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INTRODUCTION

PHYSIOLOGICAL PSYCHOLOGY

ABEKDEEN UNIVERSITY PRESS.

INTRODUCTION

PHYSIOLOGICAL PSYCHOLOGY

DR. THEODOR ZIEHEN

Professor in Jena

Translated by C. C. VAN LIEW, Ph.D., and OTTO W. BEYER, Ph.D.

WITH 21 ILLUSTRATIONS

SECOND EDITION, ENLARGED AND IMPROVED

SWAN SONNENSCHEIN & CO.
NEW YORK: MACMILLAN & CO.
1895

ROYAL eOLLF.P^ Of rHYStCUNS

i.nv.iinY

^ CLASS t

i SOUKOL j
I DATfc

AUTHOR'S PREFACE.

The present work originated in lectures on physiological
psychology that I have delivered at this university for
several years. The doctrines herein presented deviate
essentially from Wundt's theory, now dominant in Ger-
many, and conform closely to the English psychology of
association. Only Miinsterberg in Germany has recently
raised objections from the standpoint of physiological
psychology to the doctrine of apperception, characteristic
of the school of Wundt. By introducing an especial
auxiliary function, the so-called apperception, for the ex-
planation of certain psychical processes, Wundt evades, it
is true, numerous difficulties in demonstration. Wherever
a psychical process that is difficult to explain appears,
it is ascribed to this apperception. At the same time,
however, all psycho-physiological explanation is aban-
doned. This book is intended to show that such an
" auxiliary function " is superfluous, and that all psycho-
logical phenomena can be explained without it.

The work was originally designed for the psychiater,
just as the study of morbid psychical phenomena gave

Preface.

the first impulse to the psychological studies of the author.
But as the circle of hearers broadened, the character of the
" Introduction " has changed. In its present form it is
designed for the student of natural science, the same as
for the physician. I have retained the extensive con-
sideration of the psychical processes of the insane with
good reason. Just as a caricature sets off a single trait
of character more forcibly, so the mental disease reveals
to us now this, now that feature of psychical life with
especially instructive sharpness, and in a measure disen-
tangled from the intricacy of other psychical phenomena.

As regards the citations, I wish to observe that it is their
purpose solely to serve as a guide to further study in
suitable channels. It has not been my intention to refer
to all the authorities upon which the statements of this
work are based

TH. ZIEHEN.

TRANSLATORS' PREFACE.

For several decades a new line of thought and research in
the sphere of psychology has been developing in Germany.
It received its impulse chiefly from the dominant tenden-
cies that characterize the modern methods of natural
science. Psychology, in endeavouring to maintain its
position as a science among sciences, was brought in
contact with the so-called natural sciences, and the result
was inevitable. The close relation that exists between
certain departments of psychology and the physiology of
the nervous system, and the efforts that have been made
since Herbart to apply the methods of natural science to
the former, inevitably led to the investigation of psycho-
logy from a new point of view (viz. the physiological) and
ultimately to the development of a new science, the science
of physiological and experimental psychology.

Brief as the history of physiological psychology is, it has
yet opened a great many new fields for investigation. The
empirical data, however, which the science has thus far
oeen able to establish, already receive a variety of interpre-
tations that are far from being concordant. In fact, as the

vii

viii

Translator^ Preface.

perusal of this work will show, two distinct interpretations
that conflict in many of the most essential points, have
become especially prominent. The one is held by Wundt
and his school, the other by Munsterberg and Ziehen.

The latter, who is well known in Germany, both as
University instructor and as a noteworthy investigator in
the lines of physiological psychology and psychiatry, has
produced the first work which gives a brief presentation of
the field of physiological psychology in general, and of an
interpretation based upon the English psychology of asso-
ciation in particular. For this reason the translators have
thought it advisable to produce a translation of the work
for English readers. The work, though small in compari-
son with that of Wundt's (" Grundziige der physiologischen
Psychologie "), or even with that of the American author,
Ladd (" Elements of Physiological Psychology ") embraces
within a small compass the essentials of the science.
It is therefore fitted to be an excellent introductory
Compendium to physiological psychology.
• The reader will note that in the opening and closing
chapters the author clearly and sharply defines the pro-
vince of his science, and fixes the limits that separate it
from other related sciences. Throughout the entire work
it has been his aim to develop all explanations as far as
possible from physical or phj'siological data, and to account
for the presence of certain functions by an application of
the laws of evolution. Hence the work can only be under-

Translators' Preface.

stood and correctly judged when regarded as treating of
physiological psychology as a natural science.

Besides being fitted for the use of the alienist and the
student of natural science, the work will undoubtedly be of
service to the educator and teacher in so far as it is a
guide to the understanding of the relations that exist be-
tween psychical states and processes on the one hand, and
nervous, especially cerebral, processes on the other.

The terminology of the subject, which is already so
highly developed in Germany, presents a series of difificul-
ties for an English translation that are by no means easily
overcome. The terminology of this translation, however,
holds, so far as possible, to already established precedents,
wherever they do not conflict with a correct rendering of
the views of the author. This second English edition
conforms throughout to the author's own revised and
enlarged second German edition, the chief addition being
chapter ix. upon the emotional tone of the ideas.

C. C. VAN LIEW.
OTTO W. BEYER.

List of Symbols frequently used in this Work, which

HAVE A constant SIGNIFICATION AS INDICATED BELOW.

C=cortex, centre.
f=cortical.

i/=distinction, difference.

.£=excitation, excitant (hence also stimulation, stimulus,

irritation and irritant).
_/"=tone of feeling.
^=gangIion-ceIls, etc.
z= in tensity and ideational.
/=idea.
latent.

M ov m =motor, kinasthetic, etc

O or iP=object.

/=peripheral.

^=quality.

^= retina.

5 or j=sensation, sensory, etc.
7" or ^=time.

TABLE OF CONTENTS.

Author's Preface

Translators' Preface

CHAPTER I.

Theme and Synopsis of Contents

The antithesis of material and psychical phenomena — The province
of physiological psychology — Pyschology as a science — Criterion
of the psychical — Reflex action — Its non-psychical character and
its fitness— Automatic action — Distinguished from Reflex action —
Two classes of automatic action — Its non-psychical character.

CHAPTER II.

Sensation— Association— Action

The elements of the psychical process— Action distinguished from
reflex and automatic acts — Sensation and association — Action
itself without a psychical concomitant — Sensation and ideation
the only psychical processes — The question of voluntary action —
Classification and division of the three forms of action — Their
anatomical localization.

CHAPTER III.
Stimulus— Sensation

Kinds and forms of stimuli — Adequate and inadequate stimulation —
Theory of specific energy — Nerve-conduction — Table of stimuli
— Qualities of sensation— Intensity of sensation— Its measurement
— Law of Weber— Fechner's formula— The three interpretations
of Weber's Law— Author's interpretation.

xii

Contents.

CHAPTER IV.

Sensations of Taste, Smell and Touch .... 62

Organ, centre, and stimuli of taste— Application of Weber's Law-
Localization of gustatory sensations — Organ, centre, and stimuli
of smell— Application of Weber's Law— Localization of sensa-
tions of smell— Organ of touch— Stimuli of touch— Cortical
centre — Classes of sensations of feeling — Application of Weber's
Law — Localization — Local signs — Theory of space-perception by
touch.

CHAPTER V.

Sensations of Hearing 86

Stimuli of hearing— Musical sounds and noises — Their analysis —
The organ of hearing — The cortical centre of hearing — The
musical scale — Its relation to Weber's Law— Theory of over-
tones— Intensity of sound and the application of Weber's Law —
Localization of acoustic sensations.

CHAPTER VI.

Sensations of Sight .... ... 102

Stimuli of sight — The organ of sight — Spectral colour — Saturated,
non-saturated and mixed colours — Theory of vision — Colour-
blindness— Intensity of visual sensations — Application of Weber's
Law — Theory of space-perception by sight — Localization of
visual sensations — Projection of visual sensations.

CHAPTER Vn.

The TiME-f'ROPERTIES AND THE EMOTIONAL ToNE OF THE

Sensations 130

Prolonged sensation — Least duration of stimulation capable of pro-
ducing sensation — Blending of successive sensations- — Number ot
sensations at any given time — Tone of feeling of sensations dis-
tinguished from that of ideas — Positive and negative tones of
feeling — The curve of feeling — Emotional tone dependent on
intenisty and quality of sensation — Pain — Dissonant and conson-
ant chords — Influence of the association of ide.is — Emotional tone
dependent upon spatial arrangement and time relations — Emotional
tone dependent on rhythm and rhyme — Theory of emotional tone
— Its importance.

Contents.

xiit

CHAPTER VIII.
Sensation— Idea— Conception 153

Deposition of the mental image — Idea distinguished from sensation
— The question of latent ideas — Physiological basis of the idea —
Synthesis of the idea— Motor ideas — The concrete conception —
general concrete conception — Abstract conceptions — Imagina-
tive ideas — The properties of the idea — The content of ideas —
The distinctness of ideas — Their emotional tone — Their relations
to space and time— Forgetfulness.

CHAPTER IX.

The Tone of Feeling of the Ideas — Emotions . . . 174

Nature and origin — Transmission — Irradiation — Law of irradiation —
Moods — Their origin — Analysis of Envy — Reflected emotional
tones — Classification — Development of the complex feelings —
Analysis of the same — Logical feelings- — Virtues — Vices — Ethical
development of feeling — Influence of emotions upon ideation and
action — Morbid emotional states and their efifects— Influence of
emotions upon the mimetic and expressive motions — Dependence
of emotional intensity upon the properties of the ideas — Law of
contrast.

CHAPTER X.

The Association of Ideas

Reproduction of ideas— Theoiy of association— Recognition— Chief
Law of association— Physiological basis of association— Associa-
tion of successive ideas— The theory of apperception— Influence
of the grouping of ideas— Herbart's computations— After-images.

CHAPTER XI.

Rapidity of the Association of Ideas— Judgment and
Conclusion

Time of association— Simple reaction-time— Time of recognition —
Abnormal association — Abbreviation of association— The judg-
ment—Its physiological basis— Its validity— The syllogism-
Apperception and association.

xiv

Contents.

CHAPTER XII.

Attention — Voluntary Thought — The Ego— Memory . 233

Attention — The conditions of attention — Attention as a feeling —
Change of attention — The associative power of a sensation de-
pendent on four factors — Contrast — Voluntary and involuntary
thought — Origin of this distinction — The ego — Development of
the idea of the ego — Its activity — Summary of the factors char-
acterizing so-called voluntary thought — Other special forms of
thought — Memory — Its physiological basis — Loss of memory and
forgetfulness.

CHAPTER XIII.

Morbid Sensation and Thought — Sleep — Hypnotism . . 25^

Secondary sensations — Photisms and phonisms— Nature of secon-
dary sensations— Hallucinations — ^Their cause — Illusions — Their
origin and nature — The delusive and the compulsory idea — Sleep
— Dreams— Character of the latter — Double consciousness —
Hypnotism — Its nature.

CHAPTER Xrv.
Action— Expressive Motions— Speech . . ' . .271

Development of motions — Of motor ideas — The motor zone of the
cortex — Reaction-time— Muscular and sensorial reaction — How
distinguished— Recognition-time and discernment-time — Selec-
tion-time— Changes in reaction-time — Forms of action— Expressive
motions — Speech — Development of expressive movements-
Origin of speech — Cortical centre for expressive motions.

CHAPTER XV.

Will— General Conclusions 293

The hypothesis of a faculty of the will— The origin of this hypo-
thesis—No special faculty of the will— Testimony of psychiatry—
The notion of freedom in actions —Etiiics and physiological
psychology— The point at which they conflict— The parallelism
of material and psychical processes— The dualistic theories— The
monistic theories— The critical stand-point— The final proposition
of physiological psychology.

INTRODUCTION TO
PHYSIOLOGICAL PSYCHOLOGY.

— ♦-♦ —

CHAPTER I.

THEME AND SYNOPSIS OF CONTENTS.

The psychology which I shall present to you is not that old
psychology which sought to investigate psychical phenomena in
a more or less speculative way. That psychology has long been
abandoned by those whose method of thought is that of the
natural sciences, and empirical psychology has justly taken its
place. Physiological psychology constitutes a part of empirical
psychology. Let us start from an antithesis which has long been
traditional in philosophy, and to which psychology in particular
owes its existence as an independent science. This is the
antithesis of material phenomena and psychical phenomena. We
shall purposely avoid the terms soul and matter, since each
introduces a new and at first purely hypothetical unit instead of
the manifold data primarily furnished us. For the present alsp
we shall not investigate whether the material and the psychical
data are equally primary or not. It shall be reserved rather for
the close of our researches to decide whether "the material" and
"the psychical" are entirely independent of each other; or
whether the former is a function of the latter as the spiritualistic
philosopher assumes; or finally whether the latter is merely a
function of the former as the materialist conversely assumes. For
ihe present we accept the antithesis of psychical and material

Introdiicttoii to Physiological Psychology.

phenomena and reserve for a later stage the finding of a unity for
the two contraries, based upon all our physiological and psycho-
logical researches. But we must here emphasize one proposition,
which we can draw directly from pliysiology and which can serve
as fundamental for the entire field of physiological psychology.
There is without doubt a certain number of psychical phenomena
or processes that do not occur independently of, or without
relation to, certain material phenomena and processes, but
that stand in obvious correlation to the latter. More briefly
stated, — certain concomitant material processes correspond to a
certain series of psychical processes, so that the latter cannot
occur without the former, nor the former without the latter. The
physiology of the brain, for example, teaches us that sensations
of sight only occur as long as the occipital lobe of the cerebrum
remains intact. If we remove this from a dog with a knife or
cautery and keep the animal alive, it will be blind for the future.
Conversely it appears that sensations and perceptions of sight
occur as long as certain material processes (the particulars of
which are as yet quite unknown to us) take place in the un-
injured occipital lobe of the cerebrum. Let us ask in general,
What material processes can be clearly shown to be accompanied
by concomitant psychical processes } Our first answer is,
physiological processes, i.e. those material processes that properly
belong to living matter ; still more specifically expressed, the
material processes of the central nervous system, especially of the
brain. Later we shall have to investigate whether such material
processes in the central nervous system accompany all psychical
phenomena, and our answer will be decidedly negative. Physio-
logical psychology, however, deals exclusively with those psychical
phenomena to which concomitant physiological processes of the
brain correspond. Hence its name. It ignores all psychical
processes for which no corresponding physiological processes in
the brain are conceivable. Hence physiological psychology is
correlated to the j^hysiology of the brain, just as psychical pro-
cesses are correlated to cerebral excitations. Wherever the
physiology of the brain does not yet offer suflScient knowledge.

Theme and Synopsis of Contents.

physiological psychology may be allowed to investigate the bare
psychical phenomena— as purely psychical — provided it is always
guided by the thought that, even for these psychical phenomena,
at least the possibility of concomitant cerebral processes must be
shown.

Formerly it was doubted whether there could be an exact
natural science of psychology at all. Even Kant shared this
doubt. One of his chief arguments is as follows : The psychical
phenomena are incommensurable because they are not quanti-
tively comprehensible. Therefore they can never be subjected to
mathematical treatment. It is not necessary for us to deduce from
the conception of psychical life the possibility of applying mathe-
matical computation to that field of science, for Kant has already
been refuted by the history of psychology. Less than forty years
after Kant had given this judgment, Herbart had already applied
mathematics to psychology in the most fruitful way. One may
agree with his results or not ; at all events the possibility of a
mathematical treatment of psychology was demonstrated by the
works of Herbart as early as 1822. Furthermore, physiological
psychology has now established important propositions capable
of exact mathematical statement. This department of physio-
logical psychology commonly receives the special designation of
psycho-physics. It was Fechner, the psychologist of Leipsic,
recently deceased, who first treated certain departments of physio-
logical psychology mathematically with positive success. We
shall become acquainted with a series of such psyclio pliysical
laws ; psycho-physics will therefore be a component part of our
science. The following scheme will make clear to us the position
of our science :

1. Speculative Psychology.

2, Empirical Psychology.

a) Autonomic^ Psychology: psychical processes jvithout

concomitant cerebral processes.

b) Physiological Psychology: psychical processes ivith

concomitant cerebral processes (integral part : metric
physiological psychology = psycho physics).

"t'rarsce^ndenur'" P^y^hology may also be designated as

4 Introduction to Physiological Psychology.

In repairing to the great world of psychical phenomena, our
first task will be that of every empirical science, viz., the search for
and collection of data, which we must first gather empirically that
we may then study iheir connection. Here we encounter the
question at once, how do we recognise psychical phenomena?
What will help us to a trustworthy diagnosis of such phenomena?
The criterion can only be worded thus, — All and only the
phenomena which are imparted to our consciousness are psychical.
That which is without us in space and time, which we assign as
the cause of our sensations, is material. The tree, whose existence
we accept as external to us when we have the visual sensation of
a tree, is material. The sensation of sight itself is psychical in so
far as it concerns our consciousness. Here at the beginning of
our investigations we find psychical and conscious to be wholly
identical, for we can form no idea at all of what an unconscious
sensation or idea might be. We know sensations and ideas only
as far as we are conscious of them. Later we shall see that many
investigators have also assumed unconscious sensations and ideas.
Let us suppose that we pass a friend, and, being absorbed in
thought, fail to see him ; but after a few steps further it suddenly
occurs to us that our friend has just passed and we then greet
him. In this case it seems rational to assume that an uncon-
scious seeing of the friend preceded the conscious seeing, that an
unconscious sensation of sight was prior to the conscious sensation.
On closer investigation, however, this assumption is seen to be
wholly arbitrary. When the friend passed, the retina and optic
nerve were irritated, and the latter conducted the excitation
farther to the occipital lobe of the cerebrum, the so-called visual
centre. We know that this excitation is a material, a chemical
process. At first no psychical process at all corresponded to the
material process. Other more intense ideas, i.e. more intense
excitations of other parts of the brain, absorbed our thoughts.
To express the fact briefly, we may say, Concomitant psychical
processes took place for the time being only in other portions of
the brain. Therefore we did not see the friend, and passed with-
out recognising him. Then, after a few steps, we were aroused

Theme and Synopsis of Contents.

from our meditations, and the ideas that had just been occupying
our attention diminished in intensity and retired. Now, for the
first time, a concomitant psychical process appears in response to
the material excitation of the occipital lobe, which has remained
persistent and gradually taken effect. Now for the first time it
occurs to us that we have seen the friend. Thus we perceive
that it is by no means necessary to assume an unconscious sensa-
tion as antecedent to the conscious. The assumption that
primarily only a physical excitation existed, which subsequently
led to psychical processes, i.e. entered into the consciousness,
is just as simple and decidedly more legitimate, since it introduces
no new and wholly unintelligible conception. Let us repeat it :
psychical" and '■'■conscious" are for us, at least at the beginning
of our investigations, identical.'^ The latter, as it were, is the
shibboleth for the former. From the outstart the conception,
"unconscious psychical processes," is for us an empty conception.
We shall meet with it again farther on as a hypothesis, though
one to be regarded from the beginning with great scepticism.

Without proceeding from a definite classification into three
mental faculties, or from any other hypothesis whatever, let us
now seek the psychical phenomena wherever we find them
in connection with the processes of the nervous system. It is

* Innumerable controversies have been spun out concerning the question as
to whether there are unconscious psychical conditions or not. A good
synopsis of these discussions is to be found in the work of G. Cesca, " Ueber
die Existenz von unbevvussten psychischen Zustiinden " ( Vierteljahrschr, f.
■wiss. Philosophic, 1885, Bd. IX.). The conclusion at which Mr. Cesca
arrives is undoubtedly wholly false. Among those treating the question
exhaustively are especially Hamilton, " Lectures on Metaphysics and Logic,"
1882; J. Mn.L, "Analysis of the Phenomena of the Human Mind," 1S78;
Lewes, " Problems of Life and Mind," 1879 > and Maudsley, " Physiology
of Mind." In the case of the passing friend, already cited, however, the
process is also frequently the following. The excitation of the visual centre
by the im.ige of the friend may, indeed, be accompanied by a sensation, which,
however, in consequence of the predominance of other ideas, is not sufficiently
intense at first to prompt any further thought, least of all the recognition of
the friend.

Introduction to Physiological Psychology.

obvious that the first beginnings of a nervous process are to be
sought where animal anatomy first meets with a nervous appara-
tus in the ascending scale of animal life. Animal anatomy, how-
ever, is far from having brought its investigations in this line to a
close. We find the first unquestionable rudiments of a nervous
system in the Medusae, on the free margin of whose swimming
umbrella Romanes has found numerous nerve-ends and conduc-
tive filaments, which penetrate the umbrella. Irritation at any
point of the umbrella causes a contraction of the lining sheet of
muscular tissue resulting in locomotion. The contraction ap-
pears to begin at some definite point of the umbrella, and eventu-
ally to become universal. A certain capacity for nervous processes
might properly be recognised in the motor activity of even the
simplest Amoebae. Let us imagine a monad to be placed before
us, and a grain to be brought in contact with it. Protoplasmic
masses, the so-called pseudopodia, stretch themselves out, en-
velop the grain, and contract again with it to the main mass.
In this process, those features are already present that we shall
recognise in the future as the essentials of nervous function, viz. :
(i) a stimulation (later we shall say a sensible stimulation) ; and
as a response to this stimulation, (2) a reaction, in fact a motor
efl"ect, that is by no means easily explicable by merely physical
laws. Hence, wherever we find contractile substance, the con-
ditions of nerve-life are already present. In the protista, one
and the same cell, as a whole, is still the seat of the reception of
the stimulus, and of the motor reaction. In a very interesting
way this is changed in the Ccelenterata. In the Hydra we find
the so-called neuro-muscular cells or epithelial muscular cells.
They are less distinctively developed also even in many Flagel-
lata (Poteriodendron). In these cases the stimulation is received
by the cell only at s (fig. i), and the motor reaction takes place
only at the points m and m', so that a separation of the sensory
and motory parts has already been eflfected. In the Medusae we
find still further development, the gradual accomplishment of
which we must conceive of as follows. Let us suppose an animal
body composed of many cells, to be brought in contact with any

Theme and Synopsis of Contents.

given stimulus. The latter is constantly transmitted as an excita-
tion within the animal along the path offering the least resistance.
Thus the excitations will come to be transmitted only along fixed
paths, the so-called paths of conduction. According to a funda-
mental law of biology, the constant execution of definite functions
also gradually effects certain structural modifications. Accord-
ingly these paths of conduction become anatomically differentiated
from their surroundings and the nerves develop into independent
anatomical tissues. Even in the Medusae we find this degree of
development. In these animals, in fact, a mediating organ has
already been introduced, in the form of a so-called ganglion cell,
between the sensory conductor receiving the stimulation and the

Fig. I.

motor conductor imparting contraction. That which we find in
the complete nervous system of the Medusas has only been de-
veloped from the imperfect capacities which were already pre-
typified in the lowest Protista, but which did not yet appear to
be anatomically differentiated. When, as in the case of the
Medusae, a stimulus acting upon the nerve-end s (fig. i) reaches a
ganglion-cell, and is transmitted by the latter along a new nerve-
patli to contractile masses, so as to impart motion, the entire
process is designated as reflex action. Reflex action is the sim-
plest nervous process of which we have knowledge. After the
■above statements there can be no objection to designating the
numerous movements of the protista, caused by the mechanical

Introductio7i to Physiological Psychology.

stimuli of light (recently described anew by Verworn) as reflex
action, although nerve-paths can in no wise be shown to exist
in these animals. Among these reflex actions are the withdrawal
of the Pseudopodium ^ when pricked, in the case of the Actino-
sphasrium, or the movements of the Flagellata in darting back
by means of the movements of their own cilia.

Let us pass at once from the Medusae to the highest classes of
animals, and seek reflex action in the latter. Here it appears
that that which we learned from the Medusae, is to be met with
again, scarcely altered, in the highest animals. We understand
by reflex action in higher animals, a motion imparted by a stimu-
lus which acts upon a sensible periphery. Think of the well-
known reflex action produced upon the sole of the foot. A prick
on the sole of the foot is answered by the withdrawal of the foot,
by flexion, and, to some extent, by the contraction of the toes.
In this case the essential anatomical elements of the process are
thoroughly known. In the sole of the foot are the terminations
of sensory nerves. These are irritated and conduct the stimulus,
or, as we shall call the stimulus as soon as it has been received by
the nerves, the exciiation to a sensory ganglion-cell 6' (fig. 2) in
the spinal cord. This cell sends the excitation received along
the inter-central path S M\.o the motor ganglion-cell M, which
in turn transmits the impulse again toward the periphery, i.e.
centrifugally, and generates muscular activity." There is a large
number of such reflex motions. They are also designated as
lower or simple reflex motions. Now, does a concomitant psych-
ical process correspond to this nervous process with which we
have just become acquainted as simple reflex action? Our con-
sciousness, as shown above, is alone able to decide the question •,
it undoubtedly answers No. If our foot is but pricked unawares,
it is only after the niDvement has been executed that we are in-

* Even here, in the cases of the simplest reflex action, " fitness," i.e.,
adaptation to a definite purpose, becomes very apparent ; for nearly all the
reflex movements of the protista, resulting from mechanical irritation, cause
the vi'ithdrawal of the organism from the irritant (negative thigmotropism).

^ In the case of many reflex motions, however, no sensory cell S whatever is
introduced in the reflex-arch. The sensory fibre divides as soon as it re.iches
the si)inal marrow. One of its branches p.-isscs directly to the motor ganglion-
cell, which it envelops with its terminal ramifications, thus transmitting the
excitation directly to M and the motor path.

Theme and Synopsis of Contents.

formed of what has taken place by a new sensation — the
sensation of motion. But other reflex motions, e.g., the reflex
contraction of the pupil when exposed to light, give us no
subsequent knowledge of their occurrence through sensation.
A further argument for the non-psychical character of reflex
action is supplied by objective investigation. Individuals
wnose psychical Hfe has been totally extinguished, who are
therefore unconscious, can still execute perfect, or even intensi-
fied reflex, plantar motions. A similar line of thought may be
applied to all the lower reflex motions in as far as they can be
subsumed under the above scheme. It is likewise valid when
several sensory fibres act upon several sensory cells, and the latter
again upon several motor cells. In fact this is already the case
with reflex action in the sole of the foot. When the sole of the

Fig. 2.

foot is touched, not one but ma?iy terminations of the sensory
nerves are irritated, and hence also many sensory and niotory
ganglion-cells are excited. In the same way, not one muscular
fibre, but a large number of fibres belonging to one muscle, or
very frequently to several muscles, are made to contract by their
respective nerve-fibres. The following characteristic, however, is
common to all these lower reflex actions : the sensible stimulus
may change, we may graze, prick, or tickle the sole of the foot,
or singe it with a flame, we may apply the irritant now at this
point, now at that, but in all cases the motor effect, the respond-
ing reHex action remains the same with stubborn monotony.

10 Introduction to Physiological Psychology.

The vigour with which the toes are contracted or the foot is with-
drawn may change, but the same groups of muscles are always
innerved, and always execute the same movements. The pecu-
liarities of the stimulus have no influence upon the motor reaction.
At this point let us call attention also to another distinguishing
feature of these lower reflex motions. Notwithstanding their con-
stancy, they are generally fitting, i.e. adapted to a purpose. Here,
above all, we must guard against the idea, too easily formed in
connection with the idea of reflex action, that the fitness of a
nervous process demonstrates its psychical nature. The colour
of the bird's plumage, the structure of the hand, and countless
phenomena of the vegetable world, in which we first meet with
expediency and organization, are fitting ; in no other sense is
lower reflex action fitting. Therefore it is no more psychical ^
than the colour of a feather. In fact, the fitness of this reflex ac-
tion, and the fitness of the bird's plumage were developed in a very
similar manner, viz. by transmission or heredity, and by natural
selection. Animals whose nervous mechanism was so constructed
that they did not respond to a prick by withdrawing, but rather
by extending the irritated member still further, were much more
exposed to injuries than those possessed of a nervous capacity,
primarily accidental, which enabled them to withdraw in response
to the irritation. Accordingly the former developed with less
vigour, did not live so long, propagated less rapidly, and conse-
quently transmitted their unfitting mechanism to a constantly
decreasing number of offspring. The constant operation of this
natural selection effected the final extinction of all animals having
an unfitting reflex mechanism. Only those animals prevailed in
which a fitting mechanism existed, as at the present time.

Moreover the fitness of reflex action by no means demonstrates
that psychical processes accompany the reflex motions. Accord-
ingly Pfliiger was wrong in assuming a special soul for the spinal
cord upon the ground of this fitness of spinal reflex action. In

> Lewes has defended the theoiy of the " omnipresence " of consciousness in
all reflex centres to the extreme, but upon quite insufficient grounds.

Theme and Synopsis of Contents.

support of his theory, Pfliiger made use of the following well-
known experiment. A frog is decapitated, and its left leg
amputated ; as soon as a spot on the left side of the body is
moistened with acid, it is immediately wiped off with the right
leg. But this experiment offers no proof whatever of his theory
of a special soul in the spinal cord: (i) because this same reflex
act takes place elsewhere as a normal phenomenon, and is some-
times diagonally executed ^ ; (2) because even the greatest fitness
is conceivable without psychical processes.

From the above explanation we shall soon be able to understand
still another point. These lower reflex movements are generally
fitting, i.e. they verify their fitness in the great majority of cases ;
but there are cases also in which they may be directly unfitting
and injurious. In such cases the characteristic constancy, that
has been inherited through many centuries by all reflex action,
is an obstacle. The reflex motion of the foot, for example, is
executed in just the same manner when a second sharper needle
is placed above the instep, the skin being thereby exposed to a
much severer injury upon withdrawing the foot. The lower reflex
motions are absolutely, and hence blindly, constant; they are
therefore only generally fitting.

Whether these reflex acts, for which psychical concomitants can-
not be shown, have originated from acts originally psychical, that is
from nervous processes having a psychical correlative (for example,
voluntary acts), is a question that cannot affect our conception
of them. We shall see later what degree of probability can be
granted this assumption. At first we are only acquainted with
lower reflex action as we 7iow find it ; we know nothing of any
psychical correlate for this reflex process.

The numerous more complicated reflex acts, with which we
are at present acquainted, are to be distinguished from these
simplest reflex acts as regards the motor part of the process. The

1 The experiments of AuERBACH (Zcitsckr. /. klin. Med., IV., 4) .ind
Sanders-Ezn (Aibeiten aus d. physiol. Anst. z. Leipzig, 1867) also demou-
btrale only reflex — hardly automatic — activity of the spinal cord. Furthermore,
repeated pricks with a needle in the sole of the foot belonging to the paralyzed
limb of one who is suffering from spinal disease, often finally produce a
tlischarge of defensive motions in the healthy limb.

12 Introduction to Physiological Psychology.

sensible stimulus, at least so far as quality is concerned, remains
the same; but the motor response becomes more complicated
in proportion as the growing intensity of the irritation sets a
greater number of muscles in action. Finally, the thrust of the
needle having become sufficiently intense, not only the one leg,
but also the arm on the same side, then even the other leg and
arm and the muscles of the face will be set in motion. But
otherwise the motion retains its monotonous character. The
withdrawal of the suckers of the starfish also furnishes a good
illustration of the gradual propagation of reflex motion as the
stimulus is increased. The movements of the Crinoidea, culmi-
nating in actual flight, offer another example. The following
experiment furnished by Goltz is also interesting.^

If, after having removed the cerebrum of a frog, we touch the
cornea of the brainless animal with a couching-needle, the first
reflex motion is the closing of its eyelid. If we repeat or in-
tensify the stimulation, the animal will strike the needle aside
with the corresponding front foot. A still further increase causes
the head and trunk to be turned away from the irritant. Finally,
upon constantly increasing both the frequency and intensity of
the irritation, the animal will retire to some other place. Vul-
pian has made a more accurate study of these more complicated
reflex motions.

Furthermore, the conditions of reflex action, the sensible
stimuli, may not only become more intense, but also more
numerous and complicated. Auerbach has observed that a de-
capitated frog, the skin of whose breast has been cauterized at
some point, executes a variety of movements according to the
position of its limbs and the location of the cauterized spot.
Hence, so-called " co-ordination " is also characteristic of reflex
action to a great extent. And yet we have no ground whatever
for assuming that these higher or more complicated reflex acts
are accompanied by psychical processes.

* Goltz, " Beitrage zur Lehre von den Functionen der Nervencentren des
Frosches," Berlin, i86g, S. 59.

Theme and Synopsis of Cotitents.

Let us now leave reflex action and pass on to the next stage.
A frog, whose cerebrum, including the optic thalamus, has been
extirpated, still leaps away when pinched ; but in so doing it
stumbles against all obstructions. Let us next observe a frog
more closely in which the cerebrum, exclusive of the optic thala-
mus, has been removed. All reflex action is retained. A prick
on its foot easily causes it to leap off. If we place an obstacle
in the path of its retreat, it avoids the obstruction, or, in rare
cases, clears it with a well measured bound.^ The mere act of
I leaping away may possibly, in case of necessity, be regarded as
1 a complicated reflex act ; but the fact that the frog avoids the
obstacle while retreating shows at once that quite another process
is concerned. This process we shall analyze. A sensible stimu-
i lation (the pricking) imparts a complicated motor reaction (the
\ movements in leaping), which thus far may be considered as reflex,
i While the latter is taking place, another intercurrent stimuliK
I appears, viz. the obstruction which we place in the way and
' which irritates the terminations of the optic nerve. Such an
i intercurrent stimulus has no influence at all upon reflex action,
; or at the most its influence is but quantitative. If we prick the
sole of one's foot and at the same time apply any other form of
stimulation by permitting, for example, the brightest light to be
flashed, or the loudest noise to be made, the motor reaction will
at most prove to be somewhat weaker or stronger, but the same
muscles will be affected. So far as quality is concerned, the
reflex motion of the sole is constant. But that complicated
process, involved in the movements of the brainless frog while
making its escape, is very different. The intercurrent visual
irritant modifies the action, and the animal avoids the obstruction.
Therefore in this case, motor reactions of quite another kind are
■ concerned. Those motor reactions that are not the invariable
; result of a definite stimulus, as are the reflex acts, but that are
i: modified while in progress by the action of new intercurrent

* Goi.TZ, " Beitrage zur Lehre von den Functionen der Nervencentren des
il Frosches," Berlin, 1869, S. 65.

Introduction to Physiological Psychology.

stimuli, we shall call auiomaUc'^ acts or reactions, in the more re-
stricted sense of the words. We find such automatic acts in-
numerable. Call to mind the pianist who executes an often prac-
tised piece of music while his thoughts are wandering elsewhere.
Despite his absence of mind, his fingers glide over the right keys
in proper succession. In this case also an automatic act is con-
cerned. The optical excitations imparted by the notes and the
tactile excitations imparted by contact with the keys, act without
interruption upon the execution of the movements of the fingers.
Or, to cite another example, we often de.-cend a flight of stairs
while deeply absorbed in thought. In this case also, as in that of
the experiment with a frog, the action of the cerebrum upon the
motions of the body has in a certain sense been removed. And
yet we are able to place one foot after the other safely. This is
another example in which a motion in progress is modified by
constantly intercurrent stimuli. These examples also show us
that we are unconscious of such automatic processes, and that
the latter are not psychical ; in fact, our consciousness is em
ployed with other things. All warrantable foundation for the
assumption of concomitant psychical processes is wanting. Self-
observation, which is alone able to demonstrate conclusively the
existence, of a psychical process, testifies to the contrary. Therefore
the automatic acts share with the reflex acts the characteristic
absence of concomitant, psychical, or conscious phenomena.
Goltz has termed the automatic movements "response-move
ments." He also emphasizes as essential the fact that they are
adapted to a definite purpose and are able to overcome opposing

* Unfortunately the word " automatic " is used with a great variety of sig-
nifications. We are especially wont to designate as automatic also those
rhythmic reflex movements which are the result of internal stimMli.— for
example, the pulsations of the heart. This second sense will be entirelv
excluded here.

2 Goltz, to whom we are indebted for the first knowledge of these motor
reactions, has assumed such a process, though of course without consciousness.
In this particular he is opposed to Lotre, but his theory is based upon insuffi-
cient grounds.

Theme and Synopsis of Contents.

obstacles. By this he also understands essentially the capacity,
already emphasized, for regulating and modifying the reactionary
movement by intercurrent stimuli.

It is difficult to state just where we first meet with automatic
motions in the animal series. At all events they are to be found
in an advanced stage of development in the Echinodermata.
Tiedemann, Romanes, and others ^ have described, that star-fish
when crawling off are able to avoid obstacles by stretching their
tentacles, armed with eyes, forward and upward. Especially the
Ophiurae know how to overcome obstructions readily, for example
a line of upright pins closely encircling them. One can easily
remove this capacity for automatic movements by completely
severing a single ray from the central disk of the star-fish. The
ray thus severed from the central nerve-ring is still capable of
locomotion, but it moves quite aimlessly ; it no longer avoids
obstacles. The movements of the star- fish in turning over, as
also those of the frog, laid upon its back, in returning to the
position upon the abdomen, are still to be regarded as very com-
plicated reflex acts. The completely severed ray of a star fish
succeeds in turning itself over, though of course very irregularly
and with extreme slowness; the frog, deprived of its brain, and
possessing only the medulla oblongata besides the spinal chord,
is able when laid on its back to resume the natural position upon
the abdomen. Preyer observed ophiurte, on a single arm of
which he had drawn a very tight-fitting sheath of india-rubber,
shove off the sheath by jerks of the two neighbour-ns: arms. In
opposition to Preyer, we must still designate this also as an
automatic act. In the protista we find no positive automalii.
motions in the sense in which we understand the latter. They
do not avoid obstacles, although a single observation of Engel-

• Preyer, " Ueber die Bewegiingen der Seesterne." Mittheiliingen aiis d.
Zoolog. St. z. Neapel, VII. i and 2; Tiedemann, Deulsches Archiv
f. d. Pliysioloj,ric, 1815; VULPIAN, Compt. rend. Soc. Biolog., 61, 62;
Romanes and Ewakp, "Observations of the Locomotor System of Echi-
nodermata," Philosoph. Transact., 1S81.

1 6 Introduction to Physiological Psychology.

mann's/ who saw a vorticel-bud suddenly change its course and
swim after a large vorticella with which it had come in contact,
would demonstrate the occurrence of reactions in these animals,
if it is correct.

At all events we can claim that the first automatic movements
to be met with in the animal series, developed from reflex action
through the agency of " natural selection." If we wish to illus-
trate the process of this natural selection, in a rough sketch,
much more simply than it has actually taken place, we may pre-
sent the following : —

Originally the amphibians that regularly avoided an obstacle
suddenly placed in the way, thereby modifying their locomotor
course, were just as numerous as those that did not. In the
struggle for existence, however, the former had a decided advan-
tage, for mechanisms situated below the cortex relieved the cere-
brum of work and other deeper nervous centres fittingly per-
formed its functions. This fitting peculiarity was inherited and
constantly bred by transmission, while those animals gradually
died out that were less favourably constituted. You will there-
fore understand also why automatic and reflex acts cannot always
be distinguished from each other with absolute accuracy ; there
are numerous easy transitions from reflex action to automatic
action.

But automatic acts are not alone the product of a progressive
development from reflex acts. By a sort of retrogressive develop-
ment, they may be the result of the so-called conscious or
voluntary acts. Call to mind once more the above-cited example
of the pianist, who plays a well-practised piece wliile his thoughts,
his consciousness wander elsewhere. We designate this playing
as automatic, although it was not automatic originally. Before
the piece can be executed automatically, the player must practise
it for hours with the application of all his energy and attention,
and many such conscious voluntary acts must take place. Hence
automatic action may be acquired by practice, i.e. by the frequent

' Pfluger's Archiv, Bd. 2.

Theme and Synopsis of Contents.

repetition of the so-called voluntary acts. These acts, executed
at first with the constant co-operation of mental images, gradually
lose their psychical concomitant and become automatic; in
this case only the first impulse still remains conscious. For
this reason, transitions from one stage to the other also char-
acterize this form of the development of automatic action. This
transformation will be fully understood as soon as we have to-
gether investigated the nature of the so-called conscious or
voluntary acts. We find that automatic acts subdivide into two
groups according to their development ; (i) those which have
developed from reflex acts in the course of long ages and many
generations, i.e. phylogenetically ; (2) those which are the product
of voluntary acts during the life of a single individual, i.e. that
have developed ontogenetically. It is very doubtful whether
automatic acts of the second class are ever directly inherited.
By committing a poem to memory during many generations,
thereby rendering the voluntary repetition of it automatic, it is
possible for all of the physical conditions of speech to be gradu-
ally perfected, but no single act itself will ever be inherited. All
automatic acts of the second class are distinguished from those of
the first class by being far too specific and complicated to be
inherited.^ This is a further distinction between the two kinds
of automatic action. The conduct of the young pointer on the
scent of the game during his first hunt, as described by Darwin,
illustrates one of the most complicated, inherited, automatic acts.
— The acts prompted by so-called instinct are also to be regarded
as very complicated reflex acts that likewise occur without con-
sciousness. At a certain time in its life the bird builds a nest ;
the developing genital organs have imparted the requisite external
irritant. This act, however complicated, must still be considered
1 reflex. Inherited ideas do not guide the bird in building its nest,
but without the intervention of any idea whatever, the stimulus

> Meynert overestimates the importance of the automatic acts of the first
class in that he derives all voluntary motions from them (" Psycliiatrie," Wien,
: 18S9) ; MUNSTERDERG underestimates their value in that he derives automatic
;. acts almost exclusively from acts of tlie will.

1 8 Introduction to Physiological Psychology.

originating in the genital organs simply arouses the action of a
reflex mechanism that is inherited. Only after the bird has begun
to build its nest does it become aware to some extent of what it
is about. Therefore these instinctive acts are undoubtedly per-
formed unconsciously ; they do not belong to the voluntary acts
with which we shall become acquainted later. Of course, how-
ever, many of these acts lose their purely reflex character and
resemble the automatic acts. When a frog whose foot has been
crushed leaps away, its movements may possibly be regarded as
purely reflex. We can conceive that, even though the frog while
hopping should not receive new sensations of touch every time it
came in contact with the floor, or new sensations of position every
time it moved its legs, the motions thus executed would still
occur in the manner in which they actually do take place, i.e. as
purely reflex action. The frog performs an automatic act only
when it avoids an obstruction lying in the way of its progress. So
the motions of the bird while building its nest are at least affected
by intercurrent sensations. The first motory stimulus originates
in the genital organs, but the resulting motions are determined
and modified by innumerable intercurrent stimuli. The bird
perceives a straw, seizes it and carries it to a tree. He espies a
flock of wool, and this intercurrent visual stimulus causes him to
seize the flock. In this way the series of motor processes is
modified and complicated. Therefore many instinctive acts are
to be regarded as automatic and not reflex. On the other hand
no instinctive act is a voluntary act.

While the reflex acts are essentially constant, the automatic
acts are characterized by great diversities. The motions executed
in deviating from a definite course vary according to the character
and position of the intercurrent stimulus that causes the deviation.
By reason of this infinitely greater variability, the automatic acts
or reactions resemble the conscious or voluntary acts. On the
other hand the automatic acts are quite like the reflex acts in
that they have no psychical concomitant. We have already set
forth above that there is no ground whatever for the assumption
of concomitant psychical processes, and the example of tlie

Theme and Synopsis of Contents. 19

pianist illustrates best that no such conscious processes accom-
pany the automatic acts. Hence reflex and automatic actions do
not belong properly to the sphere of physiological psychology.
Our consideration of the acts of will in the next chapter will
introduce that subject for the first time. The reflex and automatic
acts present merely the physiological, not psychological, ante-
cedents of voluntary acts.

CHAPTER II.

SENSATION, ASSOCIATION, ACTION.

We have become acquainted with " constancy " as characteristic
of reflex action, at least as regards quality. As a criterion of
automatic acts, we fixed on " the modification of a motion by
external intercurrent stimuli." Let us recall to mind the frog,
deprived of its cerebrum, that is still able to avoid an obstruction.
Neither reflex nor automatic acts have a psychical correlative ;
in other words, both are performed unconsciously. At least we
found no authority for the assumption of concomitant psychical
processes. Let us now analyze a simple conscious action resulting
from an external stimulus. We see a friend, for example, and
greet him. In this case the image of the friend, which produces
a visual sensation, is the external stimulus ; the salutation with the
hand is the resulting action, or, as it has also been termed, reaction.
What was it that co-operated in the production of just this motion ?
It is obvious that a sufficient cause is not to be found in the external
stimulus alone, for if it had been some other person not our friend,
the salutation would not have taken place. It is plain that the
memory of having already seen this same person occurs to us.
A mental image stored up in some manner in the brain, the image
of our friend as it is carried with us in memory, the residuum, of a
former sensible excitation, has influenced cr modified the m.otor
process. If it had been our enemy, we might possibly have
turned away or looked elsewhere. But the memory tells us that
it wour friend ; we recognise him as such and the salutation follows.
In this case, therefore, the course of the reaction is influenced by
intercurrent menial images, which have been called forth from their
state of latency by the sensation itself, or, materially expressed, by
the residua of former sensible excitations. We shall designate the
mental image by / (idea) (Fig. 3), and indicate the modification
of the reaction at first simply by a series of lines connecting /with the
tract SM. The contrast with automatic acts becomes at once
very obvious. The latter are characterized by the modification of

Sensation, Association, Action.

-o nf

motion through the agency of external intercurrent stimuli; "action "
is characterized by the modification of motion through the agency
of intercurrent mental images. The automatic acts are uncon-
sciously performed ; " action " takes place consciously. We there-
fore designate the latter as "conscious," or sometimes as " voluntary
action " ; but we must always keep in mind that these expressions
are simply synonyms for " motion that is modified by intercurrent
mental images," or, " motion accompanied by psychical processes."

Viewed from a purely material point of view, it is impossible to
distinguish many automatic acts at
all from actions. In the case of the
piano player, mentioned above, the
flow of finger-movements is obviously
determined also by the residua of
former sensible excitations. If he
had never experienced the optical
excitations produced by the notes or
tactile excitations produced by the
keys, or if such excitations had
vanished leaving no trace, the flow
of finger-movements could not take ^
place as it actually does. The
material characteristic of action, viz.,
that the motion is influenced by the ^•
residua of former excitations, is also peculiar to many automatic acts,
— in fact, to those which develop from conscious actions during the
life of the individual through practice. Hence such automatic acts,
although they have lost their psychical concomitant, are still some-
times regarded as actions. In the following we shall always draw
the line at the psychological characteristic, and only call those
movements actions that are accompanied by conscious processes.

The above is also a typical case of all psychical processes.
There is no psychical process having a physiological correlative,
i.e. no psycho-physiological process, that the above-described
process does not comprehend. A survey of its single elements
furnishes us at once with the best classification and summary of
our science. The external stimulus £ (excitant), with which we
shall begin, is a purely physiological element. By irritating the

22 Introduction to Physiological Psychology.

extremities of the sensory nerves, this external stimulation be-
comes a nerve-excitation. This nerve- excitation is another
physiological process, that may also be properly regarded as
physical or chemical. This physiological process of excitation is
transmitted toward the centre along the path of the centripetal
nerves, and finally produces an excitation in the cerebral cortex
at 5 (sensation). The first psychical element, the sensatioti,
corresponds to this cerebral excitation. Therefore, the first part
of physiological psychology treats of the theory of sensation. In
the above case we have assumed one sensation as the starting-
point of the " action." Generally, however, many sensations
take effect at the same time, and the action occurs as the resultant
of several or many sensations. But it is not always necessary
that these sensations operate at the sarne titne. On the contrary,
they may also appear in part as intercurrent factors while the
mental images that have already taken effect are still active, as in
the case Of the automatic acts. Accordingly, the scheme of the
simplest action wiil appear as represented in Fig. 3. The difference
between simple action and automatic action consists only in the
fact that in the former, in addition to the intercurrent sensations,
intercurrent mental images appear and modify the motion. In
the above statement we have silently accepted the hypothesis
that " action " is always accompanied by a psychical process. In
fact, self-observation teaches that every action is attended by a
psychical process ; but this connection is not absolutely necessary
It is possible to conceive that all our actions, even the most
complicated, abstractly considered, have a purely mechanical or
material cause. Ordinarily we imagine that all the complicated
actions of human life are more easily explained by introducing
the help of psychical processes. The opposite is correct; all
actions, even the fittest and most complicated, can be understood
as the effect of the material processes of the brain. But, on the
contrary, there is something wonderful and inexplicable in the
fact that only a certain part of these cerebral processes, certain
processes of the cerebral cortex called " actions," are accompanied
by psychical processes, and are therefore connected with a new

Sensation, Association, Action.

series of phenomena that can only be known through the con-
sciousness. Considered as purely material, the process of " action"
is as follows : A certain stimulus imparts a cortical excitation ;
the latter, however, is not transmitted directly to a muscle along
a centrifugal path until after it has been essentially modified by
the action of the residue of former cortical excitations imparted
by former stimuli. The cortical excitation corresponds to the
sensation, S; the residua of former cortical excitations correspond
to the mental images or ideas, /. By natural selection, this
mechanism of the brain has been so developed that the residua of
former excitations can be utilized in the most complicated
manner.^ Therefore every action can be conceived of as a
purely physico-chemical process. It is only through self-observa-
tion that we know our actions are accompanied by psychical
processes. Hence we are justified in ascribing concomitant
psychical processes to all those animal actions that cannot be
accounted for without assuming the co-operation of ideas {i.e. the
residua of former cortical excitations occurring in the life of the
individual), although our conclusion is drawn merely from prob-
abilities.

The statement, made above, that one simple sensation rarely
operates alone, requires still further confirmation. Let us con-
sider a well known experiment of physiological optics. Suppose
a point of homogeneous red light to flash upon the dark field of
vision. Suppose, furthermore, that this point, on account of its
infinitesimal magnitude, can irritate but a single sensitive ele-
ment of the retina. In this case it might seem as if but one
simple sensation were really active. But think of the innumer-^
able sensations of touch, constantly produced by our clothing and
the surrounding air, which is never quite calm. That many
sensations would still be present, in this case, is obvious. If we
consider further what an exceptional case is assumed in the
above-mentioned experiment, it becomes dear to us at once that
many sensations are constantly taking effect. Sensations which

' MuNSTEUBERG, " Willenshandiung," S. 55.

24 Introduction to Physiological Psychology.

are incapable of further analysis in consciousness, we call simple
sensations. Let us call attention expressly to the fact that the
external stimuli may be very numerous and yet the sensation may
remain simple, as in the case of a tone struck on the piano.
With the exception of individuals that are musically very gifted,
most persons have a simple sensation, although six or more
" overtones," ^ besides the fundamental tone, are produced by the
vibrating cord, and each tone is furthermore composed of a large
number of single vibrations. It is also worthy of notice here
that the same external stimulus, or the same group of external
stimuli may be perceived differently by different individuals. One
may perceive a simple, another a complex sensation. In fact,
even during the life of the same individual, a simple sensation
may become complex, or a complex sensation may become
simple. At first, when C is struck on the piano, we hear but a
single composite sound. Despite the consonant overtones the
sensation is simple. By practice, however, we can also cultivate
the ability to distinguish the overtones in the composite sound
from the fundamental tone C ; thus the simple sensation will
have become complex. On the other hand, several sensations
that often enter consciousness together may blend to a single
sensation. For example, the taste of an apricot is composed of
innumerable sensations ; yet we experience but one sensation of
taste when we eat the fruit.

As soon as the sensation is associated with the ideas, the play
of motives (deliberation) commences. With a view to future
considerations, this play of motives, or deliberation, may be
termed more properly the activity of Association. This name
shall designate the sum of all psychical processes that are in-
duced by sensation and that result in action, i.e. all intercentral
processes occurring between S and M (fig. 3). Association
makes use of the sensations received at S (including those that
may appear later as intercurrent) and the mental images that have
originated in former sensations. The latter are briefly designated

1 Also called "partial tones" or "harmonics."— 7"j

Sensaiiofi, Association, Action.

as ideas ; the sensations themselves, in so far as they enter into
the function of association, are termed perceptions. In the Htera-
ture of psychology a remarkable confusion prevails as regards
the conceptions " sensation," " perception," and " idea." For this
reason let us be sure to remember that perception and sensation
are to be understood as referring essentially to the same phenome-
non. In a certain sense, sensation is the unused raw material ;
perception is this same material in use. We shall make no dis-
tinction between mental image and idea. Such images exist
without doubt. The sensation of sight, imparted by a rose that
we once beheld, is not totally lost after the flower has disap-
peared. If we see the rose again, it does not appear wholly new
and strange as at first ; but we recognise it as one that we have
seen before. We can, in fact, reproduce its image in thought by
the help of the imagination without its reappearance before our
eyes. The existence of images of memory is therefore indis-
putable. It is supposed that they are deposited in the cells that
presumably constitute the fixed points of rest in the confused
interlacing of cortical fibres. This conception, at least in its
native simplicity, is not correct. We will therefore postpone the
question concerning the material basis of these mental images —
where and how they are deposited — until we come to the second
part of our science, which treats especially of ideas.

The theory of association, by far the most interesting and most
important one of our subjects, constitutes the third part; the
theory of action resulting from association, constitutes the fourth
part. With refefence to the last, let us guard against a certain
erroneous idea from the beginning. Action itself, as motion of
the muscles, has no psychical correlative, and is therefore a
purely physiological process. During a conscious or voluntary
motion, i.e. a motion which is neither automatic nor reflex, there
are but two psychical phenomena of which we are conscious.
Let us take, for example, the intentional movement executed
with the right arm in trying to grasp an object lying before us
and acting as an incentive. In this case the only conscious
phenomena are as follows : —

26 Introduction to Physiological Psychology.

1. The idea of the motion required in grasping the object.
This idea of a motion that we have often executed is the purpose
or motive of which we are conscious in the first moment. Such
mental images are termed " ideas of motion."

2. The sensations by means of which we become aware that
the motion has been executed. We see the arm moving, we feet
the object seized, and finally the sensory nerves in the interior of
the right arm inform us that the muscle has contracted. This
last most important sensation is designated as a " kinaesthetic
sensation " or a " sensation of motion " in the narrower sense.

That no conscious factor is inserted between the idea of the
desired motion and the sensation of the executed motion, is a
fact that can be easily confirmed by the test of introspection.
No psychical process intercedes between the idea of motion and
the sensation of motion. At one moment we have the idea, at
the next the sensation of motion. Thus we see that when action
is subjected to analysis, it is reduced to two psychical elements,
the idea and the sensation. Besides these there is no other
psychical element that is characteristic of action. The fact that
we have experienced a sensation leads us constantly to assign
some stimulus as the cause of our sensation. We conclude that
a contraction of the muscles and a movement of the arm have
taken place only when we have a sensation of motion, which is
confirmed by sensations of touch and sight.

We have found that the motor scheme begins on the one
hand with external stimulation and sensation and closes on the
other hand also with sensation and external stimulation. The
entire psycho-physical process is brought in as an accessory
current. Through this psychological view, the antithesis of sen-
sory and motory elements loses a great deal of its significance.
Motor elements, in the strict sense, do not participate in the
psychical life ; all conscious phenomena are either sensations or
memory images. A third psychical factor does not exist, unless
we wish to consider the association of sensations and ideas as such.

The investigation of the important general and, in part, philo-
sophical deductions, that may be drawn from the above discussion.

Sensation, Association, Action.

is foreign to our present purpose. At present we wish to demon-
strate that all psycho-physical processes are included in the above
scheme. There is no psychical process whatever that is produced
by the operation of other elements than those named above ; nor
is there any psychical process that does not make use of these
two elements by means of the association of ideas. It is true,
however, that many of our psychical processes are shorter than
ihe process just described. In the first place, it is not necessary
that the association of ideas, caused by sensation, should always
result in motion. The influence of the ideas may moderate and
finally inhibit the motor process. Conduction having been thus
checked in the internuncial paths, the intercentral incitation caused
by the sensation either awakens no idea of motion at all, or only
an idea that is not sufficiently intense to impart the motion. Let us
take the example of a rose. The external stimulus, the rose in the
garden of a stranger, imparts a visual sensation or perception.
We see the rose. Instantly numerous mental images or ideas
become active. We remember the fragrance of the rose and
fancy our room decorated by it. These are all ideas that urge
us to act, to perform the motions of seizing and plucking the
flower ; hence, as we shall say, their effect is positive. But other
ideas also occur to us ; we remember that the garden is the
property of another, and that a penalty awaits us if we take what
does not belong to us. These ideas have a negative effect ; they
tend to restrain our hand and arrest the act. This may lead to a
genuine conflict between sensations and ideas, or between oppos-
ing ideas. The play of motives (deliberation) becomes a struggle
between motives (hesitation). The action is the product of the
stronger motives, and may therefore often remain wholly un-
executed. Hence the final element of the pyschical process may
be suppressed. The process ceases with perception and delibera-
tion and no motion ensues. Furthermore, it should be expressly
emphasized that, also in case of introspection, we oftan overlook
the action because it is very slight. Thus Lange has shown that
the simple mention of the word " tower," for example, or our own
voluntary reproduction of the idea of a tower, generally causes

28 Introduction to Physiological Psychology.

motions of the eyes that correspond to the contour of the object ;
the acoustic stimulus of the spoken word still causes certain
slight motions. One reason that motion does not always ensue
may be found in the relative weakness of the stimulus. Every
sensation, indeed,_has a motor tendency — it tends to generate
muscular action ; but different sensations have this tendency in
very different degrees. The sensation must have a certain in-
tensity in order to overcome the resistance to conduction in the
intercentral paths and to produce a motor effect. The associa-
tion of ideas may either increase or diminish the resistance to
conduction. A very singular position is occupied by those
actions in which the motion is not confined to the one occupying
the mind, but is accompanied by other motions that are seem-
ingly superfluous. The person who is about to strike a blow,
clinches his teeth ; often before the blow is given there is an
almost universal tension of the entire muscular system, such as
is characteristic of animals while crouching in " intense " expec-
tation. Scarcely perceptible tensions of the frontal muscle very
frequently accompany our actions, especially where strong emo-
tions are present at the same time. Such actions as these we
are especially inclined to designate as voluntary actions, kwt
i^oxw. This tendency, assisted by the fancy that we act from
choice in the association of ideas, has led to the assumption of
a special faculty of will. But that which we call will, on strict
analysis, is reduced essentially to the sensations of tension ac-
companying the association of ideas and the action. The feeling
that we exercise a free choice in the association of ideas and in
action, is easily explained by the fact that, in distinction from
automatic acts, association and action are not only determined
by external stimuli, but are also influenced by ideas, the sum
total of which we may designate as our empirical " Ego." A
definite action must follow certain external stimuli and certain
ideas according to an inevitable law of causation, just as a stone
detached from its support must fall in a certain direction with a
certain velocity. Accordingly, physiological psychology acknow-
ledges no freedom of the will. Since Spinoza, our great philoso-

Sensation, Associatioti, Action.

phers have been agreed in this point. But we believe that we
exercise a free choice because, (i) we ourselves are conscious^
participants in the active association of ideas ; and (2) although
the result of this association or, in other words, the result of the
play of motives, is not distinctly foreseen, it is nevertheless anti-
cipated ; (3) because the decision is also finally made by a part
of the Ego, i.e. the prevailing ideas.

We shall always speak simply of actions; we may add the
term " conscious " and speak of conscious actions, but we must
always keep in mind that every action, in distinction from reflex
and automatic acts, has a psychical correlative, and is therefore
psychical or conscious. The action is also frequently designated
as a voluntary action or action of the will. But this is also a
pleonasm. Every action, as such, is a voluntary action or an act
of the will. We may make use of this combination of terms also,
but we must not associate with it the false idea that actions are
produced by a special faculty, the will. There is no such special
faculty of the will. The expressions "action of the will,"
" voluntary action," and '•' conscious action " signify no more to
us than the simple term "action."

We have seen above that the psychical process as traced by us
consists of three chief factors, (i) the sensation or perception, (2)
the play of motives or association of ideas, and (3) the action. It
has already been emphasized that the result of the play of motives
is often negative ; the action prompted by the association of cer-
tain ideas is not performed because other ideas, more numerous
and energetic, arrest it. Let us consider another very striking
example of this fact. While hearing a play in the theatre
innumerable visual and acoustic stimuli affect us. Numberless^
ideas are constantly being associated with the perceptions that
have thus arisen. A certain character in the play is killed.
Many ideas urge us to the aid of the imperilled individual, but
they subside before the far stronger recollection that it is all only

» Consciousness is merely an abstraction. The association of ideas, with
its accompanying sensations and images, is consciousness itself.

30 Introduction to Physiological Psychology.

semblance, and that we should make ourselves ridiculous if we
attempted to rescue. Therefore we remain quietly seated; no
action takes place. We have already seen above, however, 'that
the motor action is often simply overlooked because it is so
slight ! Who has not at times noticed an almost imperceptible
quivering of his limbs while witnessing such a scene as the one
just described ? The omission of the final motor stage of such
psychical processes is remarkably frequent, when the processes
have originated in weak sensations or in sensations that have but
a slight motor tendency.

One would suppose that in very rare cases both the second and
the third stages— the association of ideas or the deliberation fol-
lowing the perception, and the motion— may possibly be omitted.
In this case we should speak of pure perception or the simple
apprehension of sensations. But if we consider that the essence
of the psychical process consists in the activity of ideas, we
shall doubt whether such pure perceptions ever occur at
aU.

■ For the same reason the middle stage of the psychical process,
the association of ideas, can never be entirely omitted. It can
only be very much shortened. For example, a person suddenly
receives a blow and almost instantly returns it. How few hasty
ideas flash through the mind in the moment intervening between
the reception of the blow and retaliation ! In this case the
counter-attack occurs almost automatically ; the reproduction of
ideas may finally be almost entirely excluded. We are acquainted
with a mental disease, mania, in which, from pathological causes,
the association of ideas occurring between sensation and action
has become regularly and excessively shortened.

The first stage of the psychical process, the sensation, can like-
wise never be entirely omitted. In fact, there is no psychical
process that cannot be traced to an external stimulus and the
sensation imparted by it.

But stimulation and sensation are often so remote or so weak
that the second and third stages seem to be independent of their
influence. Let us suppose, for example, that we have chanced to

Seiisatioti, Association, Action.

see a friend. Now, this one perception is followed by the recol-
lection of numerous ideas ; with these we constantly associate
new lines of thought that ultimately have no connection what-
ever with the friend. These lines of thought, if they have a
motor tendency, may produce action ; or, as we have seen, the
I action may be entirely arrested. In the first case the action
I seems to be the immediate result of the reproduction of ideas
I without external stimulation, and is then commonly designated
I as spontaneous. The second case is exemplified by so-called
I simple reflection or thought ; the primary stimulus of sensation is
I so remote and the motor tendency is at the same time so slight
i that action cannot take place.

It is also difficult to determine where action (a nervous process
undoubtedly accompanied by a psychical process) is first met
with in the animal series. It does not appear that such a process
has been demonstrated with absolute certainty even in the
Echinodermata.

Let us now briefly review all of the functions connected with
the life of the nervous system. We have classified as follows : —

1. Reflex action: Motion constant and generally fitting;

results from one or more external stimuli; no psychical
correlative.

2. Reaction (automatic acts) : Motion modified by one or

more intercurrent stimuli ; generally fitting ; no psychical
correlative.

3. Ideational Actions or Acts (conscious or voluntary

actions or acts of the will) : Motion results directly or
indirectly from one or more external stimuli ; modified
by the association of intercurrent sensations and ideas ;
generally fitting ; with psychical correlative.
Since action furnishes us with an outline of the psychical

process, we have at the same time learned the psychical elements

of action.

1. Sensation or perception.

2. Image of memory, or idea.

There is no ground for the assumption of any other elements

32 Introduction to Physiological Psychology.

in the psychical process. This process itself is divided into three
stages : —

1. Sensation or perception ;

2. Association of ideas or Ideation (also called the play of

motives or deliberation) ;

3. Action, sensu stricto ; the resulting idea of motion precipi-

tates the act.

The omission of the third stage and the disappearance of the
first stage give rise to a subordinate form of psychical function
that is of especial importance. This is simple reflection or
thought.

We will now briefly attempt to form a conception also of the
anatomical localization of the three nervous processes— reflex
action, automatic action, and voluntary action. The brain of
vertebrates consists of gray and white masses, the ganglion-cells
being the most essential constituents of the gray masses. The
white mass consists chiefly of nerve fibres. Besides the proto-
plasmic processes, that do not interest us here, every ganglion-
cell has one so-called axis-cylinder, which divides dichotomously
(often in the shape of a T), or often traverses long distances
comparatively undivided. The accompanying figure presents a
scheme of the most important fibre-connections of the central
nervous system, s represents the peripheral termination of a
sensory fibre that may be conceived of as ending either in the
retina, cochlea, or the outer skin. Leading toward the centre, it
reaches the spinal marrow {Sp) by means of the so-called posterior
roots. Here it sends off" numerous lateral branches. The most
important of these to us is the lateral branch s'^, which envelops
with its terminal ramifications a motor cell of the anterior horn of
the spinal cord, thus transmitting its excitation to the cell by
contact. This envelopment of a cell by the terminal ramifications
of a nerve-fibre is always represented in the figure by an arrow-
head directed toward the cell. The main branch of the sensory
fibre ascends further toward the centre, giving off" lateral branches
still more frequently all along this part of its path. Thus, for
example, in Fig. 4, a lateral branch is indicated, which is sent

Sensation, Association, Action.

Fig, 4.

Scheme illustrating the course of nerve-fibres in general. C = cerebral cortex ;
T = thalamus opticus ; Sp = spinal cord ; M = muscle ; s = peripheral ter-
mination of a sensory fibre ; g* = cortical ganglion cells ; t = motor cell
of the thalamus opticus ; h = cell of anterior horn of the spinal cord ; mc mt mp
= motor paths , i' = sensory paths ; a* = associative fibres.

34 Introduction to Physiological Psychology.

off in the region of the optic thalamus, and envelops the thalamic
motor cell t. The last terminal ramifications of the sensory fibre
envelop a sensory cell of the cortex g^. The axis-cylinder
process of the latter is converted into a fibre a}, which sends off
numerous branches ; it finally passes into one of the branches of
another axis-cylinder process (divided in the shape of a 7) uniting
with another ganglion-cell, ^^ The other branch of this axis-
cylinder process is continued in the fibre a^^ which finally envelops
the motor cell of the cortex, g^. The fibres d}- and which
connect with one another, are called "fibres of association," or,
" associative fibres " ; to the physiological psychologist they have
a very special significance. It was the notable service of
Meynert,^ the recently deceased alienist of Vienna, to have first
discovered the extraordinarily important function of these associa-
tive fibres in the mechanics of the brain. The motor cells of the
cerebral cortex, as g^, together occupy a definite region of the
cortex, which is briefly designated as the motor region. From g^
issues an axis-cylinder process which, without giving off any
important lateral branches, passes into a motor fibre, im. All
such fibres having their origin in the motor region of the cerebral
cortex, are together designated as the " pyramidal tract ". The
fibre m extends without interruption to the motor cell of the
anterior horn of the spinal cord, which it envelops with its terminal
ramifications. The same cell h is also encompassed by the
terminal branchings of the fibre trf, which takes its rise in the
motor cell / of the optic thalamus. The cells of the anterior
horns of the spinal cord receive motor impulses both from the
cerebral cortex, the large ganglia, and ^. The peripheral motor
fibre mp issues from the axis-cylinder process of the cell //, leaves
the spinal cord by way of the anterior roots, and finally terminates
in the muscle M.

Besides the cerebral cortex, which encompasses the cerebrum

1 Meynert, " Zur Mechanik des Gehirnbaues," presented at the assembly
of natural scientists in Wiesbaden ; also printed in the "Sammlung popularer
Vortrage Meynert's," 1892. Vienna, W. BraumUller.

Sensation, Association, Action.

like a thin shell, the optic thalamus, and the gray masses of the
spinal cord, there are numerous other gray masses, among which
we may take note here of the corpora quadrigemina and (in
certain animals) bigemina, and the gray masses of the cerebellum/
Both in the gray masses of the spinal cord and in the higher
situate optic thalamus, cerebellum and cerebrum, the sensory
fibres are connected with motor cells either directly or by means of
ganglion-cells and internuncial fibres. Hence a sensible stimulus
can be transferred to motor elements at various places, anc
impart motion. One gray mass produces chiefly reflex action, a
second chiefly automatic action, and a third only conscious
action.

Now physiology teaches that the reflex action of vertebrates
generally originates in the spinal cord, although in the case of
the frog the corpora bigemina and the cerebellum are also chiefly
involved in the reflex mechanism. The movements of the frog
when it wipes off the skin on the back that has been moistened
with acid, when it hops away after its foot has been pinched,
when it recovers the natural position upon the abdomen after
having been placed on its back, when it balances itself while sit-
ting upon a hand that is revolving, are all reflex acts that can be
shown to depend upon the spinal cord, the cerebellum, the so-
called medulla oblongata, and the corpora bigemina. We have
not vet been able to localise these motor functions in higher ani-

^ The above sketch is neither complete nor as yet verified in all particulars
by investigations at present available. Its aim is merely to furnish us v\ith an
approximate picture of the complicate connection existing between cells and
fibres of the central nervous system. It is based especially upon the most
recent labours of Golgi, Flechsig, v. Kolliker, Ramon y Cajal, Forel, ^
and others. For more exact instruction regarding the anatomical relations of
the bram and spinal cord, see Wernecke, " Lehrbuch der Gehirnkrank-
heiten," Bd. I., Kassel, i88i ; Obeksteiner,, " Anleitung beim Studium
des Baues der nervosen Centralorgane," Vienna, 1892, 2d. ed. ; or Edinger,
"12 Vorlesungen iiber den Ban des Centraliiervensystems. " Finally, if one
desire to read special chapters upon the details of cerebral anatomy and
physiology, he is referred to the author's article in the " Reallexikon der
niedizinlschen Propadentik," edited by J. Gad, Vienna and Leipsic, 1S93.

hitrodtiction to Physiological Psychology.

mals so exactly, although in these the chief organ of reflex action
is also the spinal cord.

In the case of the frog, reactions or automatic acts only occur
when at least the optic thalamus, corpora bigemina, cerebellum
and spinal cord are retained. We have already seen that a frog
in this condition avoids an obstruction that has been placed in
the path of its progress, showing that it is able to react automatic
ally. It is also probable that the optic thalamus is the chief
centre of automatic action in the higher orders of animals, in-
cluding man.

Voluntary actions were characterised by the intercurrence of
ideas. Experimental physiology indicates with the greatest prob-
ability that ideas are deposited only in the cerebral cortex, and
that therefore actions originate only in the cortex. If the cortex
of the occipital lobe of a dog be removed, the animal . loses all
visual sensations and ideas, i.e. also all the images of former sen-
sations of sight.i Corresponding results have been obtained for
all the senses. Therefore the cerebral cortex is the seat of that
nervous process, which alone, as we have shown, is certainly ac-
companied by a psychical process ; it is therefore the seat of all
psychical processes, sensation or perception, the association of
ideas and voluntary action. This view also agrees very well with
the anatomical fact, that the pyramidal tract, through which, as
we have shown, our voluntary motor impulses are conducted to
the muscles, extends uninterruptedly from the cerebral cortex
through the deeper ganglia until it reaches the spinal cord. In
the same way that the reflex acts depend upon the spinal cord,
and the automatic acts upon the optic thalamus, the voluntary
actions depend exclusively upon the cerebral cortex. Still

* MuNK was the first experimenter who showed that an animal in this con-
dition no longer has visual sensations or ideas. It lias not yet been experi-
mentally determined vviih certainty whether the movements of a dog or rabbit
that has been deprived of the cerebral cortex, are still influenced l)y visual
stimuli, i.e. whether in the dog or rabbit, the same as in the frog, the optic
thalamus is sufficient for the production of automatic action (for example, the
avoidance of an obstruction).

Sensation, Associatiott, Action.

another fact agrees with this statement. Animals in wliich all of
the cerebrum except the optic thalamus has been extirpated, are
characterised by great restriction of the so-called spontaneous
motions, i.e. motions that are not tlie immediate result of external
stimuli. These spontaneous motions are chiefly acts that result
directly from ideas whose primary external stimulus is very re-
mote. Like all actions, they also depend upon the cerebral cor-
tex, and must disappear when the latter is destroyed. However,
a few spontaneous motions still take place, as in the case of a
pigeon from which the brain has been removed. This is ex-
plained by the fact that internal stimuli (hunger, thirst, etc.) still
continue to produce reflex motions which we are accustomed to
designate as spontaneous,^ because these internal stimuli are in-
visil)le. In such cases the circulation of the blood carries the
excitation imparting motion to the centre, thus taking the place
of excitation through the centripetal nerves.

In the course of the phylogenetic development of the animal
series, many a function will have changed its location. The
cerebellum of the frog without the corpora quadrigemina, for
example, is still able to impart the reflex motions of hopping,
while the rabbit requires at least the anterior and posterior corpora
quadrigemina, in addition to the cerebellum. In no respect, how-
ever, has the phylogenetic development changed the chief facts of
localization, as above stated.

The localisation of reflex action, automatic action, and con-
scious action in the invertebrates, is far less certain. So little has
been established, especially concerning the voluntary actions of
these lower animals, that attempts at localization have thus far
been too hasty. Our future investigations will therefore be con-
fined to vertebrates, particularly to man. The latter is alone able
to give us any information concerning his psychical processes ;
for, to repeat it, we only know that phenomena are psychical
when we ourselves are conscious of them.

Preyer designates them as impulsive. Bain as automatic motions.

CHAPTER III.

STIMULUS — SENSATION.

In this lecture we begin the discussion of the single elements of
the psychical process with the first element — sensation. As we
have seen, the external stimulus first imparts the sensation. Only
motion, in the broadest sense, acts as stimulus upon the peri
pheral organs of sense. But not every motion can produce an
excitation of the terminal ramifications of our sensory nerves that
will be conducted toward the centre, and finally generate a similar
excitation in the cerebral cortex and, as a correlate of the latter, a
sensation. Let us first briefly review the various kinds of motion
to be met with in nature, that can act upon the peripheral organs
of sense. They are as follows : —

1. Motions of impact : This class-name designates all those
motions that may be regarded as the impact of elastic or inelastic
bodies. In this case a definite motion is executed in a definite
direction by a material body, i.e., by an entire complex of number-
less molecules. To this class belong all the stimuli of contact
and pressure. The latter we can conceive of as motions of
impact having the approximate velocity of O.

2. Chetnical ?fiotions : These motions result in chemical changes
within and among the molecules. Besides the stimuli of taste
and smell, many visceral stimuli also probably belong to this
class.

3. The motions of ether : Physiological psychology must accept
the hypothesis of physics, that particles of ether pervade the space
between the molecules of matter, and that the vibrations of this
ether, according to their velocity, produce the phenomena that

Stimulus — Sensation.

are designated as " light," and " radiant heat," " magnetism " anc
" electricity ".

The acoustic stimuli, and the thermal stimuli in so far as the
conduction of heat is concerned, are to be classed under motions
of impact. As yet we know but little of the special characteristics
of thermal stimuli. In distinction from other motions of impact,
acoustic stimuli are characterised by the fact that the projectile
motions of the single molecules of the vibrating body, produce a
wave of motion in a definite direction, which is immediately fol
lowed by a recurrent wave in the opposite direction.

The number of stimuli that produce direct excitation of the
nerve-ends, and that are therefore to be considered by physio-
logical psychology may be still further reduced. We know that
those motions of ether that produce light do not act directly on
the retinal terminations of the optic nerve, but produce chemical
changes, or, as we may also say, chemical motions, in the retina.
It is only these chemical processes that act as stimulus upon the
ends of the optic nerve.

Therefore only two chief groups of sensible stimuli remain;
they may be designated as chemical stimuli and mechanical
stimuli. To these we may add the electric stimuli of sensation
as a third group, not ignoring the fact, however, that the electric
stimuli may also first produce chemical changes in the fluids of
the tissues wliich envelop the nerve-ends, and that these chemical
processes would then be the immediate irritants.

As yet we are too little acquainted with the physical character-
istics of radiant heat to be able to determine whether it acts
directly upon the nerve-ends, or through the mediation of chemi-
cal changes. It is also questionable whether radiant heat, as
such, acts directly upon the nerves as a stimulus at all; or
whether it must not first be converted into conducted heat.^ It
is at least probable that the sensation of heat in the hand, when
near a glowing stove, is produced in the following manner :—

» But the question is still undecided as to whether the epidermis is diather-
ous or not ; Masje claims that it is, Goi.Dsc it rider that it is not.

40 Introduction to Physiological Psychology.

The surface of the hand next the stove is first warmed by radiant
heat ; the heat thus produced in the surface of the skin is then
eondiicted inward to the nerve-ends.

Finally, the irritation of the nerve-ends by magnetism has never
been observed with certainty. On the contrary, Hermann's ^
experiments seem to demonstrate the inabihty of magnetism to act
as a nerve-irritant ; he placed both animals and parts of animals
within the magnetic field of a large electro-magnet, and observed
no effect whatever.

Hence two forms of the motions of nature, magnetism and
radiant heat, in the light of our present knowledge, seem to be
excluded from the list of nerve-irritants ; even the other forms
of motion are effective only within certain limits. For example,
motion that produces sound must have not less than sixteen nor
more than 40,000 vibrations per second ; otherwise no irritation
of the nerve-ends seems to be produced. Similar Hmitations are
found in the case of ultra-red and ultra-violet rays of light. It is
already probable that the non-nervous elements of the sense-
.organ that first receives the external stimulus, act like a sieve,
arresting certain qualities of the irritating motions and permitting
certain other qualities to pass on and irritate the nerve-ends.
Thus, to a certain extent, the organs of sense have a power to
select which is doubtlessly a natural fitness, brought about by the
struggle for existence. There is no ground whatever for refernng
the exercise of this selection to the activity of cerebral centres.
It is much more probable that the selection, which is apparent in
the exclusion of ultra-red and ultra-violet rays of light and of
sound-waves, having too great or too little velocity, is accom-
plished at once in the peripheral organ of sense. Therefore we
piay assume that certain mechanical and chemical motions pro-
duce no nervous excitation whatever. This peripheral selection
is essentially determined by the quality of the stimulating motions ;
we shall presently learn of another form of selection that is ac-
complished in the central nerve-organs and which is determined

' Pfluger's Archiv, Btl. 43.

Stininlns — Sensation.

by the intensity of stimulation. It has often been claimed that
the power of qualitative selection is exercised by the nerve-ends
to a still greater extent. For example, it has been supposed that
the terminations of the optic nerve are only sensitive to chemical
stimuli produced by the vibration of ether, and the terminations
of the auditory nerve only to acoustic stimuli. This question is
closely related to the theory of the so-called specific energy of the
sensory nerves.

The latter has often been attacked recently, and in consequence
the theory has had to be greatly modified. The following state-
ments, taken from the theory of the specific energy, are of funda-
mental importan'fce to our future considerations ^

According to the above statement it is very doubtful whether
any kind of stimulus whatever is capable of irritating the ends of
any nerve, i.e., whether the nerves are characterized by receptive
indifference. The selection exercised by the non-nervous elements
of the sense-organ in fact is followed by another in the nerve-ends.
Every sensory nerve has its specific or adequate stimulus. Light
is the adequate stimulus for the eye, sound for the ear, etc. On
the other hand, however, wholly disparate or inadequate stimuli
may also sometimes cause irritation of the nerve-ends. If
the retina be twitched, for example, this mechanical irritation
produces a glimmer of light. Particularly the mechanical and
electrical stimuli seem to be nowhere wholly excluded from
reception as irritants of the nerve- ends.^

But an excitation produced by some inadequate stimulus in
the nerve ends, in being conducted to the central organs of sen-
sation, will traverse paths and reach terminal centres that have
been fitted by transmission and exercise for the reception of
very different excitations. This excitation, therefore, will not iiar-
monize well with the nervous elements upon which it has been

• WuNDT, "Physiolog. Psycholosie," I, S. 332 and ff. Munk, Sitzungs-
ber. d. Konigl Pr. Ak. d. Wiss., 1S89.

* GoLhseuniDitR assumes, it is true, that whenever they appear as inadequate
stimuli, they act directly upon the ncrve-fil)rLS instead of upon llie end-organs
of sense themselves.

42 Introduction to Physiological Psychology.

forced. Despite the fact that they are not fitted for the reception
of different stimuli, however, the elements of the path and
terminal centre, will at least endeavour to harmonize to some
extent with the inadequate excitation, coming from the peri-
phery, and to receive and transmit it. But they will be able to
actually receive and transmit only a small part of E. All that is
specifically characteristic of E is therefore lost; there will remain
but a very vague excitation as the residue of E, and even this
will have been transformed so as to render it capable of affecting
a path and centre that have been trained for the reception of
other specific excitations. We can pull the optic nerve in any
way we please, but we always produce the same sensation of light.
It is uncertain whether this adaptation of nervous elements to
inadequate stimuli is accomplished chiefly in the nerve-path or in
the nervous centre ; probably in the latter. The most important
fact is that such an adaptation is effected, both in the non-
nervous elements of the peripheral organ and in the nerve-ends,
nerve-path, and, finally, especially the nervous centre. In this
sense the theory of specific energy is properly to be understood.
To deny the validity of the theory, as thus understood, would be
to contradict all the fundamental principles of evolution, which
assert that every function determines the character of its organ,
or, in a certain sense, trains its organ for its own use. Therefore
we must reject Wundt's assumption that all paths and centres are
functionally indifferent, and that the processes generated in the
central cells are only different because the stimuli are differentj
and because the irritation is transmitted to the nerve-paths in all
Its native individuality.

As yet we have no sure knowledge as to the nature of the
excitation while being conducted through the nerves. We were
formerly inchned to assume conducting currents of electricity,
while more recent views more correctly regard conduction in the
nerves as a chemical process. In connection with the latter
hypothesis, the theory of specific energy may still assume that
the excitation is conducted through the nerves in different ways,
according to the diff"erence in stimuli. That each nerve-path,

StiDiulus—Sensation.

including peripheral terminations and centre, is not only fitted
for a single quality of excitation, but also for a series of similar
qualities, agrees very well with the above theory. Hence it
follows that the constitution of the nervous system is an essential
factor in determining the quality of sensation. This fact reveals
the obvious error of former centuries, first refuted by Locke,
though still shared by naive thought to-day, that the objects about
us themselves are coloured, warm, cold, etc. As external to our
consciousness, we can only assume matter, vibrating with mole-
cular motion and permeated by vibrating particles of ether. The
nerve-apparatus select only certain motions of matter or of ether,
which they transform into that form of nerve-excitation with which
they are familiar. It is only this nerve-excitation that we perceive
as red, warm, or hard.

The following table gives a comprehensive review of the
different forms of irritation : —

Stimuli.

Intermediate Process
IN THE Peripheral
Apparatus.

Organ.

Vibrations of ether ;
400-900 billion (Eng.
num.) vibrations per
second.

Transformation into in-
tra-molecular cliemi-
cal motion.

Eye.

Intra-molecular (chemi-
cal) motions.

Wanting.

Mucous membrane of
the Mouth and Nose
and Organsof General
Sensibility.

Mechanical stimuli (pro-
jection, impact, pres-
sure).

Wanting.

All Organs of .Sense.

Heat.

Wanting.

Organs of General Sen-
sibility.

Electricity.

Possibly, transforma-
tion into chemical
motion.

All Organs of Sense.

Molecular motions of
Sound ; sub-contra
C-eg ; 16-40,000 vi-
brations per second.

Wanting.

Ear.

44 Introduction to Physiological Psychology.

We have now reached one of the chief results of these investi-
gations for physiological psychology. A given stimulus, E
(excitant), generates an excitation in the peripheral ramifications
of the nerves, which we shall designate as Ep (peripheral excita-
tion). This Ep, which has already become different from E,
ultimately reaches the cerebral cortex by way of the complicated
nerve-paths, and, during conduction, undergoes still further, final
modifications. We shall designate that which Ep has become
when it has reached the centre in the cerebral cortex, as Ec
(cortical excitation). In a given case we can determine E exactly
as to quantity and quality, though often with difficulty. Ep and
Ec are almost entirely withdrawn from our observation. Now Ec
is that material process of the cortex to which the sensation .S
corresponds as a correlated psychical process.^ Of course the
exact physical ox physiological measurement of this 6' is likewise
impossible ; but the ^ is a fact of consciousness, and as such is
directly known by us through consciousness. Now what pro-
perties do we perceive in our sensation, or by what characteristics
are our sensations to be distinguished from one another? We
are acquainted with three such distinguishing features; as the
first of these we shall mention the quality of sensations. The
sensations of red and of green, of the tone C, and of the taste of
sugar are different in quality. A further distinguishing feature of
sensations is their intensity. If the tone C is sounded louder and
louder, or if the tongue is moistened with a more and more con-
centrated solution of sugar, the intensity of the sensation varies
without a change of quality. It would be wholly false to reduce
differences in intensity to differences in quality; it is always possible
for the intensity of a sensation to be gradually reduced to zero,
but not for the quality. A third and last characteristic we
designate as the accompanying tone of feelijig. Introspection
teaches that every sensation is accompanied by a feeling of
pleasure or pain (displeasure). This emotional emphasis of
sensations may diminish to zero ; as a rule, however, it is present.
In every sensation, therefore, we distinguish the quality {q), tbn

1 The older psychology was always erroneously inclined to regard the
sensations as " cof^nilions ". This is entirely arbitrary ; the sensation is the
effect of stimuli, and can serve as a means to cognition of the latter, but is
itself not knowledge. Comp. Teichmui-I.e K, Neue Grundlegung der Psycho-
logie u. Logik, S. 66 ff.

Stimulus — Sensation.

intensity (/) and the tone of feeling (/), and indicate them by
placing q, i, and /as the indices oi S,—-Sq if. Later we shall
become acquainted with two other characteristics of sensations
in connection with another subject, — their localization and their
duration.

j Let us now consider the intensity oi sensations. We at once
encounter the question : If the intensity of the stimulus E be
known, what is the / of the accompanying sensation Sf We
I have no means whatever for the exact measurement of the inten-
! sity of our sensations. If we allow two sources of light to act
I upon the eye, we can easily estimate the intensity of each by
I comparison ; but this estimation is only possible as a comparison,
i and even then is capable of but very inexact numerical expression,
i At first, therefore, we shall do better to express the problem as
I follows : Given two stimuli, and E.^, E^ being by a definite
j ratio greater than E.^ (for example, E^ is twice E-^ ; in what
relation do the two intensities of the accompanying sensation
I stand to each other ? As the simplest solution one might at first
1 suppose that is also twice as intense as S-^, since E^ has twice
I ihe intensity of ^1 ; in this case .S would simply be proportional
i to E. To illustrate this relation graphically, one might measure
1 off the stimuli upon an axis of abscissas (fig. 5), and the intensities
1 of the sensations perpendicular to this axis as ordinates. By
simple proportion the series of intensities of sensation would then
produce a straight line (a-e).

If ab (fig. 5) represent the magnitude of the stimulus E^ and
ac the magnitude of the stimulus E^., ac being equal to 2 ab, tiien
ec (the intensity of ^2) is twice as great as db (the intensity of S^.
Closer consideration, however, causes such a simple proportion,
assumed before the application of any experimental test whatever,
to appear improbable. We have already seen that E is received
as Ep, and finally reaches the cortex of the cerebrum as Ec ;
hence E is subject to a long series of modifications before the
correlative process S is imparted. It will be strange, indeed, if
these modifications are shown to be so exact for all the different
magnitudes of E, tiiat Ep always remains proportional to E, and
Ec proportional to Ep. To begin with, it is much more probable

46 Introduction to Physiological Psychology.

that the exact relation between 6" and E is far more complicated,
even though .S increase in general with the augmenting E. Of
course a definite decision can only be furnished by experiment.
However, before we enter into a discussion of the numerous
experiments that have been employed since Fechner to ascertain
the connection between ,5 and E, we must briefly discuss the
meaning of 5 and E. By our own experience we know directly
what is meant by "intensity of the sensation" ; but what is to be
understood by the " magnitude of the stimulus"? Obviously the
quantity of living force contained in the stimulus. It is self-
evident that the measurement of this force is in many cases like-

Fig. s.

wise difficult or impossible. For example, who could determine
exactly the kinetic energy of a source of light ? Only very
recently have we been furnished with exact results in this depart-
ment of scientific research through the investigations of Thomsen
and Tumlirz. But here again we must liave recourse to the
comparison of two stimuli. By permitting the same source of
light, for example, to act first at a definite distance a, and then at
the distance 2 a, we have an intensity of light in the second case,
at least, whose relation to the first intensity can be easily
estimated.

We shall begin our experimental investigations with the follow-
ing simple test. We i)lace ourselves at a distance of 10 m. from

Siimulus — Sensatio7i.

j a trumpet which is blowing with a uniform intensity, and then
I recede from it gradually until we reach a point where we can just
I hear the sound, and then one where we just fail to hear it any
j more. Suppose the latter point to be about 120 m. from the
1 trumpet At this distance the sound-waves still reach our ear, it
j is true, but whether they produce an excitation in the nerve-ends
1' {Ep) or not is doubtful ; it is still more doubtful whether an Ec
I takes place ; but beyond all doubt no S is produced. It follows
! that there are stimuli which produce sensations, the sensible
; intensity of which is equal to O. The stimulus must first reach
a definite intensity before it can impart a sensation, i.e. we must
approach to 119 m. from the trumpet before we hear it. There-
fore, that intensity of stimulus which is just sufficient to impart a
sensation we designate as the " minimum of stimulation " {Reiz-
sc/twelle — threshold of excitation).

We now approach the trumpet gradually ; accordingly the
acoustic stimulation, and likewise the intensity of the sensation
increase. At the distance of 8 m. the sound already imparts a
piercing sensation. We continue to approach, but can now per-
ceive no further increase of the sensation, or, in other words, the
sound is so loud that we do not perceive any further augmentation.
We have reached the point where our sensation is no longer
capable of further increase; hence that intensity of stimulus,
which imparts a sensation incapable of further augmentation, is
designated as the "maximum of stimulation" {Reiz/!dhe=\\e.\g\\X.
of excitation). In the unlimited series of intensities of stimulus
rising from o to cx) , the first section imparts no sensation what-
ever; in the second section the intensity of the sensations increases
with the stimulus ; in the third and last section of the scale of
stimulus, the sensation remains constant at a maximum of inten-
sity, despite the further increase of the intensity of the stimulation.
The graphic expression for this is presented in fig. 6. The curve
of sensations only rises above the axis of abscissas, representing
the various intensities of the stimulus, at a definite distance (the
"threshold," or minimum of excitation) from the zero point; it
then gradually ascends, as the stimulus increases, to a certain

height, and finally, at a definite distance from the zero point (the
" height " or maximum of excitation), ceases to rise, and extends

Stimulus — Sensation.

as a constant parallel to the axis, ^j, E^, etc., (tig. 6) to E^^, are
too weak to produce an S; only at E^^ is tiie tirst S perceived;
J?i2 produces a stronger sensation than E^^, E^^ a stronger sensa-
! tion than E^„. Thus the 6''s augment with the increase of the
£'s, until a sensation generated by ^30, the maximum of stimulus,
I has been reached. Then the folio wmg E.^^ does not impart a
I stronger S than the preceding ^'s, but simply the same 6*30 im-
: parted by E^^. In the same way, all subsequent ^'s are unable
I to raise S above the intensity ^'30. E^^ is the minimum (thres-
hold), the maximum (height) of stimulation.

In this case we have left the question entirely open as to how
the intensities of sensation increase between E^^ and -£30 : whether
in proportion to the increase of the ^'s, or in some other ratio.
A very simple experiment is sufficient to show us that the sensa-
tion does not increase in proportion to the stimulus. Let us
together observe a light, that gradually becomes brighter the
nearer we approach it. By careful self-observation we perceive
that at first the intensity of the light (z.<r. as regards our sensation)
: seems to augment very rapidly, while later it apparently increases
j but very slowly. Therefore, in the graphic illustration, the in-
; tensities of sensation will present a curve that rises at first swiftly
I and abrupdy above the axis of abscissas from the point represent-
; ing the minimum of stimulus, then more and more slowly, until
I it finally vanishes at the point corresponding to the maximum of
stimulus, and becomes a straight line parallel to the axis.

These three essential features of the sentient life — the presence
I of a minimum and maximum of excitation, and finally the increase
I of the intensity of sensation, that takes place between the mini-
I mum and maximum of stimulation, at first rapidly, and then
I gradually more slowly — are, as we can easily conceive, exceed-
ingly fitting. These peculiarities have been developed simply
because they are fitting in the struggle for existence. Natural
selection is just as efficient in the development of psycho-physio-
logical characteristics, as in the development of the purely physio-
logical. The existence of a minimum of excitation protects us
from an inundation of small stimuli, that would flood the con-

Introduction to Physiological Psychology.

sciousness by their very superabundance, and prevent the employ-
ment of the greater, more important stimuli. The existence of a
maximum limit of excitation prevents a superabundance of too
powerful stimuli, and secures the medium stimuli and their con-
comitant sensations from being overshadowed and overlooked.
Both the distracting preponderance of many insignificant stimuli
and the partiality and tyranny of one or a few too potent stimuli
are avoided by this restriction of the sentient life to a range lying
between a maximum and minimum of stimulation. But the third
peculiarity of our " curve of sensation " (its ascent at first abrupt,
then gradually slower) is also generally fitting. In consequence
of this peculiarity (i) we are very sensitive to those small stimuli
that are just sufficient to produce sensation, in fact, we are very
liable to over estimate them ; (2) we estimate the medium stimuli
very accurately, since here the curve approaches a straight line ;
and (3) we begin to lose the ability to distinguish the difference
in the intensity of only those stimuli that approach the maximum
limit.

The attempt has frequently been made to find an exact
mathematical expression for the increase in the intensity of
sensation in its relation to the increase of stimulus, or, in other
words, to determine the path of the curve more exactly. Ernst
Heinrich Weber first employed experiments that seemed to
present a fixed law for the relation between stimulus and sensa-
tion. If we stretch forth the hand and let small weights — at first,
for example, one decimilligr. — be laid upon it, we feel nothing at
all. We lay greater weights upon the hand, to the amount of li
mg. and still perceive nothing. These stimuli are evidently too
small ; they lie below the minimum of stimulus necessary to pro-
duce excitation. Only when we have laid 2 mg. upon the hand
do we have a slight sensation. Therefore the minimum of
stimulus sufficient to produce the sensation of pressure upon the
palm is, apparently, 2 mg. Weber now proceeded with the fol-
lowing experiment. The hand is loaded with a weight of i lb.,
i.e. a weight far above the minimum of stimulus. Now if we add
2 mg. more to the i lb., the sensation remains unchanged. We

Stiimdus — Sensation.

lay more and more upon the hand, but the sensation does not
change until we have added \ lb., or about 160 g., to the i lb.;
then we perceive a change, an increase of the sensation. This
increase of stimulus, that is just sufficient to produce a change ot
sensation, we shall designate as the "absolute threshold* of
difference," the change of sensation itself, as d S. Therefore
only when ^ lb. is added to the i lb. do we distinguish or feel the
increase of stimulus, while before 2 mg. upon the empty hand
was sufficient to make the increase of stimulus perceptible. We
now load the hand with 2 lbs., and add ^ lb. to that ; but the
addition of ^ lb. produces no distinguishable increase in sensa-
tion, and we find that we must now add f lb. in order to obtain
any change of sensation whatever. We take 3 lbs., and as a
result, find that an addition of f lb. is necessary to produce
a noticeable change of sensation. The addition of § lb. to
the previous weight of 3 lb., of f lb. to the previous weight of
2 lb., of \ lb. to one lb., and the laying of 2 mg. upon the un-
weighted hand, all produce in the same manner the sensation of
difference, or, more correctly, a barely noticeable change of
sensation, d S. Now let us consider whether the nerves of the
hand, which was empty before the 2 mg. were laid upon it, were
■really free from the effects of stimulation by pressure? Certainly
not. Both skin and air already pressed upon the nerves of the
skin. The reason that this pressure is not perceived is probably
to be sought in the fact that the pressuro of the skin and air has
existed constantly since birth, and that, as we shall presently
learn, we generally only perceive chajiges in stimulation, and not
stimuli that have long remained the same. This is, for example,
the reason that we have no sensations from the visceral organs,
despite the abundance of their nerves. The fact that we must'
consider here, however, is that the constant stimulation by the
air and skin may still be increased almost 2 mg. without the ap-
pearance of a sensation. But our experiments also teach that
not every change of stimulus produces a sensation ; the latter
appears only when the change of stimulus has reached a certain
limit or magnitude, but this magnitude is determined by the
relative change; the absolute change of stimulus is of no im-

52 Jntrodiictioii to Physiological Psychology.

portance whatever. The law embodying this fact we designate
as the " Law of Weber." In the above experiments the stimulus
must always be increased one-third, in order to produce a cliange
in the sensation. We saw first that a change in sensation, d S,
was produced by a weight of 2 mg. Next, Fechner, going beyond
the limits of Weber's law, assumed that exactly the same sensa-
tion d S\5 produced when i lb. is added to i lb., or f lb. to 2 lb.
and that, therefore, this d S is constant, although it corresponds
to very different absolute increases in stimulation. At first we
shall adopt this hypothesis as assumed by Fechner, the father of
psycho-physics, although, as will appear later, it needs correction.
Accordingly the stimulus must always increase one-third, or reach
four-thirds of its original magnitude, in order to produce d S. If
we designate the number \, the ratio of the barely perceptible
increase of stimulus to the original stimulus, as the "relative
threshold of difference," the Law of Weber may be formulated
thus : The " relative threshold of difference " is constant. There-
fore, beginning with the minimum of stimulus 2 mg., we can
construct a complete scale of stimuli, in which each successive
member is f of the preceding, and in which the difference be-
tween any two adjacent members always produces the increase of
sensation d S, which, according to Fechner's assumption, is
always constant.

This series, therefore, is as follows : —

2-2(|)-2a)2-2(f)3-2(i)4

■ — . — - — r— — . — — . — - , etc.>
dS dS dS dS

Hence the stimuli increase in geometrical, the sensations in
arithmetical progression. Any stimulus E may accordingly be
expressed as 2 times a given power of f . Thus for example :

» We -shall for the present disregard the fact that the Law of Weber is not
exactly valid for very sliaht stimuli.

Stinmliis — Sensaiion.

Then tne sensation S„ produced by E„ is obviously equal to

xy.dS and Sy is equal to j x dS. Therefore :

XY. dS X

— = or -.

yy.dS y

Now we can easily compute the value of x in the above com-
parison logarithmically. If

E^=2 X (!■)*, then
log. ^;.=log. 2 + ^ log. f,

log- ^.-iog- 2

•* i 1 '

log. f

log, ^^-log. 2 .

^ log. f '

Therefore,

S^^ log, jg^-log. 2
Sy log. ^^-log. 2*

Observing, further, that log, 2 (milligr.) is almost infinitesimal,
and may therefore be disregarded, we then obtain briefly,

^^_log.
Sy log. E'y

Therefore two sensations are in the same ratio as the logarithms
of their stimuli, or the sensation is proportional to the logarithm
of its stimulus. This remarkable proposition was designated by
Fechner^ as the "fundamental formula" of Psycho-physics. As
already mentioned, it is only a result of the law of Weber when
one admits the assumption that dS, the barely noticeable sensa-
tion, is always constant. We designate it therefore as the
" Formula of Fechner " in distinction from the " Law of Weber,"
which expresses only the constancy of the " relative threshold of
difference." Others, in fact, have rejected the formula : dS is
constant, and have substituted instead : dS is proportional to
dS

or _ is constant ; among those who make use of the latter are

' Fechner, "Elemente der Psychophysik," and "Revision der Haupt-
punkte der Psychophysik."

54 Introduction to Physiological Psychology.

Plateau and Brentano. In this case the sensation does not
depend upon a logarithmic ratio, but upon the formula 6" = CE^ ,
C and k being constants. Retaining the formula of Fechner until
we shall have examined it more closely later, let us next ask :
Does it correspond to the above-estabHshed characteristics of
the curve of sensation ? We answer in the affirmative. In fact,
the logarithviic curve also belongs to the many curves that are
characterized by ascending, as the magnitude of the abscissas
increases, at first rapidly, then more slowly, becoming constantly
flatter, and finally vanishing in a parallel to the axis.

The experiments intended to demonstrate either the so-called
Law of Weber itself or the Formula of Fechner, have been often
repeated since they were first applied, but the original results
have only been partially corroborated. Many, besides us, have
found the existence of such a simple algebraic relation between
material stimuli and psychical sensations too strange. A great
many sagacious methods have been devised to establish this
relation with empirical exactness. We shall become acquainted
with some of these when we come to discuss the qualities of
sensation separately. In general the most reliable recent in-
vestigations demonstrate that the Law of Weber itself is strictly
valid only within certain limits ; that in the case of very strong
or very slight stimuli, it has but an approximate validity.
Whether the Fornmla of Fechner necessarily follows from the
Law of Weber, even if the strict validity of the latter be granted,
is a question that requires another special discussion. In place
of the former, Helmholtz and others have sought to substitute a
more complicated formula that should conform more closely to
experimental results, but without success.

A still more spirited controversy has been associated with the
interesting question as to what this connection, expressed by the
law of Weber and Fechner, means. There have been investi-
gators who thought they could solve one of the great problems
of the world by this law. Among these also was Fechner, the
founder of psycho-physics, the one whom we have to thank for
the most thorough investigations and discussions in this field.

Stimulus — Sensation,

He assumed that the law is directly valid as expressing the
relation of the psychical phenomena to the physical. We remem-
ber that the stimulus E becomes first Ep and finally Ec.
Fechner assumed that the material cortical excitation Ec remains
proportional to the acting stimulus itself {E) and that only the
sensation 6' following the Ec in the cerebral cortex bears that
remarkable logarithmic relation to Ec, and hence also to E. As
we see, a sort of bridge would thus span the chasm between the
physical and the psychical life ; at least the quantitative connec-
tion between the two would be established. However, we must
reject this bold interpretation. To assume that the excitation
•changes in so simple a manner during the process of conduction
that the ultimate Ec still remains proportional to Ep is wholly
arbitrary and improbable. This, Fechner's, interpretation of the
law may be called the psycho-physical interpretation.

On the contrary, the physiological interpretation assumes that
the excitation is transmuted in the very path leading from the
peripheral surface of sense to the nervous centre according to the
logarithmic formula of Fechner's Law. Hence Ec would be
proportional to the log. of E, but the sensation 5 proportional
to the Ec itself. Very naturally we know nothing whatever yet
as to how the peripheral excitation is changed on the way to the
•cerebral cortex, or by what ratio the cortical excitation augments
with the increase in stimulation. The botanist Pfeffer^ has, in
fact, shown by some interesting experiments that the logaritiimic
relation expressed by the Law of Weber is likewise valid in a
very different sphere where only a physiological interpretation
•can be concerned. For example, if the zoosperms of the fern
are placed in solutions of malic acid, the latter attract the former
with a certain force. It appears that the force of this reaction
is proportional to the log. of the stimulus, the latter being a
given concentration of the solution of malic acid. Here we have
an analogy, even though remote, to the relations existing between
stimulus and sensation. In fact, Pfeffer has placed his experi-

' Untersuch. a. d. botan. Inst. z. Tubingen, lid. I, H. 3, 1884.

56 Introditctio?t to Physiological Psychology.

ments on the scales in favour of the physiological interpretation
of Weber's Law. Empirical data, however, that would tend to
substantiate such a physiological interpretation are still too
limited, although the latter has the undoubted advantage of
being able to explain or account for Fechner's Formula entirely
in accordance with the spirit of the natural sciences, and without
a new hypothesis. From the standpoint of the above theory, of
course, only an approximate validity of the logarithmic relation
can be granted ; for we would not be justified in assuming that
a relation so simple and invariably exact as the logarithmic, is
preserved in all cases, despite the various complicated modifica-
tions which the excitation must undergo while being conducted
to the cerebral cortex i

A third interpretation, whose dhief representative is Wundt, is
designated as the psychological. Wundt regards the Law of Weber
as only a special case of the universal law of relativity applicable
to our psychical processes in general. In accordance with this
law, consciousness is only able to measure the intensity of its
present conditions by a relative standard, not by an absolute
standard. Hence "apperception" measures every mental con-
dition by some other, and we become aware of a definite differ'
ence only when the increase of one sensation has reached a
certain constant fractional part of another sensation that eitlier
preceded or accompanied it. This interpretation, as we see,
introduces a wholly new and hypothetical mental faculty that is
an important factor in Wundt's psychology. It is to a certain
extent an "over-soul," the so-called "apperception," which notes,
estimates, compares and combines the lower psychical processes.
As we shall endeavour to show at some length in the future,
there is no demonstration whatever that can be found to prove
the existence of this apperception. The sensation is there, and
of a definite intensity ; it does not need to be estimated first
Therefore we shall reject this arbitrary assumption including
Wundt's interpretation of the Law of Weber. i

In our interpretation of the Law of Weber we prefer to start
from the simple fact that a central process of excitation {Ec) in
the cerebral cortex, produced by a sensible stimulus {E\ must.

Stimulus — Sensation.

J the same as E, have a certain living force or energy in order to
produce any psychical process or sensation whatever. Now the
cerebral cortex is never a complete " tabula rasa " ; it is never
entirely without excitations resulting from certain sensible stimuli;
the first excitation was present as soon as the first nerve had
developed. Therefore some Ec is always at hand. Now the
Law of Weber states : If no sensation is yet present, one will
only appear when Ec or E has reached a certain magnitude,
namely, the minimum of excitation. Furthermore, if a sensation,
corresponding to an E or Ec above the minimum excitation, is
already present, in order to produce a change of sensation, there
must be a change of stimulus, whose absolute magnitude
varies greatly, and, in fact, always constitutes a definite frac-
tional part of jE. This rule is valid, however, only in the most
favourable case, when all other sensations and ideas then occu-
pying the attention are reduced to a minimum, leaving but one
simple sensation in the consciousness. We make use of this
most favourable case when we test tlie Law of Weber in the
usual manner; we then direct our entire attention to tlie antici-
pated sensation, i.e. we make ourselves as free as possible from
other disturbing ideas. Let us recollect our experiences with
the tooth-ache ; how often an interesting conversation can cause
us to forget the pain for a moment ! What happens in such a
case as this? We often answer falsely, — the sensation has not
come into consciousness. But «;2conscious sensations do not
exist ; the real process in such a case is as follows : The stimulus
continues to act, but although its intensity is unchanged, it
generates no sensation because of other more intense sensations
and ideas, i.e. more intense Ed?>. For this relation, Hering has
formulated the following fundamental law: "Tlie purity, distinct-
ness or clearness of any sensation or idea depends upon the
relation in which the weight of the same {i.e. the magnitude of
the corresponding psycho-physical process) is to the collective
weight of all simultaneously present sensations and ideas, i.e. to
the sum of the magnitudes of all corresponding psycho-physical
processes." Therefore, whether a stimulus generates a sensation

58 Introduction to Physiological Psychology.

or not, and what the strength of the imparted sensation is, depends
upon the total strength of the other E<^% in part merely material,
in part accompanied by sensations and ideas that are present in
the cerebral cortex at the same time.^ Now the Law of Weber
is only valid for the special case in which one sensation, similar
to another one about to be experienced, occupies the conscious-
ness to the exclusion of almost all others, and is therefore also
essentially greater than the supervenient sensation. The greater
the Ec or the S, already present, just so much greater must the
supervening dEc be in order to impart a dS, or change of sensa-
tion. The Law of Weber is a law of association. The dEc must
have a certain magnitude, not for the purpose of being " apper-
ceived " by some hypothetical faculty of " apperception," but in
order that the material process dEc may produce a corresponding
psychical process, dS. What is meant in general by the com-
parison of two E<^%'i They may occur either successively in the
same cells of the cerebral cortex, or in entirely different cells, or
in cells that are partly different and partly coincident. We
generally regard this process of comparison as a very elementary
and frequent phenomenon. Close introspection, however, teaches
the contrary. As a rule, we merely pass from sensation to
sensation ; our sensations, successive as well as simultaneous,
are different, although we do not always become especially
cognizant of this difference. Most of the operations of sentient
life, as a rule, have no time to stop for the purpose of making
comparisons. But what does take place when, for some reason
or other, we really compare? This "comparing" is no inborn
capacity, no metaphysical faculty belonging to mankind; it is
rather an accomplishment, a power of association, laboriously
acquired by practice. As children we learn to construct very
slowly and laboriously the idea of "greater"; this idea, the same

1 In the discussion of the theory of attention we shall return to the question
as to whether the decrease in the intensity of sensation with the decrease in
the intensity of the stimulus and the decrease in the intensity of sensation with
the diversion of the attention are psychologically identical.

Stimulus — Sensation.

as every image of memory, is deposited and retained as a verbal
idea in a definite portion of the cerebral cortex. All our sensa-
tions, in so far as their intensity and their relations to space and
time are concerned, when two or more appear eitlier simul-
taneously or one after the other and the circumstances are
favourable for association, may act upon this idea of "greater,"
and tend to rouse it into action. Now during childhood the
idea of "greater" is so deposited in the brain that it always
responds to the stronger excitation imparted by the more intense
of two homogeneous sensations acting upon it. It is, therefore,
always associated with the stronger sensation. Then we are
wont to say, "this sensation is greater." If both sensations are
alike, their influence upon the idea "greater" is destroyed in a
certain sense by interference. But also very slight differences in
magnitude are insufficient to excite and reproduce the dormant
idea "greater." Generally the discipline of this capacity, as of
•every other, is inexact ; cases of false comparison occur besides
those of correct comparison. Where large differences between
the stimuli occur, the absolute difference in stimulation is the
essential determinative factor in comparison. Hering observes
very correctly,^ that if we place a weight of loo g. in the left
hand and i,ooo g. in the right, and then add loo g. to the
former and i,ooo g. to the latter, despite the uniformity in the
relative increase of the two stimuli, the increase of sensation
perceived in the right hand is considerably greater than the
increase perceived in the left. Only when the difference, repre-
senting the amount by which the first stimulus is increased, is
less than the first stimulus can the relative diiTerence be, in fact,
the essential determinative factor as set forth by the Law of
Weber. Now if two but slightly different stimuli take effect, it
is very possible that the consequent excitation of the idea
"greater," to which the brain has been especially trained, cor-
responds to the relative difference between the stimuli. We can
also understand, as shown above, tiiat such discipline of the brain

' Sitzungsber. d. Wiener Acad. d. W., 1875, S. 323.

6o Introdiictioti to Physiological Psychology.

is fitting. Every estimation and comparison of sensations, there-
fore, already involves associative activity. Hence, in the strict
sense, we should not speak o{ sensations of "larger" or "smaller,"
but only of such ideas. Of course the sensations themselves are
already different in intensity, but we only acquire an idea of this
difference by association. The child when very young already
has sensations of different intensity, but as yet no idea of their
different intensity. The latter is not grasped at once by the
consciousness at all; we only acquire the ability to compare by
slow degrees.

Hence the Law of Weber proves to be explicable, in fact,
within certain limits. The conclusions that Fechner on the one
hand and Plateau on the other have drawn from this fact, all
proceed from the false hypothesis that the intensity of sensation
can be ascertained by mathematical computation the same as
other material magnitudes, that also in this case, for example,
S + S = 2S. But this is wholly undemonstrated. On the con-
trary, accurate introspection shows that it is not the case.
Wundt proposed^ to decide the controversy concerning the
interpretation of Weber's Law by the so-called " method of
average gradations," and the attempt was made accordingly by
Delbceuf and Merkel. Thus, for example, the attempt is made
to select that stimulus which produces a sensation, the intensity
of which is just the mean between the sensations imparted by
two stimuli of very different intensity. This mean is

However, this search for the mean sensation is quite impossible,
as one quickly perceives by the embarrassment in which he finds
himself on attempting to carry out the experiment. We have
only acquired our estimation of about where the mean is to be
sought by experience and that which affects our judgment chiefly

' Before this, also Plateau, " Uber die Messung psychischer Empfindungen
und das Gesetz, welches die Starke dieser Empfindungen mit der Starke der
erregenden Ursache verkniipft." (Pogg. Ann., 1873, S. 466.)

Stimitlns — Sensation.

is just th'is experience as to the magnitude of stimuli. Accord
inyly the results of Meri^el's experiments showed that the medium
stimulus, thus experimentally determined, corresponds neither to
the arithmetical mean, as required by Plateau's theory, nor to the
geometrical mean, as required by Fechner's theory, but lies
between the two. Mathematics is not at once applicable to
psychical intensities as it is to the various intensities of an electric
current.

Let us now review the outcome of our experiments and
deli'.jerations. We have obtained two chief laws :

(1) The sensation increases considerably slower than the
stimulus.

(2) The increase of stimulus sufficient to impart a barely
perceptible growth of sensation generally stands in an approxi-
mately constant relation to the original magnitude of the stimulus.

We shall learn of many limitations of the latter rule in detail.
The numerous deviations from Weber's Law rest upon the fact
that on the one hand the modification of the excitation, while
being conducted to and in the cerebral cortex, probably varies
in a very complicated way, according to its intensity ; and that
on the other hand the degree of perfection acquired by associa-
tive discipline varies.

CHAPTER IV.

SENSATIONS OF TASTE, SMELL, AND TOUCH.

We have discussed the intensity of sensations at some length,
especially in their relation to the original stimulus. The second
property of every sensation is its qtcality ; the sensations of red,
of the tone C, of heat and of sweet are all different in quality.
We shall now become acquainted with these qualities more
exactly in detail. As regards quality, we generally distinguish,
according to the organ receiving the stimulus, five chief groups
of sensations ^ or modes of sensibility, sensations of smell, taste,
feeling, hearing and sight. We shall presently learn, however,
that the sensations of feeling undoubtedly require a still further
classification ; that the surface of the skin contains several quite
different organs, capable of imparting sensations that are very
different in quality. Sensations of feeling and hearing are more
closely related in so far as they are caused by mechanical stimuli,
while sensations of taste, smell, and sight, are produced by chemi-
cal stimuH. On the other hand, sensations of feeling and light
are capable of very exact localization ; hence they are intimately
concerned in our perception of space. We see and feel in space,
but how inexactly we localize a sound, taste, or smell ! In
general, we hear, taste, and smell, without localizing at all, while
feeling and sight are pre-eminently the senses that refer to space.*
We shall first discuss the sensations of taste. Separate organs
of taste are not yet developed in the Echinodermata, and they
have not yet been shown to exist in the insects. On the other
hand, taste-sensibility has been shown to exist in some of the
Coelenterates, especially in the Actiniae. If paper balls, part of

^ Ilelmholtz desig^nates those differences in quality, so essential that no
transiiion whatever from one to another is conceivable, as " modalities,"
modes of sensibility.

^ The term feeling, as used in this chapter, is to be understood only in its
more restricted sense as one of the five senses, whose organ consists of the so-
called general nerves of sensation. In this sense feeling includes touch, the
latter being the more specific term, the former the more generic. — Ts.

Sensations of Taste, Smell, and Touch.

which have been saturated with fish juice, part left unsaturated,
\re brought in contact with the tentacles of an Adamsia, this acteria
will seize the balls that are saturated with fish-juice.^ In verte-
brates the organs of taste consist of the so-called gustatory bulbs
which are scattered with comparative irregularity over the tongue,
palate and epiglottis, and are only clustered more thickly in the
so-called papillae circumvallatae and foliatse. Only fluids can be
tasted, solids and gases must first he reduced to a liquid state
before they can be tasted. Only four qualities of taste are to be
distinguished with certainty : sour, sweet, salt, and bitter. Without
sufficient grounds,^ some writers add alkaline and metallic to this
list as special qualities of taste. We might cite, in opposition to
so limited a list as that given above, the multitude of tastes that
we distinguish in our food, but to infer that these are pure sensations
of taste is incorrect. What we designate as taste, aside from these
four qualities, is smell, for some of the food is vapourized in the
back part of the cavity of the mouth and thence reaches the
cavity of the nose where it is smelled. The sense of taste, there-
fore, has but an extraordinarily limited variety of qualities. The
numberless acids of chemistry all excite but 07ie sensation of taste,
which varies only in intensity. Likewise the distinction of dif-
ferent bitter substances in solution is rendered impossible by the
choice of suitable degrees of concentration ; for example, a solu-
tion of quinine in the proportion of 1:100000 cannot be distin-
guished from a solution of morphine in the proportion of 1:3000.
The terminations of the gustatory nerves are probably only sensi-
tive to chemical irritation ; stimulation by pressure is very doubt-
ful. The sour or alkaline sensation of taste that is produced
when a galvanic current is passed through the tongue does not
necessarily depend directly on stimulation of the nerve-ends by
electricity, but may be caused by the products of the electrolysis,
produced by the galvanic current. The central terminations of
the gustatory fibres are probably to be sought in the Gyrus hippo-

* Pollock and Romanes, Journ. Linn. Soc. , Vol. 16; W. Nagel, Zool.
Anzeiger, 1892, Sept. Concerning the sense of taste in mollusks, see R.
Diitiois, Comptes rendus, 1890, No. 9.

^ Also gustatory k>iobs or flasks. — T'i.

' Linn£ distinguished even ten qualities.

64 Introduction to Physiological Psychology.

campi of the cerebral cortex. It is not probab'e tliat all four
qualities of taste are received and conducted to the cerebrum by
all the nerve-fibres in a like degree, for the base of the tongue is
chiefly sensitive to bitter tastes, the point and lateral parts of the
tongue to the other qualities. Oehrwall ^ has also found that on
stimulating single papillae fungiformes, some of the papillae are
sensitive only to acids and not to sugar or quinine ; he has there-
fore assumed specifically different terminal apparatus for the
■different qualities of taste. Even the new-born babe probably
distinguishes all four qualities of taste with comparative certainty,
if the solution to be tasted is sufficiently concentrated.

Frequent attempts have been made to prove the validity of
Weber's Law for the sense of taste. A method has been used
for this purpose, that has frequently found application in testing
the Law of Weber. This method is designated as the " method
of the correct and false (mistaken) cases." We shall become
acquainted with its characteristic features later in the discussion
of sensations of pressure. The application of this method resulted
in demonstrating only the approximate vahdity of the Law of
Weber for sensations of taste. The minimum of stimulus for
sugar maybe expressed in the ratio of 1:83; for quinine, 1:33000;
for saccharine, 1:200000; for strychnine, 1:2000000 (Venables).
The threshold value of a galvanic electric current just strong
enough to produce a perceptibly sour taste, has been fixed by
L. Herrmann at yi^ milliampere. It is claimed that this strength
of current is not yet sufficient to produce a sensation of contact.

The important question as to how the sensation changes when
•the same stimulus affects many adjacent nerve-fibres, is one that
will constantly occupy our attention. Is the intensity, quality, or
any other property changed ? In the case of seeing and feeling
the answer can be given at once ; the functions of the adjacent
nerve-fibres are in general identical. If the stimulation aflects a
large number of nerve-fibres, at the same time, the sensation re-
ceives the spatial character of a surface. In the case of the sense
of hearing we shall find that very many quite identical nerve-
fibres probably do not exist, but that almosj: every fibre transmits

' .'•^kandinav. Arch. f. Physiol., ii, I, 1890.

Sensations of Taste, Smell, and Touch.

a different quality of sensation. Neither of these characteristics
appear in the senses of taste and smell. Aside from the above-
mentioned four qualities of taste, the numberless gustatory fibres
are all functionally identical ; but if the stimulus is distributed
over a large surface of the tongue, we do not receive the image of
a tasting surface, but merely notice an increase in the intensity of
the sensation of taste. The sense of taste has no reference to the
relations of space, as have the senses of touch and sight ; the
sensation is made stronger, or, as we may say, more distinct by
the superficial extension of the stimulus, but otherwise it remains
unchanged.^ This explains our inability to localize sensations of
taste accurately ; We should perhaps be wholly unable to do so,
if sensations of taste were not also always accompanied by sensa-
tions of touch imparted by the tasted body.

Let us. pass on to sensations of smell. The sense of smell seems
to have become differentiated from a common sensory surface in
much lower forms of animal life than the sense of taste. At any
rate, it is already well developed in the Echinodermata. A blinded
star-fish, even at some distance, can scent the crab which serves
as its food. In how far certain apparatus in the feelers of insects
are to be regarded as organs of smell is doubtful. May ^ has
shown that certain organs of smell exist in the outer branches of
the antennules of many crabs. In vertebrates we find the organs
of smell in the regie olfactoria of the nose. They consist of so-
called neuro-epithelial cells, whose external processes are elonga-
lud into cilia, upon the surface of the mucous membrane. Exner
considers that the olfactory nerve is connected wiih all the epi-
thelial cells of the regio olfactoria ; in fact W. Krause has found
very fine hairs also in the common epithelial cells ; Lustig has
likewise confirmed the results obtained by Exner.

The number of qualities of smell is exceedingly large. As the

• Compare Camerer, Ztschr. f. Biologic, xxi, Tab. 8, S. 580.

* May, B., Diss., Kiel, 1887. Compare also Dahl, " Versuch einer Uar-
stellung der psychischen VorgSnire in den Spinnen." Vierteljahrsch f. wiss.
Philos., 1885. Prouho, " Du sens de I'odoraL chez les etoiles de raer. Comptes
rendus," Vol. III.

Introduction to Physiological Psychology.

sensations of taste unite readily with those of smell and touch, so
also the sensations of smell unite readily with those of taste and
touch. Many of the simple qualities of smell are apparently pro-
duced by the co-operative stimulation of the senses of touch, taste,
and smell. It is impossible to classify the different qualities of
smell, or to arrange them in definite series, as can be easily
accomplished in the case of the higher senses of sight and hearing.
The irritation of the ends of the olfactory nerve is only possible
by means of a chemical process, but since only gases smell,
solid bodies and fluids must first evaporate in order to produce
any effect upon the olfactory nerve-ends. It is very doubtful
whether mechanical stimuli are effective, but galvanic stimuli *
have recently been shown to be capable of irritating the olfactory
nerves. This fact was tested as follows : The nose was filled with
a solution of chloride of sodium, one electrode placed in the nose
and the other upon the forehead, whereupon many persons on
whom the experiment was tried perceived sensations of smell.
This experiment, however, does not exclude the possibility of
electrolytic action. The central terminations of the olfactory
fibres are also probably to be sought in the Gyrus hippocampi of
the temporal lobes.^ In animals, below man, the Gyrus margin-
alis and the olfactory bulb, which is often developed into an
independent lobe, are also probably to be designated as the
cortical centre of the olfactory fibres.

No attempt has yet been made to establish, experimentally, the
validity of Weber's Law for the sensations of smell. The mini-
mum of stimulus for many substances is extraordinarily small ; for
example, Teooioooo mg- mercaptan is sufficient to produce a
sensation of smell.^ The localization of our sensations of smell
is, if possible, still more inexact than the localization of sensations
of taste, for the former receive no assistance from accompanying

1 Aronsohn, Centralblatt f. d. med. Wiss., 1888.

» Compare Brain, 1889, Oct., and ZucKERKANDL, "Ueber d. Riechcen-
trum," Stuttgart, 1887.
« Fischer and Penzoldt, Liebig's Anna!., Bd. 231.

Sensations of Taste, Smell, and Touch. 67

sensations of touch. Experience has taught us to seek the cause
of a sensation of taste in the cavity of the mouth, the cause of a
sensation of smell in the air that enters the nose ; more exact
locahzation than this is impossible. All fibres of the olfactory
nerve are probably identical in function ; each one can transmit
every sensation of smell, but the sensations transmitted by
adjacent nerves do not arrange themselves into an image of sur-
face.

The so-called sensations of feelittg in the skin and mucous
membrane must occupy our attention considerably longer. The
sensibility of the skin is the first sense that appears, and the one
from which all others have probably developed by a gradual pro-
cess of differentiation and selection. Sensibility exists wherever
animal life is to be found, long before any separate nervous
system, the presence of which can be demonstrated, has de-
veloped. The moner, that changes its form when touched,
already possesses sensibility in this sense. The anatomical
apparatus that receive the stimulus are the so-called "tactile
corpuscles " and " end-bulbs," which appear in the most varied
forms. Besides these, free ends of the sensory nerves are also to
be found in the tissues. Mechanical, electric, and caloric stimuli
are the chief excitants of the sensory apparatus of the skin. The
chief form of mechanical stimulus is impact; even the slightest
contact is impact. Uniform statical pressure is also apparently
effective, though much more seldom than one would at first
assume. When a weight simply lies at rest upon the hand, it
seems as if all dynamic pressure is excluded ; but this is not the
case. The hand does not remain immovable; its involuntary
motions and the pulsation of the blood constantly impel the
surface of the skin against the weight resting upon it. For this
reason we shall not be able to separate the sensations of static
pressure from those of contact or dynamic pressure. Cold and
heat themselves do not act directly as caloric stimuli, but only
indirectly by warming and cooling the skin beyond its so-called
physiological zero-point. The number of qualities of sen.sation
imparted by the sensibility of the skin is comparatively limited.

68 Introduction to Physiological Psychology.

We recognise only sensations of heat, cold, and contact ^% positively
different qualities of sensation received by the sense of feeling.
The differences in the local extension, intensity, and duration of
these qualities of sensation are probably the conditions that deter-
mine those fine nuances of tactual sensation which we designate
as smooth^ rough, slippery, sticky, velvety, etc. But we must also
consider that after frequently appearing simultaneously, sensations
of touch may blend with one another or with those of temperature
into a sensation that, to the conscious individual, has but a single
quality.

Since the experiments of Magnus Blix,^ it has become very
doubtful whetlier each nerve-fibre can receive and transmit to the
brain all qualities of sensation of feeling {i.e. contact, including
pressure, heat, and cold) in the same degree. This experimenter
has shown on the contrary that upon one spot on the skin only
cold is perceived, upon another only heat, and upon a third only
contact. We can easily convince ourselves of this fact by applying
a cold point of steel here and there upon the fore-arm ; by this
means we easily discover regions on the skin having an area of
about one square centimeter that receive no sensation of cold
from the point of steel, although sensations of heat or contact
appear at once if we apply the proper stimulus. But close
beside the spot thus tested we find points that are intensely
sensitive to cold, though no sensations of warmth or contact can
be perceived there. There are therefore separate spots for heat,
cold, and contact, and each nerve-fibre transmits but one sensation.
A spot for either heat, cold, or pressure evidently corresponds to
each termination of the nerve-fibres. The stronger stimuli of
pressure, however, impart slight sensations also outside of the
so-called "pressure-spots"; but we may justly a.ssume in this
case that the mechanical stimulus is transmitted to the next
neighbouring " pressure-spots." Goldscheider,^ to whom we are

» Magnus Blix, "Exper. Beitr. z. Losung der Frage iiber die spec.
•Energie d. Haulnerven." Ztschr. f. Biologie, 20 iiwA 21.

^ Archiv. f. Physiolog.. 1885. Compare also especially Dessoir, " Uber
den Hautsinn," Arcliiv f. Physiol., 1S92.

Sensations of Taste, Smell, and Touch.

indebted for some excellent investigations in this field, assumes
another diffused ge?ieral sense of feeling as operating between the
different points of pressure. His hypothesis does not seem to
be well grounded. Electrical stimulation, especially that of
faradic electricity, acts upon all points of sensation, whether of
temperature or pressure ; but it imparts only sensations of cold
at the " cold-spots," only sensations of heat at the " heat-spots,"
and only sensations of touch at other points. According to
Goldscheider, a strong mechanical stimulus applied to the spots
for temperature imparts a corresponding feeling of temperature.
It must also be mentioned that there is still considerable doubt
as to what the real, active element is in the case of caloric
stimuli. E. H. Weber thinks that irritation is produced by the
rise and fall of the temperature of the skin ; Vierordt thinks it is
produced by the direction of the current of heat passing through
the skin; Hering ascribes it to the absolute deviation of thf
temperature of the cutaneous nerve-apparatus itself from a physio
logical zero-point of temperature at which neither warm nor cold
is perceived. It has not yet been determined as to where the
central terminations of the sensory fibres of feeling are to be
found. At one time the Gyrus fornicatus was designated as the
cortical centre for sensations of feeling ; then it was thought that
this cortical centre coincides with the so-called motor region in
which the path for the conduction of voluntary motor impulses
originates.

But the skin is not the only organ containing sensory nerve-
ends. We find them also scattered through all the organs of the
human body. These so-called "organic sensations" are dis-
tinguished by great indefiniteness and slight intensity under
normal conditions. Only one more group of the more deeply
seated sensory nerves deserves mention as being of special im-
portance ; it is that group of nerves whose terminations have
been shown to penetrate the synovial duplicatures of the joints,
the ligaments, tendons, and muscles. By means of the sensory
nerves of the ligaments and muscles, for example, we perceive
the condition of the muscles, their contraction and tension

70 Introduction to Physiological Psychology.

The sensory nerves of the joints transmit to us those peculiar]
sensations which appear when the ends of the bones forming the
joint are pressed against each other or when their surfaces glide
over each other during motion. Considered apart from their
connection with the functions of the body, these sensations have
but slight importance ; taken together, however, they constitute
those complex sensations by which we perceive the position of
our limbs, and which we therefore call "sensations of position."
If we close our eyes, for example, and direct our attention to the
position of the closed right hand, the nerves in the joints inform
us as to how far their surfaces touch each other ; the nerves of
the tendons inform us that the extensors of the fingers are relaxed,
the flexors contracted and shortened. Sensations of contact upon
'.he skin also assist very considerably in producing these sensa
tions of position, for in the case just cited the sensory nerves of
the skin inform us that the tips of the fingers touch the palm of
the hand. Let us now imagine a continuous series of these
sensations of position, gradually passing from one to the other.
Accordingly let the closed hand open by slow degrees ; the sen-
sations of position that follow in regular succession inform us as
to the movement of the hand. In this manner " the sensations of
motion " ^ are produced. We distinguish passive and active sensa-
tions of motion according to whether our fingers are moved by
another person or by ourselves. Goldscheider's more recent in-
vestigations, furthermore, have made it probable that the sensation
of passive motion depends less upon the successive sensations
imparted by diflferent positions of the limb at rest, than upon
sensations of pressure or friction in the joints, directly imparted
by the motion itself. According to this the sensibility of the
joints would be almost the only essential factor in the production
of sensations of passive motion ; while in the production of the
sensations of active motion the sensations of position are also of

» A much less familiar, but very fitting synonym for " motor sensation " is
" kinfesllietic sensation." Kinsesthesis is the perception attendant upon the
movements of the muscles only. " Kiniesthetic sensation" is therefore less
comprehensive than " motor sensation " in its general application. — T's.

Sensations of Taste, Smell, and Touch. 71

very great importance. Introspection shows that there is still
another difference, apart from the sensation of touch produced
by contact with the skin of another person during passive motion.
In the process of thought, the ideas that cause the active motion
precede the sensations of active motion, while such ideas do not
precede the sensations of passive motion. There is no immediate
reason ^ for assuming special " sensations of innervation " that
instruct us during an active motion as to the amount of innerva-
tion employed. The capacity for sensations of position and
motion has been expressed by the collective term " musadar
sense." The term is not very well chosen, for the sensibility of
the muscles is of the least importance in the production of such
sensations. The combination of sensations of motion with sen-
sations of touch received from the same object is of special
importance. By moving the hand over the surfaces of an object,
we inform ourselves as to its form. This succession of combined
sensations of contact and motion is designated as sensation of
active touch.

The number of such complex sensations is exceedingly large,
as may be easily realized by calling to mind the peculiar com-
plexes of sensation produced by lifting weights or by colliding
with some obstruction. However, the most important classes of
these sensations of feeling are the four just described : — ■

1. Sensations of position.

2. Sensations of active motion.

3. Sensations of passive motion.

4. Sensations of active touch.

' The lively sensations which cripples claim still to peiceive in the maimed
parts of the body when they tiy to move them gave special occasion for the
assumption of particular sensations of innervation. We sliall return to this
question later.

' Active touch is to be distinguished from passive touch in tlie same way
that active motion is distinguished from passive molion, viz. by the precedence
of motor ideas. In fact, there is a motor element in active touch ; in this sense
only are the two expressions to be distinguished in this work. As soon as a
motor element appears in thought the sensation becomes one of active touch
( Taslemp/iniiung). — 7 's.

72 Introduction to Physiological Psychology.

According to more recent pathological experiences, we may
probably locate the central terminations of the sensory paths
communicating with the tendons, muscles, and joints, in the
cortex of the upper parietal lobe.

It was while investigating the sensibility of the skin, in fact,
that E. H. Weber first discovered the fundamental relation
expressed in the Law of Weber, Since then these experiments
have been often repeated. The minimum of stimulus proves to
be very different for separate regions of the skin, in the case of
common sensations of contact or pressure. On the forehead, the
pressure of even a weight of 0*002 g. is perceived, but on the
abdomen, only that of a weight of 0*005 §• According to the
greater or smaller area touched by the same weight, still other
diff"erences also appear. The "discriminative sensibility"^ in
the case of stimuli of pressure, has been investigated since E. H.
Weber's time by Biedermann and Lowit, and by Dohrn and
Merkel.2 -phg barely noticeable difference, according to the
investigations of Merkel, for example, for a previous weight of —

0-32 g.

0-96 „

1-40 „

2-04 „

xoo

7 "4 »

500

33-9 >.

1000

8i- „

4000

156- »

Tlierefore if a weight of 4,000 g. press ^ upon a finger of the •
hand while resting upon a support, fully 156 g. must be added to •
it in order that any difference in weight whatever can be perceived.
We shall now test these numbers more exactly and see if they

• Unterschiedsempfindlichkeit — T's.
» Philosoph. Stud., V, S. 2.

■ The constant area of contact in this particular series of experiments .
rmounted to I sq. mm. With a greater area of contact the discriminative
sensibility is mure limited.

Sensations of Taste, Smell, atid Touch.

agree with the Law of Weber. The latter states that not the
absolute but the relative differences of stimuli are determinative,
i.e. the increase of stimulus requisite to effect a perceptible differ-
ence in sensation is always the same fractional part of the
original stimulus. If the original stimulus is E and the increase

dE . . , , ,

of stimulus dE, then is constant without regard to the

magnitude of E. Let us determine this fraction for each of the
above pairs of numbers.

0-32

=0-32

096

= 0-19

I "40 :

= o'i4

2'Q\

= 0"I0

100

= o"07

38-9

500

= 008

1000

= o-o8

156-

4000

=:0*04

Thus we see that the above-mentioned fraction remains ap-
proximately constant only when the original weights lie between
TOO g. and 1000 g. Only within these limits must the increase
of stimulus reach the same fractional part of the primary stimulus
in order to be just observable. Therefore Weber's Law is valid
only when the stimuli are of medium intensity ; the relative
sensibility to difference is smaller in the case of very small stimuli
and greater in the case of very large stimuli than the Law of
Weber requires. This fact is designated as the " upper and lower
deviation" of Weber's Law. The discriminative sensibility, there-
fore, increases in proportion as intensity of stimulation is greater.

The discriminative sensibility proves to be essentially greater
when the weights are not placed upon the hand at rest, but when
we execute the motions of lifting the weights while they lie on the
hand. In the latter case, of course, the sensation is much more
complicated ; sensations of position and motion are associated
with those of pressure. We are also assisted by being able to
compare the sensible effects of the same stimulus in different

Introduction to Physiological Psychology.

positions. In investigating the discriminative sensibility in the
case of lifted weights, Fechner applied a special method desig-
nated as the " method of correct and false (mistaken) cases."
The nature of the method is made clear by the following ex-
ample. We shut our eyes and a friend lays first a weight of
300 g. and then one of 312 g. upon our hand. We must now
state which of the two weights is the heavier. The additional
weight of 12 g. more than the original 300 g. is so small that the
difference is not constantly perceived with certainty. However
we state the difference more often correctly in favour of the
second weight than falsely in favour of the first weight ; some-
times we also remain undecided. Thus, for example, Fechner
found that in one hundred such trials as the one described above,
in which of course sometimes the lighter, sometimes the heavier
weight was first laid upon the hand, the answer was given cor-
rectly sixty times. Therefore the number of correct cases
amounted to 60 %. Now a second series of trials is made, the
beginning weight being 600 g., the additional weight remaining
at first 12 g. It then soon appears that the number of false
estimations has greatly increased ; the number of correct cases,
perhaps, amounts to but 40 %. We next take a larger additional
weight and compare, for example, 600 g. and 620 g. in a new
series of trials. It now appears that the number of correct cases
has considerably increased, although the old number of 60 % has
not yet been reached. In order to attain 60 % of correct cases
again, as in the trials with 300 g. and 312 g., we must raise the
additional weight to 24 g., the beginning weight being 600 g.
Therefore, although the additional weights are imperceptible,
their magnitude still had some influence upon the probability of
a correct estimation of the sensation ; in fact, as we have just
seen, not the absolute difference but the relative difference is
determinative. If the beginning weight {E) is doubled, the ad-
ditional weight (dE) must also be doubled in order that the
probability of a correct discrimination between the two remain
constant. This fact is quite in accord with the spirit of Weber's
Law : the difference between any two stimuli is estimated as being

Sensations of Taste, Smell, and Touch.

the same, and the probability of a correct judgment or discrimina-
tion of this difference is constant if the ratio of the stimuli re-
mains unchanged. These are the essential features of Fecimer's
interesting method; in its practical application and the employ-
ment of the numbers, of course, many difficulties and doubts still
arise that complicate one's procedure.^ In the most favourable
case a relative difference of -^-^ is still perceptible. Also in the
case of sensations of pressure, therefore, the Law of Weber is
verifiable only within certain limits of stimulation.

Goldscheider has also recently determined the minimum of
stimulation, at least in the case of single sensations of passive
motion. It appears, for example, that a swing of the arm
amounting to 0*22° — o"42° is sensibly perceived in the shoulder
joint. He was also able to determine the minimum velocity
necessary to cause sensations of passive motion. This minimum
velocity for the shoulder joint amounts to o"3°-o"35° in a second
of time. It is conceivable that a minimum velocity of stimulation
can be determined also for sensations of passive motion, for they
are not imparted by sensations of static pressure, but chiefly by
slight sensations of dynamic pressure within the joints; and velocity,
of course, is an essential factor in the sensible effects produced
by impact.

It is remarkable that in the case of a swing executed by some
member of the body, the minimum of excitation is but very little
smaller for the sensations of active motion than for sensations of
passive motion.

Finally, there remain the sensations of heat and cold. In how
far the Law of Weber is valid for these sensations has not yet
been established with certainty. Under the most favourable
circumstances the threshold of difference appears to amount to
o-2° C. It is possible ^ that the minimum of stimulus for sensa-
tions of warmth lies somewhat higher than for sensations of cold.

* liesides Feciiner (" Elemente der Psychopliysik " and" Revision einiger
Hauptpunkte der Psycliophysik ") compare especially G. E. Muller, " Zur
Griindlegung der Psychophysik."

According to Goi.i>.sciieii)KR, contrary to Eui.ENnURCj.

76 Introduction to FliysiologicaL Psychology.

Experiments are rendered more difficult by the constant change
in the temperature of the skin itself, to which the pliysiological
zero-point of the skin seems also to adapt itself.*

We should here call attention to the fact, still further, that
certain sensations can be misjudged. If the skin on the nape of
the neck is first lightly touched with a small brush, then warmed
by a match that has been lighted near it, we are sometimes unable
to distinguish whether heat or touch acts upon tiie skin. Obviously
the quality of very weak sensations is often too indistinct or in-
sufficiendy pronounced to recall the ideas and words that were
previously associated with the pronounced sensation. It is also
interesting to note that cold weights appear to be heavier than
warm weights of the same value.

Let us now consider the question once more as to how those
sensations of pressure and temperature vary that are produced by
the separate irritation of different nerve-fibres or by the simul-
taneous irritation of many nerve-fibres. The answer for sensations
of heat and cold is in part similar to that for sensations of taste.
If the same caloric stimulus irritates a large number of nerve-
ends, i.e. if the stimulus spreads over a large area of the skin,
neither the quality of the sensation changes, nor does its super-
ficial character ^ become essentially more pronounced ; but the
intensity of the sensations of heat and cold augments. It is
different in the case of sensations of pressure. If the same
stimulus of pressure act first upon a certain spot on the skin of
the thigh and then upon a certain spot of the same size on the
skin of the cheek, by the exercise of sufficient attention we can
observe a slight difference in quality that is independent of the
difference in localization, despite the identity of the external
stimulus in each case.

It is hardly to be assumed that the nerve-fibres which receive
the stimulus in the skin of the forehead are essentially ditferent
from those in the skin of the abdomen ; but the external stimulus

» Hering, Sitzungsber. d. Wiener Ak., LXXV., III. Ablh.
» Fiulher investigations by Goluscheiijkr have also determined the
capacity for localising sensations: of temperature : Archiv f. Physiol., 1S85.

Sensations of Taste, Smell, and Touch.

does not reach the nerve-ends directly. It is variously modified
by the structure of the skin (including its hairs) which intervenes
between the nerve-ends and the acting stimulus. The same
external stimulus will therefore be modified on the way to the
terminations of the nerves according to the locality of the skin
upon which it acts, and will hence prove to be everywhere some-
what different. The constitution of the nerve-ends receiving the
stimulus may also change somewhat according to the extent of
the nerve-tracts. Hence the structure of both skin and nerve-
ends gives the sensations of pressure their so-called " local stamp."
Let us cite one of the rougher, but most striking, examples of
this fact. If we touch the skin of the cheek, the sensation of
pressure has a very characteristic stamp which is especially con-
ditioned by the absence of a firm substructure, the flaccidity of
the skin, and the insertion in the skin of the muscular fibres.
By means of these characteristics we are able to distinguish the
sensation of pressure on the skin of the cheek in quality from
similar sensations of pressure on other parts of the body. In
accordance with Lotze's precedent these " local stamps,'' char-
acteristic of sensations of pressure, are also designated as local
sigfis." In fact these " local signs " materially facilitate the local-
ization of sensations of pressure. Hence if the same stimulus of
pressure act upon different nerve-fibres separately, some difference
in quality, though small in fact, is already perceptible. But in-
dependent of these local signs, we are also able to localize at
once, and with comparative certainty, any sensation of touch
whatever. In so doing, of course, we commit a certain so-called
" error in localization " which has a constant value for each region
of the skin. This error is very great, for example, when we at-
tempt to localize sensations felt in the leg and toes. Certain in-
dividuals possessed of healthy nerves, but unpractised in self-
observation, have been known to mistake the second toe for the
third, or the third for the fourth in attempting to localize sensa-
tions of touch. But whence arises this faculty of localization ?
How do we know instantly that in one case the leg, in another
case the foot is touched, although exactly the same stimulus acts

78 Tnirodiiction to Physiological Psychology.

upon both and produces sensations that are but little different in
quahty? The sensation itself does not furnish this localization;
it only assists us somewhat to localize by means of its local sign.
The localization is rather an achievement of association. The
associated by practice with the sensation of contact in each region
of the skin. The usual localizations of the sensations of pressure
This process of association takes place in a manner which we
shall discuss more thoroughly in the future. If the foot is
touched these ideas are awakened with the speed of lightning ;
the form and motions of the foot and the word "foot" occur to us
and these images of memory also guide the hand in pointing out
the region touched when we are requested to do so. Especially
this motion executed in indicating the spot touched is closely
sensation of contact in the foot is associated with numerous ideas
of the foot, especially with ideas of sight, motion, and speech,
does not consist at all in the projection of tlie sensations into
abstract space, but rather in their association with definite ideas
of sight, motion and speech. Hence we can understand more
readily why localization in general becomes more accurate as the
intensity of the stimulus increases. The so-called "eccentric
projection" is also only to be understood as the result of these
associations. By " eccentric projection " we understand the fact
that a sensation produced by the stimulation of the nerve-/ru;ik
instead of the neive-emls is regularly attributed to irritation of
the peripheral ramifications of the nerve. It is known, for ex-
ample, that persons who have lost a foot may still feel pains in
the amputated member. In this case the old, familiar associations
have not yet received sufficient correction, rendered necessary by
the amputation. We shall return to this subject in connection
with tlie theory of the so-called " intuition of space."

The first part of our question is now answered. How do the
sensations of pressure differ when the stimulus acts upon different
nerve-ends separately ? The second part of the question remains
to be answered. If the same stimulus reaches many adjacent
nerve-ends at the same time, thus acting upon a larger area of
the skin, what is the sum of the sensations thus imparted? In

Sensations of Taste, Smell, and Touch. 79

general we find neither an increase in the intensity of sensation
(i.e. an actual summation), nor a change in its quality, but the many
sensations arrange themselves into a form or image with which we
are not yet familiar. This image is a form of spatial extension
known as surface. Here we confront one of the greatest puzzles
of psychology. Let us present clearly to mind the peculiar aspect
of the facts in hand. Suppose that 1,000 excitations, proceeding
from 1,000 nerve-ends in a given area of the skin that has been
touched, reach the cerebral cortex and impart 1,000 sensations.
Two questions now arise : (i) How are two sensations that were
produced by the excitation of neighbou7-i7ig nerve-ends combined
into an image of space? (2) How can we account for the origin
of this remarkable arrangement at all? The second question
cannot be answered at all by physiological psychology. We here
confront one of those psychological facts that are as yet incom-
prehensible in the light of physiological psychology, and. that will
perhaps always remain so. A great deal of pains has often been
taken to explain the development of our intuition of space in a
purely genetic way, either by the local signs or by the combina-
tion of ideas of pressure with those of motion. We shall not
trouble ourselves with these attempts at explanation, which have,
in fact, been fruitless. We project all our sensations into space,
even the tone heard and the taste received upon the tongue.
Physiological psychology must accept this fact without being able
to explain it. At first this projection is quite indefinite ; the
senses of hearing, taste, and smell still illustrate this first stage
of space-perception, in which the localization is quite indistinct.
The sensibility of the skin shows us the next higher stage of space-
perception ; the localization is already more definite. For
example, if we close the eyes and let a very small piece of
board of unknown dimensions be placed upon the hand by another
person, we are able to tell about what place upon the hand is
touched, and also to state approximately the boundaries of the
surface thus touched. If we compare the capacity of the sense
of touch for localization with that of the sense of sight, the
deficiency of the former becomes clearly apparent : on the other

So Introduction to Physiological Psychology,

hand the localization of the visual sense appears unique to us
because, in fact, we can make no comparison with another sense
in which the ability to localize is still more highly developed.
Let us consider the process of this superficial localization in the
■case of the sensibility of the skin somewhat more exactly (fig. 7).
H and H' represent the cross-section of some area of the skin, —
on the hand, for example ; a, b, c, and d are nerve-ends. Tracing
the nerve-fibres along their entire course to their cerebral cortex,
we find them terminating in the ganglion-cells a', b\ eH, which
are all probably connected with one another. It is furthermore

Fig 7.

possil)le, though improbable, that the succession of the nerve-
I'ibres at their peripheral terminations is retained undisturbed
during their long course through the spinal chord and cerebellum,
•despite frequent intervenient interruption in the ganglion-cells, and
that thus exactly the same order recurs in the cortex of the cerebrum.
In the illustration, therefore, it is assumed that the succession
has been altered ; d is now adjacent to // which terminates the
series. Now let a homogeneous object, which we shall at first
conceive of as having only length, touch the skin and irritate the
four terminations of the nerves. Four excitations, almost absolutely
identical in qiialitj', will then be transmitted to the brain ; here

Sensations of Taste, Smell, and Touch.

like excitations will occur in the four ganglion cells and impart
four like sensations of pressure. At first we are not conscious of
anything more than these sensations, which, if there is any definite
succession at all, are given in the order a\ <f, d\ b'. We further-
more accept, as a fact, the projection of the four sensations into
space. But now what causes us to correct the order of the series
to a certain extent, and to so project the four sensations a', d,
b' into space that their order becomes a\ b', d', thus correspond-
ing to the order of the nerve-ends touched, and of the points on
the stimulating object? The cause lies in the ideas of motion
which are associated with each one of the ganglion-cells. For
example, if we move the surface of the skin represented in the
illustration a short distance, the point a is first brought in contact
with an object at x (fig. 7) ; a somewhat greater movement brings
the point b to and so on until finally the greatest movement
places the point d in contact with x. On the other hand, we
might have placed the object also at x', in which case the
slightest movement would have produced contact with d, the
greatest movement contact with a. In either case the order of
the nerve-ends, whether a, b, c, d, or d, c, b, a, is constant in so far as
the magnitude of the motions requisite to bring the four nerve-ends
in contact with a given object, is concerned.^ The experience as
above described is repeated numberless times during the lifetime
of the individual, until it finally becomes fixed in memory. A
memory or idea of a motion having a definite magnitude is associ-
ated with the sensation received from each nerve-end. For
example, let us suppose this idea of motion to be i;// for a, 2m
for b, yn for c, and 4;// for d. Now if an object touch b, c
and d at the same time, the sensation produced by the excitation
a^' unites with the idea of motion i //; ;

the sensation bV with the idea of motion 2m ;

» >' ■>■> >i )) J) I) 3'" »

» " '^'i' » j> » >> » 4

' The importance of conceiving of the elements, by means of which we per-
ceive space, as a series, and the possibility of inveiting its order, were tii>t
empliasized by Herbart (" Psychologic als Wissensch.ift ").

82 Introduction to Physiological Psychology.

Thus this scale of intensities representing the concomitant ideas
of motion, determines the order in which the sensations are
locaUzed in space. Tlie sensations are not arranged according to
the order of their position in the cerebral cortex, but according to
the scale of the accompanying ideas of motion. What we have
thus demonstrated in the imaginary case of linear contact, may
also be applied somewhat more minutely to superficial contact,
and to the taction of solid bodies. In this case also we first
project the sensations of contact into space without regard to order ;
only the accompanying ideas of motion that we acquire, cause us
to project the sensations received from the surfaces bounding an
object in just the same spatial order in which the points are really
arranged on the surfaces of the external object. It is furthermore
obvious that ideas of motion may also be acquired indirectly, not
when the hand is moved along the object x, but when the object
X is moved over the hand under our eyes.

Hence a perception of the world as it exists in space may be
developed within us entirely without the help of the visual sense,
although, of course, it remains more or less incomplete. The
well-known patient of Chesselden,^ who was born blind, and later
in life received the power of sight by an operation, only dis-
covered after the operation that all things are solids ; before he
had only known of surfaces. On the other hand, Franz ^ related
that a certain individual, who had been born blind, was unable
to form any idea of a square, even upon seeing it after his sight
had been acquired by an operation, until he began to perceive a
sensation in the tips of his fingers as though he was really
engaged in touching the object at which he was only looking.
The patient had constant recourse to his sense of touch, just as
the normal man resorts to his sense of sight in the recognition of
objects. When we come to consider the theory of visual sensa-
tions, we shall have to return to these cases, which are of extra-
ordinary importance for physiological psychology, and to the

1 Philosoph. Transact., 1728.

« Philosoph. Transact. R.S., 1841.

Sensations of Taste, Smell, and Touch.

entire subject of space-intuition in general. At present only one
more conclusion is to be mentioned as a direct result of the
preceding. The ability to distinguish two sensations that arise
in neighbouring nerve-ends, can be considerably cultivated by
practice, since it is also chiefly dependent on accompanying ideas
of motion. If we place the two points of a compass upon the
thigh at a distance of 6 cm. from each other, we generally per-
ceive but one touch ; we are able to perceive two touches only
when the distance between the points of the compass amounts
to 7 cm. This smallest distance within which two sensations
may still be distinguished from each other is designated as the
" minimum of space " ^ that can be perceived or the "just per-
ceivable amount of space," and the region of the skin within
which we still feel two sensations as one is designated as the
"sensation-circle" in accordance with the precedent established
by E. H. Weber. Within the area of a single " sensation-circle,"
therefore, the local signs and the associated ideas of motion are
not sufficient to render two sensations distinguishable when they
are caused by like stimuli. Thus we can also easily understand
why the " sensation-circles " are very large in those regions of the
skin which have very few nerves and are little used in active
touch, as the trunk, thigh, etc. It is a fact of great importance
that two points of contact may be also felt as otie when both are
at pressure-spots separated by one or more other pressure-spots.
It appears therefore that the distribution of pressure-spots is by
no means the only factor determining the ability for localization,
but that the local signs and particularly the accompanying ideas
of motion exert the chief influence. The partition of the sensi-
bility of the skin into pressure-spots only renders possible the
separate appearance of two like cortical excitations in different
cortical elements ; but the distinction of two sensations does not
depend on this simple fact of anatomical separation. We may
here make the paradoxical statement that if all the nerves of
the skin and their cortical terminations were anatomically quite

Germ. Rautnschwelle = space-threshold. — T's.

§4 Introduction to Physiological Psychology.

identical, and if all were irritated by the same stimulus at the
same time, only a single sensation would appear. The distinc-
tion of neighbouring sensations from one another is only possible
by means of local signs and ideas of motion. That the sensation-
circle becomes smaller when just two /rmar^-spots are touched
may be partly explained by the fact that the intensity of the
sensations is greater on the pressure-spots than elsewhere ; and
within certain limits at least, the distinction of sensation becomes
easier, the greater the intensity of the sensation.

A further explanation may be sought in the fact that a single,
isolated "local stamp" or "coloring" and a single, isolated
complex of motor ideas appear only on irritation of a pressure-
spot ; if a point between two pressure-spots be irritated, the
stimulus acts upon several such spots ; the sensation is therefore
associated with several local signs and complexes of motor ideas,
and the differences between sensations are thus directly obliter-
ated. In regions that possess an abundance of nerves the
sensation-circles are smaller. A greater abundance of nerves
renders possible a greater variety and speedier change of the
local signs and a more extensive association with separate com-
plexes of motor ideas.

In conclusion one fact must seem remarkable to us. We have
succeeded in explaining how the separate sensations of pressure
are discretely projected into space in a definite order; in so
doing, however, we have simply obtained a regular contiguity of
numberless discrete sensations. But whence arises the con-
tinuity of the impression produced by an object touching the
skin ? We do not feel numberless points, but a continuous sur-
face. This fact may be explained as follows : It is true that the
pressure-spots are discrete ; but we have already demonstrated
at some length that, strictly considered, the same stimulus acting
upon different neighbouring pressure-spots, can impart but a
single diffused sensation, the localization of which is quite in-
definite, somewhat as in the case of sound. Our sensations of
touch are only separated spatially and arranged so as to produce
a surface by their association with local signs and ideas of

Sensations of Taste, Smell, and Touch.

motion. But the local signs and ideas of motion are regularly
graded and therefore form a continuous series. Hence we can
easily understand also that the separation of the tactual sensa-
tions and their arrangement in a surface has this continuous
character. When the continuous gradation of the local signs
and ideas of motion is wanting, the sensations do not blend into
an image of surface. If we place three needle-points, for
example, at a distance of 2 cm. from each other upon the hand,
the three sensations will never blend into an image of surface.

We have now finished the discussion of that mode of sensi-
bility from which all the other senses have probably developed,
the sensibility in the narrower sense of the term. We shall next
turn to the highest senses, hearing and sight.

CHAPTER V.

SENSATIONS OF HEARING.

We have now come to the discussion of acoustic sensations.
The external stimulus producing these sensations is, in fact, very
exactly known. It consists exclusively of longitudinal periodic
vibrations of the molecules of air. Thus if A (fig. 8) designate
a source of sound which sends out waves of sound in all direc-
tions, a particle of air at M will first move to the point N, then

Fig. 8.

return to M 2,n6. pass on to Z, finally returning to M again.
The motion along the entire path M N M L M is called a
vibration, and is executed in a single straight line. The latter is
somewha*: altered in the figure in order to illustrate visibly the
reversal of the path, hence the particle of air does not appear
to have returned to the exact starting point. In illustrating a
series of vibrations it is best to depart still further from a
straight line and represent the path of the particle as a wave.
This may be accomplished most advantageously by letting the
abscissas (fig. 9) indicate the time that has elapsed since the
beginning of the motion, while the ordinates indicate the vibra-
tion that has taken place. These vibrations are periodic in that
they are continuously repeated. A definite number of vibra-

Sensations of Hearing.

tions takes place in a second of time. These periodic vibrations
may be regular, i.e. the form and number of the vibrations re-
main constant. Such vibrations impart sensations of musical
sound] the accompanying external stimulus is designated as a
musical sound.^ On the other hand, the periodic vibrations may
be irregular ; form and duration of the vibration change. In
this case sensations of noise are produced and the accompanying
external stimulus is designated as a noise.

Fig. 9 I, represents the wave-line of a tone;* fig. 9 II, the wave-
line of a noise.

A single wave reaches from a to ^ (fig. 9 I). This distance
corresponds to the length of time required for the vibration of
one particle. The curves, ab, be, cd, etc. (fig. 9 I), all represent
a single vibration of the particle of air ; likewise a'b', b'(^, dd\ in
the second curve (fig. 9 II). The greatest breadth of displace-
ment of a vibrating particle is called the amplitude of vibration.
The lengths of the straight lines ab, a'b\ be, b'd, etc., represent the
■duration of each vibration. We see at once that in the first curved
line both the form and duration of the single vibrations is always

1 Compare also, however, R. KONIG, " Uber Klange mit ungleichfbrmigen
Wellen. Wiedemann's Annalen, Bd. 39.

^ In this chapter the term "tone," when used without modification, is to
be understood in its restricted sense as designating only a " simple tone," not
a " composite tone" or " musical sound." — Ts.

Fig. 9.

Introductioji to Physiological Psychology.

the same. This is characteristic of the tone. On the contrary
the form and duration of the vibrations in the second curved hne
are constantly changing, as is characteristic of a noise. The
rustling of the leaves is a noise ; if we strike the key of a piano,
we produce a musical sound ; both are complex products, as we
shall soon see. Both musical sounds and noises may be reduced to
simple acoustic elements, or tones, by mathematical computation
(construction) or by the use of special instruments, the so-called
"resonators." Both noise and musical sound consist of a series
of simple tones. The wave-line of both the noise and musical
sound may be graphically represented as the product of several
wave-lines of especial simplicity, viz. the so-called sinusoids" or

Fig. 10.

"curves of sines." Expressed in the language of physics, all the
regular, periodic motions of musical sound and all the irregular
periodic motions of noise may be reduced to a certain number of
regular periodic motions of exceeding simplicity. These com-
ponent vibrations, to which both a musical sound and a noise
may be reduced, all have the same general form of vibration, the
sinusoid, as represented in fig. lo.

Aside from their amplitude or intensity, the vibrations are to
be distinguished from one another merely by their duration, or.
in other words, by the number of vibrations per second. We
may therefore express this general proposition as follows : Each
sound, whether musical sound or noise, may be reduced to
a series of simple component tones, which, irrespective of their
intensity, are to be distinguished from one another merely by
the number of vibrations. Musical sound and noise are differ-
ent in that the numbers of vibrations producing the component

Sensations of Hearing.

tones of the latter conform to no definite law of proportion, while
the numbers of vibrations producing the various component tones
of a musical sound stand in a very simple numerical relation to
each other. For example, if that component tone (or partial tone)
of a musical sound which has the smallest number of vibrations,
possesses n vibrations per second, then all the other component
tones of the same musical sound have a number of vibrations
which is just sufficient to produce an exact multiple of n ; the
numbers of their vibrations therefore amounts to 2«, 3«, or 4«,
etc. Also when the lowest tone has a number of vibrations equal
to 4«, and the following tones have numbers equal to 5«, 6«, etc.,
the form of vibration still remains regularly periodic. It is only
essential that the relations between the numbers of vibrations for
each component tone are expressed by whole numbers that are
not too large. Only tones whose numbers of vibrations stand in
such a simple numerical relation as the one above cited, together
compose a musical sound.

Therefore, to recapitulate briefly, the specific physical stimulus for
the organ of hearing consists of simple sound-waves that unite some-
times as musical sound-waves sometimes as sound-waves of noise.

It is difficult to determine exactly wliere organs of hearing first
appear in the animal series. Without doubt, however, such organs
are already present in the Arthropoda.^ It is often particularly
difficult to determine whether the so-called otoliths of the Cteno-
phora and other similar animals are organs of hearing or organs
that serve to keep the body in balance. The organ of hearing
has been developed into a very complicated structure. A peri-
pheral apparatus, which includes the external meatus, the mem-
brana tympani and the auditory bones, serves especially to keep
back all stimuli from the nerve-terminations, except the adequate
• stimuli of sound. These latter they transmit to the nerve-ends in
the most suitable form possible. The final terminations of the
auditory nerve lie partly in the organ of Corti in the cochlea,
partly in the ampullae of the semicircular canals ; in both they
come in connection with the so-called "hair-cells." The part of the

^ A. FoREL (Experiences et remarques sur les sensations des insectes, 1SS7)
does not grant to ants the sense of hearing. A tolerable compilation of mor-
phological facts concerning the ear of vertebrates is to be found in .\vers,
The vertebrate ear. Journ. of Morphology, 1892, May.

go Introduction to Physiological Psychology.

auditory nerve that ends in the cochlea is designated as the nervus
cochlearis ; the part which ends in the ampullae, as the nervus
vestibularis. In their course through the brain they separate again ;
the nervus vestibularis reaches the cerebellum, while the nervus
cochlearis, which probably performs the chief part of the function of
hearing, reaches the cortex of the temporo-sphenoidal lobe in the
cerebrum. Now the left auditory nerve, in fact, terminates chiefly
in the cortex of the right temporo-sphenoidal lobe, the right
auditory nerve in the cortex of the left temporo-sphenoidal lobe.
The auditory centre is therefore to be sought in the temporo-
sphenoidal lobe. It has not yet been decided whether the am-
pullae and the nervus vestibularis take any part in the functions
of hearing whatever or whether they simply transmit those sensa-
tions which assist us in retaining our balance ; the sensations of
noise have also been ascribed to them. In the organ of Corti
the nerve-terminations lie in an expanded membrane, the breadth
of which is very different in different parts. Sounds that have a
large number of vibrations will cause particularly the narrower
parts of the membrane to vibrate sympathetically ; sounds having
a small number of vibrations, the broader parts. One can con-
ceive of the entire membrane as composed of numerous transverse
chords, gradually decreasing in length from one end to the other,
each of which is tuned to a definite tone. If a musical sound
or a noise reach the ear, it is analyzed into its component tones ;
i.e. the membrane is set in vibration at different points, each of
which corresponds to a definite component tone.

Sound-waves act as stimuli upon the peripheral terminations of
the auditory nerve. They constitute the specific adequate stimu-
lus. Sensations of musical sound can also be produced by electric
stimulation of the auditory nerve ; in this caise it is probable that
the trunk of the nerve is chiefly irritated. Mechanical stimuli,
such as the pressure of tumors on the auditory nerve, for example,
also produce sensations of hearing. Those sensations of hearing
that are not produced by adequate stimuli are always exceedingly
simple and monotonous.

Thus far we have dealt with those certain or probable facts

Sensations of Hearing.

offered by physiology and anatomy. Let us now analyse the
sensations of sound psychologically. We shall first seek their
different qualities. From the beginning we may be allowed to
exclude that large class of sensations known as noises ; they com-
pose an especial group of sensations that are hardly accessible
to investigation. We shall occupy ourselves only with the simple
sensations of tones and the sensations of musical sounds. We
have already heard that the so-called tones of the piano are not
simple, but complex; they may be more correctly designated as
musical sounds. Simple tones are produced most easily by strik-
ing a tuning-fork ; the flute also gives comparatively simple tones.
The only difference in the quality of all sittiple tones lies in the
pitch, to which the number of vibrations per second in the stimu-
lating medium corresponds. We perceive a tone to be higher the
greater the number of its vibrations. The lowest audible tone has
sixteen vibrations/ the highest about 40,000 vibrations per second.
But the various sensations of pitch are not irregularly distributed
between sub-contra c and the eight-times-marked e (e^), as is the
case, for example, with the different qualities of the sense of smell ;
on the contrary, the sensations of pitch constitute a continuous
series which corresponds to the constant increase in the number
of vibrations of the acoustic stimuli. Without the omission of one
interval, we can ascend from sub-contra c to ^ by a regular scale
of simple tones. Strictly speaking, however, there are numberless
tones between the lowest and highest tones. For reasons which
we shall learn to understand more fully later, we distinguish only
a very limited number of tone-pitches. For example, in the interval
between the tone of 256 vibrations (^•), and the tone of 1,024 vibra-
tions {(fi), there are only 14 whole tones, including the lower tone
The chief factors that determined the historical development
of this scale were aesthetic. All those tones that directly or in-
directly harmonized with were sought and the above-mentioned
14 tones were the result. A more thorough analysis of this develop-
ment does not fall within the province of this discussion. Especi-

WuNDT claims to have heard even eight vibrations per second.

92 hitroduction to Physiological Psychology.

ally the tone having twice as many vibrations as c^, or a tone of 5 1 2
vibrations per second, produces a very harmonious accord with c^.
Likewise tones that have three and four times as many vibrations,
etc., harmonize with c"^ remarkably well. Between and
f^, and fi, etc., are six intermediate tones of harmonious char-
acter, with the six following tones were embraced in one so-
called octave, — likewise and the six following tones, etc. We
have thus obtained a division of the long series of tone-sensations
which was determined by aesthetic factors. The series of tones
is divided into octaves, and each octave into seven notes. We
are acquainted with the seven notes in their various octaves as
^ di ^tfi ^> ^- Next the octave was completed by a series of
hitervening tones (f sharp, d sharp, / sharp, etc.), which were also
determined by aesthetic reasons. Thus the scale of simple musical
tones has been developed from the natural series of numberless
simple tones. This classification of the sensations of pitch was
first developed historically. For this reason the demarcation of
the octaves and the number of tones within the octave long
varied.

In calling to mind the musical scale, the thought readily occurs
to us to test or establish our sensibility to differences of pitch.
How does the sensation of the pitch of tones increase or, more
properly, vary when the number of vibrations changes? This
question has frequently been conceived of as a special case for
the application of the Law of Weber. It is obvious that there
are no grounds whatever to warrant such an application ; the
Law of Weber compares the intensity of stimulus with the ijitensity
of sensation. We shall presently apply the Law of Weber to sen-
sations of sound in answer to the question as to how the intensity
of acoustic sensations increases in proportion to the increase of
the acoustic stimulus, i.e. in proportion to the increase in the in-
tensity of the sound. The question occupying us at present, how-
ever, is quite different : — How does the sensation of the pitch
of a tone change when the number of its vibrations changes ?
Neither has the sensation of pitch anything to do with the in-
tensity of the sensation, nor the number of vibrations anything

Sensatio7is of Hearings

to do with the intensity of the acoustic stimulus. On the con-
trary, a sensation of pitch depends merely upon the quality of
sensation and the intensity of the acoustic stimulus upon the
amplitude ot vibration. Hence the Law of Weber has no direct
connection with the question. In a former chapter we sought the
true nature of Weber's Law in an act of association and the
incitation of the idea " larger " or " smaller." The comparison
of tones of different pitch by means of association with the idea
"higher" or " lower " is, of course, somewhat analogous to the above
case. For this reason it is conceivable that if the law of Weber is
valid in the one case within certain limits, similar mathematical
relations may also be valid in the other case. A large numbei
of experimental investigations have been employed in this line,
the most reliable of which were made by E. Luft.^ The result
of these investigations shows that the relative discriminative sen-
sibility is not quite constant, as required by the Law of Weber.
If we sound a tone of 120 vibrations and then one of i2oi vibra-
tions per second, we can distinguish the pitch of both tones
clearly. Hence, at a pitch of 120 vibrations, a difference of i of
vibration is required to render two tones distinguishable, or the
barely perceptible difference amounts to of a vibration per
second. If we now choose as the beginning tone one with four
times the number of vibrations, i.e. with 480 vibrations per
second, the barely noticeable difference, according to Weber's
Law, should also be four times as great. Thus the two tones
should only be distinguishable when we increase the number of
vibrations by the addition of 4 x i or -f of a vibration per second.
This is not the fact however. On the contrary, experiment proves
that the addition of only -1^ of a vibration is sufficient for the
distinction of both tones. If we select another pitch twice as
high as the last and begin with a tone produced by 96b vibra-
tions, it appears that a tone of 96o|- vibrations can be clearly
distingjLiished from the first tone of 960 vibrations, while accord-
ing to the Law of Weber an increase of pitch should only be

' Philosoph. Stud., Bd. IV, S. 4.

94 Introduction to Physiological Psychology.

distinguished when the difference is 8 x i or more than one vibra-
tion per second. Therefore the relative discriminative sensibility *
is not constant, while, on the contrary, the absolute sensibility
for medium pitches seems to deviate but little from a constant
average magnitude. The threshold of difference only varie?
from I- to -1^ vibration per second, but may be materially affected
by practice and musical talent. Persons who are not naturally
musical err in the judgment of pitch, even more than we should
suppose. For example, Stumpf found that persons not at all
musical were mistaken once out of four times when they attempted
to tell which of two tones, separated by the interval of a third,
was the higher. The ability to distinguish is very limited, especi-
ally when the tones are very low or very high,^ for the individual
is not assisted by the experiences of daily life. Still it is astound
ing to reflect how exceedingly sensitive the organ of hearing is
in general. We even notice a change from i,ooo to i,oooi
vibrations per second ; at the latter limit the quality of sensation
has already changed. Some persons have been pleased to speak
of this facility as an " unconscious counting " of the vibrations,
and have been astonished at the certainty and rapidity with which
the soul accomplishes this enumeration. It is unnecessary for us
to be shown that no such enumeration takes place. It is only
necessary to conceive of the chemical combinations in the termi-
nations of the fibres from the auditory nerve as extraordinarily
complicated, in order that so slight a difference in the mechanical
stimulus may produce a difference in the central chemical process
sufficient to render the tone distinguishable as higher or lower.
Here for the first time we meet with time as an essential factor
in the analysis of sensations. The quality of the sensation of
tone corresponds to the number of vibrations of the sound-wave
per second ; it is therefore dependent on the duration of the

* Expressed by the ratio, while the absolute descriminative sensibilitj

is expressed by the ratio,

* above c'.

Sensanons of Hearing.

single vibtations, every change of which is followed by a corre-
sponding change in the sensation with remarkable precision.

But the qualities of the sense of hearing, however, are not ex-
hausted with the simple tones, even though we exclude noises,
as we have already done. Apart from the scale of comparatively
simple tones, such as the flute produces, we further distinguish
a large number of qualities that belong to sensations of sound.
The of the piano sounds very different from the pure of the
tuning fork or flute, despite the sameness of pitch \ and the of
the violin is distinguished from both of the others. Or, if the
human voice sing a vowel at the pitch of c^, we can distin-
guish this also from the of the tuning fork, piano, and violin.
Furthermore, the human voice can sing the vowels a, o, e, i, u,
etc., to the same note. All these differences in the quality of
acoustic sensations that are distinguishable even when the pitch
remains the same, are included under one conception, — timbre
or colour-tone. The same tone upon each instrument and each
vowel of the human voice has its special timbre. Helmholtz ^
first showed what physical differences in the stimulus condition
this difference in the quality of the sensations of sound when the
pitch remains the same. As already briefly mentioned, the so-
called tones of the violin, piano, horn, and human voice are in
fact not simple tones at all. At most, only the tones of the tuning
fork and flute may be considered simple. The tones of all other
instruments and of the human larynx are composed of several,
often of numerous, simple tones. Since the numbers of vibra-
tions producing the component tones stand in very simple rela-
tions to one another (they are in general multiples of the same
number), their combined effect should therefore be designated
more properly as a musical sound. Thus, for example, if we
strike upon the piano, six more tones sound with it, g^, c^, e^,
etc. The musical sound on the piano is therefore composed
of seven simple, component tones, or, as it is also expressed, of
one fundamental tone and six overtones. The fundamental tone

" Lehre von den Tonempfindungen."

•96 Introduction to Physiological Psychology.

IS loudest, the intensity of the over-tones diminishes as the pitch
increases. Let us now compare this with of the vioHn. In
this case also over-tones sound in harmony with the fundamental
tone ; in fact, we find not only the over-tones c^, g^, e^, etc.,
again, but also from four to five more than before. Hence the
intensity of the higher over-tones on the violin is essentially
greater than upon the piano ; by this means the violin receives
the peculiar timbre characteristic of all stringed instruments. The
component tones of the human voice have likewise been recently
determined by Helmholtz, Hermann, and others.^

The physical basis for the differences in timbre, therefore,
depends upon the difference in the number and intensity of the
overtones blending with the fundamental tone of the musical
sound. This analysis of the musical sounds of instruments into
their composite tones can be accomplished by means of special
resonators. But the musician, and after some practice even one
who is not musical, is able to distinguish by the sense of hearing
without resonators, at least the lower overtones of c\ struck on
the piano, from the fundamental tone. The theory of partial
tones or overtones is of the greatest importance in musical
aesthetics.

Among the various qualities of the sensations of noise, the
most important are those that are produced by the consonants
of the human voice. A physical analysis demonstrates that the
consonants are essentially noises, i.e. they are composed of
simple tones, the numbers of whose vibrations do not stand in
simple numerical relations to one another.

This finishes the consideration of the various qualities belonging
to sound. It is obvious that the iniejisiiy of acoustic sensations
increases with the strength of the sound. The latter may be sub-
jected to a still more exact physical analysis. The intensity of a
sound is in fact directly dependent on the amplitude of the
vibrations produced in the sounding body. The proper formula
is more exactly stated as follows: ; is proportional to a^n*.
Therefore the intensity {1) of the sound grows in proportion as
the square of the amplitude (a), it being understood of course

1 Comp. Hermann, " Pfliiger's Archiv.," Bd. 45, 47, and 48, and Pipping,
" Zur Klangfarbe der gesungeiien Vokale," Zeitschr. f. Biologic, Bd. 27.

Sensations of Hearing.

that the number of vibrations («), or in other words, the pitch,
remains the same. Now is the Law of Weber valid in the case of
, sensations of sound ? Is the absolute "threshold of difference"
in consent, direct proportion to the primary or beginning
stimulus ? In the investigations that were undertaken for the
purpose of solving this question, great difficulty arose in produc-
ing any desirable gradation of the intensities of sound. Recently
metal or ivory balls, that are allowed to fall upon an ebony or
iron plate, have been applied with great advantage. In these
experiments the timbre changes but very slightly^ with the
change in the height of falling and in the weight. On the other
hand, the intensity of the sound is, within certain limits, pro-
portional to the height of falling, the weight being constant, or
to the weight, the height of falling being constant. Hence, by
selecting balls of different weights or by altering the height of
falling, one can vary the objective intensity of the sound at
pleasure. The results have shown that Weber's Law is valid and
comparatively exact for the intensity of acoustic sensations. A
so-called " lower deviation " is met with in this case also, although
it may possibly be caused by concomitant noises which are never
wholly avoidable. The average relative threshold of difference is
about one-third. The minimum of stimulus, or the least amount
of acoustic stimulus that imparts any sensation at all, has not yet
been determined with sufficient precision.^ The following series
of experiments by Merkel is interesting. He permitted the per-
son on whom he was experimenting to hear two stimuli of sound,
alike in quality but different in intensity, and then requested him
to determine an acoustic stimulus that should impart a sensation
lying directly midway between the first two sensations. This
" method of mean gradations " showed that the stimulus of sound
which produced the mean sensation resulted in the approximate
arithmetical, but not geometrical, mean between the two beginning

> Starke, Philosoph. Stud., Bd. V, H. i. Merkel, Philosoph. Stud.,
Bd. V, H. 4.

^ NoaR's values appear to be too high (Zeitschr. f. Biologic, 1879).

98 Introduction to Physiological Psychology.

stimuli. If Fechner's construction of Weber's Law is correct, i.e.
dE

if not only — , but also dE, is constant, and if therefore 5 is

also proportional to log. E, the geometric mean should be the
result. In the case of sensations of sound, therefore, Fechner's
formula is shown to be wholly invalid ; the assumption of Plateau

is more correct ; _ is constant. Let us here call to mind once

more, however, that neither the geometrical nor the arithmetical
mean results for other sensations ; the actual outcome is a value
between these two. We have already referred to the esseritial
scruple that can be brought against the "method of mean
gradations."

We shall now turn to the question also in reference to sensa-
tions of hearing, that has previously been asked concerning other
sensations : How is the sensation modified if the same stimulus
of sound act on several nerve-terminations ? In the case of the
sensibility of the skin it appeared that, aside from the three
qualities manifest in sensations of pressure, cold and heat, all
nerve-terminations are practically identical in • function, and that
when the stimulus spreads over a larger number of nerve-ends the
numerous like sensations are so arranged with reference to each
other as to produce an image of space. In the case of the sense
of hearing the result is different The number of qualities here is
much larger ; each pitch represents a special quality of sensation.
We have already mentioned that the physiological structure of the
organ of hearing renders it very probable that each nerve-end of
the nervus cochlearis can only be irritated by one pitch, or at
most only a very small number of pitches. One and the same
stimulus of sound, therefore, cannot act at the same time upon
many nerve-ends, as our question would imply, but simply upon
one or at most a few neighbouring terminations. The qualitative
adaptation or differentiation of the auditory fibres is so far
developed that in general no two fibres ^ can partake of the same

* The membrane of Corti is set in vibration only at a definite place by a

Sensations of Hearing.

kind of excitation. Accordingly a distinct spatial contiguity in
the arrangement of several tones heard at the same time is never
developed. All sensations of sound are different in quality ; but
the favourable condition for the development of the spatial char-
acter of our sensations is the simultaneous existence of several
sensations alike in quality. Like all sensations, the sensations of
hearing are projected out into space; but this projection is
extraordinarily inexact. It is of especial importance that the
sensations produced by the excitation of different nerve-ends may
be projected to about one and the same place. For example,
some one strikes a chord on the piano, in wliich perhaps eighteen
simple tones are contained. At least eighteen different nerve-ends
are irritated in each auditory nerve, and still we do not project
the sensations produced by these excitations into space either
separated or side by side, but altogether to about the place from
which the tone seems to proceed. This fact cannot be suffi-
ciently explained by the highly developed differentiation of the
auditory fibres and their adaptation to the numerous qualities of
sound ; for the separate projection of the sensations into space is
conceivable, even though they are wholly different in quality. In
this connection we must consider that association with sensations
and ideas of motion, which is so essential for the development of
space-perception in the case of touch, is very incomplete in the
case of the sense of hearing. We cannot let the ends of the
auditory nerve glide over a sounding body, as our hands did over
an object, nor construct an image of space from the successive
impressions received by sensations of increasing motion. We
can, it is true, turn the head from or toward the sounding body ;
we can approach it or recede from it ; but in so doing no other
nerve-ends are brought in contact with the stimulus. On the
contrary, the same nerve-ends are irritated, and only the intensity

definite pitch ; each nerve-fibre thus becomes to a certain extent accustomed
and especially sensitive to a certain pitch.

100 Introduction to Physio logical Psychology.

of the stimulus increases in the one case and decreases in tiie
other. A person with one ear, and without the abihty of moving
from place to place or of turning the head, would project all
tones into space quite indefinitely and without regard to the
direction from which they came. Of course the localization of
sensations of sound by the normal human being is somewhat
more definite, since he is able to observe how the intensity of a
sound varies on turning the head or moving from one place to
another, and can therefore form some conclusion as to the direc-
tion of the sound. When the head is held at rest, we are often
mistaken in judging of the direction of a sound, exchanging befon
for behind, above for beloiv, etc.^ Slight concomitant sensations of
touch on the skin, appearing in different localities according to
the direction of the sound, are produced by delicate sympathetic
vibrations of the hairs in the concha, and possibly also by vibrations
of the bones (cranio-tympanal conduction). These sensations
often render at least an approximate judgment possible. Sounds
coming from the right and left are also difficult to distinguish when
the head is motionless. In this case we are aided in distinguish-
ing the direction from which a sound proceeds by our knowledge
of the fact that a sound coming from the right is physically com-
pelled to produce a stronger excitation in the right ear than in the
left. In this case, therefore, in view of the fact that most of the
auditory fibres proceeding from one ear cross to the opposite side
of the brain, the cortical excitation is also greater in the left
temporo-sphenoidal lobe than in the right. Conversely, in
response to a sound coming from the left, the cortical excitation
is greater in the right temporo-sphenoidal lobe. This fact renders
the distinction of direction possible, to a certain extent, for it is
very probable that the acoustic fields of the two hemispheres have,
for purposes of association, very different connections. But a
slight turning of the head still remains the most important and

* Preyer (Arch. f. d. ges. Physiol., Bd. XL) has recently ascribed the
function of localizing the acoustic impressions to the semi-circular canals, but
apparently witliout sufficient grounds.

Sensations oj Hearing.

loi

natural mearrs for determining the direction of sound. Finally,
the localization of our impressions of sound is quite uncertain as
regards the distance to which we project sensations. The sensa-
tions of touch on the skin are referred directly to the surface of
the skin because experience teaches that only mechanical stimuli
produce sensations of touch by direct contact. As regards the
sensations of sound, we likewise permit ourselves to be guided in
general by experience ; weaker sensations of sound are projected
to a point remote from us, stronger sensations to one nearer us.
In such cases we are assisted by an experiential knowledge of the
strength which the sounds of certain things have at a certain
distance previously estimated by the eye ; hence after having
acquired this experience we are also able to determine with closed
eyes whether a distance is less or greater by the greater or less
intensity of a sound.

We see that the localization of the sensations of hearing is
determined in part at least by processes that are essentially
associative and to some extent comparatively complicated. The
acoustic sensations have no direct spatial relations such as we
found for the sensations of touch or such as we shall find most
highly developed for the sensations of sight which are presently
to be considered. The sense of hearing is not, in fact, a sense
that brings us in close relations with space. We may designate it
briefly as a purely qualitative sense ; but by virtue of the extremely
delicate gradation and the exceedingly rapid perception ^ of the
qualities of stimulation, the sense of hearing is fitted to receive
the best means of communication employed by mankind, the
spoken language.

^ Even eighteen vibrations are sufficient for the itcognition of the pitch
quality of a tone, if the experiment is properjy arranged.

CHAPTER VI.

THE SENSATIONS OV SIGHT.

The adequate physical stimulus of the eye is furnished by the
vibrations of the ether. We conceive that imponderable particles
of so-called ether are distributed in infinite numbers between the
atoms or molecules of matter. The physics of to-day teaches
that light is diffused through space in all directions by the vibra-
tion of these particles of ether. These vibrations are not executed
longitudinally, as are the vibrations of the molecules of a body
conducting sound, but transversely ; in other words, the direction
of vibration is perpendicular to the direction in which the rays of
light are transmitted. The vibrations of light may also be repre-
sented best as wave-lines, governed by laws very similar to those
for waves of sound. The vibrations of light without exception
are to be regarded as regular periodic vibrations. Not all velo-
cities of ethereal vibration impart a sensation of light to the eye :
the number of vibrations per second may be too large or too
small to produce such a sensation. In general only more than
400 billion and less than 912 billion vibrations per second are
capable of exciting visual sensations.

Let us now consider the organ that receives this stimulus — the
eye. Even in the lowest animals, the Protozoans, we find spots
in the protoplasm that are sensitive to light, and marked by the
deposition of special pigments. They may therefore be designated
as pigment-spots. Also in the eye of the most highly developed
vertebrates the rays of light are conducted through many refract-
ing media and finally reach a layer of the so-called retina con-
taining pigment. This layer of the retina, which covers the inner

102

TIic. Sensations of Sight.

103

jurface of the posterior wall of the eye-ball, is designated as the
" layer of rods and cones." Here numerous structures, part in the
form of rods, part in the form of cones, are arranged mosaically,
their bases turned toward the inner part of the eye. These rods
and cones are connected with the terminations of the optical nerve,
but it is not probable that a fibre of this nerve is allotted to each
one of the rods and each one of the cones. The most familiar
pigment of the retina is the " visual purple " discovered by Boll,
which speedily bleaches when exposed to light. This visual
purple, however, is only present in the rods. The cones, which
are far more numerous in that part of the retina which is of service
in sharp, steady sight, contain no visual purple. It is also entirely
wanting, for example, in the eye of the snake. Besides the visual
purple, the so-called pigment-epithelium of the retina should be
taken into consideration, although we cannot undertake the expla-
nation of its anatomical arrangement here. The process of an
act of sight is as follows : — The vibrations of ether, having reached
the retina, decompose its so-called photo-chemical or visual sub-
stances, which are sensitive to light. (There are numerous
analogies to this decomposing action of light.) By means of this
decomposition, the nerve-ends laden with visual substances are
set in commotion. The iibres of the optic nerve then conduct
this excitation to the occipital lobe of the cerebrum. On their
way to the brain, part of the optical fibres of the two nerves
cross, part remain on the same side. Hence all the impressions
from the right half of the space viewed reach the left hemisphere,
all the impressions from the left half of the field of vision reach
the right hemisphere.

We may here at once observe that, besides the adequate stimulus
furnished by the vibrations of ether, the universal nerve-stimuli
(mechanical and electrical) can also impart sensations of light.
If we press against the eyeball anywhere along the edge of the
orbit, an impression of light is produced which is known as a
"phosphene." The cause of this phenomenon is obviou.sly
mechanical stimulation. When, on account of being geneinlly

I04 Introduction to Physiological Psychology.

diseased, the eyeball is extirpated and the optic nerve severed,
the patient on whom the operation is performed sees great masses
of light during the moment in which the nerve is being cut.
Volta was the first one to establish the electric excitability of the
organ of sight. It has been observed that a flash of light appears
both on opening and shutting the galvanic current ; it is sufficient
to place an electrode upon each temple.

After these preliminary observations we can now undertake the
psychological analysis of the sensations of sight. We at once
meet with numerous qualities of visual sensation, which we desig-
nate as colour in the broadest sense. There are no other qualities
except those of colour ; these we shall now consider more
thoroughly in their relation to the physical stimulus. A long
series of colour-sensations is directly produced by the so-called
" colours of the spectrum," which include violet, blue, green,
yellow, orange, and red. These sensations of colour corre-
sponding to the spectral colours compose a series similar to that
produced by the different sensations of pitch. Red, which has
the least number of vibrations, would correspond to the lowest
tones; violet, having the greatest number, would correspond to the
highest tones. Below the following line the series of spectral
colours is arranged in order.

Red — orange— yellow — green — blue — violet.

The red rays both have the greatest wave-length and are least
refrangible.

Of course we at once observe a difference between the series of
sensations of spectral colour and the series of tone-sensations. In
considering the latter we discovered certain harmonious relations,
the nature of which we shall investigate later. Guided by these
relations and proceeding from any given tone, we found it pos-
sible to discover all those other tones which stand in certain
harmonious relations to the first tone. In tiiis manner we obtained
a hmited scale whose tones are separated by definite intervals,

The Sensations of Sight.

105

instead of an uninterrupted series composed of an endless number
of tones. It is different with the series of sensations produced by
the colours of the spectrum. In this case there are no sucli har-
monious relations, and hence there is no colour-scale. AVe can only
select special colours that seem to us to be particularly striking, or
that we find occurring very frequently, the intervals between them
being thus determined quite arbitrarily. For this reason the
designation of colours among the ancients was very indefinite.
According to Helmholtz,^ for example, the Greeks appear to have
designated the entire series of colours from golden yellow to
bluish green by the term " xanthos " (^av<?os). The colour of the
sky derived its designation, cseruleus, or cerulean, from the term
meaning sky, cxlum. In a similar manner the German word
" blau " (blue), related to the English word " blow " (Germ.
blasen), was derived from the colour of the air, or that which
moves when the wind blows. The esthonian word for "green,"
" rohilane," properly signifies " grass-like," etc. One can, of course,
construct a scale of colours, similar to the scale of tones, according
to the relations which the numbers of vibrations bear to each other.
This has been done by Newton, and later, especially by Drobisth.^
The arrangement of the seven chief colours of the spectrum,
still in use (violet, indigo, blue, green, yellow, orange, red), was
first used by Newton simply in analogy to the musical scale.*-
But these are merely the theoretical figments of physics that
have no foundation whatever in the sentient life. So far as
sensation is concerned, the series of spectral colours is quite
continuous; it is not divided into a scale of various shades of
colour.

In our future considerations we shall notice many more differ-
ences between the sensations of pitch and those of colour. Let
us next ask if there are not still other sensations that are not pro-
duced by the colours contained in the spectrum, besides those of

' " Physiologische Optik '

' Poggendorf's Annalcn, Bd. 88.

* Thus the breadth of the spectrum was divided in proportions analagous to
the whole tones of an octave.

io6 Introduction to Physiological Psychology.

the seven spectral colours ? To this question we answer, Yes.
Brown/ with all its varieties, purple, black, grey in all its shades,
and white are not contained in the spectrum. One might at first
doubt whether black, with all its transitions through grey to
white, ought to be included in the list at all. The objection may
be offered that white is no definite colour, black simply the nega-
tion of colour, and that finally grey is merely a white of diminished
intensity. As regards the facts of physics this is correct. Accord-
ing to physics, black is in fact the absence of all vibration of ether ;
but psychologically black is as genuine a sensation as any of the
other sensations of sight. If we look straight ahead of us into an
entirely dark space, we are still able to distinguish the dark field
of vision before us from that which lies behind us, and which
produces no sensation of sight at all.^ In the same way it is
possibly correct, according to physics, that white is not a definite
colour. On the other hand^ it is for psychology to gather all the
qualities of visual sensation, and from this standpoint white is a
quality or a colour, the same as green or yellow. Finally as to
the different grades of grey between pure white and pure black,
it is psychologically quite false to designate the sensations of grey
as less intense sensations of white. According to this conception
white would also be a more intense grey. In this case also one
must guard against introducing physical propositions directly into
psychology. In physics the proposition may be correct ; the physi-
cal stimulus that imparts the sensation of grey may be less intense
than that imparting the sensation of white, for a body is grey
that reflects only the same fractional part of all the rays of light
falling upon it. But in psychology the difference between white
and grey is one of quality and not of intensity.

We must therefore regard brown, purple in all its varieties, grey
in all its grades, white and black, as special qualities of visual sen

1 Brown is here chosen as an example only.

^ In this connection it is also very convincing to note that in cases of hemi-
anopsia and peripheral blindness of many years' standing, the sensation of
darkness disappears.— WiLBRAND, " Seelenblindheil," S. 82.

The Sensations of Sight.

sation, the same as the sensations of the spectral colours. Now
what physical stimulus produces these sensations ?

Let us begin with the sensation of purple. The sensation of
purple in its different grades is produced by mixing those simple
colours that stand near the ends of the spectrum ; especially by
mixing red and violet, or also orange and blue. By a suitable
choice of the proportions in which the elementary colours are
mixed, a continuous graded series of purple colours may be
produced between violet and red. Therefore, while the series of
physical, spectral colours themselves is represented by a straight
line, the series of corresponding colour-sensations may be repre-
sented as a circle by the addition of tlie sensation of purple (fig.
II).

The question as to the physical stimulus for the sensation of
black has already been answered above. In this case, vibrations
of ether that come to the eye from without, and reach the termin-
ations of the optic nerve, are wholly wanting. For this reason,
the sensation of black must be produced by those chemical
excitations which accompany rest, and the restoration of the
previously decomposed visual substances, or the previously irri-
tated terminations of the optic nerve. Therefore the sensation
of black is just as positive as the sensation of any colour, and
corresponds to the external stimulus, ^ = (9. This fact coiiKli-
tutes a further important difference between sensations of sight
and those of sound.

Introduction to Physiological Psychology.

The se?tsation of white is always produced by the combined
action of several spectral colours. It is produced,

I. By the union of the rays of all the colours of the spectrum.
This takes place, for example, when the colours of the spectrum,
artificially produced by analysis, are again united by a prism.^

a. By the union of two definite spectral colours. Each colour
of the spectrum, having a certain wave-length of vibration, when
combined with only one other colour of the spectrum, produces
the sensation of white. Thus, for example, red and greenish
blue, yellow and indigo-blue,^ etc., are colours which together give
the sensation of white, and are therefore designated as "complemen-
tary colours." Considered strictly in the light of physics, two com-
plementary colours have no especial relation to one another; they
«nly become complementary in our nervous system, in our sensa-
tions. There is no simple spectral colour which will give the
sensation of white when combined with pure green. On the
ether hand, purple proves to be the complementary sensation
for green. It would seem natural to compare white to a complex
tone or to an accord. An essential difference exists between
the two, however. By the sense of hearing we can distinguish
the single tones of a chord with greater or less ease ; the organ
of hearing analyses it. On the contrary, the sensation of white
contains nothing of the sensations of those colours which compose
the physical stimulus of white in any given case. l"he physical
stimulus of the sensation of white is complex ; the sensation of
white itself, however, is simple. We are accustomed to ascribe
a special central position to the sensation of white, setting it
in opposition to all other sensations of colour (fig. 12). This
is justified by the fact that any two complementary colours

* White-coloured objects are those which reflect all the rays of light, un-
absorbed and undecomposed.

^ The artist's formula, adopted by Goethe also, according to which yellow
and blue mixed produce green, may be offered in opposition to this statement-
It is, in fact, correct in the case of the artist's colours, but it can be easily
proved that in mixing material colours an addition of coloured light, such as
we desire, does not take place.

The Sensations of Sight.

together give the sensation of white. But in our estimation
of the sensation of white, we are inclined to go still further
and identify it directly with a hypothetical sensation of colour-
less light. We imagine that light in itself is white, white being
therefore synonymous with brightness. In so doing, vtc arc
chiefly influenced by the fact that our most powerful source of
light, the sun, imparts approximately white light. We then
come to the further conclusion that white, as a sensation of light,
is in itself the absolute and only antithesis of black, the sensation
of the absence of all light. But, in fact, the above conclusions do
not represent the true relations in the case. We perceive " bright-
ness " in a room also that is lighted by the homogeneous yellow
light of natrium. It may be dazzlingly bright in a room that
does not contain a single white object, with only the blue sky
before the window. Hence white and brightness are not identical.
Brightness is an attribute of all sensations of light, the sensations
of spectral colour, as well as the sensations of white or jiurple.
White simply presents a mixture of spectral colours, especially
important to mankind. In this connection it is particularly
necessary to consider that the sun emits white light ; coloured
bodies are characterized by absorbing a part of the rays con-
tained in the white light, and by reflecting only the remaining
part to the eye. They are thus coloured, but weaker in liglit.
Since the white bodies of our sun-lit surroundings in nature
reflect all the rays of light, they are also always brightest, or
strongest in light. Thus arises the error of supposing that white
and brightness are identical.^ But if a definite intensity of bright-
ness belongs to each sensation of spectral colour as well as to the
sensation of white, it is also false to regard the sensation of
black merely as the opposite of the sensation of white. The

^ This same error is favoured by the fact (to be noted later) that, if the
intensity of the light of the spectrum gradually increase to a certain degree,
all colours finally pass into white.

I lO

Introduction to Physiological Psychology.

sensation of black stands in just as much of an opposition to the
sensations of all the other spectral colours. The sensation of
black IS characterized by an intensity of brightness equal to o; or,
in other words, the light-intensity of the stimulus causing the'
sensation of black, equals o. By reducing the light-intensity of
any spectral colour whatever, the corresponding sensation of
colour finally changes to a sensation of black.

Black

Fig. 12.

Let us consider these transitions somewhat more minutely.
The physical stimulus of a red, weak in light, produces the
sensation of reddish-brown ; that of a yellow, weak in light,
the sensation of brown ; that of a weak green, the sensation
of greenish-brown, or olive-green ; that of a weak blue, the sen-
sation of greyish-blue, etc. Jf the intensity of light is still further
■diminished, reddish-brown, brown, olive-green, and greyish-blue.

The Sensations of Sight.

1 1 1

all finally pass into black. We can produce a graphic represea
tation of these transitions, by uniting (fig. 12) by straight lines a
point representing black, situated in the axis of the circle of
spectral colours, with the different points of the circle drawn
above it. These connecting lines then represent the diff'erent
transitions of the single colours of the spectrum to black, on
reducing the intensity of light. It is well worthy of notice, in
connection with the colour-sense, that a decrease of the intensity
of the physical stimulus produces not only a decrease of the
intensity of the sensation, but also a modification of its quality.
This agrees with the fact just mentioned, that the intensity of
light, o, does not produce a sensation of the intensity o ; that is,
no sensation at all, but a positive sensation, the sensation of
black, which, moreover, is just as positive psychologically as the
sensation of white. If we observe a red surface at a constantly
increasing distance, or, in other words, in a light that is constantly
diminishing in intensity, the intensity of the sensation also changes
in fact, but the change of quality is particularly noticeable. There
is no true scale of intensities for the sensations of light, corre-
sponding to the scale of intensities for sensations of sound. This
transition to black, however, is not characteristic of spectral
colours alone, but also of all mixed colours, including especially
white. We have already become acquainted with the transitions
of the latter to black, as the sensation of grey in its various
gradations.

But after having added to the sensations of the spectral colours
the sensations of black, white, purple, grey, brown, grey-blue, etc.,
we have not yet exhausted all the qualities of the sensations of
colour. It is vain to seek simple spectral colours for the colour-
sensations of sky-blue, sea-blue, pale green, flesh-colour, and rose.
This last group of colour-sensations is essentially characterized by
the partial absence of that which we designate as '■'■colour-satura-
tion.'''' The physical stimulus that produces these sensations of less
saturated colour consists of a mixture of any given spectral colour
with white, or a mixture of two suitably chosen spectral colours
that are not complementary. In the same way, without the ad-

112 Introductioji to Physiological Psychology.

mixture of white, each spectral colour becomes ligliter, or, in
other words, less saturated when the intensity of light is increased.
If one gradually adds more white to the mixture, or increases the
intensity of light, each one of the spectral colours finally becomes

Black

FIG. 13.

apparently white. We may now add, therefore, that a sensation of
white is produced not only by mixing two complementary colours,
but also by the excessive increase of the intensity of light in
which any given spectral colour appears. Thus red gradually
passes through flesh-colour, blue through sky-blue, purple through

The Sensations of Sight.

113

rose into white. If we wish to represent these colours also to-
gether with white in tlie illustration, we must place white in the
centre of the plane of the circle representing the colours of the
spectrum (fig. 13). The radii of the circle then represent the
gradations between complete saturation and white. With these
colour-sensations produced by the admixture of white, the quali-
ties of sensations of light are exhausted. By mixing the qualities
thus obtained, no other new colours are produced ; only the old
colours are reproduced according to fixed laws. We are indebted
to Newton for the most important of these laws of mixture.

As a brief summary, we may state that the qualities of the sen-
sations of light do not present a simple series as do those of the
sensations of tone, but can only .be represented by a structure of
three dimensions (fig. 13).

We are now confronted by the question : In the case of the
sense of sight, is each nerve-end trained to a certain pitch, i.e. t®
vibrations having a certain definite wave-length, as is the case in
the sense of hearing ? We answer this question decidedly in the
negative. In the case of the membrane of Corti it is indeed true
that each one of its numerous fibres transmits essentially but me
shade of sensation. On the other hand, the simplest obserratioa
shows that in general every spot upon the retina is sensitive to ali
shades of colour. Only those parts of the retina that lie riear the
periphery are characterized by insensibility to green, the outermost
parts by insensibility to red and green. It appears beyond doubt
that all terminations of the nerve-fibres in the central parts of the
retina must be very sensitive to many if not all colour-stimuli.

To-day physiologists in general assume that only three different
photo-chemical substances are to be found at the terminations of
the optic nerve. All rays of light act only upon these three sub-
stances. The red rays decompose perhaps only one substance,
the yellow rays perhaps only half of one and half of another — the
orange-coloured rays half of the first, one-third of the second, and
one-sixth of the third visual substance, etc. In short, the action
of each ray of coloured light is undoubtedly limited, and dis-
tinguished from all others in that it decomposes a definite relative

114 Introduction to Physiological Psychology.

fractional part of each of the three visual substances. This frac-
tional part is constant for a given wave-length. One can carry
this supposition still farther, supported by the so-called " Young-
Helmholtz hypothesis." This theory makes a strict application
of the theory of specific energy, and assumes accordingly that a
special kind of fibre in the optic nerve, a special central connec-
tion and a special fundamental sensation correspond to each
visual substance, and that therefore every particle of the retina
contains three specific nerve-ends. However, it is just this hypo-
thesis which is psychologically difficult to maintain. It is not for
us to discuss here in how far the theory of Hering, as opposed to
that of Helmholtz, corresponds to the requirements of physiologi-
cal psychology. It is sufficient here to simply emphasize the fact
as undoubtedly established, that a photo-chemical process im-
parts the action of the rays of light to the ends of the optic nerve.
Both the number of visual substances and the arrangement of
the single substances with reference to definite colours, or even
to special kinds of fibres, are still quite uncertain. They are also
psychologically of less importance than the above-mentioned re-
presentation in which the qualities are arranged in three dimen-
sions. A presentation of the most important physiological theories
is to be found in the writings of Helmholtz, Hering, Wundt and
Kries.*

It is interesting to note that in the development of both in-
dividuals and nations, as also in certain pathological cases, the
number of qualities of visual sensation varies. At the age of
two years the child gradually learns to name the colours cor-
rectly, first yellow, then red, and somewhat later, green and blue.
Especially blue is for a long time recognised only with difficulty,
being often designated as "grey," or "gar nix" (nothing at all)
(Preyer). All the colours are not named correctly before the be-

* HuLMHOLTZ, " Handbuch der physiolog. Optik," 1st and 2nd editions ;
Hering, Sitzungsber. d. Wiener Acad. Math.-naturwiss. Klasse, Bd. 66,
68, 69; Pfluger's Archiv., Bd. 40-42; Wundt, Philos. Studien, Bd. 4;
Kries, Arch. f. Augenheilk. , Bd. 17, and Du Bois-Reymond's Aicb.,
1882.

The Sensations of Sight.

115

ginning of the fourth year. This may be explained by the fact
that the action of blue and green rays of light on the child's eye
is weakened by purely physiological circumstances. We should
furthermore consider that there may be possible differences in the
ability to discriminate between the various single sensations of
colour as regards quality.

Pathological defectiveness in the qualities of visual sensation is
generally designated as colour-blindness. Total colour-blindness
has been observed in rare cases ; the individuals perceived some
difference in brightness, but no difference in quality or colour. All
nature, therefore, with its great variety of colours, appears to these
individuals as a sort of silhouette, having only different shades.
So-called violet- blindness is somewhat more frequent. It may be
artificially and temporarily produced in a human being by the use
of santonin. Violet and yellow appear to be alike to persons
that are either colour-blind to violet, or under the influence of
santonin. Still more frequent are " red-blindness " and "green-
blindness," or cases of colour-blindness, in which red and green
cannot be distinguished. Those who are colour-blind to red see
but two chief colours in the spectrum, which they generally de-
signate as blue and yellow ; red, orange and green appear to them
like their yellow, violet like their blue. In the same way thosa
who are colour-blind to green, distinguish two qualities of colour
which they designate as blue and red. It has been claimed that
colour-blindness existed at certain stages in the cultural develop-
ment of nations, and that it still exists among certain peoples that
have fallen behind in culture. On the other hand, we find un-
doubted cases of the distinction of colour even in insects. In
1858 the youthful EngUsh statesman, Gladstone, claimed that
the Greeks were colour-bhnd to blue. He based his claims
chiefly upon the fact that Homer had no proper terms for blue.
The fact that, in describing the colours of the rainbow, some of
the colours were entirely omitted and others exchanged has been
cited in favour of the existence of partial colour-blindness among
ancient peoples.* It has, however, been shown that a deduction
cannot be made with certainty from the different designations of

* Comp. also, e.g., Odyss. Z. 231 and ^157, Kti/tar vaKivOivtf &vdii ifioias.

[

1 1 6 Introduction to Physiological Psychology.

colour that appear in the literature of a language. A reference to
the pages of some of our most modern poets will bring to light
some of the most nonsensical designations for colours (as one
authority has shown by actual count), which might likewise sug-
gest the diagnosis of colour-blindness. It appears to be a fact,
however, that sensibility to colours produced by short wave-
lengths of vibration (for example, green and blue), is noticeably
slight in ancient peoples, in modern peoples living in a state of
nature and, we may also add, in the new-born child. Therefore
just these colours are often insufficiently designated in a language
and the ability to distinguish them is deficient.

The Bongo negroes in Central Africa seem to have only the
word " red " for all colours produced by long waves of vibration ;
and the word " black " for all those produced by short waves.
There can be no doubt that our colour-sense has developed
gradually. We are also all colour-blind in the peripheral parts of
the retina, and are placed in a condition similar to that of colour-
blindness when the coloured objects are very far distant from us.
All objects then appear to us to be more and more like black in
proportion as the intensity of light decreases. In a similar
manner the greatest increase in the intensity of light causes the
apparent ultimate transition of each sensation of colour to a sen-
sation of white ; in other words, the ability to distinguish quality
is entirely removed.^

In a manner similar to that employed in the last chapter for
sensations of tone, we shall now determine the sensibility to
differences in colour-qualities in the case of sensations of colour
perceived by the normal eye so fixed that objects are imaged
upon the centre of the retina. We shall limit ourselves to the
series of spectral colours. Here we find^ that we perceive shght
differences in " colour-tone " best in the yellow and blue of the

1 See further on, however. As to peripheral colour-blindness, comp. Hess.,
Graefe's Arch. XXXV.

2 KoNiG and Dieterici, Ann. d. Phys. u. Chem., 1884. Brodhon,
Verh. d. physiol. Ges. zu Berlin, 1885-86. Uhthoff, Du Bois-Rkymond's
Arch., 1889.

The Sensations of Sight.

117

spectrum. A change in the wave-length amounting to f millionth
inilliineter is sufficient to cause a difference in the sensation of
blue (or greenish-blue). The sensibility to differences in quality
is considerably less in the case of the other spectral colours. For
some distance at the ends of the spectrum we recognise no change
of colour-tone at all, but only changes of brightness.

We have now finished the consideration of the qualities of
visual sensation, i.e. the sensations of colour ; we turn next to the
theory of the intensity of colour-sensations. Intensity or bright-
ness obviously depend on the amplitude of vibration ; the same
as the intensity of sensations of tone. We have already men-
tioned above, however, that sensations of light cannot be re-
garded as having a proper intensity. A distinct positive sensa-
tion, black, corresponds to the intensity of light o. Here, of
course, it is impossible that all stimulus is wanting; we must
assume chemical processes, characteristic of the retina at rest,
which continually irritate the ends of the optic nerve, thus impart-
ing a sensation of black. If we now permit the light of a spectral
colour, red, for example, to act with gradually increasing intensity
upon the retina previously at rest, both the intensity and the
quality of sensation change at the same time. We perceive at
first a very dark reddish-brown, then a lighter reddish-brown,
and finally a complete red. This change is due to the fact that
the sensation of black produced by a condition of rest in the
retina, is mingled with the sensation of red produced by the irri-
tation of the retina, in constantly decreasing proportions. If
very weak red rays reach the retina, the sensation of black, when
mingled with the weak sensation of red, still retains nearly its
complete normal intensity ; the sensation of dark reddish-brown
is thus produced. Black becomes less and less a factor in the
production of the sensation in proportion as the red rays are
intensified, and the retina more severely irritated, until finally a
sensation of saturated red is produced. On account of this con-
stant commingling of the sensations of black with those of red,
we are wholly unable to arrange a scale of the sensations of red,
beginning with the intensity o, and ascending without change of

Il8 Introduction to Physiological Psychology.

quality to constantly greater intensities of brightness. The scale
of intensities for sensations of light does not correspond to the
scale of tone-intensities characteristic of sensations of sound. This
scale, for example, begins with the softest and ascends to the
loudest O- without a change of quality. The scale of intensities
for sensations of light is mingled with a scale of changes in quality.
Therefore observations of pure intensity cannot be employed in
the case of sensations of light. If the latter remain the same in
quality, it is impossible to obtain any scale of intensities whatever.
Even the sensation of white not only loses intensity when the
strength of light is decreased, but is also modified in quality by
passing through grey into black. The quality may, however, at
least be regarded as approximately constant on a very small tract,
situated in that part of the mixed scale of intensities where the
sensations of red, white, etc., are most saturated. This tract
could be applied in the measurement of the intensity of sensa-
tion. (Fig. 14.)

Before we pass on to these measurements, however, let us carry
the above experiments still further. By constantly increasing the
intensity of light up to a certain degree we have obtained the
sensation of saturated red. Now what takes place when we in-
crease the intensity of light still further ? As has already been
mentioned above, each simple sensation of spectral colour then
passes into a sensation of white. It is inexpedient, however, to
consider the transition of sensations of spectral colour to the
sensation of white, caused by the constant increase in the in-
tensity of light, as parallel to the transition of these same sensa-
tions to the sensation of black, caused by the constant decrease
in the intensity of light. In the former process it is possible that
other complicated phenomena, due to over-irritation and con-
trast, are concerned.^ It is obvious, however, that a pure scale

' For example, a very intense green light, despite the continuity of its
action, might directly produce the contrasting sensation of red. In conse-
quence of the blending of the two sensations of colour, a sensation of white
would be produced.

The Sensations of Sight.

119

of intensities rising from saturation to white, is also an impossi-
bility, for the quality changes in proportion as the shades of colour
gradually approach white.

For the reasons just given, the testing of Weber's Law will
always be more or less uncertain when the law is applied to the
intensity of visual sensations. The approximate validity of this
law is, of course, at once apparent. As we have already learned,
the Law of Weber states that we distinguish between intensities
of light by virtue of their relative, but not their absolute, differ-
ence. A simple demonstration of this may be obtained by the
use of Masson's disks (fig. 14). A broken black line of a

FXG. 14.

definite breadth is drawn in the path of a radius upon a white
circular surface. If the disk is rapidly revolved, each component
line blends with the white belonging to the same ring of the
circle, into a grey ring. The innermost grey ring is darkest and
the other grey rings are lighter in proportion to their nearness to
the periphery, because each one of the successive components of
the broken line occupies a so much smaller part of the ring in
which it lies, and is consequently blended with so much more
white the nearer it is to the circumference of the disk. Let us
next assume that the disk is illuminated by the light of o?ie candle,
and that the grey ring already produced by the black component
line 4 is so light that we cannot distinguish it from the white
back-ground. We now light six candles instead of one, and find
to our astonishment that despite the great change in the absolute

I2.0 Introduction to Physiological Psychology.

intensity of light, the grey ring No. 4, is still the one that cannoi
be " just distinguished " from the white back-ground. It is
obvious that in this experiment the absolute difference in bright-
ness was completely changed, while the relative difference re-
mained the same. Hence, in accordance with the Law of Weber,
the discriminative sensibiHty also remained unchanged.

Fechner, the founder of psycho-physics, has called attention
to a very striking example of the approximate validity of Weber's
Law when applied to sensations of light. It has already been
stated that this law may also be formulated as follows : The
intensity of sensation increases in an arithmetical ratio while the
intensity of stimulus increases in geometrical ratio. For ages
the astronomers have classified the stars according to the in-
tensity of the sensations of light which the stars produce in the
eye of the observer. On this basis they distinguish stars of the
first magnitude, stars of the second magnitude, etc. Since this
classification was first made on the basis of subjective impressions,
we have succeeded in determining the objective brightness of
these stars by the help of photo-chemistry. As a result it has
been shown that the apparent (subjective) brightness increases in
arithmetical ratio, while the real (objective) brightness increases
in geometrical ratio. The most recent, thorough experiments
upon the intensity of sensations of light have been made by
Merkel,^ Konig and Brodliun.^ The result of their experi-
ments demonstrates that the relative discriminative sensibility, in
the case of light stimuli having a medium intensity, is approxi-
mately constant and corresponds to the Law of Weber. Devia-
tions occur when the stimuli are very weak or very strong, as in
the case of the other senses. The so-called " lower deviation "
is due in part to the fact that the retina has a " light of its own "
(Eigenlicht). The weak sensations of light are disturbed by
slight irritated conditions of the retina that can never be wholly
removed. They appear, for example, as a spotted glimmer in the

^ Philosopb. Studien., IV, H. 4-

« Sitzungsber. d. konigl. preuss. Akad. d. Wiss.. 1S88. Schirmcr ha^
recently fixed the discriminative sensibility at , J-r to ^^^(Graefe's Arcii., Bd. 36).

Tlie Sensations of Sight.

121

field of vision when the eyes are closed. This light, which is in
the retina itself, also renders it almost impossible to determine
accurately the minimum of stimulus for sensations of light.'

The threshold of difference appears to average about
for stimuli of white lighc It is larger for very weak and very
strong stimuli, especially for weak rays of spectral red. Let us
remember that we should not rely too implicitly upon these
measurements of intensity, especially in the case of great or
slight intensities of light. As regards the medium intensities of
light and their variations, with which we are daily familiar, it can
easily be conceived that in the course of development by natural
selection the sense of sight was trained to perceive chiefly the
relative differences of brightness and to ignore the absolute.
If the law of Weber did not have at least an approximate
validity, and the absolute differences of brightness were per-
ceived very vividly, at every flash of sunlight and every time the
sun was concealed behind a cloud, all the shades of our environ-
ment would be so distorted as to render an accurate and clear
perception of the projections and depressions of objects exceed-
ingly difficult. The accuracy with which we form our conceptions
of the objects of the world as solid bodies, is essentially depen-
dent upon the constancy of the relative threshold of difference
for a medium intensity of light.

Finally we again raise the important question. How is the
sensation affected when not one but several fibres of the optic
nerve are simultaneously irritated by the same stimulus of light?
We have already seen that the fibres of the optic nerve are, in
general, of equal value, i.e. each termination of the optic nerve
receives a stimulus of any wave-length whatever. Even if we
accept the assumption of Helmholtz, that there are three different
terminations for each nerve-fibre in each element of the retina,
we must still remember that this triad is repeated in all parts of

* The more recent experiments of Ebert's are very worthy of notice.
Wiedemann's Annalen, i888, and Langley, " Energy and Vision," Am.
Joum. of Sc., XXXVI. Helmholz has recently develojied a formula for the
" low<:r deviation," from which a hyperbolical nerve results.

122 Introduction to Physiological Psychology.

the retina. The obtusion of the sensitiveness of the peripheral
parts in the retina to red, and especially to green, may be dis-
regarded here. Hence, in the case of the sense under discussion,
we find relations bearing a close resemblance to those already
considered with reference to the sense of touch. These rela-
tions depend on a series of terminations of nerve-fibres that are
all essentially identical in function. In fact, the sensations of
light produced simultaneously by the excitation of different parts
of the retina stand in a relation to one another very similar to
that of the sensations of active touch when excited simultaneously
on different regions of the skin. They neither blend to a unit
in quality nor increase their reciprocal energy, but are arranged
together spatially so as to form an image of surface. In the
sphere of visual sensations also we must abandon the attempt
to explain the fundamental fact that the sensations of sight are
projected into space, as are all other sensations, thus producing
the so-called field of vision. We have simply to accept the
general fact that our sensations are combined so as to present
a contiguous arrangement ; we can only attempt to explain the
order of this adjacent arrangement. We must therefore restrict
ourselves to answering the question : How does it happen that
two sensations arising in neighbouring ends of the optical fibres
are also combined contiguously in the field of vision.? In an-
swering this question we shall make use of means (Fig. 15)
similar to those employed in the fourth chapter.

RR' is a cross-section of the retina ; CC is the corresponding
cross-section of the cerebral cortex ; ML represents the so-called
Macula lutea, the part of the retina most sensitive to light, which
is therefore generally fixed directly upon the object for the pur-
pose of distinct vision. The ends of the visual fibres aa\ bb', of,
dd', are arranged in the retina in the definite order just given.
In the cortex of the cerebrum this succession has been materially
changed. In the most favourable case we might suppose that a
certain region of the occipital lobe corresponds to the upper parts
of the retina, and another to the lower. But it is wholly improb-
able that the succession of the single fibres in the cerebral cortex

The Sensations of Sight.

123

remains the same as in the retina. We know, in fact, that the
fibres of the optic nerve from the retina of the left eye, for
example, terminate partly in the cortex of the left hemisphere
and partly in the cortex of the right hemisphere of the cerebrum.
Now how does it happen that in spite of this change in the order
of the fibres, the sensations which they conduct to the cortex are
arranged so as to correspond to the order of the fibres in the
retina, and hence also to the order of the visual stimuli, and of
the objects that are seen? Avery accommodating, but untenable,
theory is the so-called nativistic theory, which assumes tliat a
definite point in space is allotted to each one of the retinal points
from birth; but the theory is not at all in harmony with the

empirical data of physiological optics. We shall therefore pro-
ceed from the getietic standpoint, and attempt to show what data
furnished by the physiology of the brain throw any light upon
the arrangement of the spatial points, or upon the characteristic
features by which they are distinguished. Suppose O to be an
approximately point-like object, situated in the upper part of the
field of vision, from which rays of light are sent to the retina
RR'. These rays are united at otie point in the retina by means
of the peculiar structure of the eye. This point may be found
by drawing a straight line from O to X, the nodal point of the
eye, and by producing this Hne until it reaches the retina.
The object O (fig. 15) therefore sends all its rays to d, and

124

Introduction to Physiological Psychology.

irritates the ends of the nerve-fibres situated at that point.
Let us now move the eye for the purpose of fixing the especially
sensitive central point of the retina at a, the Macula lutea,
upon the object O so as to obtain a more distinct image of
the latter. In so doing the retinal image passes from d
over the points c and b to a. On moving the eye a certain
distance, it reaches c, a. somewhat greater distance b, and a
still greater distance a. As the eye is turned, and the retinal
image of the object passes from d to a, we have a continuous
series of motor sensations.^ A motor sensation, having a definite
magnitude, is associated with each termination of the nerve-fibres,
and the intensities of these sensations of motion form a constant
series. One retinal point, situated between two others, is con-
stantly associated with a sensation of motion whose magnitude
lies between the magnitudes of the sensations of motion with
which the two adjacent points are associated. In this associated
sensation of motion, each termination of the nerve-fibres possesses
to a certain extent an acquired local sign. By repeatedly passing
over all lines of the retina numberless times both from a and
toward a, each retinal point is associated with a definite magni-
tude in the system of motor ideas. Thus a foundation is obtained
for the localization of sensations. If a larger object 00' irritate
the four retinal points, a, b, c, d, simultaneously, four excitations,
d', a', b', d, will appear in the cerebral cortex followed by the
corresponding sensations. The localization of these sensations
in space takes place neither in complete confusion, i.e. according
to an arbitrary arrangement, nor according to the succession of
the ganglion-cells, d, a\ b', d. On the contrary, we localize the
sensations of light according 'to the scale of sensations or ideas
of moLion associated with them. In this way each sensation is
referred to its definite place. The order of sensations accord-
ingly corresponds to the order of the points on the retina, and
hence also to the order of the points on the object. It is clear
that an infinite advantage was gained in the struggle for existence

1 The chief features of the theory here presented originated with Lotze.

The Sensations of Sight.

123

by the first animal that localized its sensations in this way. If
the protist, with its pigment-spots sensitive to light, has any
sensations of space whatever, it must localize them almost wholly
without regard to order. At most those protists in which the
direction of the rays of light determines the direction of locomo-
tion (Phototaxis, Strassburger) by the association of the sensation
of light in one case with the motions of flight, in another case
with the motions of approach, have obtained some basis for the
distinction of two directions and for the localization of impres-
sions in two directions. In the course of the phylogenetic
development of the animal series that capacity to localize visual
sensations was first developed which made the eye a proper organ
for the perception of space. We find the wonderful rapidity,
with which this arrangement of the sensations is accomplished,
inconceivable; at once and without a moment's thought the
image is before us, well arranged and unmarred by the slightest
error. To be sure, a process of evolution extending through
almost endless ages was necessary to produce and train a cortical
apparatus of vision that can react with such fitness. The new-
born animal or child inherits this apparatus.^ Each single in-
dividual does not need to acquire it again laboriously, but only
to learn to use it. A person who is born blind and receives his
eyesight by an operation later in life, at first sees only coloured
spots floating before his eyes. He recognises a circle or a square
only with difficulty. It is only by degrees that he learns to use
his cortical apparatus, and to associate the sensations of sight
with ideas of motion and touch.

In concluding these investigations we can again render the
development of spatial localization clear by comparison. Let us
call to mind the position of a musical conductor who leads an
orchestra for the first time. Numerous sounds from a large
number of instruments are poured into his ears at the same

^ Munk's more recent investigations, perhaps, throw some light on the
physiological and anatomical structure of this cortical apparatus. Sitzungs-
ber. d. konigl. preuss. Akad. d. Wiss., 1890.

126 Introduction to Physiological Psychology.

instant, and at first he is only able to project the masses of sound
outward in confusion. But he gradually learns that the tone of
this violin always comes from below to the left, the tone of that
flute from the right, etc. In short, he learns to localize the tones
of the different instruments by means of distinctions that are
almost unnoticeable. Certain subtle distinctions in musical
sound and in the sensations on the skin that accompany the tones
according to the direction from which they proceed, assist him in
localizing at once the tone of one violin in this place, and the
tone of another violin in that place. In fact, the musical director
is finally able to project the tones outward in the exact order in
which the sources of sound are really arranged in space, even
with the eyes entirely closed. Orehestral leaders have been
known to construct in this manner a genuine "field of hearing"
similar to the field of vision. This projection is accomplished
very rapidly, and entirely without deliberation ; it is just as direct
and exact (that is, in accordance with the arrangement of the
external stimuli) as the projection of sensations from the visual
centre.

It is very striking, especially in comparison with the localiza-
tion of tones which are heard simultaneously, that our visual
impressions are characterized by continuity. A gap between
them never occurs ; in fact, even defects in the continuity of the
nerve-ends of the retina, the so-called " blind spot " for example,
are involuntarily repaired. We see the object, or the part of an
object, corresponding to the blind spot, in the colour of its
environment.

An anatomical explanation of this continuity in the arrange-
ment of projected visual sensations may possibly be found in the
anastomosis of the nerve-ends of the visual fibres in the retina,
or in the universal interconnection of the ganglion-cells of the
visual centre by means of the nerve-processes.^ The chief ground

' In fact, according to more recent investigations, these connections are
made not by the so-called protoplasmic processes, but by the axis-cylinder
processes. Compre Golgi, "Sulla (ina anatomia degli organi centrali del

The Seiisations of Sight.

127

for the continuity of sensations of sight, however, must be sought
chiefly in the continuity of the associated ideas of motion.

The following facts in the sphere of visual perceptions are still
to be investigated and explained in detail. First, the retinal
image in the eye of the vertebrates is inverted ; that which is on
the right and above in the real object, is on the left and below
in the retinal image, and vice-versa. Still we do not see the
object inverted, corresponding to the image on the retina, but
right side up, corresponding to the object itself. How can we
explain the fact that the retinal image is thus fittingly r^-inverted?
In reply we may first observe that the spatial succession in which
the visual sensations are projected is not altered at all ; it is
simply a question of projection in its totality. So far as the pro-
jection as a whole is concerned, the re-inversion of the retinal
image is determined and controlled by sensations of touch. In
general we project our sensations of sight so that they agree with
the tactual sensations by which we are guided to a certain extent.
This capacity has also been acquired phylogenetically and not
ontogenetically. We should here call attention to the fact that
the inversion of the image on the retina which necessitates to
a certain extent a second psychical inversion, is specifically
characteristic of the eye of vertebrates. The composite image in
the compound eye of the glow-worm, for example, is not an
inverted, but an upright retinal image. The glow-worm or fire- fly
can therefore project its sensations of sight exactly in the position
indicated by the retinal excitations.^

A second question is suggested by the fact that we see with two
eyes, hence a double retinal image is produced by the majority of
the objects seen. How is it that, notwithstanding this fact, an
object generally appears single to us? Why does it appear
double only in very rare cases, — for example, when we push on

sistema nervoso," 1885; and Flechsig, Arch. f. Physiolog. (Du BoiS
Reymond), 1889.

* See ExNER, "Das Netzhautbild des Insectenauges." Sitzungsber. d.
Wien. Akad. d. Wiss., 1889.

128 Introduction to Physiological Psychology.

the side of the eye-ball with a finger while gazing fixedly at an
object? This question has given rise to numberless physiological
and psychological investigations and discussions. It is sufficient
here to notice that, physiologically, the union of the two retinal
images is already accounted for by the peculiar partial crossing of
the optic nerve-fibres. By this means the excitations produced in
the left half of both retinas are conducted together to the right
hemisphere of the brain, and vice-versd,. The blending of the two
images is provided for psychologically by the association of like
ideas of motion, in general, with those points that are situated
alike in the two retinas. It is for physiological optics to decide
how far these two factors suffice, in a single case, to explain the
blending of the two images.

The final question is suggested by the fact that the retinal
images are superficial or planiform. It asks, Whence do our
visual sensations receive their stereometric character ? We see
solids and not plane surfaces. In this case also it is obviously a
question of association with ideas of motion and touch. It is at
least very doubtful whether the two eyes, remaining wholly at
rest, could ever achieve the construction of a stereometric image
of space. ^ But our eyes are moved, there is a constant play of
the muscles of accommodation (the ciliary muscle and the recti
interni), the head is turned, the entire body is moved forward,
the sensations of sight are controlled by the sense of touch. In
this way a large number of new associated ideas of motion and
touch is acquired. It is only by association with these ideas that
our visual perception receives its stereometric character. Strictly
considered, this perception in itself has neither a planimetric nor
a stereometric character, since our sensations are at first projected
merely in a definite direction, leaving it quite indefinite as to how
far from us in that direction the object lies. For example, a
person that is blind from birth and receives his eyesight later in
life, conceives all objects to be directly in contact with the outer

1 As to possible physiological conditions, also concerned in this case, see
Hering, I.e., Helmholtz, I.e., and others.

TJie Sensations of Sight.

129

surface of the eyeball. He only learns by degrees to project liis
sensations of sight accurately also as regards distance and hence
as regards stereometric relations.

It is self-evident that experiments, applied for the purpose of
ascertaining the degree of certainty with which sight-impressions
are localized and distinguished in space, may also be employed
in the case of vision in accordance with the Law of Weber. Such
experiments have shown that^ in general, an object can be no
longer recognised, even by direct vision, when the visual angle in
which it appears becomes less than one minute. As regards the
estimation of magnitudes of extension, it has also been demon-
strated that the Law of Weber is only valid for the mediicm dis-
tances {e.g. lines). It appears, for example, that in attempting to
determine one distance that will equal another given distance,
the average error is about in proportion to the magnitude of the
distance.^ If the distances that are to be estimated become very
large or very small, the " relative threshold of distinction " seems
to be no longer constant. Furthermore, in the above experiment
the individual variations are very great.

We have now essentially completed our investigations of visual
sensations. The senses of hearing and sight represent the
culminating points of sentient life. In future chapters we shall
also find that higher intellectual processes are chiefly dependent
upon the sensations of sight and hearing.

This method is designated as the "method of the average or mean error."

CHAPTER VII.

THE TIME-PROPERTIES AND THE EMOTIONAL TONE OF THE

SENSATIONS.

We distinguish three properties in each sensation : quahty, in-
tensity, and accompanying tone of feeling. To these are also to
be added those characteristics of the sensations that have reference
to space and time. The qualities, intensity, and space-properties
of the sensations, have been discussed at length in the preceding
chapters. In this chapter we turn first to the time -properties of
sensations. Each sensation has a definite duration which in
general corresponds to that of the stimulation. In the case of
the excitation Ec in the cerebral cortex, we must accept this
statement as unconditionally valid. On the contrary, the state-
ment that the duration of sensation corresponds to the duration
of irritation is not quite correct as regards the excitation at the
periphery, Ep. As an example taken from the sphere of visual
sensations, let us call to mind the so-called "after-images" that
appear in colours like, or complementary to, the colour of the
primary image. If we observe a bright red disk and then close
the eyes, we often see a red or light-coloured after-image which
lasts some seconds after the external stimulus has vanished.
This after-image then appears in blue green, the colour comple-
mentary to red, and is often very intense. This phenomenon is
produced, as we know, by the after effects of stimulation upon
the retina; the external stimulus E therefore was shut off by
closing the eyes, but not the peripheral retinal excitation Ep.
For this reason the sensation lasted longer merely as the result
of a physiological phenomenon.

130

Time-Properties and Emotional Tone of Sensations. 1 3 r

Let us now ask first, In what relation does the intensity of a
sensation stand to the original stimulation when the latter con-
tinues for some time ? We can easily employ an experiment to
answer this question by listening to the approximately constant
rushing of water through the faucet of a water-pipe. If we
watch our sensations attentively, we observe that some seconds
pass before they reach their greatest intensity; then they retain
this maximum intensity for some time with but very insignificant
deviations, after which they very gradually but not altogether
constantly lose their intensity. The constant increase noticeable
at the outstart of the experiment is obviously to be explained by
physiological adaptation, especially in the peripheral organs.
To some extent the ear must first be placed in a position favour-
able to stimulation. The quite unimportant variations in in-
tensity during the maximum of sensation plainly have an ap-
proximately rhythmical character. According to the experi-
ments of Lange ^ the intensity of sensation swells regularly once
in about every 2*5-4 seconds. The length of these periods
appears to differ for different sensations. We can perceive the
fact most easily ourselves by holding a watch at such a distance
from the ear as to render its ticking barely audible. By this
means we are able to follow best the swelling and ebbing of sen-
sation. It is very probable that these periodic variations in
intensity are dependent on variations in the excitability of the
auditory path from the labyrinth to the auditory centre in the
temporo-sphenoidal lobe. Other slight variations are probably
due to the fact that we cannot always regularly exclude other
intercurrent sensations and ideas. The ultimate definite decrease
in the intensity of sensation is undoubtedly due to a physio-
logical fatigue that begins to be felt along the entire course of
the sensory paths to the cerebral cortex, and to the simultaneous
appearance of other ideas which constantly become more and
more intense.

A further question is as follows : How long must stimulation

1 Philosoph. Stud., IV.

132 Introduction to Physiological Psychology.

last at least in order to impart a sensation? At first it would
appear that, in general, an immeasurably brief duration is
sufficient to produce a sensation. The intensity of stimulation,
however, and in the case of optic stimuli the magnitude of the
spatial image also, are of great importance. It appears further-
more that stimuli of very short duration impart sensations that
are no more distinct in quality than sensations produced by very
weak stimuli. At least, when the change of stimuli is too rapid it
is impossible for us to recall correctly, by association, the quality
of a sensation (whether colour, pitch, taste, etc.) after it has taken
place. The quality was too indistinct to awaken the related
image of memory. Thus at least two vibrations are necessary
in order to produce any sensation of tone at all, and a somewhat
greater number that the pitch of a certain tone may be recognised.^
Since this law appears to be valid with approximate uniformity
for high and low tones, the absolute duration of stimulation, in
the case of the sense of hearing, is of less importance in the
recognition of a tone than the absolute number of vibrations.^
It is very difficult to decide experimentally the degree of sensi-
bility to differences in time, as in the case of acoustic impressions.
It is worthy of mention, however, that Mach ' found the difference
noticeable when a tone lasting ^ of a second is compared with
one of 2, second longer. As far as these experiments have
been carried at present, the Law of Weber does not appear to be
valid in the above case.

Two or more sensations that follow one after the other at
very short intervals blend into a single sensation in time in a

1 Pfaundler, Vienna, Sitz.-Ber., 1877. Kohlrausch, Wiedemann's Annalen,
1880. Thus far investigations have not yet resulted in complete agreement,
Exner (Pfliiger's Arch., Bd. XIII.) found seventeen vibrations necessary to
recognise a tone in its definite pitch.

GoTZ Martius has recently estabhshed the fact that the number of
vibrations necessary for the production and recognition of a sensation of tone,
gradually increases with the ascending pitch, at least as far as c^. Comp.
also Stumpf, Tonpsychologie.

' Sitzungsber. d. Wien. Akad., Bd. sr.

Time-Properties and Emotional Tone of Sensations. 133

manner very similar to the way in which sensations produced by
adjacent stimuli in space blend into a line. The interval of time
that must elapse in order that two sensations may be perceived
as separate in time varies exceedingly, according to the quality of
the sensation. For the eye an interval of at least -n^ of a second
is requisite, while only an interval of -g-^o of a second suffices
for the ear. This blending of sensations that follow one after
the other very closely, is probably due to physiological causes.

On the other hand, however, let us call attention expressly to
the fact that the projection and arrangement of our sensations
with reference to time, the same as with reference to space, can-
not be explained psycho-physiologically ; we must simply accept
the fact for the present, although we shall touch upon the question
asain at the close of these lectures. In this connection let us
call attention to an essential difference between the perception
of space and the perception of time. We project our sensations
into a space of three dimensions, while not only our sensations
but also their mental images, the ideas, are arranged with refer-
ence to time in but one dimension.

We can now introduce the question as to how many sensations
we can have in general at the same time. The number of sensa-
tions possible from one sense at the same time is almost unlimited.
We have already seen that co-existent sensations of sight and
feeling are arranged together so as to produce an image of space
and that co-existent sensations of hearing are blended to a complex
of sound. But it is much more doubtful whether we can perceive
a sensation of sight and one of hearing, i.e., two or more sensa-
tions from different senses, simultaneously. In this case the
weaker cortical excitation produced by a slight momentary sound,
for example, often remains without a concomitant psychical pro-
cess, or, as we may say, unnoticed in consequence of the pre-
ponderance of another stronger cortical excitation, such as an
intense stimulus of light acting at the same time. Therefore the
sensations or, more properly, the sensory cortical excitations
arrest one another, in very much the same way that, as we shall
see in the future, the ideas check each other. This question

134 Introduction to Physiological Psychology.

must not be confounded with that as to how many simultaneously
appearing sensations can be recognised or counted. CattelH has
made experiments for the purpose of investigating the latter
question. He found, for example, that from 3 to 6 lines, visible
o-oi second, can still be correctly counted. In this case it is
obvious that the facts of sensation are not alone concerned, but
also the association of ideas, especially of ideas of number. This
association is only possible in the case of a limited number of
simultaneous, momentary sensations.

The last property of the sensation is its accompanying tone of
feeling. We have already made use of the sign /to indicate this pro-
perty. As we have seen, this tone of feeling is nothing more or less
than the feeling of pleasure or pain (displeasure) that accompanies
our sensations with varying degrees of intensity. At this point, how-
ever, we must beware of mistaking the words, " feeling of pleasure
or pain ". If we see a friend, we are glad ; but this joy has
nothing to do with the feeling of pleasure or pain accompanying
the sensation, for it is not the sensation of seeing the friend in
itself that produced the feeling of joy, but the idea associated
with the sensation. The thought that he is our friend, that we
can speak with him, etc., first awakens in us the feeUng of
pleasure. We must therefore make a sharp distinction between
the tone of feeling which accompanies the sensation as such,
and the tone of feeling that accompanies the ideas or images of
memory whose activity has no direct reference to the sensations.
We shall here refer at first only to the former. Let us cite a few
simple examples of the tone of feeling accompanying sensation.
If we strike the chord c-e-g, the sensation of sound is accompanied
by decided feelings of pleasure. We therefore speak of the chord
as harmonious. On the other hand, if we strike c and d together,
the sensation of hearing is accompanied by a lively feeling of
displeasure ; in this case we speak of a discord. The feelings of
pleasure are designated as positive, the feelings of pain or dis-

1 Philosopb. .Stud., III. Cattell's interpretation, however, cannot meet
our approval.

Time- Properties and Emotional Tone of Sensations i 3 5

pleasure as negative tones of feeling. These concomitant feelings
of pleasure and pain vary greatly in intensity. The chord c-^-g,
the so-called minor chord, also produces a sensation of hearing
that is accompanied by a feeling of pleasure ; but the latter is
considerably less intense than in the case of the major chord c-e-g.
A solution of quinine has a more or less unpleasant taste, accord-
ing to the degree of concentration. Finally, there is a long series
of sensations that to a certain extent occupy a neutral position as
regards the tone of feeling ; that is, they are accompanied neither
by a distinct feeling of pleasure nor by a distinct feeling of dis-
pleasure or pain. To this class belongs by far the greater part of
the sensations received through the highest senses. How many
visual images, musical sounds and noises daily throng our con
sciousness ! How few of them are associated with any feeling
whatever ! The few that do give us positive feelings of pleasure
or pain do not possess this emotional effect in the mere sensation
itself. The emotional effect is for the most part a result of the
ideas with which the sensations are associated, as in the above
case, when one sees a friend. The emotional tone, or tone of
feeling, is therefore by no means a necessary property of sensation.
Between the scale of pleasurable feelings and that of painful
feelings there is a zero-point or point of indifference. Only a
limited number of sensations rises above or falls below this point
as regards the emotional tone.

Let us now ask : On what does the emotional tone of a
sensation depend ? The tone of feeling obviously depends
mainly on the intensity of the stimulus, or, more specifically, on
the intensity of the sensation. A simple tone, lightly struck,
generally leaves us indifferent. Feelings of pleasure appear and
increase slowly, in proportion to the gradual swelling of the
tone. The pleasurable impression of the pure tone has reached
its absolute height as soon as the sensation has attained a medium
intensity. If the intensity of the tone is further increased, the
feeling of pleasure diminishes rapidly and finally passes into a
feeling of pain. If the tone reaches the maximum of stimulus
the piercing sensation of sound is accompanied by an intense

136 Introduction to Physiological Psychology.

feeling of the greatest pain and displeasure. Similar effects can
also be produced in the case of any one of the other senses.
The intense light that blinds us is unpleasant ; light of a medium
intensity imparts the most pleasurable sensations. We can also
express this dependence of the emotional tone on the intensity of
the sensation, diagrammatically by a curve. The unbroken
lines of the drawing (fig. 16), are already familiar to us.
They represent the relation of the intensity of sensation to the
intensity of stimulation. The intensities of stimulation are re-
presented by the axis of abscissas, E. jE-min, designates the

Fig. 16.

minimum, and E-niax. the maximum of stimulation. The un-
broken curve indicates the path described by the increasing in-
tensity of sensation, following the increase in the intensity of
stimulation. The intensity of the emotional tone accompanying
the sensation is designated by a dotted curve. That part of the
dotted curve lying above the axis of abscissas designates a
positive feeling, or a feeling of pleasure ; the part lying below
the axis indicates a negative feeling or a feeling of pain. We see
that at the minimum of excitation or upon the appearance
of the slightest sensation, the curve of feeling rises above
the axis of abscissas. It reaches its height at the medium

Time- Properties and Emotional Tone of Sensations. 137

intensity of sensation. Thence the feeling of pleasure decreases
rapidly and changes to an increasing feeling of pain ; the curve
falls abruptly and sinks below the axis of abscissas.^

In certain mental diseases the tone of feeling is very charac-
teristically changed. Thus, for example, melancholia is charac-
terized by a sudden conversion of the feeling of pleasure to one
of pain, even in response to much slighter intensities of sensation.
Finally, the disease reaches a stage in which the curve of feeling
no longer rises above the axis at all ; a feeling of pain is coupled
with the slightest sensation. Everything that is perceived is
accompanied by painful feelings.

The dependence of the emotional tone on the quality of
sensation is more complicated. Among the sensations of taste
the quality of sweet is decidedly more closely associated with
sensations of pleasure, and the qualities of sour, salt, and
especially bitter are more closely associated with sensations of
pain or displeasure. More accurate observations, however, show
that in this case also the intensity chiefly determines whether the
sensations are pleasurable or painful. We like our food a little
salty, and we find a slight taste of bitter or sour pleasant, while
on the other hand the most concentrated solutions of sweet are
distasteful to us. Thus pleasurable feelings are coupled with the
slighter intensities of sensation and painful feelings with sensa-
tions of greater intensity. It is worthy of mention that bitter
produces feelings of displeasure even in degrees of intensity that
are relatively much slighter ; sweet, on the contrary, awakens

^ HoRWicz (Psychologische Analysen, II, 2, S. 26), emphasizes several
not unjust objections to this presentation, which has been essentially adapted
from Wu.NDT. He also emphasises (with Benekf.) that very weak sensations
are not seldom associated with feehngs of pain. Hence the cnrve of feeling,
before rising at all above the line at the zero-point, would first sink beneath it
a short distance, at least in the case of certain qualities of sensation. — An
acceptable synopsis of the appertinent literature is to be found in Cksca,
" Die Lehre von der Natur der Gefiihie". Vierteljschr. fiir wiss. Phil.,
1886, X. Compare also in the same Ztschr., XI, O. Kulpe, " Zur Theorie
der sinnlichen Gefuhle."

138 Introduction to Physiological Psychology.

such feelings only when the degrees of intensity are relatively
very much greater. It is obvious that this fact is to be under-
stood as merely a product of phylogenetic development. The
mother's milk contains a 4% solution of sugar, besides its fatty
and albuminous constituents. The sucking babe, in which
especial feelings of pleasure were coupled with the sensation of
sweet, sought the mother's breast more zealously, was better
nourished, and consequently enjoyed better chances of growing
up. This peculiarity has been nourished thousands of years
until to-day it is universal.

The tone of feeling accompanying sensations of smell has
quite the same characteristics as in the case of sensations of taste.
The intensity of sensation also chiefly determines the character
of the emotional tone; the most unpleasant smell is converted
into a perfume by appropriate attenuation.

The tone of feeling accompanying dermal sensations is of
especial importance. In this case, indeed, the concomitant feel-
ings of pleasure are considerably less pronounced than the feel-
ings of pain. Tepidity, slight cold, a soft touch, impart but very
slight positive tones of feeling. But the feehng of displeasure is
jubt so much more pronounced when the sensation of warmth,
cold, or pressure rapidly increases. In the case of heat, cold,
and pressure, these intense feelings of displeasure are generally
designated as pains. Pain, therefore, is no especial quality of
sensation, but merely a special designation for the painful or
unpleasant feeling that accompanies very intense dermal sensa-
tions. We also speak occasionally of a " painfully piercing tone,"
or a " painfully blinding light." It is worthy of mention in
connection with painful dermal sensations, however, that the
negative tone of feeling frequently obscures the quality of the
sensation in consciousness. When very powerful effects are
produced by heat, or cold, or by some very potent mechanical
stimulus, as, for example, the thrust of a sharp instrument, we
are finally convinced that we feel only pain, i.e., we perceive
the tone of feeling quite apart from the sensation. On this
account some authorities have often designated the sensation

Time- Properties and Emotional Tone of Sensations. 139

of pain as an especial quality of the dermal sensations.^ But
neither special "pain-spots" on the skin, nor a stimulus especially
adapted in quality to cause sensations of pain have been shown
to exist. It can be very easily understood also, why, on account
of very intense stimulation, the feeling of pain has such an
ascendancy only in the case of dermal sensations. As we
shall find later, the voluntary action following a sensation is
essentially dependent on the accompanying tone of feeling, as
regards both its character and the rapidity with which it is exe-
cuted. The more disagreeable a sensation, just so much more
speedily and energetically do we seek to remove it ; we either
flee or defend ourselves. Now in the development of the animal
series, the earliest, greatest, most frequent, and most direct
dangers to the animal organism consist of mechanical and caloric
stimuli. The animal organism must be able to accommodate
itself to these stimuli, to respond with extraordinary rapidity by
the execution of motions in defence or flight. Such reaction is in
fact most fittingly attained by the association of a feeling of dis-
pleasure, so completely dominant as that of pain, with all sensa-
tions produced by intense mechanical and caloric stimulation.
The claim has also been advanced that the sensation of pain is
especially produced by irritating some part of the nerve trunk, or
one of its chief branches, instead of the nerve-ends. This claim
is sufficiently accounted for by the fact that irritation of the nerve-
trunk of course affects a much larger number of fibres. It has
also been thought that separate paths of conduction must be
assumed in the spinal cord for sensations of touch and those of
pain. The reasons for this assumption are twofold, (i) Schifi"
has observed isolated analgesia (insensibility to pain) in animals

' RiCHET, "Recherches sur la senjibilitd " ; GoLDSCHEinER, Arcli. Du
Bois-Revmond, 1885, S. 90. The remarkable statement of the latter, that
even the intense caloric stimulation of heat-spots and cold-spots produces hut
a relatively slight pain (at least considerably slighter than that produced by
the stimulation of the cuticle between temperature-spots), still requires ex-
planation and confirmation.

140 Introduction to Physiological Psychology.

after having severed the grey substance of the cord, the removal
of the sensibihty to pain being accomplished without disturbing
the sensibility to touch ; (2) in certain diseases, such as tabes,
analgesia occurs without anaesthesia, i.e., without the loss of
sensibility to touch. In fact, it frequently happens in the case of
tabes that the patient, on being pricked with a sharp instrument,
first reports a sensation of touch, and a few seconds later one of
pain. Schiff's experiments in this line, however, are by no means
free from all objections, and it is possible to explain all the other
phenomena just quoted without assuming that there are separate
paths of conduction in the spinal cord for sensations of touch and
sensations of pain. It is sufficient to assume that, in the case of
tabes, for example, the nerve-fibres are sometimes altered by the
pathological process so that they can still receive the weak stimuli
and conduct the excitation to the cerebral cortex, although unable
to transmit the more intense stimuli. If the latter produce any
effect whatever, they are either first weakened before transmission,
or the greater part is conducted more slowly.* Since we are
almost entirely ignorant of the nature of the pathological changes
affecting the conductivity of the sensory paths, however, it is
difficult to see why this assumption should be rejected a priori.
It is sufficient to explain both " analgesia without ana2sthesia "
and the separation of a sensation into two successive sensations,
viz., a weak, painless sensation, and a strong, painful one. As
a result of these considerations we find that there is no ground
whatever for regarding pain as a special quality of dermal sensation.
On the contrary, we define that it is merely the strong /tf<?//«^ of
pain accompanying the dermal sensations.

The emotional tone plays an important part in the so-called
organic sensations, the same as in dermal sensations. Let us
remember that under normal conditions the intensity of these

1 The more recent investigations by GoLGi, Ramon y Cajal, and Kolli-
KER should be considered in connection with this question. According to
these the sensory fibres, having entered the spinal cord, divide and also send
off innumerable collateral processes further on.

Time- Properties and Emotional Tone of Sensations. 141

sensations is exceedingly slight. Our attention is only called to
most organic sensations by the disagreeable accompanying tone
of feeling the pain.^

The tone of feeling that accompanies sensations of simple tones
having a medium intensity is not very strongly marked. There
is a large number of qualities that exert no influence whatever
upon the tone of feeling. Only very high or very low tones are
generally more likely {ceteris paribus) to be accompanied by
negative tones of feeling. The influence which is exerted by the
quality of a tone-sensation is much more noticeable in the case of
sensations of noise or musical sound, i.e., in the case of acoustic
sensations that are produced by the combination of several simple
tones. The most important fact for our consideration is that
the irregularly periodic vibrations characteristic of noises, are, in
general, not accompanied by positive tones of feeling ; only the
regularly periodic vibrations of musical sounds can impart a
positive emotional tone. As we have already mentioned, when a
key is struck on the piano we really hear not a simple tone, but
a musical sound ; that is, we hear a chord with very distinct over-
tones, which decrease in intensity in proportion to their distance
from the fundamental tone, and the numbers of whose vibrations
stand in a simple numerical relation to each other. Each pure
tone of the piano generally imparts a slight feeUng of pleasure,
and is, in fact, as we already know, produced by the regularly
periodic vibrations of the particles of air. But we also know that
certain combinations, both of simple tones and of musical sounds
(the chords of a piano for example), possess a consonance in-
comparably more pleasant than that of either the simple tone or
the simple musical sound. These are the so-called consonant
chords. It is one of the most interesting and difficult problems
to determine under what general conditions a combination of
tones is consonant or dissonant, i.e., imparts a positive or

' Here we should also make mention of the almost exclusive connection of
genital sensations with positive emotional tones.

142 Introduction to Physiological Psychology.

■negative tone of feeling. To begin with, it is conceivable, in fact
obvious, that the consonant chords (for example, the common
C-major chord, c-e-g) must consist of tones, the numbers of
whose vibrations stand in a simple relation to each other. For
■we know it is only when this condition is fulfilled that a chord
■can be produced by a regularly periodic form of vibration. A
regularly periodic form of vibration is the " conditio sine qua non "
of strong positive emotional tones. In fact, the numbers of vibra-
tions of the tones c-e-g, for example, stand in the relation of the
simple numbers, 4:5:6. Not all chords whose component
tones possess numbers of vibrations standing in so simple numeri-
cal relations, however, are consonant. For example, the simple
•chord c-d generally sounds quite dissonant, that is, it produces
an entirely negative tone of feeling, despite the fact that it is a
musical chord. The numbers of vibrations producing c and d, in
fact, stand in the relation of the simple numbers 8 and 9. Hence
not every chord of a regularly periodic form of vibration imparts
the feehng of pleasure that accompanies a consonant chord.
There are chords whose form of vibration is quite regularly pe-
riodical, but which are nevertheless dissonant. Now, why is the
•chord c-e-g consonant and the chord c-d dissonant? Both are
not noises, but musical chords in the broadest sense ; ^ both de-
pend upon the regularly periodic vibrations of the particles of air.
We might take into consideration the influence of the overtones
that are mingled with each tone of the piano, for example, and
refer the dissonant character of the chord c-d to the fact that in

1 A musical sound (Klang) is in general any combination of tones that has
a regularly periodic form of vibration, or, in other words, a combination of
simple tones whose numbers of vibrations stand in simple numerical relations.
A lone of the piano is a special case of the simplest form of a musical sound.
In this case the numbers of vibrations producing the separate component tones
are in the relation i : 2 : 3 : etc., and in the intensity of the component tones
decreases the higher they are above the fundamental tone. Conversely, the
chord is a musical sound, or combination of musical sounds, whose component
tones are all of approximately like intensity, and whose number of vibrations
stand in the relation m:n:o: p, etc., the letters m, «, 0, /, representing only
whole numliers in general.

Time-Properties and Emotional Tone of Sensations. 143

this chord the over-tones disturb the regularity of the form of
vibration, which is not true of the chord c-e-g. This attempt
at explanation fails, however. C-e-g is consonant and c-d dis-
sonant also when the chords are produced by tuning forks that
have no overtones. Of the many answers that have been given
to the above question, we shall consider only the one which
Helmholtz has given in his noted "Theory ot the Tone-Sensa-
tions." In framing this theory Helmholtz proceeds from the fact
that when two tones having but slightly different numbers of
vibration sound simultaneously, numerous so-called " beats''^ or
" throbs " can be distinguished ; that is, the intensity of the sound
alternately swells and diminishes. The number of these "beats"
per second corresponds exactly to the difference between the
numbers of vibration. These "beats" are also very unpleasant
to the ear, especially when some twenty to forty of them occur in
a second. The chord receives by means of these beats a pecu-
liarly rough character. It can also be shown that the chord
c-e-g produces no unpleasant beats, but that the chord c-d
produces very unpleasant beats. In order to establish this separ-
ately for each chord in each octave, it is necessary to take inta
consideration more exactly the overtones mingled in the chord,
and also the so-called "summation tones," "difference-tones,"
and those tones which Konig designates as " Stosstone." By
this means, at least, Helmholtz thought to reduce the dissonance
of discords without exception to the production of unpleasant
"beats." It is probable, however, that still other elements act
in connection with these beats to render one chord consonant,
another dissonant to the ear. Perhaps, for example, the fact
should also be considered that in dissonant chords the numbers
of vibrations are generally in a more complicated relation (8 : 9
or 8 : 15), and that therefore the so-called "period of the wave

' The accepted term in acoustics is " beat." — T's.

^ Concerning these comp. especially the more recent works of R. Konh'.,
Wiedemann's Annalen, Bd. 39, and W. Prevf.r, Wiedemann's Annalen,.
Bd. 38.

144

Introduction to Physiological Psychology.

is considerably lengthened. In the case of the combination of
musical tones into consonant chords, it is possible that the
agreeable character of the latter is determined in part by a
number of partial tones common to all the members of the
chord, as urged by Wundt.

The simple visual sensations having a medium intensity are
accompanied only by a very slight positive tone of feeling. Even
our joy in beholding the blue sky does not belong to the mere
sensation. Associated ideas — such as the idea of the infinity of
the blue vault above us, etc. — accompanied by their tones of
feeling are also active to a great extent. Therefore the quality
of the visual sensations, colour, has almost no significance for the
tone of feehng. It is true that older psychologists, such as
George, attempted to compare each colour with a definite taste ;
by this means they hoped to be able to ascribe a definite tone of
feeling to each colour. Thus red was to correspond to salt, yellow
to sour, blue to bitter, and white to sweet. These are, however,
mere subjective comparisons suggested by associated ideas (for
example, " white," " sweet," " milk "). On the other hand, Goethe
distinguished a plus and a minus side in the series of spectral
colours. Red and yellow were to constitute the plus-side and act
as excitative ; blue and violet, the minus-side, acting as depressive.
Green was to be the transition between the two sides. In view
of this classification Italian psychiaters have proposed to bring
individuals afflicted with melancholia into a room containing red
light, and those afflicted with mania ^ into a room containing blue
light, for the purpose of dampening the morbid inclination to
■extreme abnormal tones of feeling. It is obvious that these
views are due to the association of certain colours with certain
ideas and their tones of feeling. Red reminds us of flaming

' The reader should bear in mind that the term "mania" is used by
•German psychiaters in a much more restricted sense than by English
psychiaters. The German alienist includes under the term " mania " only
those mental diseases that are characterized by the presence of morbid, gay
emotions. It is to be understood in this sense, of course, in this translation.
See also Chapter XII.— T's.

Time-Properties and Emotional Tone of Sensations. 145

fire; yellow of the life-giving light, etc. Hence in these cases
the tone of feeling does not accompany a sensation but an idea.
At most we may state perhaps that the qualities of sensation
produced by dark colours, especially by those that represent the
transitions of the spectral colours to black, such as red-brown,
are less easily united or associated with positive tones of feeling.
The tendency of black itself to produce a negative tone of feeling
is due, in part at least, to the idea of something dismal and
dangerous with which it is associated.

There are no "colour-accords" in the same sense that there
are musical chords. Mixtures of colour produce sensations of
colour that are just as simple as those produced by simple colours.
We are unable to analyze the sensations produced by rai.xed
colours. Therefore the consonances or dissonances of different
colour qualities must be sought only in their spatial arrangement.
In fact, a comparison of the paintings by the best masters of the
Italian schools shows beyond a doubt that certain combinations
of colours are decidedly preferred. Thus Helmholtz calls
attention to the triad, — red, green, and violet, that are in fact
combined in so many pictures with wonderful effect. However,
we know nothing as yet concerning the constancy and the exact
conditions of this consonance of certain colours.

Besides intensity and quality, the spatial arrangement of the
sensations is an essential factor in determining the accompanying
tone of feeling. In this connection we shall consider only sensa-
tions of touch and sensations of sight as products of those senses
that are characterized by the most highly developed and perfect
relations to space. As regards the former, it is sufficient to
mention that in general the positive tones of feeling accompany-
ing sensations of touch produced by extended contact with a
surface, are in proportion to the constancy and regularity of the
surface.

The unpleasant sensations of a rough surface are produced
particularly when the tactual sensations arising from extended
contact with a surface are irregularly distributed and of unequal
intensity ; when some few z/;zirritated nerve-ends always intervene

146 Introduction to Physiological Psychology,

between the /n-itated nerve-ends. The spatial arrangement cf
the visual sensations is of much more importance for the tone of
feeling. Let us observe a straight Hne for the purpose of desig-
nating some point upon it that seems to us to divide the line
into pleasing proportions. Fechner put this question to a large
number of persons. As a result it appeared that, besides the
point bisecting the line into halves, one other point was especially
preferred, viz., the point that divides a line approximately in the
extreme and mean ratio, or the "golden section." It is also
exceedingly instructive to study the Italian works of architecture
of older times ; their wonderful effect is due almost wholly to
their wonderfully symmetrical arrangement, i.e., to the division
of the lines bounding the mass as a whole. However, regularity
and especially symmetry in the spatial arrangement of visual
sensations are by no means the only conditions of positive
emotional tones. ^

As a rule the periodic recurrence of a certain spatial arrange-
ment produces a positive tone of feeling. It is much more
difficult to establish a universal rule for curved lines. No one
beheves any more in Hogarth's absolute curve of beauty. In the
case of curved lines the constancy of the sensation is a very
essential factor in the production of feelings of pleasure ; as a
rule a straight continuous line makes a more agreeable impression
than a row of points. The very minuteness of the interruptions
in the sensations disturbs the impression. A crooked hne con-
stantly imparts associated sensations of motion ; to a certain
extent the eye follows the entire course of the line. The
appearance of positive tones of feeling is largely conditioned by
the constancy of the associated sensations of motion. The radius
of curvature, therefore, should not change suddenly, particularly
the constantly repeated slight. Irregular changes also have a
very disturbing effect upon the sensations produced by crooked
lines. The sensation must change either by a constant ratio, or
if the change is very sudden it must also be very great. For this

^ Fechner, " Vorschule der Aesthdik." Th. i, Abschii. XIV.

Time- Properties and Emotional Tone of Sensations. 147

reason gentle arches play such an important role in ornamentation,
and very flat angles are rarely found. But we have room here for
only a very few short suggestions. As regards these same spatial
forms, the Eesthetical department of physiological psychology is
still in its infancy.

Finally, the time-properties of the sensation have an important
influence upon its tone of feeling. A long duration of sensation
generally dampens both positive and negative tones of feeling.
The manner in which several sensations follow one another in time
only has an essential influence on the tone of feeling accompany-
ing sensations of musical sound. A series of like sensations of
tone, following one after the other, generally becomes wearisome ;
even when the quality of the tone changes an unpleasant feeling
soon appears.

In order to obtain the pleasurable feeling belonging to
rhythmical division, either the intensity or the duration of the
single tones must be subjected to a more or less regular periodic
change. In musical tempo and the versification of poetry we
have sequences of acoustic sensations in which certain sensations
are especially accented or intense, and all together have a definite
duration.^ In this connection it is not necessary to consider that
two quarter-notes or a triplet can take the place of a half-note,
etc., or that two short syllables may be substituted for one
long, or two unaccented for one accented short syllable. Such
uniformity, which we generally designate as tempo or verse, is
constantly repeated with but slight change. At all events, the
total duration of the sensations of sound and the arrangement of
accentuation is constant for each new tempo or kind of verse.
The qualities of sound, i.e., the notes and words, change, but the
intensities of tone, the accentuations and diminutions, constantly
recur at definite intervals or periodically. In poetry the close of
such rhythmical periods can often be emphatically marked by

^ The old style of metrical composition places more weight on the duration,
the new style more upon the accentuation. The Alexandrine regards merely
the number of sensations of sound.

148 Introduction to Physiological Psychology.

choosing very similar lories with which to close the periods. In
this form of emphasis lies the importance of the rhytiie.

As regards the succession of sensations, therefore, a regular
periodicity is the chief condition for the appearance of feelings of
pleasure. It is not mere chance that maniacs and those afflicted
with emotional paranoia often speak in rhythm and rhyme. Such
phenomena harmonize rather with the morbid, positive emotional
states characterizing these forms of psychosis.

From the preceding considerations we conclude that the
appearance of positive or negative tones of feeling depends on
very different conditions. This conclusion brings us to a problem
thai is just as interesting as it is difficult to solve. It is the
question as to whether these various conditions may be com-
prehended under one common point of view, — the problem as to
the nature of these tones. In answering this question it must be
taken into consideration that, as mentioned in the beginning,
not only the sensations, but also without doubt the ideas, have
their emotional tones. Therefore we can first put the question
as to whether the ideas borrow their tone of feeling from the
sensations, i.e., whether they have simply received the tones of
feeling belonging to those sensations of which they are the
images of memory. This supposition is undoubtedly to be
granted in many cases. The idea "enemy" and the idea "hate,"
therefore, are only associated with feelings of displeasure because
we have often feli the attacks of foes and the effects of enmity
to be unpleasant. But, on the other hand, it cannot be denied
that the reverse is also true. Ideas often transmit their tones
of feeling to the sensations. Thus, as children, or perhaps later,
we have heard a certain musical combination produced frequently
in connection with a certain mournful song. The succession of
tones in the chord itself does not partake of a mournful character,
but the words that are sung to this series of tones produce
mournful ideas. The negative emotional tone of the latter is
thus gradually imparted to the musical sensations; finally the
chord itself is sufficient to produce a negative change in our tone
of feeling that is quite independent of the mournful words. All

Time- Properties and Emotional Tone of Sensations. 149

attempts to assign certain constant tones of feeling to definite
chords rest upon just such a transmission of the tone of feeling
from the idea to the sensation with which the idea is associated.^
The sensation of black, as mentioned, probably produces a feeling
of displeasure the more easily because the idea of something
dismal or dangerous is associated with darkness. Hence, although
the mere sensation of black is not necessarily connected with
negative emotional tones, the colour of black has become the
symbol of mourning among occidental peoples.

If certain sensations have thus undoubtedly borrowed their tone
of feeling from previously formed ideas, it is still apparent that
ultimately such borrowed tones of feeling may be reduced to the
emotional tones of sensations ; for the ideas from which the
sensations have borrowed their tone of feeling owe their emotional
tone on the other hand, however, to sensations, viz., to those from
which they themselves were developed.

It is probable that the quality of sensations, in general,
originally influences the tone of feeling only in this indirect way
by means of their association with pleasurable or painful ideas,
and that therefore only the intensity of the sensations and their
succession in time and space have any direct effect upon their
tone of feeling. A universal rule has not yet been found which
shall state just what intensity and what arrangement in space and
time produce feelings of pleasure or feelings of pain ; and since the
influence of these factors has been developed phylogenetically and
will continue to so develop, no such rule can ever be formulated.
As to the nature of emotional tones, it is obvious that they are to
be regarded as qualitative characteristics of the sensations. Hence
another quality, a feeUng of either pleasure or pain, is often to be
added to the qualities of sensation already discussed. This new
quality, the tone of feeling, is capable of increase in intensity

^ As regards chords, E. T. A. HofFiMANN has probably talcen the most
extreme standpoint, since he believed that he was able to characterize each
cliord by a special state of feeling; — for example, the chord of B-major was to
express harmless joy ; C-major, wild desire; A-flat minor, longing.

ISO Introdtictiofi to Physiological Psychology.

quite the same as the other qualities of sensation. To make use
of an explanatory comparison, which is, however, somewhat inexact
as to particulars, each sensation may be regarded as mixed with
a certain proportion of black or white. The tone of feeling re-
presents, as it were, a sixth sense which has only two chief qualities,
— feelings of pleasure and feelings of pain or displeasure. One
of these two qualities is united with impressions received from the
other senses, and, under certain conditions, also with the ideas ;
the emotional tones never occur wholly independently of sen-
sations or ideas. But, apart from their dependency on other
psychical states and their relation to ideas, these emotional feel-
ings are essentially distinguished in still another important respect
from the proper sensations. The common quality of sensation is
determined (i) by the nature of the external stimulus E, and (2)
by the structure of the sensory apparatus (including from the
peripheral sensory organ to the cortical centre) that receives the
stimulus and converts the E first into an Ep and finally into an
Ec. The simplest illustration of this is furnished by the mechani-
cal stimulus, which imparts a sensation of pressure when applied
to the skin and a sensation of light when applied to the retina.
Innumerable qualities of sensation correspond to the inuumerable
qualities of stimulus. But the tone of feeling has at first only
two chief qualities, — the feeling of pleasure and the feeling of
displeasure or pain. The emotional quality of sensation is, in
fact, also dependent on the external stimuli and the sensory appa-
ratus ; but at first only the two emotional qualities of pleasurable
and painful feelings, in their different degrees of intensity, cor-
respond to the numberless qualities of stimulus and the different
sensory apparatus. Each stimulus may be subsumed under one
of these two qualities. Those properties of the stimulus and of
the sensory surface receiving the stimulus, therefore, that cause
the appearance of emotional tones, must be of a very general
character. We must assume that indifferent stimuli merely pro-
duce an Ec in the cerebral cortex, while stimuli that are not
emotionally indifferent (for example a too dazzling light) add
something else to the physical process Ec in the irritated cortex

Time- Properties and Emotional Tone of Sensations. 1 5 i

of the cerebrum, the psychical correlative of which is the emotional
tone. Therefore, properly considered, this emotional tone involves
a reaction of the cerebral cortex upon the stimulus coming from
without. This also explains the fact that like stimuli of the same
intensity do not always impart the same definite tone of feeling.
The qualities of sensation, sensu siricto, also depend in fact on
the constitution of the cerebral cortex ; but they are determined
by constant properties of the latter, while the tones of feeling
are determined by its variable properties. For the sake of com-
pleteness and perspicuity, let us cite once more the example of a
light falling upon the eye. The excitant ^ is a light of medium
intensity which produces a cortical excitation JSc and a sensation
6" corresponding to this excitation ; if the intensity of the light
increases, both Ec and .S also increase. While the intensity of
light thus increases, Ec and 6' do not simply augment, but at the
same time that Ec and S are increasing, a new physical process
is associated with Ec, and an emotional tone with the sensation.
Naive thought is therefore quite right in generally ascribing a more
subjective importance to the tone of feeling, and a more objective
importance to the common qualities of sensation. This accords
with the fact which has recently been especially emphasized again
by Lipps, that we do not project the emotional tone along with
its sensation into space. We call an object green, not " green
stimulating," but on the other hand, "joy-giving," not joyous.

A phylogenetic factor of great importance should be included
in the characterization of the emotional tone. Those stimuli that
are associated with feelings of pleasure in many cases directly
accompany the acts necessary for the nourishment and propaga-
tion of animal life ; those that are associated with feelings of
pain often accompany situations in which animal life is en-
dangered. Accordingly the stimuli of the first class generally
incite approach to the stimulus, those of the second class urge
withdrawal or flight. It is quite possible that this peculiar
property of the cerebral cortex which enables it to react upon
stimuli that are either generally injurious or useful with an entirely
new psychical process, or, in other words, to add the so-called

152 Introduction to Physiological Psychology.

tone of feeling to the common sensation, has been developed
phylogenetically to a higher degree of excellence from these
motions of flight or approach. In the lowest stage of develop-
ment the sensation directly imparts a motion that is generally
fitting ; in the highest stage the tone of feehng is introduced
between sensation and motion. This tone of feeling, as we shall
see, is of the greatest importance in voluntary action. It is of
great advantage to us to possess the capacity for emotional
tones, for the sensation itself generally furnishes the appropriate
warning or allurement, but at the same time, by postponing the
act of flight or approach, time is gained for the association of
ideas and the play of motives. These conclusions v/ill become
more intelligible as soon as we have investigated the emotional
tone of the ideas, the influence of the emotions upon the associa-
tion of ideas, and the motions of expression. We shall then note
especially that the emotional tones of the sensations are, in fact,
chiefly distinguished from each other by their intensity and their
general character, but that besides these they also possess certain
qualitative nuances that are of paramount importance to the
emotional life. Let us, therefore, for the present, regard this
simple distinction of emotional tones into positive and negative
feelings of different ititensiiy, merely as tentative and not exhaustive.

CHAPTER VIII.

SENSATION — ID E A — CONCEPTION.

In the preceding chapters we have followed in detail the develop-
ment of sensation from external stimulation. Now, what be-
comes of the sensations which have appeared corresponding to
the excitations of the cerebral cortex in the manner described,
and which now become factors in the activity of association ?
Let us at first assume one of the simplest cases.

The complex sensation of a rose, for example, appears for the
first time as the psychical correlative of an excitation in the cere-
bral cortex. This sensation is followed at once by the conscious
play of motives or the association of ideas. But at the same
time an image of the rose seen is deposited in the memory, or,
expressed in the language of physiology, a trace of the cortical
excitation that has taken place, is left in the cerebral cortex. We
are compelled to come to this last conclusion by the fact that
we recognise the rose when we see it again, that we are able to
remember it, and that we can reproduce its image in memory.
This image of memory or mental image that is deposited by each
sensation we have designated as an idea?- What are the psycho-
logical elements of this image of memory, and by what excitation
of the cerebral cortex is it produced ? The older psychology
pronounced the ideas to be only copies of the impressions or
sensations, and to be only distinguishable from the sensations by

' The use of the German word " Vorstellung" in this more restricted sense
was first introduced by Hegel and his disciples. It has since been used in the
same sense, especially by LoTZE.

(According to the standpoint of the author, as expressed in his introduction,
the corresponding English word is "idea." — Vs.)

153

154 Introduction to Physiological Psychology.

their slighter vivacity. This view was emphasized most forcibly
by Hume, whose noted " Treatise of Human Nature " cannot be
too well recommended as a propaedeutic course in psychology.
On the contrary, however, we must now emphasize that imnges
of memory or ideas are quite different from the sensations them-
selves. The idea of the sun, which is merely recalled to memory,
has nothing of the brightness or splendour of colours which
characterize the real sun, or the sun when seen. The idea of the
sun is therefore by no means merely a faded sun ; in this respect
the great English philosopher is mistaken. It is not a difference
in intensity between the idea and the sensation, but above all a
qualitative difference.^ The sensual vivacity, characteristic of
every sensation, does not belong at all to the idea, not even in a
diminished intensity. The ideas of the slightest rustling and of
the loudest thunder, therefore, exhibit no difference in intensity
whatever ; in fact, all sensual vivacity is wanting in both. Hence
we conclude that the different intensities characteristic of thun-
der and rustling as sensations are lost in the ideas. We may
easily have an idea of the greater intensity of one sensation, but
the idea itself is no more intense on that account. If we try to
imagine thunder ever so vividly we do not hear the slightest
rolling. But in what does the qualitative difference between
sensation and idea consist ? Or, to put the question in another
form, what process takes place when a sensation disappears and
its image is deposited in memory.? Apart from the rare phe-
nomena of "after-images" the sensation generally disappears
almost instantly upon the removal of the stimulus. But with this
removal of the stimulus the cortical excitation is not wholly
obliterated, for the cerebral cortex never fully returns to its
previous condition ; some sort of material change still remains
as a trace, a sign (o-Ty/xaov), as Plato calls it.2 This so-called

> Also Bain ("The Senses and the Intellect," 3rd ed.) denies the qualita-
tive difference between the sensation and its image in memory. His views
are not based on sufficient grounds, however.

2 Beneke ("Lehrb. der Psychologic als Naturwissensch.," 2nd ed., 1845,

Sensation — Idea — Cojiceplion.

155

" deposition " of the image in memory takes place entirely un-
consciously ; it has no concomitant psychical process whatever.
We see a rose for the first time ; the sensation of sight causes a
series of actions : we stop, perhaps, stoop to the rose and then
pass on, other visual sensations soon occupying our attention.
We are by no means aware that in the mean time a trace of the
visual sensation of the rose has been deposited. This is accom-
plished, as we say, latently, or without our being conscious of it ;
we only conclude that a latent image was left in the memory by
the first sensation, because we are able to recognise the rose
when we see it again. Let us, therefore, guard against the rough
conception that the mental images are deposited in the ganglion
cells of the cerebral cortex as an indefinite psychical product, an
unconscious idea. On the contrary, there is no psychical element
left of the sensory excitation Ec corresponding to the sensation,
but only a permanent material change which we designate as El.
This El, the remanent material trace, has no psychical correlate
whatever. We can conceive of this El most easily as a definite
arrangement and constitution of the molecules composing the
ganglion-cells; in other words, it is a latent disposition. This
purely material trace only becomes psychically active as an image
of memory or an idea when we see the rose again or when, by
means of the association of ideas or the play of fantasy, some
related idea occurs to us ; as^ for example, the idea of red or of a
fragrant flower. In order that the dormant image of memory,
which is as yet only potential, may be aroused, therefore, the
ganglion-cell having the disposition El, must first receive a new
impulse from a new and similar sensation, or from some related
idea with which it is associated ; that is, the El must be still
further changed in some definite way, becoming an ideational
excitation which we shall designate as Ei. Hence the ganglion-
cell is trained to a certain extent for a de:inite idea. We can

§ 27) veiy aptly designates El (latent excitation) as disposition (" Angelegt-
heit ") but ascribes a psychical existence to the EFs without sufficient
jjrounds.

156 Introduction to Physiological Psychology.

illustrate this by comparing the ganglion-cells to the wheels, stars,
monograms and other figures formed out of gas-pipes, as we see
them used in illuminations. Unlit, they resemble the so-called
latent images of memory ; the disposition is aheady there in the
form, structure, etc. But a spark must first light the gas that
escapes from the innumerable holes of the pipes, in order that
the latent form may become a living reality. It cannot be too
urgently emphasized that the sensation in the psychical sphere
corresponds to the excitation of the cerebral cortex imparted by
the stimulus, but that nothing of a psychical nature corresponds
to the residue of this material excitation. The designation
" latent image of memory " is very convenient, but it contains a
contradiction. Only either a new and similar sensation or the
association of ideas can so change this residue of the material
excitation as to produce a concomitant psychical process, a con-
scious image of memory or an idea. In the future we shall often
designate these material traces or dispositions simply as images
of memory, but only for the sake of brevity, and always with the
restriction just mentioned.

Let us now follow the same process also physiologically. On
seeing a rose, innumerable nerve-ends of tlie retina are irritated,
and innumerable fibres of the optic nerve transmit the excitation
to the visual centre in the occipital lobe of the cerebrum. It is
very probable that the relations of the retina are to a certain ex-
tent reproduced in the visual centre, so that the superior margin
of the retina, for example, corresponds to the anterior margin of
the visual centre, etc. When the rose is seen, numberless gan-
glion-cells are excited in definite regions of the visual centre that
correspond to the irritated portions of the retina. To this excita-
tion of numerous ganglion-cells corresponds the visual sensation.
But now where is the mental image of this sensation of sight
deposited? In the same elements whose excitation produced
the sensation ? Physiological psychology can aftbrd to quietly
await the answer of physiology and pathology to this question ;
its conclusions harmonize just as well with the supposition that
sensation and idea are dependent on the same cortical elements

Sensation — Idea — Conception.

157

as with the contrary supposition. Nevertheless, for the sake of
clearness, it is advisable to adopt one or the other of these two
suppositions as a basis in the following researches. Therefore, if
we assume in the future that sensation and idea depend upon
different cortical elements,^ it is because this supposition seems
to correspond better to the physiological and pathological science
of to-day. For example, it has been sliown that the extirpation
of a definite portion of the visual centre of a dog, or also the
disease of definite parts of the human occipital lobe produces the
condition of so-called mental blindness ; in other words the
animal on which the above-mentioned operation is performed
and the diseased human being still continue to see, as appears
from the fact that they follow objects held before them with the
eyes, and avoid obstacles placed in the way ; but they no longer
recognise what they see. The dog no longer crouches before the
threatening whip, nor dodges the stone thrown at him; the man
stares at the most familiar objects of his environment as if they
were wholly unknown to him and recognises them only when he
touches them. This condition of mental blindness ^ without
physical blindness, as also the analogous condition of mental
deafness without physical deafness, must in fact be explained by
the assumption that the sensations and the images of memory are
dependent on separate elements of the cortex. Those who wish
to investigate this very interesting question more particularly can
refer to the competent treatises of Munk, Mautlmer, Nothnagel,
Wilbrand and others.^

* The antiquated idea of Schroeder von der Kolk, which has recently-
been adopted again by the school of Meynert (Vienna), does not place the seat
of sensation In the cerebral cortex, or at least only partly. It substitutes for the
latter, either exclusively or in part, the corpora quadrigemina. The first of
these two suppositions is wholly incompatible with more recent pathological
experiences ; the second can only be made to agree with them with difficulty
'compare also Chapters I and II).

^ The cases of the loss of visual phantasy, described by Charcot, are also
worthy of mention. Also experiences concerning so-called " sensorial aphasia ".

* Munk, " Ueber die Functionen der Grosshinirinde," Berlin, 1881 ;
Mauthner, Wien. med. Wochenschr.. 1880: Wii.hrani), "Die Seelen-

158

Introduction to Physiological Psychology.

We assume^ therefore, that the sensation of the rose is pro-
duced in certain ganglion-cells, and that these numerous sensory
cells transmit their excitation further to one other ganglion-cell, a
memory-cell} Hence if b, c, d, e,/ represent ganglion-cells of
the visual centre to which the fibres of the optic nerve lead, and
if the rose, for example, excites only those fibres of the optic
nerve which lead to the ganglion-cells l>, c, d, the visual sensation
of the rose corresponds to the actual material excitation of the
ganglion-cells d, c, d. As soon as the rose disappears, the
material excitation of the cells b, c, d is extinguished and at the
same time the concomitant sensation vanishes. Only a part of
the material excitations of b, c and d is secured in the distant
ganglion-cell / where it leaves a merely material trace or change,
the image of memory. In a manner which we shall describe later
more exactly, this image of memory becomes psychically active
only when we see the rose again, or when it is reproduced by the
association of ideas. Let us remember that this scheme is by no
means the only one conceivable, but it is the one most in har-
mony with present scientific knowledge. We shall ourselves be
able to apply all the following discussions without difficulty to
any other scheme, for they are essentially independent of this or
any other physiological hypothesis.

Let us now continue our discussion, still retaining some de-
finite sensible object, such as the rose, for example, from which to
proceed. The rose not only produces a sensation of sight and its
proper image of memory, the visual idea, but its fragrance also
produces a sensation of smell, and its soft leaves produce a sen-
sation of touch. These sensations also leave images of memory,
an idea of smell, and an idea of touch. Hence, at least three
images of the rose, different in quality, are deposited in memory,
corresponding to the number of sensual organs upon which the

blindheit als Herderscheinung," Wiesbaden, 1887 ; Nothnagel, Vorlr.Tg
auf dem VI. Congress fiir innere Medicin ; Reinhard, Arch.f. Psycliialrie,
XVII and XVIII ; Lissauer, Arch. f. Psychiatrie, XXI.

1 The expression "memory-cells," so far as we know, originates with
IIORWICZ, Psycholog. Analysen, I, S. 287 ff.

Sensation — / den — Conception.

159

rose acted as stimulus. But the olfactory centre is far remote
from the visual centre, and both of these are far distant from tlic
centre of touch. Therefore, latent ideas are deposited in three
oan"lion-cells that are far remote from one another and in quite
different parts of the cerebral cortex. The following sketch re-
presents in rough outlines a hemisphere of the cerebrum. At V
lies the visual centre, at 7^ the centre of feeling (in the restricted
sense including touch), at JET the centre of hearing, and at Sm tlie

Fig. 17.

olfactory centre. Three component ideas of the rose have been
deposited in the ganglion-cells a, b, and c. The ganglion-cell a
is connected by the associative fibres with both b and c, and in
the same manner (J and r are connected with each other. Further-
more a, b and c have been often incited simultaneously, — that is,
we have often seen, touched and smelled the same rose at the
same time, and the corresponding images of memory were ac-
cordingly deposited in the cells «, b and c. As a result of this

i6o

Introduction to Physiological Psychology.

frequent simultaneous appearance of the three component images,
if b is excited, a and <: are also always excited sympathetically.
When we discuss the laws of association in a future chapter (IX), we
shall learn why only the cells a and c are sympathetically excited
by b with which they have often been simultaneously active,
although b can be shown to be connected by associative fibres
with many other ganglion-cells. For the present it is sufficient to
know that the component ideas of an object of sense are deposited
in different parts of the brain, that these component ideas are
connected with one another by associative fibres,^ and that there-
fore, if one of these component ideas appears, the others are
•called into action by association. The totality of the component
ideas thus associated with one another constitutes the idea of the
object. The idea "rose," therefore, is not simple but complex,
its unity depending merely on the reciprocal association of its
<:omponent parts. But language furnishes us with another unity
for these complex ideas of sensual objects. Thus far the ideas
with which we have become acquainted are entirely independent
of language, and therefore probably belong also to the lower
animals. But man names his ideas; we articulate the word
" rose " in connection with the complex idea above described.
In other words, we execute a peculiar combination of motions of
the larynx, lips, tongue, and palate with the result that another
person hears us articulate the word " rose." We have already
hecome acquainted with ideas of motions as the cause of most
voluntary actions. For example, the idea of a motion used in
grpsping the pen comes into the mind and without further impulse
we seize the pen. In a similar manner we must conceive
•of the ideas of articulation as the cause of the motions of
speech. These ideas of articulation are mental images that have
been laboriously acquired by the repetition of the motions neces-
sary for speech.2 This assumption has received a very decided

* Herbart designates this associative connection of component ideas, im-
parted by different senses, as "complication."

^ The contradiction that seems to be contained in this statement will be
•explained in a subsequent chapter (XIII).

Sensation — Idea — Conception,

i6i

confirmation from pathology. If the portion of the brain repre-
sented by the hatched spot in the drawing is destroyed, we
observe a remarkable phenomenon. The person thus afflicted
still retains command of all his sensual ideas ; he still understands
what we say to him ; he moves the tongue, the larynx, the lips,
and the jjalate the same as before the appearance of the disease.
But he has irretrievably lost the delicate combination of move-
ments performed by the tongue, larynx, lips, and palate, necessary
for the articulation of any word, — "rose" for example. The
mental images or ideas of his motions of articulation have been
destroyed.

These ideas of articulation, which can be shown to be deposited
in the posterior, inferior part of the frontal convolution (at d, fig.
17), are connected with the component ideas of an object of
sense by the associative fibres. Thus for example, as the accom-
panying illustration shows us, the ganglion-cells a, b, c, in which
the component ideas, or images of memory, of the fragrance,
colour, and form of the rose ^ are deposited, are not only connected
with one another by paths, but also with a single ganglion-cell or
complex of ganglion-cells situated in the frontal lobe and con-
taining the complicated idea of motion, necessary for the articula-
tion of the word "rose." In the drawing we distinguish all the
cortical elements that stand in relation to speech by the shading.
The same facts that characterized the component ideas a, l\ c in
their relations to one another also characterize the idea of articu-
lation d in its relations to a, b and c. As soon as a, b or ^ appears,
d, the word for the thing seen, smelt or felt occurs to us, and
vice versa. The idea of articulation d is especially adapted to be
a higher unity for the three component ideas, because it is
uniformly and directly connected with these three ideas, without
being itself a component idea immediately dependent on a special
object of sense. Hence its general character.

But the idea of articulation d does not constitute the sum total

* In the case of an object acting also upon our senses of hearing anfl taste,
of course, two more component ideas would be added.

1 62 Introduction to Physiological Psychology.

of all the elements of speech related to the whole idea " rose."
When we hear the word " rose," we understand what the word
means, and the colour, form and fragrance of the rose occur to us.
Therefore an image of this sensation of hearing the word which
we have heard spoken by another must exist in the cerebral
cortex and be in connection with a, b, c and d. It is obvious that
this " acoustic image " of the word " rose," or the idea of the
spoken word " rose " which we have heard, is to be sought in the
auditory centre in the temporo-sphenoidal lobe. In fact there is
quite a definite region in the superior temporal convolution at e,
the destruction of which by disease leaves all the functions of
the human brain, including speaking and hearing, intact with the
exception that the ability to comprehend words is removed. A
person in whom the region at e has become diseased still hears
words that are spoken to him very well, but does not understand
what he hears. Once familiar words sound to him as if they
belonged to a foreign language ; but if he sees the same words
written, he knows at once what they mean. Evidently this in-
dividual has lost the acoustic images of memory that once gave
him the power of recognising words ; in the language of anatomy,
he has lost the acoustic memory-c^%, but retained the acoustic
sensation-ctSS.'s, \ he is mentally deaf to words. Hence the complex
idea " rose " is still further aided by the " idea of the spoken word
as heard " (tf) ; the latter idea is connected with a, b, c and d, and
also contributes towards establishing a unity for these partial
ideas. This explanation can be carried still further ; the educated
person has a visual idea (/) of the word which he has read, the
anatomical location of which is also comparatively well established,
and an idea {g) of the motion used in writing the word. Both of
these ideas must be taken into consideration. However, it is not
necessary here to continue the discussion of these component
ideas further, for analogous deductions can be made in each case
without difficulty.

We can sum up the foregoing deliberations as follows : — The
idea " rose " consists of three partial or component ideas, corre-
sponding to the same number of qualitatively different sensations

Sensation — Idea — Conception.

163

imparted by the real rose ; with these are also associated two
ideas of language, the idea of the motions used in pronouncing
the word and the acoustic idea of the word as heard. The total
complex of these five ideas we also designate as a sensual or
concrete coiiception of the rose. A single definite rose produces
but one single idea which consists of various partial ideas. These
single ideas as a rule are not connected with the special idea of a
word, except in the case of proper names. Only after many
single roses have deposited their images of memory or single
ideas in the mind, are all these single ideas connected with the
one comprehensive idea of speech, "rose." The sensual or con-
crete conception, therefore, has in almost every case a certain
general character. The development of concrete conceptions, as
we understand them, is therefore closely connected with the
development of speech. We may here mention a fact incidentally
that is very interesting. Pathology demonstrates almost beyond
a doubt that the component ideas constituting a concrete con-
ception (a, b and c, for example) all exist twice in the brain.
Each hemisphere has its visual idea of the rose. For this reason
complete mental blindness is only known to occur in human
beings when the corresponding regions of the occipital lobe are
destroyed in both hemispheres. On the other hand, in the case
of man, the linguistic ideas, both those of articulation and those
of hearing, are deposited in the two specified regions of but one
hemisphere, — in the left hemisphere of right-handed persons, and
vice versa. We must refer to the physiology of the brain for an
explanation of this fact, which at first seems to be exceedingly
strange.^

The first and simplest concrete conceptions are the most
specific. We see a hundred single roses, and thus repeatedly
experience a constant combination of a definite colour, form,

» Wernicke, in his little work " Ueber das Bewusstsein," (AUg. Zeitschr.
f. Psych., Bd. 35), was the first to analyze concrete conceptions physiolo-
gically in a manner similar to the above presentation. Meynert also pursues
a similar course in his "Mechanik des Hirnbaues."

1 64 Introduction to Physiological Psychology.

fragrance, etc., but with different surroundings. These repeated
experiences are sufficient to produce a somewhat more general
conception of the rose in the cerebral cortex and to associate it
with a word or, more correctly, with ideas of language. A much
greater generalization is requisite for the deposition of the far
more general conception '^pla?it" in the cerebral cortex and its
association with ideas of speech. The most of these more
general conceptions are produced in the following manner.
Experience furnishes the cerebral cortex with numerous concrete
individual conceptions consisting of several component ideas,
for example, the concrete conceptions of tulip, rose, oak, etc.
Despite great differences, some of the partial ideas of these
single conceptions possess certain similarities. Therefore,
according to a law of association with which we shall become
more exactly acquainted later, these similar ideas become
associated with one another. For example, all have tlie green
colour of the leaves in common. Therefore, while the component
ideas of the rose together constitute a very compact complex with
which the word " rose " is associated, the totality of the concrete
conceptions of rose, tulip, oak, and numberless other plants,
constitutes a far more comprehensive but less compact or definite
complex with which the word " plant " is associated. The
appearance of the conception " plant " in consciousness is also
accompanied (i) by the appearance of the linguistic ideas of the
word " plant " both as spoken and heard, (2) by the sympathetic
excitation of the innumerable component ideas belonging to the
concrete ideas of all single plants, or as it has often been ex-
pressed, by their "sympathetic vibration." For this reason the
more general concrete conceptions are not so simple as has been
presumed ; on the contrary, the more general a concrete concep-
tion is, the greater is the number of loosely associated, single
ideas which it sympathetically excites whenever it appears in
consciousness, and hence the greater is its complexity. An
apparent unity is only furnished by the idea of the one word with
which all these individual ideas are associated. Hence when we
think of " plant," and, apart from the word, endeavour to define

Sensation — Idea — Conceptioti.

the content of this conception more accurately, definite individual
plants appear before the mind's eye at once, though somewhat
indistinctly. These are in fact those very individual ideas that
were sympathetically excited by the appearance of the conception,
and especially those that we have met with most frequently, and
which therefore act most forcibly. Hence a physiological process
that extends over almost the entire cerebral cortex corresponds to
the act of thinking a concrete general conception ; the extent of
this physiological process is much greater than that accompanying
the thought of a concrete individual conception. For this reason
the ideas of words, both as articulated and heard, are of greater
importance to the more general conceptions than to the more
specific conceptions. The loose complex of ideas constituting
the former would not hold together without the common bond of
connection between the component ideas which is furnished by
the idea of the word. The manner in which we acquire concrete
general conceptions goes far towards proving this presentation.
As children we often see a rose, a tulip, or an oak ; at the same
time we hear the word " plant " pronounced, and we repeat it.
Thus both a motor and an acoustic idea of speech are formed
and associated with numerous concrete individual ideas all of
which have a certain similarity to one another despite all differ-
ences. The entire system of these associations of concrete
individual conceptions, with the idea of the one word applied to
all, constitutes the general concrete conception " plant."

Another particular kind of concrete conceptions consists of
those which are produced by associating the idea of a sin-;le
word with a series of successive concrete ideas. To these be-
longs the concrete conception " thunderstorm," for example ; it
comprehends a series of visual and acoustic ideas representing
events that do not all occur simultaneously, but in part succes-
sively.

As we have seen, concrete conceptions consist either of com-
plexes of ideas, or of a succession of such complexes tliat are
associated with an idea of speech. These complexes of ideas are
all directly derived from certain sensations; for example, tlie

Introduction to Physiological Psychology.

concrete conception of a thunderstorm may be reduced to a
succession of ideational complexes — dark-grey clouds, rain, light-
ning, thunder, etc. All of these ideational complexes further
consist of ideas produced directly by sensations; for example, the
complex "rain" consists of the component acoustic idea, acquired
by having heard the pattering of the rain, and the visual idea,
acquired by having seen the falling drops.

In the concrete conceptions with which we have thus far be-
come acquainted all the component ideas refer directly to the
sensations. All conceptions also that express the relations of
concrete objects to one another may be directly referred to sen-
sations, and are therefore to be considered as concrete concep-
tions in the sense understood by us here. Let us take the con-
ception " similarity " for example. On innumerable occasions,
when the child sees two or more similar objects, it hears the
word " similar " pronounced, perhaps at first with reference to two
similar play-things. In the beginning the child has similar
sensations from both objects, but as yet knows notliing about this
similarity of its sensations. Then it hears the word " similar " in
reference to the two playthings for the fi^st time. The word
"similar" at first signifies to the child only those "two definite
similar playthings." But the child hears the word "similar"
frequently on other occasions ; it hears two similar trees, two
similar houses, etc., designated as similar. In other words, the
child's idea of the word " similar " becomes associated with
innumerable pairs of similar concrete images of memory. The
idea of the word " similarity," that originally signifies to the
child " two definite similar playthings," gradually changes as more
and more of these different pairs of similar ideas are associated
with it. The ultimate result is the idea of a word that is associ-
ated with numerous pairs of similar ideas whose specific content
(playthings, trees, etc.) it has entirely lost. The content of the
idea " similar " thus finally dej^ends merely upon the fact that
certain pairs of ideas are similar. Such concrete conceptions we
shall designate as co?icreie coiuepiions of relation. We have just
seen how the child, the individual, acquires these concrete concep-

Sensation — Idea — Conception.

167

tions of relation, and what their physiological basis is in the adult.
The difficult question as to how these conceptions of relation
have developed phylogenetically, that is, in the human race, does
not demand our attention here. A subsequent chapter (X)
will explain how it is that we are able to find the pertinent con-
ception at once on seeing an object, or the appropriate conception
of the relation of similarity when two objects are seen. At pre-
sent let us call attention to the fact that primarily these concep-
tions of relation are also concrete, i.e. they are derived directly
from sensations. This is made still further evident by the fact
that the terms of a language for such conceptions of relation as
*' proportion," " sequence," " consequence," etc., are derived al-
most without exception from special concrete cases.

With the above we have exhausted the most important kinds of
ioncrete conceptions. From these we shall now pass directly to
the physiological deduction of abstract conceptions. Logicians
have by no means always understood the same thing by " abstract
conception." The scholastic philosophers called " white " a
concrete conception and " whiteness " an abstract conception-
Likewise, in the present century, the famous author of " A
System of Logic, Ratiocinative and Inductive,"^ John Stuart
Mill. Others have designated that which we called a general
conception as an abstract conception ; accordingly, " this rose "
and " this plant " would be concrete conceptions ; but on the
other hand, "rose" and "plant" would be abstract conceptions.

Physiological psychology leaves but litde room for the assump-
tion of so-called abstract conceptions. We shall designate as
abstract conceptions those conceptions that cannot be directly
reduced to sensations and their mental images. We have already
seen above that the simplest concrete conceptions consist of a
complex of component ideas that are associated with one another
and with the idea of a word. This association of the comfjonent
ideas, as, for example, the fragrance, colour, and form of the rose,
corresponds to the combination of sensations which we have often

* People's Ed., p. 17, § 4.

l68 Introduction to Physiological Psychology.

experienced and which produced the ideas. In fact, the combi-
nation of ideas is merely a consequence of the combination of
sensations. But our ideas are not only produced when awakened
by sensations ; they are also produced when there is complete
absence of sensation ; when eyes, ears, and all the other organs of
sense are at rest, our imagination or thought may still be active.
Thus, in a manner well known to us, the component ideas that
have been derived from the sensations are brought into new com-
binations or complexes which do not occur at all among the
sensations. These new combinations of component ideas we shall
designate as imaginative ideas or reflective ideas. If we imagine
a garden, it may, indeed, be some definite garden that we have
often seen ; the partial ideas that are reproduced are chosen and
combined in exactly the same manner in which the sensations
were often actually produced by that definite garden. But the
association of ideas, which in the special case about to be con-
sidered we are wont to designate as fantasy or the faculty of
imagination, can select and combine the component ideas " tree,"
" bed," " rose," etc., in a new complex different from any that
ever really occurred with the sensations. Then we have the idea
of an imaginative garden that we have never actually seen.
These imaginative or reflective ideas do not originate directly
from tlie sensations ; in other words, they do not refer directly to
an external object. The imaginative ideas also occur successively
or in series, the same as the concrete conceptions that are derived
directly from the sensations. Of still greater importance is the
fact that these ideas of the imagination may also be generalized
the same as the concrete conceptions, and that even the most
gf n al concrete conceptions may be newly combined in thought.
By this means we also form general conceptions and words that
have no direct relation to any object outside of our consciousness.
Such conceptions we may designate as abstract, in case we desire
to employ this term which is not, however, entirely suitable.
Here we shall pause.

It is sufifiiient to have established the manner in which the
stimulus produces the sensation, to have shown how the latter

Sensation — Idea — Concepti on.

169

leaves its idea or image in memory and how the idea becomes a
concrete conception through its association with ideas of speech
as heard and spoken, thus reaching the first degree of generahza-
tion. The concrete conception may then be more and more in-
volved in generaUzation or it may also express relations, but it
always refers directly either to sensations of concrete objects or
to the ideas originating in these sensations. The abstract con-
ceptions represent combinations of ideas to which analogous com-
binations of sensations have never corresponded. We see that the
preceding conclusions have prepared the way for a new classifica-
tion of our psychical processes. This further analysis of the data
with which we are furnished, the sensations, ideas, and concrete
and abstract conceptions, requires the assumption of two parallel
worlds — the world of physical phenomena and the world of
psychical phenomena, to the latter of which belong the sensations
that should be considered as the effects of the physical phenomena.
This classification of phenomena is further warranted by the
observation of our fellow-beings, who give us oral information as
to their inner conscious life. The further continuation of this
subject, and especially the question as to whether this division of
phenomena can be justified or not, we must leave to quite another
science, namely, epistemology.

The more exact deductions of this science would necessarily
depend to a great extent upon that conception of relation which
we designate as cause or causality. For the purposes of physio-
logical psychology it is sufficient to accept both series as given ;
this science merely borders on the problems of epistemology in
the deduction of the abstract conceptions.

Let us now return to the images of memory or ideas having a
concrete content. We remember that in connection with the
theory of sensation we distinguished three properties of sensation,
(i) quality, (2) intensity, (3) tone of feeling or emotional tone.
To these were also added under certain circumstances, those pro-
perties of sensation that refer to space and time. Now can we
distinguish similar properties also in the mental image of the
sensation, in the idea ? The simplest deliberation demonstrates

170 Introduction to Physiological Psychology.

that ideas differ from one another first as to their content or, as
we may also express it, as to their signification or meaning. For
example, the ideas "king" and "plant" have very different con-
tents. A seco7id difference lies in the vivacity or distinctness of the
ideas. For example, we have a very lively or clear idea of a
"rose." We have experienced the complex of sensations im-
parted by the rose so many times, that the image of memory or
the idea " rose " is very vivid and distinct. Our idea of a rhodo-
dendron's blossom is probably much less distinct and vivid. The
reason is obvious, the complex of sensations produced by the
blossom of a rhododendron has been much less frequently ex-
perienced by us. But the vividness of the idea varies also when
the content remains the same ; the botanist or the gardener has
a much more vivid idea of the flower of a rhododendron than one
not schooled in botany. In fact, our own idea of the rhodo-
dendron's flower changes in the degree of vividness and distinct-
ness. If we see the blossom of this plant to-day, perhaps for the
first time, to-day and to-morrow its idea or image in memory
remains very vivid. After a few days ^ the distinctness of the
image is seen to have diminished somewhat ; in case we do not
see the flower again, the lapse of a year will suffice to remove both
clearness and vividness almost completely.

A third property of the ideas, besides content and vivacity, is
their emotional tone. The idea of this man is accompanied by a
pleasant tone of feeling ; the idea of that man, by an M;zpleasant
tone of feeling ; in other words, the general idea " friend " is

* The investigations of Paneth (Centralbl. f. Physiol., 1890, No. 3) is very
interesting. According to these investigations it may be assumed that the
mental image does not diminish perceptibly in sharpness at all during the first
five minutes after the sensation has vanished. It then begins to lose its sharp-
ness slowly. This gradual loss of the power of distinct recollection is by no
means merely a diminishing of the intensity. At the same time that the
latter decreases, a peculiar constant change takes place in the quality of ihe
image. This change is hardly to be described, but is generally designated by
us as the fading of the image from memory ; it is identical with that which we
designate as the loss of distinctness or sharpness.

Sensation — Idea — Conception.

171

accompanied by a feeling of pleasure ; the general idea " enemy,"
by a feeling of displeasure. We shall devote a special discussion
to these tones of feeling, which, together with the emotional
tones of the sensations, constitute the foundation of the emotional
life.

Finally, we have to consider the characteristic features of ideas
with reference to time and space. As regards space it is obvious
that the ideas are not generally projected into space in just the
same manner as are the sensations. The complex of sensations
produced by a definite tree is decidedly of a spatial character.
The idea or image of this definite tree in memory, an image which
we reproduce in recollecting this definite tree, also has a certain
decidedly spatial character. But many ideas, especially those
that are most general, are not characterized by any reference to
space whatever. Even the general idea or conception "tree"
has almost wholly lost its spatial character ; this is still more the
case with the more general conception " plant." The spatial
characteristics of the conceptions generally become less pro-
nounced in proportion as the ideas are combined in more ex-
tensive generalizations. Tlie ideas partake of the character of
time quite as much as do the sensations, i.e. they are charac-
terized by a certain duration and sequence. One idea occupies
us perhaps but a moment, another two seconds, etc.

We now pass at once to the question as to whether more than
one idea ever appears at the same time or not. Simultaneous
ideas blend to complex ideas ; hence two separate ideas cannot
appear in the same moment of time.

Thus we find that the images of memory, or the ideas, also
have three properties apart from those characteristics which refer
to space and time. But let us guard especially against the
erroneous conception that the content of the idea corresponds
exactly to the quality of the sensation, the vivacity of the idea to
the intensity of the sensation, and the emotional tone of the idea
to the emotional tone of the sensation. Only the emotional
tone of the sensation is transferred, chiefly in a simple manner
to the idea ; but the quality and intensity of the sensation doth
enter into the content of the idea, and a similar process is char-

172

Introduction to Physiological Psychology.

acteristic of the time- and space-properties of the sensation. The
content of many ideas is conditioned by still another factor; if
we see but two definite kinds of dogs during our lifetime, as a
greyhound and a poodle for example, the general idea "dog,"
which we construct from our ideas of these two kinds, would receive
a very different content according to whether the poodle or the
greyhound had been seen more frequently. The idea would in
fact bear a decidedly greater resemblance to the animal that had
been more frequently seen. Therefore not only the quality and
intensity, but also the relative frequency of the separate original
sensations determines the content of the ideas, — at least, the
content of the more general ideas. The sharpness of the ideas
depends first upon the intensity of the original sensation. An
intense flash of chain-lightning will generally leave a more vivid
image in memory than faint sheet-lightning. But other factors are
just as important for the sharpness of the images. In this case the
frequency with which the complex of original sensations has been
experienced is of especial importance. If we ofteii see a certain
man, the latent material trace of this complex of sensations is more
deeply imprinted on the elements of the cerebral cortex than when
we see him but rarely. We can recall the idea of this man more
accurately and more sharply if we have seen him often. As above
mentioned, we must imagine this material trace El, which we
designated conditionally as a latent image of memory, to be in
reality a definite spatial arrangement and a definite constitution of
the molecules. Originally this arrangement is very unstable ;
not until after the same sensations has been very frequently ex-
perienced does the molecular arrangement, which it creates and
leaves, become stable. Only after the ganglion-cell has acquired
in this manner a very definite and fixed disposition of its mole-
cules can a clear idea be awakened from this disposition by
association. Besides the three properties already named, which
belong alike to latent images and actual ideas, the latter have
still a fourth property ; the intensiiy of the idea itself varies greatly
according to the strength of the impulse which the ganglion-cell,
with the disposition EL receives. If we see rain-clouds on a hot

Sensation — Idea — Conception .

175

day, for example, the association of ideas immediately following
the visual sensation, gives an impulse to two ideas, the idea that
our person will be drenched and the idea of the cool refreshing
air that is to be expected. In this case the former idea will
probably receive the stronger impulse, and will therefore appear
most vividly in consciousness. Hence we can advantageously
distinguish the sharpness of ideas which depends upon the more
or less complete stability of El, and is accordingly intimately
concerned in the distinctness of the content of an idea, from the
intensity of the ideas which depends on the energy of the
impulse that changes El to an actual idea or the latent image of
memory to an active image of memory.

The sharpness of the idea is dependent in part upon the
intensity of the sensations that gave it origin ; the intensity of the
idea has nothing to do with the intensity of the sensations whose
mental image it is. The intensity of ideas may therefore be
fittingly called their energy. The energy of ideas at first appears
to be merely a property of actual ideas. We shall find, later,
however, that the latent mental images also mutually impart to
one another associative impulses, thus, in part checking, in part
stimulating, each other. In this sense the latent ideas also have
a certain intensity or energy as a fourth property.

Finally, we can draw one more simple conclusion with reference
to the latent images of memory. If these are in fact only material
dispositions, the material change in the ganglion-cell will not be
without influence upon this molecular disposition. In other
words, if new and more or less similar sensations do not again
renew this disposition, in the course of time it will imperceptibly
lose its stability and be finally obliterated. The simplest intro-
spection agrees with this statement. This loosening and final
destruction of the latent mental images is nothing more than that
which we call forgetfulness ; we forget ideas that are not con-
stantly and repeatedly re-excited by similar or like sensations.

With the above we have essentially completed our theory of the
idea or image of memory, and are acquainted with the entire
material of which the association of ideas makes use. Only the
emotional tones of ideas still require a special discussion.

CHAPTER IX.

THE TONE OF FEELING OF THE IDEAS — EMOTIONS.

The older psychology, almost without exception, regarded the
emotions as the manifestations of a special independent faculty
of the soul. Kant places the feeling of pleasure and pain as a
special faculty of the soul, between the cognitive faculty and the
appetitive faculty, and emphasizes expressly that a further reduction
of these three faculties to a common source is impossible. On
the other hand, our previous discussions have already taught us
that the feelings of pleasure and pain by no means exist inde-
pendent of other psychical phenomena ; that, on the contrary,
they appear only as properties or qualities of sensations and ideas,
I.e., as their so-called tone of feeling. We have already become
quite familiar with the emotional tone of the sensations ; let us
now investigate the emotional tone of the ideas. Ultimately the
■emotional tones of all ideas may be reduced to the emotional
tones of sensations. A sensation disappears with the cessation
of the stimulus, and leaves behind a mental image or an idea.
Along with its other properties it transmits to the idea its tone
of feeling, be it positive or negative. The pricking sensation of
the rose-thorn does not leave behind an indifferent image of
memory ; if one think of the prick again, or, otherwise expressed,
if the mental image of the prick appears again in the course of
his association of ideas, the memory will be accompanied by a
feeling of pain. The idea has inherited its emotional tone from
the sensation.

This proposition, that all ideas ultimately draw their tones of
feeling from the sensations, is of great importance. A priori or

174

The Tone of Feeling of the Ideas — Emotions. 175

absolute emotional values do not exist, therefore, in any ideas
whatever. All our ideas are the offspring of our sensations, not
only as to their content but also as to their emotional value.
The idea of gratitude or of any other virtue would never be
accompanied by a positive tone of feeling, if we had not at some
time rejoiced over grateful deeds that we had heard or seen, or in
other words, perceived through the senses. Finally, the commenda-
tion of the teacher alone sufifices to connect in our minds some
quality, an example of which we have never experienced, with a
positive or negative emotional tone. But the emotional tone of
an idea never develops without the emotional tone of some
sensation as its basis.

Of course this connection between the emotional tone of the
idea and that of the sensations is often much more complicate
than in the example mentioned above. This is due to an im-
portant characteristic of the emotional tones of ideas, viz., their
easy transmission. If we have suffered an accident or injury in
some place, the memory of the injury is not only accompanied
by a feeling of pain in the future, but frequently we disrelish the
memory of the place itself, i.e., it is also connected with a painful
emotion. We can resist this motionless feeling of displeasure
in so far as its influence upon our actions is rendered ineffective
by opposing ideas ; but upon accurate self-observation, we shall
seldom fail to find this transmitted feeling of pain within us.
Let us analyze this psychological process somewhat more exactly.
A definite locality stimulates in us the visual sensation Sloe, and
at the same time we have the tactual sensation Stac. from the
injury. Sloe, is accompanied either by no tone of feeling at all,
or by but a very slight one. Stac. is painful, and therefore ac-
companied by an intense negative tone of feeling. Sloe, leaves
the mental image Hoc, and Stac. the mental image Itac, Hoc.
and / tac, as simultaneously deposited ideas, are closely associated
with each other. At first Hoc. lacks any tone of feeling ; / tac.
receives the intense negative emotional tone of Stac. The law,
which we have just stated, is exemplified in the present case as
follows •. / tac. now transmits its emotional tone either in full or

1/6 Introduction to Physiological Psychology.

diminished intensity to Hoc, with which it is associated, so that
in the future the memory of the place will be accompanied by a
feeling of pain, although its original sensations were never char-
acterized by a negative tone of feeling. In this case, therefore,
one idea does not owe its tone of feeling directly to its funda-
mental sensation, but to another idea with which it is associated.
It is obvious, however, that even here the emotional tone of the
idea is ultimately due to the emotional tones of sensations. The
•emotional tone of Stac. is the final cause of the emotional tone
of Hoc. ; only the connection with sensations is much more
complicate, — not direct, but indirect. We have already met
one phenomenon dependent on this law in a former chapter.
If we see the locality again, i.e., if Sloe, is repeated, it is frequently
accompanied by a feeling of pain, even although liac. does not
especially appear. In this case Hoc. has transmitted its tone of
feeling, drawn directly from Itac, indirectly from Stac, to a
second Sloc.;^ the sensation has therefore drawn its tone of
feeling from the idea. This has already been illustrated by the
example of a melody accompanied by sorrowful words. This
transmission of the emotional tone, therefore, may complete the
circle — from sensation to idea and back to sensation again.

The transference of the emotional tone of one idea to another
may also be termed " irradiation '' ^ of the " intellectual feelings."
We here understand intellectual feelings to mean the emotional
tones of ideas or mental images, as opposed to " sensorial feelings"
i.e., the emotional tones of the sensations. Numberless examples
of this irradiation may be cited. The memory of a flower of
disagreeable odour is, as a whole, disagreeable ; the component

^ Many cases of psychosis in which the mental disorder recurs whenever one
or more of the circumstances attending the occasion of its first appearance
reappears, illustrate the pathological distortion of this characteristic of the
emotional life (Germ. Intentionspsychosis).

^ The expression " irradiation of emotional tones " is here a literal trans-
lation of the original " Irradiation der Gefiihlstone." The meaning is obvious,
— akin to radiation or diffusion in physics, an " overflow " of emotional colour-
ing from one mental image to another. — T'i.

The Tone of Feeling of the Ideas — Emotions. 177

idea of its odour has transmitted its emotional tone to the entire
concrete conception. Thus both our entire emotional and voli-
tional life is ruled by these irradiations. Our antipathies and
sympathies, prejudices and prepossessions, flow chiefly from this
source.

Let us next consider the following consequence of this law of
irradiation. If during a certain period of time we experience
several sensations or ideas of the same intense emotional tone,
or even a single sensation or idea of a strong emotional tone,
the many other sensations and ideas appearing in the same
period of time, either accompanied by a weak tone of feeling or
lacking all emotional shading whatever, are coloured by the
emotional tone of the former. Thus it happens that all our
sensations and ideas within a certain period of time very frequently
show similar tones of feeling. The resultant of these similar
emotional tones, belonging to the sensations and ideas experienced
during a definite period of time, constitute the " mood." Hence
the " mood " is not an independent, self-active, psychical process,
but an abstraction from the sitnilar emotional tones of the ideas
and sensations that appear together during some definite period
of time. If several ideas of strong but antipathetic tones of
feeling appear at the same time, it would be absurd to speak of
a uniform frame of mind or mood.

We can now understand at once, furthermore, that by virtue of
this irradiation the emotional tone of most ideas, and especially
of the more general, is the result of a very complicate develop-
ment. Some idea, as /S has numberless associations with other
ideas ; the emotional tones of each of these other ideas, in so far
as they have any appreciable intensity, are irradiated to
Thus the tone of feeling of is the resultant (i) of the emotional
tones belonging to the sensations that gave rise to /\ and (2) of
the emotional tones of the ideas with which is associated.
Considering that itself is often composed of many component
ideas or even of entire associative systems, as was set forth in the
last chapter, we can now judge how minute the gradations and
how complicate the development of our intellectual feelings.

178 Introduction to Physiological Psychology.

Of course this complexity would at once be removed if all our
feelings of pleasure and pain were to be distinguished from one
another merely as regards their intensity. Then the emotional
tone of even the most complex ideas would have to be regarded
simply as the algebraic sum of the emotional tones of the funda-
mental sensations and the associated ideas. Unfortunately,
modern psychology has subscribed too confidently to this false
hypothesis, although its erroneousness is apparent. The countless
feelings that thrill the human heart, envy, anger, ambition, love,
etc., are obviously different in quality. It would be doing
violence to facts to force all these emotions into the two classes,
feelings of pleasure and feelings of pain. When the major chord
c e-g, and the minor chord c-eO-g are struck successively upon the
piano, two qualitatively different sensations are produced. Let
us now notice the relation of the pleasurable feeling to the sensa-
tion in each case. In the first place, the feeling of pleasure
produced by the major chord is undoubtedly greater ; but it is
just as certain that accurate introspection shows the feeling of
pleasure accompanying the minor chord to be also different in
quality. Even those unschooled in psychology often give ex-
pression to this difference in quality by using the terms " major "
and " minor." Still more striking are the qualitative differences
of pleasurable feeling when we compare impressions from the
different senses with each other. The agreeable feeling of
comfort that accompanies the sensation of warmth in the
neighbourhood of a stove in winter, is entirely different from the
pleasant feeling accompanying the accoustic sensation of a
musical chord or the visual sensation of a beautiful ornament.
This difference in the emotional quality is, of course, conditioned
by the difference in the quaUty of the sensations, but is by no
means identical with it.

The qualitative difference in the tone of sensuous feelings is
transmitted also to the tone of intellectual feelings. Hence the
emotional tones of different ideas are exceedingly complex, not
only as regards their intensity, but still more as regards their
quality. That simple algebraic summation is tiot valid, because

The Tone of Feeling of the Ideas — Emotions. lyg

it does not take place. Each idea receives from its fundamental
sensations, and by irradiation, a great variety of emotional tones ;
these differ (i) as to intensity (even their general characteristics
are in part very unlike), and (2) as to quality. Thus arise the
complex feelings and moods in all those countless shades that
almost constantly accompany the more highly developed intel-
lectual life. Let us examine the feeling of envy, for example.
Envy is a complex tone of feeling that often accompanies, under
varying circumstances, the visual sensation or the idea of another
person. We think, for example, of an acquaintance that has
gained possession of something which we were unable to attain,
and which, for the purpose of concrete illustration, we may
suppose to be a rare mineral. How is our idea of this acquaint-
ance affected by irradiation? Even before he had come into
possession of the mineral, thereby becoming the object of our
envy, the idea of the envied acquaintance itself had a definite
peculiar tone of feeling that was generally slightly negative.
Furthermore, the idea of the stone itself has been associated
with the idea of our acquaintance since he obtained the stone.
This idea of the stone is associated with a peculiar feeling
of pleasure which it transmits, although only to a slight degree,
to the idea of the acquaintance. Moreover, it is associated
with the idea of my own collection of minerals, which lacks
just this mineral ; this idea is accompanied by a strong nega-
tive tone of feeling of peculiar quality, which is also irradiated
to the idea of the acquaintance. The ideas of the useless
exertions we had made to get the stone must also be taken
into consideration ; their intensely negative and very peculiar
emotional tones still further influence the idea of the ac-
quaintance. This analysis might be carried into still more
minute details. Enough has been said to make it clear that the
envious feeling accompanying one's ideas of an acquaintance is
the resultant of a long series of irradiated emotional tones from
associated ideas. Some of these irradiated shades of feeling are
merely peculiar to the special case assumed above; others are
typical of all feelings of envy. To the latter, for example, belong

I So Introduction to Physiological Psychology.

especially the negative emotional tone of one's own privation ;
the latter would therefore be included in a definition of envy in
general. As a rule, however, we should beware of such general
definitions of the feelings ; it is vastly more profitable to undertake
psychological analysis such as we have just briefly and incom-
pletely made of the feeling of envy. Here, of course, it is
impossible to attempt such an analysis for all or even a few of
the more complex emotions. It would carry us too far ; but the
preparation of these analyses cannot be recommended urgently
enough. We have observed either in ourselves or in others a
complex feeling, the emotional accompaniment of a definite
idea. In such a case we should take pains to determine the
fundamental sensations, the associated ideas, and finally the
irradiation of the emotional tones of the latter. By this means,
the only way of arriving at an explanation of the countless nuances
of our intellectual feelings, we shall obtain the most thorough
insight into the emotional life.

We have already seen that the irradiated emotional tones of
the ideas may react upon and be imparted to the sensations.
Thus it happens that the complex feelings, just discussed, not
only accompany the ideas but also the sensations. If we see
another in possession of a treasure that we lack, this visual sensa-
tion is also associated with the emotional tone of envy. But
although these more complicated emotional tones are by no
means confined to the ideas, their connection with sensations is
nevertheless always due to the association of the latter with
ideas.

A further task of psychology in this field might be to attempt
a classification of these complex emotions. From the first, how-
ever, we shall be disposed to regard such a task, in so far as the
attempt to draw sharp limitations is concerned, with distrust.
The specialization of these tones of feeling is endless ; the envy
of love is distinct from the envy of the collector, and this again
from the envy of honour. On the other hand, there are always
transitional shades between the apparently most disparate feelings.
Everyday life proves this ; in fact, after the above deliberations

The Tone of Feeling of the Ideas — Emotions. i8i

we should not expect it to be otherwise.^ Even a space-arrange-
ment of these qualitatively different emotional tones is as im-
possible, for example, as a space-arrangement of the sensations
of smell. Even the classification that first seems most natural,
the division into positive and negative feelings, leaves us in the
lurch. It is true that many of the feelings, such as sadness,
anxiety, etc., consist chiefly of negative tones of feeling, while
others consist chiefly of positive tones of feeling,-- in time we
shall devote a special discussion to these. Many feelings, how-
ever, cannot consistently be assigned to either one or the other
of these classes. Recall, for example, "humour," in the good old
meaning of the word, which, as we are wont to say, is often so
wonderfully compounded of tears and laughter. It only remains
for us to select from the endless and confused multitude of
feelings those which, on account of their frequency or their
relation to certain sensations and ideas, or finally, because of
their important influence upon the association of ideas and motor
innervations, appear to us to be especially important. It is only
to these, in fact, that mankind has given certain terms.

Without laying any claims to completeness or universality
whatever, therefore, let us briefly trace the growth of our most
important complex tones of feeling, proceeding from the simple
emotional tones of the sensations. The theory of sensorial

1 The older philosophy teems with fruitless attempts at the classification of
the emotions. Most deceptive of all has always been the division into two
classes, feelings of pleasure and feelings of pain, from which a process of pure
reasoning then sought to develop the other emotions. The most consistent
attempt of this kind was made by Spinoza. who deduced all feelings from the
laetitia and the tristitia (comp. his Elh. P. IV., Prop. 8), which he in turn
reduced to cognitive acts (laetitiae aflfectus = cognitio boni ; bonum = quod
nostro esse conservando prodest). Whoever has traced this and similar
deductions must have realized that it is impossible to do justice to the mani-
foldness of our feeling in this way. The noted quadratic arrangement of the
emotions by Hume also belongs to this class. Especially the table of " all "
qualitative feelings prepared by HoRWiCZ is very instructive (Psychol.
Analysen, I., 2). Other attempts at classification have originated with Bain,
DuMONT, SiBERN, Nahlowsky, Lehmann, and others.

1 82 Introduction to Physiological Psychology.

feelings, esthetics in the narrower sense, we have discussed in full.
It now remains for us, therefore, to deduce from the latter the
more complex emotional tones of the ideas that arise from
irradiation, and the more complex sensorial tones of feeling
arising by the reilection of emotional tones from the ideas to the
sensations, as has just been described. The simplest emotional
tones, both positive and negative, are the accompaniment of
positive sensations which in turn correspond to positive stimuli.
Even the sensations of hunger and thirst, which are accompanied
so early in hfe by keen feelings of pain, are, as physiology teaches,
positive sensations whose primary stimuli are to be sought in
certain changes in the chemical composition of the blood. As
the mental images and their associations increase, this is changed.
The child sees a piece of sugar. The visual sensation awakens
the memory of one of the component ideas of the same object,
viz., the idea of the taste of sugar. The gustatory sensation of
sugar was accompanied by a strong positive tone of feeling ; sO'
also the idea of the taste of the sugar had its accompaniment of
pleasant feeling. This tone of feeling is now transferred to the
associated visual idea and thence also to the present visual sensa-
tion. The child rejoices over the sugar which it sees. This
sensation now becomes the cause of motor discharges ; the child
tries to reach the sugar, but his movements fail despite repeated
attempts. Thus far there have appeared in the child's brain only
the visual sensation of the sugar, and, by association, the idea of
the taste of the sugar, both accompanied by a positive ton.' of feeling.
Since the motions made in attempting to seize the object fail, the
expected sensation of taste, coupled with an intense feeling of
pleasure, is not realized. Finally, the unavailing motor efforts
create an intense sensation of weariness, accompanied by a strong
feeling of displeasure. This negative emotional tone is trans-
mitted to the visual sensation and to the whole idea of the sugar.
All the feelings seem to be changed The negative emotional
tone is also transmitted to all the other simultaneous, sensations,
and ideas ; the entire mood is changed ; the child cries. Thus
negative tones of feeling arise which seem to accompany no

Tlie Tone of Feeling of the Ideas — Emotions. 183

positive sensation whatever, but rather the noti-appearance of a
pleasant sensation. These feelings of " deprivaiion" which vary
greatly in their individual characteristics, have as yet received far
too meagre attention from psychology. As soon as the above
process has been often repeated in the same or a similar manner,
the vain attempts to grasp and the resulting sensation of weariness
are no longer necessary for a complete metamorphosis of the
emotions. The Idea of the useiessness of all attempts to get
possession of some object is sufficient to beget the emotional
tone of deprivation, and to extend the corresponding feeling of
displeasure to all simultaneous sensations and ideas. The above
explanation may be applied to many similar cases. In the case
of the child in the above example, the impelling motive is a piece
of sugar ; in the case of the adult it becomes the sum total of
all that he regards as essential to his " happiness" — honour, love,
money, ornament, and countless other things. Accordingly, the
emotional tone of deprivation appears in numberless qualitatively
different shades.^

Just as the sensations of weariness, following vain attempts
to seize an object, produces the negative feeling of privation,
so the sensation of rest after successful attempts at flight from
disagreeable sensations begets the positive emotional tone of
safety, which is also developed in a great variety of forms.
Finally, it comes to be an almost universal accompaniment ol
the idea of the non-appearance or absence of any unpleasant
sensation.

Primarily, therefore, ideas are only accompanied by the emotional
tones of gratification or of affliction, corresponding to the positive
•or negative emotional tones of actually present sensations ; but in
time there appear ideas of absent sensations accompanied by the
feeling of deprivation or of security. The sensation or idea of
the fortune or misfortune befalling one's fellow being is a special
case that demonstrates most clearly this expansion of the emotional

^ Furthermore, the development from sensations of weariness is by no means
the only mode in which the emotional tone of deprivation may be developed.

184 Introduction to Physiological Psychology.

life. The visual sensation or idea of the injury that has befallen
some fellow mortal, by virtue of its associations, is at first char-
acterized by a complex negative tone of feeling. But the above
discussion has shown us that it is possible for this same sensation^
or this same idea, occasionally to receive positive emotional tones.
Malignity may take the place of pity, and in a similar manner,
envy the place of participation in the joy of others : both, let us
repeat, have their countless shades.^ The predominance of one
tone of feeling or another in a certain individual, and in a
particular case, i.e., the emotional reaction, depends upon a great
many special circumstances, upon the present associations and
the emotional tones of the different associated ideas. We may
speak of characteristic emotional reactions, i.e. , emotional reactions
peculiar to the character, in so far as the same feelings or moods
constantly and uniformly recur in the same individual.

The development of our complex tones of feeling takes place
along another line, as follows : Thus far we have considered the
emotional tones of the sensations independently of their time-
relations. Time is a factor that conditions still further changes
in the tones of feeling with which we are already acquainted.
The complex emotional tone of hope arises from a special com-
bination of the emotional tones of present privation and future
gratification, and, in a similar manner, the peculiar feeling of
fear with its multitude of varieties (care, anxiety, solicitude, etc.)
from a special combination of the feelings of present security and
future affliction. The interesting, but little investigated, emotional
tones that characterize the act of "seeking," in the broadest sense,
should be included here. A further modification of the emotional
tones takes place when they are transferred to ideas which we
view in the light of their causal relations to certain other ideas
and sensations having distinctive tones of feeling. We construct
a causal relation between the concrete conception of bread and

1 Of course it is impossible for speech to do justice to all these countless
shades. Note, for example, the subtle distinction between envy, jealousy, and
grudge, or between sympathy, pity, participation in other's joy, etc.

The Tone of Feeling of the Ideas — Emotions. 185

numerous individual ideas and sensations that have reference to
the same object, e.g., the agreeable taste, the appeasing of the
hunger, its value as nourishment, etc. Accordingly the idea of
bread receives an emotional tone which we commonly designate
as that of utility. This emotional tone of utility, like the analogous
feeling of noxiousness, has received a special designation in the
language only in so far as it is connected with the ideas of objects.
In a manner not psychologically justifiable, we ascribe these
feelings to the object itself, as quaUties (usefulness and harmful-
ness). This changes as soon as these same tones of feeling
accompany ideas of persons ; for these feelings the language
then has the subjective designations of " love " and " hate." The
feelings of thankfulness and resentment are specialized feelings of
the same class. All these feelings also often appear as char-
acteristic emotional reactions in the sense explained above, e.g.,
the feehng of thankfulness becomes the characteristic trait of
thankfuluess,^ the feeling of resentment becomes the characteristic
trait of resentment. Anger, esteem, admiration, contempt, disdain,
are also examples of this class of emotions. The specialization
of the feelings becomes still more extensive when they refer to
persons with whom we have certain definite relations ; they include
all feelings toward relatives, and, in a broader sense, also the
feelings toward the state, the fatherland, etc. Finally, still
another group of feelings is composed of those which accompany
the Ego-idea, the so-called feelings of self, or egoistic or personal
feelings (pride, vanity, humihty,^ bashfulness, etc.).

In passing from the single ideas to the association of ideas, we
encounter still other tones of feeling. As we shall learn more in
detail later, intense thought is characterized by the habitual inner-
vation of numerous muscles, e.g., the musculus frontalis. When-

1 It is hardly necessary to mention that he term "ingratitude" does not
express any tone of feeling, but, like " apathy " and " indifTerence," is rather a
word for our conception of the lack of any definite tone of feeling.

^ To these belong the emotional delusion of personal greatness that often
accompanies mania, and the emotional delusion of personal insignificance that
often accompanies melancholia.

1 86 Introduction to Physiological Psychology.

ever the conclusion of an ideational series is retarded, these
innervations are intensified and muUipHed ; accordingly, there
appear sensations of weariness with a pronounced negative tone
of feeling. According to the law of irradiation, this negative
emotional tone is transmitted to all the ideas of the series ; hence
arises the disagreeable feeling or mood characteristic of mental
inhibition. This feeling is also met in the most diverse forms.
The peculiar emotional tones that accompany doubt and contra-
diction in thought, or contradiction between thought and sensation,
belong to this class. On the other hand, the corresponding
positive tones of feeling are those that accompany mental success
and harmony in thought, or between thought and sensation.
Wundt has very aptly designated these feelings as logical feelings.

The feelings experience their last and most important complica-
tion when transmitted to the sensations and ideas of our own
actions, or of the actions of our fellow beings. At first, of course,
these sensations and ideas are also accompanied by the emotional
tones with which we are already familiar. The beneficent deeds
of the mother, that produce numerous sensations of a positive
emotional tone, are accompanied by feelings of thankfulness, love,
etc. All these feelings still centre entirely in the ego, i.e., they
are intimately connected with the interests of self. As yet they
presuppose no feeling human beings besides ourselves. Even
the original forms of pity and participation in others' joy, as
described above, are still "egocentric." The visual sensation,
or the idea of a wounded fellow-being, is only associated with
painful feelings in so far as it reminds us of our own painful
wounds. The sight of a neighbour's good fortune causes us to
rejoice only in so far as we are reminded of a similar good fortune
of our own. We first imagine ourselves, as it were, in another's
place; only by this means is it possible for us to pity or to
participate in the joy of others. But this is changed as soon as
we discover that our fellow mortals also feel, i.e., have sensations
and ideas characterized by definite emotional tones. Heretofore
we had only had ideas zvith emotional tones : now we construct
ideas of these feelings, both as manifested in ourselves and

The Tone of Feeling of the Ideas — Emotions. 1 87

especially in our fellows. We construct, for example, the ideas
"Affliction," "Gratification," "Pity," "Participation in others'
joy," " Love," " Hate,'' etc. The development of the emotional
tones of these ideas in detail varies greatly. By virtue of its
contents, the idea of another's affliction is connected with a
negative, of another's gratification with a positive, tone of feeling.
Thus our feelings of pity or of joyful participation in the fortunes
of others, which were originally closely connected with the interests
of self, i.e., were ego-centric, are strengthened by irradiation and
receive an altruistic stamp. The development of the emotions
that accompany our ideas of the feelings of others is more
complicated, but at the same time more important. For example,
we observe that many of the feelings which actuate our fellow-
beings lead to deeds that produce in us either feelings of pleasure
or feelings of pain. Accordingly, the ideas of the former class
(as pity, participation in others' joy, love) receive a positive tone
of feeling; those of the latter class (as hate, envy, malignity) a
negative tone of feeling. These tones of feeling are also trans-
ferred to the deeds which these feelings actuate. We give
language expression to the emotional tone of ideas of the
first mentioned feelings by designating them as " virtues ; " to
the emotional tone of our ideas of feelings belonging to the
second class, by using the term " vices." Deeds that are actuated
by the former are called "good;" those actuated by the latter
are "bad." It is obvious that at first these emotional tones
characterize only our ideas of the feelings and actions of others.
This altruism at first appears to be still purely egoistic; these
virtues seem to be identical with utility, these vices identical
with perniciousness. It can be shown without difficulty, how-
ever, that the emotional tone of the idea or sensation of one's
own, and that of another's, action toward a third are influenced
in a similar manner. Let us take a definite example. We
ourselves, or others, spring to the aid of some one threatened
with danger (= one's own or another's action). We see, and
if we perform the act ourselves, we also feel this action, or
we have an idea of it (= sensation or idea of one's own or

1 88 Introduction to Physiological Psychology.

another's action toward a third). What will be the emotional
tone of this sensation or idea ? In accordance with the previous,
discussion, it is obviously determined by the irradiating emotional
tones, which in this case are very numerous. We may name, for
example, the primary form of pity, malignity, fear (of perishing
in the attempt to rescue), and perhaps also love or hate, according,
to the person in danger. It is quite impossible to determine in
general the resultant of all these tones of feeling. Individual
differences in the characteristic emotional reactions, and the
fluctuations of the irradiating tones of feeling according to the
varying circumstances, are far too extensive. In the midst of
this contest among the various irradiating emotional tones, there
now appears the positive feeling characterizing the ideas of a
compassionate act, or, popularly expressed, we feel that it would
be "noble"' to take pity upon and help one who is in danger.
Of course this positive emotional tone originally had reference
only to those actions of others that benefited us. Even now, to
some extent, we still mistake the situation ; but this mistake has-
its foundation in the entire intellectual and emotional life. At
first the positive emotional tone belonged only to a complex
association of ideas ; we thought of some compassionate deed,
and ourselves as its object. The separate ideas composing this
ideational complex, when isolated from it, also retain somewhat
of its positive emotional tone. The idea of a compassionate act,
as such, regardless of who performs it, or whom it affects, retains-
a positive tone of feeling ; although it is much too weak to-
determine each individual in every case in favour of the positive
emotion accompanying the specific act. There will be many men
who will regard such an act (running great danger to help one's
fellow mortals) as foolish, despite the positive tone of feeling
accompanying a good act, i.e., they will prefer to regard the act
overwhelmingly in the light of a strong negative feeling, and, in
a given case, to leave it unperformed. In others, on the contrary,
this positive emotional tone, characteristic of the idea of a good
deed, will be strong enough to be imparted to the idea of some
specific helpful act, despite the irradiation of other conflicting tones

The Tone of Feeling of the Ideas — Emotions. 1 89

of feeling. The sensation or idea of the act will be accompanied
by the emotional tone of a good deed, although the deed itself
perhaps is of no use to us, but may rather threaten us with danger.

Thus we see how considerably the emotional tones of our
actions, i.e., our ethical tones of feeling in the narrower sense,
fluctuate. The fact that, despite these fluctuations, civilized
peoples have constructed a canon of the emotional tones, as it
were, so that we now agree tolerably well in designating such
actions and feelings as the above, "good," i.e.., in associating our
ideas of them with a peculiar positive tone of feeling, is to be
explained as follows. Mankind has founded states and other
communities for the sake of self-preservation and self-protection ;
the ethical emotional tone of actions, already discussed, is indis
pensable for the maintenance of these institutions. Without
social community this ethical tone of feeling would presumably
have retained the special character given it by each individual.
Our ethical characteristics have not been produced by social
communities at once, but by a process of gradual development.
Individuals who lacked these qualities were cast out of society^
Communities, the majority of whose individuals lacked them,
were destroyed. Hence a natural selection has taken place in
this case also, and has permitted states to rise and exist only
when the majority of their individuals have possessed ethical
emotional tones of at least average intensity. Laws and educa-
tion, with their "thou shalt " and "thoushalt not," with their
punishments and rewards, have, as servants of the state, continued
constantly to strengthen that canon of ethical emotion. Perhaps
we would ask : but what becomes of the absolute moral law, of
which so many philosophers have spoken ? We reply, — psychology
has nothing whatever to do with the question as to whether there
are objective moral values or not. If metaphysics or religion can
prove their existence, the merit belongs entirely to them. Our
psychology has only to demonstrate how the subjective ethical
emotions develop. Innate ethical tones of feeling exist no more
than innate actions. The ethical emotions are the product of
a long, complex, ontogenetic and— phylogenetic de-

IQO Introduciion to Physiological Psychology.

velopment. The chief features of this development have been
set forth in the above ; their application in detail falls to the special
science of ethics.

In reviewing this entire presentation of the development of the
complex intellectual feelings, and of those that are reflected back
upon the sensations, let us remember that it is not to be regarded
as a classification. It is impossible either to give a complete
■enumeration of all these tones of feeling, or to set forth all the
relations which those already mentioned bear to one another.
This is in part due to the science itself, which, formerly engrossed
in speculative investigations and at present absorbed in the study
of certain physiological effects of the emotions, has neglected the
simple, empiric, but scientific accumulation and observation of
■experiences bearing on the emotions. The countless relations
which the feelings bear to one another, and their many transitional
tones, also render a treatment of them especially difficult. This
accounts, too, for the ambiguity and vagueness of our language
expressions for many feelings. A scientific nomenclature is entirely
lacking. The succession in which the intellectual feelings develop
is also subject to numerous individual variations, because the
sensations whose original emotional tones ultimately lie at the
basis of the intellectual feelings, and of those which are reflected
back upon the sensations, come to different individuals in very
•different order, selection, and intensity. Our treatise, therefore,
cannot pretend to be a universally valid presentation of the
ontogenetic or phylogenetic development of the feelings. We
Iiave attempted to reveal only their most important architectonic
relations, or, as it were, the style and principle of the entire
complex structure, especially as regards its foundations, the sensa
tions, and ideas.

Let us now consider the influence of the feelings upon ideation
and motor innervations. In so far as the feelings influence
(move) both, they are termed the emotions. The influence of
the emotions upon the formal association of ideas depends almost
entirely upon their tone. The law which applies here is usually
formulated as follows: Emotions that are chiefly or exclusively

The Tone of Feeling of the Ideas — Emotions. 191

positive accelerate the association of ideas, while emotions that
are chiefly or exclusively negative retard it. The same is true,
in general, of their influence upon action. Depressive emotions
lead but slowly and sparingly to actions, the exalted emotions
quickly and abundantly. We should not forget, however, that
this influence is mutual; we have already seen above that the
inhibition of ideation begets negative tones of feeling, its accelera-
tion positive. In certain mental diseases this remarkable circle
of emotional influence produced by ideation and action upon the
emotional tones, and reflected back again from the latter to the
former, attains an enormous significance.

But there are some exceptions to the law that has just been
stated. There are negative emotions whose influence is directly
favorable to forcible motor discharges, — for example, anger and
anxiety. Anger tends very strongly to violent motor outbreaks.
It is the emotion that prompts to an attack, kot' Ikaxhv- It is not
difficult to determine the positive element in the emotion of anger ;
the very intense idea of injuring an opponent, which suddenly and
directly follows the sensation of some wrong one has suffered
at his hands, excludes all other associated ideas, and imparts its
positive emotional tone to the idea of the motion of attack, thus
assisting its abrupt and vehement discharge. That this discharge
sometimes also affects lifeless objects and innocent persons de-
pends on the oft-mentioned process of irradiation.^ Similar
relations are characteristic of the emotions of fear and anxiety.
Despite its negative tone of feeling, fear universally induces the
speedy motor discharge of flight or of defence. The idea of self-
preservation, with its positive tone of feeling, appears, overwhelms
for the time being all other ideas, and by virtue of its favourable
position transfers its positive emotional tone to the motor idea of
flight ; thus, despite the fact that the tones of feeling are otherwise
chiefly negative, the latter is enabled to prevail. Therefore, the

1 Recollect also the interesting clinical fact that morbid gaiety is very often
associated with morbid anger. Both appear to the clinical observer to be as.
closely related as anxiety and sadness.

192

Introduction to Physiological Psychology.

strong motor tendency of fear and anger, despite their negative
emotional tone, must be explained as follows : The motor ideas
of attack or flight, which are associated with ideas coloured by
anger or fear, offset these emotions by their own intense positive
tone of feeling. The law as stated above, therefore, has not
universal validity. A special investigation is still always necessary
to determine whether, in the case of a negative emotional tone,
■certain motor ideas do not have a positive emotional stamp, and
vice versa in the case of a positive emotional tone, whether certain
motor ideas do not have a negative emotional stamp. If the
latter is the case, the motor effect may be delayed or prevented
•despite the fact that, in general, the emotional condition is
positive. Ultimately the effect is determined by the character of
feeling peculiar to the 7notor ideas that are associated with the
content of consciousness at the moment, i.e., whether the motor
ideas have positive or negative tones of feeling. In general, the
motor ideas having a positive tone of feeling lead to action.
Pathology provides an excellent proof of this fact. Melancholia
is a mental disturbance characterized by the morbid predominance
of negative emotional tones. Accordingly the hypochondriac
generally manifests the greatest restriction of motor power, to-
gether with a pronounced inhibition of thought processes. At
times the patient requires a full minute or more to execute the
simple motion of guiding the spoon to the mouth. Such patients
will lie almost motionless in bed for months at a time and then
dash to a window, — which some indiscreet nurse has chanced to
leave open but for an instant, — with astounding rapidity, for the
purpose of throwing themselves out of the room. The motor
interdict, as we may call it, has suddenly been broken. The
explanation is obvious ; to the hypochondriac the idea of throwing
himself out of the window has an intense positive emotional tone ;
he regards death as a release from his anxiety, as a welcome
expiation for his supposed guilt. The positive emotional tone of
this particular motor idea, or rather of the corresponding complex
•of ideas, takes effect as soon as the opportunity awakens this
idea in the otherwise inactive brain, bursts all other barriers, and

The Tone of Feeling of the Ideas — Emotions. 193

thus prompts the appropriate action. The other actions of many
insane persons, caused by anxiety, that often appear with explosive
suddenness and vehemence, may be explained in a similar manner.

Finally, the so-called expressive motions constitute another
very peculiar motor effect of our feelings. Later we shall discuss
these motions of expression more fully in connection with the
chapter upon action. They include not only the mimetic motions,
such as laughing and crying, but also certain motor innervations,
such as the contraction of the peripheral arteries during emotional
excitement, which take place in the non-striated or involuntary
muscles. These motor innervations can only be determined by
means of especial apparatus. We make mention of this fact here
merely because the newer psychology has frequently sought to
explain the emotions simply as the sensations of these muscular
contractions. James,^ for example, has expressly declared : " We
do not cry because we are sad, but we are sad because we cry."
The adherents to this view^ have tried to establish a specific
combination of such motor innervations for all the most important
types of emotion. Thus, for example, Lange has prepared the
foUowins; table : —

Weakening of voluntary innervations = disappointment.

-t- vascular contraction = care.
4- vascular contraction -I- spasm of the organic

muscles = fright,
-f incoordination = embarrassment.
'+ vascular expansion = joy.

Weakening of voluntary
innervation

Strengthening of volun-
tary innervation

-)- spasm of organic muscles = expectation or
suspense.

^ -J- vascular expansion H- incoordination = anger.
Fere ' found that feelings of pleasure increase the muscular

» " Mind," April, 1884.

^ C. Lange, "Uber Gemiithsbewegungen." Translation by Kurella,
Leipzig, 1887. MiiNSTERBERG, " Beitrage zur experimentellen Psychologic,"
Heft 4, S, 216. Compare also Wundt's excellent critique, "Zur Lehre von
den Gemiithsbewegungen." Philosoph. Studien, Bd. 6.

' "Sensation et Mouvement." Compare also Mosso, " t)ber den Kreis-
lauf des Blutes im menschlichen Gehirn," Leipzig, 1881, and " Die Furcht,"
Leipzig, 1889.

194 Introduction to Physiological Psychology.

power and the volume of blood in the extremities, while feelings
of pain or displeasure reduce both. We owe still more exact
investigations to Lehmann.^ Finally, Munsterberg has recently
claimed that all agreeable emotional conditions manifest a ten-
dency to extend the extremities, all unpleasant conditions a
tendency to contract and bend them.

All these investigations still leave a great deal to be desired in
the way of exactness and completeness. It has only been de-
termined with exactness that certain emotions result in certain
changes in the activity of heart and lungs, in the contraction of
the peripheral arteries and in the mimetic motions. In detail,
these changes are still almost wholly unknown. It is also quite
possible that they constitute the specific physiological character-
istics of many emotions ; but it is by no means permissible to
identify the sensation of these concomitant changes with the
emotion itself. Vascular contraction and weakening of voluntary
innervation, which, according to Lange, are the characteristic
physiological accompaniment of care, also occur numberless
times without the feeling of care. If, as these hasty pseudo-
empirics assume, the emotion were really the concomitant
psychical process of the sensible excitations which those motor
innervations transmit to the brain, then their proposition should
admit of inversion. If the motor innervations are present the
appropriate emotions should also appear. In reality, however,
this is not the case ; their hypothesis is thus shown to be in error.
This instance should serve as a warning in general against con-
cluding that because two processes, the one physiological and the
other psychical, often appear simultaneously they are parallel,
i.e., invariable concomitants of one another in the sense which
we have accepted as the foundation thought of our physiological
psychology. Such hasty conclusions would very soon bring our
science into disrepute.

1 " Die Hauptgesetze des menschlichen GefUhlslebens," translated by
BENDiXifN, Leipsic, 1892. Compare also the very similar theoretical views
of Grant Allen, " Physiological ^stlietics," 1877.

The Tone of Feeling of the Ideas — Emotions. 195

The motor, particularly the vaso-motor innervations, therefore,
have nothing to do with the existence of the emotions, although
they may at times add new and peculiar sensations to the original
sensations and ideas that are the bearers of a certain emotional
tone. Such, for example, are the peculiar sensations of paralysis
or lameness that often accompany vehement terror. The second-
ary paresis of the entire muscular system, which sometimes follows
a sudden and terrifying sense-impression, produces in addition to
the latter a sudden sensation of swooning. The so-called feelings
of expectancy produce secondarily peculiar contractions of the
muscles of accommodation and attention ; accordingly, besides
the ideas or sensations accompanying the feelings of expectancy,
special secondary sensations of tension appear. These secondary
sensations play an important role also in the case of anxiety. The
emotion of anxiety disturbs the regular rhythm of respiration and
the activity of the heart, and causes an intense contraction of the
peripheral arteries ; accordingly we feel an inner unrest, a sense
of oppression ■ located in the breast, particularly in the region of
dhe heart, and a general thrill.^

We might further ask whether the intensity of the positive or
negative tones of feeling depends with any regularity upon the
properties of the ideas they accompany. We remember that we
have already established such a regular relation between the
intensity of the emotional tone of a sensation and the intensity of
the sensation. But our knowledge of the intellectual emotional
tones is considerably more limited. We only know that a certain
minimum intensity of the idea is necessary to produce an
appreciable tone of feeling. Both the positive and negative
emotional tones of an idea also appear to increase with its
intensity and vivacity. The duration of an idea, within certain

" In the case of the anxiety of many insane persons, which is accompanied
by oppressive precordial sensations, and of many afflicted with neurosis of the
heart, the precordial sensations seem to be the primary phenomenon, and the
anxiety to appear as their emotional tone.

196

Introdtcction to Physiological Psychology.

limits, appears to have no influence ; if it exceeds these Hmits the
tones of feeling are dampened. The intensity of an intellectual
tone of feeling is very strongly influenced by the emotional tones
of other simultaneous or immediately precedent sensations and
ideas. Similar laws hold good for the sensorial tones of feeling.
One of the most important is as follows : After an unpleasant
sensation or idea, the intensity of the emotional tone of the
following pleasing sensation or idea is generally greater than it
would have been without a contrasting antecedent. The chord
of f-major is especially agreeable when it follows the dissonance
of the chord of the 7 th, g-e-d-f. The so-called resolution of chords
in the theory of harmony rests essentially upon this rule. Sur-
mounted obstacles heighten the joy after victory. A hopeful idea
can exert a more cheering effect when one is in doubt than when
he is free from care. This law, numberless examples of which
may be cited, may be designated as the law of contrasting feelings,
or still better, as the law of the relativity of emotional intensities.
The intensity of our feelings, like the intensity of our sensations,
has no absolute magnitude, but is dependent on the intensity
of simultaneous and preceding emotions. Both these phenomena
are due to the fact that no excitation of the cerebral cortex
takes place in entirely isolated and previously unstimulated ele-
ments, but in elements that have already been the seat of
excitation and are connected with countless other elements by
associative paths of conduction. One of the most satisfactory
among the future tasks of our science is the investigation of the
separate phenomena bearing upon the relativity of our feelings.
Of course such investigations cannot avoid the difficulties arising
from the fluctuations in the quality of emotional tones that are
due to irradiation.^ In this connection let us make mention once

^ That such investigations should not consider merely the Europeans of the
nineteenth century ought to be a matter of course, and yet with few exceptions
(Taine, " Philosophic de I'art," Grosse, " Ethnologic u. Aesthetik "),
aestheticians have almost wholly ignored ethnology.

The Tone of Feeling of the Ideas — Emotions. igy

more of Fechner's " Vorschule der Aesthetik," which has gathered
together the typical phenomena bearing upon this subject and
arranged according to uniform points of view. Such investigations
are far more fruitful for the advancement of our knowledge than
the numberless, at least immature, theories concerning the nature
of feeling, with which speculative psychology and philosophy have
presented us for centuries.

CHAPTER X.

THE ASSOCIATION OF IDEAS.

The association of ideas is accomplished by the use of two kinds
of elements ; new sensations are received from the external world
and the mental images of former sensations are already at hand
in the cerebral cortex. These latent ideas are constantly called
up in consciousness and associated with the new sensations. We
see a dark cloud, i.e. a stimulation, Ec (cloud) has been trans-
mitted from the retina to the sensory cells of the cerebral cortex.
The psychical correlate of this material excitation of the cortex
is the visual sensation of the dark cloud. A series of related
ideas are connected with this sensation by association, — for
example, among others, the idea of rain. The material excitation,
Ei (rain) in the memory-cells of the cortex corresponds to this
idea of rain, which is associated with the visual sensation of the
cloud. This material excitation Ei (rain) did not exist before,
only the material disposition El (rain) was already at hand in the
memory-cells where it had been deposited by one or more former
visual sensations of rain. Previous to its excitation no psychical
process corresponded to this El ; it was merely a material trace —
a latent image of memory. Only after the association of ideas
has changed the El into Ei does a psychical phenomenon, the
idea of rain, also appear as the correlative of Ei. In the same
manner this one idea is followed by numerous others ; latent
images of memory are constantly called up above the threshold of
consciousness, or, as it is often expressed, reproduced. It is just
this process of reproduction that we designate as the association
of ideas or ideation. We must, however, guard against viewing
the association of ideas either as an active or passive bei7ig. Oi.
the contrary "association of ideas" is a brief term designating

the process of the reproduction of ideas. Our present task is tc

198

The Association of Ideas.

199

establish the laws according to which this association of ideas
takes place, and to render them physiologically intelligible. Why
is the sensation of a grey cloud followed by the idea of rain, and
the latter by the idea of being drenched, of returning home, or of
raising the umbrella? This is all that we are called upon to ex-
plain in the general laws of the association of ideas. We shall
now consider the process somewhat more accurately, and for this
purpose we shall distinguish two cases. The sensation that in-
troduces the association of ideas may either be more or less new,
or we may have experienced it before in a more or less similar
manner. Accordingly the content of the first idea with which the
sensation is associated is either like or different from that of the
sensation. We have already often seen just such a grey cloud,
or at least one very nearly the same in appearance ; but we have
probably never seen the "northern lights." Upon seeing the
grey cloud or an old acquaintance, either one is recognised at
once ; upon seeing the aurora borealis there is no recognition.
In the first case the idea of a like cloud, formerly seen by us, may
appear. In the second case the idea of a similar sensation of
light — the sun, for example, may be reproduced. Therefore the
association of ideas may begin either with or without a recognition.
Let us next consider the first case and attempt to explain the
physiological basis of recognition. We see a grey cloud for the
first time ; let us assume that a series of sensory ganglion-cells, for
example, c, d, e, in the cortex of the visual centre are stimulated.
In the manner explained above a latent image of memory is now
deposited in another ganglion-cell. Let this other ganglion-cell,
the memory-cell, be designated by a. This a (fig. 18) is probably
connected either directly or indirectly with all of the sensation-
cells, a-i, etc. On the other hand, many other memory-cells
^, 7, 8, etc. (only one of which, y8, is represented in the drawing)
are also connected with the sensory cells a-h, etc. The sensa-
tion is associated with the latent image of memory deposited at a
instead of the one deposited at /3, simply because the resistance
to conduction happens to be least in the paths leading to a.
Now let us suppose that a rain-cloud appears in the visual field

200 Introduction to Physiological Psychology.

for the second time. The psychological process is clear; when
the cloud is seen again, the mental image of the cloud that we
formerly saw occurs to us again. But what is the physiological
basis of this process ? Let us assume that upon seeing the rain-
cloud for the second time, certain other sensation-cells, as h, i,
for example, are excited. How does it happen that upon seeing

Fig. 1 8.

a cloud for the second time the mental image of the first cloud is
recalled, or, in other words, that the excitation of the sensation-cells
g, h, i, is transmitted directly to a and not to one of the other
memoiy-cells connected with g, h, i, as y8 for example ? The ex-
planation of this fact is as follows : The ganglion-cell, a, and the
paths of conduction leading to it have been definitely trained or,
as we may say, " tuned " by the first excitation ; that is. since they
were first stimulated they have been much more sensitive^ to
every similar excitation and much less sensitive to every dissimilar

^ Charles Bonnet, in his " Essai analytiqtie sur Tame" (1760), has given
similar expression to this proposition in the following words : " La souplesse
ou la mobilite des fibres augmente par le retoiir des memes eljranlements " (the
suppleness and mobility of the fibres increases tlnough the return of the same
excitations). Comp. also Locke, "Essay concerning human understanding,"
n.>33. §6.

The A ssociation of Ideas.

201

excitation. This sensitiveness to a definite excitation is in-
dicated in the illustration by cross-lining the paths da, ca and
da, etc. The specific sensitiveness however is not restricted to a
and the paths ba, ca, da, that were directly stimulated when the ob-
ject was first seen, but extends also to all paths leading to a, — a a,
ea,fa, ga, ha, t a, x a, y a, z a, etc. Hence if we see a cloud for
the second time and the sensory cells g, h, i, are thereby stimu-
lated, the excitation of g, h, i finds numerous paths open by way
of which it may be conducted to various memory-cells — to a,
or y for example. But since the cloud was first seen, certain of
these numerous paths (viz., those leading to a, — g a, ha, and i a)
have been much more definitely "tuned" or highly sensitive to
that special excitation which produces the image of the cloud.
For this reason the seeing of the cloud is the only visual sensation
that calls up just the mental image of the cloud from but the
one memory-cell and no other, no matter what sensation-cells may
be excited. Therefore in a certain sense a selection is made from
the paths that are open to the further transmission of the ex-
citation after it has arrived in the cerebral cortex.

In the above paragraph we have attempted to explain in brief
what physiological processes may occur in the cerebral cortex
during an act of recognition. Let us call attention, however,
to the fact that, in view of our limited knowledge concerning the
processes of excitation in the cerebral cortex, this explanation is
wholly hypothetical as to particulars ; it can therefore be abso-
lutely correct only in its fundamental features. We have already
mentioned in a previous chapter that the local separation of the
sensory elements from the memory elements has not yet been
demonstrated, although it is comparatively probable. With very
little trouble we can transform the presentation given above so
that it will harmonize with the assumpdon that sensation and
memory depend upon one and the same material substratum.
We have furthermore always spoken of sensory cells as the sub-
strata of the sensations and memory-f(?//y as the substrata of the
mental images ; but this is also hypothetical. It may be that it is
not the ganglion-£-^//y, but the network of fibres in the cerebral

Introduction to Physiological Psychology.

cortex that experiences the excitation corresponding to the sensa-
tion and that acquires a certain fixed material disposition cor-
responding to the images of memory. It is also comparatively
unessential whether the above-mentioned fixed disposition be
regarded as confined to the cells or as extending to the paths of
conduction as well.^ The essential features of the process as just
described remain entirely untouched and unchanged by these
various different assumptions. A certain stimulus causes a
material change or excitation, Ec, whose psychical correlative is
the sensation. This Ec does not wholly disappear when the
stimulus vanishes ; on the contrary, it leaves behind a trace of the
excitation, the disposition El. If a stimulus, similar to the one
that first produced the sensation, again acts upon the cortical
elements, the excitation thus caused finds numberless EP^ already
at hand. By virtue of the above-mentioned fixed and specific
dispositions characteristic of the different elements, this second
stimulation acts only upon that El which was formerly produced
by the same or similar stimuli, and changes it into Ei ; thereupon
the latter is accompanied by a parallel psychical process that
was wanting in the condition El. Only this 07ie El " responds,"
as we may express it. But as soon as El becomes Ei, the image
of the cloud formerly seen comes into the mind ; we recognise the
cloud.

Let us not imagine, however, that this recognition takes place
as a special act in the case of every sensation that is perceived
again after having been once experienced. Commonly we do
not recognise the things with which we are already familiar at all ;
we simply perceive them.^ The appearance of the mental image
of former similar sensations to a certain extent determines only

1 The disposition of the memory-cells would then be simply identical with
El.

* MUNSTERBERG, Beitrage z. experim. rsychol., H. I, S. 136. Erdmann,
I.e. The latter is quite right in empliasizing that in the case of recognition
the sensation and the idea of former like sensations do not appear separ.itely,
but as a single process or phenomenon (Herbart's " Verschinelzung "=
"blending ").

The Association of Ideas.

203

the starting point and chief course of the ideation that follows.
This is already the case in the example which we cited at the
beginning of this lecture. Especially those ideas that, combined
with the image of memory which first appeared, constitute the
concrete conception of the object, are as a rule immediately
associated. We see a rose in the distance and at once recognise
it as such ; the visual idea " rose," deposited in the memory by
the sensations of many former roses, has directly occurred to us.
Very often, however, this does not take place at all as a special
act ; but the other component ideas which together constitute
the concrete conception of the object rose — the ideas of its
fragrance, of the smoothness of its leaves and, above all, of arti-
lulating the word " rose " — are directly associated with the visual
sensation. If the last of the above-mentioned ideas— the idea
of articulating the word " rose " — is sufficiently intense, it im-
mediately imparts the movements of articulation, and we exclaim
" a rose ! " ^

Let us now pass on to the second case : we have a sensation
that we have never formerly experienced. It is obvious that such
a sensation finds no path that is entirely suited to it ; the excita-
tion will therefore doubtlessly follow that path which is best adapted
for its conduction. Strictly considered, almost all our sensations are
new \ a sensation rarely recurs in exactly the same manner or form.
When we see a definite rose again that we have seen before, the
mental image of the same rose as formerly seen recurs in the
mind. In this case, of course, one might say that the sensation
first reproduces an idea of like content. But if we see any rose,
whatever, or some flower that is entirely unknown, only the general
visual idea " rose " or " flower " appears ; we have never before
seen a rose or flower with which the one that we now perceive
exactly corresponds. Therefore in this last case the sensation
first reproduces an idea having a somewhat similar or related
content ; an idea having a content like that of the sensation does
not exist at all. But absolute dissimilarity as distinguishing a

* Compare Lehmann, Philosoph. Studien, Bd. V.

204 Introduction to Physiological Psychology.

new sensation from all other former sensations is still more rare
than absolute likeness between a new and a former sensation.
Let us remember that our sensations are generally complex and
that therefore certain similarities between the elements that com-
pose both the former and the new sensations will very rarely be
found to be entirely wanting, despite the fact that the newly
experienced sensations are more or less distinctively characterized.
Therefore the investigations that we have made above in connec-
tion with the first case may also be applied in the second case
when the sensation is apparently quite new. We may recapitu-
late botli cases as follows : The first idea which is associated with
the introductory sensation is determined by its complete likeness, or,
more frequently, its similarity to the latter. The association of the
following ideas or, in the language of physiology, the further pro-
pagation of the excitation within the cerebral cortex, is accom-
plished according to another law, with which we must now
become accurately acquainted.

This chief law of the association of ideas, psychologically ex-
pressed, runs thus : Each idea reproduces as its successor either an
idea that is similar to it in content, or an idea ivith which it has
often appeared simultaneously. Association of the first kind may
be also designated as internal, that of the second kind as external
association.^ The principle of external association is simultatieous-
ness or synchronism, that of internal association, likeness or
sitnilarity. We think of a landscape and at the same time the
idea of the friend in whose company we have seen it occurs tO'
us. This is a case of external association. Associations of
similarity are considerably less frequent. When a sensation
enters into the association of ideas, the first idea with which it is
associated is always reproduced by some similarity between the
two, as we have seen above. But when the first idea has been once
iwakened by the sensation, the further ideas follow almost ex-

1 The external association corresponds approximately to Herbart's " indirect
reproduction," the internal association to a combination of the "indirect and
" direct reproduction." The external association corresponds to Teichnuiller's
" historical relationship " (historische Zusammengehiirigkeit).

The Association of Ideas.

205

clusively according to the principle of simultaneousness, i.e. by
external association. Let us above all, however, guard against
considering the so-called external association as unessential or
superficial, and the internal association as closer or more in-
trinsic. The contrary is true. The entire process of education
endeavours to awaken related ideas in the child simultaneously, i.e.
to combine them by means of external associations. The child
asks : " What is that ? " and he is answered, "A tree." Thus the
first external association between a visual idea and an idea of
hearing is established. The ideas of sight and hearing are wholly
unlike each other, but by virtue of constant simultaneous appear-
ance they become very closely associated. We shall trace this-
influence of external association even as far as the logical pro-
cesses of thought. On the other hand, the internal association of
ideas or the association by similarity is very superficial wherever
it occurs in its pure form; it is probably confined almost exclusively
to the acoustic ideas of words that sound alike. Thus, for
example, the acoustic idea of chest can reproduce the idea guest;
the acoustic idea of pain, the idea raitt.
Let us now seek some physiological basis for external associa-

FiG. 19.

tion. The question arises first : Why does one idea reproduce
only some other idea with which it has often appeared ? Let a,
b, c (fig. 19) be three ganglion-cells in which, under the condi-
tions already often mentioned, we conceive three mental images
or ideas to be deposited. All three are connected with one

2o6 Introduction to Physiological Psychology.

another and with numberless other cells by fibres. Let us suppose
the three ideas corresponding to the three ganglion-cells to be
wholly different from one another ; furthermore, let the ideas a
and b, or the sensations corresponding to them, be supposed to
have appeared very often simultaneously, but not a and c nor b
and c. Whenever a and b are stimulated at the same time a
sympathetic excitation takes place in all the paths issuing from a
and b. It is obvious that this sympathetic excitation is particu-
larly great in the path ab, uniting a and b. In consequence of the
more frequent simultaneous excitation of a and b the path ab will
become more practised, i.e. it will acquire an entirely specific
disposition fitting it for the transmission of an excitation taking
place at a, to b, or of one taking place at b, to a. By means of this
frequent sympathetic excitation, the resistance of the path ab to
conduction is diminished, and accordingly every excitation taking
place in a or ^ will follow the path ab as the best conductor.
Expressed in the language of psychology, — if a given idea a is
present in consciousness this moment, the next idea to be associ-
ated with it will be b, which has already often appeared sim-
ultaneously with a.^ But this is nothing more or less than the law
of external association of ideas stated above, which, as we have
seen, governs the process of association almost exclusively.

It is unnecessary to deduce a similar physiological basis for the
law of internal association of ideas. On the one hand we should
only repeat essentially that which has already been stated con-
cerning the fitness of paths for the association of the first idea
with a given initial sensation ; on the other hand this internal
association plays a very insignificant part in thought. The
internal association of ideas can sometimes predominate over the
external in cases of mental disease, especially whenever the
so-called "flight of ideas" (Ideenflucht) rules. These maniacs
at times combine rhyming words in entirely senseless associations,
— hound — bound — sound, for example. Here the similarity of

* Ultimately, of course, this coexistence of the ideas a and b may be
reduced to the coexistence of the sensations from which they originated.

The Association of Ideas.

107

the ideas of articulation produces these combinations. Formerly
association by contrast was also assumed as co-ordinate to the
association by similarity. Contrast, however, is only a special
case of similarity. Only, and in fact, just those ideas contrast that
differ in one point while they are similar in very many other
points. Therefore association by contrast is but a special case
of association by similarity.

The following proposition is merely a deduction from the chief
law of the association of ideas. Complex ideas that have certain
component ideas in common also reproduce each other recipro-
cally. Thus the idea of a sleeping person may reproduce that of
a corpse. The idea of a sleeping person is to be regarded.

psycho-physiologically, as composed of very many component
ideas that correspond to numerous excitations in very different
parts of the cerebral cortex. The same is true of the complex
idea of a corpse. In the above diagram (fig. 20), for example,
the excitation of the ganglion-cells a, b, c, d, corresponds to the
idea of sleep ; the excitation of the cells e, /, g to the idea of
death, so that the excitation of the cell c corresponds to the
component idea of rest common to both the complex ideas of
sleep and death. Let us now ask whether it is an association of
similarity or of simultaneousness when the idea of sleep repro-
duces that of death ? It is obviously an association of simul-
taneousness, for the component ideas a, b, c, d are associated
with one another, and the component ideas c, e, f, g, with one

Fig. 20.

2o8 Introditction to Physiological Psychology.

another according to the law of synchronism. Now if the com-
ponent ideas a, b, c, d, which together compose the idea of sleep,
are present in consciousness during the first moment, each one of
these component ideas is capable of reproducing in the second
moment another series of ideas with which it has been previously
associated according to the law of synchronism. But the com-
ponent idea c is also associated with e, f, and g in accordance
with the law of simultaneousness, and is therefore able to repro-
duce these component ideas also, and hence ultinfiately the idea of
death. Hence the principle of simultaneousness is quite sufificient
to explain the association of two such ideas as " sleep " and
" death." Expressed in more general terms, the association of
those complex ideas which have one or more component ideas in
common, is effected according to the law of synchronism. These
complex ideas, on account of their common component ideas,
are obviously internally related or similar to each other ; and
yet, as we now see, their association is accomplished according
to the law of simultaneousness, and not according to the law of
similarity. The foregoing statements now enable us to fully
understand our previous assertion that the association of ideas by
resemblance is extremely rare. The resemblance of ideas depends
chiefly upon common components, and complex ideas that have
common component ideas reproduce each other mutually by an
association of contiguity.^

We have still a few words to add with reference to the principle
of synchronism that governs the association of ideas to so great
an extent. This principle is not to be understood as signifying
that the simultaneousness must be complete or absolutely exact
in every case. On the contrary, ideas mutually reproduce one
another also when they themselves, or the sensations by which
they were produced, follow one after the other in direct succession.
The idea of the blow see>t, and that of the blow felt, are
essentially connected by such an association of succession in

1 J. Stuart Mill and Bain, on the contrary, have in vain attempted to
reduce all association by contiguity essentially to association by resemblance.
James Mill (Analysis of the Human Mind, 1829), on the contrary, recognizes
only association " per contiguitatem."

The Association of Ideas.

209

time. This direct succession operates quite the same as simul-
taneousness; in this case also a certain path of association is
specifically fitted for conduction. The word " contiguity " very
suitably comprehends both ideas, simultaneousness and direct
succession. Such ideas as " lightning " and " thunder," produced
by sensations that do not follow one after another in direct
succession, but are separated by a greater or less interval of time,
owe their association to the fact that they are generally and pre-
ferably combined into a concrete conception (thunderstorm), in
the manner formerly discussed, by means of a common idea of
articulation. The ideas "lightning" and "thunder" are syn-
chronically contained in the conception of thunderstorm, though
the sensations that lie at the foundation of these ideas in reality
always occur successively.

In our further discussions we shall proceed entirely from the
chief law as just discussed, that the successive members of a series
of ideas are associated by simultaneousness or contiguity. Let
us now recollect once more that the above presentation of the
law of association by synchronism represents the simplest case of
association. We conceived the simple idea present during
the first moment, to be followed by the simple idea b in the
second moment, and both a and b to be located each in one
cortical element. But most of our ideas are in fact not simple
but very complex ; accordingly, as we have seen, each complex
idea is not connected with one, but with many elements scattered
over the entire cerebral cortex. Most ideas are units only in
so far as they are psychical phenomena, not as physiological
phenomena. Accordingly the association by simultaneousness
does not occur in reality between two simple elements a and b.
but between the numberless component ideas, or component ex-
citations contained in a and b. Without further explanation we
can see that the deductions made above are also equally valid for
the most complicated ideational combinations. But now let us
consider that every total idea, as a, is not only associated with one
other total idea b, but also with many, b, c, d, etc., and that
furthermore all the component ideas contained in a (a^, a^, ag.

210 Introduction to Physiological Psychology.

etc.), participate in a large number of other associations, in part
with total ideas, in part with component ideas. The question
now arises at once, — which one of the many ideas associated with
a or its components will actually follow a in consciousness ? In
other words, why is a followed by b in one case, and by c in another,
etc. ? Why is the image of a friend followed in one case by the
idea of a landscape that we have seen in his company, in another
case by the idea of the city in which he now lives, and in a third
by thie motor idea of going to him ? In a certain sense there is a
contest between numerous ideas for the next place in the moment
following the appearance of a. As the simplest self-observation
teaches, only one of these ideas is victorious ; this one may be
very complex, i.e. numerous component ideas may be excited
sympathetically ; but with the exception of this one, all other
ideas remain latent as purely physiological dispositions without a
psychical correlative. They remain E^s without becoming Els.
Now what decides in favour of oJie idea to-day, and in favour
of another to-morrow ? One theory, that may be designated as
the theory of apperception, and which is still very popular in
Germany, assumes that a faculty of apperception has control
over the association, and, as a superior power, decides or chooses
to turn the attention now to this, now to that idea. Thus to a
certain extent it controls the association of ideas. It can be
easily seen that this theory creates a very problematical, hypo-
thetical faculty of the soul, thereby rendering a relapse to the
old unscientific psychology inevitable. We must therefore ask
whether the elements contained in the association of ideas itself
are not sufficient for the explanation of this " choice " from among
a large number of ideas. An accurate investigation shows be-
yond a doubt that this choice may be very satisfactorily explained
by facts with which we are already familiar. In the first moment
we have the idea a ; of the ideas b, c, d, e, etc., that may be pos-
sibly reproduced in the second moment, some are very closely
associated with a because they have very often appeared simul-
tanecfasly with it. Here the time that has elapsed since their last
simultaneous appearance is also of undoubted importance. The

The Association of Ideas.

211

cultivated tendency of the associative paths is also gradually lost
if there is no simultaneous excitation. We could easily conceive
the idea following a to be already unconditionally determined by
this factor. Ideas that formerly often appeared simultaneously
with a, but that have seldom appeared recently, will generally be
overcome in the contest. How many of the oft-repeated associa-
tions of childhood are " forgotten," as we say, at a more advanced
age. The path of association has lost its capacity for conduction
in consequence of the material changes that have been in progress
many years, and the absence of any new actual excitations.
We could easily conceive the idea following a to be already
unequivocally determined by the intensity of this associative
relationship. If this was the only determinative factor, that idea,
as b, which has most frequently and recently appeared simul-
taneously with a, would always immediately follow the idea a.
But other just as essential factors must be considered here. One
of the chief among these is the clearness of the different mental
images in question. Although clearness has less significance for
the chief form of ideation, simultaneous association, the clearness
of latent ideas is the most important factor in associations of
similarity, and hence especially in recognition. Only when the
ganglion-cell has preserved its peculiar disposition El and the
paths which lead from it, their distinctive sensibility, is association
by similarity possible. The more this distinctive disposition and
sensitiveness are retained, so much the greater chance has the
idea to be aroused by the corresponding sensation. We shall
meet this factor again in the discussion of attention. Of much
greater importance as a determinative factor in the usual course
of ideation is furthermore the emoiio?ial tone of the ideas. Those
ideas that are accompanied by the more vivid emotional tones, be
they positive or negative, always have the best chance in the
contest of association, and are far more liable to leave their latent
state El, and becomes ^,'s. Let us think, for example, of the
university town in which we have formerly studied; the verbal
idea of the name of the town will, in by far the majority of cases,
remind us first of our pleasant or unpleasant experiences there.

212 Introduction to Physiological Psychology.

All those ideas will first occur to us that are accompanied by any
comparatively intense emotional tone. In short, we give our
attention to those ideas that are most interesting to us.

Therefore the choice of ideas is not alone determined by the
energy with which the latent ideas in question are associated with

a, but also by their clearness and, especially, tone of feeling. The
co-operation of all these factors alone is sufficient to make sure of
great variability in the association of ideas ; but there is still a fourth
important factor to which we must now turn our attention. Let

b, c, d, e, f be five latent ideas, that may be considered as possible
successors of a. As a rule, these ideas, b, c, d, e,f themselves,
are associated with one another by direct or indirect paths of
association. In this connection we shall make use of an impor-
tant law which we derive from the general physiology of the
nerves. A statement of this law, suitable for our purpose, is as
follows : — If an excitation of a definite intensity (;«) take place
in one cortical element, b, and another excitation of a different
definite intensity {n) take place at the same time in another cor-
tical element, c, which is connected by a path of conduction with
b, the two intensities of excitation may reciprocally modify each
other. This modification may manifest itself either by arresting
or by inciting the excitation. Let us now return to the latent
ideational excitations, b, c, d, e, /, all of which, in a certain sense,
desire to become psychical. In accordance with the law that we
have just cited, these latent ideas, which are at first material ex-
citations, all stand in a complicated reciprocal relation ; they
mutually inhibit or incite each other.^ In consequence of this
reciprocally inhibitory and incitant influence, an idea that is af-
fected chiefly by inhibitions may be overcome in the contest of ideas
despite its greater distinctness, its more vivid emotional tone and
its closer association with the initial idea a. On the contrary, an
idea that is perhaps less favourably conditioned as regards these

* To the above should also be added particularly the arrestive or inciiant
influence that is exerted upon the nascent ideas to a great extent by those pre-
decessors of a that were actual ideas shortly before a's appearance.

The Association of Ideas.

213

three factors, but that is aided by the incitant influence of other
latent ideas and by the absence of any inhibitory influence, may be
victorious, that is, it may be associated with the initial idea a
Hence a fourth factor which conditions the succession of ideas,
must always be taken into consideration. We may designate
this factor briefly as the "grouping" ' of the latent ideas. Fur-
thermore, we can easily perceive that this grouping is exceedingly
changeable. For this reason the series of ideas will constantly
change. To-day c follows a ; at some other time a will be fol-
lowed by h, which will have been freed from its inhibitions in the
meantime. Only by this means can we explain the wonderfully
great multiplicity of our thoughts. The same sensation, the same
idea can remind us of one thing to-day, and of another to-mor-
row ; to-day it can reproduce the thought of that which is nearest
our environment, to-morrow the idea of that which is most
remote. The favourableness or unfavourableness of this "group-
ing " may obviously be conceived of as a transient heightening or
diminishing of the intensity, /'.e., energy of the favoured or preferred
idea.

Wahle'^ relates a very beautiful example illustrating this in-
fluence of the grouping of latent ideas. For a long time he had
had no recollections whatever of Venice, although the Gothic
Rathhaus' of his native town, which he daily passed, with the
lattice-work on the arches of the windows, was well fitted to recall
to his mind a memory of the arches in the arcades of the Venetian
palace of the Doge. The Rathhaus brought him numberless
other associations, but never one of Venice. Suddenly, one day,
upon seeing the Rathhaus, the image of the palace of the Doge
recurred to him. After some reflection, he remembered that two
hours before he had seen a brooch, in the form of a Venetian
gondola, worn by a lady. In this case the influence of the group-
ing of latent ideas is obvious.

^ In the Original, "Constellation." — Ts.

* " Beschreibung und Eintheilung der Ideenassociation." Vierteljahrschrift
i. wiss. Phil., 1885, Jahrg. 9.
» City-hall, or town hall.— T'f.

214 Introduction to Physiological Psychology.

Herbart, the psychologist of Konigsberg, was the first to teach
this reciprocally inhibitory or incitant influence of dormant ideas,
although he did so in another form, and without any knowledge
of its physiological basis. He thought it possible, in fact, to esti-
mate the effect of an inhibition mathematically. His reasoning was
about as follows : Given two ideas, A with the intensity a, and ^
with the intensity b. Herbart now assumed that the total inhibitory
force is equal to the intensity of the stronger idea, i.e., equal to b,
for example. This arrestive force b is sustained by A and B in
common, and, in fact, in an inverse ratio to their intensity. Let
A have a portion of the inhibitory force equal to x, and B a por-
tion equal to y. Let us now compute the values of x and y.

x+y = b,
and X : y=b : a ;
hence x : x-{-y=^b : b + a, or
b^

'a + b'

J <^b.

=a + b-

Therefore A loses by the process of reciprocal inhibition

and B loses

(7 + b' 'a + b

Of course this calculation of Herbart's is undoubtedly incorrect
chiefly because the relations are far more complicated than Her-
bart assumes. Particularly the content of the two ideas is by no
means unimportant in determining the force of the inhibition. The
above computations may, however, give us some approximate idea
of the quantitative relations that exist between the inhibitory forces
of different ideas.

The succession of our ideas, or, expressed physiologically, the
path of excitation in the cerebral cortex, is unequivocally de
termined by these four factors : — associative relation, clearness,
emotional tone and grouping. The processes of thinking art?
strictly necessitated. The condition of the cerebral cortex in any
one moment necessarily follows from its condition in the pre-
ceding moment ; the idea a corresponds to the latter, the idea b

The Association of Ideas.

215

to the former, etc. We do not need any faculty of apperception,
which might be regarded as ruhng over the ideas at will, for the
explanation of either the normal or the pathological psychical
process. The victorious latent idea, whose reproductive power
as determined by all these factors was greatest, becomes an actual
idea ; its El is converted into an Ec. Again, the energy with which
this conversion takes place depends upon these same factors, and
in part also upon the energy of the association of ideas in general.
The actual idea receives greater or less energy, in the sense already
explained, according as the energy with which its transfoimation
from the latent state takes place, is greater or less.

Thus we have become familiar with the fundamental features
of the association of ideas as it takes place when introduced by
either a sensation or an idea. The process of association there-
fore presents a series of pyschical phenomena, which we can
render easily intelligible as follows : — — — /o — 1^ — A — /s — I^,
etc. We are already acquainted with the laws that determine the
choice of these 7's. We have now only one more question to
ask : Is it always necessary that only ideas follow the first sensa-
tion produced by an external stimulus ? May not one sensation
first impart another sensation before it imparts any ideas, and
without a second external stimulus ? To put the question in
general terms, can a sensation be produced without an external
stimulus? Among the normal psychical processes this phe-
nomenon is exceedingly rare. We probably recall in this con-
nection what has already been said concerning the so-called after-
sensations. If we gaze steadily at a light green square for some
time, after closing the eyes we see also a similar square in the
•complementary colour, purple. In this case one sensation appears
to directly impart a second without the intercession of a new
•stimulus. But this is not true ; on the contrary, it is highly
probable that the inner process of stimulation is not extinguished
when the external process of stimulation produced by the piece
•of green paper ceases, but that a new process of excitation — prob-
ably induced by exhaustion or weariness — as a secondary inner
stimulus produces the after-sensation. We shall therefore not

2i6 Introduction to Physiological Psychology.

occupy ourselves with this so-called " successive contrast " here
We certainly meet with cases in which sensations occur without
an adequate external stimulus when the brain is pathologically
affected ; the series of /'s is suddenly interrupted by one or
more »S's. We shall have occasion to refer to this subject briefly
when we come to the discussion of the abnormal processes of
thought.^ Our chief task in the next chapter will be to become
familiar with those facts of the association of ideas that have
reference to time.

1 See Chapter YAl. — Ts.

CHAPTER XL

RAPIDITY OF THE ASSOCIATION OF IDEAS. JUDGMENT AND

CONCLUSION.

In the last chapter we became acquainted with the chief law for
the association of ideas. It runs thus : The ideas follow one
another by association in a definite order, according to the various
combinations in which they have simultaneously occurred at some
former time. We shall now attempt to estimate the rapidity of
these successive associations. In so doing we must again pro-
ceed from the introductory sensation S, which the series of ideas
/i, /g, I3, etc., follows. We have already seen that generally a
complete recognition of .S does not take place at all ; in other
words, the idea of like sensations that have been formerly ex-
perienced is not generally reproduced at all. If we see a rose at
some distance, our thought represents at once its perfume ; we
associate the idea of the perfume of the rose, or the word-idea
" rose," directly with the sensation of sight. The idea of visual
sensations formerly produced by definite, similar roses does not
appear at all. The complete recognition involves a comparatively
complicated judgment ; the new sensation of sight must be de-
termined as like or similar to a series of former sensations of
sight. Hence the method of recognition is but little fitted for
experiments in measuring the average velocity of association. It
is much more expedient to measure the time that intervenes be-
tween one sensation and the first new idea following it. Various
apparatus, often very ingeniously constructed, have been used for
this purpose. In all of them the scheme is essentially the follow-
ing : (i) The moment at which the sensible stimulus takes effect

217

2l8

Introduction to Physiological Psychology.

IS marked upon a rotating drum ; (2) The person upon whom
the experiment is being made gives a signal-motion, previously
arranged, as soon as the first idea,/i, follows the sensible stimula-
tion. It is also expedient to command the person who is being
tested to pronounce at once distinctly the word for the first idea
that appears. The signal-motion is so arranged as to close an
electric stream, so that by this means the moment of its execution
is also marked upon the drum. If the velocity of the rotation of
the drum is known, the space lying between the two points marked
upon the drum may be employed in directly estimating the time
that has elapsed between the sense-impression and the motion.
This entire time we will designate as T. It consists of several
sections as follows : —

(1) The time which the stimulus needs in order to pass from
the peripheral sensory surface to the sensitive cortex of the
cerebrum, where it imparts a sensation.

(2) The time that elapses between the sensation and the
appearance of the first idea.

(3) The time that elapses between the appearance of the first
idea and the appearance of the ideas of motion requisite for the
production of the signal-motion and the pronunciation of the
word.

(4) The time necessary for the transmission of the central
motor excitation to the muscle, and the production of contraction
in the latter.

We shall designate these four parts as t^, t^, t^, ; hence T =
i^-ir + + 1^. We determine the sum total, T, by experiment.
We wish to determine /g. the time of association elapsing between
sensation and idea. Both and t^, the duration of centripetal
and centrifugal conduction, are known to us, approximately at
least, through physiology ; is quite unknown to us ; it obviously
represents the time of association between two ideas. Let us
now consider that the idea of motion which closes the section
is very easily excitable on account of our close attention ; in other
words, the paths leading to this idea of motion are especially
cap ible of conducting the excitation. Hence is much shorter

Rapidity of the Association of Ideas. 219

than the time of association that intervenes between any two
ideas, but it is not to be ignored on this account. For this
reason we must abandon the attempt to ascertain alone ; we
can only determine t^^-^t^. It is impossible to determine the
amount of time that intervenes between the sensation and the
first idea following ; for the present we can only measure how
much time elapses between the sensation and a motion that
directly follows the first idea imparted by the sensation.

In the light of the experimental investigations that have been
employed up to the present time, what is the magnitude of /g + ^3 ?
Unfortunately these experiments are very limited. The reason
for this scarcity of available trustworthy investigations lies
•especially in the fact that a certain theory, which is to be men-
tioned at the close of this chapter, and which is, in fact, incorrect,
has forced the experiments into a very different line. Only the
investigations of Trautscholdt ^ are applicable, in part at least, in
answering this question. Galton had already made similar
experiments before Trautscholdt. They should be mentioned
despite their obvious inexactness, because they are to be very
highly recommended as preliminary experiments which we can
easily repeat. Galton ^ wrote seventy-five words on different
strips of paper, and at intervals of several days he laid such a
strip, at first half concealed, under a book so that he could only
read the word when he leaned forward. As soon as he leaned
forward and saw the word he started a chronometer, stopping it
again only after some four ideas suggested by the visual sensa-
tion of the word, had occurred to him. The result of these
experiments showed that 660 seconds were necessary for 505
associations of ideas, according to which the average time of
association would amount to almost seconds. We recognise
the errors in this method at once. It is only necessary to men-
tion one of them. At the same time that Galton himself set the
chronometer in motion a new sensation of sight and a new
motion were introduced. Trautscholdt, on the other hand, spoke

' Philosoph, Studien. I, S. 213.

' Brain, 1879, July.

220 Introduction to Physiological Psychology.

a monosyllable to the person on whom the experiment was being
made, and the latter gave a signal by a simple motion of the
hand, thus breaking a galvanic current the moment the first idea
was awakened by the sensation of sound. The person thus tested
only gave oral expression to the associated idea after the current
had been broken by the motion of his hand. As a result, in num-
berless experiments, the entire time of reaction, from the calling of
the word to the execution of the signal motion, amounted on the
average to from o'9-i'o of a second. The following experiment
is then employed for the purpose of facilitating the computation
of the association-time. Another monosyllable is spoken to the
person whom we have previously tested, and he is requested to
make a signal at once as soon as the word is heard. By estimat-
ing the time intervening between the call and the signal move-
ment, we obtain various results varying from o"i to 0*225 seconds.
Later we shall have to consider this so-called " simple reaction-
time " ^ more exactly for the purpose of learning what can be
assigned as the cause of its variable magnitude. The first
reaction-time that we obtained above, 0*9-1 "o seconds obviously
corresponds to -1- /g -t- ^3 + The simple reaction-time corre-
sponds to t^-\-t^-\-t^, since, in fact, the time that elapses between
the sensation and the idea is omitted in the second case.

Of course we must here take into consideration that does not
have the same value in both cases. Hence, by subtracting the
physiological time from the more complicated time found above,
we can only expect an approximately correct value for t^, or the
time of association between sensation and idea. According to
the numbers given above the association-time is to be estimated
approximately at o'j-o-p seconds.^

It is not to be wondered at that the time of association is

* Also called physiological time. — Vs.

' Trautscholdt's computation is different, since he ^ees with Wundt in
assuming the interposition of an apperception that stands above the associ.i-
tion. However, the assumption that the word called must first be recog-
nised as such by an apperception is wholly arbitrary, for a special recognition
in very many cases never takes place.

Rapidity of the Association of Ideas. 221

subject to such great variations. There are individuals in whom
every sense-impression awakens ideas by association with the
greatest rapidity, and there are others that react much more
slowly in this respect. Not only does the speed of association
vary among individuals, but the time of association varies con-
siderably also in the same individual according to his state of
feeling, physiological condition, etc. We shall hear still more
concerning these differences later. From the standpoint just
mentioned it will appear to us improbable a priori that the time
of association should be invariably constant.

We have now established, at least approximately, the amount
of time that elapses between a sensation and the first idea that is
associated with it. It is a much rarer special case when the first
idea associated with the sensation is the image that former like
sensations have left in the memory, i.e. when a complete recog-
nition takes place. The attempt has also been made to deter-
mine the duration of this so-called " tiyne of recognition" but this
is just the case in which the results are most uncertain.^ We are
much more interested in the further question as to how rapidly the
ideas and continue to follow one after another as soon as

has appeared. It would obviously be natural to assume that
/g generally follows just as rapidly as follows S, for in both
cases it is merely a question of the reproduction of a latent image
of memory. The experiments in this case especially have given
very mutable results. Ideas that rarely appear together require
more than a second for their mutual reproduction, while ideas
that have been associated with one another very frequently repro-
duce each other within one-third of a second. Ideas, whose
relations to one another are very complicated, especially complex
ideas, reproduce each other much more slowly than ideas less
intricately related, as, for example, the ideas of words that rhyme.
On the other hand, a complex idea, whose component ideas are
so constituted that only a single other idea is associated with
their totality, reproduce this one idea very quickly. Therefore

* In this case the above-mentioned judgment of likeness is introduced.

222 Introduction to Physiological Psychology.

the question, " Name a work of Goethe's ! " is much more slowly
answered than the question, "What is the first drama of Goethe's?"
Association of the latter kind is said to be unequivocally deter-
mmed. The less equivocal the determination of an association
is, i.e. the smaller the number of possible associations is, just so
much more rapidly does the association take place as a rule.^
The relation between the contents of the ideas that are associated
also has considerable influence on the rapidity of association.
The same is true of the above-mentioned grouping of the latent
ideas. It is generally an unfavourable, accidental grouping of
the latent ideas that renders it occasionally difficult for us to
recall a name or any other word. But the rapidity of association
varies also for the same act of ideation ; it is different in different
individuals and varies in the same individual with his changing
moods. There are individuals in whom the association is accom-
plished with greater rapidity, others in whom it takes place more
slowly. To-day our thoughts seem to fly, and to-morrow when
we are tired they seem to crawl. Above all, the infl.uence of the
emotions on the rapidity of association is very important. If
ideas and sensations that are accompanied by feelings of pleasure
predominate, the thoughts flow more easily and rapidly ; on the
contrary, feelings of pain or displeasure exercise an inhibitory in-
fluence upon the association of ideas. We find the most interest-
ing illustrations of this influence of the emotional tone in the
sphere of mental diseases. Psychiaters are acquainted with two
forms of mental disturbance, known as melancholia and mania.
They possess diametrically opposite psychological characteristics
in almost every respect. Melancholia is characterized by the
morbid predominance of feelings of displeasure that border on
pain and are entirely without a motive ; mania is characterized
by the morbid predominance of feelings of joy without a motive.
In what relation do the two diseases stand as regards the rapidity
of association? Innumerable experiences demonstrate that the
association of ideas is very greatly retarded or inhibited in the

' Compare Munsterberg, I.e.

Rapidity of the Associatioji of Ideas. 223

case of melancholia, but exceedingly accelerated in the case of
mania. We therefore sometimes designate the ideas that occupy
the thoughts of an individual afflicted with mania as " flight of
ideas." This acceleration of the association of ideas reacts, on
its part, upon the content of the ideas. In fact those ideas are
associated by preference, which stand in a merely superficial
associative relation, as, for example, that of similarity or rhyme.
We have already seen above that such relations evince a remark-
able capacity for speedy association. In the following example
we have a typical case of such capricious ideation in a slighter
degree. It occurs in the letter of a young maniacal woman to-
her brother, and runs thus : " Es griisst Dich und alle die nach
mir fragen mit Zittern und Zageu. Es hatte einen Haken und
nun sind wir frei. Eure Schwester in Christo aber nicht in Misto
sonst kommt Mephisto." ^ On the contrary, a woman suffering
from melancholia often requires several minutes before she is able
to associate the necessary ideas and to give the correct answer as
to the date of her birth, for which she has been asked. We can
designate this disturbance of the association of ideas as difficult
recollection or mental inertness ; the mental images, or the so-
called memory, are still intact, but the association of these images
of memory is accomplished with extraordinary difficulty and slow-
ness. A very apt illustration is furnished by alcoholic intoxica-
tion. After the first glasses of wine have been drunk the thoughts
flow more rapidly ; the association of ideas is unusually accele-
rated, the state of feeling is pre-eminently gay. But after a
certain point has been reached the thoughts flow more slowly
again in proportion as the number of glasses increases, until

' The sense of this passage, so far as it certains any sense whatever, is
about as follows : " A greeting to you and to all who inquire after me in fear
and trembling. There has been a hitch and now we are free. Your sister in
Christ, but not in dung, else the devil will come." In this case the selection of
the words " fragen," " Zittern," " Zagen " (ask, tremble, fear) and " Christo,"
"Misto," "Mephisto" (Christ, dung, devil or Mephistopheles) seems to
have been determined entirely by the possibility of rhyme and alliteration. —
T's.

224 Introduction to Physiological Psychology.

finally an abnormal heaviness and inertness appears in the asso-
ciation of ideas.

We must now make the acquaintance of another way in which
ideation may be accelerated. Let us turn our attention to a
series of ideas I^, /g, which are connected with each

other by association. We remember that these three psychical
elements correspond to the material process Ei^, Ei^, Ei^ .
and that the EV^ originated in El'% that had no concomitant
psychical processes. Let us take, for example, the series of ideas :
cloud, rain, umbrella. The associative connection between them
is at once plain. Some one says to us, for example, that there
are clouds in the sky. The idea of clouds causes us to think of
the possibility of rain, which reminds us of our umbrella. In
fact, however, we think much more rapidly ; the intervening idea
of rain is very often entirely omitted. In this case the cloud
reminds us at once of the umbrella, although the idea of rain
does not expressly appear in our consciousness. The entire pro-
cess is obviously the following. At first Ei-^ is produced from El^
or, expressed in the language of psychology, the idea of the cloud
(/i) first appears. The material excitation is now transmitted
still further and reaches El^ ; but instead of changing the latter
to Ei^ so as to produce the idea of rain (/g), it either touches El^,
but lightly, or at least so little that Ei^ and I^, do not appear at
all. But on the contrary, only as soon as the excitation has been
conducted to El^, does the latter receive an impulse that is suffi-
ciently long and intense to convert it into Ei^, upon which the
idea of the umbrella (/s) appears. There is no good reason for
speaking of an unconscious idea of rain (/g) in this case. As we
already know, unconscious psychical processes do not exist. We
must simply grant that the intervening idea, " rain " (/g) has been
omitted ; expressed with reference to the material processes that
take place, the transformation of Eh to Ei^ has been omitted.
El was touched by the excitation in the course of its conduction
and undoubtedly influenced the latter ; at all events, it underwent
certain changes, but these changes were either not suflScient or
not of the right kind to convert El^ into Ei^ and produce the idea

Rapidity of the Association of Ideas.

225

/g. In the above process we recognise another very important
form or way in which the acceleration of ideation may be accom-
plished : intervening ideas may be omitted, and the association
of ideas thereby abbreviated. Our thinking would be an im-
mensely tedious ^ task, if we had to go through the process of re-
collecting all the intervening ideas every time. In our usual
thought we constantly skip numberless ideas ; in fact, the genius is
distinguished from other less gifted individuals in that he omits
greater series of intercedent ideas, and therefore, figuratively
speaking, advances in seven-league boots. On the other hand,
that which we call practice also frequently depends upon such an
abbreviation of the association of ideas. The practised chess-
player, for example, skips numberless intercedent ideas in his
combinations or associations, while the amateur is compelled to
think through the entire series according to the order in which
the ideas occur. If we now conceive of this process of practice
as still further perfected by the omission of all intervening ideas
whatever, including ultimately also the idea of motion which
imparts the final action, we have an automatic act. In this con-
nection it is only necessary to recall what was said in a former
chapter concerning the gradual development of automatic action
from the so-called voluntary action. It is hardly necessary to
emphasize that practice as such tends to directly facilitate the
association of ideas besides exercising an indirect influence by
abbreviating the process of thought. The shortening of the pro-
cess of ideation is also often facilitated pathologically ; in such
cases we often speak of thought as " incoherent."

Thus far we have considered the association of ideas merely
as a succession of discrete ideational elements. The only bond
connecting the successive ideas /j, /g, /g, etc., was, in accordance
with the chief law of the association of ideas, either their frequent
previous simultaneous appearance or their similarity. We have
now to learn the more complicated forms of ideation. In fact, we

' Ger. " langweilig," which in this case may also be understood in the apt
literal sense, as signifying *' great length of time." — T's.

226 Introduction to Physiological Psychology.

do not constantly think in simple, progressive series of ideas ;
a higher stage of thought consists of the so-called judgments
and conclusions. Let us now inquire whether these two chief
logical functions of judging and concluding may also be subsumed
under the processes of ideation, or whether we must regard then»
as entirely new, heterogeneous psychical faculties. Of course
we shall decide in favour of the latter only in case of necessity.
It will undoubtedly be more satisfactory if we are able to reduce
logical thought, i.e. the judgment and the conclusion, also to the
simple process known as the association of ideas. Let us begin
with a simple judgment, — for example: "The rose is beautiful."
In this judgment we have two ideas, (i) the idea "rose," and (2)
the idea "beautiful." It is evident that these two ideas are not
associated because of some merely incidental connection between
them in the sense of the simple law of ideation with which we are
thus far acquainted, but that the second idea stands in some much
more intimate relation to the first. This more intimate relation is
expressed by the word " is," it is true ; but even if we regard this
" is " as an intermediate idea, we by no means avoid the fact that
the judgment is not concerned with three ideas that are merely
arranged in succession. On the contrary, we must correctly
assume that the mediate idea " is " not only refers to the preced-
ing idea "rose," but also to the succeeding idea "beautiful."
Now is it quite impossible to explain the origin and development
of this double relation of the mediate idea " is " physiologically ?
By no means. Thus far we have not investigated the material
process that takes place in the cerebral cortex during the associa-
tion of ideas as a continous whole ; we have only selected a few
single moments of the process in which certain phases correspond
to separate ideas. It is evident that this is not quite correct.
Between the material condition Ei^ and the material condition
Ei^ there is a mediate material process, and we have no cause
whatever for assuming that this intermediate process takes place
entirely unaccompanied by a psychical correlative. On the
contrary, it is highly probable that the foundation for the con-
tinuity of our judgments, or, in other words, for the reciprocal

Rapidity of the Association of Ideas. 227

relation that exists between the ideas as combined in the
judgment, is furnished by this process of conduction. In
addition to this, all excitations in the nervous system, even those
corresponding to ideas, need a certain portion of time both to
rise and subside, to flow and ebb ; thus the rise of L can take
place during the ebb of 7i, so that a partial concurrence of two
ideational excitations in time is possible. It should finally be
considered that in the majority of judgments only the words,
i.e. the motions of articulation, form a successive series, while the
two ideas ('-rose" and " beautiful " for example) appear simul-
taneously as the component ideas of a complex idea. The
separation of the ideas and their arrangement in a continuous
series is only accomplished when they are expressed in language.
Of course the above explanation is at present purely hypothetical.
Furthermore, in view of the limited knowledge on this subject
which we now possess, we need not yet attempt to give a really
adequate psycho-physiological explanation of the continuity of our
thought in judgment On the contrary, it is sufficient to have
demonstrated the possibility of such an explanation. We have
shown that such an explanation is possible upon the grounds of
physiological psychology and without exceeding the bounds of
the association of ideas or fabricating a new, entirely hypothetical
psychical faculty.

From the above standpoint, therefore, the formulation of
judgments is to be regarded as a higher stage in the development
of that which we commonly designate as ideation or the associa-
tion of ideas ; the former process is by no means wholly dissimilar
to the latter. But what has thus far been said does not constitute
a complete presentation of the psychological characteristics of
the judgment. An essential feature of the judgment is its depen-
dence on a much more intimate and abundant association of its
component ideas. Supported by this close relation of its com-
ponent ideas, we are able to claim for the judgment the right to
be valued as correct. Psychologically " to be held as correct "
simply means the absence of contradictory ideas. The common
series of associated ideas, " rose— leaf— summer," depends on no
other condition of association than some former incidentally

228 Introduction to Physiological Psychology.

simultaneous appearance of the ideas or their corresponding
sensations. The judgment, "the rose has dentate leaves," is
distinguished from the simple series of associated ideas just
mentioned (i) by the thorough relation of the ideas to each other
(2) by the much more frequent former simultaneous appearance
of the ideas contained in the judgment or of the sensations that
produced them. In fact, contradictory ideas are entirely wanting
in consequence of the very intimate association of the ideas
composing the judgment; this absence of contradictory ideas (in
the above case, for example, the idea of smooth-edged leaves)
gives us the right psychologically to consider our judgments
correct The association, " rose — leaf — summer," rarely occurs
without other intermediate members ; for this reason it bears the
character of a chance association. On the contrary, the associa-
tion of ideas in the case of the judgment is, almost without
exception, an intimate association of simultaneous ideas, and an
association in which conceptions of relation are of especial
importance. Of all possible associations, a judgment is just that
select association in which no contradictory ideas occur.^

Hence we find that our conception of the association of ideas
must be somewhat modified, if it is to include the judgment also.
The association of ideas is not a process in which we consciously
leap, as it were, from one discrete idea to another.' On the con-
trary, we must claim for the judgment, as a psychical process at
least, the same continuity that the concomitant material process
undoubtedly possesses. The association of ideas that are less
closely related, with which we first became familiar, is therefore
but one form, and the so-called judgment a second form of
ideation.

" School-logic " teaches further, that judgments are combined
to form conclusions. Let us recollect the well-known, —

' This jif/tff/zfwis especially emphasized by Herbart. Lipps (" Grundthat-
sachen des Seelenlebens," Bonn, 1886), has emphasized with undue partiality,
as characteristic of the judgment, the fact that we are conscious of its reality
and hence of its validity.

* In pathological cases salient association of ideas often entirely suppresses j
rational association, especially in aggravated cases of "flight of ideas. " This
symptom is also called " Verbigeration. "

Rapidity of the Association of Ideas. 229

Caius is a man —
All men are mortal —
Hence Caius is mortal.

It is indeed without doubt an interesting fact that our logical
series of judgments can be arranged according to the above
scheme, or any one of the other schemes familiar to the logicians.
For certain purposes it may even be quite advantageous to arrange
our series of judgments according to such a scheme. But we
must decidedly oppose the idea, that our common^ naive course
of thought ever conforms to these syllogistic forms of the school-
logic. When we think naturally, we know nothing of a major
premise or a minor premise ; we simply make use of the associa-
tion of judgments, — " Caius — man— mortal," and the conclusion
has been reached. For example, we see " Caius " ; with the
visual sensation is associated the idea " man," with the latter
the idea " mortal." Therefore every conclusion, like every
judgment, is merely the association of ideas ; but as a distinct
form of association it is of almost no importance whatever
psychologically.

It is of course impossible here to develop the entire structure
of scholastic logic upon this psychological basis. We have only
space for a cursory glance over the field of logic here, as formerly
over the field of esthetics. It is for physiological psychology to
establish merely how thought actually takes place and what
material processes accompany it. The problem of logic, as to
which formal processes of thought lead to the so-called true judg-
ment and which do not. does not belong to the sphere of
psychology. The great problem of physiological psychology
consists in the reduction of the many different forms of thought,
including even the most complicated demonstration, all to the
simple ideation or the association of ideas and its laws. But physio-
logical psychology is still far from having reached a complete
solution of this problem ; for this reason we have only been able
to sketch in about what direction the solution is to be sought. It
is probable that some of our deductions will undergo still further
modification when the light of continued investigations is brought

230 Introduction to Physiological Psychology.

to bear on them. The fundamental conception that all processes
of thought can be reduced psychologically to the association of
ideas, will at all events endure.

Of course we shall not attempt to disguise the fact that
particularly in Germany another school of psychology is pre-
dominant, that does not recognise this fundamental thought.
Wundt 1 stands at the head of this school. He and his scholars
claim that there is a large number of ideational combinations that
cannot be explained merely by the association of ideas. They
therefore assume a special psychical faculty, superior to the
association of ideas, which they designate as apperception. The
association of ideas constantly supplies this apperception with new
material for ideas, and the apperception itself selects from this
material. It turns tirst to this then to that idea, and is then called
attention ; or again, it combines one idea with another and forms
a compound idea ; finally it imparts volitional motor impulses
through the nerves and is then called will. We see that this
hypothesis is very convenient. All that cannot be easily ex-
plained by the association of ideas is ascribed to the activity of
a higher power or special psychical faculty. The latter, however,
is an entirely unknown factor. All of the arguments that have
so often and so justly been advanced against the theory which
assumed so-called " faculties of the soul," may be also directed
against this metaphysical theory of apperception. The theory of
apperception also arbitrarily assumes an active subject as the
efficient cause of a series of conscious processes. Wundt has
also given his theory a physiological tinge by adding the hypothesis
that this apperception is located in the frontal lobes of the brain.
In making this assumption, however, he only succeeds in placing
the contradictory features of the entire conception in a still more
glaring light. A supposed psychical faculty which, according to
the very hypothesis in which it is assumed, acts independently oi'

' Wundt's "Grundziige der physiolog. Psychologic " ; besides in this worlv.
a presentation of the theory in question is also to be found in WUNm '.-

"Logik, ' Bd. I, s. 10 nr.

Rapidity of the Association of Ideas. 231

all mechanical causality, is thus localized in a definite part of the
brain for the purpose of gaining some connection with the
physiology of the brain and of rendering the theory more
harmonious with the spirit of natural science characteristic of the
present age. But the physiology of the brain must reject this
connection and with it the entire theory and hypothesis of ap-
perception. The frontal lobes of the brain do not possess this
function at all. Large portions of the frontal lobes of the brain
may be destroyed without disturbing ^ that activity of the intellect
which the school of Wundt ascribes to apperception. Changes in
character and certain mental disturbances may appear in any
disease of the brain, no matter where it is located. A great deal
of argument has often been based upon the fact that part of the
encephalon of lower animals corresponding to the frontal part of
the human brain is relatively dwarfed. This fact has been used
in attempting to explain the supposed absence of apperception in
the lower animals. This application of the fact, however, is not
justifiable. The motions used in speaking and writing, and finally
also the motions of the trunk, are imparted by the cortex of the
frontal brain j accordingly speech, writing and upright locomotioii
are wanting in the animals below man. If we take the absence
of these three characteristics into consideration, the frontal brain
of the ape is, relatively at least, just as large as that of man.
Therefore there is no ground whatever for assuming that this
hypothetical apperception is localized in the frontal brain. Thus
another prop, which was subsequently introduced for the support
of the theory, falls. For reasons above discussed, we shall reject
this metaphysical assumption of a psychical faculty. Instead we
have attempted to explain the more complicated processes of
thought, without apperception, by making use of the association
of ideas. To do this requires, of course, much more pains than
to simply refer or ascribe all of the more complicated processes
of thought to a problematic apperception. Furthermore, in
making such an assumption we make no progress toward an

• Compare L. Wet,t, Dissertation, Zurich, 1888.

232 Introduction to Physiological Psychology.

explanation of the processes that occupy our attention ; on the
contrary, we deprive ourselves irretrievably of the possibility of
understanding them in the light of psycho-physiological research.
Let us repeat — many of our explanations may still need cor-
rection, but the way now opened before us is undoubtedly
correct ; it is the only acceptable way for physiological psychology.
Our explanations at least demonstrate that we can succeed with-
out the assumption of a new psychical faculty, even though the
progress of knowledge may correct them somewhat ; we have
demonstrated the possibility of reducing all the so-called higher
processes of thought to the association of ideas. In a certain
sense we regard the ideational life as republican. All of the
latent ideas enter into the contest, each one wishes to push its
way into consciousness ; but it is not a higher power which hovers
over the ideas and determines the victory of one idea over
another and thus fixes the order in which they appear, but merely
the clearness, the accompanying emotional tone, the grouping and
the associative relations of the ideas themselves.

CHAPTER XII.

ATTENTION — VOLUNTARY THOUGHT — THE EGO — MEMORY.

In the last chapters we became acquainted with the chief char-
acteristics of the association of ideas. We investigated the
simple recognition and reproduction of mental images. We
found that the reproduced images of memory appear together
first in less compact series, then in combinations of a higher
order, the judgments. Thus far in our discussions we have
intentionally ignored one element which, however, plays an im-
portant part in the processes of thought. This element is that
which we commonly call ^'■attention." We say that "we turn our
attention now to this sensation now to that sensation," or that
" we turn the attention now to this line of thought now to that."
It seems to be left to our option; apparently we direct our
attention to this or that sensation, this or that idea by preference.
Hence we might fear that we shall yet be compelled to decide
in favour of assuming an apperception, which is superior to the
association, and which attends to, or disregards the sensations
and ideas at will. This is not the case however. Let us first
investigate the attention as directed to the sensations, making use
for this purpose of a definite example. Suppose the left eye to
be closed and the right eye to be open and motionlessly fixed upon
the field of vision before us. Let the field of vision be designated
by the circle, fig. 21, which contains a large number of objects.
In the figure, but three of them are designated by letters ; one,
situated somewhat apart from the centre of the field of vision and
corresponding to the macula lutea of the retina, is designated by
C, and two others, situated anywhere near the periphery, by

233

234 Introduction to Physiological Psychology.

and P^. Now it is an undoubted fact that we generally turn our
attention to the object C situated in the middle of the field of
vision. We fix the eye, as it is commonly expressed, on the
object C, and we believe tliat we are able to do so with greater
or less energy. Does this mean that an apperception generally
prefers this C, to which it accordingly voluntarily turns the at-
tention ? Certainly not. On the contrary the facts in the case
are as follows : C is the point situated near the centre of the field
of vision corresponding to the macula liitea of the retina ; hence,
according to the teachings of physiological optics, it is much
more distinctly seen than all other points situated nearer the

Fig. 21.

periphery. P-^ and P^ in general cast but comparatively confused
and indistinct images upon the retina. Consequently the sensa-
tion produced by C, i.e. the material cortical excitation Ec
corresponding to the sensation, will also be far more intense and
correspond much more closely to former sensations produced by
similar objects than the sensations produced by the objects Py
and P<^ which are located nearer the periphery. In this case,
therefore, we find several sensations active at the same time and,
in a certain sense, entering into a contest for the privilege of
awakening the next image of memory and determining the course
of ideation. The result of this contest, as we have termed it,
depends upon two factors, (i) the intensity of the sensation, and
(2) its agreement with some latent mental image in the cerebral
cortex. It is obvious that the stronger sensations, or the more

Attention— Voluntary Thought— The Ego— Memory. 235

intense material process accompanying them, possess a far
greater ability for converting latent ^/'s into Ei^ or, in other
words, for awakening the images of memory and determining the
course of ideation. But the already mentioned agreement of a
sensation with some acquired disposition is also essential. We
have often distinctly seen a tulip, for example ; hereafter it will be
quite essential whether a new visual sensation of the tulip is like
the former, i.e., equally distinct and sharp, or whether it is unlike
former visual sensations, i.e., is indistinct and confused, the object
tulip, being too far off or being seen only by the peripheral parts
of the retina. It is obvious that in the latter case recognition of
the object will be more difficult, for the sensation finds no latent
mental image with which it quite agrees ; let us recall in this
connection what was formerly said concerning the training of the
nerve-paths necessary for recognition. The indistinct sensation of
the tulip finds no path exactly trained for its purpose. For this
reason, both the first reproduction, the awakening of similar images
of memory formerly experienced, and the excitation of other ideas
associated with the mental image of the tulip, will be rendered
exceedingly difficult. This agreement of a new sensation with
former sensations, or rather with the mental images of f6rmer
sensations, corresponds, in the sphere of the sensations, to that
which we met in the sphere of mental images, as the sharpness of
the idea. The two factors are exactly correlative. In fact, we
may analyze this agreement into two factors; it is important (i)
whether the new sensation resembles the old, and (2) whether
the mental images of the old are still sharp or distinct. Both
the agreement and the intensity of the sensation are the most im-
portant factors in determining which sensation will prevail in the
contest with others, i.e., draw the attention, cause the reproduction
of certain mental images, and thus determine the association of
ideas. This also explains why only the object situated in the
centre of the field of vision generally determines the association
of ideas ; it is, as physiological optics teaches, just the object
that produces the most intense and distinct sensation. The
images upon the macula lutea, and hence also their corre.sponding

236 Int7-oduction to Physiological Psychology.

sensations, are the most intense.^ It is the latter, therefore,
which, on account of their superior intensity, are ahuost the
only sensations that deposit mental images in the cerebral
cortex. Hence all future sensations of the same object agree
most closely with the appropriate mental image when they are
produced by the excitation of the macula lutea. The fact, that
in general the sensations of the macula lutea possess to so high
a degree the power of directing the attention, rests therefore
both upon this greater agreement and their greater intensity.
No ''apperception" exercises any arbitrary control over the
process whatever. The association of ideas is inevitably neces-
sitated from the beginning to the end. Such are the objective
facts accompanying the phenomena of attention. But whence
arises the peculiar sensation of self-activity characteristic of
attention? Self-observation teaches that this sensation is a
sensation of motion produced by the innervation of numerous
muscles (particularly the muscles of accommodation and the
musculi recti interni) which serve to fix the eye upon an object.
By means of this fixation of the eye, the distinctness and intensity
of the retinal images and hence of the corresponding sensations
are increased. The feeling of a greater or less tension of the
muscles regulating the eye, is itself produced by association; it is
imparted by the stimulus which acts upon the macula lutea. The
tension thus perceived, in its slighter degrees of intensity, is the
product of reflex action ; in its greatest degrees of intensity it is
voluntary action proceeding from the cortex. Particularly in the
latter case, the innervation that has taken place imparts very
numerous and intense motor sensations which are the cause of
the exceedingly intense feeling of close attention. Therefore the
feeling of attention is in fact merely a concomitant phenomenon.
The essential objective characteristic of attentive or active sensa-
tion, in distinction from the merely passive sensation, is the

^ Since they at the same time correspond most accurately to the object, the
sharpness of the sensation may also be regarded as a factor 01 attention.
^ According to M UNIC it is reflex action proceeding from the cortex.

Attention— Voluntary Thought— The Ego— Memory. 237

influence which the former exerts in determining the choice and
order of ideas by which it is followed. This influence is not at
all characteristic of a merely passive sensation to which the
attention is not directed.

In the light of what has been said above, the following will at once
prove intelligible. We will now assume that P^, one of the objects
situated near the periphery, possesses a very unusual intensity of
stimulation ; for example, a dazzling light suddenly appears near the
periphery of the field of vision. What happpens in this case ? It
is true that P is very unfavourably situated for producing an exact
image on the retina and that C's situation is far more favourable ;
but the greater intensity of light in the former case will more than
equalize the unfavourableness of situation. Despite its peripheral
location, will produce a stronger excitation of the retina and
consequently a more intense sensation than C. Hence, in this
more exceptional case, the attention is turned to the more intense
sensation P-^, despite its greater indistinctness. Again, this
" turning of the attention " is strictly necessitated ; it means
nothing more or less than (i) the sensation 7\ (and not C), by
virtue of its greater intensity, reproduces the next following
images of memory and thereby determines the further course of
the association of ideas ; (2) either automatically or voluntarily
(j.e. consciously) the eyes are turned to the dazzling light and
the motion of the eyes thus executed produces motor sensations
which constitute the peculiar feeling of activity accompanying the
change of attention. Therefore in this case also we discover
nothing more than a process of association with certain muscular
sensations. With some pains we can also occasionally succeed it>
directing the attention to the peripheral object without making
the movement of the eye necessary to bring P^ within the range
of the macula lutea. But if we observe sharply during sucli an
experiment, we perceive a constant inclination of the eye to move
so as to bring the image of the object upon the macula lutea.
Generally we are unable to entirely repress these motions ; our
eyes occasionally deviate in fact toward one side or the other,
although we again instantly correct each lateral deviation. Hence,

238 hitrodtiction to Physiological Psychology.

in this very exceptional case alao, motor sensations and motor
ideas influence the feeling which accompanies attention.

Let us now consider certain other factors, besides the intensity
of the sensation and the degree of its agreement with the ap-
propriate mental image, that help to determine the influence
which a sensation exerts upon ideation. Let us retain the
example of the eye at rest, as used above. We shall suppose
that the object situated near the periphery of the field of
vision, produces a stimulation of but very slight intensity; it
iherefore imparts a sensation that is but little fitted to draw the
attention or to determine the association of ideas. Let us now,
however, also assume that the object /2 produces a very lively
feeling of pleasure ; in other words, the sensation imparted by /g
is accompanied by a very strong positive tone of feeling. For
example, a star, faint indeed, but glimmering with the most
beautiful colours, appears within and near the periphery of the
field of vision. Despite its slight intensity of light and greater
■or less indistinctness, this retinal image will at once attract the
attention. The eye is accordingly turned toward the star and the
following ideas are determined by this sensation and not by that
imparted by C. The same thing is just as true of sensations that
are accompanied by strong negative tones of feeling; despite
their shght intensity and distinctness, such sensations, by virtue of
their strong accompanying feeling of displeasure, are able to
divert the attention from sensations that are more intense and
<iistinct, but that have a weaker emotional tone. In a certain
sense they contest, as it were, with the latter for the influence
upon the course of ideation. For example, a soft chord can
fetter the attention in the midst of numerous louder noises. We
hearken — that is, we tighten the ear-drum and turn the head in
order to hear the chord as distinctly as possible, and our thoughts
become occupied with the chord. In this case we again find all
the elements characteristic of attention in general. A sensation,
by virtue of certain of its properties (in the above case, for
■example, by virtue of its strong positive emotional tone) produces,
either by reflex or conscious action, certain motions, and, what is

Attention— Voluntary Thought— The Ego— Memory. 239

still more essential, determines the course of ideation. The motor
s-Bnsation produced by the motions gives the attention that
peculiar feeling of activity by which it is characterized. A very
similar process takes place when a slight, but very unpleasant,
discord occurs in the midst of a number of tones or noises. It
likewise attracts the attention very forcibly. Hence we find that
still a third factor also largely shares in the influence which the
sensation exerts upon the association of ideas ; the ifite7isity of the
emotional tone is to be added to the distinctness and intensity of
the sensation. But we have not yet exhausted all the factors
that mfluence the attention. The decision of the question as to
which sensation shall determine ideation is by no means wholly
independent of the ideas that have preceded in the last few
minutes or hours. It is not a matter of indifference as to which
of these ideas are still very active and which are not, or as tO'
which are mutually inhibitory or mutually incitant. In brief, that
which we formerly designated as the groupmg of the ideas, likewise
exerts an influence upon the attention. Let us take another
simple example. While we are taking a walk, numberless visual
sensations constantly throng oar consciousness. If the idea of
meeting other strollers, for example, is in condition to be easily
reproduced, the visual sensation of an approaching friend or
stranger attracts our attention and determines our further move-
ments and ideas j but if this idea is checked by the predominance
of other thoughts, we pass the approaching person in a state of
absent-mindedness without heeding him ; we turn our attention to
the landscape, for example, which happens to produce a visual
sensation more favourable to the momentary grouping of the
latent ideas. Under certain circumstances the visual sensation of
a friend may be ever so distinct and intense and possess ever so
strong an emotional tone, and yet in consequence of an unfavour-
able grouping of the latent ideas, other sensations will prevail,
and determine the course of ideation. The phenomena which
we designate as "seeking " and " intense expectation " are typical
cases of the influence exerted upon the attention by the grouping
of the ideas. The visual idea of the object sought or expected.

240 Introduction to Physiological Psychology.

constantly fills the mind ; numberless sensations appear, but de-
spite their distinctness and intensity, none of them fix the attention.
On the other hand, as soon as the image of the object sought but
appears near, and within tlie periphery of the field of vision, be it
ever so weak and indistinct, it is at once noticed and the atten-
tion directed to it; it then determines further movements and
ideas. In this case the grouping of the latent ideas is the factor
that governs the attention ; it is aided especially by the feeling of
pleasure which accompanies the desired sensation, and which is,
in fact, the cause of the seeking.

We shall designate the totality of all factors that decide whether
:a sensation shall become the object of attention and determine
the following association of ideas or not, as the associative
impulse of the sensation. We have seen that the associative im-
pulse, or the associative power of a sensation is dependent on (i)
the intensity, (2) the agreement with the latent mental image,* (3)
the strength of the accompanying emotional tone, and finally (4)
the chance grouping of the latent ideas.

These four factors decide in favour of one among several
concurrent sensations. We have undoubtedly already noticed
the analogy that exists between the contest of the sensations
for the attention ^ and the contest of the latent ideas for the
position /g. Tliis analogy is easily understood if we recollect
that the succession of ideas can be conceived of as the attention
passing from idea to idea. There is, however, an essential difler-
ence between the two contests ; the sensations that enter into a
•contest are all conscious, i.e. actually present as psychical pheno-
mena, while the ideas that are struggling for the supremacy, with
the exception of the one momentarily prevailing, are psycliically
'latent. Furthermore, the external associative relationship, de-
pendent on simultaneity is the determinative factor in the contest

J In this case the "distinctness" of a sensation, as one of the conditions
•of the " associative impulse," might also be designated as the " associative
iielationship."

2 In a certain sense, for the right of naming the first idea, /j.

Attention-^Volujitary Thought— The Ego -Memory. 241

of the ideas, the internal associative relationship, dependent on
similarity, in attention.

Tlius far we have not especially mentioned the contrast of
successive or simultaneous sensations among the factors that
constitute the associative power of a sensation, although it un-
doubtedly exerts some influence upon the attention. We find
that a small black spot upon a white cloth is especially striking ;
and the more suddenly an object appears with its full intensity
upon a differently coloured background, the more forcibly does it
attract the attention. It is obvious that this influence exercised
by contrasting sensations, whether simultaneous or successive, can
be reduced to the factors already mentioned above. As we have
already seen, a sensation that is characterized by great uniformity
or monotony in its relations to space or time, rapidly loses its
intensity and the strength of its accompanying emotional tone.
The activity of the ideational process is soon exhausted, the
favourable grouping of latent ideas is expended. It can therefore
be easily understood why each new sensation that suddenly
appears in contrast with these monotonous sensations prevails
over them in the contest for the attention. Generally, in the
case of the contrast of simultaneous sensations, both the strong
emotional tone and the grouping of latent ideas exert an influence
in favour of the single contrasting sensation.

Let us again emphasize that in by far the greater number of cases,
the first idea to be imparted by the prevailing sensation is an idea of
motion. In fact, it is generally the idea of just that motion which
is fitted to adjust the organ of sense so as to receive the prevail-
ing stimulus, thus heightening the distinctness and intensity of
the sensation still further. We already know, furthermore, that
the motor idea (its sufficient vivacity being assumed) is itself
an ample cause of the respective motion. Therefore the first
consequence of most sensations to which we direct the attention,^

' We designate those sensations to which the attention has been turned as
ferceptwn ( Wahrnehmungen). The word perception, however, has been used
by psychologists in so many different meanings that its applicability has been
impaired.

242 Introduction to Physiological Psychology.

is a motion which serves to place the organ of sense in
a favourable position. These movements are most highly de-
veloped for the eye and ear. When the attention is drawn to
sensations of the skin, a general tonic contraction of the neigh-
bouring muscles usually first appears ; only then does the associ-
ation of ideas follow. According to these facts we may conclude
that each sensation possesses a certain motor power or motor im-
pulse. It is without doubt extraordinarily fitting and the outcome
of a long process of natural selection, that this motor impulse
always tends to render the sensation more distinct and intense by
a more favourable adjustment of the sense-organ with reference
to the stimulus. The sensation that is to occupy our thoughts is,
to a certain extent, preparatively intensified before any thought
occurs. We can easily imagine how the phylogenetic develop-
ment of this expedient connection between the motor impulse
and the subsequent association of ideas has been accomplished.^
It is only necessary here to emphasize once more that many of these
accommodative movements take place without our being conscious
of them j in other words, they are purely' material processes^ either
reflex or automatic actions. The motor idea is omitted from
consciousness; only the fact that the movement placing the
organ of sense in a favourable position has been accomplished,
makes us aware that a latent motor idea has been excited. For
example, the turning of the head in the direction of a sound is in
many cases an entirely unconscious act. Finally, there are certain
movements by means of which certain organs are adjusted, such
as those executed by the optic muscles of accommodation, which
take place constantly, or almost constantly, as purely reflex acts.

We have already become acquainted with the further course of
the association of ideas after having been once excited by sensa-
tions, in previous chapters. This further process of thought may
be of two kinds. We generally distinguish between so-called
voluntary thought and involimiary thought. This is not a funda

^ At first, especially because it renders possible more complicated and more
exact defensive movements.

Attention— Voluntary Thought— The Ego— Memory. 243

mental distinction, however. Our thinking generally seems to
us to be voluntary when we are occupied with those phenomena
of consciousness which we designate as " reflecting," " trying to
recollect," " making up the mind," etc. The laborious mental
occupation of the child with its puzzle, or of the adult thinker
with his problem, are both simply varieties of that psychical pro-
cess which we variously designate as "reflection," "contemplation,"
" meditation," and " cogitation." Now what causes the process
of reflection to seem like a voluntary act Let us have recourse
to accurate introspection. The so-called voluntary thought is
characterized by the fact that the desired idea is always known
to be already contained in the initial ideas that introduce the
associative series, as well as in the following ideas ; the associations
necessary for its discovery, however, are often very complicated.
But there is still another important factor characteristic of volun-
tary thought, as it is called. When we are occupied with deep
reflections, a series of slight muscular innervations appears ; these
are only to be discovered upon close introspection. This muscular
'nnervation is seldom entirely absent whenever we are occupied
with so-called voluntary thoughts. We wrinkle the brow slightly,
press the teeth somewhat more firmly together, and frequently
there appears a slight tonic contraction of the lips and the muscles
of the neck.^ All these innervations of the muscles are gener-
ally accomplished unconsciously. Furthermore, we have no isolated
sensations of the single motions, but their combined action pro-
duces that peculiar total sensation which we generally have when
"trying to recollect," or when absorbed in so-called voluntary
reflections. The English language very aptly designates this con-

^ Compare the somewhat similar deductions in Munsterberg's " Die
"Willenshandlunc;," Freiburg, 188S.

* It is interesting to note that among the lower animals, particularly in the
case of the ape, the wrinkling of the brow, as a motion expressive of attention
does not seem to occur. Darwin, however, observed a young orang-outang
which undoubtedly produced motions expressive of aLtenlion by closing and
protrudmg the lips.

244 Introduction to Physiological Psychology.

dition as "attention" (primarily from tendo, to stretch).^ This
combination of motor sensations often gives our thought the char-
acter of attentiveness and an appearance of volition and self-
activity which in fact do not belong to it at all. We cannot
think as we will, but we tnust think as just those associations
which happen to be present, prescribe.

But there is still another circumstance which would seem to
strengthen this appearance of volition. In the course of the
ontogenetic development of the individual, a peculiar complex
of associated images of memory is constructed, which we desig-
nate as the idea of the " Ego." The child laboriously acquires
the idea of its own body as distinct and separate from the rest
of the world about it. In the beginning the child knows no
difference between the hand touching and the object touched.
The moon which it tries to reach, and its own foot which it
grasps, seem to the child to be equally near to it. This condition
of affairs changes but gradually. The child learns to distinguish
between those objects, or spatial complexes of visual and tactual
sensations, that are associated with active sensations of motion
and those that generally appear without active motor sensations.
The former, in their totality, correspond to the idea of one's own
body j the latter, to the idea of all objects of the external world.
Many other factors tend to fix and complete this distinction.
When two complexes of visual sensations of the second kind, i.e.
two external objects touch each other, no sensation of touch
appears. If on the other hand two complexes of visual sensations
of the first kind, i.e. two parts of one's own body, as the hand
and face for example, touch each other, a double sensation of touch

^ It is very initeresting to note that in the case of the observations made by
Lange, aheady mentioned, the appearance of visual images of memory is fre-
quently accompanied by slight unconscious movements of the eyes. For ex-
ample, one thinks of a long street, and at the same time unconsciously moves
the eyes sliglitly from one side to the other, as if following the line of building-.

The English expression "attention" corresponds exactly to the Gcrm.-iii
" Spanimng " — 'J^s.

Attention— Voluntary Thought— The Ego— Memory. 245

appears. Finally, if a complex of visual sensations of the first
kind, {e.g. the hand) touch one of the second kind {e.g. any ob-
ject), a simple sensacion of touch appears. The totality of all
sensations of the first class — in other words, the sum total of all
the distinct and separate sensations of one's own body, leaves a
composite image in memory, the idea of one's own corporeal ego.'
At first this idea varies considerably. Primarily the ego of child-
hood or babyhood is nothing more than alternate feelings of
hunger and satiation, or pain and joy in beholding a light or
in self-motion. The idea of the surface of one's own body as
the limit of a definite portion of space, and with it the idea of
one's own body as a whole, are only developed gradually. To the
latter is also added by degrees the slowly developing idea of one's
own mental ego — that is, a total idea of all the images of memory
deposited at any given time in the cerebral cortex. This complex
idea of the intellectual ego is much more laboriously acquired
than that of the corporeal ego. At this point we must refer to
what has already been said in a former chapter concerning the
development of conceptions without an external or objective
foundation in the sensations. We demonstrated that our entire
psychical being is composed of sensations and ideas ; that the latter
are primarily produced as a rule by the combination of sensationSj
but that combinations of ideas also take place within the mind
itself, and in their totality correspond to no actually experienced
combination of sensations. On the contrary, these ideas represent
wholly subjective ideational combinations. In this manner a com-
plex of ideas is also developed, in which our paramount, most
intense lines of thought, accompanied by the strongest emotions,
participate as elements. The sum total of our present inclinations
and our actually dominant ideas constitutes an essential part of
our idea of the ego. But besides the idea of one's present cor-
poreal and mental ego, there is still a third member participating
in the usual ego-idea. This is the very essential total idea that
has been deposited in memory by the succession of one's most

' Compare Meynert, " Gehirn und GcsiUung," Vienna (18S9).

246 Introduction to Physiological Psychology.

importiinl mental and physical experiences in the past. It will
seem striking to us, perhaps, that the ego-idea, which is designated
by the short, small word " I," should be such a complex structure,
composed of three chief members in which thousands and thou-
sands of component ideas participate. But let us reflect ; the
word is, indeed, short, but that its intellectual content must be
very complex is readily shown by the fact that we should be at
once embarrassed if called upon to state the mental content of our
so-called " idea of the ego." We should at once think of the
body, of our relation to the external world and our relations to
family and to property, of our name and title, of our chief in-
clinations and dominant ideas, and finally of our past experiences.
In so doing we should demonstrate for ourselves how exceedingly
complex this idea of the ego is. The reflective person, of course,
reduces this complexity of the ego-idea to relative simplicity by
placing his own ego, as the subject of his sensations, ideas and
motions, over against all objects and other egos of the external
world. To be sure, this simplification of the ego-idea by placing
it as subject in opposition to the rest of the world as object, has
a deep foundation in epistemology ; but regarded purely in the
light of psychology, this simple ego is but a theoretical fiction.
Empirical psychology recognises only that complex ego whose
chief characteristic features we have just briefly described. When
■yve are occupied with the common processes of natural thought
we pass from idea to idea and trom judgment to judgment with-
out the appearance of this complicated idea of the ego. It is
very different in the case of the so-called voluntary thought to
which we have already referred above. Here the idea of the ego
often appears between the single ideas and judgments ; in this
case we make a mental reference to the ego-idea as the cause of
the series of ideas and judgments with which it is associated.
Language, which in a certain sense always registers our sensa-
tions and ideas, also contributes, by means of motor sensations
of speech that are seldom entirely wanting even in the case ol
silent thought, to the deception that an "ego" presides over
and registers our sensations and ideas. However, the concomi-

Attention— Voluntary Thought— The Ego— Memory. 247

tant activity of the idea of the ego is not always present. In
the case of very deep refection or rumination we often forget
that it is we ourselves who are thinking. But in general it is
true that the so-called voluntary thought is accompanied by the
idea of the ego.

Let us now recapitulate the three factors that characterize so-
called voluntary thought. They are as follows: (i) The pecu-
liarity that the idea desired and sought is known to be already
contained in the initial series of ideas. (2) A complex of accom-
panying muscular tensions that produces the kinsesthetic sensa-
tion characteristic of attention, and finally (3) the concomitancy
of the ego-idea with the series of ideas that constitute thought.
We have also seen that these three factors are all generally, but
not always, present at the same time, and that they appear singly
also in the case of involuntary thought. From what has been said,
however, we may also conclude that this voluntary thought by no
means occupies a unique or peculiar position among psychical
processes. On the contrary it remains quite within the limits of
the association of ideas with which we are already thoroughly
familiar. Our thoughts are never voluntary ; like all events, they
are strictly necessitated. The freedom, which we think to possess
in the so-called voluntary processes of thought, is only semblance ;
but this appearance of freedom is fully explained psychologically
by the three above-mentioned factors.

Both the common usage of language and of philosophical and
psychological theories, have distinguished many other special
forms of the association of ideas besides those that we have men-
tioned. These special forms have received special designations,
such as "understanding," "reason," "power of judgment,"
"sagacity," " fantasy," etc. At the same time there has always
been a tendency to render these special activities, that may be
distinguished more or less justly, independent entities by ascrib-
ing them to just as many different psychical faculties. On the
contrary, however, we shall hold to the fact that all these activities
simply represent varieties of the association of ideas. It would
not be at all difficult to reduce all these forms to the one funda-

248 Introduction to Physiological Psychology.

mental form of association by purely psychological reasoning. The
dittiCLiliies that cling to these conceptions are due to their alli-
ance with certain conceptions of metaphysics and epistemology
and to the fluctuating applications in which the corresponding
terms have been used by different peoples and philosophical
schools. We shall now emphasize only one other phase of the
association of ideas, the memory or faculty of recollection. In this
example (the memory) we shall illustrate how such psychical
activities are to be viewed as a rule and how they are to be reduced
to the association of ideas. It is obvious that two things are
necessary in order that we may recall the mental image of an
object or sensation : (i) the image of the object in memory must
be intact, and (2) the association as such must take place normally.
The latter is abnormal only in cases of great fatigue or of mental
disease. Under such circumstances the association of ideas may
be so retarded that it is finally completely arrested ; no mental
image or idea is reproduced. The latent mental image El is intact,
but the material process, which should convert this El into Ei,
and thereby bring the image of memory into consciousness, is not
sufficiently vigorous to accomplish the task. This forgetfulness
is but transitory. But the loss of memory, caused by the destruc-
tion of the mental images themselves, is a very dilTerent matter.
We have already heard in a previous chapter that during the first
five minutes after their deposition the images of memory lose very'
little or notliing at all of their intensity and distinctness. Then
the slow process of material change begins, gradually efficing the
material dispositions — the EV?,. To express it in the language
of psychology, the images of memory gradually lose their dis-
tinctness. The more seldom they are reproduced, the more
rapidly does this change progress. Also different individuals
are very different in this respect. In one person tiie images
are less firmly deposited and more speedily eradicable than in
another. In this case we ascribe a " good memory " to the
latter, and a " bad memory" to the former. But even with a due
consideration of all these circumstances, " memory " and " loss of
memory" still remain compsratively relative conceptions. Let

Attention-Voluntary Thought— The Ego-Memory. 249

us consider that the reproduction of an idea at any definite
moment also depends upon both its tone of feehng, associative
relation to the preceding idea, and the grouping of latent ideas.
If these are unfavourable, even the most distinct mental image
may remain latent. We are then accustomed to say that this or
that thought or idea " does not occur to us." We see, therefore,
that this apparently simple faculty of memory resolves itself into
a much more complicated process. In all its variations, however,
it depends on nothing more or less than the association of ideas
and its laws, with which, we are already familiar.^

From the above we can judge how extraordinarily difficult it is
to investigate experimentally either the retentive power or the
forgetfulness of the mind. It is hardly possible, for example, in
attempting to determine the influence of passing time upon the
retentiveness of the memory, to retain all other factors, such as
the state of feeling, grouping of ideas, attention, etc., entirely
constant during the full series of experiments. However, in the
case of the memory we have the very trustworthy, painstaking
researches of Ebbinghaus.^ Ebbinghaus arranged syllables in
series of different lengths, but without regard to sense. He then
memorized these series by repeatedly reading them aloud until he
was just able to reproduce them. After certain intervals of time
(for example, 20 min., or i or 2 days) had elapsed, he deter-
mined by experiment how many times he had to ;r-read the
partly forgotten syllables in order to be able to reproduce them
again. By this means he obtained a standard for measuring the
degree of forgetfulness. As the result, it appeared that the process
of foij£;etting progressed very slowly at first, then more rapidly

* Hering (" Ueber das Gedachtniss als eine allgemeine Function der
Materia, " 1876) has ascribed memory to all organized matter. In this case the
word memory is also applied to processes that cannot be shown to be accom-
panied by parallel psychical processes. We shall here exclude this expansion
of the conception. Compare also Meinong, Vierteljahrschrift f. wiss. Philos.,
X. Juii. HuBER, " Das Gedachtniss," 1878. Plato, "Theretet."

* EnBiNGHAUS, "Ueber das Gedachtniss." " Untersuchungen zur e.Kperi-
mentellen Psychologie," Leipzig, 1885. Wolfe's dissertation (Philos.
Stud., HI.) contains a special investigation of the memory for tones.

250 Introduction to Physiological Psychology.

and finally very slowly again. An hour after the series had first
been memorized, the process of forgetting had advanced so far
that more than half the time originally employed was requisite for
committing the series to memory again. Eight hours later two
thirds the original time was required for learning it anew, a month
later about four-fifths the original time. These numerical rela-
tions may be expressed, approximately at least, in the following
law : " The quotients of the amounts retained by the amounts
forgotten are to each other inversely as the logarithms of the
various periods of time that have elapsed." The result obtained
by the same author, in making use of series in which the syllables
are arranged so as to produce sense, is worthy of mention. For
example the verses of an epic poem can be ten times more easily
retained than senseless series of syllables. Without investigating
the correctness of the number ten, we see that it is undoubtedly
true that the ideas composing a series are more firmly fixed in
memory when they are more closely associated with each other,
especially by means of judgments. Ideas thus thoroughly asso-
ciated mutually assist one another in reproduction by means of
that which we have designated as the grouping of ideas. As
Herbart expresses it, they are " mutual aids " (Hiilfen). Ebbing-
haus found further that one reading is suflicient to memorize a
series of from seven to eight syllables, but that forty-four repeti-
tions are necessary for a series of twenty-four syllables.

Investigations that are just as exact as those supplied by
Ebbinghaus for the memory, are wanting for most of the other
pyschical processes. We must therefore restrict ourselves to re-
peating once more that they may all be explained without diffi-
culty by the association of ideas and its laws.

CHAPTER XUJ.

MORBID THOUGHT— SLEEP — HYPNOTISM.

Thus far we have considered only the thought-processes of the
healthy man in his waking moments. Let us now descend, as it
were, into the labyrinthic reahns of insane or morbid psychical life.
Right among these psychical anomalies we shall observe numer-
ous phenomena that confirm the propositions thus far advanced.
We remember that we reduced every psychical process to essen-
tially the same simple scheme. An initial sensation S is followed
by a definite series of ideas, I^, /g, 1^, etc., in accordance with
the laws of association. The sensation .S is always conditioned
by an external stimulus £ ; the ideas I^, /g, I3, etc., originated in
former sensations. These material dispositions, the B/'s that have
been left by former sensations, are changed by the associative pro-
cess into Ez's, or I's, and are thus reproduced, i.e. called into
psychical life. Now what deviations from this normal process occur
in the conscious life of the insane ? Let us here first call attention
.to a peculiar phenomenon that has been termed " secondary sensa-
tion."^ This phenomenon occurs when a sensation of one quality
that has been normally produced by an adequate external stimu-
lus, at the same time imparts a sensation of an entirely different
quality for which there is no corresponding external stimulus.
A simple example of this secondary sensation is as follows : We
hear a very loud, shrill sound, and at the same time see a flash of
light before the eyes. In this case the visual sensation of the
flash of light has been produced without any adequate stimulating
cause in consequence of a normal sensation of hearing. On the
other hand, a bright light sometimes produces the secondary

1 Gad and Goldscheider (Verhandl. d. Berl. physiol. Gesellsch., Oct., 1890)
have recently designated a very different process as "secondary sensation."
After repeated induction shocks, or a single application of some mechanical
stimulus, besides the first sensation, a second similar sensation appears about
0*9 sec. later. The secondary sensation which probably arises from a peculiar
summation of separate stimuli, has nothing to do with the secondary sensations
which we are discussing.

951

252 Introduction to Physiological Psychology.

acoustic sensation of a high tone besides the primary sensation
of light. It is obvious that this phenomenon depends on the
sympathetic excitation of the elements of the auditory centre to
which the cortical excitation primarily produced in the visual
centre has been transferred by means of the associative paths.
This process differs from the process of association with which we
are already famihar only in the fact that the latter is the associa-
tion of mental images or ideas, while the secondary sensations, on
the contrary, are produced by the association of sensations. The
image of fire may remind one of a crackling noise ; the sound of
a trumpet may recall the idea of yellow. In both cases, how-
ever, the association is accomplished by means of ideas and only
the mental image of red or yellow is reproduced. On the con-
trary, in the case of secondary sensations the primary sensation
directly imparts another sensation.

We shall do better therefore to avoid the expression " associa-
tion " in connection with secondary sensation and make use of
the term " radiation." We are all aware that the pain caused by
a carious tooth may often spread in a somewhat remarkable way
until it finally attacks the entire half of the head.^

The effect which prolonged pain produced in the case of one
sense is transferred in the case of secondary sensations from one
sense to another. Among the secondary sensations, "photisms "
{i.e. secondary sensations of light or colour) are decidedly the
most frequent ; " phonisms " ^ (/.e. secondary sensations of tone
or noise) are considerably rarer. The quality of the secondary
sensations is always the same in the same individual, but on the
other hand, often different in different persons. For this reason
it is only possible to formulate a few general laws. As a rule,
bright photisms are produced by sensations of high tones, or also

1 The interesting observations of Urbantschitsch's upon the changes in
the sensibility of the trigeminal nerves accompanying diseases of the ear, also
present a certain analogy. Compare also PFLlicER's Archiv, Bd. 42.

2 The use of the words "pholisni" and "phonism" has been borrowed
from the German for the sake of brevity. Their meaning is parenthetically in-
dicated above. — 7"'j.

Morbid Thought—Sleep— Hypnotism. 2-5 3

by intense pain and sharply defined sensations of touch ; dark
photisms are produced by sensations of an opposite nature. In
the same manner high phonisms are produced by sensations of
bright light and sharply defined sensations of touch (small,
pointed objects). The phonisms generally partake of the quality
of noises ; the photisms generally appear in the colours of red,
yellow, brown or blue. Sometimes a definite colour is associated
with a definite pitch, vowel or noise. There is a case of one
German lady ^ who is known to associate the acoustic sensation
a with the sensation of the colour yellow, a with white, e with
blue, o with red, and 06 with black. The same lady also sees
the printed vowels glimmer in the same colours whenever she
reads. In accordance with a proposition made by Fechner, the
academic philosophical union in Leipzig instituted a collection of
statistical data on a large scale. The result of these data showed
that on the average, though not always, lighter photisms corre-
spond to the vowels a, a and e, and darker photisms to the vowels
6 and 60. Both diphthongs and polysyllabic words appeared to-
the above-mentioned patient in mixed colours. French authors
have very characteristically designated this as " audition colorde,"'
or "coloured hearing." The localization of the secondary sensa-
tions is also interesting. Photisms produced by sound, i.e.
secondary sensations of light induced by sensations of tone, are
generally localized in the field of hearing from which the primary
sensation proceeds ; the rare photisms produced by sensations of
1 taste are generally localized in the appropriate region of the
buccal cavity, and photisms produced by sensations of smell, in
ithe neighbourhood of the object smelled, or in the cavity of the
nose. Much more rarely the localization is within the head (de
Rochas, Ughetti). It is also well worth mentioning, that an un-
pleasant emotional tone accompanying the primary sensation may
be followed by an agreeable emotional tone accompanying the
secondary sensation. In by far the majority of cases the second-
ary and primary sensations seem to appear simultaneously ; in

' A patient of the author s — 7"j.

254

Introduction to Physiological Psychology.

rarer cases an interval of some seconds has been observed to
■elapse before the appearance of the secondary sensation.

The question now arises : are these phenomena pathological
■or normal experiences of the psychic life? Bleuler and Leh-
mann ^ found such secondary sensations in one-eighth of all the
men whom they investigated. The questions (Fragebogen) of
Fechner 2 brought together 347 reliable cases in which colours
were associated with sounds. Of course it is probable that not
all of these cases are genuine, but that on the contrary, in a part
■of them, certain associations of ideas, originating partly in earliest
■childhood, are the cause of the secondary sensations. It cannot
■be doubted, however, that genuine cases occur. In these
genuine cases, almost without exception, we find a neuropathic
■disposition. The above-mentioned lady suffered from severe
reflex neurosis. At the time that Nussbaumer^ first imparted
his self-observations to Germany before the medical fraternity of
Vienna, Benedict had already called attention to the psycho-patho-
logical features of these symptoms. In very many cases there is
■an inherited disposition. Nussbaumer's brother had likewise had
■secondary sensations ; also several of Bleuler's relations besides
himself. In mentally healthy individuals, who are free from all
■neuropathic disturbances, these secondary sensations are at least
just as rare as the hallucinations that are to be considered pre-
sently. There is no doubt that inherited associative paths of
abnormal capacity for conduction are, in the above cases, the
means of communication between the separate cortical centres of
sensation.

1 " Zwangsmassige Lichtempfindungen durch Schall und verwandte Er-
■scheinungen auf dem Gebiet der anderen Sinnesempfindungen," Leipzig, iSSi.

2 STEiNBRiJGGE, " Ueber secundiire Sinnesempfindungen," Wiesbaden, 1SS7.
In this work are also to be found further, though incomplete, literary re-
ferences. To the above work should be added Girandeau, " L'encephale,"
1885 ; DE ROCHAS, " La Nature," 18S5 ; and numerous Italian authors. The
first description was given by Lussana as early as 1865.

8 Wiener med. Wochschr., 1873. Fechner's first communication ap-
peared independently of Nussbaumer's in the "Vorschule der Aesthetik,"
1876.

Morbid Thought— Sleep— Hypnotism. 255

Normally, the sensation should always cause the appearance
of ideas only, and not of sensations ; the sensations themselves
should not appear without adequate stimulation. The secondary
sensation is not produced by adequate stimulation, but by the
action of some other sensation ; it therefore departs from the
nature of the normal or primary sensation. We shall now con-
sider another case of morbid sensation — the hallucination. In
this case not only the adequate external stimulus, but also the
primary sensation are wanting. The persons subject to halluci-
nations sees persons and landscapes in the cloudless sky, and
hears voices in the most profound stillness. At the same time
his visions are often so realistic and so true in colour, and the
auditory hallucinations ^ that he hears are so loud and distinct,
that it is absolutely impossible to distinguish them from the
reality. They appear when the eyes and ears are closed the same
as when they are open. They often correspond to the actual
content of the invalid's thoughts ; in this case he complains that
all his thoughts are at once " set in scene " and " illustrated," or
that they " become loud." Again, the visions are often entirely
strange and surprising to the patient himself ; he sees faces that
he never saw before, and hears words that have not the remotest
connection with his thoughts or even combinations of syllables
that he never heard before. In still other cases the invalid
possesses the power of producing this or that hallucination at
will, somewhat as Goethe relates of Ottilie in his novel, " Wahl-
verwandtschaften." ^ Genuine hallucinations of taste, smell and
touch are considerably more rare. Certain hallucinations in the
case of motor sensation are highly interesting. One invalid told
the author that he felt his larynx and tongue move as if he heard
the word " parricide " issuing from them. It is not improbable
that such hallucinatory motor sensations at times cause actual
involuntary motions, thus producing the articulation of the respec-
tive word. As regards localisation, the voices heard are occasion-

• Ger. Akoasmen. — T's.

' Natural or elective affinities. — T's.

256 Introduction to Physiological Psychology.

ally, the visions very rarely located within the head ; much more
frequently both are projected outward. Their location, when per-
ceived as external to the invalid himself, appear to vary ; the
variation is only in part dependent on the movements of the
invalid's eyes while experiencing the hallucinations. Those cases
are remarkable, in which the hallucinations are always heard with
but one ear, or seen in but one half of the field of vision. The
author also recollects a case in which the agreeable voice always
spoke into the right ear, and the disagreeable voice into the left
ear. Squinters often see their visions double. Sometimes it is
necessary for the invalid to give especially close attention, in order
to distinguish words among the indistinct hallucinatory murmur-
ings. The hallucinations generally have a stronger influence
upon the association of ideas than the concomitant normal sensa-
tions, which are often, in fact, overshadowed. For this reason,
when a large number of hallucinations continues many years they
very rarely fail to beget insane ideas.

In many cases of hallucination a disease of the invalid's organ
of hearing or sight can be diagnosed ; but in numberless cases no
■such disease of an organ of sense is present. Individuals whose
optic nerves have been atrophied for a number of years can have
visions. On the contrary no persons have ever been known to have
optic or acoustic hallucinations, who were born blind or dumb.^
The stillness of solitude, as in the case of solitary confinement
for example, favours the appearance of acoustic hallucinations ;
'the darkness of night or the bandaging of the eyes after an opera-
tion for the removal of a cataract, favours the appearance of
visions. These two statements do not express entirely universal
rules, however. On the contrary, there are even cases in which
•slight stimuli of sight or hearing, of any kind whatsoever, are
sufficient for the appearance of hallucinations. It also appears
in some cases that a normal sensation of one quality is requisite
to produce hallucinatory sensations of another quality (Kahlbaum),
•so that in a certain sense a primary sensation is still necessary.

1 Leidesdorf, "Lehrb. d. psych. Krankli.," 1865.

Morbid Thought — Sleep— Hypnotism. 257

Hence many hallucinations vanish when the eyes are closed ,
many do not.

Now, how shall we explain the origin of these hallucinations ;
how can a sensation be produced without stimulation ?

Let us remember the former distinction that we made between
sensation-cells and memory-cells. We have already shown that
the sensation and image of memory are probably not connected
with the same material elements. We designated the material
process in the sensory cells, corresponding to the sensation, as
Ec; the material disposition that remains in the memory-cells,
as El ; the material process attending the awakening or repro-
duction of the latent image of memory and corresponding to the
conscious idea, as Ei. Normally, the sensation-cells are only
excited by stimulation coming from the periphery ; Ec is only
produced by a stimulus E that acts upon the sensory path. This
is different in the case of hallucinations. In this case it is the
images of memory that produce lively sensations without external
stimulation ; the EV?, or Ei'?> are the cause of AVs. The process
of sensation which normally always proceeds from the sensory
elements to the memory elements, now takes the reverse course
from the latter to the former. Generally, this only occurs under
pathological circumstances. It is only when the sensory cells
are morbidly irritable, that they react upon a stimulation from the
memory cells, which, under normal conditions, would have no
effect upon them, but which has been pathologically intensified.
The sensation-cells are sympathetically excited, as it were. It
is obvious that but two chief cases are to be distinguished. The
ideas that sympathetically excite the sensory cells are either ihe
ideas actually present in consciousness at the time {i.e. the Ei'%),
or the ideas that are psychically latent, i.e. more accurately
expressed, the material dispositions that still lie below the
tlireshold of consciousness. In the first case the hallucinations
correspond to the momentary content of consciousness, as has
■already been described; in the second case they emerge from
among the latent ideas very suddenly, surprising even the invalid
Ihimself It is evident that in general hallucinations of the second

258 Introduction to Physiological Psychology.

class occur only when very considerable changes in the excita-
bility of the sensation-cells have taken place, while the actual
conscious ideas produce hallucinations even when the excitability
of the sensation-cells has but very slightly increased. For this
reason hallucinations of the second class are generally much more
vividly perceived than those of the first class, since in the former
case the sensation-cells are more affected by the morbid pheno-
mena than in the latter. As we already know, both sensation-
ceils and memory-cells are located in the cerebral cortex; the
hallucinations are therefore decidedly of cortical origin. The
assumption that the peripheral parts of the sensory nerve-paths
(corpora quadrigemina, retina, etc.) are sympathetically excited to
a certain extent in case of hallucinations, wants sufficient grounds.
On the other hand it can be shown that in a large number of
cases of hallucination, some external stimulation in the broader
sense is not entirely wanting. It appears, in fact, that subjective
sounds, produced in the peripheral parts of the organ of hearing,
or entoptic disturbances in the vitreous body for example, and
especially excessively augmented " mouches volantes " are very
frequently the cause of hallucinations. Such subjective sounds,
resulting from peripheral causes, may exist for years and be per-
ceived in their true nature, i.e., for example, as a simple buzzing
or humming in the ears. If, however, a mental disturbance is
developed in the individual, these noises are soon heard as words
and voices. In a similar manner the "mouches volantes" appear
to one delirious from the use of alcohol to be numberless mice or
bees swarming about him. It is very apparent that in this case,
and in many other similar cases, the sensation-cells do not receive
excitation from external stimuli in the narrower sense, that is, from
such as are external to the body, but from those external stimuli
that are situated in the sense-organ or in some part of the sensory
nerve-path up to the cerebral cortex. Under normal circum-
stances a very simple sensation corresponds to this excitation ;
the individual hears a buzzing in the ears or sees dark spots in
the visual field. Under abnormal circumstances the memory-cells
act upon the sensation-cells in such a manner as to transform

Morbid Thought — Sleep— Hypnotism,

259

the excitation into more complicated sensations ; the buzzing in
the ears becomes words, the dark spots become forms. In many
respects these hallucinations ^ already approach the illusions which
we shall forthwith discuss more fully.

Also, in this connection, we shall now ask whether the halluci-
nations may occur in healthy persons, or whether their appearance
is limited merely to mental diseases ? An exact investigation of
this subject shows that in this case also the many individuals who
have inherited tendencies toward mental diseases, although not
mentally deranged themselves, experience hallucinations. Of
still greater importance to us is the fact that even men who are
very gifted mentally, particularly artists who possess a very vivid
imagination, have hallucinations. The Italian painter, Spinello
Aretini, is said to have copied his Madonnas, as it were, from a
vision j an Italian composer is said to have composed his sonata
in imitation of music heard during hallucinations. The well-
known vision of Goethe's — the rider in pike-grey mantle upon
the Sesenheim ride — was probably a simple illusion. Halluci-
nations are recorded of Schumann,Pascal, Cardanus, Mendelssohn,
Jean Paul, Spinoza, Byron, Tieck, Johnson, Pope, and numerous
others. To be sure, in many of these cases we have to deal with
very doubtfully authenticated reports ; in many the phenomena
may have also been mere illusions. In the normal man, at least,
even the liveliest emotions generally produce nothing more than
illusions, never hallucinations. Fechner and Henle report of
themselves that at night objects with which they had been
occupied during the day often appeared to them again as
phantasms in the dark. The peculiar hypnagogic hallucinations

* The literature upon the subject of hallucinations is extraordinarily com-
prehensive. At the present moment extracts from over 300 works lie before
the author. As a preparatory introduction to the theoiy of hallucinations,
Hagen, Allgemeine Zeitschrift fiir Psychiatric, Bd. 25, is to be especially
recommended. Also Kahlbaum, ibidem Bd. 23. Lazarus, Zeitschr. f.
Volkerpsychologie, Berlin, 1867. Kraepelin, " Ueber Trugwahrnehin-
ungen," Arch. f. Psych., Bd. 14. Kandinsky, Arch. f. Psychiatric, Bd. 11.
A brief presentation of the doctrine of hallucinations is to be found in
Mendel, Berl. klin. Wchschr., 1890.

26o

Introduction to Physiological Psychology.

that appear just before falling asleep are also very interesting.
They have been most exactly described by Hoppe.^ Almost
every one can observe these in his own case occasionally. They
appear only upon closing the eyes, and are, without exception,
visions of but slight sensual vivacity, generally indistinct visages
or landscapes.

By illusions we understand those sensations that are, in fact,
produced by external stimuli, but that do not correspond to the
same in quality. We are all familiar, perhaps, with the poem of
Schiller's, which runs as follows : —

'* H6r' ich das Pfdrtchen nicht gehen ?
Hat nicht der Riegel geklirrt ?
Nein, es war des Windes Wehen,
Der durch diese Pappeln schwirrt."

"Seh' ich nichts Weisses dort schimmem?
Glanzt's nicht wie seidnes Gewand ?
Nein, es ist der Saule Flimmern
An der dunklen Taxusvvand." *

Or let us recollect the well-known example of an insane person
who, while observing a real portrait, suddenly perceives the
painted head protrude its tongue, the vision possessing all the
sensual vivacity of the real act. Again, a lady who was mentally
deranged once related to the author that as often as she travelled
upon the railway, she heard a voice call out from the rattling of
the wheels, " crazy Bremer, crazy Bremer," — Bremer being the
patient's name.^ Let us now inquire what processes lie at the

' HOPPE, "Erklarungen der Sinnestauschungen," Wiirzburg, 1888.

' The above selection is from Schiller's " Erwartung." The reader who is
not versed in German will probably be able to derive greater benefit, so far as
its specific application above is concerned, from a more literal translation in
prose than from a free poetical translation. The former is as follows : "Do
I not hear the wicket open ? Was it not the bolt that clicked ? No, it was
only the wind sighing and murmuring through these poplars. . . . But do I
not see something white, gleaming there ? Is it not the flash of a silken robe ?
No, 'tis but the columns that glisten against the dark wall of yews." — T's.

^ The German words, when regularly repeated, bear more or less resemblance
to the rhythmical, but monotonous noise of car-wheels in motion. " Verriickte
Bremer, verriickte Bremer" v.^-^, w-v^-v^). — T's.

Morbid Thought — Sleep — Hypnotism. 261

foundation oi" these phenomena. It is obvious that at first a sen-
sation is produced in the normal manner. The sighing of the
wind in the tops of the poplar-trees, the white columns seen
against the dark background of yews, the portrait, the rattling of
the railway coaches, etc., are the external stimuli that impart
sensations. But these sensations are transformed. The rustling
of the poplar leaves sounds to the expectant person like the noise
of an opening door; the white column assumes the form and
appearance of a white robe ; the head protrudes the tongue ; the
rattling is changed into words. This transformation is produced
by the influence of actual, or, in the last two cases, of latent
ideas. The memory-cells, as it were, add certain hallucinatory
elements to the sensations. Such transformed sensations are
designated as " illusions." It should be carefully noted, however,
that these are not merely cases of mistaken or deceived judg-
ment. The rustling of the leaves in the wind is not falsely
judged in the case of illusion, but the quality of sensation itself is
directly changed ; it has a sound different from that corresponding
to the stimulus. On the contrary, our judgment is often able to
rectify such illusions.

These illusions are of frequent occurrence, and appear in con-
nection with all of the senses. In fact, we may say that the
influence which the images of memory exert upon sensation is
never entirely wanting. The proper nursery of the illusions,
however, is the emotional life ; among the various emotions, ex-
pectation, both when accompanied by fear and by hope, is of
especial importance. We shall now understand also why we
formerly regarded those hallucinations, that depend upon entoptic
and entotic stimuli, as closely related to illusions ; they are obviously
merely the result of a transformation of sensations imparted by
actual stimuli. Without doubt the illusions are also produced
through the influence of a recurrent excitation of the sensation-
cells by the memory-cells.

We can dispose much more briefly of those pathological dis-
turbances in which the images of memory themselves, and the
association of ideas are aff"ected. We shall very briefly mention

262 Introduction to Physiological Psychology.

only the most important, and for normal psychology the most
interesting phenomena. One of the chief among these is im-
becility or demetitia. We remember that the most probable
anatomical basis for the association of ideas was found to consist
of numberless so-called " associative fibres," which connect the
ganglion-cells with one another by running through the white
matter, partly in arcuate courses, from one part of the cerebral
cortex to another. The ganglion -cells themselves are most
naturally to be regarded as those elements which we have desig-
nated as memory-cells, and in which the so-called latent images
of memory are deposited. Now it is of the greatest interest that
the investigations of pathological anatomy have furnished positive
results in the case of that mental disturbance which inevitably
leads to complete imbecility, the so-called softening of the brain,
or dementia paralytica. It consists particularly in the destruction
(i) of the ganglion-cells themselves, and (2) of the associative
fibres uniting them. We find that these facts, to a certain extent,
once more confirm all our previous deductions, a posteriori.

The abnormal acceleration and inhibition of the association
of ideas, and also its morbid incoherency have been already men-
tioned above. It only remains for us to consider briefly two other
psychopathic phenomena that deserve a very especial interest, —
the delusive idea and the compulsory idea. The two phenomena
are alike in being associations of judgment that have no suflScient
foundation in the external world. They differ from one another
in that in the former case the invalid believes in his delusion,
while in the latter he is fully conscious of the incorrectness and
morbid nature of the idea which is forcing itself upon him. A
patient who believes that he is Jesus Christ is suffering from a
delusion ; one who, while cutting his bread, is constantly
harassed by the thought that he is cutting his brother in two,
and who, although he recognises the idea itself to be false
and laughable, is still unable to rid himself of it, and is driven to
the point of refusing nourishment, is the victim of a compulsory
idea, or an idea which forces itself upon him. How do ideas
of these two kinds arise? Normally the association of ideas,

Morbid Thought — Sleep — Hypnotism. 263

especially association that produces judgments, develops under
the constant influence of sensations, that we are always experi-
encing anew from moment to moment j the latter condition and
determine the former. This influence of the sensations affords
the possibility of a constant correction of the judgments that
are being produced by the association of ideas. Incorrect
judgments are suppressed in the very act of formation. Thus
both fantasy and judgment are under the control of the external
world, and may never become too contradictory to it. We com-
mit "errors" of judgment, in fact, because our sensations them-
selves do not always correspond exactly to the external excitants,
and particularly because the chief law of the association of ideas,
the law of simultaneousness, obviously permits or even causes at
times quite illogical conclusions and unwarrantable generaliza-
tions;^ but such errors become neither delusive nor compulsory
ideas. In general the parallelism of the associations of judgment
and the series of external excitants or processes of the external
world remains comparatively intact. In invalids who are suffering
from delusions or compulsory ideas the regulative influence of
the sensations or of the external stimuli upon ideation has either
been removed or has lost the persistency of its action. Hence
the association of ideas produces judgments that are completely
contradictory to the processes of the external world. In fact, in
the case of these invalids the process is reversed ; the association
of ideas influences the sensations. The latter are interpreted so
as to harmonize with the existing insane ideas and remodelled
accordingly; a further stage brings illusions and hallucinations.
It is not mere chance that illusions and hallucinations so very
frequently accompany delusive or insane ideas. All three are
symptoms that the ideational life has been wrested from the
control of the sentient life. Delusive and compulsory ideas are
only distinguished from each other as regards their origin. In
the latter case corrective 'yid.gm&n'v!, are still made as well as incorrect,

^ MUNSTERDERG is right in declaring that the errors of judgment can be far
more easily explained psychologically than its constant correctness.

264 Introdtiction to Physiological Psychology.

and greatly exceed the latter in numbers, while in the former
case, on the contrary, correct judgments are not formed at all, or
at most only in very limited numbers.

We must now content ourselves with these few hints con-
cerning the theory of morbid disturbances in mental activity, and
pass on to the psychological presentation of a condition that has
often been directly compared, though of course without sufficient
grounds, to the morbid mental conditions, viz. the condition of
sleep with its dreams. We do not yet know with certainty what
the physiological basis of sleep is, whether merely a chemical
exhaustion of the cerebral cortex, or a universal or partial change
in the circulation of the blood.^ Psychologically, sleep appears
to be a more or less complete removal of all psychical processes.
One might designate this condition, if so desired, as uncon-
sciousness. The E(fs of the cerebral cortex remain too weak to
produce a concomitant psychical process or sensation, and the
EPs are not aroused from their state of latency. Psychical
processes appear in but one form during sleep, — in the form of
dreams. The study of dreams is extraordinarily interesting, and
urgently to be recommended as a subject for introspection. The
results of our self-observations will only be exact, however, if we
follow the example of Lazarus by laying paper and pencil beside
us before falling asleep, so that, as soon as we waken in conse-
quence of a dream, its contents can be written down at once.
If we wait longer, till morning perhaps, the greater part of it
will have vanished from memory. An accurate analysis of the
process of dreaming shows that its elements are imaginative ideas
(in the sense which we have already discussed above), but that
these ideas are also often equipped with almost as great a sensual
vicacity as the sensations themselves. On this account they may
be regarded as peculiar somnial hallucinations that appear in
longer successive series, but that are generally even more closely
connected with one another than the hallucinations experienced

1 More recent investigations seem to indicate at least a partial auamia of
the cerebral cortex. Comp. also Binx, Uber den Traum, Bonn, 1S78.

Morbid Thought — Sleep — Hypnotism.

265

when awake by those who are mentally deranged. It can be
shown that in very many cases, at least, the somnial phantasms
are more or less due to peripheral stimulation. For example,
a severe neuralgia not infrequently causes the somnial sensation
of a dagger-thrust in the neuralgic part of the body ; with this
sensation the image of the murderer and his threatening words
are then associated, appearing with all the vivacity of hallucina-
tions. At first, therefore, an illusion, and not a hallucination,
appears ; the hallucinations are only secondarily associated with
the illusions. Generally those mental images are reproduced as
somnial hallucinations, that participated in the association of
ideas not directly, but some hours before falling asleep. This is
not unexceptionably the case, however. It is often very striking
that the somnial visions are colourless, although of course the
most vivid colours occasionally appear. Above all, the almost
complete absence of motor reactions is also characteristic of
somnial phenomena. The muscular system seems to be lamed ;
even in the deepest sleep the phenomena accompanying the
activity of the tendons, otherwise so accurate an index of the
existing muscular tone, have disappeared. We have, indeed,
motor ideas ; in our dreams we believe that we are walking or
fighting, and yet we scarcely move. It is only in the most vivid
dreams that either men or animals (especially the hunting dog,
for example) give a weak expression to the somnial ideas of
motion by a few slight movements of the trunk and extremities.^
In sleep, therefore, (i) the initial element of the psychical pro-
cess, the sensation, is produced by ideational stimulation, and
(2) the final element, the motor idea or the action, is almost
entirely omitted.

One characteristic of the dream, its speedy disappearance from
memory, deserves an especial discussion. As a rule the repro-

* It is of interest in this connection that Laura Bridgman, who was bora
blind and deaf, is said to have gesticulated with her fingers during sleep a
great deal. In this case intensified motor ideas to a certain extent compensate
for the absence of visual and acoustic ideas.

265 Introduction to Physiological Psychology.

duction of even a vivid dream is no longer possible with any
degree of completeness five minutes after one has wakened.
But we are also unable to reproduce a long series of sensations
or ideas that have been experienced in waking moments entirely
without omission. Let us remember that the association of two
ideas which have no other connection than that of mere suc-
cession in time is very loose ; on this account we reduced the
association of ideas by succession, in so far as the latter is not
quite direct, to the association of simultaneous ideas. Such
associations as the latter are never entirely wanting. Hence we
are able to reproduce even the long series of our experiences
that we have when awake, passably well. In so doing we are
also aided especially by the vivacity which the images, left in the
memory by the successive sensations, possess in different degrees
■ and by the complete and close relation existing among the
successive sensations or ideas. The series of somnial sensations
or ideas offer much less favourable relations for reproduction.
The sensations in dreaming are always less intense and much
more disconnected ; they are characterized by many abrupt
transitions. The separate successive ideas are but rarely com-
bined into conceptions, and conceptions of relation are rarely
introduced.

Finally a sudden awakening produces abrupt changes in the
circulation of the blood which are followed by immediate and
important changes in nervous excitability that are probably not
the same for all parts of the cerebral cortex ; numberless stimuli
act at once upon all the sensory organs, and produce an equal
number of sensations. By this means that which we designated
as the grouping of latent ideas is wholly changed ; the new
grouping is in all respects unfavourable to the mental images
that have been deposited by the somnial sensations. This
explains the difficult reproduction of the images of a dream, or,
as it may also be expressed, the amnesia of somnial processes.
However, the nature of the dream-images is by no means less
psychical than the series of sensations and ideas that are ex-
perienced when one is awake. If we have entirely or almost

Morbid Thought — Sleep — Hypnotism. 267

entirely forgotten a small occurrence that happened while we
were awake a short time ago, we are not on that account justified
in concluding, however, that we had no proper psychical process,
and were hence unconscious. The same is true in the case of
dreams. The fact that we have forgotten them is not sufficient
ground for the conclusion that during the dreams we were not
fully conscious or that we were unconscious.^ The psychical
phenomena of the dreams and the conscious life of waking hours
are different, but the two do not have a different psychical value.
A removal of psychical processes, i.e. unconsciousness, occurs
only in the case of sleep without dreams, which is comparatively
rare.

Besides sleep there is still another series of different alterations
in the psychical life, all of which are characterized by a greater
or less derangement of the conditions attending normal excita-
bility of the cortex, and by a consequent more or less complete
amnesia. To these belong particularly the dazed or stupefied
conditions of many epileptics, in which they perform the most
complicated actions, or sometimes even commit crimes, that they
are afterwards totally unable to recollect.^ In very rare cases it
sometimes happens that both phases of psychical life, with their
different groupings of latent images of memory, alternate ; each
phase is characterized by amnesia of the preceding unlike phases
but by recollection of all former like phases. This morbid phe-
nomenon has received the very unsuitable designation of double
consciousness." ^

Hypnotism is another phenomenon that claims especial interest
Under this term we shall comprehend all those data that remain
after a thorough critical elimination of the phenomena of animal

' The use of the word " unconsciousness " also in forensic psychiatry, and
especially the concltision that there must have been «<«consciousness because
there was amnesia, are thus placed in a very unfavourable light.

* Compare Samt, Arch. f. Psychiatric, Bd. 5 and 6, and also the manuals
of psychiatry by Griesinger, Krakft-Ebi ng, and Schule.

' Compare Emminghaus, " AUgemeine Psycliopalhologie." Kibot, " Les
maladies de la personnalite," etc.

268 Introduction to Physiological Psychology.

magnetism, mesmerism, etc., and that have now become an object
of exact scientific investigation. Hypnotism depends chiefly on
the fundamental fact that certain individuals may be placed in a
remarkably changed psychical condition. This condition is itself
designated as Hypnotism. It is produced either by requiring the
person that is to be hypnotized to gaze at a glittering object and
then by gently stroking his forehead, or by constantly telling the
subject, "you must sleep, you shall sleep." The first-named
method we designate as the physical method ; the second method
is commonly known as " suggestion." Both methods can be
still further modified in various ways. In general " suggestion "
is the more effective. Bernheim has recently attempted to re-
duce all hypnotism to " suggestion," and to this end has sought
to show that a hidden indirect suggestion of sleep is always con-
tained in the acts of fixedly gazing at an object or stroking the
forehead. Success is most rapid when one makes use of both
methods, the stroking of the brow and the suggestion of sleep.
But the essential peculiarity of the hypnotic condition, without
regard to the manner in which it is produced, in fact, probably
the only peculiarity common to all hypnotic conditions, is the
power of suggestion. We may command the hypnotized person
to perform any actions we please ; he performs them like an
automaton. We may suggest any sensations whatever to him
and he has them at once, just as vivid and realistical as if they
were hallucinations. If we tell him that his left arm is insensible
to pain, he does not feel or notice the severest thrust of a needle
into that arm. We may suggest any idea to him that pleases us,
for example, the delusion that he is king ; the subject conducts
himself at once as a king. If we fold his hands as if in prayer,
these passive motor sensations at once produce the hallucination
of a church, a priest, etc. In short, the person who is hypnotiz-
ing excites in the brain of the hypnotized individual, either by
speaking to him or in some other manner, any idea that he de-
sires, and the idea thus aroused at once assumes sway over the
association of ideas. All contrary ideas and even the sensations
that are actually present are suppressed, and the ruling idea

Morbid Thought — Sleep — Hypnotism. 269^

almost alone determines the course of association, while, at the
same time, the mental images reproduced acquire a sensual
vivacity amounting to hallucination. If the delusive idea of
being king is suggested, the hypnotized patient forgets his real
title and beholds himself clad in the coronal robes instead of in
his own simple garments. It is obvious that this condition in
which the subject can be swayed by the power of suggestion,
presents a peculiar change in the cortical conditions of nervous
excitability. This change is manifest chiefly in the disarrange-
ment of the grouping of ideas, in the alteration of the intensity
of latent mental images, and in the abnormal receptivity of the
sensation-cells for stimuli imparted by the memory-cells. It is
impossible here to give even an approximate idea of all the num-
berless variations of the hypnotic condition.* In what manner
the above-mentioned methods produce this condition is as yet
entirely unknown.^ The hypnotic condition is followed by a
more or less complete amnesia of all its processes. Of course,
when the amnesia is complete, it is still a matter of doubt (as
also in the case of the total amnesia of acts that occur during the
stupefied condition of epileptics), whether despite their compli-
cateness, all the acts of the hypnotized individual are not motions
accomplished without any concomitant psychical process. Since
the person who has been the subject of experiments is unable to
give any account whatever of possible conscious processes during
the hypnotic state, the criterion which we formerly employed in
distinguishing between voluntary actions and automatic actions
now leaves us in the lurch. . We cannot decide with certainty
whether actual, i.e. psychical or conscious images of memory have

' A good introduction to the subject of Hypnotism is given in the two
articles upon hypnotism by Preyer and Binswanger in the Eulenburg
" Realencyidopadie der medicinischen Wissenschaften." Max Dessoir (Ber-
lin, 1889). has furnished a very complete summary of the entire literature upon
the subject of hypnotism. The first supplement to this bibliography appeared
in 1890. The vast literature upon Hypnotism and Suggestion, however, teems
with thoroughly unreliable and uncritical works.

* Perhaps a dim light is thrown upon the subject of the production and
nature of the hypnotic condition by the experiments of BunNOFF and
Heidenhain; Pfluger's Archiv. Bd. 26.

270 Introduction to Physiological Psychology.

accompanied the psychical acts or not. It is sufficient here to
state the problem ; in the closing chapter we shall meet it again
in a general form and attempt to solve it. At all events the
amnesia as such cannot be cited as an argument either for or
against the existence of concomitant psychical processes during
the hypnotic state.^ It is equally probable that the sudden
change in the cortical excitations, as soon as normal conscious-
ness returns, renders the association of the ideas experienced in
the normally conscious condition, with those of the hypnotic con-
dition impossible, or that both ideas and sensations are entirely
absent in the latter state.

We are now familiar with the most essential deviations from the
normal association of ideas, and can therefore turn to the final
element of the psychical process, actio?i, in the following chapter.

* Even the recollection of the hypnotic psychical processes would not
necessarily argue in favour of their existence during the hypnotic state. Let
us call to mind a former example, — that in which we pass a friend without
noticing him ; it only occurs to us subsequently that we have seen him. For
obvious reasons, however, this subsequent appearance of the psychical process
is only possible within a very short interval of time after the appearance of the
stimulus.

CHAPTER XIV.

ACTION ^ — EXPRESSIVE MOTIONS — SPEECH.

The psychical process began with the sensation. The associa-
tion of ideas, ie. a series of successive ideas, followed the sensa-
tion. The result of this association of ideas may be a motion,
and such a motion we call "action." The association of ideas
immediately preceding an action we generally prefer to designate
specifically as the " play of motives." Let us begin by asking,
How has this new element, the motion or the motor innervation,
been added to the sentient and ideational life ? How has man
acquired his motions — motions that are, in fact, advantageous,
that in general correspond with remarkable accuracy to his ideas,
and show the highest degree of fitness ? That much neglected
department of psychology which seeks to establish some theory
as to the evolution of the child's soul, is alone able to assist us
in obtaining the correct answer.

The new-born child, the same as the new-born animal, at first
executes very few, if any, movements that could be designated as
voluntary motions or actions. It performs only reflex or auto
matic acts, although part of these are already extraordinarily com-
plex. This statement agrees well with the fact of physiology and
anatomy, that the nerve-fibres leading from the thalamus opticus
to the periphery are already fully developed in the new-born child,
i.e. in particular, they are already encased in medullary sheaths ;
while the large nerve-path, which extends from the so-called
motor region of the cerebral cortex to the anterior horns of the
spinal cord and thence to the different parts of the muscular
system, and which, as has been demonstrated, conducts the in-

* By "action" the author signifies that which has generally been termed
"voluntary action." The latter expression in the present work is only ac-
ceptible wlien understood in the sense of "conscious" or "desired action
as the result of ideation," not " m/«//«(/ action. " See pages 25-29, 247 and
265-269. — 7"f.

271

272 Inti-oduction to Physiological Psychology.

tiervating excitations to the muscles in the case of voluntary acts.*
has not yet been provided with medullary sheaths. It also agrees
with the further fact that electric stimulation of a definite part of
the motor region in the adult cortex always produces movements
of the opposite arm, stimulation of still another part movements
of the opposite leg, and stimulation of a third part motions of the
opposite facial muscles ; but that electric stimulation of all these
parts of the motor region, in the case of the new-born animal,
produce no results whatever. From all these facts we must con-
clude that during the first months of its life the child gradually
learns to make use of voluntary motions, or, as it may be more
correctly expressed, of motions that are conditioned by psychical
activity. We shall now inquire into the particulars of the process
by which these actions are acquired. From the moment of birth
the brain of the new-born animal, at first only capable of impart-
ing "infracortical" reflex and automatic motions, is thronged with
numberless sensations, produced by the numerous stimuli that
stream in through all the sensory avenues. These sensations
leave in the cerebral cortex (particularly in its sensory regions)^
mental images which correspond to the material processes of
excitation. At once the association of ideas begins. The sensory
excitation is propagated along the paths of association and every-
where reproduces images of memory in the cerebral cortex. The
material excitation thus propagated in the cerebral cortex also
reaches the motor region by means of associative paths and is
discharged toward the periphery along the great motor path, the
so-called pyramidal tract At first this motor " discharge " is
quite irregular. Certain paths of association, however, will have
inherited specific capacities for conduction, which render them
better prepared than others to receive certain specific stimuli.
On this account the excitation will be directed along these paths

1 This is shown simply by the fact that if this path is broken by disease, all
voluntary motions are no longer possible.

' In this connection it is not necessary to take into consideration the state-
ment of many authorities on the physiology of the brain, that the size of the
cortical centre for dermal sensations, the so-called " centre of feeling," cor-
responds to the size of the motory region.

Action — Expressive Motion — Speech. 273

from the beginning. These statements explain the fact that the
chick, which has just been hatched, is able to pick up corn at
once.^ It is not necessary in this case, however, to assume that
the chicken has inherited ideas of the kernels of corn ; on the
contrary, it is sufficient to suppose that at birth it already possesses
an inherited associative path which is especially fitted for con-
duction between the visual centre and that part of the motor
region from which the innervation is discharged to those groups
of muscles active in the motions of picking up food. But apart
from such dispositions as these, which the child possesses from
birth, its first movements are not in general fitting. An object
brought in contact with the surface of a child's hand is only grasped
by its fingers for the first time in the third month. The child
reaches after objects which it sees toward the end of the fifth
month with some degree of certainty; only from the sixth to
the seventh month does it begin to guide its hand the shortest
way when reaching after an object. Raehlmann has observed
that young parrots also often fail in trying to seize branches.
The selection of fitting motions is only accomplished gradually
and by practice ; the child acquires these motions in very much
the same way that the adult, later in life, acquires a new motion
•or a series of motions, as in playing a selection on the piano, for
example. The extraordinary rapidity with which a child learns
to execute so many and so complicated motions is to be explained
:simply by the inheritance of a favourable disposition in the
associative mechanism. The exercise of this mechanism consists
in the constant repetition of motor discharges until the irritant is
removed. The child continues to reach after an object that acts
as an irritant upon his sense of sight, until, after numerous un-
suitable motor discharges, the fitting motion is at length hit upon.
As soon as the object is seized the stimulation disappears and the
motions just previously executed in trying to grasp the object
■cease. More correctly stated, the stimulation changes as soon
as the object is seized, its position changed and the consequent

1 Not excluding the possibility of an automatic act in this case, however.

274 Introduction to Physiological Psychology.

sensations of touch appear; then the child is at once occupied in
attempting to execute new motions that have different ends in
view. In this manner a gradual process of selection, that is in
fact astounding, produces the thorough fitness of our so-called
voluntary motions. They are gradually adapted with extraor-
dinary exactness to the stimuli of the external world, or — which
is the same thing — to the sensations. In the meantime, however,
another still higher stage of perfection is gradually effected in the
cortical motor apparatus. The motor discharge that has just
been described, is at first accomplished entirely without a con-
comitant psychical process. It is true that sensations and ideas
may precede the motor discharge, but primarily they contain no
element that is concerned in the resulting motion. It is only
after the motion has taken place that the child acquires any
knowledge of its own motor act. This knowledge is acquired by
means of the sensations of active motion that we have already
described in full. The active motions stimulate the nerves of the
joints, tendons, ligaments, and skin, and the complex sensation
thus produced we briefly designate as a motor sensation. Also
the visual sensation, by which we are made aware that the position
of the limbs has been changed by the active motion, blends with
the motor sensation ; by the latter term we shall hereafter desig-
nate a complex sensation which includes both the sensation of
sight and the feeling of motion. Therefore the sensation of
motion, which informs us that a series of ideas has resulted in a
definite motion, directly follows the ideas immediately preceding
it without the aid of any intervening element. An idea is now
deposited by this motor sensation, just as mental images or ideas
are deposited by all sensations. Hence we have also designated
the image of a motor sensation in memory as a motor idea. Like
all other ideas, these ideas of motion also participate henceforth
in the association of ideas ; like all other ideas, they also acquire
the ability to produce motor discharges. At first only the visual
sensation and idea, or the tactual sensation and idea of an object
produce the motion which is executed in grasping it. After the
motion of grasping has frequendy taken place the motor idea of

Action — Expressive Motions — Speech. 275

grasping the object is itself able to impart the motion. The
complete associative connection that exists between the initial
elements of the voluntary motor path and all cortical elements, is
of just as much advantage to the motor ideas as to the ideas
produced by any other sense; in other words, an especially
intimate associative connection is established between the motor
ideas and the excitations in the initial cells of the motor path.
In fact, every single movement produces a synchronous association
between the ideas and the excitations in the motor path, thus
specifically training the associative path for conduction. Hence
the motor ideas that were entirely secondary products, and that
were only associated with the motor elements secondarily, finally
acquire an almost complete sway over these motor elements.
Later, when a series of ideas, /x, /g, /g . . . composed of
ideas of sight, hearing, and touch, appears, they generally do not
directly impart the motor innervation ; on the contrary, the asso-
ciation of ideas first produces the appropriate motor idea, and
only the latter causes the motor innervation. Recently Miinster-
berg ^ has justly called attention to the fact, that it is this pre-
cedence of the motor idea, indeed, which causes the motion to
seem voluntary. " We will execute a certain motion " properly
signifies, " we are conscious of the idea of the motion," or, " of
the motor idea." The feeling which leads us to suppose that we
are exercising a will-power is strengthened by the simultaneous
innervation of certain muscles of the body, the musculus frontalis
for example. This muscular innervation accompanies the volun-
tary movements the same as every effort of attention, and gives
rise to peculiar concomitant kinaesthetic ^ sensations.

The results of modern investigations in the field of cerebral
physiology also harmonize well with the above presentation of
the subject. The so-called motor-zone of the dog, that region of

* The above presentation of this subject agrees with Munsterberg's writ-
ing, "Die Willenshandlung " {Freiburg, 1888) in the most essential points,
ahhough it deviates from it in some of the less essential particulars.

' Motor sensations in the restricted sense. —

2/6 Introductiofi to Physiological Psychology.

tlie cerebral cortex which produces contractions of the muscular
system when electrically irritated, contains the primary elements
of the motor path. In the dog the motor sensations and the
motor ideas also appear to be located in this same region. At
least this conclusion may be drawn from the experiments made
by Munk ; according to these experiments, the extirpation of the
motor region from one hemisphere removes all ideas of move-
ments performed by the opposite half of the body. In fact, ac-
cording to Munk, both sensations and ideas of active and passive-
touch and of position, in the case of the dog and ape are de-
posited in this same region. If the motor region governing the
muscles of the dog's fore leg be extirpated from the left hemi-
sphere, the right fore leg may be placed in the most uncomfortable
position, and the animal makes no attempt to correct it. In
descending a flight of stairs it misses the steps and frequently
slips with the right fore foot. If it was trained to offer the right
fore paw in response to one definite signal and the left in response
to another, the latter is offered as before, but not the former.
The dog that has thus undergone vivisection only reaches for a
piece of meat with the left foot, never with the right foot, the
cortical centre of which has now been extirpated. We see, there
fore, that in these animals the ideas of position, touch and
motion are also located in one and the same cortical region. In
the case of man a greater local separation of these functions seems
to have been effected. We should also consider that the motor
idea is complex and that it contains a visual element besides the
tactual. From the facts that we have thus far presented, it is at
least obvious that the material process which takes place in the
large initial cells of the motor path during innervation, occurs
without a concomitant psychical process j psychical processes
only accompany those physical processes that correspond to the
antecedent motive sensations and ideas and to the motor idea
following these and immediately preceding the motor innerva-
tion. Only sensation and idea are psychical processes ; the
motion or motor innervation has no psychical concomitant and is
only the effect of a psychical process.

A ction — Expressive Moiio?is — Speech.

277

Of course a great deal of interest centres in the question as to
how great the velocity of the nerve-process is in certain simple
cases of action. We remember that, in connection with our ex-
periments for determining the velocity of the association of ideas,
and in anticipation of future investigations, we have already em-
phasized the importance of exhaustive researches in this sphere.
In fact a large number of experimental works upon this subject
have appeared, the majority of which are productions of the
Wundt school. We shall here present the results of these investi-
gations briefly, although the interpretation of the numbers given
by the Wundt school will have to be greatly modified of course
in order to harmonize with our standpoint.

When a very simple sensation imparted by a momentary
excitant, produces a movement that is as simple as possible — a
movement of the hand for example — we have the simplest case
of action. In accordance with the precedence of Exner and
Wundt, we designate the time that elapses between the stimula-
tion and the resulting motion as the simple reaction-time.^ It is
of course very important that this simple reaction-time should
also be determined when the person who is being tested does not
know beforehand what stimulus will probably act upon him and
when he has not been previously told to react with a certain
movement. However such an arrangement of the experiments,
especially as regards the second point, is obviously difficult to
attain. On the contrary, the experiment is generally so arranged
that the person who is being tested knows beforehand the
stimulus which he has to expect and a definite movement which
has been previously determined. The experiment is further ar-
ranged so that both the moment in which the stimulus takes
eff'ect, and the moment in which the reactionary movement is
executed, are registered upon a rotating drum. We cannot here
enter into a description of the numerous apparatus that have been
applied in ascertaining the reaction-time ; it is sufficient to name

' In accordance with our nomenclature, we should prefer the designation
"simple action-time." (Also called " physiological time." — T's.)

278 Introduction to Physiological Psychology.

simply Hipp's chronoscope and Wundt's chronograph.^ The
reaction-time is generally stated in thousandths of a second (o-).

These experiments for measuring the reaction-time very soon
showed that the latter varies considerably, according to whethei
the tested person directs his attention to the expected sense-im-
pression or to the hand which is to perform a certain movement.
In the first case we speak of a sensorial reaction, in the latter case
of a muscular reaction. The muscular reaction is always con-
siderably quicker than the sensorial, the difference being ^ about
-Yo second or 100 cr. The muscular reaction is therefore designated
also as the shortened, and the sensorial as the complete reaction-
time. According to the experiments of Ludwig Lange, the simple
reaction-time in the case of stimulation by light, electricity and
sound, amounts, in round numbers, as follows : —

Stimuli of —

For sensorial reaction.

For muscular reaction.

Light

2900-

1700-

Electricity (on the skin)

2100-

looo-

Sound

2300-

1200-

The most noticeable fact, at all events, in the above table is
that the reaction upon impressions of light is considerably slower
than in the other two cases. Individual differences are strikingly
slight as soon as each person tested complies with the proper
conditions, and turns his attention either exclusively to the sense-
impression or exclusively to the movement. The reactions of one
who undertakes to become the subject of experiments for the first
time without preparation, are at first half muscular and half
sensory, the attention is divided and fluctuates between the ex-
pected sense-impression and the movement agreed upon. On
this account the reaction-time in this case varies greatly also ac-
cording to the point toward which the attention is chiefly

' Compare LuDW. Lange, Philosoph. Stud., Bd. 4, S. 457.
'- WuNDT, "Physiol. Psychol.," Bd. 2, S. 267; L. Lange, Philos. Stud.,
l!d. 4, S. 479-

Action — Expressive Motioiis — Speech. 279

directed. In registering the time of astronomical phenomena,
this vacillation of the reactions has been found to affect the
accuracy of observations. A slight difference in the time of
registration appears when two observers view the same pheno-
menon ; it is in this case necessary to make use of especial so-
called " personal equations " for the purpose of eliminating the
error. Only a few trustworthy series of experiments have been
made with the other modes of sensation. The statement made
by v. Vintschgau and Hbnigschmied is very interesting ; accord
ing to this, the time of reaction is greater when the tip of the
tongue is stimulated with quinine than when stimulated with
sugar, while the relation between the two reaction-times is re-
versed when the back part of the tongue is tested. This recalls
the fact already mentioned, that the nerve-fibres which impart the
sensation of sweet are located chiefly in the anterior third of the
tongue, and those that impart the sensation of bitter, chiefly in
the two posterior thirds of the tongue. There are as yet no con-
cordant experimental results in the case of olfactory irritants.
V. Vintschgau ^ and Steinach have determined the reaction-times
in the case of mechanical and thermic stimulation of the skin.
For pressure the reaction-time amounts to about 120-1500-.
When the stimuli are applied to one and the same region on the
skin, the reaction-time in the case of heat-stimulation is longer
than in the case of stimulation by cold, and the reaction-time in
the latter case is longer than for stimulation by pressure. The
reactions appear more quickly when stimulation by heat or cold
is applied to the right half of the face than when applied to the
left half. The fact that individual differences are very consider-
able, as mentioned above, is of great interest.

Now what do these numbers signify ? It is obvious that the
action-time as just determined is occupied by three processes : (i)
the centrifugal conduction of the stimulation from the peripheral
sensory organ to the centre of sensation in the cerebral cortex, (2)
the intercentral process of association which takes place within the

Pfluger's Arch., Bd. 43.

2 8o Introduction to Physiological Psychology.

cortical elements, (3) the centrifugal conduction from the motor
region of the cortex to the muscle. We shall disregard any possible
periods of latency or inhibition at present, for the sake of simplify-
ing our investigations. Only the second of these three processes is
accompanied by a concomitant psychical process. Since the dura-
tion of the first and third are known to us through physiology, at
least approximately, the duration of the second process may also
be computed with comparative accuracy. Thus, for example, in the
case of electric stimulation of the skin, some 6o-8oor of the 2100-
complete reaction-time, may be calculated for the sensory an<^
motory conduction, leaving only about o"t-o'i5 sec. for tht
psycho-physical process of association. In the case of muscular
reaction a still smaller fractional part of a second remains. This
last statement harmonizes well with the fact that reactions often
go astray in the latter case ; the tested person often executes the
movement agreed on before the stimulus has taken effect at alU
Now in what particulars are the two forms of reaction to be dis-
tinguished from each other ? It is obvious that the direction of
the attention to the expected sense-impression means nothing else
than that, before the sensation appears, ideas which bear some
relation to the impression, are already present in the mind of the
person upon whom the experiment is being made. Among these
ideas is especially the mental image of the expected sense-impres-
sion, which is already familiar from the fact that its effects have
been previously experienced. This psychical state is very closely
connected with a corresponding physical phenomenon, the inner-
vation of the muscles of accommodation governing the respective
organ of sense, particularly of the musculus ciliaris and the tensor
tympani.

These phenomena are changed in the case of muscular reaction.
Here the attention is directed to the motion that is to be
executed,— in other words the motor idea, specifically the idea
of the movement of the hand agreed on, occupies the mind of
the person who is being tested at the time the sense-impression
appears. This psychical state generally manifests itself in a slight,
constant, tonic contraction of the muscles of the hand and arn>

Action — Expressive Motions — Speech. 281

which is present long before the reaction takes place. Hence
the difference between the two reaction-times is very satisfactorily
explnined. The predominant mental image of the stimulus, in
the case of sensorial reaction, acts almost as a direct check. The
especial reproduction of this image is not at all necessary in the
entire process of association, — in other words, an especial recog-
niuon of the excitant is superfluous. Therefore, while the tension
of the muscles of accommodation in sensorial reaction can, in
fact, generally facilitate the process of reaction, the image of
memory which is present in consciousness at the same time com-
pels the association to take an indirect course, as it were, or to
introduce a superfluous, intercedent act of recognition. In the
case of muscular reaction the reception of the stimulus is neither
facilitated nor delayed ; but by means of the dominant motor idea
the intercentral paths of conduction, the motor centre, the motor
paths of conduction, and finally even the muscular system are to
a certain extent adjusted and prepared for the coming stimula-
tion. The stimulus only needs to barely tilt the full vessel, as it
were. The excitability of the paths of conduction is heightened
by the idea of motion. This very favourable disposition of motor
elements explains the remarkable abbreviation of the process
which characterizes muscular reaction. ^

Muscular reaction is very apt to become an automatic action,
that is, a reaction in the proper sense ; after some practice the
concomitant psychical process is easily omitted and the movement
of the hand is mechanically executed. This is much more seldom
the case with sensorial reaction. This fact is easily explained by
what has been stated above; in the case of purely muscular
action the psychical act is to be regarded as of minimum duration,
since the innervation, as such, has no psychical correlate what-
ever. In muscular reaction also the sensation exerts a much less
essential influence ; it merely imparts the reaction. Many psycho-
logists assume that in such cases, where the voluntary action be-

* There are no sufficient grounds whatever for the subcortical or cerebella
localization of muscular reaction assumed by Lange.

2 82 Introduction to Physiological Psychology.

comes automatic by practice and the psychical process is at the
same time lost, the material process of excitation gradually takes
another shorter path. They imagine that the intermediate cortical
centre is entirely omitted from the process, and that the trans-
mission of the excitation from one sensory centre to another
motor centre is accomplished below the cortex. This assumption
unavoidably leads to contradictions. In those cases where the
psychical acts become automatic, the path leading across the
cortex is more and more thoroughly trained in consequence of
constant practice; now the same thing occurs that we have already
met in the case of the association of ideas, — intercedent ideas are
omitted in proportion as the process is more and more facilitated.
If the process is constantly developed, one intercedent idea after
another is omitted until the last one finally drops out. Thus,
when a high degree of practice and facilitation has been attained,
the entire psychical process is omitted, especially if at the same
time the intensity of the initial sensation is reduced by other more
intense sensations or ideas approximately to zero. The path of ex-
citation in this case probably remains quite the same; it is simply
more rapidly traversed. In this manner reactions and even reflex
actions are developed from psychical acts. The above-mentioned
psychical omission of a cortical centre as an element in the pro-
duction of action is only accomplished phylogenetica'ly.

But let us return to our experiments for measuring the time
of actions. Thus far we have only investigated the simplest form
of action. We shall now consider some more complicated cases.
We next require the person whom we are testing, to execute the con-
certed movement of the hand only when he has expressly recognised
the sensible stimulus, i.e. when a complete recognition has taken
place. The reaction-time will, of course, be rendered consider-
ably greater by this means. Apart from the special reproduction
of the mental image, another process, a judgment, is generally
introduced, for the person only reacts after having made the judg-
ment " now I have recognised the light " or " the sound." We
must observe, however, that no well-defined distinction exists be-
tween this act of recognition and the simple sensorial reaction

Action — Expressive Motions — Speech. 283

for (i) in the case of sensorial reaction in its most complete form,
the appearance of the mental image and the introduction of a
judgment similar to the one just mentioned, are hardly to be
avoided ; (2) in the case of reaction after recognition the attention
of the person who is being tested is generally directed chiefly to
the expected sense-impression. As may be easily seen, those
experiments employed to determine the reaction-time in the case
of recognition are best in which there is a constant change of
sense-impressions selected from a definite number. By this means
the person who is the subject of the experiment is most easily
compelled always to introduce the above-mentioned deliberation
and recognition, instead of simply reacting. Thus the recog-
nition-time becomes also the " discernincnt-time " or " distinction-
iitne."

A still further complication of the process may be presented by
so arranging the experiment that upon one definite sense-impres-
sion reaction always takes place with the middle finger, upon
another always with the fore-finger. In this case a choice must
be introduced in addition to the distinction or recognition ; accord-
ingly the reaction-time becomes still greater and is designated as
" selection-time." For obvious reasons it is difficult to obtain
either purely sensorial or purely muscular reactions ; in experiments
of this kind the mode of reaction is generally more or less mixed.
Finally, if we introduce one or several more ideas, i.e. a complete
association of ideas, between the sense-impres-iion and the move-
ment, we obtain an example of action in its most complex form
and return once more to the problem of the velocity of associa-
tion which we have already discussed in full. We shall purposely
avoid stating more exact numbers for the so-called "complex
reaction-times " just discussed, for the reason that the experi-
mental investigations made byCattell, ^ Friedrich,^ Miinsterberg, '

* " Psychometrische Untersuchungen," Pliilosoph. Stud., Bd. 3, S. 305
and 452, Bd. 5, S. 241, Rd. 2, S. 635.

* "Zur Methodik der Appeiceptionsversuche," Bd. 2, S. 66, and Bd. 1,
S. 39.

* " Beitriige zur experimentellen Psychologie," H. i.

284 Introduction to Physiological Psychology.

and others in this field, despite their numerousness and tlie care
that has been devoted to them, are not yet sufficiently concor-
dant.

On the other hand, we shall find still another question of
interest. How does the simple process of reaction vary when
the different psychical factors vary ? The most important fact
bearing upon this question is that the reaction-time decreases as
the intensity of the sensation increases. Furthermore, the
reaction-time is always considerably lengthened by the simul-
taneous presence of other sensations or ideas which, as it is ex-
pressed, divert and distract the attention. Wundt has also
established the interesting fact in i)articular, that the disturbing
effect of synchronous sensations is greater when the stimuli are
disparate than when they are of the same kind. Therefore if
the subject of the experiment is to react upon a spark of light, a
synchronous noise is more disturbing than a synchronous light.
Finally, the state of feeling which is dominant in the subject at
the moment of experimentation, is not without influence upon
the reaction-time, as may be easily understood from former dis-
cussions. By " state of feeling " we understand the resultant of
the positive and negative emotional tones that appear at any
definite time. The more the positive tone of feeling predominates
in the state of feeling, the more rapidly, ceteris paribus, do all the
reactions take place. Among other things this accounts in part
for the abnormal acceleration of motor reactions, the so-called
motor excitement, accompanying mania, which, as we have
already mentioned, is characterized by the predominance of
positive emotions.

The reaction-time is also changed by the use of toxicants. For
example, Kraepelin ^ found that certain drugs, such as nitrite of
amyl, ether and chloroform, first increase and then shorten the
reaction-time, while alcohol, on the contrary, first shortens and

* Philosoph. Stud., Bd. I, S. 417 and 575 ; also recently a discourse
before the Jahresversammlung des psychiatrischen Vereins, 1889. Compare
also DiETL and v. ViNTSCHGAU, Pfluger's Archiv, Bd. 16, and especially
Kraepelin's most recent monograph, " Uber die Beeinflussung einfacher psy-
chischer Vorgange durch einige Arzneimittel," Jena, G. Fisher, 1S92.

jtl ction — Expressive Motions — Speech.

then lengthens the reaction-time. In these experiments of course
the difference between muscular and sensorial reaction has not
yet been considered. Furthermore, in proportion as the doses
of alcohol are increased, that phase of its effect which is char-
acterized by an abbreviation of the reaction-time becomes less
and less pronounced and noticeable.

We shall now turn from these experiments for measuring the
time required for the discharge of an action to the different
forms of action that may be distinguished. Here it is psycho-
logically most important to determine whether the hiitial sensa-
tion, or the total content of the mental images participating in the
play of motives, or the emotional tone of both sensations and
ideas has had the predominant influence upon the character of
the resulting motion. In the first case we speak of an " im-
pulsive action " or an " action from impulse," ^ in the second of
an " intellectual action " or an " act of calm deliberation," in the
third case of an " emotional action." The movement of defence
that one makes in response to the visual sensation of a threaten-
ing blow is an impulsive action. The numberless actions that
are daily and hourly performed for the satisfaction of some desire
are emotional actions. Most deliberate actions are intellectual
actions in the sense in which we understand them. This dis-
tinction, however, is by no means always so sharp as may appear
from the above statements. Most actions are affected by all
three factors ; the impulsive acts are always more or less deter-
mined also by some emotion. The voluntary motion in the
narrower sense, i.e. that motion which is accompanied by the
most deceptive feeling of free and voluntary choice, finds no
especial place in this classification. We have already mentioned
the characteristic features of this voluntary action. We may
here add tiiat in the most pronounced cases such action is always
chiefly emotional : in fact, the predominant factor is the positive

* WuNDT designates as impulsive actions those movements that are un-
equivocally determined by a single motive. It is obvious that the two defini-
tions only partially agree.

286 Introduction to Physiological Psychology.

tone of feeling accompanying the motor idea that precedes the
motion. The impulsive act approaches most closely, of course,
to the automatic act ; ^ the intellectual action is furthest removed
from it.

Of far greater importance than the classification just given is
the distinction of a definite group of actions from another stand-
point. This group is composed of the " motions of expression"
or '■'■expressive movements." All movements of expression are
ahke in being the motor discharge of a psychical process, but the
chief effect of this motor discharge consists merely in betraying
the psychical process to other individuals. Every other move-
ment has some other definite external effect, and only incident-
ally and indirectly betrays the psychical state of the person who
is acting. But on the contrary, in the case of motions of ex-
pression, any further external effect is merely incidental. If we
seize a glass of water, it is simply incidental that others perceive
in this movement of the hand our intention to drink. On the
other hand, if we laugh, the chief effect is the expression and
ultimate betrayal of our state of feeling to others. We designate
the grasping of the glass of water as an intended or voluntar}'
action, while many expressive motions, such as laughing, crying,
etc., we generally designate as more or less involuntary. Finally,
there is a series of expressive movements also that are produced
by non-striated muscles, which, according to the common termin-
ology, are never subject to the will at all ; among these are
blushing, crying, the bristling of tlie hair, the ruffling of the
feathers, and other movements affecting the various cuticular
appendages, etc. These expressive movements of the face and of
the dermal appendages do not of course exhaust the series of
expressive motions. The gesticulations of the hand, the shrug-
ging of the shoulders, the bowing of the head, the bending of the
body, and others are all also to be reijarded as expressive move-
ments.

1 Meynert {" Psychiatrie," Wien, l88S) has attempted to demonstrate
that all voluntary motions develop from automatic motions ; such a develop-
ment in fact seems to be conceivable for many impulsive motions.

Acitof{ — Expressive Motions — Speech. 287

The most important group of expressive movements is that
which comprehends the movements of speech As we know,
these motions represent the sura of extraordinarily complicated,
co-ordinated muscular movements of the lips, palate, tongue and
larynx. While the expressive motions first mentioned — laughing,
crying, etc. — generally express especial emotions, the movements
of articulate speech become the expression of our sensations and
their images of memory the ideas. The enormous number of
actual sensations and ideas naturally requires a correspondingly
large variety of articulative movements. Both speech and thought
are the result of a parallel development ; each one is developed
in and ivith the other. The importance of the articulative move-
ments for the combination of component ideas into uniform con-
ceptions we have already discussed in a former chapter. We shall
now understand also why the expressive movements of speech
have so great an influence in determining the higher development
of man. This fact may be further shown in the anatomical
structure of the surface of the brain. If we compare the brain of
the ape with that of man, we find in the latter a complex con-
volution on the back part of the lower frontal convolution, that
is as entirely wanting in the brain of the ape as if it had been
scooped out with a gouge. At this place, as science has known
for fifty years, lies the cortical centre of articulate speech. If
this so-called "convolution of Broca" is destroyed in the left
hemisphere in consequence of having become the seat of disease,
the invalid is still able to execute the grosser movements of the
lips, tongue and larynx, but has lost the finer complex movements
of these organs that are necessary for speech, and will never
recover the control of them. The function of the corresponding
place in the right hemisphere of the human cerebrum is not
exactly known. It is probable that it is more or less concerned
in the articulation of interjections, such as, " my God ! " " yes,"
and "no."^ At the same time that the development of this

* Compare Gowers, " Vorlesungen uber die Diagnostik der Gehirnkrank-
heileii," Vorl. 9 and 10.

288 Introdtiction to Physiological Psychology.

motor-centre of articulate speech is taking place an auditory
word-centre, in which the mental images of words that we luar
articulated are deposited, is developed in the auditory centre of
the cerebrum in the temporo-sphenoidal lobe. If the so-called
region of Wernicke in this centre be destroyed in the left tempo-
ro-sphenoidal lobe, words are still heard, indeed, but not under
stood. Finally in the case of the civilized and cultivated man a
new stage of expressive movements appears in the motions of
writing to which the visual ideas of reading correspond in the
sensory sphere. It is only possible here to cast a very hasty
glance at these highly interesting relations of the cerebrum to
speech ; the study of the respective writers on this subject is to
be urgently recommended.^

The development of expressive motions is a question of para-
mount interest. Duchenne, the celebrated author of "Physiologic
des mouvements" and "Mecanisme de la physiognomie humaine,"
still considers the expressive movements to be a gift with which
God has especially endowed mankind. Either the divine wisdom
or the divine fantasy, according to this conception, has arbitrarily
designated this or that muscle as the means by which mankind
is to give expression to a definite emotion. Darwin^ was the
first to open the way for a phylogenetic explanation of this
subject. The expressive movements of man are also developed
through thousands of years from the expressive movements that
are found in the lower animals. It is very probable that almost
all motions of expression have only developed secondarily from
the common inexpressive psychical actions. Let us take a
definite example : The facial expression of rage and hate in man
is manifested chiefly in the retraction of the lips and the exposure

* Wernicke, " Der aphasische Symptomencomplex," Breslau, 1874, and
also especially the more recent compositions of the same author in Fried-
lander's Fortschritten der Medicin, 18S6. Further Grashey, Arch. f.
Psychiatric, 1885. Lichtheim, Deutsch. Arch. f. klin. Med., Bd. 36.

* "The Expression of the Emotions in Man and the Lower Animals."
•glh Edition, 1876.

Action — Expressive Motions — Speech. 2^9

of the teeth; particularly the corners of the upper lip are
elevated so that the canine teeth become visible. This move-
ment is undoubtedly inherited from the lower animals. In quite
the same way the dog, cat and ape expose the canine teeth in
the presence of a foe whom they intend to attack, or by whom
they expect to be attacked. Originally this movement is not an
act expressive of passion in these animals at all ; on the contrary,
it is a highly fitting preparation for the impending battle. Be-
cause of its fitness, this motor discharge, produced by the
unpleasant sensation of seeing a foe, has been fostered by a
process of selection until it has become a universal phsnomenon
in this series of animals. In the case of man the original
advantage accompanying the movement has disappeared, since,
in fact, the teeth rarely serve mankind as a weapon in battle at
the present day ; but the movement has been retained as the
expression of the specific painful emotion which accompanies
the seeing of a foe. But still further, other sensations that
resemble the visual sensation of a foe as to their tone of feeling,
or that are associated with the idea of a foe, also impart this
same movement of expression. This is true also in the case of
the lower animals very often when the possibility of battle and
of using the teeth is entirely excluded. A passionate person also
often shows his teeth when fortune has failed to fulfil some
desire. We should also mention that in the large majority of
cases, in fact, these expressive motions lose their original and
immediate advantage (defence, etc.), but at the same time
gradually gain another just as great advantage. The young
animals' cries of distress call the mother to their side ; the adult
animal's cry of rage teiTifies the intruder. In by far the greater
number of cases it is useful to animals thus to become cognisant
of one another's passions. In man the development of these
expressive movements reaches its highest stage. Since language
has a special word, i.e. a special expressive movement executed
by the muscles of the larynx and mouth, for each sensation and
each idea, and not alone for the emotions, as is the case with
the expressive movements of the lower animals, social community

290 Introduction to Physiological Psychology.

and culture are possible, and man gains an immeasurable advan-
tage in the struggle for existence.

It is still very uncertain from what special expressive move-
ments language or speech has developed. ^ It is by no means a
human invention, as has been recently asserted, that has come
into use in consequence of a universal agreement. On the other
hand, the construction of words appears to have taken place
chiefly in two ways : (i) by development from the animal's cry of
emotion, (2) by so-called onomatopoeic development. The animal's
cry already expresses manifold psychical states, although they are
chiefly of an emotional nature. As the enticing call of the male,
it expresses sexual feelings ; as the cry of distress, it expresses
the fear of impending danger ; as the cry of rage, it expresses
hate, etc. Particularly the suddenly appearing visual stimuli (a
passing animal in flight, lightning, etc.) impart a cry that ap-
proaches very closely to the nature of reflex action. By the
process of selection these cries become differentiated more and
more, in the manner that we have so often noted, until finally
they become the colossal treasure of words that constitute a
language. Onomatopoeia has exerted a more secondary modify-
ing influence upon language. It is especially ^ important in the
case of acoustic stimuli. A sound that is often heard in nature,
is imitated ; in other words, the motor discharge which is imparted
by the acoustic sensation of a roll of thunder, for example, is
gradually modified until the movements of the organ of speech
finally produce a sound resembling thunder. We are as yet far
from having arrived at an understanding of this imitative impulse
from the standpoint of the Darwinian theory, but its importance
in the development of language is not to be doubted. That
many individuals are able to understand a large number of words

^ Compare P. Regnaud, " Origine et philosophic du langage ou principes de
linguistique indoeurop6enne," Paris, 1889. Unhappily Regnaud does not fully
recognize the value of onomatopoeia. Marty's articles (Viertljahrschr. f. wiss,
Phil., '85-92) furnish a review of all controversies relating tp this subject,
although they lead to very doubtful conclusions.

But not exclusively ; compare Lazarus, " Leben der Seele." Steinthal,
" Abriss der Sprachwissenschaft."

Action — Expressive Motions — Speech. 291

thus developed may be easily explained in both cases by laws
of association with which we are already familiar. Let us con-
sider that both the reflex cry and the onomatopcetic imitation,
111 the case of one and the same sensation, would necessarily
result the same, in different, but similarly constructed individuals.
The great influence which heredity exerts upon the movements
of expression is most forcibly revealed by the fact that persons
who are born blind and deaf (as Laura Bridgman for example)
express their joyful emotions by the typical form of laughter.
In the development of the normal child, most of the expressive
motions only appear comparatively late; for example, weeping
seldom appears before the third month after birth.^ It is very
interesting to note that in almost all the races of mankind the
mimic motions expressing feeling are very nearly identical. As
regards the movements of expression in speech, we know that
comparative philology has already established very great analogies
between the different languages. We have already mentioned
above that the lower animals also exhibit numerous expressive
movements that resemble those of man in a high degree.

Another very interesting part of this subject is the anatomical
localization of the nerve-paths and nerve-centres for motions of
expression. As we have already heard, the centre for the most
complicated expressive movements, those of speech, is un-
doubtedly located in the cortex. The path that conducts the
motor impulse of speech from the cortex to the muscles of articu-
lation appears to be contained chiefly in the pyramidal tract ; no
interruption of this path whatever takes place in the large ganglia.
This is different in the case of the mimic movements of expres-
sion. Their centre is probably located in the Thalamus opticus.
After the entire cortex of the cerebrum has been removed from
a rabbit, it still performs its characteristic movements of expres-
sion— the bobbing of the tail for example.^ According to the

' Compare Preyer, " Seele des Kiiules." Binswanoer has observed
laughing already in the 15th week after birth ; smiling appears in the 7th
and lOlh weeks.

* Bkchterevv, Virch. Arch , Bd. loi. Ziehen, Arch. f. Psycli., XX

292

Introduction to Physiological Psychology.

more recent clinical observations of Nothnagel's,^ the Thalamus
opticus seems to be undoubtedly of great importance also in
the case of the mimic expressive movements of man. This infra-
cortical localization is also justified by the psychological fact that
the mimic motions of expression — laughing, for example — are
imparted by a psychical factor, indeed, but that they are very
little subject to the process of association. In fact, we may say
that they take place almost involuntarily. It is obvious, however,
that there must be still another path to impart to the Thalamus
opticus the cortical excitation which corresponds to the psychical
state of the gay mood. Such internuncial fibres are, in fact,
known to exist in large numbers between the Thalamus opticus
and the cortex of the cerebrum. Finally, certain expressive
movements, such as the bristling of the hair, blushing,' etc.,
probably have their centre in still deeper parts of the brain,
particularly in the Medulla oblongata. This again harmonizes
with the fact that these expressive movements also result from
psychical causes, but are virtually not subject to the volition or,
more properly, to the process of association at all ; they cannot
even be voluntarily suppressed.

We must now content ourselves with this hasty view of
"actions." The task next awaits us of determining what place
in our psychology shall be assigned to the so-called will.

1 NoTHNAGEL, Zeitschr. f. klin. Med., 1889, Bd. 16, H. 5 and 6.

^ In a certain sense, the peculiar changes of the pulse that accompany the
emotions of excitement belong to this class of expressive movements. Com-
pare Ziehen, " Sphygmograph. Untersuchungen," 1887.

CHAPTER XV.

WILL — GENERAL CONCLUSIONS.

We have traced the cortical excitations back to the numberless
material stimuli of the external world ; in the psychical sphere
the sensations correspond to the cortical excitations. We also
followed the cortical excitation in the cerebrum by way of certain
associative fibres to the motor centres. From these the excita-
tion is again conducted toward the periphery to the muscular
system, and imparts certain muscular contractions. Psychically
the process of the association of ideas corresponds to the material
process of nervous excitation that takes place in and across the
cortex ; to the resulting motion we gave the psychological desig-
nation of " action." We were able to deduce action very
satisfactorily from the sensation and the mental images of former
sensations, the ideas, in accordance with the laws of association.
In so doing we had traced the psychical process to its close. At
this point, however, we meet a hypothesis that has been taught
by all former psychologies almost without exception, — a hypothesis
at which, as it would seem, the common understanding of
humanity has arrived naively and unconsciously. This is the
assumption of an especial will as the cause of our actions. This
hypothesis introduces between the process of ideation and the ac-
tion the further activity of a special psychical faculty. The associ-
ation of ideas only supplies the motives ; it is the will that finally
decides which of these motives shall prevail. While the other
faculties of the soul (understanding, judgment, etc.), as such, have
rapidly lost ground since Herbart, the doctrine of the existence of

an especial will-faculty still obtains with the greatest pertinacity.

293

294 Introduction to Physiological Psychology.

Now, as we have already seen, nothing has as yet compelled us
to assume a new and entirely hypothetical factor in the conscious
life. We can therefore with complete justice shift the onus pro-
bandi on to the shoulders of those who champion the doctrine
of a special faculty of the will. We have explained all psychical
processes without it; they would not be rendered any more
intelligible by using it, What does it mean when we say " I will
go " ? or, to state the question more correctly, what psychical
content do the movements of speech producing the words, " I will
go," express ? Obviously they only express the fact that the
motor idea of going occupies the consciousness with great inten-
sity, and is accompanied by a very pronounced positive tone of
feeling. At the same time the grouping of latent ideas is such that
those ideas which aid the appearance of the motor idea of going
predominate over those ideas that would arrest its appearance.
When we imagine how fine it would be to climb yonder mountain,
this idea may be very vivid and yet we may not come to the conclu-
sion that we will go up there. In this case a visual idea accompanied
by a positive tone of feeling almost exclusively occupies the
attention ; there is only a very weak idea of the motions to be
performed by the limbs. Numerous inhibitory ideas, as that of
the remoteness of the mountain, etc., do not permit the motor idea
to gain strength. We go one step further and say, " I would like
to climb yonder mountain." What does this " would like " — this
" desire " mean ? In this case also the content of the idea
remains the same; the motor idea is still checked despite the
great increase of its positive emotional tone. Finally, the last step
is taken when we say, " I will climb yonder mountain." Tlie
motor idea has become extraordinarily intense, the positive tone
of feeling has reached its height, and, above all, the assistant ideas
predominate over the inhibitory. The expression " I will" desig
nates not only the subjective consciousness at a definite moment,
but also the objective status quo of the brain, in particular the
grouping of latent ideas. Here we may distinguish three cases.
If another person says of us that we will do this or that, he means
properly that the grouping of our latent images of memory is

Will — General Conclusions.

S95

favourable to the appearance of this or that idea of motion
accompanied by a strong positive emotional tone, or to the ap-
pearance of the appropriate action. On the other hand, when we
will do something, our own psychical conte?it at that moment is
only distinguished from other psychical contents by the fact that
the idea of a desired action, accompanied by a positive emotional
tone, is already contained among the sensations and ideas that
are then actually present. In addition to this also, those peculiar
oft-mentioned motor sensations appear, which are produced by
the unconscious innervation of the appropriate muscles correspond-
ing to the increase in attention. Finally, still a third case is to
be distinguished, — our own psychical content when we say, "/
7vill do sofiieihing" i.e. when we interrupt the voluntary action for
a moment and reflect upon it. This " I will do something," when
spoken, is a series of motor ideas of speech with which are associ-
ated (i) the Ego-idea in the sense formerly discussed ; (2) the
idea of a future act, accompanied by a positive emotional tone ;
(3) motor sensations accompanying attention ; and (4) the idea
of a causal relation existing between the Ego-idea and the desired
action.^ All of these elements are already known to us ; none of
them is new. The idea of a causal relation is an idea of relation
quite the same as the idea of similarity, formerly discussed as a
paradigm of all ideas of relation. Therefore this analysis also gives
no ground for the assumption of a special faculty of the will.

Psychiatry also furnishes an interesting confirmation of the
above conclusion. It has arrived, quite empirically, at the
assumption of two chief forms of psychosis, the one originating
in the intellectual sphere, the other in the emotional sphere of
psychical life. Psychiatry knows of no special psychosis of the
will. The attempts to set up special diseases of the will under the
name of monomania, or a general disease of the will designated as
moral insanity, have all been recognised failures. All disturbances
of voluntary action that we find in cases of mental disease, without

' Compare the discussions of Th. Wai i z, "Lehibiich der Psycliologie al
Naturwissenschaft," that in many rcs]5ects already anticipate this standpoint.

296 Introduction to Physiological Psychology.

doing violence to or neglecting any facts, may be reduced either
to disturbances of the sentient life, especially of the emotional tone,
or to intellectual disturbances, i.e. disturbances of the ideas or of
the association of ideas. The so-called loss of volition (abuHe),
the inability to come to a decision, for example, is a frequent
symptom of mental disease ; but this so-called loss of will-power
may always be reduced either to the exceeding sluggishness of
of the association of ideas, to the abnormal negative tones of
feeling, or to other similar afflictions. Pathology, therefore, also
argues against the assumption of a special faculty of the will.^

We have yet to discuss the question as to how we come to
regard the idea of our ego as the cause of our actions ; and finally,
whence the feeling of freedom that accompanies our actions arises.
It is obvious that we finally come to regard the ego-idea as the
cause of our actions because of its very frequent appearance in
the series of ideas preceding each action. It is almost always
represented several times among the ideas immediately preceding
the final movement. But the idea of the relation of causality
is an empirical element that always appears when two successive
ideas are very closely a.ssociated.

The feeling of freedom in actions is to be explained the same
as the feeling of freedom in the association of ideas formerly
described. We must here emphasize once more that this feeling
of freedom depends upon the absence of external compulsory
motives, and therefore upon the fact that not the sensations alone,,
but also the images of memory, determine our movements. This
notion of a free will is also furthered by the fact that the idea of
" not performing " a movement, or the idea of another movement
than the one wliich is accompanied by the stronger tone of
feeling, and which is finally actually executed, appears and takes
part in the play of motives. But that which finally causes the
latter idea to prevail and suppresses the former is not a special
faculty exercising free will, but only the stronger emotional tone

• Compare RiBOT, " Les maladies de la volonte," a work, however, that
ascribes decidedly too much importance to the ego in acts of tlie will.

Wz7/ — Getter al Conclusions.

297

and greater associative affinity of the prevailing idea, combined with
the favourable grouping of the latent mental images. Our actions
are as strictly necessitated as our thoughts ; ^ we cannot but come
to this conclusion, for both action and thought are in fact quite
identical when viewed in the light of their fundamental psychical
characteristics. Thought consists of a series of ideas, and the
psychical element of an action is likewise a series of ideas whose
sole specific characteristic is that its last member is an idea of
motion. Both are governed by entirely the same laws ; both are
associations of ideas. The final motor effect in the case of
action, according to this standpoint, is rather an incidental
accession which in itself has no concomitant psychical process.
We should not forget, furthermore, that slight motor elements —
the slight muscular tension accompanying attention, for example
— affect the process of thought. On this account thought has
also been very suitably designated as inner action ; and action
that is manifested in the contraction of the muscles, as external
action.

In this connection we must consider another reason that many
seem to regard as of especial importance in arguing the freedom
of the will. It is a common belief, in fact, that if the will in
general and the freedom of volition in particular are denied, all
ethical distinction between actions and all accountability for
actions are thereby removed. Let us consider the two arguments
separately. Psychologically an " ethical distinction " means that
certain actions (for example, murder) produce a negative tone of
feeling, others a positive tone of feeling. This difference between
the accompanying tones of feeling is by no means destroyed by
any of the doctrines that we have advanced. In the sphere of
etliics "good" and "bad" designate respectively positive and
negative tones of feeling, just as " beautiful " and " ugly " express
respectively positive and negative emotional tones in the- sphere

'■■ The memorable expositions of Spinoza (" Ethik," P. II, Propos. 49, and
especially the following Scholium) should also he compared with the ahovc
conclusions.

298 Introduction to Physiological Psychology.

of aesthetics. The ethical feelings, the same as the aesthetic,
cannot be reduced by the empirical psychologist to a certain
chief formula. It can be shown that almost all actions, which
we now regard as crimes, have at some time been regarded
as good by human beings of other ages or of other places,
z.c, they were accompanied by positive emotional tones in
mankind. Absolute ethical laws are as little to be expected
from psychology^ as absolute sesthetical laws. Both the ethical
and sesthetical emotional tones fluctuate, (i) historically : they
are the product of an historical, if not phylogenetic, develop-
ment; and (2) also among the same people at any definite time ;
they are fully agreed upon only by a large majority and not by
all. We shall certainly not condemn empirical psychology for
not establishing ethical laws, for of what assistance would any
possible laws which the psychologist might establish be to the
moral philosopher ? They could only have an empirical charac-
ter, and not that absolute character customarily required by the
ethical philosopher. In this work we are only concerned with
laws in us, and not laws above us.

It is very different with the conception of moral accountability
or responsibility. This conception, in fact, is contradictory to
the deductions of physiological psychology. The latter teaches
that our actions are strictly necessitated ; they are the necessary
product of our sensations and ideas. Therefore, according to
physiological psychology, we could no more hold a man guilty
and accountable for his bad action than a flower for its ugliness.
Hence the action remains bad, even when viewed psychologi-
cally, but in itself does not impart guilt. The conceptions of
guilt and accountability are — to designate the antithesis briefly —
either religious or social conceptions, and on that account may
be disregarded here. Psychology, let us repeat, does not deny
absolute sesthetical or ethical laws in so far as they can be de-
monstrated from some other standpoint ; but psychology itself,
limited to empirical data, can only establish empirical laws.'

' The following authors are to be especially recommended for a further,

Will — General Conclusions.

299

Hence the investigation of the so-called voluntary processes
has given f.s no grounds whatever for the assumption of another
psychical " something " in addition to the series of sensations and
ideas.

The metaphysician can perhaps arrive at the theoretical fiction
of a being which is the subject of the sensations, ideas, and
actions, and may name this subject Ego or Soul. Physiological
psychology, however, cannot exceed the bounds of its empirical
data ; at the close of its investigations we have simply to ask
whether it can offer us any further empirical facts that will throw
some light upon the nature of that parallelism which, from the
beginning, we have supposed to exist between the psychical
processes and the material physiological processes of the brain.

Let us now briefly consider how science has hitherto accounted
for this parallelism, which primarily means simply a regular
coexistence. For this purpose we distinguish dualistic and
monistic theories.

The dualistic theories all accept the dualism of the two series
(material and psychical), and avoid every attempt to resolve it.
In so doing the complete interdependence of the two series, in
fact the very thing that we have called parallelism, remains
wholly unintelligible. On this account Leibnitz, one of the chief
champions of the dualistic theory, was forced to have recourse to
the theory of a pre-established harmony. Geulinx's occasional-
ism also belongs to this class of theories. Of course the fact that
the psychical series of phenomena is much shorter than the
material or physical series is somewhat unfavourable for this

more exact study of the theory of the will : Herbart, " Psychologic als
Wissenschaft " ; Spencer, "Principles of Psychology"; Lipps, "Grund-
thatsachen des Seelenlebens " ; Steinthal, "Einleitung in d. Psycholoi^ie
u. Sprachwissenschaft " ; Bain, "The Senses and the Intel'ect," and "The
Emotions and the Will." The views of Wundt, which are in general diame-
trically opposed to the views of these researchers, and which agree with older
authorities in the assumption of a special faculty of the will, are to be found
in his "Grundziige der physiologischen Psychologic," and also in his
•' Ethik."

300 Introduction to Physiological Psychology.

dualistic theory. Experience demonstrates parallel psychical
processes for only a small part of the material processes, namely,
for the physiological processes of the brain. For this reason the
attempt has been made to equalize this difference in " length " —
if we wish to preserve the comparison with lines — by hypotheti-
cally lengthening the psychical series. Hence certain philosophers
came to assume parallel psychical processes, not only for all
physiological processes of the brain, but also for all organic
material processes. This hypothesis may be designated as the
animistic theory. Among its champions is Wundt.^ Finally the
doctrine of hylozoism goes still further, and ascribes life, and
hence parallel psychical processes, to all inorganic processes.
Fully and logically applied, this theory views each atom and each
molecule as the possessor of a concomitant psychical substance.
In opposition to all these theories, it should be remembered that
they all lead unavoidably to the assumption of unconscious psy-
chical processes, an assumption that is in itself contradictory, as
we have already seen.

Among the monistic theories we shall consider those first that
assume the subordination of one series to the other. Here but
two theories are possible ; either the material series of pheno-
mena is to be regarded as a function of the psychical, or the
latter as a lunction of the former. Neither the first-mentioned
spiritualistic view, nor the last-mentioned materialistic view is
able to give any sufficient ground whatever for the subordination
of one series of phenomena to the other which it assumes. Those
monistic theories that preserve the co-ordination of the two series,
but would still establish their unity, have sought to accomplish
the task by regarding both series as attributes of one substance.
Accordingly Spinoza ascribed the two attributes of extension and
thought {extensio and cogitatio) to his one absolute substance, the
Deus sive mundus. This view of Spinoza's is in harmony with
that of many natural philosophers who ascribed (i) extension

* WUNDT (System der Philosophic, Leipzig, 1889) has recently designated
animism as that view " which regards the essence of mental life as comprehended
in the will."

]ViIl — General Conclusions.

and (2) a psychical property, as memory, for example, to their
molecules, in that it merely creates a formal logical unity for the
two separate series. But these undemonstrated hypotheses do
not give us any insight whatever into the connection that exists
between the two series.

Another variety of the monistic theory likewise accepts the two
series as co-ordinated, but attempts to remove their difference by
more or less sophistical arguments. The two series are supposed
to be originally and properly identical "in the absolute," and to
have become differentiated only by a " disunion of the absolute.'^
The metaphysical histories of creation, found in the " philosophy
of identism," or the "doctrine of identity," belong to this class
of theories.'

The last of the monistic views may be designated as the critical.
It is the only one that remains within the bounds of empirical
psychology as a natural science. This critical view does not
accept the two series without further test ; on the contrary, it
investigates the manner in which we have come psychologically
to assume the existence of two series and endeavours to deter-
mine whether the material and psychical data are equally primary
or not. Such a critical test demonstrates quite irrefutably that
our first data are only those contained in the psychical series of
phenomena.^ We shall now discuss somewhat more thoroughly
this last and most important proposition of empirical psychology,
a proposition that is too easily ignored, especially on the part of
the natural sciences.

We first became familiar with reflex and automatic acts.
Neither is accompanied by a psychical process. Such a process

1 The view also entertained by many modern psychologists that matter is
that viewed from without which tlie psychical is viewed from within (Hoffdinjr's
" Hypothesis of Identity ") is not much more than a play of words. One
might fitly ask to what observer or the observed belong.

that strictly speaking only the psychical series of one individual is
primarily given, may here be disregarded. The exclusive consideration of
this fact leads to so-called solipsism or egoism in epistemology. Ccmp. r.
SCHUBERT-SOLUERN, " Hampf um die Transcendenz. '

302 Introduction to Physiological Psychology.

appeared first as a concomitant of action. We should not forget,
however, that action is not produced because a concomitant
psychical process is introduced. By no means. On the contrary,
the material process that lies at the foundation of an action is
complete in itself, exclusive of the concomitant psychical process;
it caij be perfectly understood also without the aid of sensation
or ideation. On the contrary, sensation and ideation to a certain
extent present complications of the process. The unintelligible
fact which requires explanation is that, contrary to the automatic
and reflex acts, the action is found to be accompanied by an
entirely new element, the concomitant psychical process. The
material elements of the action are in themselves quite clear.
The action would not be any different even if the excitation of
the sensory cell should not produce its correlate, the sensation,
nor the material disposition left in' the brain (the El or Ei\ its
correlate, the image of memory or idea. We could render the
general fitness of our actions just as intelligible as the fitness of
automatic and reflex acts, or the fitness of a bird's plumage. In
both cases the process of selection is the essential factor in the
development of this fitness. In the case of the bird's plumage, of
reflex action, and to some extent of automatic ^ action this selec-
tion is essentially a phylogenetic process ; in the case of actions
it is an ontogenetic process. Strictly considered, all actions must
first be attained by practice during the ontogenesis of the indi-
vidual,— for example, the practising of a selection for the piano.
Only the cortical mechanism, an apparatus highly adaptable to
the training of voluntary actions, is phylogenetically acquired, i.e.
inherited. Therefore the fitness of actions is quite conceivable.

The above throws new light upon the nature of the automatic act, the
intermediate position of which has already been mentioned. In fact, apart
from the absence of concomitant psychical processes in the case of automatic
action, and their presence in the case of action, a well defined distinction
between many automatic acts that are ontogenetically developed and pure action
is impossible. The unconscious automatic playing of the piano, acquired by
practice, as a material process, is hardly to be distinguished from the conscious
act in any essential point.

Will — General Conclusio7ts.

303

at least, as the result of material laws ; as a simple matter of ex-
planation, the parallel psychical processes are useless and super-
fluous. Let us repeat that, according to the above statements,
the appearance of concomitant psychical processes themselves is
the only fact that needs explanation. Accordingly the question
arises : What material processes are accompanied by these psy-
chical processes ? It is not sufficient to answer that the cortical
processes alone are accompanied by psychical processes. Num-
berless material processes of the cortex take place without the
concomitance of psychical processes. One and the same Ec
produces a sensation to-day, but none to-morrow, according to
the variations in the grouping of the latent ideas. There is no
answer to the above question whatever. But empirical psycho-
logy now raises that critical and decisive question, by means of
which it tests its own foundations : How do we come by this
separation of the empirical data into two series, the material and
the psychical ? With which series are we directly and primarily
furnished ? Let us test the matter upon ourselves. We see a
tree, for example. Apparently in this case both series of data are
already present, the seeing and the tree. But is this an exact
statement of the facts in the case ? By no means. That which
is empirically furnished us is simply and alone our visual sensa-
tion, tree, i.e. merely a psychical process. We only employ this
sensation in a very remarkable way by constructing an idea of the
object tree as the cause of our sensation tree. The same is true of
all objects of the external world. In every case we have only the
psychical series of sensations and their ideas. We only adopt a
universal hypothesis, when we assume that a material series
exists in a causal relation to the psychical series. Epistemology
and metaphysics, in so far as there is such a science, must decide
as to the justice of this hypothesis. The proposition itself, that
the material and psychical series of phenomena are not equally
direct and primary as factors in cognition, contains all that is of
importance to us here. We are only directly and empirically
furnished with the psychical series of phenomena; the other
series is simply inferred. The material series may be regarded as

304 Introduction to Physiological Psychology.

an idea that we have abstracted from our sensations and their
ideas. Modern physics also harmonizes well with this view.
Ultimately nothing of the so-called matter is left to the natural
scientist but infinitesimal points in space, that are conceived of
as possible centres of power, i.e., that can effect sensations. This
so-called matter, apart from its hypothetical causal relation to the
sensations, is otherwise an entirely unknown element. Now the
same thing is true of the material cortical processes that is true
of all material processes. They are also merely inferred, and not
primary, empirical data, as are the psychical processes. Strictly
speaking, we arrive at the inference of a material series of pheno-
mena as follows : We have numerous sensations, and by means
of these we acquire ideas ; we then assume external objects as the
causes of these sensations and ideas. Among our sensations are
also those with which we have met in our anatomical and physi-
ological investigations of the cerebral cortex. Here, the same as
in the case of all sensations, we also assume that a material cause,
the cerebral cortex, produces the sensations which we have in
seeing and investigating the same. Further research shows that
just these material cortical processes also have a very special
relation to all psychical processes ; that, in fact, the former never
occur without the latter, nor the latter without the former. Em-
pirical psychology does not need to occupy itself with a further
solution of this complicated problem. Every attempt to reach
a complete solution would necessitate its departure from empiri-
cal grounds. It therefore relegates the further handling of the
problem in so far as it is capable of any solution whatever, to a
possible metaphysics, or to epistemology. On the other hand,
our science must depend so much the more upon the empirical
fact itself, that primarily we have only psychical data, and nothing
outside of or beyond these. Thus far psychology remains within
the bounds of natural science, and is quite true to its empirical
character. It is of interest that in this last proposition our
science stands in the closest harmony with the founder of the
critical philosophy, Kant. Locke, Berkeley, and Hume had pre-
pared the way for the great truth which Kant finally expressed.

Wz'// — General Conclusions.

that primarily we have only the psychical series, the series of
appearances or " phenomena," as he called them. The hypothet-
ical "cause" of the "phenomena," or of the psychical series, is
(i) merely inferred, and (2) a factor of which we know absolutely
nothing.

Thus the psychophysical dualism or parallelism finally proves
to be only a semblance.

Hence, since the psychical series is the primary series, we can
also understand why we frequently met with psychical factors in
our previous researches for which there was no material basis.
Let us recollect, for example, the projection of our sensations into
space and time, a psychical fact for which we were unable to
obtain any psycho-physiological explanation.

With this last proposition our task is completed ; the sphere of
empirical physiological psychology is brought to a close. Each
further step would be a metaphysical procedure, and would in-
evitably lead to a problematical metaphysics. Physiological
psychology, however, must remain a natural science or betray its
cause.

!
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Full text of "Introduction to physiological psychology"

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