriter or about to pick up a toy, 
whereas hungry subjects were inclined to 
see it as a child about to stick his finger 
in a pie or in some other way reacting to 
a food situation. 

Tests comparable to those just described 
for hunger have been used to determine, 
by an analysis of subjects' responses, the 
relative strengths of other needs. Addi- 
tional tests which have been used for the 
same purpose are a musical reverie test, in 
which, while a number of phonograph rec- 
ords are played, a subject allows a fantasy 
to develop which he later reports to the 
experimenter; an odor imagination test in 
which, as each of a number of odors is pre- 
sented, a subject invents some episode or 
story from the first idea or image which 
comes to mind upon smelling the odor; and 
a thematic apperception test in which the 
subject is presented with a number of pic- 
tures and asked to make up a plot or story 
for which the picture might serve as an il- 
lustration. Such tests have been used for 
the measurement of needs on the assump- 
tion that the stronger a need the greater 
will be its effect in organizing the field. 
This means that in these tests the stronger 
needs of the individual determine the con- 
tent of the fantasies which are evoked and 
the nature of the interpretations and com- 
pletions of the material which are made. 

Since, in thus reorganizing the percep- 
tual field in accordance with his own needs, 
the subject is projecting his own needs into 

the situation which he faces, these means 
of assessing needs have been called pro- 
jective techniques, procedures which have 
become important tools in the assessment 
of personality. (See pp. 495-497.) 

Effect on Sensitivity 

There is evidence that need may deter- 
mine an increase in sensitivity. Fasting 
persons have frequently reported that they 
are more sensitive to odors and sounds dur- 
ing fasting than at other times, and for 
such statements there is some experimental 
confirmation in other sensory fields. In 
one case it was found that, as the fast was 
prolonged (it lasted altogether thirty-one 
days), the abilities to discriminate tactually 
between two adjacent points on the skin 
and visually two points on the retina were 
increased. Studies of animals and infants, 
in which the ease of evoking a response is 
taken as a measure of sensitivity, also indi- 
cate an increase of sensitivity to various 
kinds of stimulation under conditions of 

In one investigation rats were allowed 
to choose between distilled water and weak 
solutions of salt. With concentrations of 
salt below the threshold of perception nor- 
mal rats showed no preference, although, 
when the concentration of salt was in- 
creased to 0.055 per cent (about one part 
of salt to 2000 parts of water), they con- 
sistently preferred the salt solution. On 
the other hand, rats, whose need for salt 
had been increased by the removal of their 
adrenal glands, could distinguish much 
weaker solutions, for they chose, in prefer- 
ence to distilled water, concentrations of 
salt as low, on the average, as 0.003 per 
cent (about one part of salt to 33,000 parts 
of water). It seems clear that increased 
need increases sensitivity, although it is 
not so clear what the mechanism is. It is 

Effect on Sensitivity and Persistence 


more likely that need heiglileiis attention 
in these rats than that it sensitizes liicii 
taste receptors. 

Eflfect on Persistence 

It the activity of an indivichial is inter- 
rupted, we should expect, from the defini- 
tion of need, that the residual tension re- 
maining after the interruption would cause 
the individual to return to the interrupted 
activity and to attempt again to reach the 
original goal. A number of experiments 
have demonstrated precisely this effect. 

In one experiment subjects, given a se- 
ries of simple tasks to perform, were al- 
lowed to complete some of them but were 
interrupted before finishing the others. 
When, with both completed and inter- 
rupted tasks within reach, the subjects were 
left free to do whatever they desired, it was 
found that, whereas they almost never took 
up the completed tasks again, presumably 
because their corresponding tensions had 
been discharged, they resumed the inter- 
rupted tasks in about eighty per cent of the 

In another investigation subjects were 
asked to help the experimenter in thinking 
of words beginning with a certain letter. 
After writing down as many words as they 
could think of within the allotted time, 
some of the subjects were told that they 
had done unusually well, whereas others 
were told that they had done very poorly. 
The intention of the experiment was to 
create for some subjects an experience of 
success and for others an experience of 
failure. When, two weeks later, the sub- 
jects were questioned as to whether they 
had thought in the interim of words begin- 
ning with the assigned letter, there was con- 
siderable evidence that they had had diffi- 
culty in keeping their minds off the origi- 

nal task. One siibject, wiio had experi- 
enced failure, reported: 

"As soon as the experiment was over C- 
words came flooding into my mind. On 
my way home 1 felt that I should go insane 
if I contiiuied to think of them, so I de- 
termined to banish them by thinking of 
other things. At intervals thereafter C- 
words would slip into my thoughts when I 
was not expecting them, but they gradually 
ceased coming." 

In general the persistence of the activity 
was greater for those who had felt frus- 
trated in the original experiment, presum- 
ably because of the greater unresolved ten- 
sion which tended to continue the original 
activity until it was terminated by the ful- 
filment of the original purpose. We often 
experience in everyday life the persistence 
of activities which have failed to reach their 
goals. Having done poorly in an examina- 
tion, we continue to think of all the things 
we should have written but did not. 
Worsted in an argument, we can think of 
nothing but the brilliant things we failed 
to say. 

Experiments such as these, as well as the 
observation of persisting activities in every- 
day life, demonstrates that tasks which have 
been undertaken, like any purpose or in- 
tention, set up tendencies within the indi- 
vidual which keep him at work until the 
goals thus set are attained. It must be 
noted, however, that in the experiments 
reported above no conflicting purposes or 
intentions were aroused, as there might 
well have been and as there often are in 
everyday life. These experiments, there- 
fore, offer no guarantee tliat all human be- 
ings will always complete their incompleted 
tasks if given an opportunity. In some in- 
dividuals tlie need for initiating new ac- 
tion may be stronger than the need for fin- 
ishing work already begun. 



Since the residual tensions of incom- 
pleted tasks may cause preoccupation with 
these activities, we should expect to find 
that incompleted tasks tend to be better 
remembered than finished ones. This ex- 
pectation is verified. If subjects are given 
a series of simple tasks to perform, are al- 
lowed to finish one half of them but are 
interrupted before they have completed the 
other half, and then are asked immediately 
after the experiment to recall all the tasks 
which they have attempted, they can recall 
incompleted tasks almost twice as often as 
finished ones. 

Frustration Tolerance 

The effects of need upon the behavior 
and consciousness of the individual depend 
to a large extent upon the degree of ten- 
sion in the given case. Some degree of 
need is necessary for psychobiological adap- 
tation, for otherwise the organism is inert. 
In order that learning may occur, there 
must be some degree of tension to reorgan- 
ize a field, but we have already seen that 
an excess of tension resulting from a pro- 
longed blocking of a strong need may cause 
a field to be so grossly distorted, as in the 
delusions of mental disorders, that it no 
longer bears any resemblance to the situa- 
tion. Tension increased beyond a critical 
point results in a failure of adjustment of 
the organism to the requirements of the sit- 
uation. These facts have suggested the fruit- 
fulness of a concept of frustration tolerance, 
which has been defined as the amount of 
frustration xuhich can be borne without a 
resultant failure in psychobiological ad- 
justment. The frustration tolerance of an 
individual is, then, his capacity to stand 
frustration without distorting his field so 
that it no longer bears a valid resemblance 
to the real situation. 

The frustration tolerance of an individ- 

ual is exceeded in all cases in which the 
increased tension resulting from frustration 
causes the individual to react inadequately 
to the situation. If, instead of modifying 
his behavior in such a way as to effect a 
satisfaction of his frustrated needs, he re- 
acts with crying, temper tantrums, regres- 
sion to more primitive behavior or a break- 
down of the personality in any of the vari- 
ous forms of mental disorder, the individ- 
ual's tolerance for frustration has clearly 
been exceeded. 

Just as there is a point beyond which the 
primary needs— for example, the need for 
oxygen— cannot be denied satisfaction with- 
out a collapse of the organism, so there is 
also a point beyond which the secondary 
needs— for example, the need for freedom— 
cannot be frustrated without a breakdown 
of the individual. One of the important 
problems of psychology is to discover the 
conditions which determine not only the 
general frustration tolerance of the individ- 
ual but also his specific tolerance for the 
frustration of different needs. 


The terms with which we characterize 
persons are often merely short statements 
about the need or needs which most often, 
or at least most obviously, motivate them. 
When we say of a man, "He is a show-off," 
we are, in eff^ect, saying that he has a strong 
need for attention; and, when we say of 
another, "He's a go-getter," we are recog- 
nizing in him a strong need for superiority. 
Such characterizations point to the fact, 
which we have already noted, that not all 
the needs of an individual are equally 
strong, and that the differences among per- 
sons are at least in part determined by dif 

Individual Differences in Needs 


I'erences in the relative strengths of iheir 

Other differences in personality are de- 
termined by differences in the relationships 
ol needs. It is important to know wiiich 
ol' an individual's needs are regularly acti- 
vated in the service of other more impor- 
tant needs. An individual may be mo- 
tivated to collect rare antiques in order 
that he may show them off to his friends 
and thus gain a satisfaction of his needs 
lor attention and superiority. If, however, 
he does not have the money with which to 
buy expensive antiques, he may be mo- 
tivated to gain his goals of attention and 
superiority in some other way, perhaps by 
developing and exhibiting athletic skill. 
We may find at different times different 
particular needs serving the dominant need 
of a given individual. We know, however, 
a great deal about a person if we know, 
over a period of time, which needs pri- 
marily determine his behavior and which 
needs are more or less consistently subsid- 
iary to these dominant needs. An impor- 
tant difference among persons occurs in re- 
spect of the subsidiary relationships which 
exist among their needs. One man may 
gain his superiority by cruelty to his sub- 
ordinates; another man may gain his su- 
periority by generosity to his subordinates 
Both may get what they want— importance, 
recognition, prestige. 

There are varying degrees with which 
one may be consciously aware of his own 
needs. At one extreme, a man may have 
no awareness at all of what he wants. He 
may not even be aware of any tension or 
uneasiness. At the other extreme, a man 
may know precisely what it is he is after. 
An intermediate degree of awareness is the 
case where a person recognizes that some- 
thing is lacking, that he is uneasy and dis- 
satisfied, and yet he cannot say exactly 

what it is he wants. No one is aware of 
all his needs at all times, but some persons 
have much more insight than others into 
their basic motivations. 

A need may fail to be recognized berausc 
it is relatively weak in comparison with 
other needs, which for the moment domi- 
nate the consciousness and behavior of the 
individual. More important in its conse- 
quences for the personality, however, is the 
failure of a person to recogni/e a need be- 
cause it is in conflict with his consciously 
recognized and accepted needs. 

The consciously recognized and accepted 
needs of the person are often called his 
ego needs, since the ego is defined as that 
part of the person which is consciously 
knowing, desiring and willing. Needs 
which are recognized as one's own and for 
the satisfaction of which one takes respon- 
sibility are ego needs. Ideals which a man 
consciously sets for himself and for which 
he strives are ego ideals. The ego is an im- 
portant factor in motivation. The need or 
needs which are most important to the ego 
are those which most clearly distinguish 
one person from another. They are the 
more enduring needs of the ego; yet needs, 
which at one time are central to the ego, 
absorbing all its energies, may at other 
times become quite unimportant. 

In general, needs -ivhich are smoothly 
and silently satisfied do not in\ol\e the 
ego. Though die need for oxygen is one 
of man's most vital needs, the satisfaction 
of it does not involve his ego, since air is 
free and he ordinarily gets all he wants of 
it unconsciously and automatically. But, 
if air were not free, if getting it depended 
upon the cooperation of others or if one 
had to compete for it, the need for oxygen 
would become an ego need as the needs for 
sex, affection, recognition, superiority so 
often are. 



Many of the effects o£ residual need ten- 
sion described earlier in this chapter are 
more pronounced when they derive from 
ego needs, and, in tlie absence of ego in- 
volvement, they may not be observed at all. 
Interrupted tasks, for example, are more 
often resumed and better remembered than 
completed ones only if the tasks which 
have been undertaken have really involved 
the ego. 

The typical shifts in a person's level of 
aspiration in attempting to solve tasks of 
\arying degrees of difficulty, the raising of 
the level of his aspiration after success and 
the lowering of it after failure, occur most 
strikingly for those tasks in which a person 
is deeply egoistically involved. If the same 
set of tasks is given twice to the same per- 
sons, once as 'practice' and once as 'a 
test,' the shifting of the level of aspiration 
—up after success and down after failure- 
is greater when the tasks are understood to 
be a test measuring the ability of the indi- 
vidual and not merely practice. In other 
words, if, when setting our level of aspira- 
tion, there is something at stake for our 
ego, we behave more cautiously. 

Other experiments as well as observa- 
tions of everyday behavior suggest that ego 
motivation tends to be strong motivation. 
Ego needs are frequently selfish needs, but 
not always. "Whether they are or not de- 
pends upon the person, for in so far as a 
person identifies himself with others and 
experiences their needs as his own, his mo- 
tivation ceases to be narrowly egocentric, 
becoming instead sociocentric. Such com- 
mon sociocentric motivation characterizes 
all successfully integrated groups which are 
held together by mutual loyalty— from the 
wedded pair up through many kinds of so- 
cial groups to the nation itself. Those per- 
sons who liopc for the democratization of 

the world ancl the achie\cmcnL of interna- 
tional peace base their aspiration on this 
possibility of combatting egocentric aggres- 
sion with this sociocentric identification. 
(For more on the ego, see pp. 567-570.) 


1. Katz, D. Anunals and men. New Voik: Long- 
mans, Green, 1937. 

A provocative discussion of problems of com- 
parative psychology based upon the author's in- 
genious observations and experiments. 

2. Kinsey, A. C, Pomeroy, W. B., Martin, C. E. 
Sexual behavior in Ihc liunian male. Phila- 
delphia: Saunders, 1948. 

A scientific account of sexual behavior writ- 
ten by leading authorities on the subject, from 
the point of vie^^' of biology, psychology and 

3. Klineberg. O. Race differences. New 'S'ork: 
Harper, 1935. 

A clear and simple survey of the findings of 
the biological, psychological and cultural ap- 
proaches to the problem of race differences. 

4. Kohler, W. The mentality of apes. New York: 
Harcourt, Brace, 1925. 

A Gestalt psychologist's report on the behav- 
ior of chimpanzees and the role of insight and 
intelligence in their solution of detour prob- 

5. Lewin, K. A dynamic theory of personality. 
New York: McGraw-Hill, 1935. 

The beginnings of this author's dynamic psy- 
chology as illustrated in his early theoretical 
discussions and experimental findings. 

6. Mead, M. Sex and temperament in three prim- 
itive societies. New York: William Morrow, 

An anthropologist's report of differences in 
culture and personality in three geographically 
closely situated primitive societies. 

7. Muenzinger, K. V. Psychology: the science of 
behavior. New York: Harper, 1942. 

A systematic introductory text in psychology 
which gives a central position to the concept of 



8. Murray, H. A., «/ «i. Explorations in per- 
sonality. New York: Oxfoid University Press, 

'Die fiii(lin)>s ol ;i (liiiic;il ;iii(l ex|jci inienliil 
study of fifty men ol rolle^c a^e |)reseiilecl in 
conjmiclion with a dynamic Ihcory o( per- 

9. Sharif, M. Tlie psychulo<^\ of social norms. 
New Yorlc: Harper, 1936. 

A clear and simple discussion of the ways 
in which individual frames of reference of ex- 
perience and social norms of behavior become 

10. VVarflcn, C. J.: Animal motivation. Sew V'ork: 
Columbia I'niversity Press, IO.?l. 

Siiidies of various drives in the uhirc rat by 
nif.ins of llic obsiruflion mcltiod. 

11. ^oMrjj;, I', 1. 'Ilir iii'itiralion of hehai'ior. 
New Vork: Wiley, 1936. 

A comprehensive review, presented in text- 
book form, of experimental investigations of 
the motivational ijases of behavior. 

12. Young, P. T. Emotion in man and animal. 
New York: Wiley, 1943. 

A comprehensive review of experimental 
studies of emotion which stresses the role of 
emotions as motivatiiif' factors in behavior. 




OUR ability to profit from past experi- 
ence is one of our most valuable as- 
sets. Learning— the process by which we do 
this— is the subject of this chapter. In it we 
shall analyze the conditions under which 
learning takes place. We shall discover 
that the same principles which account for 
our learning of desirable and appropriate 
reactions also explain our acquiring of un- 
ilesirable bad habits. 

We can best appreciate the important 
role which learning plays in our lives if we 
recall what a limited repertoire of re- 
sponses a human infant possesses at birth. 
As we have seen, all learning depends upon 
maturation, which fits the organism for 
learning. On the other hand, all the in- 
crease in capacity and complexity which 
cliaracterizes mature adult behavior must 
be attributed to learning. We learn, for 
instance, to eat the things we eat in the 
way we eat them, to respond as we do to 
other people and— the crowning achieve- 
ment of the human being— to use language. 
We learn not only to use language for com- 
munication but to use it also to satisfy our 
needs and to control the behavior of other 
people. Nor is learning only intellectual. 
Likes and dislikes, emotional responses, 
most of the complex pattern of reactions 
which we call personality, all are learned. 
Most of this learning occurs informally in 

the give and take of daily life, for learning 
is by no means always intentional or 

The very fact that learning is so per\'asive 
and bound into the warp and woof of our 
daily lives results in the process going al- 
most unremarked. When we notice it at 
all, Ave think of it in rough, unanalytic 
terms; but, if we seek to understand it and 
its principles, detailed analysis is essential. 
As a consequence, much of our understand- 
ing of learning behavior is derived from 
controlled laboratory experiments. The 
careful laboratory analysis of learning re- 
quires the use of materials, methods and 
concepts which at first appear to be strange 
and divorced from the learning of every- 
day life. Nevertheless, learning in the lab- 
oratory is really the same in kind as the 
learning which pervades evei^day life. 
What the laboratory does is simply to pro- 
vide a better situation for analyzing the 
learning process. 


Learning varies greatly in complexity. 
We shall begin oiu- analysis with a very 
simple type, associative learning, which 
consists of the formation of associations be- 
tween responses and the stimuli which are 
present when those responses are made. 

This chapter was prepared by Carl I. Hovland of Yale University. 




Assoriatiun is a toinmoii phenomenon, ex- 
emplified by our 'being reminded ol' an ex- 
jjeriente by stimuli wlii<li were present 
durinf^ the experienee. Tlie odor of a burn- 
ing wood fire may lecall a Cinistmas vaca- 
tion in the north woods, or magnolia blos- 
soms may remind us of a (hildhood trip 
to the Soutli. Often, l)ut l)y no means al- 
ways, wc have been aware of lliese stinudi 
in the oiiginal situation of which we are 
now reminded. 

Ihis phenomenon has, oE course, been 
known lor a long time, and philosophers 
lor two centuries have called attention to 
the "association of ideas." Careful study 
of the conditions under which stimuli and 
responses are associated is, however, much 
more recent. It really begins about 1903 
with the work of Pavlov, which we have al- 
ready noted in a previous chapter. Pavlov, 
while studying problems in the physiology 
of digestion, made the observation that ani- 
mals salivate not only to food but also in 
response to the various stimuli which in 
their experience invariably precede the in- 
troduction of food, like the clicking of a 
food release mechanism. Salivation to 
stimidi of this type, which were not orig- 
inally effective, he called "psychic secre- 


I'his phenomenon fascinated Pavlov, 
and as a consequence he devised a series 
of experiments to determine the conditions 
inider which it occurred. Mostly he used 
dogs as the experimental animals. He 
chose the salivary response for study be- 
cause it provided a sensitive measure of 
the magnitude of response. (See Fig. 45.) 
He performed a simple surgical operation 
by which the flow of sali\'a from the dog's 
jowl is transmitted through a glass tubing 
to a measuring instrument. 

To establish a connection between a re- 
sponse, like salivation, and an initially in- 
effective stimulus, like the sounding of a 
buzzer, Pavlov found that it was essential 
to pair the presentation of the new stimu- 
lus with the one which was originally ef- 
fective. I'or example, he would sound the 
buzzer at the time he presented the food to 


The unconditioned stimulus (food) is presented 
automatically in the small dish through the win- 
dow. At the same time, or earlier, the conditioned 
stimulus (the ringing of a hell) is given. The saliva 
which flows through a tuhe from the dog's jowl is 
collected in the graduated class receptacle. As the 
saHva flows into the receptacle, it strikes a small 
disk which depresses the lever just in fiont of the 
animal. This downward movement is transmitted 
to the lever behind the screen, and an automatic 
tracing is thus secured upon a smoked drum or 
kymograph. The kvmographic record tells the ex- 
perimenter how many drops of saliva have been 
secreted and how regular the flow has been. [From 
R. M. Yerkes and S. Morgulis, The method of Pav- 
lov in animal psvchologv, Psychol. Bull., 1909. 6, 

the dog. or just before. The response 
which ^vas thus learned he called a condi- 
tioned response because it was dependent 
upon conditions. The process is still re- 
ferred to as conditioning. The stimulus 
which originally produced die response A\as 
called the unconditioned stimulus, and tlie 
new one -with which the response was be- 
ing connected bv conditioning was called 



the conditioned sdiniilus. In Pavlo\ 's lab- 
oratory food Avas customarily the original 
stimulus, and the sound of a bell or buzzer, 
the conditioned stimulus. After a nimiber 
of trials the sound of the buzzer alone elic- 
ited some secretion of saliva. \Vith more 
trials the amoimt of saliva secreted for the 
buzzer alone would increase until it finally 
became nearly as great as to the sight of 
food itself. 

We can diagram this process c^uite 

Before Conditioning 

Conditioned Stimulus 

Buzzer > Listening, etc 

Unconditioned Stimulus 
Sight of Food — ♦ Salivation 

After Conditioning 

Conditioned Stimulus 

Buzzer , 

Unconditioned Stimulus i 

At an earlier period of time, when the 
dog was a tiny puppy, the response of sali- 
vating to the sight of food was established 
through conditioning. Food in the mouth 
was at that time the unconditioned stimu- 
lus. This initial conditioning would be 
diagiammed as follows. 

Before Conditioning 

Conditioned Stimulus 

Sight of Food * Looking at 

it, etc. 

Unconditioned Stimulus 
Food in Mouth — ♦ Salivation 

After Conditioning 

Conditioned Stimulus 
Sight of Food 

Uncondition-ed Stimulus 

Food in Mouth — > Salivation 

Factors AfFecting Conditioning 

Pavlov and his students kept careful rec- 
ords of some of the factors influencing the 
association formed between the condi- 
tioned and unconditioned response. These 
relationships have been further studied in 
American laboratories so that today we 
know a great deal about the phenomena of 
conditioning. Some of the more impor- 
tant conclusions follow. 

(1) Acquisition. Repetition of the pair- 
ing of the conditioned and unconditioned 
stimuli increases the strength of the con- 
nection until a point is reached where no 
further observable gain is obtained. A 
sample acquisition curve is shown in Fig. 
46. These results correspond to our every- 
day experience that learning is favored by 


Sight of Food — ► Salivation ~ 

6 8 10 12 14 16 

Units of training 


Composite curve of the data from four clop;s. [As 
given by N. Kleitman and G. Crisler. and plotted 
by C. L. Hull in Handbook of general experimental 
psychology, 1934, p. 425; by permission of the Clark 
University Press.] 

(2) Time faclors. There is an optimal 
time between the presentation of the con- 
ditioned and unconditioned stimuli, and 
time intervals more remote from the latter 
are progressively less effective. The graph 
(Fig. 47) shows the percentage of condition- 
ing at each of several different time inter- 
vals between the conditioned and uncon- 
ditioned stimuli. The unconditioned stim- 
ulus in this experiment was an electric 
shock which produced finger withdrawal, 
and the conditioned stimulus was a sound 
signal which initially produced no finger 
response. In this case the optimal time 
interval was that in which the conditioned 



stimiiliis was presented about a half -second 
before the unconditioned stinndus. I'lie 
situation in wiiich the conditioned stinndus 
comes after the unconditioned stimulus 

witJi a pitch corresponding^ to 1000 cycles 
per second, the j^reatest response will \}e 
made to this Irefjuency, a smaller response 
to a frefjuency ol 800 cycles, and a still 

(called backward rnndilioninii) produced smaller response to 600 cycles. Fif^ure 48 

presents an experimentally derived curve 
of generalization. 

(4) Differentiation. As learning pro 
ceeds, the range of stimidi which touch oil 
ihe ccjnditioned response becomes jjrcjgres- 
sively reduced. This process is called 
differentiation. Thus after a while the 

O ^ -H ^ 

Number of seconds by which 
conditioned stimulus preceded 


Graph shows greatest efficiency when conditioned 
stimulus precedes unconditioned stimulus by halt 
a second. Negative times means that the uncondi- 
tioned stimulus precedes the conditioned stimulus. 
[After H. M. Wolfle, from C. L. Hull in Handbooli 
of general experimental psy etiology, 1934, p. 420; 
by permission of the Clark University Press.] 

soine learning, but it was not nearly so 
effective as the situation where the condi- 
tioned stimtdus was presented before the 
unconditioned stimulus. 

(3) Stimulus generalization. In the ini- 
tial phases of learning, the organism re- 



Shows amount of galvanic skin response, after 
conditioning to various standard tonal stimuli (0 in 
the graph), that is given for other tones removed 
from these standards by 25, 50 and 75 just dis- 

sponds not only to the exact conditioned criminable differences (represented by 1.2 and 3 in 

stimulus used in the original learning but S'^'P^^- [J"™'" C. I. Ho^land, /. geu. Ps,c},ot., 1937, 

r .,..., * , 17, 136.] 
also to a variety of stimuli similar to the 

one used. The response is generally great- animal conditioned to a tone of 1000 cycles 

est to tlie conditioned stimulus and pro- „o longer responds to tones of 600 or 800 

gressively less to stimuli more and more cycles, but onh- to those nearer 1000 cvcles. 

dissimilar to the one originally used. If, for By giving food simultaneously with the 

example, the conditioned stimulus is a tone conditioned stimulus and not giving food 



with any other stimukis, you can finally 
produce very fine discrimination so that, 
for example, an animal will salivate to a 
tone of 1000 cycles but not to one of 1002 
cycles. If you press discrimination too far, 
however, differentiation is broken down 
and disruption of behavior occurs, produc- 
ing sometimes a pattern of nervous irrita- 

Extinction trials 


Diminution of response in successive trials with- 
out reinforcement. Response is plotted as per cent 
of the response in the first trial. [From C. I. Hov- 
l:nid, Proc. Nat. Acad. Sci., 1936, 22, 431.] 

bility which has been called 'experimental 
neurosis.' (See pp. 526 f.) 

(.5) External inhibition. When stimuli 
other than those used in the conditioning 
are presented simidtaneously with or just 
before the conditioned stimulus, they fre- 
quently serve to reduce the size of the re- 
sponse to the conditioned stimulus. Pav- 
lov's students often found that, having set 
up a conditioned response in a dog, they 
could not exhibit it to Pavlov becatise his 
presence in the room inhibited it. This 
phenomenon is called external inhibition. 
We notice an analogous phenomenon in 
more complex types of behavior. For ex- 
ample, recently acquired acts of skill may 

be disintegrated by a distraction. When 
one has jtist mastered a difficult passage on 
the piano, the appearance of a stranger 
may prevent its execution. 

(6) Extinction. Just as repetition of the 
pairing of the conditioned stimulus and 
the unconditioned stimulus strengthens the 
connection, presentation of the conditioned 
stimulus without its being followed by the 
tuiconditioned stimulus resiUts in a pro- 
gressive diminution of the response. The 
dog no longer salivates at the sound of the 
bell after the bell has been rung a certain 
number of times without food following it. 
The size of response on successive trials of 
this type is shown in Fig. 49. These lab- 
oratory extinctions of conditioned re- 
sponses are, however, not necessarily per- 
manent. A response that has been 'extin- 
guished' may recur later, a phenomenon 
called spontaneous recovery. 

(7) Higlier order co)iditioning. We have 
seen how Pavlov chose as his unconditioned 
response the production of salivation in a 
dog by the dog's sight of food. We have 
remarked how this 'unconditioned re- 
sponse' is itself a conditioned response, for 
it had to be learned by the dog when a 
puppy. The original tuiconditioned re- 
sponse was the production of salivation by 
the feel and taste of food in the dog's 
motith. That response was inherited and 
developed early in the course of mattira- 
tion. Then, by conditioning, the sight of 
food was substituted for the feel and taste 
of food. Pavlov's substituting the sound 
of the buzzer for the sight of the food 
was conditioning at a second level. When 
conditioning is established to a new stimu- 
lus on the basis of a previously conditioned 
stimulus, we have what is called higlier or- 
der conditioning. It is an extremely im- 
portant aspect of conditioning in human 
beings because it permits learning by asso- 



(iation to stimuli more and more remote 
Irom the one that was biologically ade(|uate 
initially. Pavlov did find, however, that 
the farther this process is carried the more 
difficult the process of conditioning be- 
' comes. 

Other investigators have studied a wide 
variety of stimuli and responses but have 
in the main supported Pavlov's original 
findings. Bechterev, a Russian neurologist 
who was a contemporary of Pavlov, de- 
voted most of his studies to a type of con- 
ditioning called conditioned withdraival in 
which a noxious stimulus producing with- 
drawal is used as the unconditioned stimu- 

Before Conditioning 

Cnndilioned Stimulus 

Buzzer ' Listening, etc. 

Unconditioned Stimulus 
Shock to 

Forepaw — + Withdrawal of 

After CoNDiTioNiNt; 

Conditioned Stimulus 

Buzzer . 

Unconditioned Stimulus 
Shocli to I 

Forepaw — * Withdrawal of 

In other respects his experimental tech- 
nicjue was essentially the same as Pavlov's, 
and it has been the method most widely 
used in America. 

Conditioned Emotional Responses 

The simple conditioned responses have 
been studied with care in the laboratory, 
but they are by no means just a laboratory 
phenomenon. They are a type of learn- 
ing that we see all around us. Language 
is acquired to a large extent through this 
means. The infant has in his repertoire of 
responses a large number of random sounds. 
The selection of the appropriate sounds to 
signify objects and events is largely deter- 
mined by adult behavior. When the child 
utters a meaningless sound, no consistent 
reaction on the parents' part is likely to 
ensue, and Ikih c no learning occurs. Hut 

when a meaningful or near-meaningful 
sound is made, the adult repeats the sound 
after the (hild and may give the child tlic 
objed named. In that way conditions arc 
established for the child's learning the 
word. Vou have perhaps observed the Ih:- 
havior of a fond father when his child 
liajipens to say a word like "ted-di." The 
father repeats the sound after the child 
and hands him the teddy-bear. After a lew 
trials the child will say "ted-di" when he 
wants it given to him. (F'or a fuller ac- 
count of the acquisition of language, see 
pp. 594 1.) 

We know from a previous discussion 
(pp. 101 f.) how experiments by Watson 
on infants showed that fears can be estab- 
lished by conditioning. It is well to re- 
peat in more detail the observations of 
his experiments. He found, first of all, 
that a neutral object could be made fright- 
ening by the conditioning technicjue. The 
striking of a steel bar near the baby's ear 
originally elicited a strong fear response. 
He used this noise as the unconditioned 
stimulus. For a conditioned stimulus he 
used a white rat of which the child was 
initially not at all afraid. Then the white 
rat was shown to the child, and just as 
he reached for it the bar was struck. The 
child responded with symptoms of fear. 
This procedure was repeated several times. 
Presently the child showed fear of the pre- 
viously neutral white rat. It was also afraid 
of a rabbit, a fur coat and even of cotton 
wool (generalization), but it did not fear 
building blocks (differentiation). Repeated 
exposure to the rat giadually reduced the 
fear when it was not followed by the sound 
of the struck steel bai- (extinction). 

A vast amount of clinical material indi- 
cates that many of the adult intense feai-s 
of objects and places {pliobias) arc trace- 
alilc to an unfortunate pairing of a stiinu- 



lus with an unpleasant experience. Often 
the person is unable to recall the specific 
conditioning experience which is, never- 
theless, affecting him. Characteristically, 
such a fear response is generalized to in- 
clude similar stimuli so that the affected 
person comes to fear a whole class of ob- 
jects. Sometimes, but not often, such a 
phobia can be removed by extinction, once 
the relevant stimulus is discovered and iso- 

Anticipatory Function of 
Conditioned Responses 

Although it is typical of conditioning 
that a new stimulus, becoming attached 
to a given response, has the power to call 
it forth, there is more to conditioning than 
this new stimulus-response connection. As 
the connection becomes established, the re- 
sponse to the conditioned stimulus occurs 
before the unconditioned stimulus. Sali- 
vation takes place before the food is eaten, 
the knee jerks before the hammer falls 
against the patellar tendon, the eyewink 
occurs before the puff of air strikes the eye- 
ball, the finger is removed from the elec- 
trode before the shock is received. It will 
be recognized that here the conditioned 
response anticipates the unconditioned 
stimulus and in many cases prevents its 

This anticipatory character of the condi- 
tioned response pervades all learning. We 
are able, because of having learned, to re- 
spond in a way which looks to the future. 
We can learn to a\oid harmfid stimidi be- 
fore they strike the sense organs. The 
child, once burned, avoids the stove. The 
cow, having been strongly shocked at the 
electric fence, never goes near it again. The 
results of such learning pyramid greatly. 
The word danger may be enough to warn 
us from a region where noxious stimidi arc 

probable. Words of all kinds accjuire the 
power to guide behavior anticipatorily. 
From the simplest forms of learning to the 
most complex, this anticipatory fimction, 
whereby we prepare for the future, is con- 

The Law of Contiguity 

From the studies of conditioning, certain 
authors have formidated what they believe 
to be a basic law of learning, the law of 
contiguity, which states that, when tu'o 
psycliological processes occur together in 
time or in immediate succession, the prob- 
ability increases that an associative con- 
nection between them will dex'elop. It 
seems clear that no learning takes place 
without fairly close psychological contigu- 
ity between the terms related in the learn- 
ing. The extent to which this principle 
must be supplemented by others, especially 
by motivation, is a matter to wliich we 
shall come presently. 


Not all learning, however, is as simple 
as the conditioned response. More fre- 
quently our task is to learn complex se- 
quences of responses or to select the correct 
response from a whole category of possible 

A good example of this type of learning is 
illustrated by an experiment of Thorn- 
dike's. A hungry cat is placed in a cage, 
called a problem box, with a small piece 
of fish lying just outside (Fig. 50). The 
box is designed in such a way that the door 
of the cage can be released by some simple 
act like depressing a lever inside the cage. 
At first we see a great deal of varied activity 
on the part of the cat: clawing at the wire, 
trying to squeeze between the bars, pawing 
and shaking movable parts of the appa- 

Trial-and-Error Learning 


ratiis. Such activity is ollcn described as 
random or trial-and-error. Alter a time 
tlie animal succeeds in operating the lever 
i)y accident, and gets out. It is tlien al- 
lowed to cat a bit ol the fish and is imme- 
diately returned to the box for another 
Irial. The second trial may not differ 
much from the hrst with useless activity 
persisting until the cat happens again to 
operate the lever; but usually the time on 
the second trial is shorter than on the first, 
and on successive trials both the time and 
useless movements decrease until after 
enough practice the cat goes immediately 
to the lever and lets itself out. The course 
of its learning is not, of course, smooth and 
regular. On a trial after one in which it 
has performed the correct response quickly, 
it may go through so much trial-and-error 
activity that it would appear that it had 
not made any progress at all. With exten- 
sive practice, however, the cat makes the 
correct response directly with a minimum 
of activity iiTelevant to the business of 
escaping from the box. It is interesting, 
nevertheless, to note instances in which 
escape is achieved by some clumsy maneuver 
which actually does release the animal. 
Often such clumsy behavior, having been 
successful, is continued, despite its ineffi- 
ciency. On the other hand, if it is fati- 
guing or inconvenient, it may later be re- 
placed by some more appropriate act. 

It is not correct to say that the cat 'un- 
derstands' wliy pressing the bar releases 
him. Thorndike found that causally ir- 
relevant acts can be taught as the means 
of securing escape from the box, as when he 
taught cats to get out of the box by scratch- 
ing themselves. Thorndike released the 
door as soon as the cat scratched himself, 
and befoie long the cat had learned to 
scratch itself immediately to escape from 
the box. 

The animal's behavior sequence in the 
problem box situation may be analyzed 
into four basic elements: response, stimu- 
lus, motive and reward. 

(I) Response. This is the center of ref- 
erence in learning since the biological use 
of all learning is the making of new re- 
sponses in new situations. The response 


[From H. E. Ganett, deal experiments in piy- 
chology, Appleton-Century, 1930, p. 107.] 

may be simple or it may be a complex 
sequence. It must be one which the learner 
is able to perform. In Thorndike's experi- 
inent pushing the lever was a response the 
cat could make. If Thorndike had required 
the animal to insert a key in a lock to get 
out, the learning would not haAC occurred 
since cats cannot turn keys in locks. 

(2) Stimulus. This is the causal factor 
which becomes associated with the response 
during learning and so becomes capable 
of evoking the response. There is initially 
a multiplicity of stimuli to whicli the 
learner is responsive, but die range becomes 
narrowed with learning. In Thorndike's 
experiment the cat originally looked about, 
sniffed and explored a host of stimuli. 



With a high degree of learning, however, 
the cat singled out the essential stimulus 
of the lever and reacted to it alone. 

(3) Motive. Although some learning oc- 
curs without obvious desire or intent to 
learn, it is true nevertheless that all learn- 
ing depends on the individual's motives. 
They may be simple, like a need for food 
or a need to avoid the light, or they may 
be more complex, like a need to gain self- 
approval, the approval of others or to avoid 
criticism. Thorndike always used hungry 
cats. If animals are satiated (and hence 
without motive), learning does not occur. 

(4) Reumvd. One generally learns those 
responses which are rewarded, the responses 
which lead to the satisfaction of motives. 
Often the rewards are not obvious, since 
they may consist of such things as self- 
approval, or the relief from anxiety or 
worry associated with fear of criticism or 
jnmishment. If Thorndike had not al- 
lowed his cats to get out of the box and 
cat the food after making the correct re- 
sponses, if he had not rewarded tliem, they 
never would have learned how to get out. 

Using these terms, we can describe trial- 
and-error behavior in simplest form as fol- 

(1) The learner has a inotive (in the 
case of the cat, to get out of the box and 
obtain food). 

(2) The motive leads to varied types of 
activity in which the learner tries succes- 
sively various responses in its behavior 
repertoire, beginning with the one which 
is most strongly established and then, suc- 
cessively, responses which are less and less 
well established. 

(3) Some of these responses ultimately 
lead to a reivard which satisfies the motive. 

(4) The responses which lead to the re- 
ward become more strongly established 
(l)ettcr learned) as a result of tlic satisfac- 

tion of the motive, being made more and 
more certainly on subsequent trials when 
the same stimulus situation is present. 

(5) Responses not leading to -the satis- 
faction of the motive tend to be eliminated 
after repeated trials. 

Thus we see that trial-and-error behavior 
is regular and predictable in that it de- 
pends upon the motives of the leainer and 
the responses in his repertory of behaviors. 
Such learning is random only in the sense 
that the learner has a problem to solve and 
cannot solve it by insight or foresight. He 
has to test out possible actions by random 
behavior until he hits upon the one that 
brings success. Then success succeeds. It 
would really be better to speak of this kind 
of learning as Irial-and-surcess, for the er- 
rors retard learning, whereas success is 
what establishes it finally. 

In Irinl-nnd-error learning we (ind again 
all tlie characteristics which belong to as- 
sociative learning. When a subject has 
learned by trial and error a response which 
leads to a reward, the omission of the re- 
ward results in the gradual disappearance 
of the Yt^pon?,e— extinction. An extin- 
guished habit may, however, reappear after 
the passage of Um&— spontaneous recovery. 
Situations similar to the one in which the 
original learning took place will also elicit 
the newly learned behavior and, the more 
similar the situation to the original, the 
greater the transfer of learning to it. That 
is generalization. If, however, reward is 
not forthcoming in the new situation, the 
generalized response will presently be ex- 
tinguished, while the primary rewarded 
response continues. That is differentiation. 
Last, time relations are as critical for trial- 
and-error learning as for associative learn- 
ing. The shorter the interval between the 
response and the reward, tlic greater the 
strengtliening of llic responsf. 

The Law of Effect 


The Law of Effect 

The inijiortanL principle whirh emerges 
Irom our discussion ol irial-ancl-error learn- 
ing is the importance of reward in fixating 
learning. This result is so universally ob- 
tained that it has become a law of learn- 
ing, the laxv of efject. The name stresses 
the importance of the effect or consequence 
of an act on its acquisition. This law was 
first formulated by Thorndike in terms of 
the satisfaction or dissatisfaction which hal- 
lows ihe making of a given response. He 
said: "When a modifiable connection be- 
tween a situation and response is made and 
is accompanied or followed by a satisfy- 
ing state of affairs, that connection's 
strength is increased. When made and ac- 
companied or followed by an annoying 
state of affairs, its strength is decreased." 

The terms satisfying state and annoying 
slate were defined by him as follows: "By 
a satisfying state of affairs is meant one 
Avhich the animal does nothing to avoid, 
often doing things which maintain or re- 
new it. By an annoying state of affairs is 
meant one which the animal does nothing 
to preserve, often doing things which put 
an end to it." 

Learning and 'satisfaction' are so closely 
related that it is difficult to measure satis- 
faction independently of learning; but that 
difficulty can be avoided if we discover what 
is satisfying or rewarding in one situation 
and then apply this knowledge in predict- 
ing the strengthening of other stimulus- 
response connections. If a certain kind of 
food is an efl^ective reward for learning one 
task, it can be used to induce the learning 
of other tasks. 

Experiments have established the gener- 
alization that the greater the reward, the 
more it facilitates learning. This rule is 
closely related to what has been called by 

'WunwiWkv ihe law of intensity. Ail evi- 
dence points to the fact that the greater 
tlie si/c of the reward, the stronger the mo- 
tivation; and the stronger the inotivation, 
tfie faster and surer the Icarrn'ng. (See 
p. 129.) 

As we have already seen, the time inter- 
\al between the response and the reward 

I I I I I M I M I I I I I I 

I I i I I I I I I I I I I I I I I 

20 18 16 14 12 10 8 6 4 
Minutes of delay in reinforcement 



The circles siiow the amount of learning for con- 
stant numbers of reinforcements plotted as a func- 
tion of the delay in the occurrence of the reinforce- 
ment. [From data published by J. B. \VoIfe, and 
plotted by C. L. Hidl, Principles of behavior, 
Appleton-Century, 1943, p. 137.] 

is an important factor to consider in pic- 
dicting the effect of reward. The strength 
of learning is greater, the shorter the time 
between the response and the reward. 
Thorndike said: "The closeness of connec- 
tion between the satisfying state of affairs 
and the bond it affects may be due to close 
temporal sequence. Other things being 
equal, the same degiee of satisfvingness will 
act more strongly on a bond made two sec- 
onds previously than on one made tv.o 
minutes previously." Verification of Thorn- 
dike's principle is shown in Fig. 51. Eight 
groups of white rats learned to find food 
in a simple maze ^vith varving delavs be- 
tween the correct choice and the food. A 



clear tendency is seen lor learning to be 
most efficient when a short time elapses 
between the response and the reward. 

These results have considerable impor- 
tance in practical learning situations, par- 
ticularly in child training. Very often 
too long a period is allowed to elapse be- 
tween the act which a parent is attempting 
to strengthen or weaken and the reward 
or punishment. If the time is much too 
long, the reward or punishment may even 
get attached to the incorrect act merely 
because it has immediately preceded the 
reward or punishment. 


Now that it is clear that the concepts of 
learning and motivation cannot be disso- 

I I I I I I M I I I M I I M 
"" ^^i^ Less hungry rewarded 
~ v^-^ >rLess hungry nonrewarded- 


2 4 6 8 10 12 14 16 18 


[From E. C. Tolman and E. H. Honzik, University 
of California Publications in Psychology, 1930, 4, 

ciated, let us examine their relationship in 
greater detail. 

As we have seen in the preceding chapter, 
motives are forces which impel to action, 
and the simplest are physiological, like 
thirst, hunger and pain. They are the mo- 

tives most frequently used in laboratory 
experiments on animal learning because 
they are most universal and easy to con- 
trol. In human learning, however, much 
more complex motives are usually in- 
volved, motives which are derived from 
the simple ones. Desire for prestige, money, 
approval, all such motives are built upon 
earlier simpler ones. 

Rewards may be thought of as e\'euls 
which satisfy motives. Thus in Thorn- 
dike's problem-box experiment the reward 
was food which reduced the cat's hunger 
drive. When an experimenter controls 
strength of motive by controlling amount 
of reward, it is not necessary for us to dis- 
tinguish between motive and reward. On 
the other hand, motive and reward can vary 
separately. The following experiment 
shows the relationship between the two. 

Rats were taught to follow a complex 
pattern of runs and turns through a maze 
to reach food. One group of rats was not 
hungry and was not given any food at the 
end of a trial; a second group was hungry 
but was not given food; the third was 
hungry and given food at the end of a trial. 
The results are shown in Fig. 52. Only 
the group that was hungry (had a motive) 
and was given food (was rewarded) learned 
appreciably. To be motivated and unre- 
warded is to have before you nothing 
worth learning. Nor is it worth while to 
work for a prize you do not want. It is 
the motive that gives the reward its value, 
and the satisfaction of reward that fixes 
the learning of which it is the effect. 

Motivation is equally important in hu- 
man learning, but here the motives are not 
usually the simple physiological needs. 
There is no doubt that human beings learn 
effectively when motivated by primary 
drives like hunger, thirst or pain, but these 
drives are rarely intense in present-day life. 

The Effect of Motivation and Practice 


The motives which ;ire involved are what 
ai'c called learned or deriwid motives. 'I hat 
is to say, they liave been associated with 
the biological needs and now operate in 
che same way as the original needs (pp. 
121 I.). An anxious parent praises a 
stubborn child every time it takes a spoon- 
lul oi Icjod. Eventually the child, even 
though not feeling hungry, will eat merely 
(o obtain the reward of its ])arent's praise 
or approval. 

The way these learned motives operate 
may be illustrated by several experiments. 
In one, students were instructed to add col- 
umns as rapidly and accurately as possible. 
One group worked without any particular 
incentive. In the second group the chil- 
dren were praised in front of the class 
for their performance, while the members 
of the third group were reproved for their 
careless and inferior work. The perform- 
ance on successive days for the three groups 
is shown in Table II. The control group 


Effect of Praise and Reproof on Learning Scores 
[Data from E. B. Hurlock, /. ednc. Psychol., 1925, 16, 

Average Scores in Addition 
Day 1 Day 2 Day 3 Day 4 Day 5 
"Praised" 11.81 16.59 18.85 18.81 20.22 

"Reproved" 11.85 16.59 14.30 13.26 14.19 

"Ignored" 11.84 14.19 13.30 12.92 12.38 

Control 11.81 12.34 11.65 10.50 11.35 

shows no consistent gain from practice. 
The reproved group shows an initial im- 
provement, but the improvement is not 
maintained. The most effective incentive 
is shown here to be praise, which results 
in consistent improvement. 

Rivalry or competition is another motive 
which has long been effectively used in 
learning, particularly in school situations. 
The competition can be either between 
individuals or between groups. A study in 

which these two types of competition were 
compatc.-d is pres(-ntcd in i able III. In 

TABLE ill 

PREFECT OF Individual and Groi.p Rivai.rv o.s 

[After V. M. Sims, /. educ. Psychol., 1928, 19, 481, 483.) 

Per Cent 

Gain in Per Cent 

Substitution dain in 

Task Reading 

Group rivalry 109.9 14.5 

Individual rivalry 157.7 34.7 

Control: No rivalry 102.2 8.7 

the first experiment one group competed 
against another in a substitution test; in 
the second matched pairs of children com- 
peted with each other in reading. The 
latter condition was found to be the more 


In learning anything of e\en moderate 
complexity, several repetitions are re- 
quired. It is impossible to master a com- 
plex or elaborate task in a single try, no 
matter what the degi^ee of motivation or 
what the value of the reward. You could 
not learn the Constitution of the United 
States in one reading, even though your 
life depended on it, e\en though the prize 
were a million dollars. A great deal of re- 
search has, therefore, been done on the 
effect of repetition on learning, that is to 
say, on practice. 

The clearest way to bring out the effect 
of practice is to graph leaining on succes- 
sive trials. Learning may be measured in 
a number of Avays. One A\ay Avith A\hich 
w'e are all familiar is in terms of tlie speed 
Avith which we can do a task. In learning 
to type, for example, at first we can do only 
a few words per minute but witli practice 



greater and greater speed is attained. Speed 
may be measured in terms of how much 
work is done in a given time or how rap- 
idly a single task is performed. A second 
way in which improxement is shown is in 
accuracy. In the typing there is a reduc- 
tion in the number of errors as practice 
continues. More difficuk to measure but 
very important is reduction in cffoit, the 

1 2 3 4 5 6 7 8 9 10 11 12 
Presentations of list 


I. earning is shown by the increase in the number 
of syllables that are anticipated in the tests for re- 
cill. This cmve is for one subject. 

energy cost in performing a task. .\t first, 
a task is difficuk and fatiguing, but with 
further practice it becomes smoother and 
requires less effort. 

A typical record showing improvement 
with practice is given in Fig. .53. Here 
is shown the number of syllables in a list 
of ten which a subject was able to recite 
correctly after twelve successive repetitions. 
The curve shows an upward course of im- 
provement, but with marked up-and-down 
fluctuations. Such yariations are charac- 
teristic of all individual learning curves 
and are the result of chance conditions 
which the experimenter has not controlled, 
such factors as distraction and fluctuation 
of motivation. 

W^hen the curves of a number of indi- 
\iduals who learned the same material are 
averaged, we can see the course of impro\e- 
ment more clearly. We find, however, 
that there is no single type of learning 
curve biu that the type depends upon the 
nature of the task and the conditions lui- 
der which the learning is done. The three 
most common types are shown in Fig. .54. 
The first type (A) is the one in which ini- 
])rovement is rapid at first biu then pro- 
gressively slower toward the end. It is 
called a negatively accelerated learning 
curve. It is the type most often obtained 
when motivation is high at first but de- 
creases as practice continues, or when the 
subject has had previous practice on a simi- 
lar task so that the learning is not really 
'from scratch.' 

The second type (B) is called a positively 
accelerated curve. Here the increments 
are relatively sinall during the early part of 
practice but increase in magnitude with 


[Cur\es A and li are from H. A. Carr, Psychology: 
a sliidy of mental actii'itv. 1925. p. 21S; rejjrinted 
by permission of Longmans, Green.] 

continued practice. Curves cannot, of 
course, be positively accelerated through- 
out, since, at the end, as perfect learning 
is approached, they necessarily level off. 

In the third type of curve there is an ini- 
tial period of positive acceleration followed 
by negative acceleration. In this case, the 
total curve is S-shaped (type C). All ini- 
tially positively accelerated learning curves, 
if canied through to the leveling-off stage, 
become S-shajjed. 



Curves of types B and C arc most often 
obtained when the subject has had very 
little prior practice, particuhirly when the 
acts learned are relatively difficult for the 
learner. The manner in which the diffi- 
culty of the material affects the type of 


[From J. A. McGeoch, The psychology of liiunan 
learning, Longmans, Green, 1942, p. 56.1 

learning curve obtained is shown in Fig. 
55. With the easy material a negatively 
accelerated learning curve is obtained; with 
hard items a positively accelerated learning 
curve is found. 

Wherever the entire learning of a task 
from zero performance to mastery is stud- 
ied, the third type of curve (S-shaped) is 
most likely to be obtained. With difficult 
material we are more likely to be starting- 
near 'scratch' with initial positive accelera- 
tion, whereas with easy material we are 
more likely to be beginning further along 

toward mastery, where negative accelera- 
tion is obtained. As learning progresses, 
what began as hard is becoming easier, and 
acceleration may therefore change from 
positive to negative— the S-curve. 


Sometimes there occurs in learning a 
long period of practice in which no im- 
jjrovement is apparent, where the trend for 
a period of time is toward a relatively con- 
stant level of performance. Periods of this 
sort in which no improvement takes place 
are called plateaus. This phenomenon was 
first noticed in certain experiments on the 
learning of telegraphy (Fig. 56). In the 
the curve for receiving telegraphic signals 
there is a period of arrested progiess in tlu- 
iiiidposition of the graph. The hypothesis 

4 8 12 16 20 24 28 32 36 40 
Weeks of practice 


Curve for one subject's learning to receive in the 
telegraphic language. "This is a curve of sample 
performance. I'he region of very little or no prog- 
ress toward the middle of the curve is a plateau." 
[From W. L. Bryan and N. Harter, Psychol. Re-,:. 
1897, 4, 49.] 

formulated by the experimenters for this 
result was that plateaus occur in the re- 
gion of transition from one tvpe of habit 
to another. In the early stages, diev 
thought, learning is by letters. Later it 
would proceed by words, and then still 



later by phrases, and thus on to the largest 
units which a skilled telegrapher can re- 
ceive as a whole. They thought that the 
change-over from one type of learning to 
the next introduced a plateau, and indeed 
that may sometimes be true when plateaus 
occur. Learning telegraphy does not, how- 
ever, usually go by jumps, nor do its learn- 
ing curves always show plateaus. Cer- 
tainly other factors enter into the produc- 
tion of plateaus. Any long-drawn-out S- 
curve would be said to have a plateau in 
the middle of it. Sometimes plateaus are 
caused by loss of interest and motivation, 
by discouragement with the slow progress 
which the difficult nature of the task makes 
necessaiy. The important thing for a 
learner to remember is that plateaus are 
natural phenomena in learning, can be 
overcome and do not last forever. If the 
learner allows a plateau to discourage him, 
the plateau by reducing his motivation will 
prolong itself. 


A curve strikingly different from the 
ones we have been considering is sometimes 
found when the fully learned response 
makes its appearance suddenly, as is the 
case when a problem is solved by the grasp 
of a single general principle or method. 
This type of learning is called learning by 
i}jsight. In a famous experiment with 
chimpanzees one of the animals, which had 
already learned to pull a banana through 
a fence by using a stick, was given two 
sticks, each one alone too short to reach 
the banana. The two sticks, however, were 
constructed in such a way that the end of 
one would fit into the other. Playing with 
the two sticks in another part of his cage, 
the chimpanzee casually fitted the two to- 
gether and then, suddenly realizing that 
he had now a long stick, rushed to the other 

side of the cage and raked in the banana. 
This 'seeing' that the two together made 
a stick long enough to get the banana is an 
instance of insight. The learning, more- 
over, stuck. Thereafter the chimpanzee 
always knew how to use the two sticks to- 
gether. (See Fig. 73, p.' 203.) 

Physiological Limits 

A consideration of learning cmves leads 
directly to the question whether— or how 
rapidly— learners reach a physiological 
limit, the level of performance beyond 
which, by reason of the physical limita- 
tions of their organisms, they cannot go. 
Since under ordinary laboratory conditions 
subjects seldom approach such an extreme 
limit of performance, one must rely for an 
answer to this question upon fragmentary 

It has been found that years of practice 
at such skills as telegraphy or typesetting 
do not commonly bring a man to his maxi- 
mal performance. Even among workers 
with many years of experience, the intro- 
duction of special incentives may greatly 
improve performance. In a printing house, 
for example, where hand compositors had 
been working at their trade for an a^■erage 
of about ten years, performance rose stead- 
ily for at least twenty weeks when a special 
bonus was introduced for output beyond a 
certain level. The increased output re- 
sidted from elimination of stabilized inef- 
fecti\e habits of work and the acquisition 
of better ones. Analogous results have 
been obtained with other kinds of work. 

The fact that in athletics and in other 
skills records are repeatedly broken under 
standard conditions is best interpreted as 
an indication of the practical remoteness 
of a physiological limit. It has, likewise, 
been found repeatedly in the laboratory 
that, after a subject has reached a rela- 

Insight and Frequency 


lively high level of performance, increased 
motivation or better methods will produce 
further substantial increments. It thus ap- 
pears that a physiological limit is not 
reached in normal persons by ordinary 
amounts of practice and, indeed, may not 
be reached even by prolonged practice un- 
der favorable conditions. On the other 
hand, there are physiological limits to the 
speed of human reaction which no degree 
of practice, insight or motivation will en- 
able the learner to transcend. 

The Law of Frequency 

The results which have been presented 
above clearly indicate that repetition is 
usually required for mastery in learning. 
This fact has led to the belief that fre- 
quency is the basic determiner of learning, 
a generalization often called the laiu of fre- 
quency. The law of frequency (or law of 
exercise) states that the connection between 
a stimulus and a response is strengthened 
by its recurrence, its exercise, its use. 

Experiments have conclusively demon- 
strated that mere repetition is itself not a 
sufficient condition for learning. If we set 
a man the task of hitting the bull's-eye 
with a rifle but do not tell him how close 
to the bull's-eye he comes, no amount of 
repetition results in his learning to shoot 
straight. Similarly, if a learner is not try- 
ing to learn, repetition becomes ineffective. 
This fact has been demonstrated in one 
study by presenting students with a series 
of cards, each bearing a printed word, a 
number and a strip of colored paper. The 
subjects were instructed to learn the word- 
number pairs, so that, when the word was 
given, the accompanying number could be 
recited. No mention was made of the colors 
accompanying the words. After several 
presentations the subjects were asked to 
name the color that went with the given 

word. Few of them had learned any of the 
colors. They knew the numbers, but not 
the colors, although they had seen the 
colors with the words as often as the num- 
bers. In the same way a man can be driven 
frec]ucntly over a route without learning 
how to go. The best way for him to learn 
is to drive the car himself; then he will 

The motive to learn is tied up with good 
attention. People can remember events 
when they have paid good attention to 
them without intending to learn them or 
expecting to have to report on them. The 
witness of an accident will recall certain 
details. Such learning is called incidental 
learning and is not very reliable. Although 
the man who stumbles in the dark over 
what turns out to be a corpse will not at 
once forget what it was he found so unex- 
pectedly, it is difficult on the witness stand 
to get an accurate report of the details of 
such an important, exciting event. If you 
witness an accident or a crime, you had 
better invoke the intent to learn at once. 
Commit to memory what seem to be the 
important factual items Avhich you ob- 
sei-ved, and then write them down later 
so that you can go to court and be a good 

There are certain schools of psycholog^ 
today which believe that all learning is 
basically instantaneous, like the flash of 
insight which gives the solution to the prob- 
lem and once seen is not forgotten, or like 
the emotional experience (the corpse in the 
dark) which leads to instant pennanent 
learning of a simple interesting fact. These 
psychologists argue that repetition is neces- 
sary only because tasks are too large to 
come all at once widiin reach of the con- 
ditions for learning. You learn most on the 
first experience. If you learn a third of 
the material the first time, perhaps -vou 



can learn a third of the remaining two- 
thirds the second time, and so on. Fre- 
tjuency is necessary, they argue, merely in 
order that all portions of the learning 
should eventually get their full oppor- 
tunity to be realized. 

Certainly the repetition of practice is 
necessary to most learning, even though 
there is this doubt that the same associa- 
tive connections need repeated reinforce- 
ment before they become fixed for the use 
of the learned man. 




We have seen how learning is affected 
by practice and by motivation. In this 
section we shall discuss some of the more 
specific factors affecting the speed and effi- 
ciency with which learning takes place, con- 
sidering successively the importance of (1) 
the learner, (2) the material learned and 
(,S) the methods of learning used. 

The Learner 

Great individual differences between 
people learning the same task are invari- 
ably found. The influence of such factors 

10 20 30 40 50 60 70 80 


The trend of mean performance in digit-symbol 
suljstitution with age. (See Figs. 37 and 38, p. 85.) 
[From R. R. Willoughby, /. educ. Psychol., 1929. 
20, 678; rcprinle<l by periiiission f)f ^Var^^■ick and 

as age, intelligence and previous training 
have been studied, but even when all are 
controlled pronounced variation still ex- 
ists. In one study made with subjects of 
the same age, sex, year in college and 
equivalent previous practice at the activity 
being learned, the fastest learners required 
8 trials to learn, perfectly and in the same 
order, a list of 8 nonsense syllables, whereas 
the slowest learners required 37 trials, 
more than four times as many. Simi- 
larly, the fastest learner mastered a maze of 
considerable difficulty in 19 trials, whereas 
the slowest took 78. When the records of 
a large group of subjects are examined, 
they are found to be distributed after the 
fashion of many large populations, with 
medium speed most frequent and the fre- 
quency of instances diminishing for slower 
and faster learning. 

Differences between the sexes in speed of 
learning are only rarely found, and then 
they are due to sex differences in interest 
and motivation with respect to the mate- 
rial being learned. 

A variable affecting learning, one which 
has great practical importance, is age. The 
curve of learning improves as one grows 
older, at least until the late teens. After 
the early twenties a gradual decline with 
increasing age is found. A sample of per- 
formance in a simple learning task at vari- 
ous ages is shown in Fig. 57. 

An interesting experiment on the effect 
of age on learning is the following. Three 
groups were studied. The young group was 
12 to 17 years of age; the middle group 
34 to 59; the oldest group 60 to 82 years. 
The three groups were comparable in so- 
cial background, native ability and will- 
ingness to cooperate in the experiment. 
The five different tasks learned by the sub- 
jects were chosen to represent different de- 
grees of dependence ujwn previous habits. 

Intelligence, Sex, Age and Material 


The investigator found only moderate de- 
cline with age in the tasks which involved 
the perfecting of previously learned habits, 
but extremely marked decline with age 
when the new learning was in conliict with 
previously learned coordinations, as in a 
task like learning false multiplication 
tables, 2X4 = 9, 5x4=14. 

These results suggest a reason for the 
greater conservatism of older individuals. 
Being less able to learn new materials, 
particularly of the type involving tearing 
down old habits of response, they are lim- 
ited in their thinking to experiences ac- 
quired in the past. The further a proposed 
change deviates from their past experience, 
the liarder it is for them to learn the new 
relationships and implications which they 
must substitute for old knowledge if they 
are to appreciate the need for change. 

Kind of Material 

We are all aware that some kinds of ma- 
terial are much easier to learn than others. 
What accounts for the difference in ease of 

Probably the most important factor is 
the 7neaningf Illness of the material to be 
learned. It is possible to rank a large num- 
ber of verbal materials from low to high 
with respect to their meaningfulness. On 
such a scale, nonsense syllables (artificial 
syllables like ROP, BAV, GEX; see p. 161) 
are placed well toward the lower end, single 
wortfs are higher, poetry and prose are still 
higher. An almost perfect relationship is 
found between meaningfulness and ease of 
learning, so that it may be said that, over 
a wide range of materials, rate of learning 
is a direct function of the meaningfulness 
of the material, provided everything else 
remains constant. The results of an illus- 
trative research on this point are given in 
Table IV. 


ErrECT OF Meaningfulness in Learning Equal 
Number of Units of Different .Materials 
[After Lyon, /. educ. Psycho/., 1914, 5, 85-91.) 

Minulei Required Jr/r 
Material Learning 200 Units 

Nonsense syllables 93 

Digits 85 

Words (prose) 24 

Words (poetry) 10 

A closely related factor is the one which 
Thorndike has called belongingness. He 
demonstrated this principle in an experi- 
ment in which he read a series of twenty- 
four unrelated sentences several times to a 
group of students. The students were then 
asked to name the word that had followed 
the word now read by the experimenter. 
In 42 per cent of the cases the students 
were able to give the second word of a sen- 
tence when the first was read, but in less 
than 1 per cent were they able to give the 
first word of the following sentence when 
the last word of the preceding sentence Iiad 
been read. The difference was attributed 
to the fact that words in a sentence 'belong' 
together in a way that the words in dif- 
ferent sentences do not. 

Another way in which the importance 
of relationship as belongingness can be 
demonstrated is in the learning of pairs of 
words. If we make up pairs like table- 
chair, green-grass, they \vill be learned much 
more rapidly than combinations like book- 
dog, candle-rose. In the first type of pair 
the relationship is familiar and meaning- 
ful with a high degree of belongingness. In 
the latter type of pair die words are unre- 
lated and more difficult to associate. 

It seems probable tliat both meaningful- 
ness and belongingness help leai-ning be- 
cause they indicate pre^ious familiarit\ 
with the terms or their relations or both 



and are seen thus to depend on the fact 
that a certain amount of learning has al- 
ready taken place. 

Closely related to the factor of meaning- 
fulness is the type of learning activity re- 
quired for mastery. It is well known that 
it is a great deal easier to learn the ideas 
in a passage than the exact phrasing used. 
The former is often called logical learning 
and the latter verbatim. In a recent ex- 
periment it was shown that logical learning 
can be three times as rapid as verbatim 
learning. It is further significant that tell- 
ing the subject to try to find meaningful 
relations in the material speeds up his 
learning. And there are also the ingenious 
learners who perpetually see meaning in 
nonsense, who perceive at once a belong- 
ingness between WED and NAG in a list 
of words to be learned, who remember the 
sequence BOS-BEN because of Boston 
(baked) beans and who, because of their 
skill at punning meaningful insights, al- 
ways rank high in learning nonsensical 

Distribution of Practice 

Given a particular material how is it 
most efficient for an individual to proceed 
in learning it? Should he try to learn the 
material in a single sitting or distribute 
his practice over a period of time, learn it 
in large units or small? Research has given 
the answers to many of these questions. 

When a period of time separates each 
trial in learning, the method is called 
distributed practice. When trials are given 
without a break, the method is called 
massed practice. Results indicate that for 
almost all situations some form of distrib- 
uted practice is more effective than massed. 
A sample study is shown in Fig. 58, where 
rate of learning nonsense syllables contin- 
uously without a break is compared with 
the rate when a short rest interval of two 

minutes was introduced between successive 
trials. We see a marked difference favor- 
ing distributed practice. This statement 
refers, of course, to comparisons of amounts 
of time actually spent in practice. Total 
elapsed time will almost always be greater 
under distribution because the time for the 
rest periods has to be added. As a conse- 

4 6 8 10 12 14 
Number of trials required 


Cur\es show a\erage number of trials to reach 
successive levels of performance by massed and dis- 
tributed practice. For example, it takes only about 
11 trials to get all 12 syllables correct by distributed 
practice, but nearly 15 by massed practice. [From 
C. I. Hovland, /. exper. psychol., 1938, 23, 176.] 

quence it is sometimes necessary to use 
massed practice under high presstire for time 
despite its relative inefficiency. 

The length of the time interval between 
trials is a critical factor in the relative 
effectiveness of massed and distributed 
practice. If the time is very short or of 
zero duration, leaining is likely to suffer 
because of reduced motivation, interference 
and fatigue. If, on the other hand, the 
interval is too long, considerable forgetting 
will occur between trials, and hence the 
efficiency of learning will be reduced. In 
practice, however, because we are more 
likely to err in the direction of too much 
massing than in too wide separation of 

Distribufed Practice: Wholes versus Parts 


trials, the admonition to distribute learn- 
ing trials is usually correct. 

For many activities a variation in the 
length of the interval between trials as 
learning progresses is beneficial. For cer- 
tain activities massing in the. early stages 
of learning, with distribtited practice later, 
is best. For others the pattern of distrib- 
uted practice at first, followed by shorter 
and shorter intervals between trials, is 

The advantages of distribution of prac- 
tice are greater when the learning is less 
meaningful and rote in character. Mate- 
rial high in meaningfulness benefits less 
from spaced practice. This difference is 
probably at least partly due to the greater 
ease in maintaining a high degree of inter- 
est in material that is meaningful or in 
which the learner sees significance. 

A number of studies have indicated that 
the longer and more difficult the task, the 
more effective is distributed practice. In 
Fig. 59 results are reported showing that 
the longer the list of syllables learned, the 
greater the advantage brought about by 
distribution of practice. 

Several factors appear to be involved in 
the explanation of the superiority of dis- 
tributed over massed practice. An im- 
portant one is fatigue. In certain learn- 
ing tasks continuous practice produces 
fatigue; then rest periods between trials 
benefit the learning. But in many situa- 
tions we obtain the favorable results of dis- 
tribution without fatigue's being a likely 
factor. In these cases we often find evi- 
dence of the formation of conflicting con- 
nections which adversely affect further 
learning. These conflicts appear to sub- 
side quite rapidly during a rest period, so 
that the positive effects of repetition can 
presently become more apparent. Moti- 
vation is also an important factor to con- 
sider in the effectiveness of spaced practice. 

Prolonged practice often results in reduced 
interest in the task, so that the learner does 
not work so eflectively. Following a rest 
pause the learner may return to his task 
with increased vigor and interest. 

1216 24 32 48 

Number of syllables In list 


Mean number of minutes required for learning 
by massed and distributed practice with varving 
lengths of lists of nonsense syllables. It is especially 
important to distribute practice with long lists. 
[Data from D. L. Lyon, The relation of length of 
material to time taken for learning, and the opti- 
mum distribution of time. /. ediic. psycho!., 1914, 
V, 1-9; 85-91; 155-163, published by Wandck S: 
York, Inc. Summarized by C. L. Hull, Massed vs. 
distributed practice, from Mathematico-deductive 
theory of rote learning, Yale University Press, 1940, 
p. 131.] 

Whole or Part Learning 

In attacking a learning problem is it 
better to try to learn it by going all the 
way through it on each trial or by breaking 
it into small portions and learning each 
in turn? The former is usually called the 
xvhole metJiod and die latter the part 

The majority of sttidies have found it to 
be more efficient to learn by tlie whole 
method than by the part, but, as in tlie case 



of distributed practice, the relative effi- 
ciency is to a large extent a function of the 
special conditions of learning. Some of the 
factors affecting the relative effectiveness 
of the two procedmes are these. 

(1) The age of tlie subjects. Children 
tend to learn faster with the part method, 
adults with the whole method. 

(2) The ability of the learner. Brighter 
children tend to learn better with the whole 
method, less bright ones with the part 

(3) The stage of practice. At first bet- 
ter results are obtained with the part 
method, but later on, after practice, the 
Avhole method usually proves to be more 

(4) The length of the material to be 
learned. If the assignment is of moderate 
size the whole method has been foimd supe- 
rior, but if it is lengthy the part method is 

These apparently conflicting results can 
perhaps all be placed under one generaliza- 
tion: Learn imits as large in size as can be 
grasped at one time. If material is diffi- 
cult in relation to the learner's ability, 
smaller units will have to be employed, but 
they should still be as large wholes as the 
learner can manage efficiently. 


Often in the acquisition of a complex 
motor task learning is facilitated by re- 
ducing it to a verbal formula. It has been 
observed, for example, that this is what 
many adults do in learning the route 
through a maze. They repeat to them- 
selves: "One to the right, then two to the 
left, and then one right again," and so on. 

The importance of verbalization in the 
learning of skills is supported by a recent 
experiment in the learning of mechanical 
puzzles. The task was the assembly of a 

mechanical puzzle. With one group of 
children the teacher demonstrated the 
puzzle silently, but the child was required to 
engage in counting, an activity calculated 
to interfere with the child's inner verbali- 
zation of the steps in solving the puzzle. 
In a second group the teacher assembled 
the puzzle silently while the child was in- 
structed to describe the procedure used by 
the teacher. In two other groups the 
teacher described the procedure of assem- 
bly while the child watched silently. In 
still another gioup the teacher coiTected 
the child's verbal formulation of the pro- 
cedure, and in the final group the same pro- 
cedure was followed except that the process 
of describing the assembly was facilitated 
by having numbers pasted on the parts in 
the order of assembly. The six groups can 
be seen thus to differ in the degree to which 
the child was aided in verbalizing the pro- 
cedure for assembly. It was found that the 
greater the verbalization, the more rapid 
the learning. The results are shown in 
Table V. 

Data from another study of this type are 
given in Table VI. Subjects who had 
learned the correct path through a maze 
were asked to describe their modes of at- 
tack and the subjective means which they 
used in learning. The means reported fall 
into three categories. (1) In verbal meth- 
ods the turns and other moves are remem- 
bered in words, so that the subject guides 
himself through the maze by saying, "First 
turn to the right, then straight ahead," etc. 
(2) In motor methods the sensory cues 
employed are predominantly the feelings 
of movement; the subject 'follows the 
lead of his hand' without consciously or- 
ganizing his movements. (3) In visual 
methods attempts are made to construct 
visual images of the maze pattern. The 
frequencies with which the three methods 

Verbalization and Active Participation 



Effect of Verbalization on Learning 

Number of trials rcquirc-d for children to learn to 
assemble a mechanical puzzle. The amount of the 
child's verbalization increases from item 1 to item 6. 
[From Louise Thompson, The role of verbalization in 
learning from demonstration, unpublished dissertation, 
Yale University, 1944.] 

A vera^e 
Number Number 
Subjects Trials 
Group Procedure Learning Required 

1 Silent demonstration. Child required 

to count so as to prevent verbaliza- 
tion. 3 25 + 

2 Silent demonstration. Child describes 

proceedings orally. 22 22.00 

3 Demonstrator describes partly. Child 

watches and may verbalize silently 25 16. 16 

4 Demonstrator describes fully. Child 

watches and may verbalize silently. 25 14.12 

5 Teacher watches but makes correc- 

tions when child's description is in 

error. 25 12.44 

6 Same as 5, except that blocks are num- 

bered in the order in which they are 

to be assembled. 25 9.52 

are used decrease in the order just given, 
with the visual methods appearing but in- 
frequently. The learning curves of sub- 
jects using the different methods show the 
clear superiority for the verbal method 
over the other two and, usually, a superior- 
ity of visual over motor cues. Table VI 


Performance Scores Made by Subjects Using 

Different Modes of Attack 

[Data from R. W. Husband, /. genet. Psychol., 1931, 



Mode of 








Verbal method 




Visual method 




Motor method 




gives a sample set of results for one section 
of a high-relief finger maze on which the 
subject, without the use of vision, learns 
to trace a raised line with one finger. Simi- 

lar results liave been found with stilus 
mazes (the maze is made of grooves and the 
path is traced with a stylus while vision is 
excluded) where the more intelligent sub- 
jects are likely to adopt the verbal method. 
Tlie pronounced superiority of the 
verbal method over the motor in the learn- 
ing of a motor problem is significant. It 
shows that tlie motor skill as actually ac- 
quired by most subjects is learned as a pat- 
tern with both verbal and motor constit- 
uents. The so-called motor learning is not 
limited to the learner's perception of his 
own movements, for the trials, errors and 
successes are often ideationally controlled. 
Learning, furthermore, proceeds much 
more rapidly when the ideational factors 
are employed. These facts also show that 
there is no clean-cut division between dif- 
ferent kinds of materials with respect to 
the activities they require. 

Active Participation 

The more the learner enters into his 
task, the more effective is his learning. 
Many times active participation is insured 
by the nature of the task, as in learning to 
pilot a plane. On the other hand, in a 
great deal of instruction in school and col- 
lege, material is presented to the learner, 
as in lectures, while the learner fails to 
participate in the learning process, merel\ 
sitting back and reacting passively. In 
these cases the teacher can improve in- 
struction significantly by demising means of 
instiring acti\e jjarticipation bv the learner. 

An experiment from tlie uaining of sol- 
diers in the Army illustrates the difference 
between active and passive learning. The 
objective was to teach the soldiers the pho- 
netic alphabet, in which word equivalents 
are learned for letters, like Able for A. 
Baker for B, Charlie for C. etc. This svs- 
tem increases the claritv and accuracv of 



material transmitted o^■er telephone com- 
munication systems. 

The standard method of instruction was 
to employ a film in which the letter, pre- 
sented on the screen, was followed by the 
equivalent word. After a number of indi- 
vidual letters had been presented, a portion 
of the list was repeated by the narrator. 

Participation method 

12 3 4 5 10 15 

Time following presentation of letter in seconds 


The subjects learned phonetic names for letters, 
like Able for A, (a) by a passive method (listening 
to the narrator repeat the letter-word combina- 
tions) and (b) by a participation method (reciting 
aloud the combinations). The graphs show the 
number of items recalled in different periods of 
time after the presentation of the letter. The active 
participation method is more efficient. [.Adapted 
from the forthcoming Experimental studies of 
Army educational films.] 

In the participation method the same film 
was used, but, instead of the narrator's re- 
peating the words in groups, the trainees 
were instructed to recite aloud the word 
equivalent when each letter was presented, 
thus insuring active rehearsal. The ef- 
fectiveness of this procedure is shown in 
Fig. 60. 

Since learning depends on motivation, 
active participation is basic to learning. 
Teaching does not compel learning, for the 
learner must himself participate. The best 

that teaching can do for learning is to pro- 
vide optimal conditions for its achieve- 
ment. The teacher makes the materials 
to be learned available to the student, he 
gives instruction as to the best methods of 
learning and in some cases requires by 
periodic examinations a favorable distribu- 
tion of practice, and then he resorts to all 
the conventional devices and the other 
means that his own ingenuity supplies to 
induce the students— to 'motivate' them— to 
participate actively in the learning process. 
The ultimate responsibility, however, is 
the learner's. It is he who must accept 
participation if he is to learn. 


One way actively to participate in learn- 
ing is to begin using the material learned 
before the learning is complete. A man 
learning a maze may rehearse verbally to 
himself the turns which he has just made, 
Avhile at the same time he is going forward 
through other sections. W^en he has to 
memorize a list of words he may try to re- 
peat the list without the copy before he has 
fully learned it. In one experiment, the 
learning of lists of nonsense syllables and 
of short biographies was practiced, some- 
times by repeated readings until they were 
learned, and at other times by reading fol- 
lowed by recitations with prompting given 
whenever necessary. The relati\e effective- 
ness of recitation in varying proportions is 
shown in Table VII, where the percentages 
of material recalled immediately at the 
close of the learning period are presented. 

These results show that direct repetition- 
plus-recitation yields larger increments of 
learning than time spent only in direct 
repetition, and that the increments in- 
crease when the proportion of the total 
learning time spent in recitation increases. 
The advantage of recitation is greater with 

Acquisition of Skills 



Infi.uf.nck of Different A-mounts of Rkcitaiion 


The figures are for subjects in Cirade VIII and have 
been obtained by computing the percentage which the 
amount learned by each method is of the average of 
all methods. [From A. I. Gates, /ink. Psycho/., 1917, 
6, 36, 41.] 

Per Cent 

of Total 




In Reci- 

Materials Learned 
























the nonsense syllables than with the biogra- 
phies, probably because the biogiaphies in- 
vite more active organization of the ma- 
terial during its repetition than the non- 
sense syllables. Other investigators have 
found that more favorable results are ob- 
tained when readings and recitations are 
interspersed than when they are grouped 

The superiority of reading-plus-recita- 
tion over reading alone results from sev- 
eral independent conditions. (1) The reci- 
tation arouses more active participation by 
the subject. (2) During recitation the sub- 
ject is practicing the recall of the material 
in the way he is to use it later when tested. 
(3) The recitation yields progressive infor- 
mation about errors and right responses, 
thereby permitting the correction of errors 
through prompting from the copy and pro- 
viding increased motivation for improve- 


When we acquire through learning a co- 
ordinated series of responses which are 

p(ii(jt MK-d wiili jjroficiency, we speak of llic 
acfoniplisfiriKrit as skill. Playing the 
piano, piloting a plane and reciting a poem 
are all skills. (Jiaractcristif ally, they in- 
volve a serial organization of responsts. 
The name serial learning is applied to the 
process of learning such a sequence of re- 

One of the commonest types of serial 
learning is the learning of verbal material, 
like a poem, so that we can recite it all the 
way through. 'Ihe process of learning 
poems has been analyzed, but for the care- 
ful study the use of poetry presents certain 
difficulties. For one thing some poems are 
easy and others hard, and it is difficult to 
know how much previous experience the 
subject has had with the particular poems. 
Even the separate words will not be uni- 
form in their associations from person to 
person. To overcome these difficulties 
many studies have used materials de\oid 
of much meaning so that all learners can 
start learning with an equal degree of un- 
familiarity with the material. The method 
of achieving this end w^e owe to the Gei- 
man psychologist, Ebbinghaus, who de\el- 
oped the system of nonsense syllables for 
use in memory experiments. They are usu- 
ally three-letter units of two consonants 
with a vowel between them. Lists of these 
syllables of equivalent difficulty can be 
readily prepared. In the laboratory the 
syllables are usually presented by an aiuo- 
matic machine, and the experimenter re- 
cords the subject's progress in learning the 

Often a motor skill also involves learn- 
ing in serial order. A device frequently 
used for studying diis type of learning in 
its simplest form is a ?naze. The maze, a 
sample of ^vhich is shown in Fig. 61, can be 
used to study both animal and human 
learning. In animal studies white rats 



have been used most frequently with mazes 
similar to the one illustrated and with 
more complicated ones. A hungry rat is 
put at one end and required to learn the 
path to the food box, where it is fed. It 

I'lGURE 61. 

11 pic:al stylus-maze pattern 

The subject learns to trace with a stylus the cor- 
rect path from the start (S) to the goal (G). He is 
hlindlolded or else prevented from seeing the maze 
and his own hand by a screen. [From C. J. War- 
den, /. exper. Psychol., 1924, 7, 101.] 

will be observed that this learning is simi- 
lar to that stvidied by Thorndike with his 
cats, except that it involves a sequence of 
acts, rather than a single one, to achieve 
tlie goal. 

Mazes have also been used with human 
subjects. .Sometimes a large maze is con- 
structed through which the subject must 
learn to walk to find the goal. More fre- 
quently, however, the same task can be ar- 
ranged by using a stylus maze in which the 
maze pattern is cut into the surface and the 
subject traces the path (constantly blind- 
folded, of course) with a stylus (Fig. 61). 

In the learning of many acts of skill the 
task continually changes as greater skill is 
achieved. This type of learning has been 
studied most extensively in telegraph send- 
ing and receiving, but an identical prob- 
lem is involved in learning to type. At 
low speeds we learn to inake an appropri- 
ate movement for each letter reqtiired, for 
example, to press the a, then the 71 and 
finally the d in and. As greater skill is 
achieved we respond with an integrated act 
of successively pressing the three keys to 
the total word and. With still greater 

10 - 

_2 6 



1 1 1 1 1 1 1 1 1 1 


Massed-,^/ S. _ 


/ ^^"x\ - 

/ '' V \ 


/ ^ ^>- X "^ 

/ '' "^'vX 


/ /'<=- Distributed "A 


// A 

/ / > 


/ (f ~ 


1 1 1 1 1 1 1 1 1 1 

4 - 

2 - 

2 4 6 8 10 

Position of syllables in series 



Composite curves showing mean number of fail- 
ines in recall at various syllable positions involved 
in the series when the subject learns the lists to 
complete mastery by massed and by distributed 
practice with a 2-second rate of presentation. The 
beginning is learned best, the middle least. Dis- 
tributed practice is better than massed. [From C. I. 
Hovland, J. exper. Psychol, 1938, 23, 178.] 

practice, phrases and even complete sen- 
tences are learned as units. 

From studies of serial learning we find 
that the various portions of a sequence 
are not equally difficult to learn. The first 

Acquisition of Skills 


responses and the last responses are easiest, 
and the middle ones the most difficull. A 
typical curve of difficulty is presented in 
Fig. 62. These results have sometimes been 
explained by the principles of pritiiary and 
recency. The first principle states that, 
other things being equal, the first experi- 
ence is most readily learned. The prin- 
ciple of recency is that recent experiences 
are remembered more vividly than earlier 
ones. Current studies indicate that the 
first and last responses are usually easiest 
to learn because of a minimum of inter- 
ference. Maximum interference is in the 
central portion of a series. 

When a rat learns a maze, the law of ef- 
fect enters into serial learning. The rat 
learns first the goal end of the maze where 
the food lies. As learning progresses his 
skill extends farther and farther backward 
from the goal, being least at the very start 
of the maze which, of course, lies farthest 
away from the satisfying goal. This in- 
creasing familiarity with the maze as the 
goal is approached is called the goal 
gradient, which thus constitutes a striking 
example of the operation of the law of 

It is clear that serial learning involves 
many different factors. A rat learning to 
run a maze is not like a person learning a 
poem. The person remembers the poem 
by its first line and can find it again 
through an index of first lines, but the rat 
must remember the maze by its last line, 
as it were, by the food to which it led. 

Basic Principles in the 
Acquisition of Skills 

All the principles of learning bear on the 
problem of obtaining efficiency in the ac- 
quisition of skills, but there are certain 
practical rules, based upon these principles, 
which may be set do^vn. Here they are. 

(I) SlreA.s the (orred prnfonnuncf; from 
I he slarl. In other words, do not let wrong 
habits get established. This rule may seem 
obvious enough, stated in this general way, 
yet you often try to learn skills in the hofx; 
that you can discover the correct way by 
trial and error. Then it is that pradice 
may not make perfect. Practice makes per- 
fect only when jjracticc is restricted to tlu- 
conect performance. Use trial-and-error il 
you must, but not when available informa 
tion will enable you to avoid error. Never 
practice errors when truth can be had for 
the asking. 

In skills, like golf or typing, you, as the 
learner, often keep practicing without im- 
provement. Guidance may be necessary to 
bring about improvement. A skilled 
teacher or coach can often demonstrate the 
exact form of the correct response, thus en- 
abling you to discriminate between corret t 
and incorrect procedures. For example, 
one of the reasons it is so difficult to stojj 
slicing in golf is that the difference be- 
tween the correct drive and the slice is not 
sufficiently obvious to you. If you felt a 
jab in the back when you took up the posi- 
tion which results in slicing, onlv a few 
trials would suffice to abolish your incor- 
rect movements. Since there is no such 
dramatic differentiation, you may ne\er b\ 
yourself develop the proper drive. ^V'hat 
the 'pro' does is to show vou the specifi( 
respects in which the right and the Anong 
methods differ, and he shows vou just Avhen 
you are about to make the response. 

(2) Concentrate on the actual task to be 
learned. This principle is closely related 
to the first. To be most effecti^e. learning 
should be directed to the actual operations 
you want to perform. Training bv trans- 
fer from a similar skill ahvays gives per- 
formance inferior to direct practice. This 
rule means that you should practice on a 



full-sized standard tyjjewritei. a full-sized 
piano keyboard, with real golf clubs. Do 
not attempt to practice tennis by playing 
squash. Anyone who has learned to type 
by the touch system after having originally 
learned by the 'hunt-and-peck' system can 
attest to the fact that just having had ex- 
perience in operating a typewriter is not 
enough; )ou have to practice the identical 
motions involved in tlie finished perform- 
ance, for otherwise old habits are always 
interfering with the new. (That is, nega- 
tive transfer; see p. 180.) 

(3) Learn in natural units, not piece- 
meal. You have seen that learning in large 
units is ordinarily more efficient than piece- 
meal learning. Too often practice is di- 
rected to small details instead of to the en- 
tire performance. This neglect of the 
larger units results in the learner's being 
able to perform the detailed acts, while re- 
maining unable to coordinate them in a 
finished performance. The natural rhythm 
of the entire operation is broken by the 
concentration on minute details. You 
sometimes see people learning to play golf 
by learning first the up stroke and then 
the down stroke; they should learn the 
total pattern into which both these two 
parts must fit smoohly. 

This rule does not mean that learning 
should not sometimes be broken down into 
convenient imits, but merely that the imits 
must be natural rather than artificial. The 
unit of practice must involve the entire se- 
quence or pattern which is essential for 
correct performance. Thus, in learning to 
drive a car, practice may be profitably 
broken up, with separate practice on start- 
ing a car from rest, but the principle would 
be violated if the learner were to concen- 
trate first on operating the clutch, then on 
the gearshift, then on the accelerator, since 
the finished pattern for this operation al- 

ways involves simidtancous movements of 
the accelerator, clutch and gearshift, and 
practice on the separate movements will 
not bring about a smooth integration of 

Learning to type is gieatly accelerated by 
applying this principle. In typing, the 
natural unit is the word; yet for years 
students were taught to practice the indi- 
vidual letters first (the well-known r-t-y-u 
method), coming to words later. Learning 
the general layout of the keyboard and 
then beginning at once to practice whole 
words instead of letters have reduced the 
number of trials required for learning by 
more than half. 

(4) Space learjiing trials. The experi- 
ment cited earlier concerning the advan- 
tages of distributed over massed practice is 
relevant to the acquisition of skills. Two 
rounds of golf on one day are likely to be 
less effective training than one round on 
each of two days. Materials learned by 
speed-up processes are also likely to be 
more rapidly forgotten, as you will recall if 
you have ever tried 'cramming.' Deter- 
mine for the skill you are learning the 
period which is short enough to avoid fa- 
tigue, boredom and interfeience effects, but 
long enough to avoid wasting time in 
getting warmed-up for the task. 

(5) Overlearn; do not count on barely 
learnijig the task. For a performance to be 
skilled it must be a smooth flawless coor- 
dination of responses. To achieve such in- 
tegration, it is not nearly enough that 
learning should continue until a single 
correct performance is reached. Any such 
minimally learned performance will be 
quickly forgotten and easily disrupted by 
even slight distraction. The armed forces 
in the late war were well aware of the im- 
portance of this principle in teaching com- 
plex military skills. Men were given prac- 

Rules for Learning 


tice long after Lhcy ihoiiglu tlicy 'knew ;ill 
about it.' This overiearning was designed 
to take care of tfie needed peiiorniante of 
these skills under battle tondilions where 
fatigue, fear and confusion would have a 
disrupting influence on any but the best- 
learned habits. You will find that any 
skill you wish to perform in public must 
be similarly overlearned to prevent its be- 
ing broken up by stage fright or distraction. 
(6) Speed or accuracy? From these spe- 
cific principles and the earlier analysis of 
learning in this chapter you should your- 
self be able to deduce the answers to many 
specific problems that arise in acquiring 
skills. Should you, for example, stress ac- 
curacy or speed first in learning manual 
skills? You know that the correct pattern 
must be practiced from the very start, if 
that is at all possible. You must, there- 
fore, analyze the operations to determine 
whether the performance at a slow speed 
is the same as that at a high speed. If it 
is, you should start your learning with em- 
phasis upon accuracy, so that the exactly 
correct performance is carried out from the 
very beginning. This relationship certainly 
holds in learning typing. No fvnidamental 
change in the nature of the moveinent oc- 
curs as greater speed is achieved. If, on the 
other hand, the operation changes signifi- 
cantly between low and high speeds, you 
should strive toward the form of the finally 
correct performance even if some accuracy 
must be sacrificed. This type of learning 
exists in bricklaying. An entirely different 
method is involved when the job is done 
slowly, one which hardly resembles the 
form used when the work is performed rap- 
idly. Speed would, therefore, have to be 
stressed from the start, even if the learner's 
work would have later to be redone by 
an experienced bricklayer. Thus the para- 
dox as to whether to stress speed or ac- 

( uracy first (an be best resolved in the par- 
ticular situation. 

(7) /low much guidance? 1 his is another 
pLi/zling problem. How much help or 
guidance should you have at the beginning 
of learning? Analysis of this problem in- 
dicates that some guidance is usually 
needed at the start to help establish the 
correct pattern and avoid practicing errors. 
But it is also ti ue that tfie learner must 
learn the task in the manner in which it 
will have to be performed later. He will 
not, then, want to become dependent upon 
someone else for help and guidance, not for 
very long. An intermediate procedure 
works best. Let the learner get help when 
he thinks he needs it but cultivate self- 
reliance in his learning. 

(8) Motivation. Attention to these prac- 
tical rules must not lead you to forget the 
great importance of motivation in the 
learning of skills and all other tasks. 
Knowledge of results, competition with 
yourself and other persons are useful mo- 
tivating devices. Enthusiasm and real de- 
sire to progiess are factors which distin- 
guish the mediocre from the exceptional 
learner of skills. The man who can bring 
zest to his learning has a great advantage, 
but the zest must be controlled by wisdom. 
Errors too can be quickly learned zestfullv. 


1. Bird, C, and Bird, D. M. Learning more by 
effective study. New York: Appleton-Centur\ . 

An analysis of factors affecting efficieno in 
study and a description of the effects of pro- 
grams designed to improve efficiency. 

2. Garrett, H. E. Great experiments in psy- 
etiology. (Rev. ed.) Xew York: Appleton-Cen- 
tiiry, 1941. Chaps. 3 to 7. 

Interesting accounts of the experimental con- 
tributions to the study of learning by Ebbing- 



haus, Pavlov, Thorndike, Woodwoitli and Wal- 
3. Guthrie, E. R. The /wvf/(o/ogv of Iraniiiig. 
New York: Harper, 1935. 

A provocative attempt to cover all tlie major 
aspects of learning in terms of the principle of 
association. Quite readable. 

t. Hilgard, E. R., and Marquis, D. G. Condition 
ivg and learning. New York: Appleton -Cen- 
tury, 1940. 

A systematic coverage of the empirical stud- 
ies of conditioned response learning and the 
implication of these studies for the general 
analvsis of all types of learning. 

r>. Hull, C. L. Learning: the factor of the con- 
ditioned reflex. In C. Murchison (Ed.) , A 
handbook of general experimental psychology. 
Worcester, Mass.: Clark University Press, 

A comprehensive review of the most signifi- 
cant experimental studies of the phenomena of 
conditioning published from 1902 to 1934. 

5. Hull, C. L. Principles of bcltavior. New 
York: Appleton-Centiiry, 1943. 

An analysis of the fundamental principles of 

behavior derived from numerous conditioned 
response experiments. Not easy reading. 

7. Hunter, W. S. Learning: experimental studies 
of learning. In C. Murchison (Ed.), A hand- 
book of general experimental psychology. 
Worcester, Mass.: Clark University Press, 1934. 

A good summary of experimental studies of 
the acquisition and retention of learning up to 

8. Kingsley, H. L. The i\ature and conditions of 
learning. New York: Prentice-Hall, 1946. 

The most recent coverage of the facts of 
learning with a good discussion of the rele- 
vance of these facts to the educative process. 

9. McGeoch, J. A. TIte psychology of human 
learning. New York: Longmans, Green, 1942. 

The most authoritative and comprehensive 
summary of present evidence concerning fac- 
tors affecting human learning. 

10. Miller, N. E., and Bollard, J. Social learning 
and iinitalinn. New Haven: Yale l'ni\ersity 
Press, 1941. 

In these chapters there is a clear and inter- 
esting analysis of learning from the point of 
view of stimulus and response, applied later tc 
problems in social psychology. 



Retention and Transfer of Learning 

IN the preceding chapter we studied learn- 
ing, the way learning is accomplished, 
the fundamental conditions which favor 
and hinder learning. Now wc must con- 
sider, first, retention of learning, and its 
opposite, which is forgetting. When do we 
remember and when forget? How fast 
does forgetting go on? And what makes 
us forget? 

In answering these questions we shall 
find ourselves studying the interactions be- 
tween different learnings. Sometimes 
learning one thing means unlearning an- 
other. Sometimes learning one thing 
makes it easier to learn another. There is 
a transfer effect from the learning of one 
thing to the learning of another, a transfer 
which may in some cases help and in other 
cases hinder the new learning. 

With these complex principles and their 
use in the formation of efficient habits of 
study, the present chapter is concerned. 


One phenomenon with which we are all 
familiar, often to our regret, is forgetting. 
We can learn the meanings of a thousand 
French words, but, unless we use them, the 
new knowledge gradually disappears until 
only a few meanings can be correctly gi\en. 

The earliest systematic study of forget- 
ting was made by Ebbinghaus. He himsell 
learned lists of nonsense syllables until he 
could recite a list of them without er)or. 
Then he tried to repeat the recitation after 

2 3 4 

Time interval in days 


Shows decrease in savings when original material 
is lelearned after different periods of elapsed time 
lip to 6 days. [Data from H. Ebbinghaus. Memory. 
I'eacbers College, Colmnbia I'niversity, trans. 191.^. 

p. 76.] 

allowing various periods of time to elapse. 
Figure 63 is his curve that shows the de- 
crease in retention with time— tire forget- 
ting curve. The figure indicates that he 
found a continuous loss in retention Avith 
increases in the length of time during the 
first six davs after the oria:inal learnina;. 

This thaptor A\as prepared by Carl I. Hovhiiul of ^ ale lTni\ersity. 



Retention and Transfer of Learning 

The rate ot loss was rapid at first and then 
much less rapid as time went on. 

How Retention Is Measured 

The simplest way to measure retention 
is to determine the amount we can recall of 
the material originally learned. This is 
usually called the method of recall, or 
sometimes the method of reproduction. 
Recall scores are usually given as the per- 
centage of the original material that can 
be recalled at a later time. If, for exam- 
ple, we learn the meaning of twenty French 
words today but can recall only thirteen 
tomorrow our recall score would be i%o 
or 65 per cent. 

Sometimes, after several years have 
elapsed, we cannot recall a single line of a 
poem we had learned earlier; yet, if we 
attempt to memorize it again, we find it 
comes back rapidly as compared with the 
original learning of the same poem. This 
fact suggests another way of measuring how 
much we retain of what we have learned, 
the method of relearning or saving which 
was first employed by Ebbinghaus and has 
been widely used since. The subject is 
asked to relearn the material after a time 
interval, and his performance is compared 
wath the amount of time, number of trials 
or number of eiTors required to learn it in 
the first place. If, for example, it took 
Ebbinghaus 33 trials to learn a list of 15 
nonsense syllables to the point where he 
could repeat them once without error, and 
after six days it took him only II trials to 
relearn them to the same standard of per- 
formance, we would say he had made a sav- 
ing of 22 trials (33 minus 11.) These re- 
sults are often expressed as a savings score 
in which the numerator is the number of 
trials saved and the denominator the orig- 
inal number of trials. In the present ex- 
ample Ebbinghaus woidd have had a sav- 

ings score of -%->, or 67 per cent. The 
curve of Fig. 63 was determined by the 
method of savings. 

A third method is the method of recog- 
nition. Here the subject is shown the ma- 
terial which he formerly learned together 
with other items which had not been 
shown him initially, and he is asked to 
identify the items which were in the orig- 


off ^4 t 
P-l hr 

2 days 

hr 1 day 

-20 min Time interval 


[From C. W. Luh, Psychol. Monogr., 1922, 31, 
No. 142, 22.] 

inal material. In one memory test, pic- 
tures of a number of persons are studied 
by the subject, and he is asked later to say 
which ones he has seen before. This pro- 
cedure is, of course, the well-known method 
used by the police for identifying suspects. 
When material has been learned in serial 
order, a fourth procedure is often used in 
which the learner is given the original 
items all mixed up and is then required to 
arrange them in the original order. This 
is called the method of reconstruction. 
The learner recalls the relationships but 
not the terms related. As a matter of fact 
a subject who can reconstruct a series can 
nearly always also identify the terms. The 
method is useful for studying the learning 

Refention and Forgetf'ing 


of series of iinrejjrodutiljle icniis, like 
odors or photof^r.iphs. 

The type of forf^cttiiig curve obtained is 
to some extent a function of the type of 
measurement used to determine it. As you 
might expect, forgetting is greatest when 
the learner must reproduce material ver- 
batim. The ability merely to recognize 
what was and what was not originally stud- 
ied (method of recognition) is retained 
longest after learning. The methods of 
saving and reconstruction show intermedi- 
ate amounts of retention. Retention meas- 
ured in these four ways is shown in Fig. 64. 

Individual Differences in Retention 

As we should expect from the close rela- 
tionship between learning and retention, 
wide individual differences exist in the 
amount of material retained over an in- 
terval. Retention plotted against age gives 
a curve closely similar to that presented in 
the last chapter for the learning ability of 
various age groups (Fig. 57, p. 154). By 
and large, we find that more intelligent 
persons retain more than those less intelli- 
gent. Closely related is the general finding 
that the rapid learner is more likely to be 
the good retainer than the slow learner. 
The slow learner gains no advantages in re- 
tention from his slowness, and the fast 
learner suffers no disadvantage from his 
fastness. There is here between individ- 
uals no benign law of compensation, as 
there is between speed and accuracy for 
the single individual. 

The Exceptional Memorizer 

Occasionally, because of remarkable per- 
formance in memorizing and retaining, a 
person attracts popular attention and some- 
times even scientific study. Persons w4io 
can learn a list of two hundred digits in 
nine minutes and retain it for some time or 

who can repeat the numbers of every car 
in a long freight train to a total wliirh fills 
several pages in the (onduclor's nrHcbook 
are cases in point. The fpicstion at ontc 
arises whether such performances are a re- 
sult of some special native ability or of 
intensive practice. Certainly these f»er- 
formances do not require high intelligence. 
One man, for example, who could give the 
populations of any of our laiger cities, had 
an IQ of only 74. The conclusion wiiich 
emerges from the available data on these 
exceptional memorizers is that their per- 
formances are a result of special practice. 
Their abilities are usually limited to nar- 
row classes of materials, such as dates, num- 
bers and similar disparate items. 

The exceptional memorizer is highly mo- 
tivated to put into relation and recall the 
materials with which he works. He groups 
the items, uses them whenever possible and 
utilizes many of the basic methods of learn- 
ing and recalling. With sufficient motiva- 
tion almost anyone could do as well. In 
one experiment the feat of a memory ex- 
pert was duplicated with relatively little 
practice by a group of college students. 
This expert could recall the order of a 52- 
card deck of shuffled cards after twenty 
minutes of study. The college students 
were able to duplicate this performance 
after an average of 5.25 practice periods of 
twenty minutes each. Two students did it 
at the first sitting and twelve at the third. 

Retention of DifFerent 
Types of Material 

A number of generalizations can be 
made about die effect of die t\pe of ma- 
terial learned upon retention. 

(1) Meaningful materials are better re- 
tained than meaningless. A comparison of 
Figs. 6S and 65 illustrates this fact. ^\'e 


Retention and Transfer of Learning 

retain better the material that we under- 
stand than the material that we do not. 

(2) The more extensive the amount of 
material learned, the better the retention. 
When materials of varying length are 
learned to the same level of performance, 
the longer series are better retained. The 
greater effort expended in learning the 
longer lists is, therefore, rewarded with a 

30 60 90 120 
Time interval in days 


[From J. A. McGeoch and P. L. VVhiiely, /. eiluc. 
Psvchol., 1926, 17, 422; reprinted by permission of 
Warwick and York.] 

higher degree of retention. Results on this 
problem are shown in Table VIII. 

(3) Materials which have pleasant emo- 
tional tone tend to be better recalled than 
those which are unpleasant. Most of us 
can find in our own experience how much 
easier it is to remember a pleasant engage- 
ment than one which we expect to be un- 
pleasant. And how much oftener we recall 
our greatest triumph than our most embar- 
rassing moment. 

In one experimental study the investi- 
gator asked his students on the first day 
after Christmas vacation to write out the 
experiences which they had during the va- 
cation period, and then to indicate which 
of the items were pleasant and which were 


Retention for Lists Differing in Length 

Method of recall and method of savings. The 
longer lists, which require more work in learning, are 
retained better. [From E. S. Robinson and W. T. 
Heron, /. exper. Psychol., 1922, 5, 443, and E. S. 
Robinson and C. W. Darrow, Amer. ]. Psychol., 1924, 
35, 241.] 

Number of Items Nonsense Syllables 

in List ' Recalled % Saved 

6 71.3 68.7 

9 78.3 78.8 

12 78.7 78.1 

15 77.0 80.7 

18 81.7 86.3 

Number 0/ Items Three-Place Numbers 

in List % Recalled % Saved 

4 60.0 25.0 

6 66.5 72.5 

8 66.6 69.4 

10 70.8 78.9 

unpleasant. Six weeks later, without any- 
thing having been said about the experi- 
ment, the students were again asked to de- 
.scribe their vacation experiences. Of the 
experiences which they had initially de- 
scribed as pleasant they recalled after six 
weeks fifty-three per cent, whereas less than 
forty per cent of those initially described as 
unpleasant were recalled on the second oc- 

Freud and the other psychoanalysts have 
explained such results in terms of the con- 
cept of lepressioti. They believe that mem- 
ories which are painful tend to be ejected 
from con.sciousness although still present in 
the 'unconscious.' 

It is likely that some of the factors ac- 
counting for the differential recall of pleas- 
ant and unpleasant material can be ana- 
lyzed without recourse to the concept of 
the unconscious. One important factor is 
the greater tendency to rehearse our pleas- 
urable experiences, a repetition which, 
under the law of frequency, results in their 

Retention as Affected by Types of Material and Original Learning 171 

better recall on later occasions. 11, more- 
over, we analyze llie initial un]jlcasant ex- 
perience, we shall usually notice that pain, 
shame or guilt are associated with some 
aspects of the unpleasant situation. Not 
remembering in these instances is a case 
of avoidance conditioning. Just as a man 
learirs to avoid people who are lui pleasant, 
so he learns to avoid activity (in this case 
remembering) which is unpleasant. It is 
also true that we learn to make other re- 
sponses to the clues which originally 
aroused the feelings of shame or guilt. 
These responses serve as distractions and 
help us to inhibit the recall of unpleasant 

Retention as Affected 
by Original Learning 

The amount of material retained is in- 
fluenced to a considerable extent by the 
method used in learning it initially. 

(1) The set with which a material is stud- 
ied affects the degree to which it is reniem- 

Time interval in days 


Shows mean recall scores at intervals of 1, 3 and 
7 days following the memorization of 12 nonsense 
syllables by distributed and massed practice. [From 
J. A. McGeoch, The psycJiology of human learning, 
Longmans, Green, 1942, p. 130.] 


1 1 1 

1 i / 






= 407 


/ _ 











/ 1 II 

1 1 

8 16 24 32 42 53 64 

Number of repetitions of original learning 


The graph shows the savings after 24 hours for 
different numbers of repetitions in the original 
learning. [From J. A. McGeoch, The psyrholo^- ul 
human learning, Longmans, Green, 1942. p. 377.] 

bered. Retention is gieater when the ma- 
terial to be learned is studied with the in- 
tent to reinember it over a long periotl 
than when it is studied with the set to learn 
it only for immediate recall. 

(2) Recitation of material during learn- 
ing increases the amount -which •will be re- 

(3) Material learned by distributed prac- 
tice is better retained than material learned 
l)\ massed practice, when both are learned 
to the same level initially. Retention 
cur\es obtained under these \.\\o condi- 
tions are shown in Fig. 66. » 

(4) The greater the degree of original 
learning, the greater the retention. This 
relationship is illusU'ated in Fig. 67. 

(5) DegTee of retention depends upon 
whether the original learning task is com- 
pleted or whether it is discontinued be 
fore completion. (See pp. 133 f.) 


Retention and Transfer of Learning 


Although rajjid initial foigeliing is the 
rule, there are some interesting exceptions. 
Sometimes we find that, when we have been 
studying material for a while, we do better 
if we lay it aside and come back again to 
it later. The psychologist, William James, 
called attention to this phenomenon in 
striking fashion when he said that "we 



1 1 1 





c 9.5 



1 ^-^ 



S. 8.5 

— ^ 

•««.,„„^_^^ — 



1 8.0 







1 1 1 

HoH 2 

5 10 

Length of interval in minutes 


The graph shows retention (correct anticipations 
in recall) as a fimction of elapsed time up lo 20 
minutes after learning. Lists of nonsense syllables 
were the material. Retention is greater at 30 sec- 
onds and at 2 nrinutes than it was at 6 seconds or 
than it will be at 5 minutes or thereafter. Remi- 
niscence is this increase shortly after learning. 
[From L. B. Ward, Reminiscence and rote learning, 
Psychol. Monogr., 1937, 49, No. 220, 17.] 

learn to skate in the summer and learn to 
swim in the winter." This phenomenon of 
improvement in performance without in- 
tervening practice is called reminiscence. 
A retention curve showing reminiscence is 
shown in Fig. 68. 

The conditions under which reminis- 
cence rather than forgetting is obtained are 
not completely known. It appears at pres- 
ent that reminiscence indicates that there 
is some interference which operates at the 
end of practice and which disappears with 
the passage of time. If this explanation is 

valid it would be reasonable to expect that, 
if we gave short rest intervals after each 
practice trial, the interferences would not 
accumulate and reminiscence would, there- 
fore, not occur. This result has indeed 
been found and is shown in Table IX. 


Reminiscrnce after Massed and after Distributed 

[From C. I. Hovland, /. exper. Psychol., 1938, 22, 212.] 

AJter After 

Massed Distributed 
Practice Practice 
(a) Number of syllables recalled on trial 
immediately after learning has reached 
the level of 7 correct syllables out of 12 6.96 8.00 

(J) Number of syllables recalled on trial 2 
minutes after learning has reached the 
level of 7 correct syllables out of 12 7.49 8.04 

Reminiscence = (i) — (a) 0.53 0.04 

The general conclusion is that both remi- 
niscence and distributed practice gain their 
advantage for recall by the removal or 
avoidance of some inhibiting factor rather 
than by the introduction of a special rein- 
forcing agent. 


It was once thought that forgetting is 
due merely to the lapse of time, that an 
impression made on nervous tissue would 
naturally fade out. There is now consider- 
able evidence to show that this simple ex- 
planation is inadequate. Both laboratory 
experiments and common sense support 
the view that the rate of forgetting during 
a time interval must be dependent upon 
w^hat is going on during that time rather 
than upon time itself. 

This conclusion receives supjjort from 
the fact that retention during active wak- 
ing hours is poorer than retention during 
sleep. Ordinarily, on waking up we can 
recall what we did before retiring better 

Forgefting and Reiroactive Inhibition 


than wc can recall in the cvciiin;^ what wc 
did that morning. 

The results of an interesting laboratory 
exjaeriment on this topic are shown in Fig. 
69. Two subjects were tested after varying 
amounts of sleep, and again after varying 




s 5 









— --- 




\ \ 













this study concluded that "forgetting is 
not so much a matter of the decay of old 
impressions and associations as it is a mat- 
ter of interference or obliteration of the 
old by the new." The old impressions fade 
because they are blotted out by the new- 
impressions of an active waking life. 

Retroactive Inhibition 

Considerable research has been devou-d 
to finding out more about this problem ol 
how intervening activities affect retention. 
Usually it is found that learning another 
sample of the same material during the in- 
terval between the end of practice and the 
measurement of retention produces a decre- 
ment in retention. Such interference is 
called reiroactive inhibition. 

The experimental procedure employed 
in studying retroactive inhibition is of the 
general form shown in Table X, where the 


Experimental Procedure for SruD-iTNG Retro- 
active Inhibition 


Two subjects learned 10 nonsense syllables. The 
graphs show tor each subject the number of syl- 
lables recalled after 1, 2, 4 and 8 hours when the 
subjects remained awake, and when they went to 
sleep. Forgetting is less during sleep and almost 
nonexistent when sleep has become sound 2 hours 
after learning. [Adapted from J. G. Jenkins and 
K. M. Dallenbach, Amer. J. Psychol., 1924, 35, 610.] 

amounts of interpolated work. The curves 

Condi - 






Final Test 

(1) Rest 

Learn (.4 ) 


Measure retention of (.-I) 

(2) Work 

Learn (.-1) 

Learn (B) 

Measure retention of (.4 ) 

letters A and B stand for two different 
learning materials. The difference between 
retention under these two conditions— 
(1) rest and (2) work— is the gross amount 
of inhibition. 

If a subject recalls ten words of list A 
after rest and onlv six words of A after the 
work of learning B, he shows a gross inter- 
ference effect of four words and a relati\e 
for the subjects when they remained awake interference of forty per cent owing to the 
fall with negative acceleration in a manner interpolated acti^itv B. The two condi- 
not unlike the forgetting curve obtained by jions must be arranged so that they differ 
Ebbinghaus (Fig. 63). The curves for the importantly only with respect to the inter- 
subjects tested after various amounts of polated activity (rest or learning) between 
sleep fall less rapidly during the first two the original learning and the measurement 
hours, and then not at all. The authors of of its retention. 


Retention and Transfer of Learning 

The experimentally obtained decrements 
from interpolated learning vary in amount 
from nearly zero to almost one hundred per 
cent. The amoimts which appear are a 
function of several conditions. (1) Over a 
considerable range of similarity, degree of 
inhibition varies directly with the degree 
of similarity between the orginal and the 
interpolated activities. "When, for example, 
the original material consists of lists of ad- 
jectives and the interpolated material of 
lists of synonyms of these adjectives, the 
amount of inhibition is maximal and de- 
creases when antonyms, unrelated ad- 
jectives, nonsense syllables and three-place 
numbers are interpolated. (2) Meaningful 
material is less susceptible to retroactive 
inhibition than unrelated disconnected ma- 
terial. (3) The longer the material and the 
more difficult to learn, the less susceptible 
it is to inhibition. (4) The amount of prac- 
tice with the original and interpolated ma- 
terials affects the amount of inhibition. If 
the learning of the interpolated activity is 
held constant, inhibition decreases with in- 
creased learning of the original activity. 
When, on the other hand, the degree of 
original learning is kept constant, inhibi- 
tion increases at first with degree of inter- 
polated learning. As complete mastery is 
approached, however, additional incre- 
ments of interpolated learning cease to in- 
crease the amount of inhibition and may 
finally even decrease it. 

Alteration of Stimulating Conditions 

Retroactive inhibition brought about by 
the interpolation of new learning accounts 
for a large share of forgetting, but another 
important factor is the alteration of the 
stimulating conditions between the time of 
learning and the time of the measurement 
of retention. Forgetting will occur be- 
cause some of the stimuli present during 

the original learning arc missing during 
recall, or it will occur when ne^v stimuli 
are present which evoke competing re- 
sponses sufficiently strong to block the orig- 
inally learned ones. These stimuli arc both 
external (like the furniture in the room, 
the ap23aratus, the experimenter) and in- 
ternal (like sensations resulting from pos- 
ture, responses made during learning). Re- 
call may be reduced merely because the 
learning has taken place in one classroom, 
whereas the testing of retention is con- 
ducted in a different room. 

Similarly, when words are learned with 
one color of backgiound, recall is reduced 
when the color is changed. A language 
learned in one setting may be poorly re- 
tained in a different setting. One person, 
for example, lived for several years in 
China and acquired considerable fluency in 
Chinese. Upon his return to the United 
States for a couple of years' vacation, he 
fotmd that by the end of the time his abil- 
ity to speak and understand Chinese had 
practically disappeared. Upon his return 
to China, however, he was astonished to 
discover that he was again able to speak the 
language fluently. This is a dramatic ex- 
ample of the familiar phenomenon of be- 
ing unable to recall material in a changed 
context, as when we are not able to remem- 
ber the name of a person who is met in a 
new environment, although his name 
comes readilv enough in the usual environ- 

Change of Set 

It is probable, although the experimen- 
tal evidence in support of it is not yet 
conclusive, that forgetting also depends 
upon our set. That interest or set in a 
given direction has a selective influence 
on recall is well known; if the set is in 
an incorrect direction, recall may fail. 

Forgetting and Unlearning 


even though with a correct set it may occur. 
Thus, it in seeking to recall a name we in- 
sist incorrectly that tJie name is Scotch, the 
search may be confined to Scotch names lo 
the neglect of others, and it will seem that 
the name has been forgotten. When the 
correct set is established, the name may be 
(jiiickly recalled. 

There is no lack of evidence that set 
helps recall. In the reaction exjxriment 
we rcmemlier lo press the key when we sec 
the gieen light, provided we are set to make 
this reaction. We start to the theater at 
eight o'clock because we perceive the lime 
and a set— a special set lor this particular 
evening— operates. Posthypnotic sugges- 
tion also shows how set affects recall. But, 
if set can make us remember something, il 
can also make tis forget something else, be- 
cause the range of human attention is lim- 
ited; and remembering one thing is neces- 
sarily, at least at the moment, a forgetting 
of everything else. 

The psychoanalysts argue that forgetting 
may be wishful, that we forget what we 
piefer not to remember. Jones is talking 
to a girl whom he is courting. Smith ap- 
pears. Jones dislikes Smith and is jealous 
of him. Jones knows Smith vei"y well, in- 
deed had called him by name only that 
same morning. But now, strangely. Jones 
is at a loss to recall Smith's name. Try as 
he will the name will not come. He is em- 
barrassed and blushes, mufFs the proper in- 
troduction to the girl. Was not Jones' ab- 
normal forgetting an intentional one? Did 
he not want to forget Smith's name, and 
succeed? It is very hard to arrange a test 
case to prove or disprove this kind of un- 
conscious intentional forgetting, for there 
are always other possible ways in which the 
forgetting might have occiured. It is. 
moreover, possible that Jones actually did 
remember Smith's name momentarily, put 

it out of his mind and then forgot that he 
remembered. Nevertheless such deter- 
mined forgetting is consistent with many 
other phenomena— with the facts of hvj>- 
nosis and with the adjustive mechanisms of 
the jjcrsonaliiy (pjj. 520 f.). 


Forgetting is (he natural dropping out ol 
one habit owing to interference by Jiew 
learning. On some occasions, how'ever, we 
wish to reduce the strength of a habit de- 
liberately, to forget by design. This proc- 
ess of 'unlearning' assumes particular im- 
])ortance when bad habits need breaking. 

Overcoming Fears 

One of the earliest studies of unlearning 
was an attempt to teach childien to get 
o\er their fears of being alone or in a dark 
room and their fears of snakes, rabbits and 
other animals. 

It is often suggested that fears will dis- 
appear spontaneously if no further contact 
with the feared object occurs. In this ex- 
periment no diminution in the strength of 
fear occurred by simply not exercising the 
fear. A'erbal appeal, in which the experi- 
menter talked about the feared object, con- 
necting it with pleasant experiences, was 
likewise quite ineffective. 

The method of 'negative adaptation' was 
also tried, a method in which the child was 
exposed to the feared object repetiti\ely. 
In one case this procedure led to consider- 
able improvement, but in other cases the 
children actually became more frightened. 
Ridicule of tlie fear caused the childien to 
hide or repress their fear without actuallv 
feeling less afraid. 

Under certain conditions distraction was 
effective. When tovs and plavthings which 
the tliild wanted ^\cre placed near ihc 


Retention and Transfer of Learning 

frightful animal the child was, in some 
cases, so eager to get the toys that he would 
ignore the animal. But this method re- 
quires the constant presence of an adult to 
arrange the distractions, and the effects 
seemed temporary. 

The two ways which -were found most 
effective in overcoming the children's fears 
were (1) reconditioning and (2) social imi- 

In the first method, direct conditioning 
was used to associate the feared object with 
a stimulus capable of arousing positive re- 
actions of acceptance and pleasantness. 
For example, when hungry, a child was 
placed in a high chair and given something 
to eat. Then the feared object was brought 
in and placed some distance away. Grad- 
ually the object was moved closer and 
closer to the child as he ate. In this man- 
ner tolerance would be giadually built up 
until the child became indifferent to the 
feared object and in some cases finally re- 
sponded positively to the object with ac- 
ceptance and interest. That is recoJidi- 
tioning. This method must, however, be 
very carefully applied. If the child fears 
the object intensely and the object is intro- 
duced too rapidly, the treatment may 
'boomerang,' so that the child learns to be 
afraid of eating instead of learning to like 
tlie rabbit or snake or whatever the feared 
object is. 

The method of reconditioning was used 
by the British during the Second World 
War as their 'battle conditioning.' The 
training was directed at reducing soldiers' 
initial fear of artillery. The British used 
the method of gradual increase in exposure, 
starting with the discharge of a gun at a 
great distance from the training ground, 
and then each day bringing discharges of 

ammunition closer and closer, luitil the 
soldiers could at least tolerate quite intense 
artillery fire without signs of fear. 

The method of social imilation is to 
allow the children to participate in the 
activity of other children who react to the 
critical object without fear. When the so- 
cial group in which the child is placed has 
great prestige for the child, he behaves the 
way the group bcha\es. When the other 
children approach the object without fear, 
the child who was afraid accepts the sug- 
gestion from the others and loses his fear. 

Breaking Habits 

A novel method of breaking habits has 
been described by Knight Dunlap. In his 
procedure the individual is taught to prac- 
tice the very error he wishes to eliminate. 
For example, Dunlap had the 'bad' habit 
of typing "h t e" for "t h e." By deliber- 
ately practicing the writing of "h t e" he 
became more fully aware of his move- 
ments, brought the misspelling under con- 
trol and thus broke the habit. If we are 
not fully aware of the undesirable move- 
ments we are making it is hard to stop 
making them. Stuttering, nail biting and 
other undesirable habits have sometimes 
been curbed by practicing them with the 
set to break them. This method may at 
first glance appear contradictory to the 
principle learned earlier that practice fix- 
ates a habit (law of frequency, p. 153). We 
shall realize, however, that deliberately 
practicing a habit we know to be bad is 
punishing rather than rewarding, and 
lience would be expected to result in ex- 
tinction of the habit (law of effect, p. 147). 
The important factor in Dunlap's method 
is, however, the having of insight into the 
nature of the habit. 

Another effective procediue is to recon- 

Unlearning and Transfer of Learning 


dition the subject by attaching new but in- 
compatible responses to the old stimulus 
which originally produced the undesired 
response. We are told to "Reach for a 
Lucky instead of a sweet." We can break 
the habit of eating too much candy if we 
can substitute for candy eating the incom- 
patible response of cigarette smoking when- 
ever we have a craving for candy. After 
that we can break the smoking habit with 
chewing gum. 

Punishment is sometimes useful in break- 
ing up habits, but it must be carefully 
timed. If applied too long after the act 
which is to be corrected, the unpleasant- 
ness is likely to be associated with the 
events just preceding the punishment 
rather than with the act to be extinguished. 
(See p. 148.) Furthermore, punishment is 
unreliable in its effects, and particularly so 
with children. It is likely either not to be 
severe enough or distracting enough really 
to break up the habit. Instead it may re- 
inforce the habit by making its perform- 
ance exciting. Excitement usually facili- 
tates the learning of habits. In this way 
the 'naughty' behavior of children may be 
encouraged by mild punishment or by 
moderate parental opposition. Once again 
we may note that reward is better than 
punishment, praise is better than reproof, 
for the facilitation of training. 


It is seldom that the situation in which 
we learn is identical with the situation in 
which we use the learning. For example, 
we learn arithmetic at school and use it in 
the grocery store. To what extent does 
learning transfer from one situation to an- 
other? In a common-sense way we know 
that old learninsf is useful in new situa- 

tions. A man who has learned to drive one 
car can drive a similar car almost a.s well 
without additional practice. That we call 
positive transfer. On the cHher hand, pre- 
vicHis learning often interferes with new 
learning. If, for example, a man learns to 
type with a special kind of keybcjard, he 
has a much more difficult time learning to 
use a standard keyboard than if he had 
started with the standard one in the first 
place. It is for this same reason that ini- 
tial learning with the 'hunt-and-peck' 
method of typing may make it actually 
harder to learn with the touch system. 
When learning one task makes learning a 
second task harder, we speak of negatiiH' 
transfer. Would you expect that it would 
be more difficult, less difficult or about 
equally difficult to teach golf to a person 
who was expert at tennis than to teach 
golf to an equally competent person who 
had not learned tennis? That is the kind 
of problem with which we are concerned 
in studies on the transfer of training. 

Formal Discipline 

Not so long ago educators had a clear-cut 
answer to these problems. They believed 
that the mind was composed of a number of 
faculties which could be improved through 
exercise, just as a muscle is strengthened 
by use. Consecjuently thev believed that 
certain subjects should be taught in school 
primarily for their disciplinary value, espe- 
cially Latin, Greek and mathematics. This 
theory is now called the doctrine of formal 
discipline, the theory that what is hard is 
good for us because it makes us suong. 
Such a statement carries ■with it a specious 
tone of morality of which we must beware. 
Learning higher mathematics A\ould bene- 
fit an astronomer but would scarcely im- 
prove the art of a glamour girl. Transfer 


Retention and Transfer of Learning 

niav be positive or missing or even nega- 
tive. Learning is not good just because it 
is hard. 

The first experimental attack on this 
problem was made by the American psy- 
chologist, William James. He determined 
to find out whether practicing the memori- 
zation of poetry really improved memoriz- 
ing ability. First he learned 158 lines of 
\'ictor Hugo's Satyr and recorded his time. 
Then he spent more than a month commit- 
ting to memory Milton's Paradise Lost. 
When he had finished with it he returned 
to the Satyr and memorized another 158 
lines. He found that these 158 lines actu- 
ally took longer than the first 158, and he 
concluded that all the work on Paradise 
Lost had not improved his ability in memo- 
1 izing. 

James' study was not ideally set up as an 
experiment and was therefore not conclu- 
sive, although it did set other investigators 
to studying the problem. We question 
whether James' learning was representa- 
tive of all learning. We do not know 
that the first 158 lines were equal in diffi- 
culty to the second. We wonder whether 
James' physical condition was the same at 
the two times. (He himself says he was 
fagged out by other work at the time of 
the second learning.) We note that the 
effect of practice itself was not separated 
from transfer of training proper. 

A Transfer Experiment 

Later experiments have corrected these 
procedural defects. A large number of 
subjects has been used. To rule out prac- 
tice effects, two equivalent groups have 
been employed, of which one was given the 
practice and the other (the control group) 
was not given any practice. This gives the 
following experimental design. 

Experimental Group 

(1) Given test on activity {A) 

(2) Then given training on activity (fl) 
{Tj Then retested on activity {A) 

Control Group 

(1) Given test on activity {A) 

(2) Then given no further training 

(3) Then retested on activity {A) 

The amoimt of transfer— the effect of 
learning [B) on skill in {A)—h measured by 
the amount of improvement— (3) minus (I) 
—made by the experimental group as com- 
pared with the improvement made by the 
control group which did not get any prac- 
tice. (See Table X, p. 173.) 

These later experiments have greatly 
extended our knowledge of the conditions 
imder which transfer of training occurs. 
Several types of transfer can be distin- 

Transfer within 
the Same Class 

Practice upon one sample of a given kind 
of material— mazes, word lists, poetry, etc.— 
usually affects favorably the learning of 
other samples of the same kind of material. 


Positive Transfer 

Effect of Learning Maze A upon Si'bseqtient 
Learning of Maze B. 

The number of trials, the number of errors and the 
time are all averaged. The time is in seconds. [From 
L. W. Webb, Psychol. Monogr., 1917, 24, No. 104, 18.) 

Measure of Performance in Maze B 

Trials Errors Time 

Mean A.D.* Mean A.D. Mean A.D. 

(1) Maze B (con- 

trol) 33.6 14.3 285.2 205.4 1166.0 514.2 

(2) Maze B preceded 

by Maze A 

(experimental) 10.8 5.9 32.4 13.7 149.4 54.7 
Number of units 
(1) minus (2) 22.8 252.8 1016.6 

* Average deviation from ihc mean 

Transfer of Learn'mg 

A sample of such positive liaiislt r is shown 
in Table XI, where the learning ol one 
maze is seen to reduce the time required to 
learn a second maze. Under certain condi- 
tions, however, negative instead ot positive 
transfer may be found. 

Bilateral Transfer 

liilateral tiansfcr, or cross-education, an- 
oilier form of the positive transfer of learn- 
ing, is the facilitation of the learning of re- 
sponses on one side of the body by the pre- 
vious learning of responses made on the 
other side. When we practice a task with 
the left hand for a number of trials, we usu- 
ally find that we can learn to do the same 
task with the right hand in many fewer 
trials than if we had not initially practiced 
with the left hand. 

Bilateral transfer has been found in a 
large number of acts, among them mirror 
drawing (tracing a diagram when we can 
see only it and our pencil reflected in a 
mirror), rapid tapping on a tapping board, 
tossing a ball at a target, finding and learn- 
ing the correct path through a maze. The 
amount of transfer varies from a small 
amount to as much as fifty per cent. Tact- 
ual discrimination of the Braille alphabet 
for the blind by subjects with normal vision 
has been found to transfer completely from 
one hand to the other. That is a positive 
transfer of one hundred per cent. Con- 
ditioned responses established on one side 
of the body have been found to appear on 
the other side with a consistency almost 
equal to that shown on the side used in 

Bilateral transfer is common enough 
when great motor precision is not required, 
as in learning to shift automobile gears, 
to manipulate the knobs on a radio, to 
handle a telephone transfer readily from 
one hand to the other. Such transfer is 

seldom ((jiiipletc at the bcgiruii 

learning on the new side is so 

it very (juickly reaches the level 

an(e which the first-trained siuc i^v,_. 

long practice to attain. 

Transfer from One 
Class to Another 

The next qucsiion, the one which is Ijasic 
in the problem (jf jonnal disiipUne, is 
whether practice upon one or more samples 
of one class will facilitate the learning of 
samples of a different class. Will practice 
at maze learning facilitate card sorting? 
Will practice at learning nonsense syllables 
transfer to learning poetry? Will studying 
Latin help in writing better English? AVill 
it help in learning calculus? AVill it help in 
learning golf? Would the formal discipline 
in learning to make discriminations help a 
rat to find the goals in mazes? 

One of the most important studies of 
transfer of academic training was made 
by Thorndike. He studied the eftect of a 
year's work in such high school studies as 
Latin, mathematics and history. All stu- 
dents used in his study were first given a 
test of "selective and relational thinking." 
An equivalent form of the same test was 
given again at the end of the vear. During 
the year some of these students took a pro- 
gram which included Latin, mathematics, 
history and other subjects, while others 
instead took subjects like shop work and 
bookkeeping. Thorndike then compared 
the relative effects of different school sub- 
jects on performance in the test. The ef- 
fects were so small that Thorndike con- 
cluded that there is no marked balance in 
favor of one rather than another school sub- 
ject in its effect on "selective and relational 

Numerous otlier experiments ha\ e tended 
to confirm these findings. The evidence 


Reiention and Transfer of Learning 

indicates that the most effective way to 
achieve a desired educational objective is 
to train directly for it rather than to hope 
to attain it as a by-product of training in 
other subjects which have been taught for 
their disciplinary value. These results sup- 
port the trend in modern education to 
teach things for their own values— social, 
esthetic, recreational or utilitarian, as the 
case mav be— rather than for a general 
training of the mind, a kind of training 
which is not known to be possible. 

On the other hand, there are all sorts of 
wavs in whicJi having learned one thing may 
help a student to learn another. Learn- 
ing Latin may help the formation of the 
habit of sitting still and paying attention 
to the contents of books, so that the Latin 
does make the learning of mathematics 
easier. If a student ^vith a poor scholastic 
record should do brilliantly in Latin, be- 
cause it is easy for him, his pride in his 
success might motivate him to work harder 
with his algebra, which is hard for him, 
and thus unexpectedly to do well in al- 
gebra. For studying one thing he may have 
to hunt up a quiet place so that he can 
concentrate on his work. Then that place 
Avill remain available for studying other 
things. So situations transfer, fundamental 
habits of study transfer, motivation and 
pride transfer from one study to another. 
Formal discipline often, not always, has 
positive transfer effects of these kinds. Yet 
even then formal discipline is inefficient. 

Positive versus Negative Transfer 

\\t have seen that while positive trans- 
fer is ^ery common, negative transfer also 
occurs. AVhat determines whether the 
transfer is positive or negative? Research 
indicates that the most important fac- 
tor is whether the new learning involves 
making an old response to a new stimulus 

or making a new response to an old stimu- 
lus. In the former case, where we are learn- 
ing to make an old response to a new stimu- 
lus, positive transfer is the rule. We shall 
see that this phenomenon is similar to that 
of generalization in conditioning (p. 141). 
The general principle is that each new 
stimulus siluation tends to elicit the re- 
sponse which has been connected u'itli 
similar stimulus conditions in the past. 

On the other hand, when a new response 
must be made to an old stimulus, transfer 
is usually negative. This result has been 
generalized as the law of associative inhibi- 
tion, which states that luhen any tivo items, 
like a stimulus A and a response B, have 
been associated, it is more difficult to form 
an association betu'een the initial item, A, 
and a third item, K. If, for example, you 
are accustomed to carry your cigarettes in 
your right pocket but shift them over to the 
left, you will observe numerous errors and 
false movements in learning to reach auto- 
matically to the new location. The stimu- 
lus, desire for a smoke, which has been 
connected with the response reach-to-the- 
right-pocket, must now become connected 
with the response reach-to-the-left-pocket. 
The formation of this new association is 
interfered with in its early stages by the 
appearance of the old response, now wrong, 
or by delay and fumbling. 

In general, it is clear why this difference 
between positive and negative transfer oc- 
ciu's in these cases. If we have learned 
the sequence stimulus-/l-to-response-fi, and 
want then to learn the sequence stimulus- 
/-to-response-B, we have positive transfer. 
AVhen / occurs, A is not there to interfere, 
and B is attached to / easily because we got 
familiar with B and made it more meaning- 
ful when we were learning A-to-B. On the 
other hand, when we wish to substitute for 
A-lo-B the new association ,^-to-A', we find 

Efficient Study 


Ji iiKikinsj; I rouble lor A'. VVIuri // (nciirs, 
B is likely to appear and prevent or dehiy 
the appearance ol A's new partner, A'. It 
is this conflict that makes (he transler nega- 


All the general principles that apply to 
learning and retention are applicable to 
the student's daily work and study habits. 
We shall, therefore, consider here use of 
these basic principles in laying down rules 
lor the improvement of efficiency in study- 


One well-known textbook advises stu- 
dents: "Be motivated!" Although we can- 
not, of course, turn motivation on and off 
on demand as this advice implies, the im- 
portance of motivation in learning cannot 
be overemphasized. The best motive for 
learning is a strong desire to achieve cer- 
tain results by learning. When you want 
to drive the family car, you don't have to 
be bribed to take driving lessons. Are you 
equally interested in the outcome of your 
school learning? It is worth while to re- 
view every now and then your ultimate 
goals to remind yourself of why you are 
studying at all. But ultimate goals are 
often too remote to provide effective moti- 
vation. We saw in the preceding chapter 
(p. 147) that the more immediate the re- 
ward, the greater the learning. One way 
of taking advantage of this fact is to set 
for yourself intermediate goals short of the 
final one. 

These subgoals enable you to see how 
you are doing and thus to guide your fu- 
ture improvement. Try to make the goals 
as concrete as possible and keep accurate 
tab of your progress in achieving them. 
Some students find it helpful to make up a 

(liart in wliifli I hey record iluir j>rogrcss 
(such as liow many foreign words they arc- 
able to translate, or the number of errors 
I hey make on successive examinations). 
J he United States Army found this tech- 
nique extremely helpful in improving per- 
formance. In some cases men had been 
instructed in learning to operate complex 
weapons merely by being told to "practice 
for a while." When a system of informing 
them exactly how well they did on each 
trial was introduced, their performance 
improved rapidly. Plotting your own per- 
formance as you go along is a way of com- 
peting with yourself. Another good mo- 
tivation booster is to compete with others 
in your class or with your roommate's per- 

Although it is helpful to maintain a high 
level of motivation, you should not attempt 
tasks beyond your ability. You must set 
your level of aspiration at a level commen- 
surate with your ability. Otherwise you 
will experience constant frustration, and 
the consequent absence of reward will re- 
duce the efficiency of your learning. 


Even with the best of motivation, studv 
cannot be efficient unless it is carefulh 
planned. Most students find it helpful to 
draw up a schedule in which are listed all 
their daily activities with a specific time 
reserved for each type of activity. Such a 
schedule, to be realistic, must include time 
for recreation and even for '^vasting.' 
Scheduling helps to separate work sharply 
from play, inaeasing the efficiency of each. 
A loose mixture of 'fiddling around' and 
work is likely to be inefficient for work and 
not much fun as play. To have dutv 
watching while you play cuts down the joy 
of playing. 

In planning a work schedule of diis sort. 


Retention and Transfer of Learning 

it is well to bear in mind the facts about 
distribution of practice (pp. 156 f.). You 
should determine for each topic the opti- 
mum length for your uninterrupted study. 
You have to hit near the happy medium 
between bareh getting warmed up before 
you shift to the next topic and keeping on 
with interference, boredom and fatigue 
working against you. 

In arranging a program, a\oid 'cram- 
ming' just before examinations. Hurriedly 
learned is hurriedly forgotten. Careful ini- 
tial learning with periodic review insures 
the best retention. 

In laving out your plans it is well for 
you to provide for a constant place in 
which to study. Such a place will come to 
provide cues for study and will lack the 
distraction which a changing environment 
is likely to have upon performance. Even 
if the place is noisy, it is better to have a 
constant noise than a variable, unpredict- 
able, imperfect quiet. You can get accus- 
tomed to the same old noise, and then it 
will not distract you, may, in fact, even 
spur you on to work a little harder, in the 
way that the continuous jumble of a radio 
can help some students to study better. 

Reading Habits 

Since learning in college deals so largely 
with verbal material, it is extremely im- 
portant that the individual be able to read 
efficiently. For efficiency, it is of first im- 
portance that your reading instruments, 
your eyes, should be up to their peak per- 
formance. A check-up on your eyes by a 
competent eye doctor wall guard you against 
defects which can be corrected by exercise 
of the eyes or suitable glasses. Headaches 
and tension aroimd the eyes are often at- 
tributable to poor vision. Also important 
for maximal visual efficiency is adequate 
illumination. Arrange for enough light to 

fall directly on the material you are read- 
ing. (For the specification of the best in- 
tensity and distribution of illinnination, 
see pages 475-477.) 

Efficient readers differ markedly from in- 
efficient in the way they read. Study of 
eve movements may help you to improve 
your efficiency in reading and learning. If 
you will take a page of reading material 
and cut a small hole in it, about the si/e 
of a dime, and will ask a friend of yours 
to read the page while you watch his eyes 
through the opening, you will be able to 
make some interesting observations. You 
will see that his eyes do not move continu- 
ously along the lines as he reads but jimip 
a few words, then pause, then jump again. 
Between the end of the last pause on one 
line and the first on the next there is a long 
sweeping movement. During this time 
the eyes are not able to see. At each pause, 
or fixation, the reader takes in several 
words. The more words w^hich he can take 
in per fixation, the fewer fixations he needs 
and hence the more rapid his reading. Slow 
readers not only take in very small nimi- 
bers of words at a time but often will be 
observed to go back and reread, a shift 
called regression in reading. Regression, 
of course, greatly reduces reading speed. 

Considerable increase in reading speed 
can be achieved through practice. In one 
experiment a poor reader was able to re- 
duce his pauses from 15.5 to 6.1 by prac- 
ticing only twenty minutes a day for twenty 
days. He Avas able to comprehend just as 
much at the increased speed. Practice 
should consist primarily of forcing yourself 
to read as rapidly as you can without sacri- 
ficing the meaning of what is being read. 
All of us can benefit by this practice, since 
nearly everyone reads less rapidly than his 
capacity permits. 

Slow readers also tend to vocalize the 

Efficient Study 


words as ihey read them, often using actual 
tongue and lip movements. This unneces- 
sary extra work lurtlicr slows down read- 
ing s|xc'd. Silent reading increases read- 
ing speed, and with practice you can learn 
to read swiftly and silently without loss of 
the significance and meaning of the text. 
One of the most common reasons for slow 
reading and eye movement regression is 
lack of adequate vocabulary. A shortage 
of familiar words can be readily overcome 
by a systematic use of the dictionary. Mak- 
ing a habit of looking up in the dictionary 
every word which is unfamiliar to you will 
save you time later, and, as your vocabulary 
increases, yoin- reading rate will also im- 


Learning the definition of all imfamiliar 
words will also help learning by increas- 
ing its meaningfulness. Another way in 
which we can take advantage of this im- 
portant factor is by getting a bird's-eye 
view of the entire material to be learned 
befoie concentrating on the individual 
parts to be learned. Such a perspective in- 
creases interest in the details and makes the 
entire task more significant. 

In learning new material always try to 
relate it to material you already know. It 
is much easier to add a new fact when you 
already have a background for it than to 
learn a new isolated fact related to noth- 
ing else in your repertoire. Translating a 
material into your own words is also help- 
ful in guaranteeing that material will be 
meaningful, as well as in adding the favor- 
able circumstance of more active participa- 
tion to the learning. When you do not 
jjaraphrase a material as you learn it, you 
may find that you have it in fairly good 
shape for verbatim reproduction but that 
you can recall the words better than the 

sense. Usually what you want to rernembei 
is the sense. C)ne good way to get more 
sense than words is to study mateiial from 
more than one source. Reading the same 
topic in several different textbooks will 
give you a better knowledge of the topic 
than a single coverage, even if the same 
points are covered. Approaching the same 
material from different points of view also 
aids in retention. It may seem confusing 
to read two books that appear to contradict 
each other, but if you put into your learn- 
ing the activity necessary to resolve the con- 
fusion and make the sense consistent, vou 
will know more than you would if you had 
had only a single clear consistent but un- 
challenging book to read. 

Active Participation 

There are many ways in which learning 
can be favored by making participaticjii 
more active. When material is studieil 
with the intent to remember, it is better 
retained than when read without intent to 
remember. Just studying with the book 
in front of you never insures learning. 
You have actively to practice what you are 
trying to learn. You can, for instance, at- 
tempt to recite the material in ^\•hate\er 
way you wish to learn it, Avords or sense. 
Close your book and see how much of the 
material you can recall. If aou are studv- 
ing for quizzes, think up questions for voin- 
self and undertake to answer them. Keep 
putting your book down to see how much 
of the material you can recite after \ou 
have read it. 

Active participation in leaining also im- 
plies paying close attention to the material 
you wish to acquire. \'arious niemoi-y 
systems attempt to guarantee this close at- 
tention by elaborate ile\ices. memory 
'crutches.' If you will spend the same time 
and effort directlv on the material that ii 


Retention and Transfer of Learning 

required to learn the system, nou will usu- 
ally be ahead of the game. 

And do not forget the importance of 
overlearning, if you want the material to 
stick. Never be satisfied with bare mastery. 
Alwavs learn your material well enough so 

that distractions and excitement will not 
interfere with your recall. 


See the references cited for learning at the end 
of Chapter 7, pp. 165 f. 


Recollecting, Imagining and Thinking 

ALL the topics to be dealt with in this 
^ chapter are frequently referred to by 
the layman as thinking. When he says, "I 
am thinking about the time my car skidded 
into the ditch," he probably means that he 
is going once more through the experiences 
of that accident, recalling the visual scene 
of the road, the snow and ice, reproducing 
the 'feel' of the car as it went out of con- 
trol and re-experiencing the fear which ac- 
companied the event. This kind of 'think- 
ing-about' in which we bring back the past 
and recognize it as belonging to the past we 
shall call recollecting. 

When a person says that he is 'thinking 
about' a plan for remodeling his house, 
his activity is probably what we shall call 
imagining. He is creating new pictures or 
scenes which are neither present nor past. 
Sometimes these imagined events are re- 
garded as future, as things which the in- 
dividual expects to occur. At other times, 
imagining has no definite reference to time 
at all. The imagined scenes are not past, 
or present, or future; they are simply un- 

The term thinking usually includes more, 
however, than the 'thinking-about' which 
is labeled recollecting or imagining. It is a 
complicated process and requires more of 
an introduction than recollecting or imag- 
ining. The kind of thinking: which leads 

to the solution of important problems ol 
personal decision, of political theory or ol 
science is more than a creation of pictures 
or images. For the sake of clarity we had 
better use the term thinking only when we 
refer to this more complicated activity with 
recollecting and imagining recognized as 
important tools for this kind of thinking. 
It is easier, as a matter of fact, to state 
what is not thinking than it is to give a 
clear and useful definition of the term. 
For the time being we can be content with 
a rough characterization and a few ex- 
amples. Later in the chapter we shall give 
a fuller description. 

Thinking is directed toward the solution 
of a problem. It is not automatic. It re- 
quires effort. It frequently uses symbolic 
short cuts and signs. And it takes us be- 
\'ond the immediate concrete situation by 
the use of concepts. A man regards his 
thinking as successful when it provides 
him with ne^\• knowledge, with better un- 
derstanding of a situation, with a decision 
which he believes to be correct, or ^\hen 
it leads to an action which is successful 
in overcoming the obstacles in his patli. 

Suppose, for example, that you are told 
that the sum of the first A' integers is equal 
to A (A" + 1) 2 and that you are unable to 
understand why this is true. Your search 

for an understanding is an example of what 

This chapter was prepared by T. A. Ryan of Cornell University. 



Recollecting, Imagining and Thinking 

we mean by thinking. It is not thinking 
if you are satisfied with the recollection that 
vou once learned this formula in an alge- 
bra class in high school. It is not thinking 
if you have already worked out an under- 
standing of the relationships involved, so 
that you simply recall the results of your 
earlier thinking. 

When you accept this problem and there 
is no ready-made answer available, you 
start on a course of thinking. The problem 
engages your attention. You 'work hard' 
(effort) trying to find the point of view 
which will make the relationships clear. 
\ou consider the various meanings which 
may be attached to numbers (signs, sym- 
bols and concepts). Your thinking ceases 
^vhen you believe that you at last under- 
stand luhy the formula works or when you 
are interrupted by other affairs. It is not 
necessary that you arrive at a solution (to 
say nothing of finding a correct solution) 
in order to call the process thinking, for the 
|jrocess has its characteristic features 
whether it is successful or unsuccessful. 
The applied psychology of thinking is, of 
course, interested in the correctness of the 
lesult; but, before we can control thinking 
and direct it toward correct solutions, it is 
necessary to understand thinking in gen- 
cial, both correct and incorrect. 

.\lthough all the above characteristics 
appear typically in thinking, they also ap- 
pear separately in many other kinds of ac- 
tivity as well. Suppose we ask someone 
to tell us which of two weights is heavier. 
We have given him a problem, but we 
would not say that his solution ordinarily 
requires thinking. Similarly when we read 
a description of a landscape we are dealing 
with symbols, but it does not require think- 
ing to understand the description and to 
translate it into an imagined scene. 


Recollection is a process by which events 
and situations from the past are recreated 
by the individual and recognized bv fiim 
as comiiig from his past. It is in the em- 
phasis on recognition that recollection dif- 
fers from recall as that term is used in the 
more general study of learning. The test 
for recall in an experiment upon memo- 
rizing is whether the individual is able to 
reproduce the words in the memorized list. 
It is immaterial whether he remembers hav- 
ing seen the words before. In learning a 
motor skill, recall is also measured by the 
accuracy of performance. Recall may or 
may not involve recollection. For example, 
when you multiply you are demonstrating 
recall of the multiplication table, but sel- 
dom do you recollect the occasion of your 
original learning of the tables. 

In other situations, however, recall may 
depend upon recollection. To describe the 
details of a picture seen in the past, we 
usually re-view the picture, reading (recall- 
ing) the details from the visualized (recol- 
lected) picture. 

As a part of his act, one vaudeville 
prodigy used to learn a 10-by-lO square of 
numbers— 100 digits in all. The numbers 
were called out at random by the audience 
at the beginning of the act. After writing 
the ninnbers down, the prodigy tinned the 
blackboard over and performed other nu- 
merical tricks. Half an hour later he would 
repeat the whole set of digits, writing them 
down in an order different from that in 
which they had been originally placed upon 
the board. The stunt might have been 
managed by tricks of memorizing, but in 
this case it was foimd to depend upon a 
detailed visual recollection. In general, a 
subject's ability to reproduce in different 



order Llic items of a material is evidence 
of visual recollection. 

Recollection, of course, is by no means 
limited to visual scenes. Any of the sense 
departments may be involved, singly or in 
combination, with each showing special 
development in certain individuals. The 

in young (lii!di(ii than in adults. I hcv 
can be defuiiteiy localized and 'projcded' 
upon a screen. 

Figure 70 is a picture that was shown to 
English school children in an investigation 
of eidetic imagery. Some of the children 
could recollect the picture in such detail 


This picture was shown to a number of English school children for 35 seconds. From an image of the 
picture the children were later able to describe accurately a very great many details, including, in some 
cases, the long German word over the entrance of the building. [Used by G. ^V. Allport, Brit. J. Psychol., 
1924, 15, 99-120.] 

prodigious feats of musical memorization 
exhibited by some musicans would be 
likely to be instances of unusually accurate 
auditory recollection. 

Eidetic Images 

At times recollected and imagined ob- 
jects can appear in extremely complex and 
clear detail, resembling ordinai7 percep- 
tions. Such images are known as eidetic 
images. They are more frequently found 

that they were able to spell the strange Ger- 
man word on the house at the left. Three 
out of thirty children could spell the word 
correctly forward or back^vard, Avhereas 
seven could spell it either way with only 
two mistakes— the same mistakes in either 

This is an example of an eidetic recol- 
lection, but similar- clear images can also 
occur ■\\ithout reference to the past. An 
eidetic image is an experience which lies 


Recollecting, Imagining and Thinking 

on the borderline between a perception 
and an image. 

Although adults do not often report 
having eidetic images, they may experience 
them under special circumstances. After 
a long and concentrated day of visual study 
of some particular material, like micro- 
scopic slides or blueprint drawings, images 
of ilie material may insist on floating in 
iront of the eyes later when the tired ob- 
server is falling asleep. A haunting tune 
may be made of auditory eidetic imagery. 

Recollection and Perception 

Recollected events are describable in 
terms of color, shape, sound, warmth, feel- 
ings of movements and the like. We de- 
scribe them in the same terms we tise for 
perceived objects and events themselves. 
A question arises, therefore, as to how 
recollected objects difi^er from perceived 
objects, a question which has troubled a 
great many psychologists in the past. Al- 
most any criterion of differentiation upon a 
descriptive basis is faulty because of the 
exceptions which occur. Recollections are 
usually less clear, less definite and less de- 
tailed than perceptions, but that is not al- 
ways the case. Some recollections, espe- 
cially the recollections of certain gifted 
individuals (like the 'prodigy' mentioned 
above) and eidetic recollections, are ex- 
tremely clear and detailed, whereas an ob- 
ject seen briefly out of the corner of the eye 
or in a mist is anything but clear, definite 
and detailed. 

The question is; How do we tell the 
difference between a bit of melody which 
has come back from the past and the snatch 
of melody heard as being played right now 
on the neighbor's piano? How can we 
distinguish, when either or both may be 
clear or unclear, loud or soft, have the 
same pitches and so on? The fact is that 

we do usually distinguish perceived objects 
from recollected objects, even when the 
recollected objects are clear and detailed. 
The difference lies in the meaning of the 
experience, rather than in the pattern of 
colors, sounds, shapes or movements. We 
can say that we 'just know' fact from mem- 
ory, perception from recollection. 

What really happens is that there are 
two worlds— the world of perception and 
the world of imagery. To the experienced 
adult the world of perception is a complex 
but unitary whole. A thing is 'there,' is 
'real' and not imaginary, if you can see it, 
touch it, handle it, find it there whenever 
you turn to it, discover that what you per- 
ceive of it depends on what you do to put 
your sense organs in relation to it. The 
hard yellow floor of your room, the blue 
walls, the uncomfortable chair with the too 
soft cushion, the brown radio with the swing 
music coming out of it, the smell of fresh 
paint from the next room mixed with the 
smell of magnolias through the open win- 
dow, all these items of experience together 
with hundreds of others make up a con- 
sistent systematic whole which we think 
of as reality. Other items that fit into the 
system are necessarily 'real,' have the mean- 
ing of reality given them. 

All is, however, not so simple. A woman 
enters your room and takes a chair. Thus 
she fits into the system, is presimiably 
'real.' But she might be a delusion. So 
might the magnolias, the music and the 
whole room. The only proof of reality 
you have is that the items of it all fit to- 
gether and are consistent with the host of 
your recollections about them and about 
the relations of things in general. If the 
woman is transparent, if she walked in 
through the door without opening it, per- 
haps she is not 'real,' for she does not fit 
past experience with 'real, live' women. 

Reliabilify of Recollection 


You have only to feel that the c;onsistenty 
ol the system is destroyed to doubt the 
• reahty of perception. Starting off to work 
in the morning when there is really no 
work because it is a holiday soon shows you 
how the system fits together. The streets 
are half empty, the other people are not 
hurrying to work, and you get first a feel- 
ing of unreality, imtil you find out what 
is wrong. You had forgotten about Wash- 
ington's birthday. 

Recollection and imagination make up 
the experience that comes into your life 
without fitting the basic perceptual pattern 
as do perceptions. You are recollecting 
when what you experience fits into a past 
perceptual system, is dated and placed in 
)-elation to past places and events. If there 
is no such specification upon the experi- 
ence, presumably it is an imagination, a 
vision, an inspiration. 


There are ways of measuring the relia- 
bility of recollection and of studying how a 
recollection changes with the lapse of time. 

Reliability of Testimony 

If you follow the accounts of a criminal 
trial in a newspaper or if you read detec- 
tive stories, you may have been impressed 
by the amount and accuracy of detail which 
the witnesses to the crime are asked to 
recollect. Actual testimony is, liowever, 
frequently conflicting and is often changed 
under cross-examination. 

Prompted by the practical problems of 
the law, psychologists have performed a 
number of experiments to determine the 
accuracy of testimony and the conditions 
imder which recollection is accurate. Their 
method is to stage a scene or event for a 

'witness' oi to sliow him a moving picture. 
Sometimes the witness knows in advan(c 
that he will be required to recall the details 
later. In other experiments the crucial 
event is introduced casually and appar- 
ently accidentally, so that the witness is 
not prepared for his later examination. 
'I'he examination of the witness takes place 
later after various periods of time have 
been allowed to elapse. 

Even when subjects have no 'axe to 
giind' and are merely collaborating in an 
experiment, their errors of recollection are 
many. Errors occur even though the sub- 
ject is instructed in advance to be ready 
for a later test of his accuracy. They in- 
crease markedly when the original event oc- 
curred 'accidentally' and without the suIj- 
ject's expecting it. Thus perception with 
the intention to recall the event later is an 
important factor in the accuracy of recol- 
lection, a factor seldom operative in court- 
room testimony. 

Another factor that can affect the accu- 
racy of recollection is questioning or cross- 
examination at the time of recall. If a 
witness is allowed to report what he can, 
without questioning, his reports may be 
fairly accurate, although still not perfect. 
Cross-examination may. however, double 
or triple the proportion of incorrect infor- 
mation which is given by witnesses. The 
leading question is very effective in induc- 
ing witnesses to recall something that did 
not appear in the original event at all. The 
leading question in the form, "^Vasn■t 
there a horse in the street?" •will often 
receive the reply "yes" if it is at all reason- 
able to suppose that a horse could have 
been there. Once such a false recollec- 
tion has been reported under cross-exami- 
nation, it tends to become fixed and to 
reappear later, e\en spontaneously. Per- 


Recollecting, Imagining and Thinking 

haps the witness did not really recollect 
the horse when the question was asked, but 
later, under pressure to be consistent, he 
becomes convinced that he is actually recol- 
lecting something he truly saw. 

These experiments differ from the real- 
life situation involved in testimony in three 
ways. First, the laboratory or classroom 
situation is relatively calm and unemo- 
tional. Emotion is likely to decrease ac- 
curacy of perception and recollection. Sec- 
ond, the experimental situation is not so 
intensely interesting as a real accident, 
robbery or similar dramatic event. Inter- 
est favors accuracy but is likely to be 
(oiipled with emotion, which favors inac- 
curacy. Often psychologists have intro- 
duced both interest and emotion into their 
experiments by staging dramatic episodes 
in I he classroom with some success in con- 
\incing the students of their authenticity. 
In one case, for example, the instructor had 
an argument with a man who interrupted 
his class. The event was carefully re- 
hearsed and staged so that the accuracy of 
testimony could be checked. The amount 
of error was found to be extremely high. 
Descriptions of the man ranged from tall 
to short, dark to blond, fat to thin and 
so on. 

A third difference between the experi- 
ment and the courtroom lies in the fact 
that errors of recollection become much 
more important in the courtroom. In the 
experiment the subject may be willing to 
report something of which he is not cer- 
tain, largely because error will not matter 
much. Often the subjects are asked to dis- 
tinguish between those things which they 
are willing to swear to and the things of 
which they are only moderately sure. See 
Table XII for the results of one experi- 
ment. Although the accuracy was higher 


Errors of Rfxollection 

Showing the errors in an experiment upon testimony. 
Subjects were shown a picture, then answered a ques- 
tionnaire about the contents of the picture at each of 
the time intervals listed. Each answer was labeled 
according to the degree of certainty of the subject. 
"Report" refers to an answer which was "just a little 
better than a mere guess." "Fairly certain" is the 
description given to the next degree of certainty. 
The last column shows percentage of errors in answers 
where the subject was "willing to give his sworn 
oath." [From K. M. Dallenbach. Psychol. Rev., 1913, 
20, 323.] 

Percentage Error 

Time of Recall Report Fairly Certain Sworn to 
Immediate 48.2 28.3 6.7 

5 days 66.6 30.7 10.0 

15 days 64.5 25.3 15.4 

45 days 55.0 31.4 19.5 

Average of errors 58 . 6 



for those reports of which the subjects were 
very sure, the percentage of error was still 

Changes in Recollection 
with Lapse of Time 

In addition to these practical experiments 
upon the reliability of testimony, the way 
the recollection of an object changes with 
lapse of time has been investigated. We 
need to know what happens to the mem- 
ory of an object or event as time passes 
and whether the memory of an object 
simply fades out, gradually becoming more 
and more fuzzy and indefinite, or whether 
it undergoes other changes. 

The experimental procedure is as fol- 
lows. An observer is shown an object, a 
series of objects or a story. Later he is 
asked to redraw the object or retell the 
story as he recalls it. (See Fig. 71.) In 
some of the experiments the observers re- 
produce each object just once, with the 

Changes in Recollection with Lapse of Time 


time intervals between initial observation 
and reproduction varying. In other experi- 
ments the observers are asked to repro- 
duce the same material over and over again, 
thus getting at the effects of repeated recol- 

Both these experimental conditions have 
their counterparts in everyday lite. Some- 
times your first recollection of an event 
occurs only after a considerable lapse of 
time. You have not thought of the event 

ToR T^Al)- J)'Hofif|^ 


The drawing at the left was observed by a person 
and reproduced by him 15 to 30 minutes later as 
on the right. Thus the figure at the left represents 
the stimulus, and the figure on the right the recol- 
lection of it. [From F. C. Bartlett, Remembering, 
Cambridge University Press, 1932, p. 178.] 

or reviewed it between the original per- 
ception and the recall much later. More 
frequently, however, a striking event in 
your life is recollected over and over again 
at intervals for many years. When you 
recall an important event of your child- 
hood, you have probably recollected it 
many times before. Your present recollec- 
tion is, therefore, a result of many previous 
rehearsals. In part this recall is a recol- 
lection of a recollection of a recollection, 
but it also may refer to the original 
observations. It is, moreover, impossible 
to be sure that the period of time between 
the original perception and the recollection 
is ever entirely free of spontaneous re- 
hearsals by the subject, and it is certainly 

not improbable that we never recall an 
event after a long time span without there- 
having been intervening rehearsals. 

When the experimenter has collected a 
great many reproductions— drawings or re- 
ports—he is likely to be impressed by the 
great variety of things which can happen 
to a recollection. To describe the mem- 
ory merely as indefinite and unclear does 
not, however, do justice to the findings. 
Some aspects of a design or a story may 
become 7nore clear as time passes. To be 
sure, these clear aspects are not necessarily 
correct, even though the observer believes 
that they are. 

Some of the changes which frequently oc- 
cur are these: 

(1) Details are omitted; only the general 
pattern is reproduced. 

(2) New details are added; for example, 
eyebrows were added to a drawing (A 
a face which originally had none. 

(3) Certain peculiarities of the original 
figure may become exaggerated in the 
reproduction; for example, slanting 
eyes become more slanted in recollec- 

(4) The resemblance between the figure 
and some familiar object is increased; 
for example, a conventional drawing 
of a cat becomes more catlike. 

(5) Different figures in the same experi- 
ment come to resemble one another 
more than they did originally. 

(6) Under repeated recollection, errors 
and changes may finally become 

(7) Stories, and sometimes figures, may 
be made more 'logical' or made to 
fit a more familiar pattern. (See 
Fig. 71.) 


Recollecting, Imagining and Thinking 

Nature of Errors in Recollection 

The factors which bring about these 
changes in recollection operate both during 







R 1 2 




Tlie fi_mircs in llie sLiimilus column were shown, 
among a niniiber of others, to a group of subjects 
for a short time. Their reproductions of these 
stimuli, made from memory, varied according to the 
meaning suggested by the figmes. Thus stimulus 1 
suggested (1) a woman's torso; (2) a "footprint on 
the sands of time"; (3) a dumb-bell; (4) a violin: 
(5) a dumb-bell. Stimulus 2 received the names (1) 
pillars with curve; (2) pillars with curve; (3) mega- 
phone in a bowl. Stimulus 3 was named (1) one 
circle inside another. The experimenter gave dif- 
ferent names to stimulus 4 as he showed it to dif- 
ferent individuals. Their reproductions varied ac- 
cording to the name: (1) bottle; (2) stirrup. Stim- 
ulus 5 was treated like stimulus 4. The names 
were (1) pine tree; (2) trowel. [After J. J. Gibson, 
/. exper. Psychol., 1929, 12, 15 and 19; and L. Car- 
michael, H. P. Hogan and A. A. Walter, /. exper. 
PsyclioL. 1932, 15, 75 and SO.] 

the original perception and afterward. If 
the original object is seen as resembling 
sotnething familiar, if it is given a name or 
if certain special features of it are noticed, 
these characteristics tend to become more 

marked in the reproduction. Figure 72 
shows some examples of this effect of the 
original mode of perception. Such char- 
acteristics are hkely to appear in the very 
first reproduction, immediately after the 
perception. As time goes on, the effect 
may become more exaggerated. Sometimes 
it appears that the observer recalls only 
the verbal identification or the general re- 
semblance to a familiar object, and recon- 
structs his recollection from it. 

We have noted that forms as well as 
stories may becoine more 'logical' or sen- 
sible in recollection. That happens most 
often when the original material is frag- 
mentary or perceived as fragmentary, as it 
may be if perceived hurriedly or under dis- 
traction. Then recollection goes to work 
to make a whole out of the parts, to com- 
plete and unify the event or form or what- 
ever it is that is being recalled. It is not 
easy to describe disconnected scraps. Recol- 
lection needs to have a total structure if it 
is to represent adequately the original per- 
ception. The same thing happens in recol- 
lecting dreams. There we piece the seem- 
ingly silly fragments together into a sen- 
sible story. 

These laboratory experiments on recol- 
lection are concerned with impersonal ma- 
terial. They differ from the recall of events 
in our own past lives, events involving 
emotional relationships to other persons, 
success and failure in work or sport. The 
emotional context of most of our oiclinary 
recollections is another factor which modi- 
fies our recollections and frequently falsi- 
fies them. 

The psychoanalysts have collected ex- 
amples from clinical practice showing the 
falsification of memories of emotional situ- 
ations and conflicts. (See pp. 175 and 520 f.) 
The experimental results we have described 
represent changes in recollection which are 

Errors and Failures of Recollecfior) 


but mild and sliglit coinpaicd to tlu: 
changes which occur in normal personal 
recollections. Autobiographies and mem- 
oirs, iMiless they are carefully authenticated, 
must be full of these personalized distor- 

Some investigators have sotight to study 
recollection of events into which an emo- 
tional flavor has been injected. In one 
experiment a subject was given various 
problems to solve. He succeeded in solv- 
ing some of them. Others, however, were 
too difficult for him and he was disturbed 
at failing. Later he was asked to recall 
the problems upon which he had worked, 
and the experimenter compared his accu- 
racy in recall of those problems in which 
he experienced failure with those which he 
solved. It was found that as a rule he re- 
called with greater accuracy the problems 
he solved than those in which he failed. 

Another way of showing how personal 
factors influence recollection is to use for 
perception and recall material which either 
accords with the attitudes and opinions of 
the subject or contradicts them. Here fol- 
lows the account of such an experiment. 

Two groups of students— one group 
strongly pro-Communist, the other strongly 
anti-Commimist— were chosen as the sub- 
jects. Each subject was asked to study two 
brief excerpts from books. One of these 
passages was a strong anti-Soviet argu- 
ment; the other was moderately pro-Soviet. 
The materials were studied repeatedly; 
hence there was more learning than recol- 
lecting going on. Nevertheless, the biases 
entered in. The anti-Communist subjects 
recalled the points of the anti-Soviet argu- 
ment better than the pro-Communist sub- 
jects did. The converse held for the pro- 
Communist passage. These differences ap- 
peared after each of the repeated periods 
of studv of the materials. After foin- such 

periods of study, the tests were continued 
lor five weeks without further opportunity 
to review the printed materials, and the 
two biases became more and more effective 
during the serifs of repeated recollections. 

Failures of Recollection 

Often recollection fails. The conditions 
seem to be right for its occurrence, yet it 
is blocked, temporarily or even perma- 
nently. Emotional factors are often to 
blame, for they may lead to a forgetting 
which is called repression, a blocking of 
recollection which can be overcome only 
by treatment, such as psychoanalysis. (See 
p. 541.) 

When forgetting is complete and per- 
sistent it is called amnesia. Amnesia mav 
occur after a bad shock like an accident or 
after an intensely emotional experience. 
The person affected may lose his memory 
for a period either before or after the event. 
In extreme cases, he may lose his memor\ 
for his whole past life, including his knowl- 
edge of his identity, of where he lives and 
so on. 

Amnesia illustrates clearly the distinc- 
tion between learning and recollection. It 
is a characteristic of amnesia that the indi- 
vidual loses recollection alone. He does 
not forget how to walk, how to speak his 
native language or even other skills ac- 
quired later in life such as typing, or his 
other occupational skills. Recollection is 
the recall of experiences in the personal 
past, and it is these experiences whicli are 
lost in amnesia. 

There is, however, a certain selectivity 
in recollection which does not seem to fol- 
low strictly from the la^\s of learning. 
Only a few past events come back out of 
the many which association might bring. 
The selection is doubtless due to the sets 
and motives that are operating. 


Recollecting, Imagining and Thinking 

A more complete analysis of the prob- 
lem of amnesia requires an understanding 
of the general problems of abnormal psy- 
chology. (See pp. 531-535.) 


Accurate recollection of the same object 
or event does not necessarily always take 
the same form. There are different kinds 
of recollection. One man may differ from 
another in the kind of recollection he uses 
most of the time. One task may differ from 
another in the type of recollection that is 
best suited to it. These differences are 
found between persons and also between 
recollections by the same person. 

One of the t-\vo most important distinc- 
tions of this sort is the difference that oc- 
curs according to the sense departments 
used. "We can recall events in visual 
imagery, or auditory imagery, or in motor 
processes. The other important distinction 
lies in the difference between verbal recol- 
lection and recollection in terms of concrete 
imagery. Take the recollection of a par- 
ticular hammer. A man may recall in 
imagery (1) the look of the hammer, (2) the 
feeling of swinging the hammer in his 
hand, (3) the sound of the blows of the 
hammer, (4) the look of the word hammer, 
(5) the sound of the word hammer, (6) 
the voice-feeling of what saying the word 
hammer is like. The first three recollec- 
tions are made of concrete imagery, visual, 
kinesthetic and auditory. (Kinesthetic 
means pertaining to the feeling of the move- 
ment of your own body and its parts.) 
The last three are verbal imagery, visual, 
auditory and kinesthetic. There are differ- 
ent combinations of these types of verbal 
imagery. For instance, auditory-kinesthetic- 
verbal imagery is much more common than 
pure auditory-verbal imagery. If you hear 

the sound of a word in imagery, you are 
likely also to feel how it is to pronounce it. 

Are there differences among persons in 
respect of these imagery types? Do some 
people prefer visual imagery, others kines- 
thetic, others auditory-kinesthetic? Yes, 
there are such persons but they are excep- 
tional. Occasionally you find a person 
who seems never to have visual imagery, 
who recollects entirely in terms of kines- 
thetic and auditory-kinesthetic imagery, 
both verbal and concrete. He will tell you 
what the colors of the rocks in the Grand 
Canyon of the Colorado look like, but he 
will be recollecting words, not actual col- 
ors. Occasionally you find a person who 
does nearly all his thinking in visual terms, 
even in his verbal thinking. Most persons, 
however, use all the types on different oc- 
casions. Versatility is the rule. 

Versatility is also more efficient. As we 
have already seen in the discussion of 
eidetic imagery, recollection of great detail 
of an object is easiest if it occurs in visual 
terms. If you can see the Mona Lisa in 
your 'mind's eye,' you can do a good job 
at recollecting it. If you have to depend 
on kinesthesis, you will be likely to get 
only the words with which you originally 
described it. On the other hand, if you 
are remembering the Ninth Symphony, 
auditory imagery is more fun, even though 
visual recollection of the looks of the score 
may be quite accurate. Kinesthesis, of 
course, fails, since you cannot sing or play 
a symphony by yourself. The best you 
could do with kinesthesis would be to re- 
member descriptive words. The stroke in 
golf which you have at last mastered; how 
do you recollect that? Kinesthesis is best 
there, though you might have a visual 
image of ho^v the 'pro' swings his club. 
Sometimes imagery type is thus related to 
efficiency in recollecting. 

Types of Recollection 


On the other hand, it is surjjrising how 
often type does not matter. Verbal recol- 
lection fits into any ol the common types, 
and most recollection can be made verbal. 
Musicians do not necessarily recall music 
in auditory terms. Geometricians do not 
necessarily use visual terms. Persons who 
have been blind and deaf from birth and 
have no visual and auditory imagery are 
capable of learning language and of doing 
any of the abstract thinking which is nor- 
mal to a person without sensory defect. 
They are shut off from certain perceptions 
and from such direct recollections, but they 
are able to substitute kinesthetic imagery. 
Blind persons learn to perceive in auditory 
and kinesthetic terms with remarkable ac- 
curacy, and their recollections take place in 
similar terms. 

One reason why type of imagery makes 
so little difference in human life is to be 
found in the fact that the most important 
recollections for civilized adults are gen- 
eral and abstract, not concrete and ob- 
jective. Most recollecting of this sort, and 
indeed most thinking, can be done in 
words, and any of the three main kinds of 
imagery will work with words. 

Verbal recollection is commoner than 
concrete recollection, less accurate as a 
rule, but more efficient in the sense that 
the telescoping of a complex object or 
event into a verbal formula is so compact 
that it gets out of the way of other recol- 
lections. Any important business of living 
is likely to include the making of judg- 
ments. You can recollect the judgment 
you previously made of an observation in 
words and do it fairly easily. More diffi- 
cult and less common is it to recollect the 
observation itself, as you might be able to 
do quite accurately in eidetic imagery, and 
then to make your judgment of the recol- 
lection. The witness on the stand is asked 

to recollect the event and to let the court 
or jury pass judgment. More often he 
recollects his past judgment of the event 
and reports it or tries to reconstruct the 
fading event from it. It is easier for a wit- 
ness to remember that he thought the 
driver who hit the pedestrian was at fault 
than it is for him to recollect just what it 
was that made him blame the driver. Ac- 
curacy and scope are here inversely related. 
You can remember best if you remember 
details of an event; but you can remember 
more events if you condense each into your 
assessment of it and remember merely the 
assessment. How often a man says: "I 
know that's a fallacy, but I can't remember 


Like recollection, imagining creates ob- 
jects without benefit of the sense organs. 
A person who is blinded during his child- 
hood can continue to imagine colors and 
shapes. A person who becomes deaf can 
still imagine sounds and melodies. Beetho- 
ven composed and conducted great music 
after he was stone deaf. 

There is no essential difference bet^veen 
the kinds of experience— colors, shapes, 
sounds— that make up perceptions, recollec- 
tions and imaginations. As we have already 
seen, these experiences differ only in their 
meaning. The perceived object is there- 
now-in-front-of-me, belonging to the svstem 
of present reality. The recollected object 
is something-I-once-saw, belonging to some 
system of past reality. The imagined ob- 
ject is the thing which is about-to-happen 
or which might happen, and it is either iso- 
lated without fitting any established system 
or else it fits temporarily and insecurelv 
into a reality system, as is the case Ashen I 
look at my empty garage and imagine a 
splendid car in it. 


Recollecting, Imagining and Thinking 

Imagination and Perception 

Since imagination is free and not tied to 
reality, there is no problem of the reliabil- 
ity of imagination. There are, however, 
the cases in which imagination occurs to- 
gether with a perception, the cases in which 
imagination gets confused with perception, 
the cases in which the imagination is mis- 
taken for a perception and the contrary 
cases in which a perception seems strange 
and is taken for an imagination. 

Synesthesia. There are a few persons (per- 
haps five per cent of the population) who 
report that they experience colors when- 
ever they hear sounds; that is to say, there 
is a definite color or color pattern which 
regularly appears when a certain soimd is 
heard. This phenomenon is known as 
chromesthesia or colored hearing. Synes- 
thesia is the general term for relations of 
this kind between sense qualities. Thus 
we may have colored odors or tastes as well 
as colored hearing. 

Colored hearing can be very stable and 
dependable. Table XIII is a record of the 


A Case of Chromesthesia Investigated in 1905 
AND Again in 1912 

The notes of the musical scale are associated with 
images of very constant colors. [From H. S. Langfeld, 
Psychol. Bull., 1914, 11, 113.) 













Soft blue 

Thick blue 


Golden yellow 




Pink, apple blossoms 


Green blue 

Blue green 


Greener blue 

Greener blue 


Clear blue 

Clear sky blue 


Cold yellow 

Clear yellow, hard, 
not warm 



Verges on orange 

Very brilliant coppery Very brilliant coppery 

colors associated with notes of the musical 
scale for one person with colored hearing. 
The two records, taken seven years apart, 
show remarkable consistency. 

Synesthesia is a special form of imagin- 
ing—apparently not imagining of objects 
but of abstract sensory qualities. It dif- 
fers from other forms of imagining in be- 
ing so closely tied to the perceptive situ- 

How synesthesia develops is not certain, 
but it is probably learned early in child- 
hood. When colored patterns are perceived 
in colored hearing they are likely to be 
familiar kinds of designs, like wallpaper 
patterns. Closely resembling synesthesia 
are number forms, in which the person sees 
any number fitted into a geometrical 
schema, and date forms, which are similar. 
A number form is likely to have corners in 
it at 'imjaortant' numbers, like 5, 10, 12, 
25, 50, 100, 1000, and 10,000. A common 
academic date form for the year is a closed 
ellipse, with the spaces for June, July and 
August much longer than the spaces for 
any other month. Such forms must cer- 
tainly be learned and cannot be innate. 

Dreams are the most familiar events in 
^vhich imagination plays the role of pei"- 
ception. Since dreams are bizarre and frag- 
mentary and do not fit in well with any 
total reality system, why do they seem real? 
The answer to that question is that dreams 
do not, as a rule, seem real. They do not 
seem unreal; that is all. Dreams occiu' 
under some strong tension or set— some- 
times in partial fulfillment of a suppressed 
wish, the psychoanalysts think. They are 
vivid and usually emotionally toned, but 
limited in scope and not fitted into any 
reality system at all. 

The hallucinations of persons with men- 
tal disease are like dreams. The schizo- 
phrenic who tells us what his voices are 

Imagination, Perception and Thinking 


saying to him, the mean, ugly, abusive 
things they say, is accepting uncritically 
imagery which does not fit in with reality; 
but then that is what schizophrenia is, the 
splitting up o£ the integrated personality 
and its reality systems. 

These instances show that the kinds of 
stuff of which perception and imagination 
are made are so much alike that without a 
label imagination may be identified as per- 
ception or at least not distinguished from 

False imaginalion. There is also the con- 
verse case in which perception is thought 
to be imagination. That is what happened 
in a well-known experiment in which the 
observers were instructed to look at a 
screen, fitted into a window in a wall, and 
to imagine a specified object projected 
upon the screen. Unknown to the observ- 
ers, a projector behind this translucent 
screen projected upon the screen a very 
dim image of the object called for. The 
observers were quite pleased that they were 
able to get their images of imagination so 
clearly. They did not guess that they 
were actually being provided with a visual 
stimulus. Even when the projected image 
failed to correspond exactly with the char- 
acter of the thing they were trying to imag- 
ine, they still regarded the object as 
'imagined.' "I can see that knife standing 
up on end," one observer said. "I should 
have thought I would have imagined it as 
lying down." It is important to note that 
the image remained even after the pro- 
jector was turned off. The imagination, 
which the stimulus helped to start, contin- 
ued independently afterward. 

Creative imagination also sometimes 
works in a similar way. An author, artist 
or musician creates his work of art— his 
story, his poem, his melody. His pride in 
it tells him that his work is new, his own 

creation; and then iomeone comes who 
tells him that what he has done is a close 
copy of what someone else has done. Sure 
enough, he really did know the work which 
he copied unconsciously, but his recollec- 
tion was separated from its proper past 
reality system and the composer— doubtless 
reinforced f)y his own wishes— mistook his 
old memory for new imagination. Many 
cases of plagiarism are uniruentional and 
to be accounted for in this sini[jle manner. 


The psychology of thinking is not, of 
course, the same thing as logic. Logic ana- 
lyzes the correctness and incorrectness of 
thinking or, more generally, the drawing 
of conclusions from premises. Thinking, 
however, may be quite illogical, even when 
it gets to the right conclusion. Often im- 
portant creative thinking goes on by trial- 
and-error. You form an hypothesis as a 
hunch. You test it out in thought, and 
find it wrong. You make up another h\- 
pothesis. Finally you get one that seems to 
work where you need it and you accept it. 
It may be an hypothesis in such form that 
you can test it by logic, but the trial-test- 
error-trial-test-success method is not the 
procedure of logic. 

We have already noted that the term 
thinking is often apphed indiscriminatelv 
to a great many different kinds of psvcho- 
logical activity— recollecting the past, imag- 
ining the future or even deciding what to 
do now. The kind of thinking which re- 
quires special and sepai-ate treatment is a 
more complex kind of performance. It 
starts with a problem which cannot be 
solved by methods ^\hich come readilv to 
hand. We have to in\ent ne^v methods for 
it or grasp new relationships; at least thev 
are new to the thinker. Sometimes this 


Recollecting, Imagining and Thinking 

kind of thinking is called elaborative 
thinking to distinguish it from recollective 
and imaginative processes. 

Starting with the acceptance of the prob- 
lem, elaborati\'e thinking progresses 
through a series of phases, reversing direc- 
tion, discovering new problems, dealing 
with concepts and symbols, recollecting, 
imagining, applying memorized formulas 
and so on. In other words, the progress of 
thinking consists of a series of manipula- 
tions of objects and of other tools of 
thinking. These tools exist in great va- 
riety. Before we can understand the total 
process of thinking, we must examine them 
and try to describe them accurately. 

Important Tools of Thinking 

Here we may list and discuss the more 
important tools of thinking— objects, con- 
cepts and symbols. 

(1) Perceived, recollected and imagined 

(a) Concrete or specific objects. You 
understand the word 'ancestor' by imag- 
ining your own grandfather. In testing 
the truth of a general statement, you 
look for concrete exceptions. In under- 
standing the word 'friction,' you imagine 
rubbing your hands together. 

(b) Objects as examples; generalized 
objects. In solving a geometrical prob- 
lem you imagine a triangle but do not 
consider it as this particular imagined 
triangle; that is to say, in the geometric 
operation you do not consider it as ob- 
tuse, acute or as any other particular 
kind of triangle. It is just an object of 
'that general kind.' Geometry always 
discusses the general but illustrates with 
the particular. 

(c) Objects with dynamic properties. 
In solving many concrete problems, ob- 

jects are seen as tools for doing certain 
things. A stone is seen only as some- 
thing heavy, something you can pound 
Avith. An object may be seen as about- 
to-fall, as instable on its base, as easily 
broken. Through past experience the 
object takes on a significance beyond 
that immediately given in the stimulus 
pattern. You see that ice is cold and 

(2) Concepts. A very important tool for 
thinking is the concept. A concept is a 
'general idea,' an item in thinking that 
stands for a general class. As an experi- 
ence the concept may seem to be nothing 
more than an ordinary image, but as a 
concept it has acquired, through learning, 
various potentialities which give it much 
more general meaning. In other words the 
concept implies the state in which there 
is a broadly generalized response. 

Consider the word dog, and also the 
concept dog which may enter into thought. 
If you read in a story the sentence, "He 
called his dog," you miy have a visual 
image of a particular dog, you get the 
meaning of the sentence, but you are not 
then using a concept. If, on the other 
hand, you read the title of an article in a 
journal, "Conditioned Responses in the 
Dog," this dog is the concept dog, for it 
means any dog and every dog, the class of 
dogs. How do these two experienced dogs, 
the particular and the general, differ psy- 
chologically? In both cases you may have 
the same visual image, an image of a dog, 
and every image is in itself particular. In 
the case of the concept, however, the par- 
ticular image is associatively connected 
through learning with all sorts of other 
images, which have in common whatever 
learning has taught you to believe are the 
essential characteristics of dogginess. Given 

Important Tools of Thinking 


a chance, a ] in the thinking process, 
a challenge as to whether you understand 
the concept, and many of these alternative 
images will actually arise, attesting the con- 
ceptual nature of the item of thinking 
which is represented consciously at the mo- 
ment only by the particular image of the 

The main thing to remember in this 
context is that thinking needs to use gen- 
eralized concepts, that the concept is neces- 
sarily represented in conscious thinking by 
some particular item, like an image, but 
that the concept is nevertheless more than 
a particular image because in thinking this 
image plays the role of a generalized ab- 
straction. Thinking, as we shall see, could 
not go on without the great economy which 
generalization makes possible. 

(3) Symbols and signs. Thinking also 
gains economy by making use of both sym- 
bols and signs. Since every symbol is poten- 
tially a sign, and every sign potentially a 
symbol, the two conceptions must be con- 
sidered together. 
^A^s^yrnboljsja. concrete particular item in 
thinking that stands for something more 
general. A particular dog— seen, imaged 
or pictured— can be the symbol for the gen- 
eral concept dog. Concepts are usually rep- 
resented in thinking by symbols. The 
word tioo is a symbol for the concept of 
duality, and 2 is another symbol for the 
same concept. A traffic light, perceived or 
imagined, may be a symbol of police power. 
The symbol is simpler and more easily used 
than the generality for which it stands, and 
the employment of symbols for thinking 
also contributes enormously to the econ- 
omy of thinking. 

Symbols tend to becomejS/g?7,y. They act 
as signals for thinking or action, as stimuli 
for conscious or motor response. The traf- 
fic light is a sign; it tells us what to do. 

The symbol for multiplication is a sign; it 
also tells us what to do. Thinking pro- 
gresses because symbols act as signs and 
carry the thinking pioccss along. 

Symbols and signs are thus seen to be 
the pawns and pieces with which the great 
game of thinking is played. It could not 
be such a remarkable and successful game 
without them. As it is, by letting a little 
symbol act for a large, complex and clumsy 
concept, we can think quickly and effi- 
ciently. We can also avoid starting our 
thinking from scratch. The original un- 
derstanding of a concept and the attach- 
ment of a symbol to represent it is in it- 
self often an elaborate job of thinking, but 
once done and the symbol given its proper 
powers as a sign, the thinking does not 
have to be done again. We use the symbol 
without stopping to recollect for what it 
stands, and we use it as a sign to indicate 
the processes which we have learned belong 
to it. 

Take the algebraic symbol of involution. 
X", the raising of x to the nth power. The 
exponent, n, written as a superscript, is the 
symbol. It stands for a generalization. We 
learn the processes of squaring and cubing 
and then of raising numbers to other pow- 
ers. Thus we get the meaning of involution 
attached to the symbol. We must grant the 
symbol the greatest generality. It means 
that .V could be raised to the power of 2. 3. 
510, %, ly,, V2 or ,r. After 3:e under- 
stand the symbol, we no longer need to re- 
call the vartous processes by -ts-TiTch it ac- 
quired its meaning. Instead we need to 
recognize it as a sign, knowing -ivhat opera- 
tions it indica.t£s_jn tlie process of think- 
ing. Mathematics constantly Builds up 
symbols for the relations of s\Tnbols, cre- 
ating new signs and proceeding ever at a 
level more and more remote from the par- 


Recollecting, Imagining and Thinking 

ticular objects whose relationships it in- 

Mathematics is, of course, a highly sym- 
bolic form of language, but in principle it 
does not differ from any other form of lan- 


Language, because it uses symbols, is the 
best medium for thinking. Ordinarily the 
symbols are words, which, of course, have 
meaning and readily act as signs. The 
words can be spoken, written or printed, 
or fingered in the manual alphabet that 
the stone deaf use. There are languages 
in which the symbols are gestures, the ges- 
ture languages of the Neapolitans and of 
the North American Indians. It is not true 
that man alone among the animals has lan- 
guage. Every animal with a conditioned 
response is reacting to a symbol, for the 
conditioned stimulus is a symbol of the un- 
conditioned stimulus. The dog who sali- 
vates when he hears the dinner bell under- 
stands the meaning of the bell, which has 
become for him a symbol for food. When 
that little bit of language has been built 
up between a scientist and a dog, it be- 
comes possible for the dog to tell the scien- 
tist whether long-continued loud noise deaf- 
ens the dog, for the dog can say "I hear the 
bell" simply by salivating, or "I do not hear 
any bell" by not salivating. Human lan- 
guage is nothing else than a high develop- 
ment of such symbolic responses. 

Human language has four chief func- 
tions. (1) It serves to communicate ideas 
from one person to another. That is its 
chief social function. It is not, however, 
its only function. (2) It serves to persuade 
or to incite others to action. That is an- 
other social function. Persuasion per se is 
not communication. Yelling "Fire!" when 
there is no fire may incite a stampede with- 

out directly communicating thought. (3) 
Language serves also to relieve tension in 
the speaker. That is its cathartic finic lion. 
Exclamations and profanity may ha\e this 
purpose, but so also does a gieat deal .of 
unilateral talk. The hypochondriac who 
wants to tell everyone his symptoms is try- 
ing less to get understanding or action in 
his vis-a-vis than he is to relieve his own 
frustration. An exclamation can be used 
to communicate, to let others know how 
you feel. However, Robinson Crusoe 
doubtless used expletives before he had his 
man Friday to talk to, because the condi- 
tioned response of talking does not become 
easily extinguished, and some action is 
needed in emotional situations. 

Those are three functions of language 
most usually cited, two of them social and 
one of them individual. There is, how 
ever, a fourth and more basic function 
(4) Language is used as a tool in thinking. 
It is the system of symbols which makes 
thinking efficient. Men think to them- 
selves in words. An argument, a discus- 
sion, an exposition is developed verbally, 
whether an audience is present or not. 
The words and phrases are symbols, and 
as such they carry with them meanings 
which have become implicit and do not 
have to be expressed. They are also signs, 
and as such they indicate, because of much 
past conditioning, the proper course of 
thought. Often a verbal argument, written 
or spoken, seems to develop of itself. Even 
its author does not know how it is coming 
out. He lets his mouth talk while he lis- 
tens, or he lets his fingers work his type- 
writer while he perceives the sentences as 
they form. The final result is a conclusion, 
one that is quite satisfactory to the author, 
and valid as far as he can see. That auto- 
matic factor in language is possible because 
so nuich learning precedes its acquisition. 

Language and Reading 


IL is a lad llial tliiiikiiij4 is, lor liic mkjsI, 
part, unconscious. J "lie symbols, actinf^ as 
signs, carry on irom symbol to symbol with- 
out the things to which the symbols refer 
getting themselves represented in imagery. 
We can see how abbreviated the conscious 
processes of language are if we consider 
the nature of reading. 


The child at first reads slowly and la- 
boriously. He does not, if he is well 
taught, read letter by letter; he reads word 
by word or phrase by phrase. That is 
what you too do in learning German or 
French. At first the word cat will evoke its 
referent, that is to say, the child will per- 
ceive the word and then see the visual 
image of a cat. Soon, however, as learning 
progresses, the symbol comes to work alone. 
There is not time in reading for imagery 
of the referent to arise. The word cat acts 
properly as a sign without arousing any 
conscious associates at all. And the word 
Katz, which at first you translated into the 
English word cat, comes, as your German 
improves, similarly to act alone without 
this extra addition of translation. 

In short, you know much more than you 
are conscious of. You can read a simple 
clear prose passage of five liundred words 
tfirough quickly and understand it per- 
fectly. Perhaps the preposition by oc- 
curred in the first sentence, and the passage 
would have been altered throughout in its 
meanings if the word had been to instead 
of by. If quizzed, you have the meanings 
correct. So you must have perceived by. 
Yet you do not remember the word, you 
did not pause to pronounce it or to let any 
imagery arise to indicate its meaning. You 
just went on and let your brain take care 
of the sense for you. If you had allowed as 
little as a second to become conscious of the 

incaiiiiig ol cadi ol those five hundred 
words, you would have had to spend about 
eight more minutes on the passage, and 
that is exactly what does not happen. You 
can read without pausing because the syn> 
bols arc safe substitutes for their referents 

Since children learn to read aloud, pro 
nouncing the seen word when reading be- 
comes for them a much overlcarned condi 
tioned response. Many adults who can get 
rid of all other associations for read words, 
still pronounce them or at least form the 
words with their vocimotor organs as they 
read. After much reading their tongues 
get tired! This translation of sight into 
movement and kinesthesis is just as unnec- 
essary for effective understanding as is the 
translation of every German word into 
English for the understanding of German. 
Skill in language means that both kinds 
of translation are dispensed with. An 
adult with a tired i-eading tongue can learn 
visual reading and gain enormously in effi- 
ciency. He may prefer to read more slowh 
and pronounce the words when he wishes 
to appreciate the esthetic beauty of prose 
or poetry; yet for the tough practical busi- 
ness of getting as much sense as possible as 
quickly and accurately as possible, visual 
reading is the correct method. 

This same principle applies, of course, to 
the use of arithmetic. How many people 
can set themselves to add, and then, seeing 
a 4 below an 8, can at once image a 12. 
without wasting time to say "four and 
eight are twelve"? Yet that %vay of adding 
is extremely inefficient. A good adder, an 
expert accountant, can perceive an 8. per- 
ceive a 4, image a 12, perceive a 9, image 
a 21 and so run his eve do^vn the column 
with partial sums popping out in imagerv 
as he goes along, and he could even learn 
to whistle while he adds. 

A visual reader ought not to be able to 


Recollecting, Imagining and Thinking 

see sense in the sentence: "Two beer knot 
tube bee thought is thick west shun." The 
slow-pronouncing reader will, however, de- 
tect a familiarity in the sound as he forms 
it, and, if he repeats the sound, with his 
eyes shut or his attention off the looks of 
the words, he will discover the sense. So 
too with "Pas de la Rhone que nous." 

The first step in the development of the 
understanding in reading is the stripping 
off of these conscious contexts from words. 
The second is for the words themselves to 
become obscure, and the imagery for which 
they are signs to occupy attention. Not 
only can you understand a text when the 
meanings of the words do not arise in con- 
sciousness, but you also can understand it 
when the words do not have time to be- 
come clear in detail. What happens is 
that symbolization goes farther. A part of 
a word becomes an adequate symbol for 
the whole word. That is why errors in 
printed matter are so hard to catch. We do 
not always see the whole word. Psycology 
seems to be what this book is about. 

The Problem and the Set 

The problem determines the course of 
thinking. Thinking is aimed at a goal, a 
solution, a conclusion. It gets somewhere 
or attempts to. We have said that it is the 
symbols-become-signs which determine the 
course of thinking, but there is no incon- 
sistency here, because the problem is the 
overlord which chooses the signs that oper- 
ate. The problem has this effect because it 
is represented by a set or attitude that it 
induces in the thinker. 

This matter becomes clearer if we go 
back to the experiments on set and attitude 
which were described in connection with 
reaction (pp. 60-62). Reaction closely re- 
sembles thought and often cannot be dis- 
tinguished from it. If you are set the prob- 

lem to press a key when you see a green 
light and not when you see a red light, and 
you press for the green light, you are 
reacting in accordance with the set that you 
have taken on from our instruction. If 
you are set the problem to decide whether 
a statement is true or false and are given 
the statement, "To give every man his due 
were to will justice and achieve chaos," and 
you decide that the statement is true (or 
false), you have done some thinking in ac- 
cordance with the set which you have ac- 
cepted from our instruction. But if some- 
one flashes this statement at you on a card 
in a stimulus-exposure apparatus, and you 
call out True or False as your decision is, 
and he measures the reaction time, why 
then surely your thinking is reacting. 

A famous experiment on set was per- 
formed by Ach in 1905. He showed his 
subjects pairs of digits, one below the other. 
Sometimes he asked them to tell him the 
sinns of each pair, sometimes the differ- 
ences and sometimes the products. Those 
operations depend on three different sets 
or attitudes which his subjects could take 
on at his behest. It was not for them a 
matter of learning. They already knew all 
the sums, differences and products perfectly. 
The discovery in Ach's experiment was that 
any one of the three kinds of answer could 
be obtained from an unconscious set. 
Asked for stuns, the subjects gave sums 
without even remembering consciously that 
it was sums they were to think of and not 
differences or products. Set for sums, they 
got no differences or products. Then, with 
the very same pairs of digits, the subject 
at a word could be reset for differences, or 
for products, and get only what the set 
called for. As a matter of fact Ach held 
that his experiments were actually an in- 
vestigation of thought, and these arithmet- 
ical reactions are indeed simple thinkings. 

Trial-and-Error and Insight 


Ach called the set a detennining tend- 
ency and he said (hat progress ol thought 
is set by a determining tendcnc y toward the 
ideated goal. Since set, attitude, need and 
determining tendency are similar concepts, 
this book gets along by using the first three 
terms but omitting Ach's. 

The notion ol' set as dcternu'ning ac lion 
and thought is further ilhistrated l)y exam- 
ples. In the morning you decide that you 
need a certain book from the library and 
that you will stop for it on the way down- 
town. Then you forget all about this de- 
cision. Yet as you pass the library you find 
yourself turning in, and you wonder for 
a moment why you are entering the library. 
Presently you recollect your original deci- 
sion. In thinking the same soit of phe- 
nomenon occurs continually. Many scien- 
tists and inventors have described this phe- 
nomenon of 'incubation' in thinking. The 
solution of a baffling problem suddenly oc- 
curs to the thinker when he is thinking 
about something else. 

Trial-and-Error and Insight 

We have ahead) seen how animals sohe 
problems by trial-and-error and by insight. 
Thorndike's cat in the puzzle box (p. 145) 
escaped to get food by trying this and trying 
that, and finally hitting upon the right 
movement. A rat in an alley maze cannot 
possibly get to his food by insight. He does 
not know where the food is and he has to 
try and try again until he finds it. On the 
other hand, a rat that can see before him 
the paths of an elevated maze may solve 
his problem by insight and without trials 
that end in errors. He examines the situa- 
tion and picks the correct path to the food, 
provided the maze is very simple. The 
chimpanzee that tries to get the banana 
from beyond the fence (p. 152) tries and 

errs, tries and errs, and then, when he real- 
izes that the two sticks will fit together 
to make a long one, a flash of insight gi\cs 
liim ific solutif>n. (See Fig. 7.^.) 


> 1 

1 ir'*^**^ -*i»* 



Having discovered that the two sticks would go 
together to make one long stick, the ape took the 
long stick at once to the other side of his cage and 
secured a banana outside the bars and too far awav 
to be got bv either short stick alone. [Comtesy of 
^V. Kohler.] 

Human thinking is not different. The 
thinker, faced with a problem, tries for a 
solution. He keeps on until a trial is suc- 
cessful. Many of his errors are errors of 
insight, false insights that come as inspira- 
tions and do not sohe the problem. His 
final success may be an act of true insight, 
or it may be a blind success, as Avhen tlie 
puzzle finally comes apart in your hands 


Recollecting, Imagining and Thinking 

and you ha\c no idea wliat it was you did 
to get it apart. 

If tlie problem is simple and the solution 
has already been learned, then there need 
be no errors and no insight. You want to 
know the sum of 4 and 8; you appeal under 
the set for addition to past learning; and 
the answer is before you, 12. 

You want to decide whether a novel 
proposition is true or false. Past learning 
is not going to be enough to decide the 
issue for you without insight. This is a 
brand new proposition and you need a little 
time, perhaps several seconds, to think. 
Images come up, and then presently some 
insight into the relations of the concepts 
decides you, and you make your judgment. 

You have a puzzle to solve. The block at 
the upper right corner must be moved to 
the lower left corner. You can work 
blindlv with trial-and-error, and you may 
indeed solve the problem thus, though you 
will not have learned it and cannot do it 
again. Or you may study the situation, 
form an hypothesis, try it out, find that 
it does not work, try out another hypothe- 
sis and continue in this fashion until one 
hypothesis or a series of partial hypotheses 
give the required solution. This is trial- 
and-error thinking, but it is also insightful 
thinking because the hypotheses are formed 
by insight and abandoned when found in- 

Here is a simple example that shows how 
problems get solved. Suppose that your 
alarm clock has stopped. You may first use 
blind trial-and-error. You shake it, ti7 to 
wind it some more, shake it again, turn it 
upside clown, change the setting and so on. 
So far you have used methods which some- 
times work, but you have shown little in- 
sight into the problem. Finally, having ex- 
hausted these possibilities, you open the 
case. You notice that the hair spring has 

been tangled, apparently because the clock 
lias been dropped. At that point, believ- 
ing that you have the solution of the dif- 
ficulty, you untangle the hair spring, and 
the clock begins to run. You piu it back 
together again, and the clock stops again. 
Your first insight may have been correct, 
but it was inadequate. You need to know 
something more. So you reopen the clock, 
find that the shaft of the balance wheel is 
out of place and replace it— another insight- 
ful trial. You put the clock together, and 
it runs. Success stops your thinking, just 
as satisfaction stops a need. 

Trial-and-error without insight would be 
the case if your clock stops, you take it 
apart, see nothing the matter with it, put 
it together again and find that it runs. 

There are problems in which trial-and- 
eiTor does not help and in which one cor- 
rect act of insight is enough. For instance, 
there is a ring problem, with two rings, 
each on a loop of cord. The ends of the 
cord are fastened permanently to a stick, 
and the cord is also looped about the stick 
through a hole in a special manner. The 
problem is to get the two rings on the 
same loop. Blind trial-and-error seldom 
helps. It gets the puzzle tangled up and 
makes solution difficult or impossible. In- 
spection of the situation shows that you 
must pass the ring along the cord, through 
a hole in the stick, aroimd a loop of the 
cord and then back through the same hole; 
but the hole is smaller than the ring, and 
the ring cannot go through it. Able scien- 
tists have worked for hours on this prob- 
lem, but the solution comes in a single 
flash of insight. You cannot put the ring 
through the hole to pass it around the loop, 
but you can pull the loop through the 
hole to the ring, pass the ring around it 
and then push the loop back. The neces- 
sary insight is as simple as that; if you can- 

Trial-and-Error and Insight 


not gel llic ling lo tlie loop, yon innst bi ing 
the loop to the ring. 

Insight is not always either false or ade- 
quate. Sometimes it is imperfectly ade- 
quate. The chimpanzees of Kig. 74 were 
solving the problem of getting the banana, 
suspended near the top of their cage, by 
piling boxes on top of one another and 
climbing up on the pile. As the figure 
shows, they could solve the problem when 
three boxes were necessary in the pile, but 
they never learned the mechanics of ecpii- 
librium. Their rickety piles often fell over, 
or else tlie apes balanced j^erilonsly on 
them as they tottered. 

When a rat begins to know the correct 
pa til through a maze, he may come to a 
place where he must choose, look down the 
wrong alley and then abandon it for the 
correct path. This behavior, since it is not 
actually an error, has been called vicarious 
trial-and-error. Human thinking makes 
liberal use of vicarious trial-and-error. 
You form your hypothesis, examine it and 
then abandon it as inadequate, without try- 
ing it out on the actual problem. 

Sometimes it has been said that solving a 
problem by trial-and-error and by insight 
are different and opposed methods of think- 
ing. Such a statement is obviously false. 
Trial-and-error is what happens in certain 
kinds of learning and certain kinds of 
thinking; but we learn by trial and success, 
and we solve problems by trial and insight. 

What is the way to solve a problem? (a) 
Inspect the situation, study it carefully, ex- 
amine it. [b) If you find you know the 
answer, the problem is solved, (c) If you 
do not know the solution, you continue 
your examination, hoping for an adequate 
insight, {d) If the insight comes and is 
adequate, the problem is solved. If it is 
inadequate, you continue hoping. (e) 
AVhen it becomes apparent that the data 

necessary for insight are not available to 
your inspection, you begin with trials, ran- 
dom trials if you have nf> insight at all to 

FIGURE 74. problem-solving: chimpanzee stacks 


The ape solves this problem but does not le.Tin 
to pile the boxes securely on top of one anoiher. 
The other ape, watching, makes a sympathetic ges- 
ture with his left hand. [From \V. Kohler. Men- 
tality of apes, Harcourt, Brace. 1927, Plate I\'.] 

guide you, like a cat in a box ■with escape 
dependent on her toudiing an object which 
the experimenter has selected. The cat 
does not kno^v the experimenter's sea"et. 
whicli is arbitrar\ and not open to insight. 


Recollecting, Imagining and Thinking 

Blind tiial is the only possible method. (/) 
As trials alter the situation, insight may 
become possible, and the problem, partly 
solved, may then be attacked at stage (r) 
or even stage (a). 

Blind trying is inferior to insight, but it 
is better than nothing; and insight is not 
always possible. Most complex thinking 
makes use of actual trials, vicarious trials, 
insights, successes and partial solutions, as 
thinking continues to the final solution. 


Thinking may completely fail to solve 
its problem. That is the safe kind of fail- 
ure, because, since it does not give satis- 
faction, the frustrated thinker continues to 
address himself to the task of finding a so- 
lution or else abandons the problem with 
no false belief tliat he has solved it. 

Thinking may, however, fail by being in- 
correct, and the thinker may accept a false 
conclusion as true, experiencing the relief 
of resolved frustration. That is a danger- 
ous event in thinking, for it lulls the thinker 
into a false sense of security. 

In this section we consider some of the 
ways in which incorrect thinking takes 
place and some of the reasons why it occvns. 


Textbooks of logic expoimd the nature 
of fallacies. Although logic is not psychol- 
ogy, correct thinking must not contravene 
the logical canons. Everyone ought to 
know the nature of the common fallacies of 
thinking, but this book is not the place to 
set them forth. We must content ourselves 
with a single example from science, the 
failure to 'control' conclusions. 

A personnel expert in a factory writes: 
"We have been trying out a new means 
for reducing absenteeism in the plant. It 

has turned out to be very good. Absentee- 
ism has dropped twenty per cent during 
the six weeks the new method has been in 
use." That sounds right, doesn't it? You 
vary x (the method) and you get a con- 
comitant change in y (absenteeism), so y is 
a function of x. Perhaps. Life in a fac- 
tory is, however, a very complex affair, and 
a personnel expert, if he is an expeit, 
woidd want better evidence before he 
reached that conclusion. Absenteeism var- 
ies for many different reasons. How does 
this expert know that it is the new method 
which is reducing absenteeism? Some 
other factor might be at work— the weather, 
the season, the fading out of an epidemic, 
a factor that arises from within the factory 
itself. He should have had a control (p. 
14). Perhaps he could have divided his 
workers into two groups, using the new 
method for tlie test group and the old 
method (or lack of method) for the control 
group. If the test group and the control 
group showed the same decrease in ab- 
senteeism, he would know that the new 
method was not working, or conversely. 

The fallacious thinking that arises from 
lack of control is similar to what is called 
the fallacy of tlie single instayice. Think- 
ers not trained in scientific research, often 
men in public affairs, accept this fallacy 
easily. You can never safely draw a gen- 
eral conclusion from a single instance. 
Any obsei'ved concomitance of events could 
happen for many different reasons or by 
chance. You must repeat the concurrence 
again and again, keeping what you think is 
important the same and letting everything 
else vary. Only in that way do you at last 
become secure in concluding that a gener- 
alization holds. If rats always have been 
found to speed up toward the end of a 
maze, you can begin to talk about a goal 
gradient. A great economic depression fol 

Incorrect Thinking 


lowed the election of Hoover as Presideiii 
of the United States. That is a single in- 
stance. Did Hoover cause the depression? 
It is (|uite iiiij)ossible to say until you have 
tried electing Hoover under a number of 
different economic (ondiiions. 

Wishful Thinking 

Opinions and attitudes are affected liy 
wishes and prejudices and tend to accord 
with what the thinker desires. The course 
of thinking is biased by desire and need. 
(This matter is discussed more fully on 
pp. 603-613.) 

You find wishful thinking in politics, in 
courts of law, in science, in everyday social 
relations. Wherever controversy exists, 
there men try to prove themselves right, in- 
stead of trying to find out the truth. Wish- 
ful thinking is so insistent when important 
human needs are involved that the law 
makes a virtue of necessity and lets the op- 
posing lawyers show how good their contra- 
dictory biases can make their cases, while 
the judge tries to transcend bias and re- 
main impartial. Scientists try to be im- 
partial judges, but scientific controversy, 
the unwillingness to accept the possibility 
of their own past mistakes, shows that ego- 
tism may control the scientists too. We 
take pride so much for gianted that we 
hardly expect a man to think correctly if 
the right conclusion to his thought would 
be humiliating to him. 


A hunch is an imperfect insight. Your 
guess that a relationship might be true 
seems right to you, and yet you lack the 
evidence to validate your guess. That is a 
hunch. The hypotheses and insights of 
trial-and-error thinking are often such 
hunches. A hunch should always be used 
as a tentative conclusion to be tested out. 

It becomes a lorm of intorrect thinking 
only when it is accejjled wiifiout subsc- 
<|uent validation. 

On the other hand, it may be said that 
human action is based on a very large nuni- 
Inr of incorrect conclusirjns, ccjnclusicjns 
tliat may never, during the lifetime of the 
person who uses them, be recogni/ed as in- 
correct. The history of thought abcjut dis- 
eases and their cures is full cjf such incc)r- 
rect beliefs. Every day every man makes 
hundreds of decisions that are based upon 
inadecjuately validated opinions which he 
holds to be facts. When a hunch is held 
to firmly and we are sure that it is incor- 
rect, we name it a siiperstilion. People 
who bet on horse races have to use hunches 
(or superstitions) because they have not 
enough else to use; they are taking action 
in the absence of adequate information. 

Word Fallacies 

The commonest trouble into which lan- 
guage can get your thinking arises from 
the same word's having several difl:ereni 
meanings. The meaning shifts as thought 
progresses from one sense in the premise 
to another in the conclusion. Said one 
newly naturalized immigrant: "Of course 
I'll vote Democratic. This country's a de- 
mocracy, isn't it? They told me so when I 
was studying to be a citi/en." And then 
there is the old joke from the Victorian 
era: "A piece of bread is better than noth- 
ing; nothing is better than Heaven: there- 
fore a piece of bread is better than 

These are crude examples. The modern 
science of semantics studies the meanings 
of words, showing how often thought is 
falsified because the meaning of a word 
shifts without the thinker's knowing that 
it has. \Vc arc advised ahva^s to be aware 
of the referents ^^•hich a ^vord has as de- 


Recollecting, Imagining and Thinking 

fining its meaning, but that advice must 
not, of course, be taken too literally. Lan- 
guage gets its efficiency from the fact that it 
uses words without their meanings having 
to become explicit. We have to trust lan- 
guage, in spite of the ways in which it be- 
trays us, becoming critical only when we 
find that our thinking is not working ac- 

There is also luord magic, the belief that 
when an unknown thing or event is named 
it is understood. Labeling tends to allay 
thinking. The lazy thinker is content with 
a name or with a classification which nam- 
ing establishes. Such naming is useful and 
safe when the object named is understood. 
"That noise is a burglar." There is a 
classification of a noise that could properly 
incite to action. But naming, when it adds 
no new information except the name, is a 
delusion if it is mistaken for thinking. 
"Why," says someone, "do you notice de- 
tails so much better than I? I suppose 
your perceptive faculty must be better." 
Noticing detail is perceiving better. Yet 
many a would-be thinker gets satisfaction 
from such redundant thinking. 


One of the most potent causes of failure 
and error in thinking is so obvious that it 
is usually overlooked. Thinking takes 
time, and it requires effort; the thinker has 
to be strongly moti\ated. Errors occur be- 
cause he does not have time or inclination 
for complete and careful analysis of the 
problem. He takes short-cuts and jumps 
to conclusions. He gives up as soon as he 
comes to a point of serious difficulty. 

This state of affairs is especially marked 
in our thinking upon political and social 
affairs. Careful assessment of the relative 
merits of political parties requires an anal- 
ysis of a mass of information which must 

be sought out from books, periodicals and 
newspapers. Some of the essential infor- 
mation may not even exist. Political prop- 
aganda, moreover, is so phrased that it 
never suggests the possibility of thinking 
out political problems. No wonder think- 
ing upon these topics is so rare. 

Tacit Assumptions 

The set or attitude under which a 
thinker undertakes to solve a problem may 
involve certain tacit assumptions of which 
the thinker is wholly unaware. Very often 
these assumptions prevent him from solv- 
ing the problem, because they exclude from 
his consideration the hypothesis which is 
necessary for his success. 

For example, consider this laboratory 
study of thinking. The experimenter gave 
the subjects a string of beads, on which two 
small white beads were alternated with one 
large yellow one. In the middle portion, 
however, there were five white beads sep- 
arating two yellow ones. The instructions 
were: "Make a single regularly repeated 
pattern without either unstringing or re- 
stringing the beads, and without knotting 
or breaking the thread." On the table 
were many assorted objects, including a 
bottle of glue, a saw, pliers, and needles. 
Most of the subjects took some time to 
reach a solution of the problem, and some 
failed altogether to solve it. The only pos- 
sible solution available was to break the 
extra beads with the pliers. It did not oc- 
cur to the subjects who failed that the 
beads might be destroyed, even though the 
instructions did not explicitly forbid it. 

Figure 75 is the horse-and-rider puzzle. 
The thinker is given two pieces of paper or 
cardboard, one square with the two horses 
printed on it, the other a strip with the 
two riders printed on it. He is told to put 
the riders on the horses without injuring 

Incorrect Thinking 


the two pieces in any way. At fust solution 
seems impossible. The riders would be up- 
side down on the horses and not adjusted 
to the horses' bodies. Solution is, however, 
possible, and it may come by blind trial, 
error and success or by insight. In Fig. 76 



The Strip with the two riders on it, B, must be 
superposed on the square with the two horses on it, 
A, so that the riders will appear in proper positions, 
each astride a horse. (Do not break, bend or tear 
the two pieces.) [From Amer. J. Psychol., 1941, 54, 
437 f, by M. Scheerer, K. Goldstein and E. G. 

the two pieces are shown together, with the 
strip, B, superposed upon the square, A. 
How is that possible? You turn the square 
through 90 degrees, so that one rider rides 
the head and forelegs of one horse and the 
tail and hind legs of the other. That is an 
utterly unexpected kind of a solution. All 
your tacit assumptions are against it. 

Some of these results may be a function 
of the experimental setting. If the prob- 
lem had arisen in the course of everyday 
events, the tacit assumption might never 
have arisen. Nevertheless, these examples 
are important because similar unrecognized 
assumptions occur constantly in the every- 
day course of thinking. In industrial pro- 
duction, for example, there are numerous 

situations in which tacit assumptions pre- 
vent the development of better rncthod.s of 
doing a job. Operation A has always pre- 
ceded operation li, so everyone assumes 
that the order cannot be changed. The 
workers make this a.ssumption without ever 
considering the need for it. To combat 
such mistaken assumptions it has been 
necessary to develop special techniques like 
time and motion studies, which locate the 
accepted but inefficient prrjcedures. (See 
pp. 470-472.) 


This figure was made by photographing the strip, 
B, of Fig. 75 lying on top of the square. A, of Fig. 
75. Can you see how it was done? 

Atmosphere Effect 

Sometimes mistakes in thinking occur 
because unrecognized and unconscious fac- 
tors attach the sense of conviction to a false 
conclusion which convinces the thinker 
that his problem is solved— when it is not 
In the case of the problem of absenteeism 
mentioned above, the personnel expert 
could have said correctly (and it was prob- 
ably unconsciously in his mind): "If tlie 
new method is a good one, its use will be 
followed by a reduction in absenteeism." 
WlvAt he did sa^ is the converse of this 


Recollecting, Imagining and Thinking 

statement, a converse that is not necessarily 
true: "If the new method is followed by a 
reduction in absenteeism, it is a good one." 
The one statement creates an atmosphere 
in which the second statement appears to 
be equivalent and, therefore, as true as the 

The atmosphere effect is sometimes pres- 
ent in syllogistic reasoning. When you 
reason from a major and minor premise to 
a conclusion, a conclusion containing the 
Avord all tends to be accepted as correct 
when both premises also contain all. Thus: 
"All X's are Y's. All X's are Z's. There- 
fore all Y's are Z's." The conclusion is 
a non sequitur, but it will be accepted by 
many. It is easy to see the fallacy when 
it asserts a conclusion that we know to be 
wrong. Thus: "All dogs are mammals. 
All dogs have four legs. Therefore all 
mammals have four legs: [or] all four- 
legged animals are mammals." Atmos- 
phere does not stifle knowledge, but it does 
seduce ignorance. 

Atmosphere also affects opinions and at- 
titudes. That fact becomes clear in the 
questionnaire studies of the values which 
people hold. The effects are very subtle. 
The way a question is worded may change 
utterly the frequencies of the different an- 
swers to it in a public opinion poll. (See 
pp. 580-584.) 

Habitual Methods of Attack 

Correct thinking is limited by the habit- 
ual methods of attack that the thinker em- 
ploys. That these methods are arbitrary 
and may not be the only possible methods, 
the thinker is usually not aware. Like 
tacit assumptions and atmosphere they con- 
stitute for his thinking a limitation of 
which he is usually unconscious and which 
he is therefore not likely easily to change. 

One kind of a problem will be translated 

almost at once by one person into an alge- 
braic equation. Another person will try 
to solve the same problem by a diagram. 
Problems in plane geometry call for dia- 
grams and construction figures, but multi- 
dimensional geometries seem to require 
algebraic expressions. A detective problem 
can be solved by systematic logic or by in- 
sight. Some psychologists like to put psy- 
chological problems into terms of stimulus 
and response and always to envision hiunan 
phenomena as they would exist in animals 
or even in robots. Others like to stick to 
the terms of experience and the data of 
consciousness. Methods of attack differ for 
different individuals. 

If the thinker is accustomed to use one 
method, it is not likely to occur to him 
that the method may be inefficient in a 
given case or even inapplicable. He will 
go ahead with the old familiar method in- 
stead of looking for a new one. The most 
successful problem solvers are those per- 
sons who are constantly on the lookout for 
new methods and on guard against the in- 
efficient use of habitual action in novel 

A famous psychologist who investigated 
the nature of thinking— his name was Max 
Wertheimer— once posed this problem. ^Ve 
have a simple organism— an amoeba— which 
multiplies by division into two once every 
three minutes. Every new organism re- 
divides every three miniUes. We place a 
single amoeba in a jar and we find that the 
jar is filled with amoebae in one hoin\ 
How long will it take to fill the jar if we 
start with two amoebae instead of one? 
Wertheimer found that his friends who 
were accustomed to the use of mathemati- 
cal procedures would start in at once to 
work oiU geometrical progressions in un- 
dertaking to answer this question. Il rc- 
(juircs a great deal of ^vork to reach llie 

Incorrect and Correct Tbink'mg 


answer in this way, but not much work or 
time by a simple insight. The student 
with this admonition and a little thought, 
with no fornuilas and no paper and pen- 
til, should be able to give the answer with 
assurance, provided only he can subtract 
and knows how many minutes there are in 
an hour. 

Faulty Transfer of Method 

A frequent source of error or failure in 
thinking is the use of a method which is 
not adapted to the problem at hand. There 
is also the tendency to take over for a new 
problem some superficial aspect of a meth- 
od successful in a different problem, while 
overlooking its fundamentally important 
feature. Another example of Wertheimer's 
will make this matter clear. 

In one case children had been previously 
taught to prove a theorem about the area 
of a rectangle by dividing the rectangle 
into unit squares. By this process they 
found, of course, that the area was the 
product of the two sides. Then the chil- 
dren were given the problem of finding 
the area of a parallelogram. Some of them 
applied the method used before in a com- 
pletely blind manner. They divided the 
parallelogram up into smaller parallelo- 
grams—which did not help them at all. 
They had transferred to a new problem a 
feature of the old method, but it was only 
a superficial aspect. They had failed to 
grasp the important part of the original 
method for finding the area of a rectangle, 
having learned to use the method mechani- 
cally without really understanding it. 

Wertheimer blames conventional and un- 
imaginative teaching for the fact that many 
children rely on this blind and superficial 
transfer. He complains that the schools 
stress drill too much and insight not 
enough. The child, after being shown how 

to do one kind of problem, practices by 
using the method upon essentially the 
same problem. Little is changed but the 
numbers and arithmetic involved. This 
kind of drill may blind the pupil to the 
essential principles involved in the proce- 
dure. y\t any rate drill is not the way to 
learn to be alert for novel relationships. 
Too drilled a child may lose the fun of 
learning to think. 

Individual Differences 

Certainly some persons are better thinkers 
than others. They are more alert to the 
perception of novel relations, to getting in- 
sight. They follow habitual procedures 
less inflexibly when insight— or a hunch- 
shows an alternative, possibly better way. 
They like problems, accepting the unsolved 
as a challenge. Their motivation to earn 
on to a solution is high; an unresolved 
dilemma keeps coming back into their field 
of attention, compelling them to work at 
it. Some men of genius fit these specifica- 
tions, but not all who are proclaimed 
geniuses by the world. 

Some people think that the intelligence 
tests could be used to measure thinking 
ability, but it is doubtful if such tests are 
good indicators of a person's insight. 


Thinking is not easy, and there is no 
easy substitute for thinking other than ac- 
cepting your solutions and beliefs read\- 
made from others without troubling to 
check their adequacy for \ourself. You 
can, however, reduce the effort of thinking 
by eliminating false starts, by avoiding un- 
necessary errors and stumbling blocks or 
by taking pains not to repeat the same 
error. There remains, ho^vever, a process 
which takes time and ^vhich those persons 


Recollecting, Imagining and Thinking 

who ha\e not learned to enjoy it regard as 

The fundamental problem of the applied 
psychology of thinking is the improvement 
of the adequacy of thinking. For the in- 
dividual thinker this means improving his 
'batting average' in the solution of the 
problems which he meets from day to day. 
For society at large it means reducing the 
gullibility of the voter, the radio listener 
and the reader. Thought in oiu" cidture 
will be improved if we better the quality of 
thinking which is broadcast, printed and 
spoken by writers, editors, speakers, com- 
mentators and men of public affairs. 

The partners in that undertaking are 
logic, education, psychology and all the 
sciences, social and natural. Logic pro- 
vides tests of the validity of thinking. Psy- 
chology fin^nishes knowledge about the 
actual thinking process and the causes of 
bad thinking. Education and the sciences 
provide the factual backgioimd which the 
individual needs in his thinking, and also 
training and practice in this difficult art. 

It is not possible to print a dozen or a 
hundred practical rules guaranteed to make 
anyone an effective thinker. Good think- 
ing depends upon (1) strong motivation for 
the particular problem in hand, (2) con- 
stant general interest in problem solving, 
(3) the alertness and flexibility that favor 
insight over the continued use of stereo- 
typed procedures and (4) the wide range 
of wisdom that gives insight— the percep- 
tion of novel relationships— something to 
work on. 

In addition to these general dimensions 
of good thinking, not all of which lie under 
voluntary control and many of which it is 
too late for the mature adult to acquire, this 
chapter suggests many rides that can be 
applied in favor of correctness and effi- 
ciency. Here are a few of them. 

(1) Because thinking takes time, best 
results cannot be obtained with rigid time 
limits. When a problem is intrinsically 
and strongly interesting there is no need for 
a time pressure. If the problem is less in- 
teresting, a time limit may serve as a con- 
venient device for maintaining motivation. 
Too short and too rigid a time limit is 
likely to reduce the quality of thinking. 

(2) Although the phenomenon is not 
well imderstood, incubation can be put to 
practical use. When thinking appears to 
be 'getting nowhere' and failure after fail- 
ure occurs, put the problem aside for a 
time. When you return to it fresh, it will 
often progress well. You may even experi- 
ence the sudden insight which comes im- 
expectedly 'out of the blue.' 

Incubation is not effective if you have 
not really tried to solve the problem be- 
fore resting. The success of incubation 
depends upon the previous labor you have 
devoted to the problem and the level of 
your motivation. Incubation cannot be 
used to avoid work upon the problem, and 
it is not a substitute for factual informa- 
tion. You will hatch nothing if there is not 
something already there to incubate. 

(3) Tacit assumptions and unrecognized 
sets are such frequent causes of failure that 
we must continually watch for them. Per- 
haps one reason for the incubation effect 
is that the intei-val permits us to lose some 
of these wrong sets. At any rate, when you 
are 'stuck,' start looking over your assump- 
tions and the conditions of the problem. 
It may be helpful to write down all the 
conditions of the problem and those as- 
sumptions which are necessary. Then ex- 
amine your procedure to see if you have 
missed some possibilities which are not 
explicitly forbidden by the nature of the 

How fo Think 


(4) Check the logical pattern of your rea- 
soning. U you have had no training in 
logic, try to obtain it. In any case, make 
sure all the steps of your reasoning are ex- 
plicitly stated. Frequently you will have 
taken for granted one or more important 
steps. If all the steps were explicitly 
stated, you might not accept them as readily 
as you do in their vague unformulated 

As a check upon the validity of reason- 
ing it is frequently useful to follow through 
a parallel argument in another field where 
the correct solution is known. For ex- 
ample, in discussing the syllogism (p. 210), 
we used first an example of a formal argu- 
ment with X's and Y's, and then we took 
a look at the same form of argument with 
animals instead of the letters. In the sec- 
ond case we found that the conclusion was 
contrary to known facts. This kind of 
parallel check with familiar materials does 
not prove that the original logic was sound. 
The parallel might be right by accident. 
But when the parallel is patently wrong, 
the original logic does, indeed, need care- 
fid scrutiny. 

Always suspect yourself when you are 
inclined to accept a conclusion while the 
details of the argument remain unclear. 
Let your knowledge of atmosphere effect 
warn you that conviction of correctness is 
not necessarily valid. Intuition and hunch 
are extremely valuable in thinking, but 
they are means for getting to a sound con- 
clusion and they are not necessarily self- 
validating. Sometimes an insight is as 
self-validating as a geometrical axiom, but 
there is still the danger that habit or at- 
mosphere or wishful thinking may have 
deceived you. 

(5) A final word has to do with motiva- 
tion in thinking. Thinking itself, regard- 
less of its practical outcome, does not have 

to be 'work'; it can be intrinsically inter- 
esting. The modern occidental culture is 
an aggressive culture. We like competi- 
tion. A fight is alway.s news. In America 
competitive sports interest almost everyone, 
at least as onlookers, most of whom like the 
indoor contests that are waged with cards 
or comparable weapons. Thinking is just 
such a game. Mostly it is solitaire, but in 
it you compete, not against chance, but 
against nature which yields up its truth 
only to those who are deft, wise, alert and 
eager to be right. 


1. Allport, G. ^V., and Postman, L. J. The psy- 
chology of rumor. New York: Holt, 1947. 

The how and why of the spread of rumor in 
relation to the psychology' of perceiving, re- 
membering and reporting with the results of 

2. Bartlett, F. C. Remembering. Cambridge, 
England: University Press, 1932. 

Descriptions of the author's own researches 
upon recollection of form, using both pictures 
and stories as materials. 

3. Bentley, M. The new field of psxchologw New 
York: D. Appleton-Century, 193-t. Chaps. 14 
and 15. 

A careful survey of all the psychological 
processes. The chapters on recollecting, com- 
prehending and thinking stress primarilv the 
descripti\e approach. 

4. Duncker. K. On problem-solving. Psxchol. 
Monogr., No. 270, 1945. 

Descriptive experiments upon problem solv- 
ing, interpreted from the point of view of Ge- 
stalt psychology. 

5. Hayakawa, S. I. Laytguage in action. New 
York: Harcomt. Brace. 1946. 

As the subtitle states, the book is "a guide 
to accmate thinking, reading and writing.'" 

6. Kasner. E.. and Newman. J. Malhemalics and 
the imagination. New York: Simon and Schus- 
ter, 1940. 


Recollecting, Imagining and Thinking 

An entertaining account ol some ol' the im- 
portant concepts used in mathematical think- 
ing: mathematical ratlier than psychological in 
its orientation, hut holding many implications 
for the psychologist. 

7. Kohler, W. The mentalily of afjes. New 
York: Harcourt, Brace, 1925. 

.'Vn interesting and detailed report of Kohler's 
experiments upon insightful hehavior in chim- 
panzees, and their use of sim|jle tools and con- 
structions in solving problems. 

S. Stern, W. General psychology. New York: 
Macmillan. trans. 1938. Part 4. Chaps. In to 

Good chapters on recollecting, imagining and 
thinking, in a descriptive survey of psychology 
from the pcrsonalistic point of view. 

9. Thouless. R..H. How lo think siraighl. New 
York: Simon and Schuster, 1939. 

The technique of using logic instead of emo- 
tion in thinking. 

10. Wertheimer, M. Pioduclive Ihinking. New 
York: Harper, 1945. 

The approach of Gestalt psychology to 
thinking is simimarized and illustrated by the 
author's own experiments with children and 
adults, as well as by certain instances of 
.scientific thinking (for example, Einstein's). 

11. Woodworth, R. S. Experimental psychology. 
New York: Holt. 1938. Chaps. 25, 29 and 30. 

Excellent chapters on memory for form, 
problem solving and thinking in an advanced 
but clearly written survey of experimental psy- 




IN the first chapters of this book we have 
studied men doing, acting and learning; 
but before men act they usually perceive, 
they sense, they note what things and events 
are about them. Perception is the first 
event in the chain which leads from the 
stimulus to action. To understand per- 
ception we must find out just what it is 
in the world that we respond to. What 
things are important for us, and why? 

In the simplest sense, a stimulus is any 
sort of energy change, that is to say event, 
which can set ofT a response. Heat or pres- 
sure on the skin, light falling into the eye, 
chemical particles carried into the nose, 
these are all stimuli in this simple sense. 
For many of the simplest organisms they 
are all that matter. The immediate physi- 
cal agent is all important. It is the water, 
as hot or cold, acid or neutral, which makes 
the amoeba swim forward or back. In the 
same way, the initial response of our sense 
organs depends upon these proximal 

As organisms become more complex, they 
no longer react just to the stimulus which 
touches the skin. They acquire also an 
ability to know something about what lies 
at a distance. The 'eyes' of starfish and 
the octopus can tell the direction from 

which light conies. The 'ears' of insects 
permit them to hear sounds made by their 
distant mates. 

The receiving equipment of mammals 
and of men is made far more complex by 
the addition of a nervous system. The 
physical and chemical stimuli, of course, 
still pass through the skin, but man's reac- 
tions are gauged to objects and events 
often quite far away. It is the steak si//ling 
in the pan, the friend walking by his side, 
the ball flying through the air which directs 
what he does. For the simple animal it is 
only the proximal events in his physical 
environment, the events that come into 
actual contact with him, which set the pat- 
tern of his action; for higher animals the 
more distant occurrences are of great im- 
portance. To describe these remote stimuli 
a more complete inventory of the human 
environment is necessary. We have to go 
farther afield to find just what it is that, 
corresponding with our experience, is rep- 
resented by that experience. Just what are. 
we ask, the more distant things in the workl 
around man to which he responds. 

It is not easy to understand fully the 
problem of perception. Reality, tlie ob- 
jects and events around us. seems so tan- 
gible, so concrete that we believe the world 
exists just as we perceive it. Our experi- 

This chapter was prepared by Edwin B. Newman of Harvard University. 




ence mirrors what is out there. Or, at its 
worst, experience is but a slightly tarnished 
copy of the world. More thoughtful peo- 
j)le realize that this view is too simple. 
The physicist tells us, for instance, that this 
hard, smooth, solid object which I hold in 
my hand is actually not solid at all. In 
his view it is many tiny bits of matter 
spinning in orbits like the moon's about 
the earth with relatively large spaces be- 
tween the particles. He may call attention 
to other 'errors' in our perceptions. White 
to the eye is a simple color; to the physicist 
it is a most complicated mixture of many 
kinds of light. Consider musical tones. 
In our experience they are smooth and con- 
tinuous. Physically they consist of a rap- 
idly alternating series of sound waves strik- 
ing our ears. Clearly then, the object out 
there, as a physical object, and our experi- 
ence of it are two quite different things. 

There are philosophers who are so im- 
pressed by the difficulty of relating our 
experience on the one hand to the physical 
world on the other, that they give up the 
problem altogether. Experience, they say, 
is the only thing which we can know with 
assurance. There is no proof of the exist- 
ence of the physical world; hence it is only 
an illusion. These philosophers are the 

Today most people reject philosophical 
idealism. We believe there is a real world 
apart from our experience of it. We ac- 
cejjt both the fact that there is a world out 
there and that we as organisms respond 
to it. The way in which an organism re- 
sponds to the world is a problem which 
is on a par with any other scientific prob- 
lem. What happens when we perceive, and 
what is it that makes it happen? That is 
the problem of perception. 


It will perhaps be well to set out clearly 
the meaning of a few of the words which 
we are going to use. Perception is the 
experience of objects and events which are 
here now. It excludes those things which 
are somewhere else, things about which we 
may think clearly but do not sense di- 
rectly. Furthermore, it is convenient to use 
the term perception for the more general 
aspects of this activity, reserving the term 
sensation for those facts in our experience 
which depend upon how the sense organ 

Some perceptions seem to us to be in 
error. If one perception does not agree 
with another, we call the unusual one an 
illusion. Everyone knows, for instance, 
that the movement seen in the movies is an 
illusion. A series of still pictures is shown 
in rapid succession. Each picture, pro- 
jected alone, is quite stationary, but when 
the series is shown at a proper rate we see 
movement. It is not true in an illusion 
that one perception is 'wrong' while the 
other is 'right.' Actually each is just as 
normal as the other. It is no easier to ex- 
plain why slow projection is seen as a series 
of objects displaced discontinuously than 
it is to explain why faster projection shows 
the same objects moving continuously. 
Both kinds of seeing are complicated and 
need a great deal of explaining. The word 
illusion is a convenient handle for desig- 
nating these luiusual perceptions, but we 
must remember that naming a phenome- 
non does not explain it. 

Hallucinations are clearly abnormal. 
They are perceptions which are unique for 
one person alone. If nine people in a room 
see nothing while the tenth sees a black 

change is the Basis of Perception 


cit, the tcnlh is jjiob.ihly li;illiic:inatcd. 
Hallircinations occur occasionally tor every- 
one. When frequent and persistent, they 
are almost always in our society regarded 
as a symptom of mental disorder. We 
send the person who has them to an insti- 
tution for special care. 


Many of the facts about perception are 
so simple that they almost escape notice. 
Let us start out, however, with some of 
these simple facts because they are very 
general and apply to almost all cases of 
perception. One such fact is that percep- 
tion is always a response to some change or 
difference in the environtnent. If the world 
were perfectly homogeneous and we were 
in equilibrium with it, we should experi- 
ence nothing. Let some condition change 
suddenly, or one receptor be stimulated 
and another not, and we sense the fact 
at once. 

Take as an example our experience of 
pressure. At the surface of the earth there 
is a presisure of 15 pounds on each square 
inch of the surface of our bodies. Yet we 
feel nothing. Let 15 pounds more press on 
a single square inch, and we feel it very 
clearly. Proof that we do not feel a uni- 
form pressure comes from aviators who go 
up to an altitude of 35,000 or 40,000 feet 
in the air. At this altitude the pressure 
on the surface of the body is but 3 pounds 
per square inch. Still they do not feel any 
pressure. The same is true of the diver 
or the sand hog who works in a caisson 
under the river. These men may be sub- 
jected to pressures as great as 50 or 60 
pounds per square inch. Of the pressure 
itself, they feel nothing. 

Rapid change of pressure is a different 
story. Sound which stimulates our ears is 
just sucli a rapid change. Tactual stimu- 
lation is a difference in pressure between 
one part of the fiody and another. A nice 
demonstration of these facts may be made 
by a very simple experiment. Plare your 


When the hand is held under water, only the 
ring around the wrist is felt. Neither the uniform 
pressure of the air nor of the water is sensed bv 
the subject. 

hand in a deep basin of lukewarm water. 
So long as you hold your hand still, you 
feel pressure neither from the "water nor 
from the air. All that you feel is the ring 
wliere the water joins tfie air, wliere there 
is a sharp change of pressure due to the 
surface tension. (See Fig. 77.) 

Temperature is another familiar illus- 
tration of this same fact. "What we per- 
ceive as hot or cold depends largelv upon 
what has just gone before. If tlie tempera- 
ture is lowered w-e perceive cold; if it is 
raised we perceive warm. This is prob- 



ably all that counts. It has been said 
that a frog, a cold-blooded animal, may be 
heated up gradually while sitting in a pan 
of water until killed by the heat without 
feeling anything, at least without jumping 
out. The problem is somewhat more com- 
plex in man who possesses a special tem- 
perature-regulating mechanism and the 
means for getting ill with fever when the 
blood gets too warm. 

The visual perceptions, white and black, 
are notoriously dependent upon differences. 
The intensity of light given off by the 
darkest black object in sunlight may be 
greater than the intensity of the brightest 
white object in a dim light. And yet the 
white object looks white and the black 
object black, even though the white object 
reflects less light than the black. What is 
most important is the relative amount of 
light from each part of the visual field, 
from the object and from its surroundings. 
Black is not just the absence of any visual 
experience. It is a definite something 
which is not-white. The person born 
blind, whose optic nerve is destroyed, sees 
neither white nor black; he sees nothing. 


A second general characteristic of per- 
ceiving is that it is selective. At any given 
moment himdreds of stimuli are reaching 
our sense organs. Out of this welter of 
forces acting from outside, the organism 
has to select the particular one to which 
it will attend, the one to which it will re- 
spond in some unified, coherent way. 
Simplicity, or singleness of response, is part 
of the basic biological nature of living mat- 

This selectivity of perception amounts 
to giving one sense impression a clear track. 
The one impression captures or preempts 

the reacting machine, momentarily shut- 
ting out all other sense impressions. For 
the moment the favored sense impression 
holds sway. Later, of course, some other 
sense impression will take over. 

In our experience we speak of these facts 
by saying that we attend to something. 
Only a small number of items can fall 
within the span of attention. Our experi- 
ence is said to have a focus and a margin. 
Those items which are clearest in experi- 
ence lie within the focus of attention. 
Mixed in with them or off to one side arc 
many less clear items which make up the 
margin. Still other things, which we 
might be experiencing and are not, lie en- 
tirely outside the field of attention. 

Yotir experience at this moment will make 
this matter quite clear. The focus of your 
attention is occupied by the words you are 
reading on this page. The margin of your 
experience is filled with such things as the 
table on which this book is lying, the sound 
of people moving near by, perhaps a pres- 
sure from your stomach which reminds you 
of lunch or a slight pain in your foot from 
an ill-fitting shoe. You have been quite 
unaware as you read this of the, touch of 
your clothes, of slight strains in your eyes 
as they move back and forth over the lines 
of print, of the soimds of your own breath- 
ing, of the color of the paper on which this 
is printed. You luere unaware of them, 
that is, until reading the preceding sen- 
tence made you attend to them! 

Attention may indeed be selective, but it 
seems to be fickle in its choices. The stream 
of consciousness is rarely smooth and placid. 
It seems rather to dart here and there, 
never continuing for long in a single direc- 
tion. Some modern writers, such as James 
Joyce and Eugene O'Neill, have made much 
of this jumpiness of experience. They try 
to portray the kaleidoscopic character of 

Perception Is Selecfive 


experience in actual words and thoughts. 
Carefully studied, however, the kaleido- 
scope turns out to be an orderly machine. 
Our attention may fluctuate from one thing 
to another but it is not really capricious. 
There arc rules which help to predict what 
will gain attention and what will hold it. 
Here are six of the rules. 

(1) The intensity of the stimulus is obvi- 
ously the most important single factor in 
determining response. A loud sound, a 
bright light, a hard slap, an intense pain, 
each of these demand action, and they 
usually get it. Of course the basic rule 
that change is the stimulus for perception 
still holds. It is the sudden loud sound, 
the flash of bright light that gets attention 
and action. When it persists an intense 
stimulus can usually be neglected. We 
work under bright lights, or ride on the 
subway train without serious results. Se- 
vere pain may even go unnoticed. On the 
other hand, a sudden decrease in intensity 
may also get attention. When suddenly the 
din of a steel mill stops, the silence 
seems almost to shout at you. Alone in a 
quiet room with a ticking clock, you do not 
hear the clock vmtil it stops. Then again 
the silence is noticeable. Nevertheless a 
racket is more compelling than a silence. 
If a whisper does not get a reply, a shout 
nearly always will. 

(2) Novelty is a factor scarcely less im- 
portant than intensity. Any mode of per- 
ception loses its effectiveness as it grows 
older. The new sight, the new sound gains 
relatively in strength because it is differ- 
ent from the old ones, contrasts with them. 
When we want something to be noticed, 
we give it a new color, a new shape, per- 
haps a new odor or taste, and see to it that 
it contrasts with what precedes it and ac- 
companies it. Just as perceiving cannot 
take place at all without there being dif- 

ference or change, so there must be differ- 
ence or change in the factor novelty. A 
strange object grouped with ninety-nine 
other strange objects does not get attention, 
because there is no reason for the choice of 
one object more than another. On the 
other hand, one familiar object placed 
among ninety-nine novel objects does stand 
out and catch the eye. Paradoxical as the 
statement is, here familiarity is novel, or at 
least rare, and strange objects are too com- 
mon to seem novel. 

(3) The repetition of a stimulus helps in 
several ways to evoke action. First of all, 
a repeated stimulus is in some senses a more 
intense stimulus. Two shots in succession 
are more likely to attract our attention 
than one; three are perhaps more effective 
than two. Sometimes regular repetition 
helps attract attention because the first few 
instances sensitize us to the later ones. 
How often do we start to count the strokes 
of a clock after two or three have gone by. 
We hear a new song tw^o or three times 
over before we really seem to hear it. 
Finally, the regular repetition of a stimulus 
often produces a set or expectation so strong 
that later members of the series are per- 
ceived the same way even when they have 
in fact been changed. An example is the 
'proofreader's illusion,' the failure to see a 
misspelled word because of expectation of 
the correct form (see p. 202). The movies 
trade on this factor when they use 'doubles' 
and 'stand-ins' which the uncritical person 
readily accepts as if the principal actor were 
continuously present. Repetition also mul- 
tiplies the chances of a stimulus' getting 
attention: if it misses on the first two tries, 
it may succeed on the third. Nevertheless, 
the effect of repetition is not primaiilv 
due to the operation of chance. Thert 
can be no doubt that the marginal occur- 



rence of stimulation helps eventually to 
bring it into the focus of attention. 

(4) hitention— the effect of set or atti- 
tude—is a very important factor in deter- 
mining what experience is selected for at- 
tention. When we intend to speak to a 
particular person, he stands out quite 


There are two equally 'good' faces shown in this 
picture. You can see one. Can you see the other? 
[.Adapted from W. E. Hill.] 

clearly as we meet him in a crowd. When 
we decide to get the hammer from the 
shop, we see it at once even though it is 
out of place on the bench. The bird lover 
at once hears the thrush's song, while the 
business inan remains unperturbed, exain- 
ining the woods as possible pulp for mak- 
ing paper. Intention is in a way a rehearsal 
of an expected experience. 'When the ex- 
perience comes, it is like meeting an old 

(5) All those forces within the individual 
which are lumped together as motivation 
act as a powerful selective agent in per- 

ception. The familiar example is the 
pretty girl of any advertisement. Sense- 
less though it seems, 'leg art' and 'cheese 
cake' are basic principles of advertising. 
Sex appeal gets attention more quickly 
than any other factor. For a half-starved 
man the values are quite different. The 
odor of food is far sweeter to his nostrils 
than the finest perfume. Sex, food, water, 
need for shelter, parental love, operate both 
in animals and men to determine jjercep- 
tion. Other needs, for social approval and 
security, for play and activity and order, 
may have less evident although perhaps 
no less real effects. 

(6) Finally, selection is determined by 
the part luhich the particular stimulus 
plays in the luhole pattern of perception. 
Each part by itself, in a figure such as Fig. 
78, stands little chance of being selected. 
But when it is given an important role in 
the scheme of things, it suddenly stands out. 
Note how this happens as you discover the 
mother-in-law. An unimportant shadow 
becomes her eye, and an inconspicuous 
band her mouth. At the same time the 
pert nose of the wife becomes only a slip 
of the artist's pen. 

The parts of the hidden figure were there 
all the time waiting for you to discover the 
object or to have it pointed out to you. 
Once the object is seen it directs atten- 
tion to its own parts, makes them signifi- 
cant and important. At the same time, of 
course, it makes other details unimportant, 
makes them just members of the crowd as 
background for the star actor. 


The task of selecting among the many 
stimuli presented to our senses would be 
almost impossible were it not for teamwork 
among the individual sense organs. Each 

Perceiving Is Organized 


element of the eye docs not report to the 
brain upon what happens to it alone; 
rather, a group of receptors sees a square 
or circle, a moving figure or patterns with 
more complex structure. The eyes and the 
brain are able to group or to organize a 
number of stimuli into a larger unit to 
^vhich the organism now may respond in a 
simple fashion. This unifying activity of 
perception makes it possible for a person 
to respond to a far more complicated en- 
vironment than he could without it. 

The way grouping works can best be 
illustrated by a number of simple examples 
chosen to illustrate the more important 

(1) If there are various objects in a field, 
those things will be grouped which are 
similar. Look, for instance, at Fig. 79. 
In the left-hand part of this figure, which 
are the obvious series of objects? In what 
direction do the sets run? Up and down? 
right and left? diagonally? What do you 
see in the right-hand part of the figure? 

In both parts it is the similar figures 
which appear linked together. In the left 
part of the figure they mark out five hori- 
zontal lines, three longer and two shorter. 
In the right-hand part the three cubes 
stand out while the small figures form a 
closely knit background for the cubes. It 
would indeed be unusual if you saw one 
of the tiny figures, such as the A^ forming 
a pair with one of the cubes, while the 
other cubes formed some other figure with 
other parts of the background. (Can you 
find the A among the other small figures?) 
Similarity may be similarity of shape, simi- 
larity of size, similarity of color or, for that 
matter, similarity in any property of an ob- 
ject which can readily be distinguished. 

(2) The second principle of grouping is 
nearness or proximity. How would you 

describe the lines at tlic left in Mg. 80? 
Everyone would say of the figures at the 
right that there were two people followed 
l^y a single person. The relative nearness 
of the two lines or of the two people makes 
them seem obviously a pair. Proximity is a 
relative matter, to be sure. Two objects 
might be separated by quite a distance and 
still form a pair if no other object of the 
same kind were in the vicinity. 


In the left-hand figure one sees five horizontal 
lines. The circles, or the crosses, are grouped to- 
gether. Three figures stand out easily on the 
right. The small similar figures of the background 
form such a firm pattern that the letter ,\ among 
them can be found only with difficulty. 

(3) The factor of proximity may be modi- 
fied to some extent by the symmetry of the 
entire figure. Compare the two sets of 
lines in Fig. 81. In the upper set. A, prox- 
imity operates so that you see three pairs of 
parallel lines. In the lower set, B, a per- 
son usually sees two sets of parallel lines 
with a single line on each end which forms 
a disturbing remainder. Set B mav, how- 
ever, be seen almost as well as three sets of 
broadly spaced parallel lines. Thus the 
pairing favored by proximity may be broken 
down in favor of a pairing which uses up 
the entire set of six lines. It is much more 
difficult to see this pairing across the broad 
space in the set A because this would in 
turn leave a remainder on either end. It 
is as if the organism abhorred something 
left over. 




To the left, one sees two lines, plus one. How would you describe the gioiiping of the three men to 
the right? 

(4) The principles of grouping deter- 
mine not only the way separate items are 
linked together but also how a number of 
parts fit together to form a figure. The 
choice of parts to be grouped would seem 
to be especially difficult if one figure is 


In A, the pairs favored by proximity take in all 
the lines. In B, the end lines work to favor a pair- 
ing across the longer distance. 

drawn over the other one as, for instance, 
in Fig. 82. Here there appear to be two 
lines. One is a wavy line, the other is like 
the edge of a wall with its square corners. 
In terms of the detail, a belongs with c and 
b with d. But proximity would favor the 
linking of a and d or c and d. In this fig- 
ure, however, the good continuation is the 
straight or continuous line, and such a 
grouping is favored over other possible 

(5) The forces which gioup visual ele- 
ments into a stationary figure are multi- 

plied in a sense many times over when 
that figure moves. The significant links 
among the parts of the figure itself remain 
constant while the relations between parts 
of the figure and parts of the background 
are constantly changing, and getting lost 
in the process. A familiar example is 
looking through a dirty or spotted win- 
dow. If the person looking holds his head 
quite still, it is not easy for him to know 
whether the spots are on the window or on 
the object seen through the window. If, 
now, he moves his head ever so slightly, 
all the spots on the window move in one 
direction while the object seen through the 
window moves in the other. What was un- 
clear a moment before is now neatly divided 
between window and object. Elements are 
linked which have a common movement. 
The same things occurs to spoil camou- 
flage. The grouse or partridge with its 
protective coloration will remain invisible 
so long as he remains still. Just as soon 
as all the spots of his checkered plumage 
move together, they are grouped in per- 
ception, and the bird is seen to be a single 

(6) Moving figures illustrate still another 
principle of considerable importance. This 
principle is that when a figure moves, the 
parts of the figure will hold constant their 
relation to one another. The parts of the 

Perceiving Is Organized 



A wavy line is drawn over the square-coineicd, straight line. In terms of the detail to the right, a is 
paired with c and b is paired with d. [After Wertheimer (1923).] 

(igtire keep in formation as they match 
along, and the role which each plays will 
determine what points are linked from one 
moment to the next. A single example 
will show what is meant. Imagine that 
you have put before you nine white spots 
arranged in a diamond-shaped pattern as 
shown by the circles of Fig. 83. Let these 
spots disappear and a moment later let 
nine similar spots appear in the places 
marked by the crosses in this figure. No- 
tice that four of the spots are exactly the 
same when they are shown the first time 
and the second time. If these four spots 
were shown alone each time, they would 
of course not move at all. We might sup- 
pose that the four spots would do the same 
when all nine were present, and the other 
five would have to move around them from 
left to right. What happens is quite dif- 
ferent. Everyone sees a diamond-shaped 
pattern which moves as a whole over to the 
right. The spot which was the right-hand 
corner in the first presentation is linked 
or grouped with the spot which is the right- 
hand corner in the second showing. 'Right- 
hand-corneredness' has more to do with 
what is linked together than the actual 
stimulation of the identical spot in the eye 
in the first and second showing. 

All the examples which we have chosen 
have been visual figures, largely because 
vision is our most complex and highly de- 
veloped sense. Grouping occurs in the 

other sense departments as well. In hear- 
ing, for instance, the appreciation of a 
rhythm depends upon the linking together 
of the proper notes or beats in a series. 
It turns out in this case that the principle 








O X ' 


The circles indicate the initial position of nine 
points of light. These disappear and are followed 
by nine lights in the positions marked by X's. All 
nine lights move equally to the right, even though 
the four center lights are identical in the first and 
second exposures, [.\fter J. Ternus (1926).] 

of proximity, expressed in time, is very 
compulsory. Pairs of beats, dit-dit, dit-dit, 
dit-dit, are invariably grouped into pairs 
that follow closely on one another. Re- 
gi^ouping across a longer inter^•al, such as 
we had in Fig. 81, does not occur in hearing 
An interesting instance of giouping oc- 
curs in the skin in what has been called 
the tau effect. Try this one on a friend, as 



it is very easy to demonstrate. Mark out 
three equidistant points on his forearm or 
the back of his hand. They should be suffi- 
ciently separated to give a clear impression 
of distance. When his eyes are closed, 
touch the three points in succession but 
with your timing unequal. For instance, 
try l-2-pause-3, or the reverse, l-pause-2-3. 
Ask him which distance is the longer. It 
will be evident at once that the distances 
which are felt on the skin depend very 
much upon the grouping of the successive 
stimuli in time. 



At the beginning of this chapter we 
noted that to understand perception we 
must find out just what it is in the world 
around us to which we respond. Before 
trying to answer that question, we took 
time to describe three important character- 
istics of the act of perceiving itself. It was 
found first that, in perceiving, the organ- 
ism always responds to some change or dif- 
ference in the environment. Second, the 
organism selects the particular stimulus or 
group of stimuli to which it will respond. 
Third, the organism links together a num- 
ber of stimuli into a group so that a single 
simple response may be made to a complex 

It is time now to return to the original 
question. Let us examine some of our sim- 
ple perceptions to see if they help to tell 
us what aspects of the world are important 
as the stimuli for these perceptions. 


The simplest perception is a single fig- 
ure which appears against a uniform back- 

ground. Imagine, for instance, that the 
cross of Fig. 84 is a white figure on a per- 
fectly uniform gray backgi^ound which ex- 
tends out beyond the limits of vision. The 
experience of such a figure represents very 
nearly the absolute minimum of complex- 
ity tliat can be obtained. Nevertheless, sev- 

lU.l HI. f']. s'Ml'l I. 1 ON LMIokM 1SA(.K- 

Imagine that the cross is a white figure on a uni- 
form dark gray background that extends out be- 
yond the limits of the visual field. 

eral things can be stated about such a 

First of all, the figure is seen as a single 
unitary thing. It has some sort of shape, 
it is spread out in space, and it is bounded 
by edges or contours. Characteristically, 
the figure seems to stand out slightly in 
front of its backgiound. It has a color, and 
this color is usually seen as a surface; it is 
dense and opaque, seen on the face of the 
figure, spread out and at a definite distance 
away. In contrast, the ground is less well 
localized and has neither a well-defined sur 
face nor bounding edges. 

The Simplest Perception: Figure on a Ground 


A simple perception such as this lies 
within the scope of animals which have a 
nervous system like man's. They respond 
as if they 'see' a figure on a ground. Such 
animals include birds and certainly all 
mammals. If you wish to train a cat or 
dog or monkey to respond to some stimu- 
lus, it is necessary that the stimulus be set 
off from its surroundings so that it is a clear 

An experiment will help make this mat- 
ter clear. Figure 85 shows a pattern which 
was used in testing a raven. The bird was 
first taught to look for food under an in- 
verted flower pot. After he had learned to 
find food under a pot, he watched while 
one of these thirteen pots was baited. If 
the food was placed under the pot A, the 
bird flew to this outstanding object at once 
and found the morsel left for him. If, how- 
ever, the food was placed under the pot B 
or any of the eleven other pots in the 
circle, the bird was uncertain and confused 
and made many errors before finding the 
right pot. 

Human memory also depends upon 
man's perception of a figure. In a way, 
this is a matter of common observation. 
What is not seen as a figure cannot be re- 
called later. In one famous experiment a 
series of odd-shaped patterns were shown, 
each of which could be seen in two differ- 
ent ways, having a duplicity like that of 
Fig. 88. Later on, the subjects were tested 
to see if they recognized the patterns as be- 
ing the same ones they had seen before. 
If they succeeded, it was always because 
they saw the same figure in the test that 
they had seen originally in the stimulus. 
But if the alternative figure was perceived 
on the second showing of the stimulus, the 
pattern seemed strange and unfamiliar. 
It is the figure, not the stimulus, we recog- 

Actually, very few figures are as simple 
as the cross or the flower-pot pattern. Most 
figures are more comjjlex and exhibit quite 
a number of properties, some of which we 
shall study in more detail when we come to 
the subject of vision. A few of the more 
important properties of figures should, 
however, be mentioned here. 



o ^ o 





A raven could be taught to find food under the 
isolated flowerpot A. It was unable to distinguish 
B, or any other pot in the circle. [After M. Hertz 


(1) All figures have some kind of shape. 
If nothing else, they are vaguely round or 
extended. Usually they have a veiy defi- 
nite form set by a sharp outline. But it is 
not enough simply to name and to de- 
scribe the shape. Shapes can be smooth or 
rough, flowing, angular, compact, regulai^lv 
stepped, etc. These properties represent 
something w-hich the organism is doing 
about shape, something which goes beyond 
the simple geometry of the stimulus. EiTist 
Mach, a famous physicist, made this clear 
by a simple example which is shown in 
Fig. 86. He dre^^• the four-sided figure in 
the two positions shown. Looking at the 
two figures, we call the one a diamond, the 
other a square. The diamond and the 



square have quite different 'dynamics,' if 
we may use the word to describe some- 
thing of the feehng we have in looking at 
them. The important difference lies in 
what is regarded as the axis of symmetry 
of each figure. In the square the axis runs 
parallel with the sides; the top is opposite 
to the bottom, and the left side is paired 
with the right side. In the diamond, on 
the other hand, the axis runs from one cor- 


The two figures are identical geometrically, but 
they are perceived as two quite different shapes. 
[After E. Mach (1886).] 

ner to the opposite one, and the sides which 
are paired are always the ones next to each 

Shape makes a difference in other ways. 
Some shapes seem to be preferred over 
others and may be more readily or more 
frequently perceived. If a simple closed 
figure like a square or a circle is broken 
or blurred, it tends nevertheless to be seen 
perfect and completed. A very small 
brightness difference on a screen will be 
much easier to see if a thin line sets off a 
figure at the point where the difference is 
supposed to appear. A very faint figure 
will be seen more readily if it is anchored 
in our field of view by an index or by ref- 
erence marks. 

(2) Simple figures appear to have a sur- 
face which is only just evident. Objects 
in perception, on the other hand, seem to 
possess a surface which is very hard and 

close and definite. The difference between 
the two lies principally in a special sort of 
detail which is present in complex figures 
and which is called microstructure or tex- 
ture. Microstructure is present when there 
is a very fine detail which is repeated con- 
tinuously from one boundary of a figure to 
the other. There are certainly other things 
which contribute to our appreciation of a 
siuface, but microstructure is probably the 
most important. 

(3) Just as surface is enhanced in com- 
plex figures, so may the impressions of 
depth and solidity be somewhat greater 
than they are in the simplest figure. The 
impression of depth increases from the 
simplest to the most complex figures as 
more lines, more surfaces and planes and 
more figures are added. Figure 87 helps 
to make this clear. These outline shapes 


Line drawings frequently appear to be solid, 
three-dimensional objects. How many bars are 
there? How many might there be? 

no longer appear flat and thin, as indeed 
they really are when printed on this page. 
They appear to extend back into space and 
to be thick and solid. In the case of the 
cubes we can readily imagine that there is 
a fourth cube behind and beneath the oth- 
ers filling out the unseen comer. In the 
other case, we see just two bars, one in 
front and one behind. The one behind ap 
pears, of course, to be continuous. 

The Simplesf Perception: Figure on a Ground 


The perception of depth is the result of 
the common action of many factors. Some 
contribute largely to the appreciation of 
distance; they tell us how far away things 
arc. Others have more to say about the 
thickness and solidity of objects. The fac- 


What do you see, the goblet or the famous twins? 
Whichever you see, try to find the other. Then, 
when you have found the other, try to turn the 
perception back to what it was at first. [After E. 
Rubin (1915).] 

tors governing depth perception will be 
taken up in detail later (pp. 298-304). 
What is important here is to point out 
that all perceptions of objects involve 
depth in some small degree and that a 
strong impression of depth or solidity can 
be created with patterns whose stimuli are 
actually flat and two-dimensional. 

(4) Often lines are arranged so that not 
one but two or three or several figures can 
be picked out. Everyone at some time or 
other has puzzled over the mosaic of lines 

in a tile floor or in a wallpaper design. 
He combines first one .set of lines and tht-n 
another to form constantly changing fig- 
ures. Such patterns, when reduced to a 
simple form, bring out a quite basic princi- 
ple in the perception of figures. For this 
purpose the psychologist (onmionly uses a 
reversible figure, that is to say, one in 
whi(h there are two equally good ways o[ 
seeing a figure, so that a person looking at 
it sees first one and then the other. Figure 
88 and Fig. 89 illustrate two common in- 
stances. Figure 78 (p. 220) is another in- 
stance. Figure 88 is the picture of a fa- 
mous goblet which outlines two human 
profiles. Can you find the two faces? 
When you have found them, what has hap- 


Keep vour eves fixed near the center of the fig- 
ine. and note whether you see an x or a +. Main- 
tain your fixation and see how long the cross at 
which you are looking lasts. 

pened to the goblet? Or examine Fig. 89. 
Keep your gaze as steadily in the center of 
the figure as possible. Do you see an X or 
a + as the figure? If you think you can 
change die figure at will, just see how long 
you can continue to see the X or tlie -f . 



Once it has started to reverse, nothing can 
keep it fixed for long. 

The principle underlying these fluctua- 
tions can be understood from an easy ex- 
periment. Gaze steadily at one of the fig- 
ures in Fig. 90 while you count slowly to 
25. Then turn quickly back to page 227 
and glance at the center of Fig. 89. Which 

first one recovers. Finally, flip, and the 
first one is back again. 

This process of satiation affects many 
characteristics of a figure. Size, shape, 
depth, perspective, direction and mode of 
movement all become weakened or altered 
through continued observation. Under 
proper conditions, the changes can be meas- 


Keep \oiii e\es fixed near the center of either figure for about 25 seconds. Tlien glance quickly at the 
reversihle figure in Fig. 89. Is the cross you see the same one as you have just been fixating? Repeat the 
experiment with the other cross. 

do you now see, the X or the +? Repeat 
the test using the other part of Fig. 90. 
W^hat do you see now? Try the experi- 
ment before reading further. 

What has happened in this experiment 
is exactly what happens all the time in a 
reversible figure. Any figure process grad- 
ually weakens itself as it continues. We 
say that it becomes satiated. In Fig. 90 
you do not notice this satiation because it 
is possible to see only one figure. In Fig. 
88, however, you see one figure which giad- 
ually weakens itself until suddenly, flip, 
the other figure is there. Then the second 
figure gradually weakens itself while the 

ured directly, but that is rather hard as it 
requires very close observation. More fre- 
quently, the satiation is noted only as it 
leads to reversals when, as we saw above, 
the stimulus can be made ambiguous. 


In reading the past few pages you may 
have liad the thought, "All this discussion 
of simple figures is well enough in a text- 
book and in the laboratory, but it has noth- 
ing to do with my everyday experience." 
You may say that your world is full of 

Objects Are Our Commonest Perceptions 


people and chairs and tables, shoes and 
books and automobiles. The psychologist 
can explain trick figures and odd happen- 
ings, but does psychology deal with the 
flesh and blood of what we see and hear 
and feel? 

Science, of course, always deals with ab- 
stractions, and the abstractions are, indeed, 
less 'real,' less palpable, than the actual 
observed things and events from which the 
abstractions were derived and which they 
are now prepared to predict. Nevertheless 
people, chairs, tables, shoes, books and au- 
tomobiles are objects, and psychology has a 
great deal to say about objects. Just what 
does it say? 

(1) First of all, objects are figures, figures 
in the jaarticular sense we have been using 
the term. An object is something which 
fills a certain part of my visual field and is 
set off sharply from the background, and 
from other objects, by a well-defined con- 
tour. Within the contour, the object, like 
a good figure, is coherent and continuous. 
What happens to one bit of an object also 
happens to the neighboring bit. A per- 
ceived object acts as a unit. It is usually 
so constructed that the forces underlying 
grouping can have their strongest effect. 
When a drawing or a picture is designed so 
that it is strongly organized, it usually 
turns out to be such a good figure that it 
looks as if it ought to be an object! 

(2) In the second place, objects usually 
present the eye with a stimulus pattern 
which produces good surfaces and depth 
and solidity. Under conditions which are 
suitable for their perception, the surfaces 
of objects almost always possess micro- 
structure. The lines and planes of an 
object give rise to light and shade and per- 
spective, which are powerful determinants 
of the perception of depth. Objects are 
commonly separated from one another in 

tfiree-dimensional space. All these factors 
contribute to the impression of an object 
as a separate, space-filling thing, 

(3) In the third place, objects almost al- 
ways involve cooperation among the senses. 
Rarely do we receive information about an 
object from one sense alfjne. There is a 
rustle beside us, we look down, and there is 
the cat. You are looking at the pages of 
this book; in a moment you will reach out 
and turn the page, touching and pushing it 
in the act. A good deal of the mutual aid 
which one sense gives to another depends 
on timing. Sight and sound happen at the 
same moment. Sometimes this results from 
what the objects themselves do. The cat 
moves, your friend speaks; such events 
themselves provide you with multiple 
clues. In other cases the perceiving organ- 
ism itself provides half the information. 
If you move your head or eyes a bit to one 
side, muscles and joints tell you about the 
movement. At the same time there are 
changes in what you see. "Whenever what 
happens to an object is sensed in more than 
one way, the resulting perception is likely 
to be more complete and more sharply set 

The contribution of the senses other 
than vision and hearing is often so subtle 
that it goes unnoticed. There is a tend- 
ency for the more highly developed senses 
of vision and hearing to 'see' or 'hear' 
everything, even though some of the infor- 
mation may have come from a simpler 
sense. Try this experiment. Turn the 
stem of your watch back'^vard -with your 
hands behind your back. Notice how 
clearly you can fee! the clicks of die ratchet. 
Now hold the watch near vour ear and 
turn the stem again. ^Vhat does the sound 
of the click do to the feeling in your 



(4) The fourth important characteristic 
of objects is that they have meaning. Every 
(onimon object in your view is thoroughly 
familiar to you. You not only see it but 
you also recognize it as being such and 
such an object. Your pencil, the crumpled 
sheets of paper, the door, the books you 
wish you were reading, none of these is 
just an indifferent object. Even something 
quite new and unfamiliar has a little mean- 
ing. It is made of a familiar material. It 
can be used for some purpose. It does or 
does not belong here. Later it may have 
a different or richer meaning, but it is at 
least not a complete unknown. Ebbing- 
haus' nonsense syllables had this kind of 
meaning. They were not meaningless. 
They had some meaning, and their great 
advantage was that this slight meaning was 
about the same for different syllables. 

Meaning in this sense, it should be 
pointed out, is not the same as a dictionary 
definition, although the two are not unre- 
lated. Psychological meaning includes 
much more. Much of it is personal and 
individual. What some picture means to 
you can be quite different from what it 
means to me. Furthermore, psychological 
meaning includes shades and nuances 
which are expressed with difficulty in 

Specifically, u'hat an object means to us 
is first of all what we do about it. This 
object is something to drink from. That 
object we use to make marks on paper. 
Almost every object is dealt with in some 
way. One of the commonest things we do 
about an object is to give it a name. A 
child picks up something and quickly 
learns to say "book" or "shoe" or "doll." 
Many objects have meanings not so much 
because of what is done with them now but 
because of something which happened in 

the past. So fundamental is this depend- 
ence of meaning on doing that it has be- 
come an important principle of education. 

Objects also have meanings because they 
are related to other objects. That is the 
rug which lies by the door. A chair is 
something which stands at a table. Horses 
pull wagons. Frequently the relations 
among objects are not just indifferent links 
but are directed in some way. This handle 
is a part of a machine. This spoon belongs 
to a set of silver. That is a leaf from the 
tree in the yard. Part of, belonging to, 
necessary for, these are samples of the many 
kinds of relations which objects may have 
to one another. 

Meaning is, of course, a much larger 
subject than has been outlined in the last 
few paragraphs. A full discussion takes 
us into the problems of language, thinking 
and concept formation. The point to be 
established here is simply that what we see 
and what we hear depend in some measure 
on what the things we see or hear mean to 
us. Especially is meaning a help when we 
are faced with something that is confused 
or overcomplicated. A student's first view 
through a microscope is usually confused 
and unclear; to the skilled biologist each 
small detail fits into place. In contrast, 
meaning contributes very little at the sim- 
plest level; complication provides an op- 
portunity for its development. 

We have been discussing how objects are 
perceived. The question might, however, 
be asked with propriety: Why do we need 
all this explanation of how an object is 
perceived? Is it not obvious that there 
are all kinds of things in the world, and 
we simply perceive what is there? The 
answer is no; it is not obvious. In fact, it 
is not true. Here are the reasons. 

7o see an object is lo have something 
happen within you. I'he object is some- 
thing that you do, an event in your brain, 
it is the result of a long series of jjhysio- 
logical events, in your eye, in your nerves, 
in your brain. These internal events have, 
in turn, been set off by proximal physical 
events, complex patterns of light waves and 
movements and pressures. 

The near-by physical event usually, but 
not always, starts from some single region 
out in space, from the 'physical object' that 
you see, and hear and feel. That thing 
out there is a red book with color and 
solidity and weight, or at least it seems to 
be. Actually that is not true. The red 
l:)ook, the puffing engine, the crying baby, 
they are events within you which are about 
to cause you to read, to step back, to pick 
up the child. The 'object out there' is a 
physical and chemical process. You know 
it only indirectly. It is but one of the 
causes, several times removed, of the event 
in your brain. 

That the object exists out there is some- 
thing that you take for granted. That is 
proper, since many of the formal properties 
of the objects are mirrored in your experi- 
ence of them. Man's adjustment to the 
world is aided by the fact that his brain 
creates an acceptable copy of what goes on 
outside himself. He sees squares as square. 
He perceives the longer of two times as 
the longer. There is a reasonable corre- 
spondence between stimuli and perceptions, 
but it is, nevertheless, contradicted by many 
exceptions. In perception, for example, 
white is simple. In light, the stimulus, 
white is a mixture of colors, that is to say, 
a mixture of many wave lengths. But seen 
white is known directly in experience. 
The wave lengths you get at only by scien- 
tific inference. 

The Consiancy of Objects 231 


It would l;(; ever so much f-asici il (>\> 
jects we once perceived stayed fixed and 
constant in relation to us. They do not, 
of course, and man is faced with the neces- 
sity of adjusting his behavior to the chang- 
ing aspects of objects around him. One of 
the major difficulties is that, having seen 
an object, we move about, towards it, away 
from it, to the one side or the other. As 
we move, the proximal stimulus (the light 
entering the eye) changes. The image on 
the retina grows smaller or larger or 
changes in shape. There is the .same trou- 
ble when the object itself moves. Or again, 
the colors and brightnesses of objects change 
as the Sim rises or sets, as we pass from 
the sunlight into the shadow, or as we add 
man-made light to that provided by nature. 

To the simplest organism all changes 
must appear alike, whatever may have been 
the cause. One thing, the immediate stini- 
idus, is altered and for all it knows the 
world itself around it is changing in its 
very nature. To man, to us, the world is 
quite different. We move around among 
fixed and constant objects. Our point of 
view may change but the things at which 
we are looking do not. This important 
aspect of perceiving is called object con- 

It is convenient to divide the total prob- 
lem of object constancy into constancies of 
the various aspects of the object itself. 
Thus we speak of size constancy, shape con- 
stancy, whiteness (brightness) constancy, 
color constancy, velocity constancy, etc. 

Size Constancy 

Constancy of size is both one of the most 
perfect constancies and one of the easiest to 
understand. Let us take it as an example 



But first of all let us review some simple 

Everyone knows that the eye acts like a 
simple camera. The lens in the front of 
the eye throws a picture of what is outside 
on the sensitive retina which lines the back 
of the eyeball. The si/e of the image on 
the retina may be determined by drawing a 

change in size of the retinal image might 
equally well be produced by a change in 
the size of the object itself or by a change 
in the distance away of a constant object. 

It is clear that a physical object of fixed 
size produces in the eye a series of con- 
stantly changing images as the object comes 
closer or goes farther away. What about 



The diagram shows how an object, represented by an arrow, throws an image on the sensitive retina 
in the back of the eye. Note particularly that the smaller image F-F may be produced either by the 
short arrow at the near distance or the large arrow at the far distance. 

Straight line from any point on the object 
out in space through a crossing point just 
behind the lens and extending it until it 
meets the retina. Such lines are shown in 
Fig. 91. Notice that the near arrow throws 
a large image on the retina, indicated by 
the letters N-N. If the same arrow were 
twice as far away, it would produce the 
smaller image F-F. .Actually, the change in 
the linear size of the retinal image is ex- 
actly proportional to the change in the 
distance. Only, of course, the changes are 
reversed. The farther the object is from 
the eye, the smaller will be the image. If 
the distance is doubled, the size of the 
image is halved. But it is more important 
for our present purpose to notice that the 
smaller image might just as well have been 
formed bv a smaller object such as the 
;iiiow marked S-S. In other words, a given 

our experience under these conditions? 
Does the size of a person's head grow larger 
as he comes toward us? Of course not. 
Only if he is very far ofE and we are not 
clearly aware of the distance, as happens 
when we look down from a tall building, 
does he seem to become abnormally small. 
Try the experiment of setting up a scries 
of cards of graded size across the room as 
shown in Fig. 92. Hold another card in 
your hand and see if you can pick out the 
card in the series having the same size. 
Usually we find that the judgment is al- 
most perfect— perfect on the assumption 
that there is a constancy! If the card in 
the hand is four inches wide and the dis- 
tance of the observer from the table is 
twelve feet, the observer is matching the 
image of the card in hand to the image of 
the card in the series, when one image is 

Size Constancy 


actually lliirty-six times as wide as the 

riic secret ol these amazing judgments 
lies largely in our ability to judge distance 
correctly. We know that the card across 
the room which throws a small image on 
our retina is at a much greater distance 

shows this same carry-over of size constancy 
into their representation of landscapes. In 
old Chinese and Japanese paintings in par- 
ticular, objects supposed to be at different 
distances from the obseiver still liave the 
same size in the drawing. An example of 
this, in exaggerated form, is shown in Fig. 


The problem is to designate the card on the table which is the same size as the one held in the hand. 
The task is accomplished easily and correctly, although the retinal image of the one in the hand is at least 
36 times as large as the retinal image of its match on the table. 

than the one we hold in our hand. Size is 
always judged as a function of distance. 

So conipulsory is constancy in the percep- 
tion of size that even an artist cannot al- 
ways overcome it. The drawings of chil- 
dren illustrate the problem in the extreme. 
A child is likely to draw a man the same 
size wherever he inay be. It is not clear 
to the child that the drawing of a man is 
something which should change constantly 
in actual size. The child does not care too 
much, for his drawings are really a way of 
telling us about something, a kind of sign 
language, rather than a picture of the 

The formal art of some Eastern peoples 

93. Note how the men drawn in the back- 
ground to the left are as large, or actuallv 
a little larger, than those in the foreground. 
It is wrong to suppose that the Japanese 
artist did not know^ better. This same 
artist, using a different stvle, might have 
pictured the sizes of objects correctly, but 
he was bound by a tradition whicli made it 
improper for him to draw figures ^vith pho- 
tographic precision. It is only that his ua- 
dition is different from ours. Even we of 
the Occident did not fullv develop the use 
of perspective in art until tfie fifteenth cen- 
tury, although the general principles were 
understood, though not ah\a\s used, by the 
ancient Greeks and Romans. 





A drawing by Sesshii in Avhich the artist followed a style which did not allow for size constancy. Note 
ilie distorted linear perspective and the large size of the more remote figures. [From J. C. Conell, Uiuler 
tlie seal of Si'ssliii, De Pamphilis, 1941.] 

(Further information abotit si/e constancy 
appears in the chapter on visual space per- 
ception, pp. 304 f.) 

Whiteness Constancy 

Tlie instance of constancy which has 
been most widely investigated is whiteness 
constancy. This visual characteristic has 
been in many ways more interesting than 
size because, since we commonly experience 
something less than perfect whiteness con- 
stancy, it has been possible to discover 
more readily which factors help the effect 
and whicli hinder it and also to meastue 
the relative importance of these factors. 

Whiteness constancy is familiar to every- 
one. Our scale of blacks and whites re- 
mains quite stable even though the level 
of ilhmiination changes a great deal. The 
most common change in illumination is 
the result of shadows. There is less light 
in a shadow, and a piece of white paper, 
for instance, will reflect much less light 
when it is in shadow than when it is in full 
illuinination. It seems, nevertheless, al- 
most as white in shadow as in bright light, 
provided we know that the object we are 
looking at really is a piece of white paper. 

To measure the effect of shadows on 
whiteness constancy an expeiiment can be 

Whiteness Constancy 


set up as shown in the plans ol Fig. 94. 
Two spinning cardboard disks, A and B, 
are set up in one end ol a room. Ihe light 
comes in from the window W at one side. 
The light falls directly on disk. B, while a 
screen S cuts off the light from disk A and 
iasts a shadow over it. A person, who is 
standing at O, compares the two disks, 
judging their relative whitenesses. 






sl^/ ^ 




I'laii I shows the arrangement for measuring con- 
stancy. Plan II shows the arrangement for the 
'reduction' equation. A and B are the disks to be 
matched. W is a window, the source of light. S 
is a screen casting a shadow on disk A. O is the 
oljserver Avho makes the judgments, ii is a reduc- 
tion screen cutting off all the field except small 
patches of A and B. 

Each disk consists of a black and a white 
sector which fuse, when the disks are spun 
rapidly by motor, to give a uniform gray. 
Let us assume that disk A which is in the 
shadow is made up of 320 degrees of white 
and 40 degrees of black. The experi- 
menter now adjusts the proportions of 
white and black in disk B until the ob- 
server says the two disks are equal in white- 

What proportions of white and black 
might we expect to find in disk B} Table 
XIV makes clear the various possibilities. If 


Rksiji.ts or Whitrness-Constancv Kxprriment 

Perfect constancy 
Actual constancy 
No constancy 

(reduction equation) 

Disk A nUk P PerrftUacc 

(in skadirw} (in li(lili ConiUinry 

320° white 320° while lOfJ 

320° while 152° while 40 

320° white 40° white 

there were perfect constancy, that is to say, 
if the observer could discount completely 
the darkening produced by the shadow, 
disk B would also have 320 degrees of 

The other end of the scale, an equation 
which would reveal no constancy, requires 
that we make a special measurement as in 
plan II of Fig. 94. Here a second screen R 
with two holes in it, a reduction screen, 
has been placed in front of the observer 
so that all he can see is a small section of 
each disk. No longer can he see that 
[here is a shadow and he has to judge the 
brightness of each disk reduced to the 
common conditions of proximal stimula- 
tion by the reduction screen. Under a 
given set of conditions, conditions which 
vary widely from one experimental setup 
to another, he might find that only 40 de- 
grees of white in disk B would be required 
in the second equation. 

Now if the reduction screen is removed 
and an equation is made with the arrange- 
ment shown by plan I of Fig. 94, we shall 
be measuring the actual amount of 'con- 
stancy' achieved. Such a measurement will 
tell us how well the shadow has been dis- 
counted. A typical result is sho^vn by the 
second line of Table XIV. Disk B \\i\\ be 
152 degrees white, a value whicla lies 
ii%,yQ of the way from no constancy to 
perfect constancy. 

From the result of experiments which 
have followed this general plan it is pos- 
sible to formulate the follo-\ving rules. 



(1) The most important single condition 
of whiteness constancy is the backgiound 
against which the disks are seen. In fact, 
it has recently been shown that almost per- 
fect constancy can be achieved if each disk 
is close to its background, and the two 
sets of disk-phis-background are well sep- 
arated. In other instances the background 
is effective only as fixing a general level in 
terms of which each item in a given part 
of the field is evaluated. 

(2) Second in importance, particularly if 
the backgiound is placed so far away 
from the disk that it can no longer play an 
important part, is the clear perception of 
the shadow. That there is a shadow may 
be seen from several details. For instance, 
the edge of the shadow may fall across the 
top of the table on which the screen and 
the disks are sitting. Or the screen may 
cast a shadow on some more remote object 
in the background. One way of showing 
how strong is the effect of the shadow is to 
mo\e the screen so that the edge of the 
shadow falls across disk A. Almost perfect 
constancy will be the result. Shadows are 
recognized as such because they usually 
have a penumbra, which is the fuzzy edge 
that most shadows have. 

(3) If there is light from some special 
source or if neither the background nor 
the edge of the shadow gives sufficient clues, 
constancy ma\' be improved by putting anv 
small object in the field of view around 
disk A. These small objects serve as tiny 
guideposts to give the observer information 
about the amount of light on disk A. 

(4) Objects in their natural surroundings 
are helped out considerably by the percep- 
tion of the whole pattern of illiunination 
in a room. There will be giadual falling 
off of brightness as one goes away from the 
window or other source of illumination. 
Furthermore, there will be the lines of 

shadows all pointing away from the place 
from which the light is coming. Often this 
sort of general information about the light- 
ing of the room helps out constancy a great 

General Explanation of Constancy 

The general problem of constancy may 
be formulated without difficulty from these 
two examples. Let us say that each case 
of constancy represents a problem of tivo 
syste??is. The organism is trying to handle 
a situation in which the stimulus is con- 
stantly changing. For practical reasons we 
prefer to operate in a world in which 
objects appear to be constant. It would 
be most inconvenient if objects were con- 
stantly shrinking and expanding, changing 
their shapes and color and brightness. 
What the organism does is to split its in- 
formation about the world into two sys- 
tems, one of which it can maintain steady 
and constant. 

In Table XV we can see just what pairs 
of systems are operating in the more fa- 
miliar constancies. The first two columns 


The Perceptual Constancies 

Proximal Stimulus: 

Size of image in eye 
Shape of image in eye 

Intensity of light in 

Spectral composition 

of light 
Intensity of sound at 


Situation of 

Stimulus Object: 


Property of 

Perceived Object: 


Distance of seen object Size of seen object 

Angle of object to the Shape of seen ob- 

line of regard ject 

Illumination on sur- Whiteness of sur- 
face face 

Color of illuminant Color of surface 

Distance of sound from Loudness of sound 

listener at its source 

Proximal Stimulus 

Condition oj 



Properly of 

Perceived Object: 


Displacement of im- Turning of head or Location of seen 
age in eye ■ eyes object in space 

Binaural difference in Turning of head or Location of sound 
time or intensity body in space 

Space Perception 


show the two variables which the organism 
integrates to achieve the constancy which 
is noted in the third column. In size con- 
stancy, for example, the proximal stimulus 
(changing size of the image on the retina) 
works concurrently with the situation of 
the stimulus object (changing distance of 
the seen object) to effect size constancy of 
the perceived object. Thus perceived ob- 
ject size becomes the system in which things 
remain constant, whereas distance is the 
system in which they vary. In whiteness 
constancy, the two systems are whiteness 
and illumination. The former is constant, 
the latter varied. 

The great utility of this arrangement to 
the organism is evident. By and large, 
physical objects in the world are constant, 
whereas conditions of observation are vari- 
able. The mechanism of object constancy 
goes a long way towards enabling the or- 
ganism to deal with the physical world in 
a manner suited to the world's actual con- 


Up to this time we have centered our at- 
tention on objects and have said little 
about the space they occupy. The objects 
themselves may be short, long, wide or 
thin, but in addition they may be located 
to the right, left, behind, above, around 
other objects in the field. Distance between 
two objects is just as real as the distance 
on the surface of one object. Space is a 
dimension of experience, a characteristic 
about which we have to ask the questions 
how far? what direction? where does it start 
and stop? 

Space does not belong to one sense alone. 
It is common to several senses. Distance felt 
on the skin is related to the distance 

through which you feel your finger moving, 
and the size of an object held in your hand 
is like the size you .see with your eyes. The 
space perceived is the joint creation of 
several senses and is richer for the contribu- 
tion of each. 

riie dimensions of perceived space must 
be chosen with reference to the problems 
to be studied. The real world of objects 
is fitted into three dimensions— uj>-do\vn, 
north-south, east-west or else some other 
system of three coordinates. The world of 
visual perception similarly has three di- 
mensions—up-down, right-left, near-far. 
Perceived up-down may approximate the 
geographical vertical or it may differ from 
it. Near-far is not perceived so precisely 
as up-down and right-left; its mechanism 
is more complex, its correspondence with 
reality not so sure. In the field of auditory 
space perception the primary dimension is 
right-left, determined by the spatial rela- 
tion of the two ears. Direction up-and- 
down is less accurately perceived, and 
near-far is so uncertain in heard space 
as sometimes not to figure at all in the 
localization of sound (see p. 337). Kines- 
thetic space— for instance, the space that 
an animal experiences in a maze or an 
automobilist in old Boston— is something 
else again. It is a space of connections and 
may have nothing at all to do with the 
points of the compass (see pp. 380-384). 

Because there is a fair degree of coiTe- 
spondence between the geometry of ph\s- 
ical space and the dimensions of \isuallv 
perceived space, it is tempting to believe 
that there is some necessary relationship 
between them. It is so easv to think that 
we see this object near by and that object 
far off simply "because that is the way thev 
are." Yet most people can realize that this 
statement is not true. 'When vou look at 
die stars, for instance, vou see them all 



roughly the same distance away. Actually, 
one star may be thousands of times as far 
away as another which looks to you equally 
distant. On the other hand, you may per- 
ceive depth where there is none. Two flat 
photographs when viewed properly in a 
stereoscope produce an impression of depth 
^vhich cannot be o\ercome. There is no 
escape from the conclusion that percei^•ed 
space, like other perceived qualities, is 
something which exists within each of us. 
How then shall we account for perceived 
space? What takes place in the eye, in the 
brain, in order that the perceiving organ- 
ism can usually respond so neatly to actual 
places and things? Let us consider first a 
few general points that answer these ques- 
tions, filling in some of the details later. 

(1) First of all the organism must have 
sense organs which are able to respond to 
the appropriate physical stimulus that is re- 
cei\ed from the object. The eye must be 
sensitive to light, the skin to contact, the 
ear to sound. Furthermore, each of these 
sense organs must be able to give a differ- 
ent response when a different space is oc- 
cupied by the stimulus object. Thus the 
eye must respond differently to a large ob- 
ject than it does to a small one; the ears 
must act differently when a sound comes 
from the right or from the left. Patterns of 
stimulation are set up in the sense organs 
which correspond in some degree with the 
properties of the world we are perceiving. 

(2) The brain and the nerve pathways 
leading from the sense organs to the brain 
must be constructed so that the informa- 
tion from the sense organs is properly trans- 
mitted and registered in the brain. It was 
once supposed that this effect was managed 
by means of a set of fixed connections, 
single nerse fibers running from a recep 
tor to a fixed point in the brain. The 
brain was thought to be like a large electric 

sign with thousands of lights, each light 
connected by a single wire to a single 
switch or photocell so that a pattern of 
light and dark falling on the bank of photo- 
cells is reproduced point by point on the 
electric sign. 

Modern physiology has made it quite 
clear that this picture of the nervous sys- 
tem is in error. True, there must be avail- 
able a number of nerve fibers and nerve 
cells sufficiently large to copy the pattern 
of stimulation. But order is maintained 
among the many impulses passing to the 
brain only by functional relations among 
the messages in the nerves and centers 
along the line. 

As an analogy we may think of the nerv- 
ous system as a football team making a par- 
ticular play. Where the play goes, the pat- 
tern of the moving men, depends neither 
upon exact distance nor upon particular 
men. Off -tackle means inside the end man 
and outside the rest of the line. Perhaps a 
better example would be a well-trained 
army as it moves forward. Each man in 
the skirmish and supporting line must 
guide his movements in terms of the men 
on either side of him. Once given a pat- 
tern or order of attack, that order is main- 
tained as the entire group moves forward. 
Pattern is transmitted to the brain by such 
team play. The physiological mechanisms 
by which one fiber works with its neighbor 
include simimation, inhibition, thresholds 
and proper timing. Order may also be 
maintained by electrical or chemical factors 
which sene to unify the actions of many 
individual nerve cells. 

(3) Once the information recei\ed by the 
sense organs has been relayed to the brain, 
the brain takes charge of the job of inter- 
preting this material. Each item must be 
located with reference to other items being 
perceived at that moment or to points sup- 

Space Perception 


plied by memory. Each item will be lo- 
cated or anchored with respect to a total 
fratne of reference. 

If a person looks at a single small spot 
of light in the dark, its location is a very 
imstable affair. The spot wanders first in 
one direction and then in another; it 
pauses and speeds up, stops and reverses, 
but the extent of the movement is seldom 
seen to be more than 40 degrees. Such seen 
luovement is called autokinetic. 

If a second spot of light is now intro- 
duced at a fixed distance from the first, 
two things happen. First of all the two 
spots together will undergo aiUokinetic 
movement, but the speed and extent of this 
two-spot movement will be less than it was 
with one spot alone. Second, the distance 
and direction of the spots from each other 
will imdergo some change. It is as if each 
of the dots were trying to move as it would 
were it alone; yet each is constrained by the 
presence of the other spot in the field. 

The introduction of a third spot, or a 
fourth or fifth, increases the effects noted 
when the second spot was added. With 
each further spot the movement of the total 
pattern is gradually reduced, and the rela- 
tions of the spots to one another become 
more and more stable. From these experi- 
ments it appears that the position of a fig- 
ure in the visual field depends in some 
measure on its anchorage to the other fig- 
ures in the field. For any given item, the 
rest of the items in the field constitiUe its 
frame of reference. Autokinetic movement 
does not occur if there is a fixed frame of 

Let us look briefly at another experiment 
which extends this conclusion. Suppose 
that we are looking at two spots of light 
in a completely darkened room. One of 
the spots is much larger than the other, or, 
better, the larger is an outline of a square 

or circle. Let one of the stimuli actually 
move back and forth. We shall fliscovcr 
at once that it makes no difference which 
stimulus actually moves, for the small fig- 
ure will always be .seen to move %v'hile the 
large one remains at rest. Particularly is 
this true when the large outlined figure 
moves back and forth with the small figure 
located within it, as shown in Fig. '.)r>. 



An observer, sitting in the dark, sees iwo dimly 
lighted squares. The large square is moved to and 
fro. The small square remains stationary. The 
observer, however, sees the small stationary square 
moving, not the large square which actually is 
moving. [After K. Duncker (1929).] 

Then the small enclosed figure will appear 
to do all the moving. We call this phe- 
nomenon induced movement. Do you re- 
member marveling as a child upon the fact 
that the moon seemed to race across the sky 
when it was the clotids which were drift- 
ing over it? Induced movement shows us 
that a larger, enclosing figure forms a more 
stable frame of reference than a small iso- 
lated figure. 

Even the rate of any movement is judged 
in terais of its particular frame of refer- 
ence. A set of dots is arranged to move 
behind each of two windows, as sho^^"n in 
Fig. 96. The dots will have to be moved 
fii'icr as fast plixsicallv in the larger win- 



clow as they are moving in the smaller in 
order to appear to have the same velocity. 
The frame of reference in which places 
and positions are anchored is not a matter 
of the present alone. Our memory of what 
has been seen in the past can serve us just 
as well. A carpenter, for instance, knows 
the size of each nail at a glance. The 
plumber picks out the right size of pipe 

throw a ball, or that when you thread your 
way through a crowd, it is the eye which 
helps you to pick out the correct move- 
ments. On the other hand, what your eye 
sees would have no meaning were it not 
for your hand. If you were to be para- 
lyzed all your life, and what happened 
around you rolled off like a movie on a 
screen, what you would sec woidd have a 


The large dots moving behind the large opening must have twice the physical velocity of the small 
(lots behind the small opening if the two sets are to appear to move at the same speed. [After J. F. 
Brown (1931).] 

or fitting unerringly. The skilled sales- 
man picks the right shoe from the shelf or 
coat from the rack without measuring the 
customer. Such standards or anchors may 
be accumulated over a long period of time 
and carried imconsciously. Since there is 
no easy way to wipe them out, it is hard 
to estimate how much effect they have 
upon present perception. 

(4) Perceived space depends on the joint 
contribution of several senses to a much 
greater degree than we ordinarily realize. 
A good many of the things which seem 
to be so natural and fundamental about 
space actually take form only when what 
we see is brought into line with what we 
hear, and with our feelings of movement. 
It is quite correct to say, for instance, that 
the hand is guided by the eye when you 

dreamlike quality indeed. The real, sub- 
stantial quality of space comes from your 
walking and moving in it, your doing some- 
thing with it. Several well-known facts 
help to make this fact clear. 

Suppose that you are looking at a movie 
on a screen directly before you. Let the 
picture jump quickly and violently to one 
side or up and down, and the experience is 
most unpleasant. Nothing is so disturb- 
ing as to watch amateur movies made by a 
cameraman with an unsteady hand. Now 
consider that the eye is far more unsteady 
than the worst of such movies. You glance 
about the room and the images projected 
on your retina will shift in bewildering 
succession. Yet in this case you see the 
world standing still! The difference lies 
in the fact that when )our eyes move you 

Space Perception 


have iul! and precise information about 
their movements; when the camera moves 
you do not. The brain is able, by a process 
which seems ahiiost miraculous, to put to- 
gether these two sets of facts, the moving 
visual pictures, on the one hand, and the 
knowledge of eye movements, on the other, 
and to come out with a stable stationary 
view of the world. 

The adjustments of this mechanism are 
not always quite perfect. When you are 
dizzy you are no longer able to discount the 
movements which your eyes make, and in 
consequence the world 'out there' seems to 
move. Ear infections and diseases of the 
nervous system can produce unwanted 
movements of the eyes with the same result. 
Another familiar experience is that of a 
person who puts on strong glasses for the 
first time. His eyes make the accustomed 
movements to bring a new object into 
focus, but the field of view shifts too far 
or too little because of the strong lens. 
Consequently he sees everything jump each 
time his eyes move. Fortunately experi- 
ence and practice gradually correct this 
state of affairs, and things eventually stay 
put the way they normally do. 

This same kind of coordination is pres- 
ent when you hear a sound coming from a 
particular direction. Hearing the sound, 
you expect to be able to look for it 'there' 
or to put out your hand and touch it if 
it is near by. A psychologist once upset 
this relation by wearing a device he called 
a pseudophone. The pseudophone is con- 
structed as shown in Fig. 97. It has one 
horn and a tube to lead to the right ear 
the sound which is ordinarily heard by the 
left, and another horn and tube to lead to 
the left ear the sound ordinarily heard by 
the right. 

Wearing the pseudophone was at first a 
most upsetting experience. There was al- 

most con)plcte reversal of sounds, right and 
left. When the device was worn out on the 
street the wearer bumped into people be- 
cause he would move in the wrong direc- 
tion when he heard them approaching. 
Automobiles at a busy intersection created 
a real hazard. If, while he was eating, a 
waiter addressed him on his right, he 


Sound from the left is picked up by the horn and 
led through the tube to the right ear. Sound from 
the right goes to the left ear. The subject therefore 
looks for the source of the sound on the wrong side 
until he has adjusted himself to this novel artificial 
situation. [.A.fter P. T. Voung (1928).] 

would turn to the left in answering him. 
If, however, he saw the lips of the person 
who was speaking to him move, he located 
the sound correctly. But more interesting 
was the fact that, after some time, the 
^vearer began to get used to the new loca- 
tions which sound had. Unfortunately a 
long experiment was not possible. If the 
experiment could be continued long 
enough, a new set of coordinations between 
sound and sight, and between sound and 
movement, would probably be developed. 
Two related experiments have been done 
in vision. In one, a set of glasses was in- 
vented which tipped everything over at an 
angle. Naturally, a good deal of difficulty 
was encountered when these glasses were 



(irst worn, but very soon everything began 
to straighten up. What had seemed tipped 
when the glasses were first put on now be- 
(anie vertical. The person wearing the 
glasses could walk about without tending 
to fall over. This experiment seemed to 
show that, when vision is distorted in this 
simple way, we can gradually readjust the 
relation between what is seen and our 

The other visual experiment went even 
farther. The glasses were constructed so 
that everything in the visual field was 
turned upside down. The subject had a 
great deal of difficulty when the glasses 
were first worn. After several days of 
continuous wear, adjustments were grad- 
ually made to the new appearance of the 
visual environment. And as the subject 
learned to carry out the necessary move- 
ments in this new world, the visual scene 
lost its character of being upside down. 
As a matter of fact, right side up and up- 
side down probably have little meaning 
except in terms of what we do about them. 
Doxvn is a direction we move our heads 
when we bend over; up is a direction we 
mo\e our feet when we lift them from the 


Time, as we experience it, is a good deal 
like space; it is something that most people 
just take for granted. We are usually so 
occupied with what is happening that we 
pay no heed to the temporal frame in 
which our experiences are set. Only oc- 
casionally does time become the specific 
object of our attention, while we are wait- 
ing for a friend to keep an appointment, 
when we suddenly realize that the hour has 
grown late, in the few minutes we have 

left for last-minute preparations. Thus, al- 
though all our experiences are, of course, 
stretched out in time, it is only when some 
importance attaches to time that Ave par- 
ticularly notice it. 

Perceived time is also like pciceived 
space in that it is easy to confuse physical 
time and psychological time. AV'hat we 
try so hard to judge correctly and what 
counts when we are making a train is 
clock time. Sometimes we succeed quite 
well in getting our personal internal clocks 
regulated so that they agree with physical 
clocks. But any person who has to 'kill' 
time is convinced that the physical clock 
runs much too slowly. Clearly, our per- 
sonal clocks do not always keep the best 
of time. The kind of time they do keep is 
a matter of perception and must be ex- 
plained by the psychologists. 

A couple of distinctions are in order be- 
fore we begin our more detailed inquiry. 
First of all we must distinguish between 
time which we can know directly and time 
about which we have knowledge. Knoivl- 
edge about time is greatly aided by hav- 
ing elaborate means of keeping time. We 
are beset on every side by clocks and calen- 
dars. Our getting up in the morning, oin- 
going to class, our meals, our entertain- 
ment, all these events are regulated by 
clocks with elaborate means to insure their 
synchronization. Furthermore our lives 
for weeks and months and years ahead will 
be regulated by calendars. In the absence 
of such formal things as hours and dates, 
men have controlled their lives by the 
rhythms of natural events, the rising and 
setting of the sun, the phases of the moon, 
the seasons of the year. So elaborate are 
the schemes of marking off time that we 
make use of long periods extending fre- 
quently beyond the life time of any one 
person. In this Avay wc know collectively 

The Framework of Perception: Time 


a great deal about spans of time which no 
one can ever apprehend directly. This 
kind of time is important for the sociolo- 
gists or anthropologists, but it is not part 
of our present problem. 

Within the range of time which we ap- 
prehend directly a second distinction is 
important. In this case we distinguish be- 
tween short intervals of time which we 
perceive directly as they pass, belonging in 
a way to the 'present,' and longer inter- 
vals of time where we judge that so much 
time has elapsed since something hap- 
pened. You may be able to judge how 
long it has been since you began to read 
this section, or how long ago it was that 
you came into the room, without your 
having been aware continuously in either 
case that time was passing. To make a 
judgment of elapsed time, you have to re- 
call specific memories. 

Let us consider the simplest case. How 
do we know that time passes at all? What 
is there about our present experience 
which makes it part of the stream of con- 
sciousness, anchored on the one side in the 
past and on the other side in the future? 
Do we have some kind of a time sense 
which, acting by itself, tells us of the pas- 
sage of time? Psychologists agree that the 
answer to this last question is pretty ob- 
viously no. Time cannot be appreciated 
directly, nakedly, as such; it can only be 
known through some process which goes on 
in time. For the physicist such a process 
may be the motion of a pendulum or the 
rotation of the earth. For the psychologist 
the processes whicli give us our impression 
of time are those which underlie the per- 
ception of what William James called "the 
specious present." We seem to sit perched 
on a sort of saddleback of time with a cer- 
tain length of its own. The present, as 
we experience it, is a very small bit of 

duiation bciuccrj llu; past and tlie future, 
the bit whidi can be spanned in any one 
instant. A phrase of a melody is somehow 
a unitary thing, spread out in time and yet 
sensed in one instant. By trying to hold 
the notes of the melody or the ticks of a 
watch clearly in mind, it is possible to ev 
timate how long is this directly perceived 
duration. Normally it is not more than 
(me or two seconds. Certain observers have 
claimed that it may stretch out to eight ot 
even twelve seconds. On what does this 
durable present depend? 

(1) First, we should note that each ex- 
perience we have persists for a very brief 
time. Cut off an experience suddenly bv 
removing its stimulus and it seems to glow 
for a moment like the tail of a comet. It 
is as if the processes underlying conscious- 
ness have a certain inertia which they have 
to expend before they can return to quies- 
cence. Our consciousness is somehow like 
the scene from the back of a moving train. 
Objects flash into view and then gradually 
fade into the distance. Sometimes this 
persistence is called memory or, more par- 
ticularly, the primary memory image, but 
in general it seems better to speak simplv 
of the persistence of consciousness. 

(2) The flow of experience must be 
marked off by distinct events. Somediing 
must flash by. If what we experienced 
in one moment were just exactly like A\hat 
we experienced the moment before, we 
should not be able to distinguish them, to 
know that the one was ne%\'. the other hang- 
ing on from the moment before. It would 
be as if our train were moving in a dense 
fog, or even in inky blackness. There 
would be nothing to tell us that we were 
moving, that time was passing. An event 
which marks off time is necessarih' a change. 
Something is present now ^vhich a moment 
before was not there, or something is gone 



now and our experience of it is fading 

Once more we see how important change 
is to perception. As a matter of fact, the 
perception of time depends so fundamen- 
tally upon the perception of change that 
in many specific cases they amount to the 
same thing. 

(3) Many of the changes which are fun- 
tlamental to the perception of time are in- 
ternal. The important background of 
events which furnishes the framework of 
time consists of subtle experiences from the 
body, the rhythms of pulse and breathing, 
occasionally the peristaltic movement of 
digestion, the flow of memories and images 
before the mind's eye. Insomnia would be 
no trial at all were it not for the insistent 
flow of these internal experiences which 
assail us when sleep will not come. They 
form the ground against which the events 
of the external world appear as clear figures. 

Experience is a continuing, unbroken 
process. The experience of each moment 
belongs with that of the moment before. 
One flows smoothly and without interrup- 
tion into the next. At the same time ex- 
perience is constantly changing. Against 
a uniform background of internal pulsa- 
tions and muscular strain, constant light or 
steady noise, one change after another 
erupts into our field of attention. Each 
momentary event appears, persists for a 
moment and then fades away. Fitted be- 
tween other events fore and aft, it belongs 
to the present; it is neither imagined nor 

The present includes everything of which 
we are aware just now. Some of these ex- 
periences, which have persisted, really repre- 
sent the recent past. And yet they do not 
seem old, for they have not yet passed the 
threshold into the past. We experience 
them as being here noic because we cannot 

clearly label them as belonging either to 
the future or to the past. To sense time 
fully, therefore, requires that we be able 
to discriminate between experiences that 
belong to the present and those that be- 
long to the past. 

It would be a mistake to think of the 
durable present as a problem peculiar to 
man's conscious experience. There are 
aspects of the behavior of animals which 
raise much the same problem. We shall 
have more to say later about certain time- 
telling rhythms which occur in animal ac- 
tivities. In addition to these rhythms, the 
simplest, free-swimming organisms possess 
a very elementary kind of memory, a mem- 
ory in the sense that the animal 'keeps in 
mind' what happens from one moment to 
the next. The best example is the collec- 
tion of bacteria in a ring about an oxygen 
bubble. They are exhibiting what Jen- 
nings called trial behavior. Imagine a bac- 
terium swimming about in a body of water 
which is short of oxygen. It comes to the 
favored zone near the oxygen and passes 
readily from the poorer area into the better 
one. Later it starts to cross tlie boundary 
in the opposite direction. Once it touches 
the unfavored area, its forward motion 
stops and it turns back into the better 
area. The bacterium has made, in its 
simplest form, a kind of successive com- 
parison. It is just this kind of reaction 
to change which is the essential first step 
in the perception of the passing of time. 

This is the place to interrupt the argu- 
ment with a brief remark. It must now be 
clear that the psychological problem of 
the present is very different from the 
philosophical one. Psychologically, the 
present is a part of a substantial con- 
tinuing process, whether it is regarded as 
our experience or as some activity in our 
brain. The psychological present is the 

Temporal Patterns 


segment ol this process which, at any mo- 
ment, can influence what we do. It is a 
good solid chunk of time even it it lasts 
only a second or two. Philosophically, on 
the other hand, the jjresent is but an in- 
finitely small particle of time which has no 
duration. It is only the boundary between 
the future and the past, like the edge of a 
sharp shadow through which events pass. 
There is no movement, no flow, no exist- 


Time not only passes; it is also patterned 
or structured. It is divided and subdivided 
by a sequence of events which follow in 
varied order. Let us see what happens as 
the rate of these events changes. Imagine 
that you are listening to a series of short 
sounds or watching a flashing light. At a 
high rate of speed the sounds or flashes 
merge into each other so that the sensa- 
tion which results is smooth and continu- 
ous. Slow down the rate of interruption 
and a point is reached at which the tone 
begins to waver or roughen, the light to 
flicker. This critical rate may be called the 
threshold of discontinuity (or the threshold 
of continuity, depending upon whether 
you are speeding up or slowing down). 
The threshold will be somewhat different 
for light and for sound or for widely dif- 
ferent conditions of stimulation. As a 
rough estimate, however, it can be said 
that sounds must be separated by at least 
one-twentieth of a second if they are to be 
heard as two, or that a light must flash less 
than twenty times per second if it is to 
appear to flicker. 

A series of clicks or flashes at a rate 
slower than the threshold of discontinuity 
will seem nevertheless to fill up the time 
as it passes. We see simply a flickering 

liglit, hear a 'beating' tone or a rough 
noise. There is no perceptible pause \x:- 
tween the ticks of a watch or the explf>- 
sions of an idling auioinobile engine. The 
sounds or flashes are bound together into a 
firm series. 

Let the time between sounds become 
long enough, however, and we begin to 
hear pauses. When more than one-hall 
second comes between two clicks, we hear 
a click-pause-click, in which the pause has 
a sensible duration. Longer and longer 
intervals will seem to last quite a while 
up to the point where the beginning of the 
interval has slipped out of mind and can 
be recalled only from memory. At this 
point, judgment of duration depends no 
longer on a perception but rather on all 
the memories which fill up the gap be- 
tween the starting point and the end. 

Short Intervals 

The accuracy with which short intervals 
of time can be estimated has been the sub- 
ject of a great many experiments. It has 
been found that intervals of less than a 
second are commonly overestimated, and 
intervals of more than a second tend to be 
underestimated. Between the two lies an 
indifference point, an interval which is 
judged correctly since it is neither over- 
nor underestimated. 

Our estimates of time are much affected 
by the way the interval is filled. If two 
clicks mark off the period of silence, the 
interval is called unfilled. On the other 
hand, a series of five or ten clicks might 
be presented in which the first and last 
clicks would define the inter\al to be 
judged. This would be a filled intenal. 
Filled intervals are perceived as longer tlian 
unfilled inter\als of the same objective 

More disturbing to the judgment of time 



than the number of events filling an inter- 
\al is the meaning of the material for the 
listener. The duration of a word, for in- 
stance, is judged to be shorter than a noise 
Avhich actually lasts the same time, and 
meaningful sentences seem to be shorter 
than an equivalent series of nonsense syl- 
lables. Other factors which increase the 
interest of the listener in what is going on 
have much the same effect. On the other 
hand, an interval with a striking beginning 
and end will be perceived as longer than 
one with indifferent boundaries. Either 
the sharp intense stimuli call particular at- 
tention to the passing of time, or they add 
a short bit of duration on either end of the 


Rhythms are patterns in time which are 
marked off by regular beats with varying 
emphasis. Simple rhythms have every sec- 
ond, third or fourth beat accented. But 
the accent alone is only part of the pattern. 
Subjectively the important thing is the way 
the beats are grouped. Thus, the count of 
one, two, three is different in grouping 
from a coimt of one, two, three, or one, 
Ixuo, three; and in poetry iambic meter 
differs from trochaic meter, depending upon 
the place of the stress in the foot. Rhythm 
depends, then, on two basic factors, group- 
ing of beats into measures or feet and the 
accenting of one or more of the beats in 
each measure. Rhythms become more 
complicated when (1) the time intervals 
between beats are no longer equal and 
regular and (2) when more than one level 
of accentuation is introduced, giving rise 
to subgroups within the measure. 

In the absence of any accentuation in 
the objective rhythms, the person listening 
will nearly always supply his own. Try to 
listen to a series of absolutely uniform 

clicks and you will find yourself involuntar- 
ily grouping them into twos, threes, fours, 
or even groups of six or eight beats. The 
commonest subjective groupings are of two 
or four beats; if a larger group of six or 
eight beats is heard, it is almost sure to be 
subdivided into two sets of three or two sets 
of four. 

For the perception of rhythm the rate at 
which the beats follow each other must 
be neither too slow nor too fast. The 
possible range is from about two-thirds 
beats per second up to 8 beats per second. 
The most pleasing rates usually fall be- 
tween 70 and 90 beats per minute or 
roughly 1.2 to 1.5 beats per second. 

Rhythm plays a great part, of course, in 
artistic expression. All the basic forms of 
music, dancing and poetry are rhythmic. 
Curiously enough, a comparable form of 
art which makes important use of visual 
rhythms has never developed. Perhaps 
this is a result of technical difficulties in 
producing rhythmic visual patterns; more 
probably it reflects rather a fundamental 
difference between the sense modalities. 
Rhythm appeals to the ear and to the sense 
of bodily movement, the kinesthetic sense. 
These are the senses which offer us sharply 
defined events against a continuing back- 
ground. Visual events are not nearly so 
abrupt and discrete as those of hearing; 
visual objects are, after all, substantial and 
do not suddenly appear and disappear. 
Sounds, on the other hand, start and stop 
imder circumstances where the seen ob- 
ject remains steadily in view. Furthermore, 
sound, or silence, furnishes us with a con- 
tinuous background whether we care to 
listen or not. Vision can be shut off by 
our own fiat; we shut our eyes or turn our 
heads away. Kinesthesis resembles hear- 
ing in these particulars. Perhaps it is not 

Orientation in Time 


so strange that rhythm belongs pcciiliaily 
to sounds and to bodily movement. 


Our ability to tell time, to wake at a 
particular hour, to judge periods several 
hours in length without recourse to a time- 
piece, presents quite a different problem 
from the one we have just been discussing. 
This ability has been tested in an experi- 
ment in which a subject spent nearly tour 
days in complete isolation in a soundproof 
room. The subject was provided with a 
bed, supplies of food and water, paper, 
pencil and a telephone with which he 
could conmiunicate with the experimenter 
at will. At irregular intervals the subject 
reported what time he thought it was then. 
Between reports he ate meals, made notes, 
slept and amused himself as well as he 
could under such restricted conditions. 
Within the first day the subject's personal 
'clock' had gained more than four hours. 
Then it began to lose and at the end of the 
experiment his guess about the time was 
less than forty minutes in error, closer to 
the correct time than it had been since the 
start of the experiment. 

How this man was able to maintain his 
orientation in time will be better under- 
stood if we digress for a moment to see 
what is known of some of the important 
time-telling rhythms in animal behavior. 
The longest, and yet highly precise, rhythms 
are those connected with the migration of 
birds and fishes. Year after year we see 
the ducks and geese flying north in the 
spring and south again in the autumn. 
Each flock sets off on its flight at almost 
precisely the same date each year. Bird 
lovers are accustomed to finding individual 
species of warblers arriving each spring 
within a few days of a customary date. 

How are these migrations controlled;' Our 
best guess at the present time is that the 
length of the day is the principal factor. 
'I'emperature and food supply appear to 
be secondary factors. Changes in the total 
light are known to produce fivefold to ten- 
fold changes in the size of the pituitary 
gland, which in turn secretes more or less 
of several hormones. These control many 
other organs of the body. Nature appar- 
ently uses this mechanism to start many 
species of birds north to their breeding 
grounds in the spring. 

Many other long-term rhythms are known 
in other animals. Arctic animals such as 
the weasel, hare and fox change the color 
of their coats with the season. Certain 
marine worms swarm with the full moon. 
Army ants alternate between a nomadic 
and sedentary life. In all these cases we 
find evidence of the same thing, emiron- 
mental control of a particular physiological 
mechanism. The animal is sensitized so 
that he can tell time from nature's clock. 

By far the most general rhythm in ani- 
mal behavior is the diurnal one, the daily 
pattern of sleep and activity. Animals 
vary, of course, as their peak activity comes 
during the day or night. But their hunt- 
ing and eating, their hiding and sleep, even 
their sex life follow a daily cycle that is 
governed by the sun. Offhand it would 
look as if this diurnal rhythm, like the 
longer ones, is controlled by light, tempera- 
ture, sound or some other environmental 
stimulus. In some measure this is true. 
Female rats, for instance, always come into 
heat at night. If the lighting cycle is 
changed so that it is dark during the dav 
and light at night, the rat's estrus peak 
comes in the dark during the day. Its oc- 
currence is obviouslv controlled bv the 
cycle of light ancf dark. But there is this 
very important difference. A blind rat. or 



one kept continuously in the light, shows 
little or no disturbance of the normal four- 
day estrus c)cle. In other words, the light 
acts only to s\ nchronize the already rigidly 
established rhythm within the animal with 
the changes in the environment. 

There is evidence to indicate that the 
diunial rhythm generally is something of 
this kind. Normally sleep and activity are 
synchronized with the environment, but in 
the absence of environmental changes the 
rhythm will maintain itself with consider- 
able precision. A group of rats were placed 
in a room with a 28-hour 'day'; lighting, 
watering and feeding were all geared to the 
longer day. It might have been thought 
that they would adapt to this new day, but 
apparently they did not, for in each 28-hour 
cycle they showed a peak of acti^'ity just 
24 hours after the time they had been pre- 
viously fed. In these diurnal and estrus 
rhythms, then, we are dealing with a self- 
maintaining physiological rhythm. 

The behavior of men does not show^ such 
neat control as the behavior of rats. Rem- 
nants of both the types of mechanisms 
which we have discussed above probably 
exist. It is not hard to believe that the 
restlessness of spring fever has its roots in 
surplus hormones brought forth at that 
season of the year. Physiologically 
rhythms such as estrus are quite clear-cut. 
Diurnal rhythms are harder to discover 
because they are so strongly reinforced by 
social conventions as to cast doubt on their 
underlying physiological nature. Trav- 
elers report, for instance, that Eskimo life 
north of the Arctic Circle continues around 
the clock during the month-long summer 
day. Nevertheless, we do get clues from 
our bodies when we make temporal judg- 
ments. Four psychologists had their alarm 
clocks set at odd hours between 12:15 and 

4:45 A.M. When awakened, they guessed 
the hour. They discovered that depth of 
sleep was one of their most obvious clues, 
followed closely by the dark brown taste 
of indigestion and the necessity to urinate. 
These clues do not belong to the basic 
diurnal rhythm, and a more clever experi- 
ment will be required to settle whether our 
sleeping once a day is a social convention 
or sound physiology. 

Two other important mechanisms can 
be recognized in our time telling. The first 
of them is the conditioning, often uncon- 
scious, of particular behavior to some clue 
in the environment. Some of the best ex- 
amples can be found in individuals who 
wake up in the morning "like clockwork." 
A careful examination nearly always shows 
that there is some particular happening to 
which each of these people responds. For 
some people the clue is the sunlight, for 
others it is the sounds of traffic or the ar- 
rival of the milkman or the early departiue 
of a neighbor for work. Similar condition- 
ing establishes our hunger at mealtimes 
or our drowsiness in the late evening. 
Daily habits of long standing apparently 
can go quite far in regulating our basic 
bodily mechanisms. These habits repre- 
sent a sort of involuntary keeping of time. 
Intentional estimates of time would be Avell 
anchored by this habitual framework. 

In addition to this subtle sort of con- 
ditioning, it is possible for us to make quite 
explicit use of memories in gauging the 
amount of time which has passed. If you 
think of how long it has been since you 
arrived home, you are able to recall that 
you went to your room and washed up for 
supper, that you talked briefly to your 
roommate, that you read a letter waiting 
for you when you arrived, that you have 
now danced over certain features of the 

Orientation in Time 


evening paper. Some memories may af- 
ford you quite exact estimates, such as the 
known time of your accustomed walk from 
school to home. In other memories the 
clue may be the sheer number and clarity 
of them which crowd into your mind. A 
morning in a new and strange place seems 
very long in retrospect because of the many 
novel experiences it contained, or, again, 
your estimate may be influenced by the 
restlessness and boredom which you recall 
or by the absence of memories of moments 
when time was heavy on your hands. What- 
ever may be the whole pattern of these 
explicit memories, it is evident that they 
form a most substantial clue against which 
we all can check our personal clocks. 

To sum up, we can say that orientation 
in time depends on four factors: (1) exter- 
nally controlled physiological rhythms, (2) 
self-controlled physiological rhythms, (3) 
habitual acts conditioned to environmental 
cues, and (4) the pattern of memories which 
belong to the interval being judged. From 
all these factors we build up a framework 
of time in which our present actions are 
set. External events and our own actions 
have special meanings for us as they fit 
into this framework. Thus we come finally 
to have a kind of 'time perspective' pointed 
both toward the past and toward the future. 


1. Boring, E. G. The physical dimensions of 
consciousness. New York: Appleton-Century, 
1933. Chap. 5. 

A fairly modern view of mind-and-fxxly. 
This chapter deals with the perception o\ 


2. Boring, E. G. Sensation and perception in the 
history of experimental psychology. .New York: 
Appleton-Century, 1942. 

Descrihcs the historical setting of the inoie 
important current problems in perception, anrl 
in vision and hearing as well. 

3. Carr, H. A. An introduction to space percep- 
tion. New York: Longmans, Green, 193.5. 

A simple, and not too complete, summary of 
the conventional material on space perception. 

4. Harrower, M. The psychologist at work. New 
York: Harper, 1937. Chaps. 2 and 3. 

A popular account of how a Gestalt (isychol- 
ogist deals with a few of the facts of experi- 
ence and their relation to behavior. 

5. James, W. Psychology: briefer course. New 
York: Holt, 1892. Chaps. 17, 20 and 21. 

James' discussion of space and time and of 
the stream of consciousness; it has been modi- 
fied by many new facts, but the breadth of his 
account is still without peer. 

6. Kohler, AV. Gestalt psychology. (2nd ed.) 
New York: Liveright, 1947. Chaps. 4. 5 and 6. 

Three chapters on Gestalt principles applied 
to some problems of perception. Still the best 
introduction to this school. 

7. Koffka, K. The principles of Gestalt psychol- 
ogy. New Y'ork: Harcourt, Brace, 1935. Chaps. 
3, 4, 5 and 6. 

Contains a comprehensive account of percep- 
tion written from the Gestalt point of view. 
Difficult and erudite. 

8. Woodworth, R. S. Experimental psychology. 
New York: Holt, 1938. Chaps. 24 and 25. 

Chapters on form, color, space and attention. 
Factual and readable, the best single advanced 
text on experimental psychology. 



Sensation and Psychological 

THE chief business of the living organism 
is adaptation to its ever-changing envi- 
ronment. The protozoan, swimming along 
near the muddy floor of a pond, turns aside 
from the sharp cold of a fresh current and 
moves toward a safer region. Man's prob- 
lems and man's responses may be more com- 
plicated than the protozoan's, yet man, 
crossing the street in traffic, dodging taxi- 
cabs in the five-o'clock rush hour, solves sim- 
ilar problems of avoidance in similar ways. 
Both cases involve perception: the proto- 
zoan perceives cold and the man perceives 
the oncoming rush of steel and glass which 
is the taxicab. All organisms, from proto- 
zoan to man, preserve themselves in a care- 
less universe by a knowledge of the external 
world which comes to them through their 
sensory mechanisms. 

The preceding chapter has dealt with 
problems of perception. In perception the 
organism does all it can to get the best pos- 
sible information about the external world. 
A piece of coal in the sunshine may reflect 
more light than a piece of notepaper in the 
shade: yet we see the coal as black and the 
paper as white. The constancy phenome- 
non has come into play here; it helps us 
to recognize these and other objects in a 

This rhapter was prepared by S. 

way which has most meaning for us. Sc 
too the organism gets the third visual di- 
mension of space; it sees that a mountain 
oi- a trolley car has not only height and 
width but also solidity. As it 'interprets' 
the data from its two eyes, so also the or- 
ganism 'interprets' the data from its two 
ears, not merely hearing a sound— the horn 
of the taxicab— but knowing also the direc- 
tion from which it came. In short, in one 
way or another the organism musters all its 
resources to the end that it may get the 
most valuable information about its en- 
vironment; and this process we call per- 

Sensation Is the Core of Perception 

The way from the external world to the 
brain is via the sense organs, and these re- 
markable organs, responding to light, 
sound, heat, cold, pressure, touch, etc., are 
the windows through which we look out at 
the world about us. The sense organs 
start the messages along the nerves, the 
high^vays to the brain. "W^hen these mes- 
sages merge at the higher centers of the 
nervous system, when they organize them- 
selves and modify one another through in- 
teractions and associations, we call the re 

Smith Stevens of Harvard University. 

Stimulus and Atiribufes 


suit perception, iiut the bare messages 
themselves, isolated and apart from their 
mutual influences, we call sensations. 

We get at sensations by analysis, by pay- 
ing attention to certain aspects of our per- 
ceptions. It is much like the artist paint- 
ing his landscape. Where the casual ob- 
server sees a valley partly shadowed by a 
rocky hill, the artist sees a patch of purple 
jutting into a field of green and speckled 
by reddish brown dots. By selective at- 
tention he analyzes the organized scene 
into patches of color and he translates these 
sensations into pigments on canvas. 

The student of sensation goes farther. 
He learns to attend not only to color as 
such but also to its several modes of varia- 
tion, to its redness and whiteness and gray- 
ness. And the object of his analysis is an 
understanding of the behavior of sensory 
processes: How do sensations arise? what 
causes them to change? how many aspects 
of them can be separately distinguished and 
how can the aspects be measured? what 
takes place in the sense organ and in the 
sensory nerves? and how do these events 
depend upon the physical, chemical or me- 
chanical happenings in the world outside? 
The answers to these questions are the laws 
of sensation, laws that are based upon care- 
ful experimental measurements. 


In order to understand the laws of sen- 
sation we must first know what is meant by 
a stimulus and by attributes of sensation 
such as quality and intensity. 


A stimulus is any change in external 
energy that activates a sense organ and its 
receptors. It is a stimulus only when it 
stimulates. Light is not a stimulus to a 

totally blind person. 1 he radio waves tliai 
fill the air are not a direct stimulus to any 
organism that we know of. Many phe- 
nomena of nature affect no sense organs, 
and these phenomena come to our atten- 
tion only indirectly by way of their effects 
or by way of the elaborate inferences of 
science. The important phenomena that 
can be classed as stimuli are mechanical, 
thermal, acoustic, chemical and photic. 

Man himself reacts to many kinds of 
mechanical stimulation. He has the tac- 
tual sense of his skin, by which he appre- 
ciates the presence, size and shape of the 
objects with which he comes in contact. 
He can feel pain, which warns him of vio- 
lent or dangerous contact. He perceives 
his own posture by means of the proprio- 
ceptive organs that lie in his muscles and 
joints. By their use and by vision he main- 
tains his erect position. He perceives cer- 
tain contractions of his stomach and calK 
them hunger. He perceives dryness in his 
mouth and throat and calls it thirst. These 
instances are samples of the wide variety 
of mechanical events which can act as 
stimuli in man. 

Therynal stimulation is also effective for 
man. He must keep the temperature of his 
body constant. If it varies a little he mav 
be ill; if it varies much he may die. Al- 
though his body is equipped with a re- 
markable system for automatic thermostatic 
control, he needs also to help out by con- 
scious adaptive behavior. The thermal 
sense tells him when to put on heavier or 
lighter clothes, when to start the electric 
fan, when to turn on the radiator. 

Acoustic stimulation affects most animals 
that live in the air and some that live in 
water. Hearing, which shares with vision 
the important function of giving informa- 
tion about distant stimuli, is a verv impor- 
tant and highly developed sense. Persons 


Sensation and Psychological Measurement 

suddenly made deaf, and depri\ed of speech 
and music, seem to suffer even more from 
their deficiency than the blind. These peo- 
ple say that they live in a "dead world." 
Sound, more than anything else, signifies 
that the world is alive and moving. 

Taste and smell are chemical senses, the 
direct descendants of the chemical sense 
of fishes. Taste is a liquid sense; it is 
stimulated only by substances in solution. 
Smell is an air sense; it is activated by small 
particles of substance diffused in the air. 
Although a highly developed sense, smell 
is little used by man, who, with his erect 
posture, keeps his nose away from the 
ground where most of the smells lie. The 
dog, nose to ground, finds how extremely 
informative olfactory stimuli can be. 

Vision is the photic sense, and light is 
man's most important stimulus, even 
though the other senses may, in the blind, 
become remarkably effective substitutes for 
vision. ^V^hereas the lower animals sense 
only the intensity of light, man and some 
of the higher vertebrates can discriminate 
its wave length as well; that is to say, they 
can see hues as well as blacks, grays and 
whites. Probably this sensitivity to differ- 
ence in the wave length of light is one of 
man's most recent sensory acquisitions, for 
the development of color vision is still in- 
complete in that an appreciable portion of 
the population is color blind. Most ani- 
mals are also color blind, responding to 
differences in the energy, but not differences 
in the wave length, of light. 

Attributes of Sensation 

Since there are many ways in which a 
sensation can change, an observer, experi- 
encing a sensation, describes it completely 
only when he has specified its value with 
respect to every possible dimension of 

change. These possible dimensions consti- 
tute the attributes of sensation. 

Suppose a congenitally blind man were 
suddenly given perfect vision and shown a 
red square. This single experience would 
not teach him anything about the attributes 
of visual sensation, but we could soon show 
him what some of them are. First, we could 
change the square in quality by altering 
its hue toward orange or purple or gray, 
telling the man that this sort of change 
is a change in the qualitative attribute of 
color. Then we could change the square 
in size to teach him about the attribute of 
extension. To change the time of its ex- 
posure would be to exhibit duration to 
him. Some psychologists think that hues 
also have an attribute of intensity, which 
they call brightness. A difficulty arises 
here, however, because brightness is white- 
ness, and white is a color quality. At any 
rate all the other sensations have an in- 
tensitive attribute. Tones can be loud, 
smells and tastes strong, pressures and pains 

It is conventional to classify the sensory 
attributes under four main heads: quality, 
intensity, extension and duration. There 
can be, however, many more than four 
sensory attributes, for there are just as 
many attributes as there are possible modes 
of variation of sensation. In his course in 
psychology the college student often dis- 
covers attributes that are new to him, for 
most people do not know, until they are 
taught, that colors vary in three dimensions 
in a system that is represented by a solid 
figure and that tones change in volume 
and density as well as in pitch and loud- 
ness. Perhaps there are some sensory at- 
tributes which the psychologist himself has 
not yet discovered. 

The problem of attributes comes up for 
animals as well as persons. For instance. 

Attribufes of Sensaiion 


size is ail attribute ol visual experiences. 
Can a rat perceive sizei' Yes, because lie 
can learn to choose, for a reward, the larger 
of two circles. Can a rat perceive shape 
as such, independently of all the other 
spatial properties of visual stimuli? Prob- 
ably not. Figure 98 shows the stimuli of an 
experiment which was arranged to test 
the capacity of human and animal subjects 
to perceive triangularity as such. The 
subject was first trained to choose the tri- 
angle and avoid the square in the standard 
pair of stimuli, S. He was then tested to 
see whether he would choose the triangle 
instead of the other figure in each of the 
other seven pairs of stimuli, A to G. If he 
chose the triangle in preference to the 
square in 5 because it was a triangle, he 
should choose the triangle instead of the 
circle in A and the inverted triangle in B; 
he should choose the triangle instead of the 
rotated square, without regard to the ro- 
tation of the triangle, in C to F; and he 
should prefer the dark triangle to the dark 
square in G. Since each pair of figures is 
equated in total area and thus in total 
brightness, and since the triangle was shown 
as often on the right as on the left, it can 
be argued that shape— not brightness, an- 
gular position or size— must have been the 
basis for the original discrimination in S. 
The general problem has proved, however, 
too hard for the rat. A chimpanzee almost 
succeeded in it, and a child did succeed. 
Thus it is apparent that a human being is 
able to analyze a perception more specifi- 
cally into its attributes than a rat or even 
a chimpanzee. 

It is important to realize that a per- 
son has to learn about particular attributes 
before he can describe experience in terms 
of them. People learn readily enough to 
distinguish between size and brightness, 

but most animals do not. Color-blind per- 
sons do not easily discover the defects in 
their color sense because they are not espe- 
cially trained to analyze their color experi- 
ences. Instead they are told that the grass 






The subject was trained to choose the triangle in 
pair S. Then the experiment was arranged to dis- 
cover whether he would choose, without further 
training, the triangle in each of the pairs A to G. 
The stimuli were large, and were presented with 
the triangle as often at the right as at the left. A 
child learned to discriminate 'pure triangularity' in 
this way: a chimpanzee almost, hut not quite, suc- 
ceeded; a rat failed. [From L. W. C.ellerman. 
/. genet. Psychol., 1933, 42, 14.] 

is gieen and tliat the rose is red, although 
these two objects may be to them the same 
color. And faced ^vith die task of making 
an impossible color analysis, thev avoid 
giving attention to color attributes, and 
rely, when they can. upon their knowledge 
of the nature of objects. Xo roses, thev 


Sensation and Psychological Measurement 

remind themselves, are green, and grass is 
never red. 


All the senses but hearing seem to be 
based upon a few unique qualities, which 
may unite in fusions to give other secondary 

In vision the seven iniique qualities are 
red, yellow, green, blue, white, gray and 
black. All other colors occur as blends of 
these unique colors. (See pp. 270-274.) 
In smell the unique qualities are fragrant, 
ethereal, spicy, resinous, burned and putrid, 
and a huge number of intermediates that fit 
in among these six. (See p. 356.) In taste 
the tmique qualities are sweet, saline, sour 
and bitter, and for these, too, there are in- 
termediates. (See p. 353.) In somesthesis, 
the body sense, the unique qualities are 
pressure, pain, warmth and cold. There 
are also a great many complex patterns of 
these four qualities, like hunger, dizziness 
and itch. (See p. 360.) Hearing is the 
one sense that cannot be reduced to a few 
unique qualities. The tones form a con- 
tinuous series of qualities from the lowest 
pitch to the highest. Instead of a mere 
four or seven unique qualities we have in 
hearing all the separate pitches the ear can 
hear, a thousand or more. 

Why do we experience different quali- 
ties? Why is a sight so different in quality 
from a sound? How can the brain tell a 
smell from a pat on the hand? Actually, 
there is almost no satisfactory physiological 
theory of sensory quality. All we know 
about quality is that the fibers for each of 
the five senses lead to a particular part of 
the cerebral cortex. It seems probable that 
of the four unique qualities of the sense 
of touch each has its special nerve fibers; 
that, in hearing, although a given tone 
excites many fibers, its quality may be de- 

pendent upon the excitation of one par- 
ticular fiber more than the others. In 
vision it seems likely that there are only 
three kinds of nerve fibers in the optic 
nerve, and that the six or seven tinique 
colors are not differentiated physiologically 
from the others until the excitation has 
reached the brain. There the mystery is 
complete. All we can say is that, when an 
organism is making a qualitative discrimi- 
nation, it is distinguishing between the ex- 
citation of different systems of nerve fibers. 
Quality indicates what neural system is 
functioning, which fibers are excited. In- 
tensity, extension and duration merely tell 
how the system is functioning. That is 
why quality seems to be more fundamental 
than the other attributes, why we talk 
about the loudness of a pitch but not the 
pitch of a loudness, about the duration 
of a red but not the redness of a duration. 


Usually the intensity of a sensation in- 
creases when the energy of its stimulus is 
increased. A paperweight makes more 
noise if it drops from the desk to the floor 
than if it drops only a few inches. On the 
other hand, intensity of sensation also 
varies with the sensitivity of the sense 
organ. In hearing, for instance, sensitivity 
is greatest in the middle of the musical 
scale. A tone in this region, therefore, re- 
quires less energy than a low tone in order 
to sound equally loud. 

Both vision and hearing are senses tuned 
to respond to certain limited ranges of a 
continuous stimulus. The electromagnetic 
waves, some of which we call light, extend 
through a long range (see Fig. 114, p. 
275); yet the retina responds to only 
a limited range of these wave lengths. The 
long infrared waves and the short ultra- 
violet waves are invisible under most cir 



cumstances. For visible light the retina is 
least sensitive at the two extremes of the 
spectrum and most sensitive in the middle. 
(See Fig. 120, p. 291.) Similarly the ear re- 
sponds to only a limited range of tonal fre- 
quencies, being completely deaf to very 
low and very high frequencies and most 
sensitive to the middle frequencies of the 
musical range. (See Fig. 154, p. 324.) Thus 
it is plain that, if we wish to predict the 
intensity of a sensation, we must know 
about the stimulus, its frequency and its 
energy, and we must know about sensi- 
tivity as well. The sensitivity of the or- 
ganism to a given stimulus is just as im- 
portant as the energy of the stimulus. 


The obvious fact about sensation is that 
it arises from an interaction. Some form 
of energy impinges upon a sensitive re- 
ceptor in a living organism, and the or- 
ganism reacts. The organism sees, hears, 
smells, tastes, feels. These reactions are 
psychological processes, set in motion by 
physical events. When we study sensation, 
therefore, what we discover is the relation 
between those two aspects of the universe 
commonly called the mental and the physi- 
cal. We learn how experience depends 
upon stimulation. We learn what it takes 
by way of a cause to set off a response in a 
perceiving organism. 

Psychophysics was christened by G. T. 
Fechner, a physicist and philosopher, who 
in 1860 gave us a treatise on a new science 
of the "relation between mind and mat- 
ter"— meaning the relation between sensa- 
tion and the stimulus that causes it. 
Fechner's basic notion was simple. He be- 
lieved that, if he could measure both the 
strength of a stimulus and the magnitude 

of the sensation it arouses, he would have a 
formula relating physics and psychology. 
He asked, for example, how great is the 
loudness we experience when we listen to a 
sound wave of a given energy. Or how 
bright, subjectively, is a light of so manv 

These are complicated questions, as later 
chapters will show. We no longer give 
them the same answers that Fechner gave, 
for psychophysics has moved ahead, and 
new methods of psychophysical investiga- 
tion have been evolved. These methods 
are used nowadays to answer practical, 
everyday questions as well as to settle 
theoretical problems. They are essential 
to engineers and designers as well as to 
psychologists. All attempts to adapt ma- 
chines and gadgets to the sensory capacities 
of human beings raise problems in psycho- 
physics which can be solved by its methods. 

The story of the telephone is a case in 
point. The earliest instruments were unre- 
liable devices. You spoke your message 
and the listener asked, "What did you 
say?" You shouted into the mouthpiece 
and he still did not understand. Trial- 
and-error on the part of in\entors brought 
improved clarity, but the last word in high- 
fidelity transmission was impossible until 
the psychophysics of hearing had been ex- 
plored. In one of the world's largest re- 
search laboratories careful studies were 
made of the behavior of the ear: its sensi- 
tivity to different frequencies, its response 
to sounds of varying intensity, its ability 
to hear tones masked by noise. These re- 
searches established the performance re- 
quirements of the telephone: how it should 
transmit the sounds of speech in order for 
them to be correctly percei^"ed. Kno^\ing 
what they ivere aiming at, tlie designers 
could then proceed. 


Sensation and Psychological Measurement 

Psychophysical Problems and Methods 

The procedures used in psychophysical 
studies are as varied as ingenious re- 
searchers confronted by complex problems 
can make them. There are two useful 
ways, however, of classifying them: (1) by 
the type of judgment or reaction made by 
the subject in the experiment; (2) by the 
method of presenting, controlling and 
measuring the stimulus. Thus the prob- 
lem has two facets: the psychological and 
the physical. There are several ways of 
getting at the psychological experience of 
the subject— ways of having him respond— 
and there are many procedures for manipu- 
lating the physical energies and forces to 
which he is exposed. In general, our choice 
of procedures is guided by the nature of 
the problem we set ourselves, but we often 
find it impossible to follow what might be 
the ideal method. We cannot, for example, 
change the intensity of a smell by known 
physical amounts in the way we can alter 
the intensity of a light. Many problems 
in psychophysics must wait on further de- 
velopments in the other sciences. 

It is the business of psychophysics to ask 
questions about the behavior of man and 
animals. And since the character of a sci- 
ence is revealed by the kind of questions 
it poses— and by the way it tracks down the 
answers— we do well to list the types of 
questions asked and answered by psycho- 
physical procedures. Of course these are 
technical, scientific questions, designed to 
reveal the laws and principles of behavior. 
They are the kinds of questions that in- 
volve measurement and experimentation 
guarded by careful controls. Broken down 
into their principal categories, we find that 
these questions raise seven kinds of psycho- 
phvsical problems. 

(1) Absolute thresholds. What is the 
smallest stimulus that will set off a response 
on the part of an organism? 

Example. How faint is the faintest 
light a man can see? (Answer. Five to 
seven quanta of light energy' falling on 
the retina may produce a visual response. 
A quantum is the smallest package of 
light energy possible in nature.) 

(2) Differential thresholds. What is the 
smallest change in a stimulus that can be 

Example. How many ounces must be 
added to a pound in order to make it 
feel heavier? (Answer. .About half an 

(3) Equality. "What values must two 
stimuli have in order to produce equality 
in a given attribute? 

Example. What intensity of red light 
appears as bright as a given intensity of 
green light? (Ansicer. The red light 
must have about eight times the physical 
intensity of the green light.) 

(4) Order. Given a set of stimuli, what 
is their order of progression from least to 
greatest with respect to some attribute or 

Example. What is the relative merit 
of the music of these composers: Bach, 
Beethoven, Chopin, Grieg, Tschaikovsky, 
Wagner? (Answer. By 308 members of 
four leading symphony orchestras the 
music of these comjjosers was preferred 
in the order: Beethoven, AVagner, Bach. 
Tschaikovsky, Chopin and Grieg.) 

(5) Equality of inten>als. When is the 
apparent difference between two experi- 
ences the same as the difference between 
two other experiences? Or. as a special 

Psychophysics and Measurement 


case, vvlu'ii docs one scnsalioii Mpixat to 
he (( hclwccn two oilier sciisa- 
I ions? 

Exdiii jilc. V\'li;ii note on ilir piano 
has a ])it(li that sonnds ('(|uidistan( Ix- 
Iwcfii middle (; and the ( fonr octaves 
above it? [Answer. N'ot the c at the 
second octave aho\c noddle (J, as you 
might sn|)|)osc, Ixit the note j^ above 
this c.) 

(fi) E<iuaHty of ralio.s. When is the ap- 
j)aitnt ratio between two experiences the 
same as the apparent ratio between two 
otiui experiences? Or what stimuli pro- 
duce sensations having a given latio with 
respect to eac h other? 

Exdinplr. How many ounces fcrl half 
as heavy as a pound? (Ansxi'er. About 
eleven oinices. Eight ounces feel much 
less than half as heavv as a pound.) 

(7) Stimulus ratiui^. How accurately can 
a person name the correct physical value 
of a stimidus which he can sense but caiuiot 
nieasine directly? 

Examples. Several of (hem, mostlv un- 
answered c]uestions: How accurately can 
aviators estimate their height in feet 
above the ground? How well can police- 
men estimate the speed of passing cars? 
How precisely can a farmer estimate the 
area of a field? In trying to answer these 
cjuestions the experimenter would usu- 
ally be interested, not onlv in the ac- 
curacy of the estimate itself but also in 
the factors which tend to increase or 
decrease the acciuacy. Some of these 
factors woidd come under the heading 
of what we commonh call illusions. 

To each of the types of problems listed 
above we can applv a ^arietv of psycho- 
physical procedures. In other words, we 

can present the stimuli in a variety of wrayt 
and wc can ask the subject to iniliraie hu 
response in several inanners. These meth- 
ods and their many variants have im{Xir- 
lant uses in psychcilcigy in all its brandies. 
.Some of them {x:rinil the detailed M.TUtiny 
of the function of the sense organs them- 
selves. .Scjnic of them enable us to measure 
sensation and tell how cjne sensory ex[x.Ti- 
ence compares with ancjther. Others have 
nicjie practical uses. They make it pos- 
sible to grade conunodities like leather and 
perfumes and wines in terms of psycholog- 
ical scales set up by experienced judges. 
They even provide the basis of techniques 
that are used in the |>olling of public opin- 
ion and in the assessment of consumer 


Measurement is the backbone of the 
scientific method. Primitive peoples usu- 
ally speak of "a lot of" this or "a little of* 
that. Scientists, trving to get away from 
being primitive, like to pin numbers on 
things. They are not content \siih the 
mere statement that something is hot or 
cold. Instead, they ask what its tenifjera- 
ture is in terms of degrees on a scale. Not 
many centuries ago there were no scales of 
temperature and no way of making hot 
and cold a quantitative matter. Methcxb 
of measining temperatme had to be de- 
vised. Someone in the middle of the sev- 
enteenth centurv had to invent a ther- 

Psychology uses many of the scales cm- 
ployed in the other sciences, and it also 
invents scales of its own with which to 
measine in psychological dimensions. We 
have scales for measuring attitudes, intelli- 
gence, learning, sensation, etc. Some of 
the scales are rather crude affairs: some 


Sensation and Psychological Measurement 

show considerable refinement. The ac- 
curacy and usefulness of any scale depend, 
of course, upon the care and ingenuity of 
its creator, but they also depend upon other 
things, particularly upon -which of the four 
basic kinds of scale is being used. These 
four categories of scales are called by the 
names (1) nominal scale, (2) ordinal scale, 
(3) intenial scale and (4) ratio scale. 

(1) The nominal scale is the most primi- 
tive of the four. In fact it is not, in the 
ordinary sense, a scale of measurement at 
all. But for the sake of completeness we 
must include it here, because it is what we 
achieve when we pin numbers on objects 
or on classes of objects in order to keep 
track of them. For example, a coach num- 
bers the football players on his team, or a 
manufacturer uses a model number to 
stand for a class of automobiles. There 
is actually more to this simple-minded pro- 
cedure than meets the eye, for if the coach 
could not tell his players apart in the first 
place, he could not give each player a dif- 
ferent number. And it is only because the 
automobile maker thinks all of a certain 
group of cars are equal in some respect 
that he gives them all the same model 

We see, therefore, that the nominal scale 
is not entirely trivial. It has great practi- 
cal importance, and, what is of more in- 
terest to us, its creation really depends 
upon our ability to determine (a) that 
something is present (so that we can give 
it a number) and {h) what other things are 
equal to it (so that we can give them the 
same number). In other words, we have 
to be able to answer the psychophysical 
problem of equality— problem 3 in our list 

(2) The ordinal scale is more interesting. 
It is the kind of scale we can set up when- 
ever we can determine the rank order of a 

set of items. Thus the composers listed on 
page 256 are arranged on an ordinal scale 
of merit, from greatest to least, in the opin- 
ion of other musicians. A scale of rank 
order cannot be set up unless we can solve 
problem 4 above: the determination of the 
direction of a difference. 

On the ordinal scale of musical merit we 
find that Beethoven is better than Wagner, 
who is better than Bach. But this scale 
does not tell us how much better Beethoven 
is than Wagner, nor whether the difference 
between these two is the same as the differ- 
ence between Wagner and Bach. In other 
words, the ordinal scale is not a quantita- 
tive scale in the layman's sense of the term 
quantitative. It is nevertheless a very use- 
ful device, as is shown by the fact that 
many such scales are in daily use. They 
are used to rate applicants for jobs, to 
scale personality traits, to measure intelli- 
gence and to grade examination papers. 
(See Fig. 99 for ordinal scales.) 

When the instructor gives you A, B, C 
or D on a term paper he is using an ordi- 
nal scale. Of course he may give a nu- 
merical instead of a letter grade, but that 
does not change the situation. When you 
get 90 and your friend gets 70, it means 
that your paper is somewhat better than his 
(from the instructor's point of view), but 
you cannot say how much better it is. This 
is true simply because there is no way of 
knowing whether the units on the in- 
structor's grading scale are equal from unit 
to unit. Is the difference between 70 and 
80 the same as the difference between 80 
and 90? Since neither you nor the in- 
structor can answer that question, we are 
forced to conclude that he grades on an or- 
dinal scale. 

Actually, if you were to count up all the 
scales described in books on psychology, 
you would find that most of them are or- 

Scales of Measurement 




■ Sweet /Red 

-S§/white rose ,\V Sour 

/^ '^/ C5> 

Cananga /Bitter / Bluish green 

Thyme / /Yellow 

'Geranium /Salt ,. . . ,, 

^ /Greenish yellow 

Least pleasant 


Odors: samples from a list of 14 olfactory stimuli 
ranked by 8 observers using the method of paired 
comparisons (each stimulus compared with each 
other stimulus) . 

Tastes: average rank order obtained from 7 to 
10 observers who rated each taste on a three-point 
scale. The concentrations used were 20 times the 
threshold concentration (the least concentration de- 
tectable as different from plain water). At other 
concentrations the rank order may be different. 
For example, at 10 times the threshold concentra- 
tion salt is preferred to bitter. 

Colors: 18 squares of colored paper were ranked 
by 1279 college students using the method of paired 
comparisons. Many factors and causes may alter a 
person's preference for colors. 

[Data from J. G. Beebe-Center, Pleasantness and 
unpleasantness. Van Nostrand, 1932.] 

dinal scales. It is far easier to arrange 
things in rank order than it is to devise 
scales for measuring them in terms of equal 
units. But rank ordering is not always 
easy. How, for example, would you scale 
the following traits in order of their im- 
portance for success in business: perse- 
verence, courage, honesty, initiative, op- 
timism, friendliness, intelligence, loyalty? 
(3) The intewal scale is one on which 
the units are equal but on which the zero 
point is arbitrarily chosen. The ordinary 
Fahrenheit temperature scale is a good ex- 
ample. The units (degrees) are equal, but 
the zero point is just an arbitrary tempera- 
ture chosen by the German physicist, 
Fahrenheit, that of a freezing mixture of 

ice and salt. The centigrade scale is an- 
other example of an interval scale, and it 
has a different zero point, the temperature 
of ice water without salt (Fig. 100). On 
both these scales we know that the units 
are equal because we set up the units by 
marking off equal distances on a column 
of mercury or alcohol, which expands with 
increasing temperature. Then each rise of 
one degree in temperature lengthens the 

Boiling — 100 ■ 



— 100 


50 — 







On each scale the units are of equal size, but the 
Fahrenheit units are five-ninths as large as the cen- 
tigrade units. Each scale has a different zero point, 
and neither zero point on the scale represents a 
'true' or 'absolute' zero in temperature. 


Sensation and Psychological Measurement 

column by the same amount. By this pro- 
cedure we solve for temperature scales the 
problem of equality of intervals, the same 
kind of problem we listed on page 256 as 
psychophysical problem 5. 

When equal intervals can be determined 
for sensation, intelligence or some other 
psychological variable, scales having equal 
units can be established. The intelligence 
tester makes the units on his scale as equal 
as possible by adjusting (a) the difficulty of 
the items on his test and (b) the numerical 
credit given the testee for passing a given 
item. He then concludes that the units 
are equal if a large group of children, 
chosen at random, make scores that distrib- 
ute themselves according to the normal 
curve (p. 262). His conclusion is correct, 
of course, only provided the intelligence 
of the children is really normally dis- 
tributed—something the psychologist can 
assume but not prove in advance. Never- 
theless, by proceeding on this assumption 
of a normal distribution, we get highly use- 
fid scales for measuring human traits and 
abilities, scales having reasonably equal 
imits but whose zero points are generally 
arbitrary. An uncritical critic might make 
the rash claim that his competitor has no 
intelligence whatever, but he would speak 
loosely, for no one knows what zero intelli- 
gence is. 

(4) True zero points are possible only on 
ratio scales. And in order to set up a ratio 
scale we must be able to determine not 
only equal intervals but equal ratios as 
well. Scales of length, weight and electri- 
cal resistance are examples of ratio scales. 
In fact so are most of the other scales used 
in physics. We can demonstrate that two 
inches is half of four inches and that four 
inches is half of eight inches. If we knew 
nothing about these ratios we should not 

know where to put the zero point on the 
scale, and vice versa. 

The stimuli used in psychophysical ex- 
periments are nearly always measured on 
ratio scales. The sensations produced by 
these stimidi can also be measured on ratio 
scales whenever we can solve the psycho- 
physical problem of sensed ratios (problem 
6, p. 257). For example, if we can find out 
what weights feel half as heavy as what 
other weights, we can set up a ratio scale of 
perceived weight, as distinct from the phys- 
ical weight which we measure in pounds 
and ounces. With the aid of the psycholog- 
ical scale of weight, we might then be able 
to tell the grocer how to package his dried 
beans so that a package of one size will feel 
fifty per cent heavier, say, than the next 
smaller size. 

Figure 101 shows a ratio scale of per- 
ceived weight. This scale was obtained by 
the simple procedure of having a group of 
subjects select from among a graded series 
of weights the one that felt half as heavy 
as a given standard. Standards weighing 
different amounts were used, of course, and 
the complete data were employed to con- 
struct the curve in Fig. 101. The dotted 
lines illustrate the basis on which the curve 
was drawn; a weight of 100 grams gives a 
psychological impression which we say ar- 
bitrarily corresponds to one psychological 
unit or, to name the unit, one veg (from 
an old Anglo Saxon word meaning "to 
lift"). Then 0.5 psychological imit must 
correspond to the physical weight that feels 
half as heavy, since 0.5 is half of 1.0. But 
our experiment tells us that 72 gi-ams feel 
half as heavy as 100 grams. Therefore our 
graph must pass through the cross and also 
through the circled point on the plot— 
the point indicated by the dotted lines con- 
necting the value of 0.5 veg on the vertical 
scale with 72 grams on the horizontal scale 

Stafistics and Measurement 


50 100 150 200 

Physical weight in grams 


Relates perceived weight in vegs to physical 
weight in grams. A veg is defined arbitrarily as the 
value of the subjective impression obtained by lift- 
ing a weight of 100 grams. By experiment it is de- 
termined that 72 grams feel half as heavy as 100 
grams. Therefore half a veg corresponds to 72 
grams. The curve shows that perceived weight in- 
creases much more rapidly than physical weight. 
[Data from R. S. Harper and S. S. Stevens, Anier. J. 
Psychol, 1948, 61.] 

By extending this logic we obtain other 
points on the curve, and eventually we map 
out the entire graph relating perceived 
weight and physical weight. 


None of the seven basic problems of psy- 
chophysics can be solved without the use 
of statistics. The reason for this is ob- 
vious. The behavior of living organisms 
is variable. Seldom does their behavior re- 
peat itself exactly from moment to mo- 
ment. Nor does the behavior of one in- 
dividual always duplicate that of another. 
For this reason the answers to psycholog- 

ical questions are nearly always statistical 
answers. They are usually given in terms 
of averages and variabilities— the elemen- 
tary but important concepts in what has 
lately become a higlily developed branch 
of mathematics. --^ / 

Central Tendency // 

The common cv^-ryday notion of an aver- 
age—so familiar to baseball fans— is usually 
one of three measures of central tendency. 
The statistician's name for the average is 
the mean. And two other measures of cen- 
tral tendency are the median and the 
mode. We shall define these measures with 
the aid of an illustration. 

Suppose we show a group of ten subjects 
a horizontal line twenty-four inches long 
and ask them to estimate its length. The 
ten estimates might give us the following 
distribution of guesses: 17, 18, 20, 20, 20, 
22, 22. 24, 27, 30. What, then, is the mean 
or average estimate? In order to obtain 
the mean we add up all the individual 
estimates (scores) and divide by the num- 
ber of scores. This gives twenty-two inches 
as the mean estimate of the group of ten 
subjects. We conclude that on the average 
they underestimated the length of the line. 

We might also ask another question 
about these estimates: ^Vhat ^■alue divides 
the scores into two groups such that the 
estimates of half the subjects are equal to 
or lower than this value and half are equal 
to or higher than this value? The answer 
gives us the median of the disuibution. In 
our example the median would be the 
value midway between the scores for the 
fifth subject, who guessed 20, and the sixth 
subject, who guessed 22. The median then 
is 21 inches. Fifty per cent" of the guesses 
lie above this point and 50 per cent lie 

The mode is simpiv the value in tlie dis- 


Sensation and Psychological Measuremenf 

tribution that occurs with greatest fre- 
quency. Since 20 inches was guessed more 
often than any other value, we see at once 
that the mode is 20 inches. 

Which of these three measures of central 
tendency should we use? The answer de- 
pends upon what we want to know, the 
kind of question we ask. Generally speak- 
ing, the mean is the mosj useful measure in 

that the line tends to be underestimated, 
but they also show that the judgments 
above the mean are spread out further 
than those below. In other words, the 
distribution tails off more gradually at the 
right than at the left. If we observed 1000 
cases instead of 10, we should get rid of 
all the small irregularities in the curve, 
but these other two features might remain 

10 12 14 16 18 20 22 24 

Estimated length in inches 


The heights of the vertical bars show how many times each value on the horizontal scale was given as 
the estimated length of a line. The dotted curve shows the shape of a normal distribution (see text). 
The distance indicated by c is the standard deviation of the distribution. 

the sense that it is the most stable. If we 
were to enlist another 10 subjects for our 
experiment and get 10 more guesses, the 
mean of the second group would probably 
not be very different from that of the first— 
not so different, at any rate, as the median 
of the second group compared with the 
median of the first. And the mode would 
be the least stable of all. This fickleness 
on the part of the mode is unfortunate, be- 
cause the mode is extremely simple to de- 
termine. Apparently what comes easiest in 
statistics is often not worth very much. 

The data for 10 subjects, plotted as ver- 
tical bars in Fig. 102, show a roughly bell- 
shaped distribution: the judgments tend 
to cluster near the mean. They indicate 

as the facts of the case, provided we still 
use this scale of inches for measuring them. 
More often than not we get underestima- 
tions, yet the overestimations, when they do 
occur, show larger departures from the 
average of the group. 

The dotted curve of Fig. 102 is the so- 
called curve of normal distribution. Ob- 
served data very often approximate it when 
the deviations from the mean are due to a 
multitude of chance factors and when the 
total number of cases is large. When the 
data do not approximate the normal curve, 
the scientist often changes the scale of his 
distribution, stretching it at one end and 
pushing it together at the other, so as to 
force the curve to be more nearly normal. 


Cenfrai Tendency and Variabilify 


He does that because he wishes to treat his 
data under the conventional rules of statis- 
tics, many of which have been worked out 
in their simplest forms only for the normal 

It is clear that when data can be prop- 
erly represented by the normal curve, their 
mean, median and mode all have the same 
value, for the normal distribution is sym- 
metrical about its single mode. (On nor- 
mal distribution, see also pp. 418 f.) 


Measures of variability tell us how widely 
the data scatter about their mean. The 
important measures of variability are the 
range, the standard deviation and the prob- 
able error. 

The range is simply the difference be- 
tween the highest and the lowest score. 
As with the mode, we come by it easily but 
it tells us relatively little. The range of 
guesses for the length of the line in our 
experiment is 30—17 = 13 inches. Com- 
mon sense tells us that another group of 
ten subjects would probably not scatter its 
guesses over precisely this same range. So 
what is needed is a more stable measure of 

The standard deviation gives us this 
greater stability and is the most important 
measure of variability in the whole field 
of statistics. In technical language the 
standard deviation, designated by the 
Greek letter sigma (a), is defined as the 
square root of the mean of the sum of the 
squares of the deviations from the mean. 
What this boils down to is simply that, in 
order to compute o-, we first find the mean, 
then we subtract the value of the mean 
from each score in turn. We then square 
each of the results, add them all up, di- 
vide by the number of scores and finally 
, take the square root. 

Apply this formula to the ten estimates 
of the length of the line, and you will find 
that the standard deviation of the distribu- 
tion equals 3.8 inches. In Fig. 102 the 
upper and lower standard deviations on 
either side of the mean are indicated by 
vertical dotted lines. 

It is interesting to note that the area ly- 
ing under the normal curve and between 
the upper and lower standard deviations is 
equal to about two-thirds of the total area. 
If we were to draw verticals to points on 
either side of the mean so that just half the 
area lay between them, we should have 
to pick points nearer the mean. Those 
points, with half the area below the curve 
lying between them, are the values de- 
fining the probable error (P.E.). In nu- 
merical terms it turns out that the prob- 
able error is equal to 0.6745(7. The prob- 
able error gets its name from this fact: If 
the scores that scatter about the mean are 
regarded as errors, the probability is 50-50 
that a particular error will lie inside the 
limits set by the probable error. 


All living organisms exhibit the phe- 
nomena known as thresholds. Some stim- 
uli affect them; others do not. Some lights 
are too faint to be seen, some sounds too 
faint to be heard. But, as the intensity of 
a light or a sound is increased, there comes 
a point at which it is seen or heard. At 
any instant, it appears, this point at which 
a stimulus just crosses the tlireshold must 
be fixed, definite and precise. But, un- 
fortunately, at two different instants the 
threshold point is not the same. The or- 
ganism's properties do not stay put. In- 
stead, its sensitivity bobs up and doAvn 
from moment to moment. Consequently, 
when we want to determine the threshold 


Sensation and Psychological Measurement 

we have to make repeated measurements 
and we have to apply statistical procedures 
to the resulting data. For this reason it is 
commonly said that the threshold is a sta- 
tistical concept. 

When we examined the seven basic prob- 
lems of psychophysics, we saw that there 
are two kinds of threshold, absolute thresh- 
olds and relative or differential thresholds. 
The absolute threshold is the value of a 
stimulus which is (on the average) just 
noticeable or just detectable. The differ- 
ential threshold is that difference between 
two stimuli which is (on the average) just 
noticeable. The measurement of both 
types of threshold has long been an im- 
portant problem in psychology, and for 
their measurement elaborate procedures 
and precise statistical treatments have been 
devised. All these methods have one aim 
in common: They try to draw stable con- 
clusions from measurements on variable 
organisms. These conclusions are impor- 
tant to science, and they are often of great 
practical importance as well. Some people 
earn their living measuring other people's 

Suppose, for example, a man is applying 
for a job as a radio operator. Obviously 
he must have normal hearing. That means 
that his absolute threshold for sound must 
not be significantly above normal. Since 
speech is the most important kind of sound 
he must hear, we might say that he must 
have a normal absolute threshold for 

Standardized threshold tests for speech 
were developed during the recent war as 
an aid in the rehabilitation of aural casual- 
ties. Carefully chosen words were recorded 
on phonogiaph records, and by means of 
special electrical circuits these words could 
be reproduced at the listener's ear in graded 
steps of intensity. The problem then is 

(1) to determine the faintest intensity at 
which the listener can hear the speech and 

(2) to compare this intensity with that at 
which a normal listener hears the words. 
How this is done can be illustrated with 
the aid of Fig. 103. We shall assume that 
our listener has a fairly large hearing loss, 
sufficient to cause his friends to raise their 

First let us consider the threshold of the 
normal listener. We find, of course, that 
at a given faint intensity he hears some of 
the words and not others, because his sensi- 
tivity varies. If we raise the intensity 
slightly, he hears a larger percentage of the 
words. Finally, if we make the speech loud 
enough, he hears all the words. If, there- 
fore, we plot the percentage of the words 
he hears at each level of intensity, we ob- 
tain the curve in Fig. 103. This is usually 
a long S-shaped curve. It approximates, in 
fact, the ogive form of the normal distribu- 
tion curve, the form which shows us, not 
the number of cases for each value of the 
stimulus, but the number of cases up to 
and including each value of the stimulus. 
It is a cumulative curve. It starts at zero 
per cent for the stimulus that is always in- 
effective and reaches 100 per cent at the 
stimulus that is always effective. 

Having plotted the percentage of words 
which the listener hears at successive in- 
tensity levels, we are ready to decide what 
value we shall call the threshold for speech. 
Both common sense and convention tell us 
that the threshold ought to be defined as 
the intensity corresponding to the 50 per 
cent point on the curve. This is the speech 
intensity that will be heard correctly half 
the time. If we regard the listener's re- 
sponses to the words as comprising a fre- 
quency distribution, this 50 per cent point 
is the median of the distribution. 

For the hard-of-hearing listener we carry 

Thresholds and Psychometric Functions 


out precisely the same procedure. We plot 
a curve showinff how his correct responses 
depend upon intensity and we pay atten- 
tion to the 50 per cent point. Then, since 
we measure hearing loss relative to the 
normal threshold, we simply take the 

measure absolute thresholds, but similar 
(unctions are obtained when we measure 
relative thresholds by the same method. 

Thus we can present pairs of stinmli 
graded as to the difjerenre between them 
and ask the subject to respond by saying 


t 70 



P 50 


° 40 - 



I 30 














of- hearing ear 






i 1 
20 30 





60 70 

/ ° 

Scale of hearing loss 



/ ^ 



^ ° 
o ^ 

/ ^ 




' o 

1 ' 












30 40 50 60 

Relative intensity of speech in decibels 





The two curves (psychometric functions) show how tlie percentage of words heard correctly increases as 
the intensity level of the speech (in decibels) is raised. The intensity at which half the words are heard cor- 
rectly is defined as the absolute threshold. Amount of hearing loss is the difference between the threshold 
of the patient and the threshold of a normal ear. 

spread between the two 50 per cent points 
as the quantitative measure of hearing 
loss. In the example before us this loss is 
45 decibels, a large enough loss to call for 
a hearing aid. (For a fuller account of the 
intelligibility of speech, see pp. 345-349.) 
The S-shaped curves in Fig. 103 are 
known as psychometric junctions. Curves 
of this sort are obtained whenever we pre- 
sent carefully graded stimuli and record 
the frequencies with which a subject re- 
sponds to them. The curves in Fig. 103 

whether the second stimulus in each pair is 
greater or less than the first. A\'e should 
then obtain two psychometric functions 
(one for judgments greater, one for judg- 
ments less). The two functions would cross 
each other at their 50 per cent points. 
This aossing would usually fall near- die 
value corresponding to no physical differ- 
ence between the stimuli. On diese two 
functions we should then have to decide 
die value of the differential direshold. ob- 
viouslv not the 50 per cent point. Here 


Sensation and Psychological Measurement 

convention tells us we should choose the 
value of the physical difference which gives 
judgments of greater (or of less) 75 per cent 
of the time. This is reasonable enough if 
you think about it. The 75 per cent point 

pair is higher or lower than the first tone. 
The percentages of correct judgments may 
then be tabulated and plotted as in Fig. 
104. There we see plots for the average 
of the group of 95 students and plots for 


-10 -5 +5 +10 

Difference in cycles per second between first and second tone 

+ 15 


Psychometric functions show how the correctness of pitch judgments depends upon the size of the stim- 
ulus difference. The dotted curves represent the composite scores made by 95 high school students who 
took the Seashore Test for Musical Talent. The solid curves are for the group of 11 students who scored 
highest on the test. The curves for the judgments higher and lower cross at the 50 per cent point, which 
coincides with zero difference between the two tones presented as stimuli. Thus, when there was no dif- 
ference to be heard, the judgments followed the chance expectancy of 50-50. 

is the midpoint of the distribution of judg- 
ments falling on one side of equality. 

Figure 104 shows how all this works out 
in a practical situation. A group of 95 
high school students was given one of the 
Seashore Tests designed to gauge musical 
ability. This test calls for the discrimina- 
tion of small differences in pitch. Pairs 
of tones are sounded, and the listener tries 
to tell whether the second tone of each 

the average of the 1 1 best students. These 
1 1 listeners are clearly better at discrimi- 
nating differences in pitch than the group 
as a whole. If we measure pitch discrimi- 
nation as the difference in frequency (cycles 
of the tonal stimulus per second) correctly 
noticed 75 per cent of the time, we find 
that the group as a whole has an average 
differential threshold equal to 7 cycles per 
second. For the 1 1 best listeners the aver 

Psychometric Functions and Weber Fractions 


age is only 2 cycles per second. On the 
average these 1 1 people could tell the dif- 
ference between a tone of 1000 cycles and 
a tone of 1002 cycles— which is very good 
discrimination indeed. 

Pitch discrimination as good as this is a 
necessary asset to a musician. But a word 
of caution is in order here. Although good 
pitch discrimination is necessary, the fact 
of having it does not make a person a musi- 
cian. Other important talents are called 
for in addition. Pitch discrimination is to 
the musician what visual acuity is to the 
artist. It is what is called a necessary but 
not a sufficient condition for success. 


There is another important aspect of the 
problem of differential thresholds that we 
must consider. It is important because it 
is a law of relativity in psychology. This 
law says that in order for it to be perceived 
the increase that must be made in a stim- 
ulus depends upon the amount that is al- 
ready there. If to two lighted candles in a 
room a third is added, there is a greater 
increase in the sensed illumination than 
there would be if a twenty-first candle were 
added to twenty. The additional light has 
more effect when added to a lesser illumi- 
nation. A cough counts for more in 
church than in the subway. In other 
words, the differential threshold for in- 
tensity gets larger as the intensity gets 

It is usual to measure relative sensitivity 
by taking the ratio of the differential 
threshold, which we may call A/, to the 
total intensity at which the threshold was 
obtained, which we may call /. This ratio 
A/// is called the Weber ratio or the Weber 
fraction, because a century ago the physiol- 
ogist, E. H. Weber, thought that it re- 

mained constant at different inten.sities. 
Modern research has corrected his view. 
Figure 105 shows the typical form of the 
Weber function, that is, the way A/// 
changes with /. Although Weber held that 
such a function would be a horizontal 
straight line, actually the Weber fiinciioii 

2 3 4 5 6 7 8 

/ in logarithmic units 


The curves show the relation between the \\'el)er 
fraction A///, and the intensity of the stimulus, /. 
Log 7 = = absolute threshold. On the intensity 
scale each unit represents a tenfold increase in 
energy. White noise is a purely random mixture 
of all frequencies. It sounds like a sustained Sh-h-h. 
It is called white because, like white light, it is 
composed of all the perceptible frequencies acting 
simultaneously. [Data from G. A. Miller, /. acousl. 
Soc. Amer., 1947, 19, 609-619.] The measurement"; 
for white light were made with a small patch of 
light (visual angle = 28 minutes of arc) falling on 
the retinal fovea. 

is, as the figure shows, a curve. The \alue 
of the Weber fraction first decreases rapidly 
as the intensity increases and then more 
slowly until it reaches a minimal value. 
Thereafter, it may remain constant, or oc- 
casionally it may again increase slightly. 

In terms of the Weber fractions, it is pos- 
sible to compare one sense with another 
with respect to differential sensitivity. 
Since the fraction vaiies within a single 
sense, we must choose for each sense some 


Sensation and Psychological Measurement 

one representative value, and it is obvious 
that the minimal fractions best lend them- 
selves to comparison, since each minimal 
fraction shows the maximal sensitivity of 
which that sense is capable. In Table XVI 


Minimal Weber Fractions 

For all cases below, except tones and smells, the 
Weber fraction has a minimal value in the middle 
range of intensities. The minimal values for tone 
and smell are for the maximal intensities after the 
Weber function has leveled off. Although each of the 
different values would be somewhat altered by a 
different choice of experimental conditions, the differ- 
ence between Ijj and \i is so very great that there 
can be no doubt about the general fact that different 
sensory mechanisms differ significantly in sensitivity. 

Weber Weber 

Ratio Fraction 
Deep pressure, from skin and subcutaneous 

tissue, at about 400 grams 0.013 1^7 

Visual brightness, at about 1000 photons 0.016 Hs 

Lifted weights, at about 300 grams 0.019 }i3 
Tone, for 1000 cycles per second, at about 100 

db above the absolute threshold 0.088 Hi 

Smell, for rubber, at about 200 olfacties 0. 104 Mo 
Cutaneous pressure, on an isolated spot, at 

about 5 grams per mm 0. 136 H 
Taste, for saline solution, at about 3 moles per 

liter concentration 0.200 '/i 

these minimal values are listed for seven 
well-established cases. It is true that these 
figures apply only to particular experimen- 
tal conditions; nevertheless, the general re- 
lation of the senses is clear. Tonal sensi- 
tivity is less than visual. The skin is not 
so sensitive to a difference in pressure as 
the muscles to a difference of lifted weight. 
Despite the fact that for a given sense 
the Weber fraction is only approximately 
constant, we must not lose sight of the 
fact that the Weber function is a general 
statement that relativity is approximated 
in the world of sensory intensities. The 
principle of relativity signifies that a little 
thing means more to another little thing 

than it does to a big thing. A dollar mean;; 
more in poverty than it does in wealth, 
whereas an error of an inch in the length 
of the equator matters less than an error 
of an inch in the fit of a shoe. Just so the 
Weber function means that differences that 
seem large at small intensities become quite 
unnoticeable at large intensities. 


1. liarlley, S. H. ]'ision. New York: Van Nos- 
trand, 1941. Chap. 2. 

A discussion of the principal facts of bright- 
ness discrimination with emphasis on the un- 
derlying physiological processes. 

2. Boring, E. G. The physical dimensions of con- 
sciousness. New York: Appleton-Century, 193.S. 
Chaps. 2, 3 and 6. 

A systematic discussion of the sensory at- 
tributes of intensity and quality in terms of 
a physical theory of mind. 

3. Boring, E. G. Sensation and perception in the 
history of experimental psychology. New York: 
Appleton-Century, 1942. Chap. 1. 

Chapter 1 summarizes the work and thought 
on sensation and perception during the last 
three centtiries. 

4. Guilford, J. P. Psychometric methods. New 
York: McGraw-Hill, 1936. Chaps. 2 to 6. 

A comprehensive treatment of the classical 
psychophysical methods and their statistical 

5. Stevens, S. S., and Davis, H. Hearing: its psy- 
chology and physiology. New York: Wiley, 
1938. Chaps. 2 to 5. 

A systematic analysis of the facts of auditory 
sensation with respect to pitch, loudness anti 
the other tonal attributes. 

6. Troland, L. T. The principles of psycho- 
physiology. New York: Van Nostrand, 1930. 
Vol. 2, especially sections 53, 54 and 61. 

A systematic account of the psychophysical 
facts of all the senses with especial emphasis on 




WHAT the eye sees is color— greens, 
oranges, pinks, grays, whites. The 
location ot the seen colors in space and the 
patterns that make up the perceived visual 
field are problems of visual space percep- 
tion with which the next chapter deals— 
the how and why of shape and size, of flat 
and solid, of near and far. This chapter is 
about the visual qualities, the relationships 
and laws of colors. 


We begin with the appearance of col- 
ors, what can be said about color without 
reference to its stimuli or to the conditions 
of its arousal. 

Color Names 

An attempt to catalogue all the various 
color qualities at first appears impossible. 
When we think of the many lavenders, 
pinks, purples, reds, oranges, yellows, 
browns, tans, greens, blues, grays, blacks 
and whites of our everyday experience, the 
accepted estimates of 100,000 to 300,000 
discriminatively different colors does not 
seem too high. Colors were first named by 

reference to paiticular objects, and many 
such terms are still retained in our every- 
day speech, for instance, orange, violet, 
olive, straw. Others have lost their object 
reference and now are simply color names, 
as purple, scarlet, sepia, maroon, crimson, 
azure, taupe. In addition, it has been the 
custom for a long time to invent color 
names, particularly for clothing, and such 
names have changed with the styles of the 
time. In the sixteenth century, for in- 
stance, French women wore colors called 
rat color, widow's joy, envenomed monkey 
and chimney sweep. The eighteenth cen- 
tury produced rcish tears, Paris mud, stifled 
sigh in France and red-hot bullets and 
smoke of the Camp of St. Roche in Eng- 
land. Only yesterday (1930) they could be 
matched with folly, lucky stone, elephant's 
breath and in 1946 with sun love, town 
blond and cocoblush or J'irginia turf, 
radar blue and avenue gray. Obviouslv. 
such fantastic names have no ^alue for 
scientific purposes, though the textile in- 
dustry has systematized them for sales pro- 

The most comprehensive dictionary of 
color gives over seven thousand samples of 

This chapter was prepared by Forrest L. Dimmick of the U. S. Naval Medical Research 
Laboratory at New London. 

The opinions or assertions contained in this chapter are the private ones of the collabo- 
rator and the editors and are not to be construed as official or reflecting the views of the 
Navy Department or the Naval Service at large. 




colors but finds only about half that many 
color names, some of them repetitions and 
others obsolete. An attempt has been 
made by the National Bureau of Standards 
and the Inter-Society Color Council to 
standardize and simplify color names. 
They have found that the long list of color 
names commonly used can be reduced to 
twelve applied singly (blue) or in combina- 
tion (bluish green) with certain modifiers 
(light blue-green). (See Table XVII.) 


Color Names 

The diagram shows how a tew color names and 
modifiers can be combined to represent a large range 
of colors in the Inter-Society Color Council and the 
National Bureau of Standards system of color names. 
The five rows give alternative names for five different 































Unique Colors 

It is not necessary to have a separate 
name for every color, because colors can be 
grouped according to their resemblances to 
a few outstanding or unique colors. A 

unique color is a color that is describablc 
in terms of itself alone, that is to say, it 
must be displayed or demonstrated. There 
are seven such unique colors, namely. Red, 
Yellow, Green, Blue, White, Gray and Black. 
No one of the unique colors looks like or 
implies the existence of any other unique- 
color, but all non-unique colors can be re- 
ferred to two or more of the unique colors 
because they resemble the unique colors. 
Thus non-unique colors fall into series of 
gradations from one unique color to an- 
other. For example, purple refers to a 
group of colors that look both reddish and 
bluish. There are bluish reds (purples), 
blue-reds and reddish blues (violets). Some 
investigators use the terms purplish red, 
reddish purple, purple and bluish purple, 
as well as red-violet, violet and blue-violet. 
Any color in the group can be described 
by giving its relative redness and blueness. 
Careful experimental observations have es- 
tablished the fact that the seveyi unique 
qualities mentioned above are necessmy 
and sufficient for precise description of all 
visible colors. 

The Color Equation 

The fact that every color can be de- 
scribed precisely by stating its likenesses to 
the several unique colors can be expressed 
in the equation: 

Color = (Red or Green) + (Yellow or 
Blue) + (White or Black) -f Gray 

or, more simply, 

C = {R, G) + (7, B) + {Wh, Bk) + Gy 

The equation pairs six unique colors, ex- 
pressing the fact that there are no red- 
green, no blue-yellow and, as a matter ol 
fact, no black-white colors. (The interme 
diate colors, from black to white, are mix 

The Color Equation 


lures of black or white with the gray color 
in various proportions,) This fact is the 
basis of the complementarisrn of colors, a 
relationship which, as we shall see, appears 
in several other ways. There are no colors 
which look reddish green or bluish yellow, 
although there are reddish yellows, bluish 
greens and reddish blues (Fig. 106). That 
is why the equation for color reduces to 
lour terms instead of seven. 

Unique colors. There are seven of 
them, R (red), Y (yellow;, G Cgrcen), 
B (blue), Wh (white), Bk (black) and 
(jy (gray). They are unique because 
they are the points of orientation for all 
the other colors and no one resembles 
any other one. They are also simplex. 

Duplex colors. They lie on the color 
series connecting any two unique colors. 
There are eighteen such series: 












The second point about the color equa- 
tion is that it shows how many different 
ways colors can vary in their relations to 
one another. The unique colors are sim- 
ple and points of reference, for all the 
other colors are designated by reference to 
them. Then there are duplex colors, like 
the carmines, purples, violets and indigos 
of Fig. 106, which form a series between 
unique red and unique blue. Unique red 
is an end point of five such duplex series, 
red-blue, red-yellow, red-white, red-gray 
and red-black. For duplex colors two of the 
four terms in the color formula are' equal 
to zero and disappear, and the other two 
terms characterize the color. When there 
are three terms used in the color equation 
the color is triplex, like a light purple 
(red -f blue -f white) or a grayish orange 
(red -f yellow -f gray). The great majority 
of colors are, however, quadruplex, like a 
light pastel jade (green -f blue + white + 

We shall do well to sunimari/e these rela- 





































In these groups what are sometimes 
called 'good hues' appear in series 1-4. 
The bright colors are in series 5-8, the 
dark colors in series 9-12, the poorly sat- 
urated or grayish colors in series 13-16 
and the achromatic colors (the whites, 
grays and blacks) in series 17 and 18. 
These series are the lines in Figs. 107, 
108, 109 and 110. 

Triplex colors. A great manv colors 
have only one term in the color equa- 
tion missing, being related to the other 
three unique colors. Such colors lie in 
the triangular spaces of Figs. 107, 108, 
109 and 110. There are twenty such 

1. R-Y-Wh 4. Y-G-Wh 7. G-B-Wh 

2. R-Y-Bk 5. Y-G-Bk 8. G-B-Bk 

3. R-Y-Gy 6. Y-G-Gx 9. G-BG^ 



](). B-R-Wh 14. Y-Gy-]V, 18. Y-Gy-Bk 

11. B-R-Bk 15. G-Gy-Wli 19. G-Gy-Bk 

12. B-R-Gy 16. 5-G>i-Tl7i 20. B-Gy-Bk 

13. i?-G)'-Ty/z 17. R-Gy-Bk 

See the triplex series from orange to 
white in Fig. 111. 

Quadruplex colors. They represent 
the great majority of colors which have 
to have positive specification in respect 
of all four terms of the color formula. 
There are eight such combinations: 




1. R-Y-Wh-Gy 

2. R-Y-Bk-Gy 

3. Y-G-Wh-Gy 

4. Y-G-Bk-Gy 

5. G-B-Wh-Gy 

6. G-B-Bk-Gy 

7. B-R-Wh-Gy 

8. B-R-Bk-Gy 

The Color Pyramid 

The facts expressed in the color formula 
can be represented in a spatial schema. If 
we put the unique colors at points and the 
various qualitative series on straight lines, 
the framework of our structure builds it- 
self. For a start let us take the four points 
and four series representing red, yellow, 
green and blue. The resulting shape is a 
square with each one of the four colors at a 






BLUE Turquoise GREEN 


Schematic arrangement of the five unique colors, 
red, yellow, green, blue and gray, showing examples 
of duplex colors lying along the straight lines con- 
necting the uniques. Triplex colors lie within the 
four triangular spates. 



Schematic arrangement of the five uniciue colors, 
white, gray, black, yellow and blue, with duplex 
colors along the lines, and triplex colors in between. 





Schematic arrangement of the five unique colors, 
white, gray, black, red and green, with duplex col- 
ors along the lines, and triplex colors in between. 

corner (Fig. 107). If we had taken blue, 
white, yellow and black, or red, white, 
green and black, similar squares would 
have resulted (Figs. 108, 109). Gray goes 
in the middle of each of these squares be- 
cause of the complementariness of the re- 
maining three pairs. You cannot go from 
red to green, from yellow to blue, or from 
white to black without passing through 

To bring these three squares together, as 
we must, since we have in all only six 
corner points, we can set white and black 

The Color Pyramid 


respectively above and below the iniddlc; 
of the red-ycllow-grecn-bluc square and 
connect them with its corners. The identi- 
cal grays at the middle ol cacli scjuare coin- 



cide in the middle of the solid figure 
which results. This figure is a double 
square pyramid or octahedron. Gray, as 
we have said, stands at one end of series 
that run to all the other unique colors. Its 
place, obviously, is at the center of the 
system. (See Fig. 110.) 

The duplex colors lie on the eighteen 

lines of the pyramid, the lines whirli form 
the edges, and the six lines which radiate 
from gray. Figure 112 is one of the eight 
tetrahedrons which make up the color 
pyramid. This tetrahedron has four 


One of tlie eight tetrahedrons in the color p\ra- 
mid. All the colors in this tetrahedron may be 
specified by the equation Red + Yellow + White + 
Gray = C. 

unique colors at its four corners, six series 
of duplex colors along its six edges, four 
sets of triplex colors in its four triangular 
faces and all the red-yellow-white-gray 
quadruplex colors inside its volume. Sal- 
mon and pink (see Fig. Ill) would lie 
near the top of the front face (Fig. 112). 

The color pyramid and its color equation 
represent every knoAvn or hypothetically 

orange Salmon 


;;:;:;|re;D ■ ^ ^_______^j^^ 



The diagram shows an orange getting whiter. The proportion of yellow to red remains the same, btit 
!hc ]>ioportion of while to orange (vellow-and-red) increases. 



visible color quality. The only oilier ways 
in which visual appearance can be altered 
are by putting cjualities from the pyramid 
into a spatial pattern or by making them 
change in time or by both together or by 
presenting simultaneously one color to one 
eye and a different color to the other eye. 
In the last case avc sometimes see luster. 

Chromatic and Achromatic Colors 

This is the newer \ iew of the classifica- 
lion of colors. The older and more con- 






ventional ^ iew separates white, gray and 
black from the rainbow colors, labeling the 
former achromatic or 'uncolored' colors 
and the latter chromatic or 'colored' colors. 
Hue, saturation and brightness are the 
conventional terms which are used to char- 
acterize the attributes of colors. Again wc 
have here simply a different set of terms, 
not any new facts. (Sec I'ig. 1 K^.) 

Brightness (sometimes called ligfitness, 
tint or value) refers to variations along the 
achromatic scale, black-to-gray-to-white. 
Since other colors also show gradations 
toward white and toward black, a chromatic 
color may also ^ary in brightness. 

Saturation is represented most simply by 
a series of gradations from one of the chro- 
matic colors, like red, to one of the achro- 
matic colors, like gray. In the conven- 
tional terminology, the series representing 
change of saturation would be all the 
radial lines that could be drawn from 
gray to the colors on the outside of the 
color square of Fig. 107. The newer view 
puts gray at the middle of the color pyramid. 
All radial lines that go from it to any color 
in the surface of the pyramid are series 
which show increasing richness of the chro- 
matic or achromatic color to^vard which 
the line leads and diminishing grayness. 
This view really makes the pyramid into a 
double hedgehog, with saturation lines 
sticking ovit from gray towaicl the other 
colors in all directions. 

Hue, in the older system, refers specifi- 
cally to the several 'chromatic' colors— red, 
yellow, green, blue and their intermedi- 


It is not enough to know the number of 
color qualities and their relations to one 
another. We must know also how the 
colors are produced, the nature of their 
physical stimuli. 

Nature of the Stimulus 

The stimulus to color is light. When 
electric charges are mo\ing through space 
at a iinifonn rate, they release radiant 
rneigx in the form of oscillations in imen- 

The Stimulus to Co/or 


sily of the elcctroinagnelic field wliciievcr 
their uniform motion is altered. This 
radiant energy is light. lis visible aspects 
are related to three important character- 
istics of these electromagnetic oscillations. 
(See Fig. 114.) 

The most fundamental characteristic is 
the distance from pulse to pulse of the 
vibration, tlie luoTr l('n<>;lli of light. Sudi 

wave lengili falls in a different jjlace. J bus 
the heterogeneous light is broken up into 
its homogeneous (oniponents. What you 
see, of course, is the spectrum, a brilliant 
band of colors shiinng out in the dark in 
which you are working. Newton called 
this apparition in the dark a spectrum 
because of its specterlike appearance. It 
is from the spec trum that the wave lengths 




y, !/,o 33 

mile mile feet 

t t t 




16 millionths inch — i 
32 millionths inch 
1 thousandth 

Transoceanic Broad Short 
cast wave 


Radiation used in 
radio communication 

Infra-red _ 


800 mn 

5 ten- 















" Orange 

" Yellow 


' ' Violet 


j^ X-ray ^ 



V ^400 m/i 

Cosmic rays 


The range is so Avide that this diagram had to be plotted on a logarithmic scale in order to place it on 
this page. Note the small portion of the spectrum in which visible light is radiated. 

wave lengths cover a wide range, from 
tJiose measured in units of 10-trillionths of 
an inch to those many miles long. Light 
waves are among the shorter ones, lying 
between 16- and 32-miIlionths of an inch 
or, in the more usual notation, between 
400 and 800 millimicrons (millionths of a 
millimeter, abbreviated m/x). A particular 
beam of light may consist of a set of waves 
that are all of a single length (homogene- 
ous), of several wave lengths (heterogene- 
ous) or of all wave lengths between the 
visible limits (heterogeneous). 

It was in 1666 that Isaac Newton dis- 
covered that a beam of heterogeneous 
light ('white' light) upon passing through 
a triangular glass prism is dispersed or 
spread out into a wide band so that every 

of light are determined. You never see 
wave lengths directly. They have to be 
computed froin physical measurements. 

In addition to wave length and homo- 
geneity, radiant energy varies also in 
amount or intensity. The intensity of the 
color stimulus is always proportional to 
the rate at which energy comes from a given 
surface. You measure amount of radiant 
energy to measure the intensity of the 

The physical stimulus may vary. then. 
(1) in iL'ove length, (2) in homogeneity 
(number of wave lengths combined) and 
(3) in intensity of luminous energy. ^Ve 
must examine the dependence of the vari- 
ous characteristics of color upon these 
physical properties of the stimulus. 



Dependence of Color on Its Stimulus 

There is a fairly simple and consistent 
correlation between wave length and the 
first half of the color equation, that is, 
red, yellow, gieen and blue (the chromatic 
colors, the hues). The long waves of the 
spectrum beginning at 700 millimicrons 
are seen as red tinged with yellow. As 
^v■e go from that point toward the shorter 
wave lengths, colors become more yellow 

wave length. At the red end there is no 
change of color toward yellow until you 
get below 635 millimicrons. The colors 
there get less black, less gray, more red, but 
not yellower. Between that point and 450 
millimicrons the difference in wave length 
necessary to get a noticeable change in 
color varies aroimd 2 millimicrons. (See 
Fig. 116.) Differential sensitivity is great- 
est near vellow and blue and least near 

Unique Unique 
blue green 

i li . 



J L 

J L 

I 510 





800 m/i 






Yellow- Oranges 



\\;i\e leiigihs of spcclral light indicated in millimicrons. Duplex colors shown below the line. Tlie 
lliree uni(|iie colors which lie in the spectrum are shown at arrows above the line, but unique red is 
:iuiispectral and does not show. Spectral "red" (about 670-800 m^) is a slightly yellowish (duplex) red. 

and less red, passing through the red-yelloW 
series until unique yellow is reached at 
about 580 millimicrons. Between that 
point and green at 510 millimicrons lie 
the greenish yellows and yellow-greens. 
Between 510 and 476 millimicrons is the 
series from green to blue. Shorter wave 
lengths, from 476 millimicrons to the end 
of the visible spectrum at about 435 milli- 
microns, give reddish blues or violets. (See 
Fig. 115.) Purples and bluish reds have 
no simple spectral correlate but must be 
obtained by mixtures of the wave lengths 
from both ends of the spectrum. Unique 
red itself requires a complex physical stimu- 
lus, since the longest wave length visible is 
distinctly yellowish. We can get unique 
red by mixing a little spectral blue with 
the yellowish spectral red. 

Changes in color through the spectrum 
are not uniform for equal steps of physical 

green. Below 450 millimicrons the only 
change in color is toward black. 

This relationship holds for the middle 
intensive range of radiant energy, but for 
high energies all the colors become whitish 
and for low energies blackish. 

The whiteness or blackness of a colo» 
depends in a general Avay upon the amount 
of visible radiant energy, upon what is 
called the total luminance. An illumi- 
nated spot will appear lighter or darker, 
whiter or blacker, as the intensity of the 
luminance increases or decreases. Whether 
the spot actually looks white or gray or 
black depends, however, upon the lumi- 
nance of the surrounding field. A spot of 
intermediate luminance may look white 
on a black field, black on a white field. 
The ratio of the spot's luminance to the 
average luminance of the entire field is 
■ ]\e determining condition. 

The Stimulus to Co/or 


For example, a spot radiating 0.2 imil oi 
energy (or, exactly, 0.2 lainberl per sc|iiare 
centimeter) set in a field which radiates 
an average ol' 1 unit will look gray. A 
spot which radiates 1 unit in the same field 
will look white. Radiation less than 0.03 
unit will look black. If, now, the lumi- 
nance of the whole field is raised to 10 
units, it will require 2 units to look middle 
gray, whereas the 0.2 unit of ihe preceding 
example will now look black. 


460 500 540 580 620 
Wave length in millimicrons (m//) 


Typical hue discrimination curve for a normal 
observer using a 2-degree stimulus. The ordinate 
gives the just noticeable difference in hue at every 
wave length throughout the spectrum. 

The whiteness or blackness of a spectral 
color depends upon the same ratios of 
luminance as those of the white-gray-black 
series. With a white surrounding field, 
emitting a luminance of 1 unit, a spot of 
any homogeneous spectral wave length (for 
instance, 520 millimicrons which looks 
green) of 0.2 units of energy will look 
neither blackish nor whitish but will have 
a brightness of gray. If we increase the 
energy of the 520 millimicrons to 0.5 unit, 
the color will appear whitish green (light 
green); if we reduce it to 0.1 imit it will 
look blackish green (dark green). These 
appearances, however, also depend on the 
laws of color constancy and may be altered 
in accordance with them (pp. 234-237). 

Purity and Saturation 

We saw that light can be l>roken up by 
dispersion into many different wave 
lengths and that each wave length gives a 
specific color. When light consists en- 
tirely of a single wave length it is said to 
be 'spectrally pure.' For the physicist 
'white' light means that the luminous 
energy is distributed at random among all 
wave lengths. It is maximally hetero- 
geneous. Its purity is zero. Between the 
two extremes of complete homogeneity and 
maximal heterogeneity are all gradations 
of spectral purity. \Vhen spectral purity 
of a light stimulus changes alone w'ith no 
change in its luminance relative to the 
field which surrounds it, the color changes 
principally in grayness. Grayness tends to 
diminish and saturation to increase as 
purity increases. That is why spectral 
lights are so impressive; the colors tend to 
be better saturated than the colors from 
mixed lights which objects reflect. 

Sensation versus Stimulus 

There are three important ways in \\hich 
the stimulus to color can change: (1) in 
wave length, (2) in energy and (3) in 
purity. The preceding sections indicate 
the more obvious ways in which color is 
affected by changes in these three dimen- 
sions of its stimulus. Change wave length, 
and you get change in tlie red-yello^s-green- 
blue dimension of color quality. Change en- 
ergy, and yoti get change in the black-gi"ay- 
white dimension of color quality. Change 
purity and you get change in the grayness 
of the color quality. That is very simple, 
but, alas, the truth is more complex! All 
three of these kinds of color cliange can 
be made to occur, under certain specific 
conditions, bv changing anv one of these 



three dimensions ot the stimulus. Here 
are the complexities. 

Change ot color in the red-yellow-green- 
blue chromatic series occurs when wave 
length changes, when energy changes (with 
iliminished energy all colors converge on 
red and green, with increased energy on 
yellow and blue) and when the hetero- 
geneity of the liglit changes (see the laws 
of color mixture in the next section). 

Change of color in the black-gray-white 
achromatic dimension occurs when energy 
changes, when the wave length of homo- 
geneous light changes (pure 'yellow' light 
is brightest, pure 'blue' light darkest) and 
when heterogeneity changes (adding more 
lights together to get greater heterogeneity 
makes the color whiter). 

Change of color in grayness occurs when 
])urity changes, when energy changes (very 
daik and very light colors have little gray 
in them; they are near to unique black or 
unique white) and when wave length 
changes (for instance, the two ends of the 
spectrum, being very black have but little 
gray in them). 

There is an important lesson to be 
learned here. You do not see the stimulus. 
Yoti see the colors which the stimulus (op- 
erating under the laws of perception) 
creates. It is not true that in seeing hues 
vou are seeing wave lengths. If you see a 
green, it is most likely a complex mixture 
of wave lengths, and there are many dif- 
ferent mixtures that will make you see the 
same green. If you see a white, you are 
not seeing an amount of energy. You 
may be seeing great energy for a single 
wave length, but more likely you are see- 
ing many wa\e lengths of whicii the white- 
ness depends in part on color constancy 
and the looks of the field around the white. 
If you see a gray you need not be seeing 
maximal heterogeneity of light, for the 

gray may come from all the visible wave 
lengths mixed together at low energy with 
a bright field around them, or from a mere 
two wave lengths mixed in the right pro- 

Physics depends on observation as much 
as psychology, but its obser\ations arc dif- 
ferent. Usually they are the visual obser- 
vations of scales on instruments. You can 
'see' a wave length by reading a scale on a 
spectrometer. You can 'see' light energy 
by reading an illuminometer. And wave 
lengths themselves are not colored, even if 
they do stimidate the retina to see colors. 


A great deal happens to light before it 
becomes a proximal stimulus to act upon 
the retina and produce color. 'White' 
light from the sun is a heterogeneous mix- 
ture of all the visible wave lengths, as well 
as the invisible infrared and ultraviolet 
beyond the spectrum. It falls upon green 
foliage and a great deal of the energy of 
every wave length is absorbed. The darker 
the foliage, the greater the absorption. The 
rest of the light is reflected, but not in the 
random balanced mixture that makes 
'white' light. Light from the green-yellow 
region of the spectrum predominates, al- 
though some red and some blue are also 
reflected. The laws of the mixture of color 
stimuli tell that the reflected combination 
is what makes the foliage look yellowish 
green. Most 'colored' objects reflect all the 
wave lengths, but in combinations that 
give the objects their specific colors. The 
color of an object is the residt of what it 
reflects and does not absorb. 

The color of a transparent object de- 
pends on w^hat it transmits and does not 
absorb. Red goggles transmit mostly the 

Color Mixture 


'red' end of the spectrum, absorbing the 
'blue' end. 

Laws of Mixture 

Three laws govern the mixture of color 
stimuli. The first two were laid down by 
Isaac Newton in 1704. The third is not 
yet quite a century old. They apply to 
what is called additive color mixture, the 
adciition of the wave lengths of one stimu- 
lus to the wave lengths of another to make 
a total wave length pattern for the mixture. 
You have additive mixture when you have 
two colored lights and can shine them su- 
perposed on the same spot on a white 
screen. Or for additive mixture you can 
use the device of Fig. 117, where light 
from one stimulus is reflected from a half- 
silvered mirror at forty-five degrees, while 
light from another stimulus is transmitted 
directly through the mirror, so that you 
get both sets of light added together along 
the same common path. Here are the laws 
of additive mixture. 

Law I. For every color stimulus there is 
another color stimulus which, when mixed 
with it in the right proportions, will can- 
cel it. The wave lengths of both stimuli 
will be present in the mixed stimulus and 
the total energies of the two will be sum- 
mated. The mixture will be the color of 
the stronger or, if the two are equally 
strong, the mixture will be gray. 

This is the law of complementaries. It 
agrees with the color ecjuation. No colors 
can be found that resemble both members 
of a complementary pair, both red and 
green, both blue and yellow, both black 
and white. Complementariness, however, 
does not always work out quite so simply. 

The mixture of black and white gives a 
perfect cancellation, leaving, of course, 
gray. Mixtuie of imique blue with unique 
yellow gives giay. The mixture of red 

and green lights on the other liand gives a 
gray so yellowish as not properly to be 
called gray. It is more usual to say that 
ihe complementary of unicpie md is bluish 
green, and the complementary of unicjue 
green a bluish red or purple. 

Law II. Color stimuli which are not 
complementary, when mixed, give re- 






The glass plate P reflects the light rays from Sj 
into the observer's eye; the ravs from So pass di- 
rectly through the glass and enter the e\e in ihe 
same direction. 

sultant colors that resemble all the com- 
ponents to the same degree that each one 
is present in the mixture. This principle 
is most ob^'ious in the combination of pairs 
of hues such as red and vellow to gi\e 
orange, blue and green to give bluish 
green or greenish blue, etc., and it holds 
equally well for the addition of black, gray 
or white to any mixtine. 

The stability of the colors obtained by 
the mixtiue of stimuli is guaranteed by 
the third law. 

Laic IIL A mixture of mixtures that 
match will match either of the original 



inixtmes (provided the light conditions 
remain constant). The law guarantees 
that colors can be dealt with as visual re- 
sultants on the basis of their resemblances 
or matches without reference to the physi- 
cal composition of their stimidi. Thus 
another wording of the law is: Colors com- 
bine no matter how they are composed. 
You cannot tell the composition of a color 
by looking at it, of course, but that fact 
does not matter— so the law says. If you 
have a red and a bluish green which mix 
to make gray, you can substitute for the 
red any other red that looks like it to the 
eye, no matter of what spectral lights it 
is composed, and the new red will cancel 
the bluish green just as well as the old. 
You can make colors gray by mixing gray 
with them, although gray can be made of 
all the wave lengths, of any two comple- 
mentary wave lengths or in hundreds of 
other ways. You have only to be sure 
that, when you substitute one gray for an- 
other, the grays match. You may need to 
keep the illumination constant, but that 
is because grays and other colors differently 
composed change color differently when 
illumination shifts from daylight to the 
depths of night vision. 

While certain exceptions occur, the laws 
of color mixture are so well established 
that the important technology of color- 
imetry is based upon them. 

Methods of Mixture 

There are three important scientific de- 
\ices for mixing color stimuli. The first 
two are additive, the third subtractive. 

(1) Two beams of light may be combined 
so that they act as a single effective stimu- 
lus. Such a mixture produces a physical 
resultant which is the sum of the physical 
components. The method already men- 
tioned (p. 279 and Fig. 117) may be used. 

'I'he simplest way to do it, however, is to 
project two beams of light upon the same 
area of a nonselective, diffusely reflecting 
surface, for example, matte white (Fig. 1 18). 
Another way is to bring the two beams to- 
gether by means of prisms so that their 

surface \ 




sources are viewed directly as in the same 

(2) Light from two areas may be rapidly 
alternated so that the two components are 
continuously effective over the whole area. 
The usual device of this sort is a rotating 
disk made up of two or more sectors. At 
four thousand revolutions per minute the 
component sectors fuse and summate pro- 
portionately, giving a single uniform color. 

This is a convenient method to use be- 
cause of its simplicity. The method is 

Co/or Mixture 


limited, however, because its summation 
is proportional, not absolute, that is to 
say, the color of each sector is effectively 
spread over the whole disk, thus reducing 
the stimulus effect per unit of area and 
making the mixture grayer. For instance, 
if you want to mix the red of a red paper 
with the yellow of a yellow paper, you 
can view both papers simultaneously in 
the same place by the use of prisms, and 
you get an orange that has in it the energ)' 
of all the red and all the yellow. But, if 
you put the two papers on a rotating disk, 
you have to make the disk half red and 
half yellow, and you get altogether from 
the disk only half as much energy as you 
would from mixing a whole red disk with 
a whole yellow disk. The result is that 
colors made by rotation of components are 
duller and grayer than they would be by 
simple addition. 

(3) When a beam of light is passed 
through two or more transparent colored 
filters in succession, we have what is known 
as subtractive color mixture. The results 
are quite different from those of additive 
color mixture. In fact, the subtractive 
procedure should not properly be called 
color mixture, although it is a way of get- 
ting new colors from the combinations of 

Two or more filters in combination will 
transmit only those wave lengths common 
to both or all. For example, if a filter 
that transmits only short waves below 550 
millimicrons is placed over one that trans- 
mits only the long waves above 550 milli- 
microns, no light will pass the combina- 
tion, and it is without meaning to talk 
about the color of the combination. It is 
not only complementary filters that cancel 
each other. A red filter may cancel a blue 
because the two filters transmit no common 
wave lengths. On the other hand, a yellow 

and a blue fdter that are foinplemcnlary 
may give a green, even though the yellow 
and blue are complementary. Why!- The 
two filters overlap in transmission. The 
yellow filter lets through wave lengths from 
the red, yellow and green regions. The 
color looks yellow because the stimulus has 
more yellow than red and green and be- 
cause the red and green tend to cancel and 
make a gray which mixes with the yellow. 
The blue fdter lets through green, blue and 
violet light, and looks blue because blue 
predominates. Together the filters let 
through only the green light which is all 
that is common to both of them. .So yel- 
low and blue, which would give gray by 
additive mixture, in this case give green by 
subtractive mixture. The yellow filter sub- 
tracts the blue and violet, and the blue 
filter subtracts the red and yellow. Only 
green is left. 

(4) In the mixture of color pigments, all 
the foregoing factors may be involved. 
Pigments consist of fine particles which 
modify the light falling upon them bv 
selective reflection, by selective transmis- 
sion, by both at once, and by refraction. 
All these effects are modified by the me- 
dium in which the pigments are suspended. 
In addition, one size or type of pigment 
particle has effects on another size or type 
that cannot be anticipated from the mere 
color of either. Therefore, although a par- 
ticular yellow pigment and a particular 
blue pigment ma)' result in a green, other 
pigments, visually identical to the original 
yellow and blue, may mix to give red or, 
perhaps, gray. In all cases the la^\-s of 
color mixture are operative, but otlier fac- 
tors control the selection of available wave 
lengths. For instance, to cliange tlie color 
of a certain yellowish red pigment toward 
bluish red, it may even be necessan,- to add 
white pigment, not blue. 




Within the last twenty years optical in- 
struments have been so developed that a 
relatively simple operation can obtain a 
precise quantitati\e physical measurement 


Curved line shows spectrum: small triangle, mix- 
lures from three spectral colors: large triangle, three 
primaries whose mixture would give all the spectral 
colors; c493.6 (red) is nonspectral and comple- 
mentary to 493.6 (bluish green). 

f)f the spectral components of any light 
source, transmitting medium or reflecting 
surface. Given a spectral distribution 
curve for some color, it is not, however, 
easy to say from the curve just what the 
appearance of the color would be. Color- 
imetry puts the three laws of color mixture 
to work so that any spectral distribution 
can be translated easily into a statement 
of what color the distribution would give. 
(See Fig. 119.) 

Since every component wave length in a 
spectral distribution combines with all the 
rest under one or the other of the first two 
laws of color mixture, and since under 
Law III any resultant is equivalent psycho- 
logically to any other resultant which it 

matches, it is possible to equate the color 
of any spectral distribution to a much 
simpler combination of wave lengths. For 
practical purposes three wave lengths have 
been found to answer most of the needs of 
such a reference system. Obviously the 
wave lengths must be carefully chosen and 
must be such that their normal colors will 
include unique red, yellow, green and blue. 
There are many possibilities, all of which 
will work out satisfactorily. The set must 
include a wave length near each end of the 


Mixture diagram according 

to the 1931 I.C.I, standard 

observer and coordinate system 


The figure shows the spectral colors plotted on 
the standard ICI (International Congress on Illumi- 
nation) coordinates. This plot permits specifica- 
tion of all unique or duplex colors. The yellow in 
this diagram can be specified by x = 0.512, y = 

spectrum and one near the middle. The 
international standard that has been 
adopted specifies wave lengths 700, 546.1 
and 435.8 millimicrons, which give, respec- 

Color Phenomena 


lively, a slightly yellowish red, a yellow 
green and a reddish blue. 

Data have been obtained which stand- 
ardize the amounts of these three stimuli 
(R + G + B) that will match evei-y one of 
the monochromatic spectral stimuli. These 
quantities are known as the tri-stimulus 
values of a color. All colors having the 
same tri-stimulus values, no matter what 
the physical composition of their stimuli 
may be, will look the same. That is l,aw 
III of color mixture. 

A still simpler form of representation has 
been made by taking the proportions of the 
tri-stimulus values, for R, G and B, respec- 
tively, that is, R/{R + G + B), G/(R + G 
+ B), B/{R + G + B). Any two of these 
proportions determine the third and thus 
specify the spectral equivalent of a stimu- 
lus, but not its black-white component. 
The trichromatic coordinates can be plotted 
on a two-dimensional diagiam (Fig. 120). 
Trichromatic colorimetry which has a wide 
field of applications is based upon this 
system of representation. 


We come now to a consideration of the 
more general psychological phenomena of 
the occurrence of color in human experi- 
ence—the laws of adaptation, contrast and 
indirect vision, and the facts of color blind- 
ness and night vision. 


When color stimulation is continued, the 
color changes, at first rapidly and then more 
slowly, tending toward gray. A bright 
light retains its extreme brightness for only 
a brief time. The sun on snow gives a 
blinding glare when we first go out of a 
more dimly lighted building, but the glare 
soon moderates. Similarly, die blackness 

of the dark does not last. The darkened 
theater is hopelessly black when we first 
enter, but when we have been there a half 
hour, the blind behavior of a new arrival 
seems ludicrous. The same thing happens 
to all the other colors. The yellowness of 
artificial illumination, as it is first turned 
on, soon disappears. 

The phenomenon we are describing is 
known as sensory adaptation and is effet- 


Steadily fixate the line between the two fields. 
Notice how the black lightens and the while 

tive for all visual qualities with one ex- 
ception, the ever-constant gray. The law 
of color adaptation may be stated as fol- 
lows: With continued duration all colors 
tend toward gray. Blacks and whites, as 
well as reds, oranges, yellows, greens, blues 
and purples, get grayer when the stimula- 
tion for them continues on the same part 
of the retina. 

Sensory adaptation can be observed and 
described most acctirately if you fixate 
steadily a small patch of color or a parti- 
colored field, to give a basis for compari- 
son. Hang up side by side a sheet of white 
cardboard and a sheet of black caidboard, 
and stare fixedly at some point on their 
line of junction. (See Fig. 121.) Almost 
at once, clotids of gray begin to form over 
the two fields, lightening the black and 
darkening the white. The clouding in- 
creases as fixation continties until both 



halves of the field approach gray. You 
could get the whole particolored field a 
uniform gray if you could but keep your 
eyes still. Instead you find that you keep 
twitching them, losing fixation and then 
regaining it. 


The effects of any visual stimulation 
persist after its removal, and the longer 


Fixate steadily, for about a minute, one of the 
eyes in this negative portrait. Then shift the fixa- 
tion quickly to a blank sheet of white paper, 
^'ou will see a negative afterimage of this negative, 
that is to say, a positive. [.After A. Noll (1926).] 

the original stimulation, the greater and 
more persistent are the after-effects. The 
glare of the sun on the snow will be modi- 
fied to some extent according to the illu- 
mination of the house from which we have 
just come. The theater is darker when we 
enter from a bright day than when the day 
outside is dull and overcast. When colored 
glasses have been worn for a time and then 
removed, everything takes on a color com- 
plementary' to the color of the glasses. If, 
after you have stared at the particolored 
card for a time, someone covers it with a 
uniform screen, the screen appears blackish 
where the card was white and whitish where 

the card was black. (See Fig. 121.) The 
effects are even more striking if other colors 
are substituted for black and white. If 
the color fixated is red, the after-effect will 
be green; if blue, yellow; and vice versa. 
Thus white follows black and black, white; 
red follows green and green, red; yellow 
follows blue and blue, yellow. This phe- 
nomenon is known as the negative after- 
image. The complementary relationship 
of the opposing color pairs of the color 
etjuation appears again. (See Fig. 122.) 

The facts of adaptation and negative 
afterimage show that we are dealing with a 
single process. Adaptation to one color 
means sensitization to its complementary. 
That is what you are seeing when you try 
to fixate the line between the black and 
white fields of Fig. 121. As your eyes 
twitch, the image of a narrow edge of white 
field falls upon the black-adapted, white- 
sensitized part of the retina, and the white 
looks even whiter than it did at first. So 
with the black, when the eyes twitch the 
other way. 

The after-effects of continued color 
stimulation are not, however, limited to 
this complementary or negative afterimage. 
There is also a positive afterimage, so called 
because its color resembles the original 
color although somewhat grayer. A color 
experience does not cease immediately 
when the color stimulus is removed, but 
persists for a measurable time and may, 
after disappearing, reappear again. It is 
the reappearance that is the positive after- 
image. Sometimes the inevitable lag of 
every sensation after its stimulus has ceased 
may be prolonged without an interval into 
the positive afterimage. Positive after- 
images, especially when they occur after 
long adaptation to the dark and short ex- 
posure to a brilliant stimulus can be very 
vivid, showing detail and reproducing all 

Afterimages and Contrast 


the colors. The circle of light produced 
by the revolving pinwhecl in a display of 
fireworks is mostly positive afterimage. 


The quality of a color varies with its 
background. If a red which is unique 
when it occupies the entire visual field is 
restricted in size and surrounded by blue, 
it becomes yellowish. If the surrounding 
color is changed to yellow, the red turns 
bluish. As we have seen, white in the back- 
ground may give an appearance of black, 
and vice versa. A green background makes 
the red redder, and conversely. The only 
background color that does not alter the 
original quality is gray. For this reason, 
when we wish to examine a color accu- 
rately, we always place it upon a gray 
background. Similarly we can study the 
effect of a background best by placing a 
gray strip or patch upon it. The gray be- 
comes tinged with color complementary to 
the background. This effect of back- 
ground upon a color is a third instance of 
the complementariness of colors. (See Fig. 

We may state the general law of contrast 
as follows: Every color in the visual field 
affects and is affected by every otJier color. 

Several secondary laws made specific the 
nature and degree of the effect. (1) The 
quality of the induced color is always that 
of the compleinentary of the inducing 
color. (2) The induction increases with a 
decrease of gray in the inducing color. 
(3) The induction is gi-eatest when there 
are no sharp outlines between the back- 
ground and the induction field. (4) The 
induction is greatest at the margins near 
the inducing field. (5) The induction is 
greatest when the background and the in- 
duction field are in the same plane. (6) 
The inducing effect of red, yellow, blue and 

green is greater wlicii there is no white or 
black contrast. 

Everyday experierue affords iriany ex- 
amples of color induction. Gray stripes 
on a green material will appear a purplish 
red. A bright light in the visual field 
makes everything else d;iik. This is one 


A \diite batkgiouml induces an increment of 
black in a small area of grav placed upon it. and 
vice versa. The grav dots and figures are all identi- 
cal but appear dark on the light background and 
light on the dark backgioinid. 



reason why the lights of an oncoming car 
'blind' you. They cover everything else 
with a black that blots out contours. A 
student of art soon learns that he can color 
some objects by painting only the surround- 
ing objects. A sailboat against a blue sky 
will be tinted with yellow. Color contrast 
contributes to everything we see and must 
be taken into account when we wish to 
specify or control the color of an object. 

A manufacturer once tried to make a 
green and gray gingham. When he wove 
the gray threads among the green, he had 
a green and pink gingham. Undoubtely 
the gingham fulfilled the conditions of the 
secondary laws of contrast. There must 
have been little gray in the green. The 
gray and gieen threads must have been 
equally white or equally black. The 
checks of the gingham must have been 
small, must have appeared to be in the 
same plane and without contours. 

Shadows, when black-white equality is 
seemed, are especially subject to red-yellow- 
green-or-blue contrast effects, because a 
shadow lies exactly in the plane of the sur- 
face on which it is projected and has no 
prominent contours. If yoti stand under 
a red neon light you will notice that your 
shadow is green. 

A piece of gray paper on a field of red 
paper looks greener if the whole field is 
covered with thin white tissue paper. Why? 
Because the tissue paper cuts out perceived 
contours and puts the red and the gray in 
the same plane, as if the gray were a 
shadow. The tissue works against contrast 
because it decreases the relative intensity 
of the red, making it giayer, but die laws 
of contour and of plane are more impor- 
tant and make up for the disadvantage of 
the grayer red. 

Indirect Vision 

The quality of a color varies with its 
position in the visual field. If, as wc 
fixate steadily on a point straight ahead, 
a color stimulus that is not too intensive 
enters the visual field from the side and 
approaches the fixation point, the color 
undergoes a series of changes. In the ex- 
treme periphery it appears gray, light or 
dark according to its whiteness or blackness. 
A little farther in, a blueness or yellowness 
may appear, but not until the stimulus has 
reached a position near the center of the 
field is it reddish or greenish. If the en- 
tire vistial field of each eye is explored in 
this manner, there will be found a fairly 
restricted zone in the center of the field of 
vision where all color qualities can be seen. 
Surrounding this area lies a second zone in 
which no redness or greenness is visible 
but where blueness and yellowness can be 
seen. In the extreme periphery all color 
experience is restricted to blacks, grays 
and whites except with very intensive 
stimuli. In this spatial distribution the 
colors have appeared again in their com- 
plementary pairs. (See Fig. 124.) 

Thus a dark ptirple disk, being moved 
from the outside of the field to the center, 
will appear first black, then blue, then 
purple. A light orange disk will appear 
first white or light gray, then yellow, then 

The boundaries of the color zones in the 
field of vision are not rigidly fixed. The 
more effective the stimulus, the farther 
from the center can the color be seen. The 
zones are larger for a spot of spectral light 
than for a patch of colored paper, because 
the spectral light is less gray. The zones 
are larger for large stimuli than for small. 
You might think that you could see your 
own color zones by looking with one eye at 

Indirect Vision 





Chart shows the portion of the visual field of the right eye within which each of the unique colors 
can be seen when the stimulus is a small patch of homogeneous light. At these intensities red and 
green are limited to an area of approximately 20 degrees about the fixation point, whereas yellow 
and blue can be seen out to 40 or 50 degrees in the vertical and 50 to 60 in the horizontal meridian. 

a large sheet of purple paper which fills 
your entire field of vision. You cannot. 
The large color stimulus is so effective that 
it causes you to see the purple all the way 
to the limits of your field of vision. 

In the course of exploration of the visual 

field of a single eye with a small stimulus 
we find an area of some size where the 
stimulus completely disappears. Known as 
the blind spot, it occurs because tlie eye's 
retina is practically blind where the optic 
nerve enters it. You do not see vour o\m 



blind spot in ordinary vision. For one 
thing, the blind spots in the two eyes do 
not coincide, so notliing is missing in two- 
eyed vision. Still you cannot see your 
blind spot for one eye when you close the 
other. That is because in perception you 
fill in the field with ■\\hate\cr the surroinid- 
ings would make you think belonged there. 
As we have seen before, perception tries 
to keep objects constant. In a neutral 
field, however, with only a fixation point 

counted. In his memoirs Sir John Dalton, 
a noted chemist of the late eighteenth cen- 
tury, gives an excellent account of the dif- 
ficulties into which his own peculiarities 
of vision had led him. His description of 
them gives us a good idea of how the world 
of colors looks to a color-blind person. 

Dalton wrote: "My observations began 
with the solar spectrum, or coloured image 
of the sun, exhibited in a dark room by 
means of a glass prism. ... I see only two 



Close your left eye, hold the book at a distance of about 14 inches in front of you, and fixate the dot 
with the right eye. If you see the face at the right, move the book a little nearer or farther awav. When 
I he right distance is found the face will disappear and the page will appear blank. 

and one other object present, the existence 
of the blind spot can be readily demon- 
strated. (See Fig. 125.) 

Color Blindness 

A certain deviation of color vision ap- 
pears as a special peculiarity. About four 
per cent of the population, nearly all males, 
never experience the color qualities red 
and green. They see only five unique 
colors, blue, yellow, black, white and gray. 
All redness or greenness of normal vision 
appears to them gray, just as they do out- 
side the central zone of the field of vision. 
They do not need a color pyramid to dia- 
gram the colors visible to them. They 
see only what appears in the color square 
for yellow-white-blue-black with gray in the 
center. (See Fig. 108, p. 272.) 

Many curious instances of this deficiency 
have been reported. Attention was first 
called to the defect by Huddart in 1777, 
but the truth of his assertions was dis- 

or at most three distinctions. These I 
should call yellow and blue; or yellow, 
blue, and purple. My yellow compre- 
hends the red, orange, yellow, and green 
of others; and my blue and purple coincide 
with theirs. That part of the image which 
others call red, appears to me little more 
than a shade, or defect of light; after that 
the orange, yellow, and green seem one 
colour, which descends pretty uniformly 
from an intense to a rare yellow, making 
what I should call different shades of yel- 
low. The difference between the green 
part and the blue part is very striking to 
my eye: they seem to be strongly contrasted. 
. . . All crimsons appear to me to consist 
chiefly of dark blue; but many of them seem 
to have a strong tinge of dark brown. I 
have seen specimens of crimson, claret, and 
mud, which were very nearly alike. Crim- 
son has a grave appearance, being the re- 
verse of every shewy and splendid coloirr. 
\Voolen yarn dyed crimson or dark blue 

Color Blindness 


is ilie same to inc. Pink scciiis to be com- 
posed of nine parts of light blue, and one 
of red, or some colour which has no other 
effect than to make the light blue appear 
dull and faded a little. . . . My idea of 
red I obtain from vermilion, minium, .seal- 
ing wax, wafers, a soldier's uniform, etc. 
These seem to have no blue whatever in 
them. . . . Blood appears to me red; but 
it differs much from the articles mentioned 
above. It is inuch more dull, and to me is 
not unlike that colour called bottle-green. 
Stockings spotted with blood or with dirt 
would scarcely be distinguishable. ... I 
take my standard idea [of green] from 
grass. This appears to me very little dif- 
ferent from red. . . . Green and orange 
have much affinity also. . . . Green woolen 
cloth, such as used to cover tables, appears 
to me a dull, dark, brownish red colour. 
. . . When this kind of cloth loses its 
colour, as other people say, and turns yel- 
low, then it appears to me a pleasant 
green." * 

In the same class with Dalton's experi- 
ence is the inability of color-blind persons 
to distinguish ripe red cheiTies from the 
foliage of the tree upon which they hang, 
and red flags of a golf course from green 
turf. We must not, however, confuse a 
lack of accuracy in color naming with the 
true lack of red-and-green color experience. 

Upon careful examination color blind- 
ness has been found to be not a simple all- 
or-none phenomenon. There are varying 
degrees and kinds of deficiency in color 
vision. A few, no more than one hundred 
cases, have been reported in which the only 
colors seen are black, gray and white. For 

* John Dalton. Extraordinary Facts relating to 
the Vision of Colours: with observations. Read 
Oct. 31st, 1794. Memoirs of the Literary and 
Philosophical Society of Manchester, 1798, 5, Part 
1, pp. 31-35. 

tlicm (<)\()r vision is reduced to something 
like the extreme peripheral vision of a 
normal observer. Most color deficiencies, 
however, involve only red and green. 

A further complication is that red-green 
color blindness is of two different types. 
Most color-blind persons see gray in place 
of both red and green with the relative 
brightnesses of the spectral colors un- 
changed. Such persons have been called 
deuteranopes. A few color-deficient pei- 
sons have color vision further complicated 
by a shift of relative brightness away from 
the long wave lengths toward the short 
wave lengths, so that in place of red they 
see black and in place of green they see a 
whitish gray. Such persons have been 
called protanopes. The names are derived 
from the fact that protanopic vision is sup- 
posed to be more primitive than deuter- 
anopic, just as all red-green color blind- 
ness is supposed to be a more primiti\e— 
evolutionarily older— kind of vision than 
normal vision. 

Between deficiencies in which all sensi- 
tivity to green and red is lacking and cases 
of normal sensitivity, lie manv degrees of 
color weakness. It appears, moreover, from 
recent measurements that red-green defi- 
ciency is accompanied by a loss in blue- 
yellow sensitivity. The color blind suffer 
an overall loss. They do not compensate 
for the loss of one pair of complementaries 
by increased sensitivity for another pair. 

In spite of their deficiency, color-blind 
persons name colors correctly more often 
than not. There is sufficient difference be- 
tween other colors and the didl dark yellow 
which they see for red, or the light yellow- 
ish gray that green appears to be. for them 
correctly to identify objects designated by 
those color names. It is undoubtedly for 
this reason that color deficiency is so re- 
cent a discovery. In our complex civiliza 



lion of today, color discrimination has in- 
creased in importance so that color defi- 
ciency is a disadvantage, often a menace, 
in numerous occupations (for instance, at 
sea or in transportation where colored sig- 
nals are used). Hence many tests have 
been devised for its detection. Identifica- 
tion of color samples or matching and sort- 
ing can be used to bring out color anom- 
alies. Accuracy of results depends on the 
care with which the color samples are pre- 
pared. In an early test devised by Holm- 
gren, the subjects were asked to find among 
a Aariety of skeins of yarn samples similar 
to three standards. From the errors ex- 
hibited, a color-blind subject should be de- 
lected, were it not for the fact that many 
such people learned to correct their errors 
and so appeared to pass the test. Matching 
tests, with carefully graded series of color 
(hips, work better and can be used to meas- 
ure the degree of the defect. 

In inany ways the most interesting type 
of test is one in which patterns are made 
up of two colors which appear identical 
to a color-blind person but are quite differ- 
ent to nomial vision, such as orange and 
yellow-green or blue-green and lavender. 
A number is oiulined in dots of one color 
on a background of the other color. The 
color-blind subject is unable to make out 
such a concealed pattern. Still other tests 
present small areas of filtered light for rec- 
ognition and diagnose color deficiency on 
llie basis of confusions of 'white' light 
with 'green,' or 'yellow' with 'red,' or 'red' 
with 'green.' With properly chosen filters 
this test can be very accurate. 

Night Vision 

Vision in the ordinary ranges of daylight 
from fairly faint twilight up to the bright- 
est blaze of the stm is called daylight insion 
or photopic vision. Nearly all the facts de- 

scribed thus far in this chapter are facts of 
daylight vision. Vision from the point 
where twilight falls down to what you see 
in the coimtry on a moonless night when 
the clouds obsctue some of the stars (you 
do not see objects unless you have been 
some time in the dark) is night vision or 
scotopic vision. In twilight, daylight vi- 
sion and night vision overlap; both func- 
tion together. The next section shows 
that we believe that there are in the retina 
two kinds of receptors for these two kinds 
of vision: cones for daylight seeing, rods 
for night seeing. That theory gives us still 
another set of names for the same differ- 
ence: cone vision and rod vision. 

What happens when the energy of the 
general illumination is gradually dimin- 
ished from a level necessary for good day- 
light vision to the level at which night 
\ision is working alone? You can see the 
answer for yourself if you watch the light 
fade on a variegated field of color samples. 
You can make the obser\ation during a 
couple of hours at twilight or you can 
hurry the process up by arranging very 
gradually to shut the door of a room 
which will be pitch dark when the door 
is completely closed. At first, as the light 
fails, the colors remain the same in respect 
of the red-yellow-green-blue series, though 
they become somewhat blacker and grayer. 
Then at a partictilar point the reds begin 
to darken considerably and the greens and 
blues to lighten. This change is called 
the Purkinje phenomenon, after the physi- 
ologist who discovered it in 1825. Red 
finally turns to black while green and blue 
become a silvery light gray. Thus in com- 
plete night vision all colors reduce to 
shades of black, gray and white. As adap- 
tation goes on, the blacks disappear, leav- 
ing onlv grays and whites, which have the 
bluish cast that is taken for granted as a 

Night Vision 


rharacteristic: of inof)nliffht. Tims in mo- 
lion pictures, almost any scene <an i)e con- 
verted into 'moonlif^Iil' simjjly by dyeing 
the whole film fjlue withoiii icducing the 
intensity of tiie illuminalion. 

We can, therefore, in tiiis continuous 
process, distinguisli two stages. In the 
Purkinje phenomenon daylight and night 
vision act together. We can still see reds, 
yellows, greens, blues and violets, but the 
reds are very dark, and the IjIucs and vio- 
lets very light. In complete night vision 
the reds have become black, the blues and 
violets light bluish gray, and the yellow- 
greens bluish white. After long-continued 
night vision, most of the blacks disappear 
under adaptation, since there is nothing 
darker than a lightless region for the night 
eye to see as black. (See Fig. 126.) 

Full sensitivity of night vision is not at- 
tained at once, if illumination suddenly 
drops to a low level. It develops grad- 
ually at a decreasing rate over a period of 
half an hour to an hour. In that time 
your ability to discriminate small intensi- 
ties of light increases by at least ten thou- 
sand times. Thus dark adaptation means 
not only that the blacks have become gray, 
but also that sensitivity has increased enor- 
mously. In the Second World War the 
psychology of night vision became sud- 
denly important, because all at once there 
was need for men to see in the dark. In 
peacetime the way to see in the dark is 
to turn on the light. In war you dare not— 
not if you are a night fighter or a naval 
lookout or an infantry patrol on duty at 
night. Such men stayed in the dark half 
an hour before they went on night duty 
so that their night vision might be maxi- 
mally sensitive after thorough dark adap- 
tation. Or else before duty they Avore red 
goggles, the kind of red goggles that let 
through only the very long wave lengths. 







' \ 



; \ 






















Fn this way they kept the rods in their 
retinas sensitive, because red light docs not 
affect the rods or <ause tfiein to becoim; 
dcscnsiti/ed. (That is why red looks bla<k 
in rod vision.) 

A third characteristic of night vision is 
that objects become more difficult to see 
when they arc lookerl at directly. That is 
[)e(aiise the very center of the retina is 
blind at night; there are no rods there. 




I 0.6 

I 0.2 


700 650 600 550 500 450 400 

Wave length (m/i) 


The solid curve is the sensitivity curve for d;iv- 
light vision, and the dashed curve is for night 
\ision. The curves show relative sensitivity, and 
hence brightness, in different parts of the spectnnn 
\\hen the light at all wave lengths is of equal 
energy. In daylight vision hues are seen at the 
various ^\ave lengths. In night vision only grays of 
different whitenesses are seen. 

You can demonstrate this fact bv setting 
in a dark room a source of light Avhich is 
completely covered except for two pin- 
holes a few centimeters apart. Try to fix- 
ate, from a distance of three or foiu" yards, 
one of the pinholes. The light ^vhich is 
fixated "ivill disappear -^vhile the other 
shows up fairly clearly. A shift of fixation 
from one pinhole to the odier Avill make 
the hole at which you look invisible and 
the hole at which you do not look directly 
visible. "With fixation else^vhere in die 
field, both points are visible. Small weak 
stimuli cannot be seen at all in the center 



of the field of vision where, in good hght, 
details arc seen best. The region in the 
center of the retina is called the fox>ea. 
One of the characteristics of night vision 
is foveal blindness. 

In summary we may note that niglit vi- 
sion differs from daylight vision in four 
ways. (1) All color qualities, except black, 
gray and white, disappear. (2) The grays 
and whites that remain are slightly tinged 
with blue. (3) The whitest colors at night 
occur for color stimuli which at normal in- 
tensities give yellow-green. (4) The fovea, 
at the center of the field of vision and the 
spot which is most competent in daylight, 
is blind at night. 


The eye is a simple form of photographic 
camera consisting essentially of a dark 
(liamber with a lens at the front and a 
.'.cnsitive film (retina) at the back. (See 
Fig. 127.) In front of the lens is a dia- 




Optic nerve 


This figure represents a cross-section of the right 
eye, as viewed from aljove. [.\fter L. T. Troland, 
The principles of psychophysiology, 1930, II, p. 98; 
bv permission of D. \'an Nostrand Company.] 

phragm (pupil) and a shutter (eyelid). The 
dark box is approximately spherical and is 
kept in shape by the liquid with which it is 
filled. The lens is a relatively thick trans- 
parent capsule filled with a liquid whose 
refractive power is different from that of 
the liquid in the dark chamber. The 
focus of the lens is altered by the ciliary 
muscle, a circular muscle attached to its 
edge, which stretches and flattens it or al- 
lows it to bulge, according to the distance 
of the object viewed. The precise nature 
of the sensitive membrane, the retina, 
which lies at the back of the dark chamber 
has been studied by physiologists and psy- 
chologists who are interested in the func- 
tioning of the eye. 

Microscopic examination of the retina 
shows that it is made up primarily of nerve 
cells and their special endings. The latter 
are of two types. One, the rod, is cylindri- 
cal in form and ends in a nerve fiber with a 
cell body somewhat removed from the base 
of the rod. The other, the cone, is shorter 
and thicker and somewhat conical in shape, 
and the nerve-cell body is incorporated in 
its base. The nerve fibers, which thus have 
their origins in the rods and cones, end 
within the retina in synaptic connections 
to another set of nerve cells, the bipolar 
cells, which in turn connect with a third 
group of gayiglion cells with long fibers 
which join to form the optic nerve and 
run back to the nuclei in the brain and 
thence to the cortex. (See Fig. 128.) 

The latest microscopic examinations 
show the neural connections at the retina 
to be very complex. A single cone is con- 
nected to several bipolar cells and by way 
of them to as many as half a dozen ganglion 
cells whose fibers form the optic nerve. 
Some bipolar cells are connected to both 
rods and cones and all of them run to two 

Physiology of Color Vision 



- — I 


The numbers on the left indicate different la)ers of the retina. The arrows indicate the direction in 
which the nerve impulse travels. The rods (a) and cones (h) transmit their excitations through the vari- 
ous kinds of bipolar cells (d, e, f, h, i), sometimes across the retina through horizontal cells {c, I), to the 
ganglion cells (m, n, s, p, o), and on through the optic nerve (lavers 9, 10) to the optic nuclei and the 
visual cortex. [From S. L. Polyak, The retina, Chicago: University of Chicago Press, 1941.1 

or more ganglion cells. In addition there 
are horizontal cells that connect one cone 
with another and with near-by rods, and 
others that make horizontal connections 
among the bipolar and ganglion cells. 
Finally, there are several different types 
of connections between the various cells. 

It is believed that all this complication is 
significant in the functioning of die retina, 
not just a matter of accident. After all. 
in inany phenomena the retina is kno^^^^ 
to act as a whole and not in isolated parts. 
\W& can, for example, see pinple at the 
periphery of the retina provided die same 



kind of sliinulalion affeds all the reniain- 
der of the retina. 

Active sensory ner\cs have been found 
to exhibit electrical phenomena in the 
form of changes in electrical potential 
which give rise to action currents. In re- 
cent experiments action currents have been 
recorded from retinal elements in response 
to light stitnuli. From them it appears 
that some retinal elements— rods or cones 
or both— respond to all ranges of light 
stimuli. Other retinal elements, however, 
respond to only limited light-wave ranges. 
Response to blue has been definitely iso- 
lated and possibly the responses to green 
and to red. 

Since the cells which give rise to the 
optic fibers lie in the innermost layer of 
the retina, the fibers, in order to leave the 
eye, must pass back through the retina. 
All the fibers come together as they leave 
the eye, producing a gap in the retina. At 
the corresponding area in the field of \ision 
there is but little sensitivity, and that 
is the region which is called the blind spot. 
Since the optic nerve leaves the eye about 
three millimeters to the nasal side of the 
center of the eye, the blind spot lies to the 
temporal or outer side of the field of vision 
of each eye. 

The diameter of the retinal blind spot is 
about two millimeters. Such an area on 
the retina subtends an angle of about six 
degrees in the visual field. 

Duplexity of Retinal Function 

An adecjuate account of the way a sense 
organ functions consists in a careful cor- 
relation of the physiological and physical 
facts, on the one hand, with the parallel 
psychological data, on the other. Usually 
not all the necessary facts in both fields are 
available, and the psychologist must at- 
tempt to put together the available facts 

in such a way as to bridge the gaps in 
knowledge. Some of the resulting psycho- 
physiological correlations are quite firmly 
established. Others are tentative. One of 
the best-established correlations is the prin- 
ciple that the retinal rods are the organs 
of night vision and the retinal cones the 
organs of daylight vision. Let us sum- 
marize the facts by which this correlation 
is established. 

Vision is of two kinds. (1) First there 
is full color vision as represented by the 
color equation, (a) Such vision is maxi- 
mal at the center of the field of vision in 
the region surroimding the point of fixa- 
tion, (b) It diminishes in regions away 
from the central zone, losing first the red- 
green member of the equation and then 
the yellow-blue member in regions that 
approach the periphery, (c) Color vision 
requires the relatively greater stimulus 
energy of daylight vision. If the energy 
of the stimulus falls below a certain level, 
color vision disappears. 

(2) Second, there is vision that consists 
(a) only of black, gray and white (modified 
by bluishness). [b) Such vision is com- 
pletely lacking in the center of the field of 
vision and improves progressively toward 
the periphery, (r) It requires a relatively 
low level of stimulus intensity, the maxi- 
mum being slightly above the minimum 
level for color vision. In some cases, there- 
fore, the two visions overlap, and we can 
then observe that various stimuli do not 
have the same effectiveness in both kinds 
of vision, (d) Red stimuli have no effect 
in low-level vision, whereas green and blue 
are relatively more effective than they are 
in color vision. Moreover, (e) low-level 
vision is not turned on immediately as 
color vision is turned off, but requires a 
considerable time to appear, during which 
dark adaptation takes place. 

Duplexify of Vision 


Now, oil I lie physiological side, wc have 
lound, firsl, tliat llic retina contains two 
distinctive tyjjcs ol nerve endings, and, 
second, that tliesc two endings have sig- 
nificant dislribiitions over the surface of 
the retina. Cones arc closely packed in 
the fovea of the retina and thin out toward 
the periphery. Rods are (ompletely absent 
from the fovea and increase in number, 
both absolutely and relative to the number 
of cones, toward tlie periphery. 

Putting these two sets of facts together 
gives us what can be called the duplexity 
theoiy, the generalization that the cones are 
the organs of daylight or color vision and 
that the rods are the organs of night vision. 

Further physiological facts are known 
about the rods, facts which fit in with psy- 
chological facts and tend to confirm the 
duplexity theory. A substance known as 
visual purple is found around the ends of 
the rods. Its chemical formula has been 
determined and many of its properties re- 
corded. It is a highly unstable compound, 
related to vitamin A. It quickly decom- 
poses in the presence of light and recom- 
bines in darkness, when the proper sub- 
stances are present. The ideal conditions 
for the formation of visual purple occur in 
the retina in total darkness, where its in- 
crease will continue for a considerable 
period of time. We can conclude, there- 
fore, that the visual purple of the retina 
acts as a sensitizer for the rods. In its ab- 
sence they fail to respond. After a large 
accumulation of it has been built up, the 
sensitivity of the rods is ten thousand times 
that of the cones in daylight. The rate of 
the accumulation of visual purple within 
the natural conditions of the retina in 
darkness parallels the progress of dark 
adaptation. Since the visual purple ab- 
sorbs yellow and green light, it responds 
more vigorously to those wave lengths. 

Correspondingly, yellow-green wave Iciigtlis 
are seen in night vision as whiter than 
other wave lengths, whereas red wave 
lengths give no white; at all and are seen 
as very dark or as black. Sudi a psycho- 
physiological correlation affords an accept- 
able theory of night vision in terms of rod 

By eliminalion, then, (olor vision is 
ascribed to the cones of the retina, fjut 
physiological facts concerning their func- 
tioning are insufficient to afford a detailed 
correlation. It has been suppcjsed that 
various cones may contain differently se- 
lective photochemicals, but no such sub- 
stances have been isolated from the retinal 
tissue. Another hypothesis supposes that 
the various connecting cells respond dif- 
ferently to give qualitative differences in 
color. We have noted that one iinestiga- 
tion has found that the electrical discharges 
from various retinal elements indicate that 
some elements respond to all light waves 
whereas others are more selective. This 
finding may mean that the early theorists 
were right in ascribing the differentiations 
among colors to the retina, but there is 
other evidence that the nerve impulses are 
not completely differentiated until they 
reach the brain. An acceptable psycho- 
physiological theory of color vision still 
waits upon future discovery. 


1. Bartley, S. H. lision. New York: \an Nos- 
trand, 1941. 

The psychophysics and psychophysiolog^" of 
most of the phenomena of visual sensation and 
perception except the correlates of wave length. 

2. Graham. C. H. \'ision: some neural correla 
lions. In -C. Murchison (Ed.1. A handbook of 
i^eueral experimental psxclwlogy. 'Worcesier, 
Mass.: Clark University Press, 193 1. Cliap. 15. 



A technical handbook account of the neural 
mechanisms involved in visual perception. 

3. Hecht. S. \'ision: the nature of the photo- 
receptor process. In C. Murchison (Ed.), A 
handbook of general experimental psychology. 
Worcester, Mass.: Clark University Press, 1934. 
Chap. 14. 

A rather technical presentation of the physi- 
ological data which form the basis for theories 
of the neural reception of light. 

4. Ladd-Franklin, C. Colour and colour theories. 
New York: Harcourt, Brace, 1929. 

Reprints of a score of the author's more im- 
portant papers on color theory and the argu- 
ment which supports her genetic theory of 

5. Parsons. }. H. .In introduction to the study 
of colour vision. (■2nd ed.) Cambridge, Eng- 
land: Cambridge University Press, 1924. 

The most complete handbook which reports 
the basic investigations on color up to 1924, 
but now out of date. 

6. Troland, L. T. Vision: visual phenomena and 
their stimulus correlations. In C. Murchison 
(Ed.), A handbook of general experimental 

psychology. Worcester, Mass.: Clark University 
Press, 1934. Chap. 13. 

An excellent and precise summary of the 
psychophysical relation of visual phenomena to 
visual stimulation. 

7. Troland, L. T. The principles of psycho- 
physiology. New York: Van Nostrand, 1930. 
Vol. II, Chap. 14. 

A full discussion of the psychophysical rela- 
tions of visual phenomena to visual stimula- 
tion, somewhat more complete than the preced- 
ing item. 



Visual Space Perception 

THE human organism lives in three-di- 
mensional space, orients itself in it, re- 
acts to stimulus objects in it and is fully 
aware of it in all its tridimensionality. It 
has equipment for perceiving space, equip- 
ment with which heredity provides it— eyes 
with retinas on which a two-dimensional 
image of the visual field can be focused, eyes 
which can do the focusing, which can con- 
verge more or less toward each other, 
which, being separate, get dissimilar views 
of the world, which move in the head, thus 
changing the visual field. It has a head to 
hold the eyes and to move them around. 
It has also mobile arms and hands to ex- 
plore the immediate universe and to re- 
spond within this universe to visual stimvi- 
lation, as well as a mobile body to explore 
the more remote world and to make more 
responses to stimulation. This equipment 
the organism uses during its early lifetime 
to build tip its knowledge and awareness 
of tridimensional space, to learn how to re- 
act with discrimination to objects in a 
three-way visual field. The retinas could 
not do this job alone. They depend on 
movements of the eyes to make images 
clear and to gauge distance, and on move- 

ments of the body and limbs to give spa- 
tial meaning to the core of the visual per- 
ception, a core which in itself consists only 
of a bidimensional pattern of colors. We 
have already seen how a man can learn 
to react properly in a three-dimensional 
world after he has become accustomed to 
wearing special glasses which turn his 
retinal images upside down and right for 
left (p. 242). That experiment showed how 
definitely the 'visual' perception of space 
depends on motor reactions to make it 
meaningful. For instance, a visually per- 
ceived object is localized in space when 
you know where to reach for it. If \ou 
reach up to get something off the floor sim- 
ply because you think the floor is above 
you (as you may if you have just put on 
these special glasses), you must learn some- 
thing before you know your 'visual' space. 
The most siuprising fact about %-isual 
space perception is that, with bidimen- 
sional retinas, we see tridimensional space. 
How do we do this? ^Vhere does the third 
dimension come from? At the retina the 
organism has stirrendered one of the three 
dimensions of space, for only up-down and 
right-left are directly represented in the 

This chapter was prepared by Forrest L. Dimmick of the U. S. Naval Medical Research 
Laboratory at New London. 

The opinions or assertions contained in this cliapter are the private ones of die collabo- 
rator and the editors and are not to be construed as official or reflecting the views of the 
Navy Department or the Naval Service at large. 



Visual Space Perception 

retinal image. Yet in visual perception it 
has got back again the lost dimension. It 
sees solid objects in tridimensional space. 
How it has contrived to do that is the topic 
of the first section of this chapter. 


You can think of the perceiving organ- 
ism as instantly knowing how to build up 

projected retinal image, the clues to depth 
and solidity that you can see with one eye 
or in a photograph. 

Implicit Clues 

There are half a dozen of these implicit 
clues to tridimensionality which merit spe- 
cial mention. 

(1) Interposition. If one object partially 
obscines another, it is perceived as nearer. 
The instantaneous operation of this clue. 


its picture of the stimulus world from clues 
which the senses furnish it. The organism 
is an instantaneous detective in these per- 
ceptual matters. It does not reason its per- 
ceptions out and sometimes it makes 
'errors.' A standard habitual error we call 
an illusion. Nevertheless the organism 
does well with its clues. It has to have 
some basis for discriminative reaction and 
for accurate knowledge, and psychology's 
business is to determine the character of 
these clues upon which the organism acts. 
The stimulation clues for up-down and 
right-left perception lie, obviously, in the 
slinuilation pattern itself. The clues to 
adequate knowledge of the third dimen- 
sion are less direct. Some of them come 
from eye movements and some from the 
disparity of images in the two eyes, due to 
I heir spatial separation; but the simplest 
are tlie dues implicit in the pattern of the 

acting by itself, is evident in simple line 
drawings like the one in Fig. 129. Its ef- 
fectiveness is increased when the images 
represent familiar objects. 

^^"^^ ' ^-i-'T 









(2) Size and linear perspective. The 
larger representation of an object appears 
nearer than a small one. Linear persjjec- 
tive consists in grading the sizes of a num- 
ber of objects to represent their varying 
distances (Fig. 130). When objects do not 

clues to the Third Dimension 


lollow lliis iti)pli<it incliciitioii ol distance, ()|)|josiu- (lii(( lion. /\s \oii i iric in a liain, 

dislorlioiis ol si/.c or ol dislaiuc result. iIk hir hills move with you; llie near feruc 

(3) Aerial pnspecline. Objcits with posts snap hackvvaids, so wliat moves willi 

sharp outlines are perceived as nearer than you is (ar. I hat is the tlue. 

ihosc that are indistiiK t or ha/y. In actual (fi) I'ixalioii. Fixated ohjccts lend to 

scenes, ohjeds vary in perceived distance appear nearer than ohjecis not lixaled, 

as (he changing clarily ol the atmosphere hut olhei im|jlicit clues, like peispective, 


alters their sharpness of outline (Fig. l.Hl). 
On the stage, depth is increased by inter- 
posing layers of netting. 

(4) Light and shade. Light is taken im- 
plicitly as coming from above. Thus high- 
lights on convex surfaces are near the top, 
shadows below. Concave areas show the 
reverse. In a photograph with strong 
modeling the protuberances and indenta- 
tions can be reversed by inverting the pho- 
tograph (Fig. 132). 

(5) Movement. Far objects appear to 
move in the same direction as the observer 
when he moves; near objects move in the 

often conflict with the clue from fixation. 
It is thought that fixation is a clue because 
aerial perspective is. The fixated object is 
clear, other objects are blurred. 

These clues are deeply ingrained in per- 
ceptions, having long histories in the ex- 
perience of an organism. They are suffi- 
cient of themselves to give an adequate ap- 
prehension of nearness or farness of objects, 
or to lead to proper responses to the dis- 
tances of objects. Soliditv. as perceived in 
pictorial art, is dependent upon the manip- 
ulation of such clues. The clues are so 
fully adequate that most persons have no 


Visual Space Perception 

difficulty in seeing moving pictures in three 
dimensions, though the presentation is 
only shadows on a flat surface. Moving 
pictures have much more depth than still 
pictures because they move. The relative 
movement of objects in the picture gives 
it great depth, which can be achieved in 


■: -iS^.:„ ' '^i^H 

';.■■ ■ LIHIfite: .. 



The dents in the monitor's turret appear as dents 
if the light seems to come from above, and turn 
into bulges if this page is turned upside down, 
provided the light still seems to come from above. 
If the light can be imagined as streaming up from 
below, the dents tmn into bulges without inverting 
the page. [Reprinted bv permission of C. H. Stoel- 
ting. Chicago.] 

Still scenes by moving the movie camera 
while taking the picture. 

Motor Context 

Accurate vision involves constant motor 
adjustment of the eyes to the distances of 
the stimulating objects. Though only a 
single visual field is seen, the two eyes 
must be aimed coordinately in the right 
direction. This adjustment requires a pat- 
tern of muscular contractions anci tensions 
characteristic of every distance. It is gen- 
erally believed that these contractions and 
tensions give rise to proprioceptive clues 

to the distance of a fixated object. The 
clues could come from the convergence of 
the two eyes upon the object— con\ergence 
—or from the focusing of a single eye upon 
the object— accommodation. 

Convergence. When the two eyes look 
at a distant object, their lines of vision are 
]:)arallel and the muscles that move them 
are relatively relaxed. When the object 
moves in nearer than fifty to sixty feet in 
front of the observer, his eyes must be 
pulled out of their parallel position so that 
the lines of vision converge and intersect. 
A new pattern of muscular pulls is rc- 
cjuired, which may provide a propriocep- 
tive clue for the perception of that dis- 
tance. Certainly the clue is there. The 
only doubt is whether the observer actually 
has the proprioception to make the clue 
available to him. He is not directly con- 
scious by somesthetic sensation of the con- 
vergence of his eyes, but not all proprio- 
ception is somesthesis. Some is effective 
without becoming conscious. (See Fig. 



In (a) the lines of sight are directed toward the 
horizon. In (b) they are converged upon a near ob- 

Accommodation. In fixating an object 
the lens in each eye must accommodate its 
focus to produce a clear image of the ob- 
ject on the retina, and this movement, if 
it gives rise to proprioception, would fur- 
nish a further clue to distance. (See Fig 

Convergence, Accommoc/afion and Retinal Disparify 


Normally actoiiiiiiodalion ami conver- 
gence work together to jjroduce sharp 
images on the corresponding jjarts of the 
two retinas. When they do not cooperate, 
vision is impaired but can be restored by 
correcting either factor. If, for a given 
distance, the eyes converge too near for tlie 
correct focus, or focus too near for the cor- 
rect convergence, the insertion of lenses to 
correct the focus or prisms to bend the lines 
of vision to the proper angle will correct 
the visual defect. 

Accommodation appears to contribute- 
less than convergence to the perception of 
distance. When convergence is partially 
removed by closing one eye, it becomes dif- 
ficult to judge accurately, by accommoda- 
tion alone, the distances of near objects and 
impossible for objects more than six feet 
away. One-eyed people must depend upon 
the implicit clues to a much larger degree 
than those with two eyes and are greatly 
handicapped when these clues are lacking. 
For this reason, monocular vision is not 
considered adequate for airplane pilots, 
and even pilots with binocular vision must 
be carefully tested for ability to judge dis- 
tance accurately when the only available 
clues are accommodation and convergence. 

As we liave already noted, it is character- 
istic of an organism that its motor re- 
sponses become stereotyped with repetition 
and that an habitual action gives meaning 
to the object or situation which touched it 
off. Accommodation and convergence are 
no exceptions to this rule. Most of the 
time our eyes aim and focus themselves 
automatically, making our perception of 
distance immediate and implicit. The first 
responses that make the perception a mean- 
ingful whole are these focusings and con- 
vergences. After them come the other re- 
actions to complete the sense. I want my 
pen. Vaguely I see it lying on the desk in 

fiont (jf me. At once and automatically 
my eyes fixate it, focus on it, converge on 
it. Tlien I verify my perception of loca- 
tion, for I reach out and take it, my hand 
finding tfie pen at cjnce. All that seems scj 
easy and natural, and yet it is part of the 
learned structure of perception. If I had 
newly put on those special reversing spec- 
tacles, the perception would start cjff in 
the familiar way, but presently my hand 
would be "rc;ninii vainly for the pen bc- 

(o) (6) 


In (a), with the lens more convex, the images are 
in focus on the retina. In (b) the focus lies behind 
the retina so that the images intercepted fjv the 
retina are out of focus. 

cause the visual clues set off the wrong 
reaching behavior. 

Retinal Disparity 

The fact that the eyes are set some 2i.', 
inches apart means that the two retinal 
pictures of an object are never identical. 
Only the point fixated and a fe^\- others will 
be projected upon identical points on die 
retinas. Everywhere else the two eyes, 
viewing the scene from different positions 
at different angles, get somewhat different 
vie^vs. This difference in the geometrv' of 
seeing is called binocular parallax, and the 
resultant difference in the two retinal 
images is called retinal disparity. Most of 
the pattern that falls on your retinas at 
any one time you 'ought' to see doubled, 
because corresponding lines in the pattern 
do not fall on corresponding lines in your 
retinas. But you do not. These doubled 
images do not remain distinct and dispar- 
ate for perception. Instead, thev integrate 


Visual Space Perception 

into, and arc perceived as, solid or tridi- 
mensional. ^Vithin limits the greater dis- 
parity gives the greater depth or solidity. 
Here, if ever, you have a rase of the ef- 
fective operation of unconscious clues. The 
disparity can be of two kinds. (See Fig. 


111 (fl) the double images of A^, a point nearer 
than the point of fixation, X, are seen at NR and 
NL. In (b) the double images of F, a point farther 
away than X, are seen at FR and FL. 

135.) If you look at a tree, X, in the mid- 
dle of a grove, a nearer tree, N, will have 
disparity in one direction, but a far tree, 
F, will have the disparity reversed. The 
clues to distance depend on which eye sees 
which image. You yourself are, however, 
wholly unconscious of what it is that you 
see with one eye and what with the other. 
(You can figure it out by closing one eye 
and seeing what is left in the scene, and 
then trying out the other eye, but that is 
an elaborate inference, not the inference 
of immediate automatic perception.) Yet 
the clues woik, even if you are not im- 
mediately aware of them, lliey enable 
yoin- brain, without your knowing how it 
works, to 'decide' what is near and what 
far, and to build up space perception in 
accordance with what actually exists in the 
stimulus world outside. That is how two 
bidimensional retinas, working together, 
can between them get back the third di- 
mension which thev seemed to have lost. 


While the best depth perception is ob- 
tained by the cooperation of all three of 
the factors we have just discussed, the two 
proprioceptive factors can be eliminated 
and an excellently deep and solid percep- 
tion obtained merely from two fiat dis- 
parate pictures, presented each to its ap- 
propriate eye. This is accomplisheci by a 
device known as a stereoscope. Two pho- 
tographs (stereograms) are taken at a cer- 
tain distance apart and are then presented 
so that the right eye sees only the right 
picture and the left eye only the left pic- 
ture. The two views are then integrated 
by the brain into a single perception that 
is solid or tridimensional. 

Figure 136 shows how a hollow truncated 
cone looks to each eye when the cone is 

Small end protruding 

Small end receding 

Left eye Right eye 

view view 


Left eye Right eye 

view view 



The small circles represent the small end of a 
hollow truncated cone, the large circles the large 
end, the straight lines the sides. In (n) are shown 
the views for each eye when the small end of 
the cone Is near the observer; in (b) the views 
for the two eyes when the large end of the 
cone is near the observer. The retinal disparity 
for (h) would be the reverse of that for (a). It is 
also proper to regard (a) and (b) as two pairs of 
stereograms which, being reversed, would give op- 
posite depths in perception. 

held near the face and binocular parallax 
is great. If these two drawings, each of a 
pair of images, are used as a stereogram 
in a stereoscope, you see down into a hol- 
low cone for the disparity shown at the 
left of the figure, and you see a convex 



(oiic lapered toward you for the disparity 
at the right. Figure 137 shows how binoc- 
ular parallax gives retinal disparity. The 
two eyes look at the cube A, and the left 
eye sees the image li while the right eye 
sees the image C. The dotted lines show 

D a 



./ shows how binocular paralle,\ gives to each eye 
a different image of a cube. B and C show what 
I he linages in the two eyes are like. [From E. G. 
Boring (Ed.), Psychology for the armed services. In- 
fantry Journal, 1945, p. 41.] 

why the views that the two eyes get are 

If desired, solidity can be exaggerated in 
stereoscopic vision. You will perceive an 
exaggerated depth if the two photographs 
are taken at a distance apart which is 
greater than the distance between the two 
eyes (21^ inches). Separating the cameras 
^v'hich make the picttires by more than 2% 
inches exaggerates the binocular parallax, 
and thus the retinal disparity, and thus 
the perceived depth. In fact this method can 
be used to reveal small differences in tlie 
distances of objects whicli are both miles 
away. It is then called telestereoscopy. In 
war, to find out which airplanes are flat 
dummies and which are solid and real, 
camouficurs in airplanes at great altitudes 

take telestereoscopic pictures of the ground 
in order to distinguish the heights of 
(ainouflaged objects on the ground. 

The stereoscope, by means of which the 
stereograms are observed, uses either a 
pair of lenses (as in Fig. 138) or a pair of 
mirrors to bend the lines of vision of the 
two eyes so that the two stereograms tan 
be shown individually to the proper eyes 
while they are converged normally at a 
point some convenient distance in front. 
Naturally, if the stereograms are re\ersed 
so that the left eye sees what was the right 
pictine, and vice versa, a pseudoscopir ef- 
fect will be produced; near things look far 
away and far things near, providing the 
implicit clues are not too dominant. If 
they are, the result is usually confused or 
flat. By reversing the stereograms, \ou 
can make the outside of a teacup look like 
an inside, you can make a tennis ball look 
like a cup, you may even make the face o( 


The double stereogram goes in the card hoKler. 
Each eye sees but one drawing or photograph. The 
lenses allow the eyes to converge so that the two 
images combine. 

a plaster bust look like a death mask, but 
you cannot turn a liimian mobile face con- 
cave. There the implicit clues are too 
strong for pseudoscopy to work. 

You can get this same reversal of the 
third dimension by looking at objects 


Visual Space Perception 

through a system of lenses called a pseudo- 
scope, which re\erscs the images to the two 


The most obvious determinant of vis- 
ually perceived size is, of course, the size 
of the retinal image, which stands in a 
fixed relation to the size and distance of the 
object. It is customary to state this rela- 
tion in terms of visual angle. (See Fig. 91, 
p. 232.) To maintain a constant visual 
angle, and thus constant size of retinal 
image, the size (width, diameter) of ob- 
jects must vary directly as the distance of 
the objects from the e)e. With an object 
of constant size, the size of the visual angle 
varies inversely as the distance of the ob- 
ject. Thus, from a knowledge of the physi- 
cal size of an object and of its distance 
from the eye, we can calculate the approxi- 
mate size of the image which it produces 
on the retina; and, on the basis of this rule, 
-^ve can predict how large the object ought 
to look at any given distance if its size 
were determined solely by visual angle. 
That is the rule for perceived size that 
Euclid, the geometrician, laid down in his 
Optics over two thousand )ears ago. 

Perceived Size and Perceived Distance 

Euclid was, howe\er, wrortg, as we al- 
ready know from the facts of object con- 
stancy (p. 231). Under ordinary conditions 
the perception of size deviates from Eu- 
clid's law. A negative afterimage, lor in- 
stance, since it subtends a constant vis- 
ual angle, has constant retinal size and 
shotdd therefore, tmder Euclid's law, remain 
constant in perceived size; nevertheless it 
appears to get larger with each increase 
in the distance at which the afterimage is 
projected. Its si/c is dctcrniiiucl not by the 

visual angle and retinal image, but by the 
percei\'ed distance of the projected siuface. 
Con\'ersely, if we look at two objects of the 
same physical size, but at different dis- 
tances, the nearer object, with the bigger 
retinal image, looks no larger than the far- 
ther object. This is the principle of size 
co7istancy, a case of object constancy, a 
principle which holds within wide limits. 

If, on the other hand, we view two ob- 
jects with one eye looking through holes in 
a screen, cut in such a way that the condi- 
tions for the perception of distance have 
all been eliminated, we find that the ob- 
ject which produces the smaller retinal 
image will also appear to be smaller. Ap- 
parently, then, the constancy of size is a 
special case of the relationship between 
perceived size and perceived distance. Au- 
toiuatically the organism makes an adjust- 
ment of the perceived size which allows for 
the changes in perceived distance. The 
screen with the holes in it is the reduction 
screen. (See p. 235.) Here it reduces the 
sensory core of the perception to the retinal 
image, eliminating all the clues to dis- 
tance by which retinally determined size 
might be corrected by the brain. 

Nor does the principle of size constancy 
hold at all distances. It fails for small ob- 
jects—such as a coin— when held within a 
few centimeters of the eye and for large 
objects at great distances. A man talking 
to you and five feet away is not five times 
as tall as the man twenty-fi^■e feet away, for 
size constancy holds appioximately; but 
the man way down the street or across the 
valley may be a tiny little creature. A fa- 
miliar object will, other things being equal, 
remain constant in size over a greater range 
of distances than an unfamiliar object. In 
general, then, you expect constancy of size 
for a middle ramre of distances. Witliin 

Visual Perception of Size 


tlial, range familiarity willi llic object in- 
creases constancy. 

Perceived Size and 
Surrounding Objects 

The relationship between si/e and dis- 
tance is one of many instances in which the 
specific perception of things is determined 
by their situations. If an object appears 
at a great distance, as in a [perspective draw- 


ing (see Fig. 130, p. 298), its size corresponds 
approximately to that distance. 

The principle holds also for bidimen- 
sional situations. The line AX in Fig. 
139r/, appears longer than the line AY: the 
former is apprehended as the diagonal of 
a larger, and the latter as the diagonal of 
a smaller parallelogram. Similarly, in Fig. 
159b the difference in size between the two 
circles must be referred to the influence of 
the included and excluded lines. In the 
familiar arrowhead illusion (Fig. 140rt) the 
line c appears longer than d because it is 
a part of the larger area suggested by the 
direction of the arrowheads. Similarly, in 
Fig. \40b it is almost impossible to see the 
distance between the outer limits of circles 

A and li as ecjual to the distance between 
the right extreme of li and the left ex- 
treme of C. The perception of the circles 
as objects constrains us to perceive the dis- 



In (a) the distance c ec]uals the distance d. In 
(b) the right side of B is equidistant from the left 
side of A and the left side of C. In 'c) there is a 
true circle which looks flattened. 

tance as between circle and circle rather 
than as between point and point. In Fig. 
141 the lower object looks shorter than the 
upper object, possibly because of a con- 
trast between the short upper line of the 
lower figure and the long lower line of the 


The lower figure looks shorter and stumpier. 

upper figure, possiblv because of a perspec- 
tive effect induced by the convergence of 
the straight lines at the two extremes. 
^Vithin limits even such factors as white- 


Visual Space Perception 

iiess may fuiu tioii as determinants of size. 
Jf two equal scjuares, one black and one 
white, arc jilaced side by side against a 
gray ground, the white will usually appear 
larger than the black. DifFerenccs in hue 

^ IN 

// \\ 

// w 

// w 

// \\ 

// w 

// w 

// w 

// \\ 

// w 

// \\ 

// \\ 

4" NN 

// w 

// w 

// \\ 

// w 

// w 

// w 

// \\ 

// \\ 

// w 

// w 

// \\ 




Distortion of siiniuhl IIik-s ;m(i |);u;illcis l)y sui- 
rouiicling olijctls. 

may also have an effect on aj^parent size. 
To most people a red object will appear 
slightly larger, and nearer, than an equally 
bright blue object, and in some patholog- 
ical cases such differences become pro- 
nounced. The apparent distance of color 
is sometimes used by artists in obtaining 
depth in their pictures. 

Apparent shape and direction of lines 
arc similarly modified by smrounding ob- 
jects that set up imjilicit pcneptual atti- 

tudes. Because of the tendency to perceive 
all objects as tridimensional, lines in a 
drawing that cross each other at ol)lic[uc 
angles aie taken imj^licitly to represent 
right angles extending into spate. For ex- 
ample, a vertical line with several oblique 
cross-lines is perceived as if set at an angle 
to the frontal plane like a telegraph pole 
with cross-arms. Similarly, all acute angles 
tend to be overestimated and all obtuse 
angles tend to be imderestimated, making 
them approach right angles. Even in draAv- 
ings to which perspective perception does 
not apply, distortion in direction of the 
lines takes place. Many of the so-called 
visual illusions are of this sort. Some of 
them are shown in Fig. 142. (See also Fig. 
1, p. 6.) 

Visual Acuity 

The smallest object that can be seen de- 
pends upon several variables. A white spot 
on a black groiuid in sunlight can just be 
seen when it subtends an angle of about 
10 to 12 seconds of arc; a black spot on a 
white ground in diffuse daylight requires 
an angle of 25 to 36 seconds. Similar val- 
ues have been determined for the smallest 
perceptible degree of separation between 
two objects, a determination which de 
pends iqDon a niunber of different factors, 
The sidewise displacement of two vertical 
lines, placed end to end, may be perceived 
when the ends are displaced by an amoimt 
etjuivalcnt to a visual angle of only 2 sec- 

The separation between points in space 
must, however, be larger in order to be per- 
ceived. In a well-lighted room two black 
dots can just be seen as two when they are 
separated by an angle of 60 seconds. In 
abnormally high or abnormally low il- 
huninations the angle must be increased, as 
it must also if lines arc sul)stilulcd for the 

Form and Movement 


(lots and the separation is ajjprehendecl as 
a gap in an otherwise complete figure. 

The threshold ol CA) seconds or 1 minute 
of arc for the just noticeable separation 
has been accepted by the cKulist as the 
standard visual acuity for normal vision. 
If the eye can see a letter the distance be- 
tween whose parts (for example, the hori- 
zontal bars of the test letter E) subtends 
an angle of 60 seconds, it is in that respect 
considered normal. If, on the other hand, 
the angle subtended by the parts of the 
letter must be, say, 120 seconds before the 
letter can be distinctly seen, visual acuity 
is said to be one-half normal. The test 
letters are, of comse, always shown under 
good illumination. 


When we look fixedly at the minute 
hand of a watch we see no movement; but 
if, after a brief interval, we look at the 
watch once more, we observe the hand in a 
new position. We perceive a change in po- 
sition but not a continuous change. When 
we see an athlete doing a standing broad 
jump, on the contrary, we see him— as we 
saw the hand of the watch— first in one 
place, then later at another place; but, in 
addition, we see him moving or changing 
his position from one place to another. It 
is the perception of this continuous change 
in position of an object that is called the 
perception of movement. 

General Conditions for 
Perceived Movement 

Usually the visual perception of move- 
ment depends upon the displacement on 
the retina of an image of the moving ob- 
ject. There are exceptions. Movement 
in the near-far dimension may occur, as 

when the approach oi an cjbject is indicated 
\)y an increase in its brightness (lights cjf an 
apprc;aching autcjmc>bile), in its distinct- 
ness (ship coming toward you through the- 
fog) or in its size (an approaching object;. 
Watch a streetcar as it comes along toward 
you through an empty street from too far 
away for the law of size constancy to apply. 
It gets bigger and bigger, by little jumps, 
and you see this increase in size as a move- 
ment of appioach. 

All seen movement is, of course, relative. 
It occurs with respect to some frame of ref- 
erence. So the clouds scurry across the face 
of the moon; or, if the larger object be- 
comes the frame of reference for the smaller 
—and that is quite usual— the moon scur- 
ries behind the clouds (as was stated on p. 
239). When the movement is a simple 
displacement, the initial position of the 
object may be the frame of reference. That 
is what happens when a spot of light is seen 
to move in the dark. \Vith continuous 
movement of an object, its background and 
the surrounding objects become important 
and ordinarily furnish the frame of refer- 

Frequently you have to include yourself 
in the system of relations which determines 
seen movement. You sit in the train in the 
station watching the other train, and all at 
once you feel yourself begin to move back- 
ward, because the other train, not yours, 
has started to move forward. You rise 
from the ground in an airplane, and sud- 
denly you are not rising; instead you see the 
ground falling away below you. There 
are no simple rules that say which part of 
the system will be the frame of reference 
and which the moving object, but it is 
clear that the system can include the per- 
ceiving organism and that the visual per- 
ception of movement is not dependent 
solely on visual factors. If the other train 


Visual Space Perception 

makes you see that you and your own train 
are moving, then you both see your train 
moving and feel yourself moving. 

Other complications arise because the 
eyes tend to fixate a moving object when 
it is the center of attention. The conse- 
quence is that the image of the object does 
not move across the retina because the eyes 
move with the object. Instead the image 
of the stationary background moves on the 
retina, looking blurred. It is really quite 
remarkable how well the neural coordina- 
tions take care of fixation when the head 
moves. You can watch a bird on a limb 
and move your body and head as you will, 
and your eyes remain fixed on the bird. 
Moving your head does not spoil your fix- 
ation for a moment. You do not have again 
to adjust your eyes after you have moved 
your head. The same innervation that 
moves the head moves the eyes compensa- 
torily, so that they stay still with respect to 
the bird. When the bird flies off, you can 
still watch him, your eyes moving and con- 
verging to keep fixation, and, if you move 
your head then, compensation stays just as 

There are really two different ways in 
which movement across the field of vision 
is perceived. (1) The bird flies across the 
field. Your eyes follow him. Other ob- 
jects look blurred. The bird has been seen 
to move. (2) The bird flies across the field. 
Your eyes remain fixed on the distant tree. 
The tree and most of the objects in sight 
are clear. The bird is blurred, because 
your eyes did not follow him; nevertheless 
you saw him move. (3) The bird sits on 
the fence. You move your eyes along the 
top of the fence. Everything is blurred 
(except when your eyes stop momentarily). 
Nothing seems to move. Your eyes are 
moving, but you do not think about that. 

How the brain puts these clues together 

in perceiving movement is not clear, but 
put them together it does. Here there are 
really five items that can change position 
in relation to each other: (1) the object of 
attention, (2) the visual frame of reference 
for the object, (3) your eyes, (4) your head 
and (5) your body. Proprioception, a 
great deal of it unconscious, tells your 
brain what your eyes, head and body are 
doing. If you are fixating an object