(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Is the latent time in the Achilles tendon reflex a criterion of speed in mental reactions?"

^^^^p^t^f l?f t"/ ^^■-■C '-' ' 



J-S The L^ilenf lirvie 

r\ Lri lerion of obeed 
in iMenial ReactiiorA^? 



ex 




::-v-: -f^f^^¥lWif^ 







llthrarg 



IS THE LATENT TIME 

IN THE 

ACHILLES TENDON REFLEX 

A CRITERION OF SPEED IN 

MENTAL REACTIONS? 



BY 
GEORGE H. ROUNDS, Ph.D. 



ARCHIVES OF PSYCHOLOGY 

E. S. WOODWORTH, Editob. 

No. 95 



NEW YORK 

January, 1028 



ARCHIVES OF PSYCHOLOGY 

Coi/tTMBiA University, New York City. The Subscription price is six dollars per volume 
of about 500 pages. Volume I comprises Nos. 2-10, Volume II, Nos. 11-18, Volume III, Nos. 
19-25, Volume IV, Nos. 26-32, Volume V, Nos. 33-39, Volume VI, Nos. 40-46, Vol. VII, Nos. 
47-52, Vol. VIII, Nos. 53-58, Vol. IX, Nos. 59-63, Vol. X, Nos. 64-68, Vol. XI, 69-73, Vol. XII, 
74-78, Vol. XIII, 79-85. The available numbers are as follows : 



2. On the Functions of the Cerebrum: The 

Frontal Lobes: Shepherd Ivory Franz. 

50c. 
8. Empirical Studies in the Theory of 

Measurement: Edward L. Thorndike. 

50c. 

4. Rhythm as a Distinguishing Character- 
istic of Prose Style: Abram Lipsky. 
50c. 

5. The Field of Distinct Vision: W. O. 
Ruediger. 70c. 

6. The Influence of Bodily Position on 
Mental Activities: Elmer E. Jones. 
50c. 

7. A Statistical Study of Literary Merit: 
Frederic Lyman Wells. 30c. 

8. The Relation Between the Magnitude 
of the Stimulus and the Time of Re- 
action : Sven Fuoeberq. 35c. 

9. The Perceptual Factors in Reading: 
Francis Marion Hamilton. 50c. 

10. Time in English Verse Rhythm : War- 
ner Brown. 70c. 

11. The Hearing of Primitive Peoples: 
Frank G. Bruner. $1.00. 

12. Studies in Development and Learning: 
Edwin A. Kirkpatrick. $1.00. 

13. The Inaccuracy of Movement: H. L. 
Hollingworth. 80c. 

14. A Quantitative Study of Rhythm: Her- 
bert WOODKOW. 60c. 

16. On Certain Electrical Processes in the 
Human Body and their Relation to 
Emotional Reactions: Frederic Lyman 
Wells and Alexander Forbes. 40c. 

17. The Relative Merit of Advertisements: 
Edward K. Strong, Jr. $1.00. 

18. Attention and Movement in Reaction 
Time : J. V. Breitwieser. 50c. ■ (Cloth, 
75c.) 

19. An Empirical Study of Certain Tests 
for Individual Differences : Mary Theo- 
dore Whitley. $1.25. (Cloth, $1.50.) 

20. Visual Acuity with Lights of Different 
Colors and Intensities : David Edgar 
Rice. 50c. (Cloth, 75c.) 

21. The Curve of Forgetting: C. H. Bean. 
4.'-)c. (Cloth, 70c.) 

23. Reaction Time to Retinal Stimulation. 
A. T. Poffenberger, Jr. 70c. (Cloth, 
9.5c.) 

24. Interference and Adaptability: Arthur 
Jerome Culler. 7uc. (Cloth, $1.00.) 

25. Reaction to Multiple Stimuli. John 
Welhofp Todd. COc. (Cloth, 85c.) 

26. A Study in Incidental Memory : Garry 
0. Mvers. $1.00. (Cloth, $1.25.) 

27. A Statistical Study of Eminent Women : 
Cora Sutton Castle. 80c. (Cloth, 
$1.05.) 

28. The Mental Capacity of the American 
Negro: Marion J. Mayo. fiOc. (Cloth, 
Br,c.) 

29. Experimental Studies i!i Judgment : H. 
L. Hollingworth. $1.25. (Cloth, $1.50.) 

30. The Psychological Researches of James 
McKeen Cattell: A Review by Some 
of His Pupils. $1.00. (Cloth, $1.25.) 

31. Fatigue and Its Effects upon Control: 
Isaac Rmrry Ash. 60c. (Cloth, 85c.) 

82. The Transfer Effects of Practice in Can- 
cellation Tests: Mklvin Albert Mar- 
tin. 60c. (Cloth, 8i5c.) 

33. The Intellectual Status of Children 
Who are Public Charges. J. L. Sten- 
oniRT, E. L. Thorndike and M. R. 
Trabub. 60c. (Cloth, 76c.) 



34. The Relation of Quickness of Learning 
to Retentiveness : Darwin Oliver Lyon. 
50c. (Cloth, 75c.) 

35. The Overcoming of Distraction and 
Other Resistances : John J. B. Morgan. 
75e. (Cloth, $1.00.) 

36. The Psychology of the Negro — An Ex- 
perimental Study : George O. Ferguson, 
Jr. $1.25. (Cloth, $1.50.) 

37. The Effect of Distraction on Reaction 
Time: John E. Evans. $1.00. (Cloth, 
$1.25.) 

38. The Effect of Humidity on Nervousness 
and on General Efficiency : Lorle Ida 
Stecher. 90c. (Cloth, $1.15.) 

39. The Mechanism of Controlled Associa- 
tion. Mark A. May. 75c. (Cloth, 
$1.00.) 

40. Recitation as a Factor in Memorizing. 
Arthur I. Gates. $1.00. (Cloth, 
$1.25.) 

41. Mental Fatigue during Continuous Ex- 
ercise of a Single Function : Thomas 
Russell Garth. 8.5c. (Cloth, $1.10.) 

42. A Psychological Study of Trade-Mark 
Infringement : Richard H. Paynter, Jr. 
85c. (Cloth, $1.10.) 

43. Individual Differences and Family Re- 
semblances in Animal Behavior : Hal- 
sey J. Bagg. 70c. (Cloth, $1.00.) 

44. Experimental Studies in Recall and Rec- 
ognition. Edith Mulhall Achilles. 
90c. (Cloth, $1.25.) 

45. The Morphologic Aspect of Intelligence. 
Sante Naccarati. 70c. 

46. Psychological Examination of College 
Students: P. Edith Carothers. $1.25. 

47. The Effects of Practice on Judgments 
of Absolute Pitch: Evelyn Gough. 
$1.25. 

48. An Experimental Study of Silent Think- 
ing: Ruth S. Clark. $1.40. 

49. Some Emperical Tests in Vocational Se- 
lection: Herbert W. Rogers. 75 cents. 

50. Adenoids and Diseased Tonsils: Their 
Effect on General Intelligence. Mar- 
garet Cobb. $1.00. 

51. An Experimental Study of the Factors 
and Types of Voluntary Choice: Al- 
fred H. Martin. $1.50. 

52. Some Well-known Mental Tests Evalu- 
ated and Compared : Dorothy Ruth 
Mougenthau. 80 cents. 

53. Mood in Relation to Performance: 
Elizabeth T. Sullivan. $1.00. 

54. The Influence of Incentive and Punish- 
ment upon Reaction Time: Albert M. 

JOHANSON. 80c. 

55. Psychological Tests Applied to Factory 
Workers: Emily Thorp Burr. $1.25. 

56. A Study of the Relation of Accuracy 
to Speed : Henry E. Garrett. $1.25. 

57. An Experimental Study of Hunger in 
Its Relation to Activity: Tomi Wada. 
$1.50. 

56. Individual Differences as Effected by 
Practice: Georgina Stickland Gates 
$1.00. 

59. Studies in Industrial Psychology: Elsib 
OscHRiN BuECMAN. 90 cents. 

60. The Mental Stntus of Psychoneurotics: 

■\LEXANDER D. TeNDLER. $1.25. 

01. Effects of Attention on the Intensity of 
Cutaneous Pressure and on Visual 
Brightness: Sidnbt M. Newhall. 
$1.25. 

62. The Measurement of Motor Ability: 
Evelyn Garfibl. 90 cents. 



(Continued on inxide hnrk cover.) 



is THE LATENT TIME 

IN THE 

ACHILLES TENDON REFLEX 

A CRITERION OF SPEED IN 

MENTAL REACTIONS? 



BY 
GEORGE H. ROUNDS, Ph.D. 



ARCHIVES OF PSYCHOLOGY 
R. S. WOODWORTH. Editob. 

No. 95 



NEW YORK 

January, 1928 



2.1 



ACKNOWLEDGMENTS 

I am particularly indebted to Professor A. T. Poffenberger 
for constant advice and criticism from the beginning to the end 
of this experiment. I also appreciate the criticism of Profes- 
sor R. S. Woodworth, given at various times; the advice and 
suggestions of Professor Raymond Dodge given at the initial 
planning of the experiment ; and the criticism of Professor F. 
H. Pike on the various physiological matters, especially in 
Chapter 11. To all my best thanks are given. 

G. H. R. 



s^ CONTENTS 



^ 



CHAPTER PAGE 



,NJ I. The Time Factor in Mental Reactions; How the 

Present Inquiry Attacks the Problem 5 






II. The Reflex Mechanism; How it is Set in Action; 
the Neural Arcs Which Cooperate to Make the 
Reflex a Unit Mechanism 12 

III, The Recording Apparatus; Is the Stimulus Con- 

stant? The Preliminary Set-up and Adjust- 
ments 18 

IV. The Latent Time in the Reflex; What it Consists 

of ; How it is Measured 27 

V. The Mental Tests; Their Administration; What 
They Measure; Are the Reactions in the Tests 
Comparable to the Reactions Which Take Place 
During the Latent Period in the Reflex? 32 

VI. The Scores on the Tests and the Latent Time. 
Graphic Representation of the Measures. Cen- 
tral Tendencies. Measures of Dispersion .... 39 

VII. The Treatment of the Test Scores 51 

VIII. Relative Importance of the Physical Speed Mech- 
anisms in Determining the Quickness of Per- 
formance in the Tests. Relative Importance 
of Mental Speed Factors in Determining This 
Quickness of Performance in the Tests 59 

IX. The Regression Line in the Present Problem. Sig- 
nificance of its Limited Prediction Value. The 
Effects of Practice on the Correlation. Con- 
clusions 73 

Bibliography 89 



Is the Latent Time in the Achilles 

Tendon Reflex a Criterion of 

Speed in Mental Reactions? 

CHAPTER I 

The Time Factor in Mental Reactions : How the Present 
Inquiry Attacks the Problem 
Is the latent time in the reflex a criterion of potential quick- 
ness in strictly mental reactions? The present point of attack 
on the problem of quickness of reaction is new — the search for 
a reliable criterion of what the individual can do. The problem 
of speed of reaction itself is old. The earlier experimental pro- 
cedure was directed to the exact measurement of a definite type 
of mental reaction ; this consisted in a simple movement of the 
hand in response to a definite stimulus such as light or sound. 
These reaction time experiments, beginning for the most part 
with Wundt and Bonders and still going on, developed the 
general law that the time of the reaction varies inversely with 
the intensity of the stimulus. Another significant fact evolves ; 
the time of reaction differs from one individual to another. 
These individual differences appear to be sheer speed differ- 
ences — within certain limits ; at least this is true for the simple 
reaction time. The precise determination of the individual time 
of reaction is far from simple. There is the stimulus to attend 
to; the movement one is about to make; the strength of the 
stimulus. When a man reacts to a light stimulus he exhibits a 
certain quickness of reaction; when light and sound stimuli 
are summed his reaction time is greatly reduced. Which is his 
normal speed level — if there is such a thing? What strength of 
stimulus will evoke this normal speed level? According to 
Ach the essential factor in determining the difference in re- 
action time in different individuals is the "observer's attitude 
toward the intention to react in its relation to the stimulus or 
to the movement."^ This is far from being a simple direction 
to follow. When will one have — under what conditions — ^the 
essentially intrinsic speed level of a given individual and how 
will he know he has it? Perhaps there is a sort of quickness 



^Quoted from Henmon: Archives of Psychology, number 30, page 30. 

5 



6 IS LATENT TIME IN ACHILLES TENDON REFLEX 

level which is preeminently characteristic of a given in- 
dividual. This level is not a fixed point; it is rather a certain 
range of speed. Various factors quicken the individual speed 
of reaction. As just mentioned the summation of light and 
sound stimuli markedly reduces the time of reaction (Jen- 
kins). Incentive and punishment likewise quicken the reac- 
tion ; punishment appears to bring out more speed than incen- 
tive (Johanson). Distraction increases the reaction time in 
both trained and untrained subjects; apparently it is never 
overcome (Evans). 

These recent experimental results illustrate the present-day 
trends in exploring the subject of reaction time. The essential 
purpose of these studies is to get in touch with the individual 
speed ability and the factors which govern it. But reaction 
time experiments are not the only methods employed to get 
data on this problem. The fact of improvability brings in- 
dividual speed ability to light. Subjects in one level of ability 
exhibit a high initial speed ; those in another level exhibit a low 
initial speed — initial, i.e., at the beginning of a practice pe- 
riod — . Given a definite practice period for all subjects; the 
subjects whose initial speed is high exhibit the greatest gains. 
Those whose initial speed is low do not even reach the initial 
speed of the other group ; their relative gain is usually less. In 
other words, the speedy individual begins at a higher level and 
after a period of practice he exhibits a greater quantity of 
gain than the slow individual. This the general rule. If the 
material is simple, such as certain cancellation tests, the 
speedy individual approaches his maximum speed; conse- 
quently the slow individual may sometimes exhibit the greater 
gain (Race). 

The various tests, intelligence tests- and others, bring out 
individual differences in speed. In the earlier testing, there 
was a rather strict time limit. There is a time limit at the 
present time, but the amount of time allowed is much more 
liberal. This is notably true in such a test as the McCall 
Reading Test. Somehow the notion creeps out that speed is 
something more or less external to "intelligence." The present 
trend is to isolate speed from other factors in mental ability 
and get at their relationships — if there are any really intrinsic 
ones. Thorndike suggests recently an analysis of ability into 
level, range and speed. Perhaps some day these three items 
in ability will be accurately measured, each independently of 
the other. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 7 

Other experimental data bring to light the fact of an op- 
timal speed for each individual. For example, accuracy of 
judgment is related to the quickness in making the judgment. 
This is exemplified in judgments on lifted weights and length 
of lines. There is an optimal exposure interval, that is, an 
optimal rate in judging the weights; too long an interval or 
too brief an interval reduces the accuracy. The rate is specific 
to the individual function ; it is similar when the functions are 
similar. An individual subject may be slow in one function 
but fast in another (Garrett) . In the more distinctly motor 
functions there is an optimal speed of movement at which the 
efficiency is maximal. Using an ergometer ; to and fro move- 
ments of the arm ; highly trained subjects ; (1) work constant ; 
very fast and very slow rates reduce the efficiency. It costs 
more to work the ergometer very slowly or very fast. There 
is an Optimal rate; the efficiency is greatest at the median 
rates and differs in different subjects. (2) Rate constant; the 
subject soon finds his optimal rate for the specific work. Here 
again there is an optimal efficiency at about the median rate — 
median for the individual subject (Cathcart) . Speed and effi- 
ciency are likewise related to the amount of effort. In general, 
the stronger effort is the most efficient ; the stronger effort has 
the greatest optimal speed. The mechanical efficiency of a 
submaximal effort is always less than that of a maximal effort 
occupying the same time. In other words, the weaker effort 
is inefficient. One man at some definite speed exhibits the same 
efficiency as another man at another speed; there is a con- 
stant optimal efficiency over a rather wide range of speed 
(Hill). 

What is the relation of quickness to intelligence? This ques- 
tion is being weighed in the balance at the present time. Given, 
for example. Spearman's theory of two factors in every mental 
performance; does speed or quickness operate as a factor in- 
dependent of general ability ? What is the relation of speed to 
the so-called "group" or specific factors? Is speed a group 
factor comparable to other group factors ? Is it possible to have 
superior mental ability regardless of the rapidity of mental 
reaction? Are quickness and intelligence independent or inter- 
dependent? Bernstein found no evidence of any such inde- 
pendent speed ability. Quickness does not appear to function 
as a group factor. Quickness and intelligence appear to be in- 
terdependent. Peak and Boring reach similar conclusions. 



8 IS LATENT TIME IN ACHILLES TENDON REFLEX 

They find a high correlation between speed in an intelligence 
test, score in an intelligence test and speed in reaction time. 
These correlations appear to depend on the time limits of the 
test; increasing the time limit destroys the correlation since 
the faster subjects have nothing to do in the additional time. 
Difference in speed appears in single test elements. Other ob- 
servers have stressed v^^hat they call "speed" and "power." 
"Power" appears to mean the level of difficulty to which the 
subject can go. It will be remembered that Thorndike uses 
the word "level" as one of the factors in mental ability ; range 
and speed being the others. Hunsicker found that rate of 
work on the no difficulty level (speed elements) is related to 
the level reached in the difficult elements (power elements) . A 
subject who exhibits a high rate of work may be expected to do 
a larger amount of the difficult elements. The correlations be- 
tween the two types of reaction are indicative of a "relation- 
ship between the rate of mental work and the level of intel- 
ligence itself." 

Other investigators have been concerned with what may be 
called the "content of speed." What makes one individual 
slower than another? This approach to the problem has to a 
considerable extent centered in the phenomenon of persevera- 
tion. It is known that a visual impression has an after effect. 
This after effect appears to be present also in the more dis- 
tinctly mental functions. After an idea has lapsed from dis- 
tinct consciousness, it may exercise an after — or secondary — 
function; it tends to rise again into consciousness. In other 
words, a psychical effect may continue after the cessation of 
the external stimulus. This unconscious perseveration may 
modify or hinder succeeding mental responses. According to 
Lankes and Bernstein, perseveration is a factor in the speed 
of mental action. It varies in different individuals and, oc- 
cording to these observers, appears to be an inborn or native 
quality of the nervous system. 

The observers mentioned in this review of recent experi- 
mental findings appear to have limited their inquiry to the 
direct study of more or less strictly mental reactions. Mental 
and motor tests and instruments were the usual materials in 
their hands. All the tests which they used exhibit both or 
either psychical and motor reactions. In all cases these reac- 
tions are learned reactions. There is no immediate learning 
of a given test. The relative and varying quickness of the 



A CRITERION OF SPEED IN MENTAL REACTIONS? 9 

reaction depends on such factors as facility in the use of lan- 
guage ; familiarity with all the items in a given situation such 
as a sentence completion test — all these and other factors Plus 
some inherent factor of speed over which the individual has 
little or no control. It is precisely at this point that the present 
inquiry attacks the problems of speed in mental reactions. The 
situation is as follows : 

1. Does the nervous system of the individual exhibit a native 
quickness of activity? To what extent does this native quick- 
ness differ in different individuals? Doubtless several plans 
might be worked out for the study of this problem. One might, 
for example, measure the chronological factor in the excitabil- 
ity of nerve tissue — the chronaxie, as it is called. Such a 
technique is by no means easy to handle in the human being. 
Furthermore, the resulting measurements, which exhibit the 
quickness of nerve action in a given individual, ought to be a 
representative sample of nerve action in the given individual. 
Some nerve fibers conduct more rapidly than others. The 
speed of performance in some single fiber or functional group 
of fibers might not be characteristic of the nervous system as 
a whole. One ought to isolate some more or less complex nerv- 
ous mechanism which will exhibit a characteristic sample of 
the speed of nerve action in the given individual. The Achilles 
tendon reflex was chosen for this purpose. This neuro-mus- 
cular mechanism is already isolated in any individual ; that is 
to say, when a stimulus is applied to the mechanism it responds 
as a unit. This reflex exhibits a speed of action which can be 
studied in a clear-cut and measurable form. Its speed of ac- 
tion appears to be inherent ; it exhibits no learning. Further- 
more, the speed of the reflex does vary. For example, its speed 
of action is distinctly slow in Myxedema. It correlates with 
the general sluggishness of mental action which characterises 
the individual in this condition. When thyroid substance is 
administered the speed of the reflex rises along with the rise 
in general mental quickness. In such an extreme illustration 
the speed of the reflex does run parallel with the speed of 
mental action (Chaney). 

Presumably the nervous system of a given individual can 
develop a certain range of speed. The reflex, for example, may 
run more slowly at some times ; at other times, and in partic- 
ular during some special stress, the inborn quickness or reac- 
tion may reach a high level for any particular individual.^ 



^ Experiments with strychnine illustrate this high level of response 
under special conditions (Sherrington 2). 



10 IS LATENT TIME IN ACHILLES TENDON REFLEX 

There is no attempt here to measure this possible range; one 
needs to keep it in mind as a possible source of error. It is 
assumed that in a given individual there is a more or less uni- 
form, normal or basic quickness which characterises this or 
that individual. The optimal speed which appears to charac- 
terise an individual in many types of reaction supports and 
illustrates this assumption. Individuals differ in the speed 
with which they can do work or, more precisely, in the quick- 
ness of their reaction to a given stimulus. The slow individual 
can never, not even with the most extravagant burst of speed, 
reach the speed level of the quick individual.^ In measuring the 
quickness of an individual one must not base the measurement 
on some supreme burst of speed nor on some extreme slowness. 
Given a condition where the individual is relaxed, quiet and 
free from disturbing influences which might accelerate or re- 
tard his speed of reaction; in such a condition the individual 
may be expected to exhibit a level of quickness which is partic- 
ularly characteristic of him. The measurements which one 
secures during this condition will best represent the inborn 
quickness of nerve action which this individual possesses. In 
the present study these measurements are concentrated on the 
latent time of the reflex. There is considerable evidence that 
the latent time runs parallel with the rapidity of the reflex re- 
action in the contracting muscle ; in fact a brief or a long latent 
time must mean a quick or a slow reflex reaction.^ Further- 



^ Recent experimental results on improvability support this point of 
view. Race concludes that the more superior the general intelligence the 
greater the improvability. The superior subject exhibits higher initial 
speed ability — at the beginning of the experiment; his gain is greater 
than that of the inferior subject. For example, a superior group shows 
an initial speed ability of 38.25; the average gain for this group is 26.25. 
On the other hand, the subjects of ordinary intelligence begin at a lower 
initial level and their gain is less than that of the superior group. For 
example, one group shows an initial speed ability of 13.875; their gain 
is 16. Here the slow subjects begin at a much lower level and their total 
gain does not bring them up to the initial level of the superior group 
(figures mean number of problems solved in a unit of time). 

* Carlson (American Journal of Physiology, 7:401 and 15:136) con- 
cludes that the most rapidly conducting nerve is connected with the most 
rapidly contracting muscle. Lapicque (L'excitabilite en Fonction du 
Temps) stresses "isochronisme du muscle et du nerf"; that is, when a 
nerve reacts rapidly, the muscle with which it is connected also reacts 
rapidly. Sherrington (Proceedings of the Royal Society, 97B:519) re- 
ports that in partial inhibition where the stimulation of the inhibitory 
nerve and the excitatory nerve is concurrent, the latent time as well as the 
rapidity and amount of the muscle contraction are changed; the latent 
time is lengthened; the amount of the muscle contraction is less; the 
rapidity of contraction is less; the amount of these changes depends on 
the relative amounts of the inhibitory and excitatory stimuli. On the other 
hand, in the supramaximal reaction where presumably the capacity of 
the nerve and muscle approaches a limit, the latent time is markedly re- 
duced; the amount of contraction is larger; the contraction takes place 
more quickly. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 11 

more, in conditions which call for an acceleration of speed the 
latent time is shortened ; in conditions which call for a slow- 
ing of speed the latent time is lengthened.^ 

2. What speed of mental action does the individual exhibit? 
Quickness in mental reaction is exhibited in functions which 
have been acquired — learned. The essential program in this 
inquiry is to measure (1) the inborn speed of reaction which 
the nervous system reveals in the tendon reflex; (2) the speed 
in strictly mental reactions and (3) to compare the results in 
these two types of reaction. There is on the one hand a native 
inborn reflex arc; on the other hand there are various func- 
tional reactions which have been acquired or constructed dur- 
ing the life of the individual. It is true that the quickness in 
these learned reactions tells what the individual does when 
tested ; at the same time this speed of reaction now, may tell 
nothing about the individual's real intrinsic speed ability or 
may give a very inadequate view of these abilities. The in- 
dividual's learning is apt to be incomplete. One may find a 
wide range of these incomplete learnings even in such a 
simple, elementary mental reaction as crossing out "A" or 
adding two or three single place numbers. Such defects in 
learning may be entirely independent of native quickness 
which the individual may possess. If one were to measure 
these defects in learning, the result might be a normal curve 
of distribution both for different individuals in the same test 
and for the same individual in different tests of presumably 
equal difficulty. In other words, there may be a wide differ- 
ence between the individual's inherent quickness and his ac- 
quired quickness in the performance of simple mental func- 
tions. The latent time in the reflex may tell what the in- 
dividual can do; it may be a criterion of his potential quick- 
ness in strictly mental reactions. 



CHAPTER II 

The Reflex Mechanism; How It Is Set in Action; the 

Neural Arcs Which Cooperate to Make the Reflex a 

Unit Mechanism. 

The peripheral components which make up this reflex arc 
are, (1) the Achilles tendon; (2) the Gastrocnemius muscle 
and, in some measure, other extensor muscles such as the 
Soleus. Both muscles, Soleus and Gastrocnemius, are attached 
to the Achilles tendon ; these muscles are extensor in function 
— their contraction extends the foot. Each of these muscles 
has an abundance of short fibers and large areas for tendinous 
attachment; in the Gastrocnemius, the fibers pass diagonally 
downward to join the sides of the Achilles tendon at various 
levels. In the reflex reaction, the Gastrocnemius muscle ap- 
pears to play the leading part. (3) The Internal Popliteal 
division of the Great Sciatic nerve ; this nerve trunk — the In- 
ternal Popliteal — sends a branch to each of the two heads of 
the Gastrocnemius muscle and to the Soleus muscle. The 
nerve contains both afferent and efferent fibers. Its origin is 
in the Sacral plexus. The fibers within the nerve, which reach 
the Gastrocnemius muscle, appear to have their origin in I and 
II Sacral segments. (4) The Tibialis Anticus muscle and its 
connecting nerve, the Anterior Tibial ; this nerve is a branch 
of the External Popliteal nerve. The fibers within the An- 
terior Tibial, which reach the muscle, appear to have their 
origin in IV and V Lumbar and I Sacral segments. The 
Gastrocnemius and the Tibialis Anticus are antagonists; the 
former extends while the latter flexes the foot. 

The Achilles tendon reflex is a myotatic reflex — a stretch re- 
flex; its normal or adequate stimulus is stretch or tension of 
the muscle ; the muscle responds to stretch with active contrac- 
tion. This reaction to stretch is not a direct contractile re- 
sponse ; the muscle fibers do not respond directly and immedi- 
ately to the stretch. Sever the motor nerve and there is no 
response. Nor is there any contraction when the afferent 
nerve supply is cut off. The contraction which follows the 
stretch stimulus is (1) a reflex effect and (2) the source of the 
reflex is within the muscle itself — the mechanical stimulation 
of certain receptors or end organs within the Gastrocnemius 
muscle. This reflex effect of stretch applied to the Gastroc- 

12 



A CRITERION OF SPEED IN MENTAL REACTIONS? 13 

nemius muscle extends to its antagonist, the Tibialis Anticus. 
Stretch of the extensor muscle does two things: it initiates 
contraction of the extensor and, simultaneously, lengthening 
of the flexor muscle. As the myotatic contraction of the ex- 
tensor reaches a maximum of extension at the foot, the conse- 
quent stretch on the flexor unfolds a myotatic contraction of 
the Tibialis Anticus and, simultaneously, lengthening of the 
Gastrocnemius.^ This interaction of the extensor and flexor 
muscles in the reflex is clearly exhibited in the relaxation pe- 
riod of the records secured in the present inquiry. The relaxa- 
tion of the extensor muscle at the end of the individual response 
— single reflex reaction — is far from being a passive return to 
the starting point or base line. The contracting Gastroc- 
nemius reaches a maximum of shortening ; stays there briefly ; 
then returns quickly to the initial condition. This quick return 
represents the cessation of its own contraction and the simul- 
taneous contraction of its antagonist. The extensor lengthen- 
ing runs parallel with the flexor contraction ; the lengthening 
proceeds slowly when the flexor stretch is slow ; rapidly when 
the flexor stretch is rapid. 

The sharp tap on the Achilles tendon — the sudden increase 
in tension — initiates the reflex response. The mere fact of 
progressive increase in stretch progressively stimulates more 
receptors in the muscle. The reflex contraction increases as 
the number of active receptors increases ; that is to say, slow 
stretch, progressively increasing, will eventually contract the 
muscle completely. The total amount of stretch at the end of 
any period of time determines the number of receptors in ac- 
tion and the consequent amount of contraction. In other words, 
given an end result — the complete contraction of the muscle 
and the full extension of the foot ; the stretch movement which 
elicits this effect may consume a long or a short period of time ; 
it may, for example, take place in 8 seconds or in .08 seconds. 
Therefore, when a considerable amount of stretch is concen- 



^ This may be illustrated in a controlled experiment. Suppose, for 
example, stretch is applied to the knee extensor and maintained; a con- 
traction of the extensor follows this stimulus. If, during this contraction 
of the extensor, the stretch stimulus being constant, — if during this con- 
stant and continued stimulus and reaction of the extensor, a stretch is 
applied to the knee flexor, there follows immediately a pronounced cessa- 
tion of the reflex contraction of the extensor. This illustrates the sharp 
and vigorous effect which stretch stimulation of one antagonist has in 
overbalancing and even extinguishing the contraction of its opponent 
(Sherrington, Proceedings of the Royal Society, 96B and 97B — 1924 and 
1925). 



14 IS LATENT TIME IN ACHILLES TENDON REFLEX 

trated into a very short period of time, a large number of re- 
ceptors respond nearly simultaneously and, in consequence, 
elicit a quick and complete contraction of the muscle. The 
sharp tap on the tendon does this very thing ; the stretch which 
it elicits is sudden and rapid ; many end organs are stimulated 
within a very brief period of time. In no case, however, is 
the stretch stimulus instantaneous as is the electrical stimulus ; 
the stretch movement usually occupies several sigma of time ; 
in the present experiment this time appears to be about 15 
sigma. It should be noted that setting up the reflex response 
depends on a certain threshold value of the stimulus; the 
stimulus must excite a certain number of end organs in a very 
brief period of time. It is very likely that the stretch stimulus 
never excites all the muscle receptors not even with consider- 
able amplitude of stretch (that is, unusual strength of stimulus 
which is conditioned by the velocity of the blow at the tendon) 
and short duration of the stretch movement. Sherrington 
holds that the amount of the stimulus in terms of amplitude 
and quickness of the stretch rapidly reaches a maximum be- 
yond which any further increase in the stimulus reveals no 
effect in the reflex response. (Proceedings of the Royal So- 
ciety, 96B; see also Fulton, same Journal, 98B: 577.) 

The reflex arc in the tendon reflex, which is the subject of 
this study, begins with the tap on the tendon. Muscle end 
organs, in response to this tap, set free afferent nerve impulses. 
These impulses enter the spinal cord through the correspond- 
ing posterior roots. What next? Is this tendon reflex a local 
spinal reflex? Does it represent the activity of one or two 
segments of the spinal cord? — those segments which belong 
to the Gastrocnemius muscle ? Does the ascending limb of the 
reflex arc run from the posterior or afferent roots directly and 
immediately to the anterior or efferent roots of the same or 
adjoining segments? — this and no more? What becomes of 
the afferent impulses after leaving the muscle? What is the 
arc over which they travel back to the muscle and elicit a con- 
traction of that muscle? Pike insisted several years ago that 
"no independent proof has ever been adduced that the reflexes 
for the skeletal muscles in higher vertebrates occur through an 
arc involving the spinal cord alone when the whole central 
nervous system is intact." At present, attention is confined to 
the highest vertebrates; to an extensor reflex in the human 
being; to a reflex originating in the Gastrocnemius muscle. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 15 

There is positive evidence of a reliable experimental nature 
that this reflex arc runs beyond the limits of the spinal cord. 
According to Spiegel the most important prespinal center in 
this reflex arc is Deiter's nucleus ; apparently other closely al- 
lied nuclei in the same region of the brain cooperate to more 
or less extent. But Spiegel is concerned with animals such as 
the dog or cat. In man it appears certain that some, at least, 
of the afferent impulses which the tap on the tendon sets in 
action pass up as high or higher than the mid brain. In ani- 
mals the efferent pathway appears to be the vestibulo-spinal 
tract. It is known that in lesions of the Pyramids the reflex is 
disturbed ; consequently the cortico-spinal tracts are concerned 
in the normal operation of the reflex.*^ Several arcs appear to 
cooperate to make the reflex a unit mechanism. There is the 
stimulation of the extensor muscle — the tap on the tendon. 
There follows the contraction of the extensor; cessation of 
contraction in the flexor; then contraction of the flexor an- 
tagonist during the relaxation period of the extensor and the 
return of the myograph lever to the base line. Very likely the 
Sympathetic nervous systems plays some cooperating part in 
the present reflex, but the available evidence is not secure 
enough to warrant any positive statement. Thus the tap on 
the tendon elicits a number of reflex reactions; some of these 
reactions are organised in — have their centers in — the region 
of Deiter's nuclei ; others are organised in the mid brain. Very 
likely some part of the Cerebrum is a constant factor in the 
total reflex response. Bremer gives evidence that the Cere- 
bellum is an essential element in the normal reflex response.'^ 



* It is interesting to note that the Plantar reflex is a Cortical reflex ; 
the efferent limb of the arc is the Cortico — spinal tract. In the normal 
condition the response is flexor; when the cortico-spinal tract is injured, 
the response becomes extensor. Minkowski studied the successive organ- 
isations of this reflex from the spinal to the cortical levels. During the 
first two or more years of infancy and in complete section of the spinal 
cord the reflex is extensor — A Pure Spinal Reflex. In the adult the 
organisation level has been shifted to the Cortex and the response is 
flexor in function. In certain pathological conditions the reflex center 
retreats to the spinal level. Rothmann found the "Beruhungs-reflex" 
totally absent in his "grosshirnlosen Hund." 

'^ The experimental evidence which supports the positive conclusions in 
regard to the reflex arc in the Achilles Tendon reflex is as follows. (1) 
The Evidence Derived from the Experimental Study of the Decere- 
brate Preparation. In the decerebrate condition the extensor muscle 
(quadriceps or gastrocnemius) is hypertonic; excessive rigidity is a con- 
stant feature; stretch of the muscle evokes contraction of the muscle; 
this contraction is reflex; the source of the reflex is in the muscle end 
organs ; stretch is the adequate stimulus of these receptors ; section of the 
afferent roots or section of the entire nerve trunk to the muscle abolishes 



16 IS LATENT TIME IN ACHILLES TENDON REFLEX 

the reflex. The afferent nerve from the muscle is the only afferent channel 
for these impulses sent out by the muscle receptors. Thus the Reflex 
Evoked by the Stretch of the Muscle in the Decerebrate Condition 
Arises Wholly in the Given Muscle and Ends Wholly in the Self- 
same Muscle. 

This Afferent Pathway Leads from the Given Muscle to the 
Prespinal Centers in the Brain Stem. Section of the posterior column 
or the direct cerebellar tract has no effect on the rigidity; section of the 
lateral column abolishes the rigidity on the same side; transection below 
or in the lower half of the bulb abolishes the rigidity — the limb immedi- 
ately becomes flaccid; swings to and fro like a flail when set in action. 
Section of Deiter's spinal tract abolishes the rigidity on the same side. 
Momentary stimulation of this — Deiter's — nucleus or its fibers causes in- 
crease in the rigidity; massage of the muscle likewise augments the 
rigidity. The mechanism which subserves the rigidity in this decerebrate 
condition is distinct from the pyramidal tracts for (a) section of the lateral 
half of the bulb Above the level of the decussation of the pyramids abol- 
ishes the rigidity on the same side; (b) transverse section of the lateral 
region of the same part of the bulb without interference to either pyramid 
abolishes the rigidity; (c) excitation of this region — lateral — of the bulb, 
reinforces the rigidity on the homonymous side. Activity in this reflex 
arc is primarily autogenic — arises in the muscle itself for (a) cooperation 
of the otolith organs and the neck receptors is not essential for the re- 
flex; (b) ablation of the Cerebellum does not abolish the reflex. It is to 
be noted that Sherrington uses the decerebrate preparation in his in- 
vestigation of the myotatic reflexes ; this myotatic reflex is a tonic or pos- 
tural reflex; in decerebrate rigidity this reflex is abnormally accentuated 
owing to the loss of higher centers which normally cooperate in the re- 
flex response. Furthermore, Sherrington used the cat in his experiments; 
in this animal, as well as in the dog, centers essential for the mainten- 
ance of the rigidity lie exclusively in the brain stem; eliminate these 
centers and the limb immediately becomes flaccid. While these brain stem 
centers are indispensable links in the reflex arc or arcs which connect the 
muscle end organs with the muscle fibers, other centers are equally indis- 
pensable for the normal and regular operation of the reflex. In the decere- 
brate the activity of the reflex is abnormally accentuated ; when the Red 
nucleus is intact; that is to say, when a reflex arc or arcs from the muscle 
through the mid brain — Red nucleus — and thence to the brain stem cen- 
ters, and spinal centers (the Rubro-spinal tract, for example) , are intact, 
the response of the myotatic reflex becomes approximately normal. Since 
these prespinal centers subserve the activity of the reflex in the dog and 
cat, the centers which subserve the activity of the same reflex in man can- 
not lie at a lower level than the brain stem and mid brain. The fact that 
lesions of the Cortico-spinal tract upset the reflex ; the fact that the Plan- 
tar reflex is organised at the Cortical level in the adult human being; 
these facts point to the participation of centers even higher than the 
mid brain in the normal operation of the reflex. 

(2) The Evidence Derived from Complete Transection of the 
Spinal Cord. There is total absence of reflex action below the level of 
the section; this "spinal shock" takes effect in the downward direction 
only; there is no upward spread; the upper limbs are not disturbed when 
the section is made at the appropriate level; the number of segments in 
the isolated spinal cord has no significance; that is, a single segment is 
fully as active or inactive when isolated as when intact with several 
other segments. In physiological transection of the spinal cord, the re- 
flexes below the point of application of the saline solution disappear; the 
reflexes above this point are not affected; when the solution is absorbed 
the reflexes return to normal action. Freezing the cord evokes a similar 
loss of reflex action below the level of the injury. This spinal shock is 
much more severe in the monkey than in the dog or cat. In a monkey, 
immediately after transection of the cord, the limbs hang limp and flaccid; 
they swing to and fro like a flail when set in motion; this condition con- 
tinues for days and even weeks ; even after the shock appears to disappear 



A CRITERION OF SPEED IN MENTAL REACTIONS? 17 

the reflex movement is slight and very erratic ; it varies much from day to 
day and is easily exhausted through fatigue; the stimulus required to 
elicit a reflex is enormously large; yet the muscle fibers are responsive, 
for stimulation of the Pyramidal tract evokes the usual variety of move- 
ments. 

Thus even after the period of shock is over, it is very difficult to set the 
reflex machinery going and keep it going. In the dog or cat, on the other 
hand, soon after the transection — minutes or hours — vigorous reflex 
movements can easily be obtained ; the movements are more forcible, more 
prolonged, more readily obtained and less easily exhausted by fatigue than 
in the monkey. Sherrington stresses the slightness of solidarity pos- 
sessed by the isolated spinal cord in the monkey; the far greater indepen- 
dent vitality of the spinal cord in the dog or cat; it is a "great physio- 
logical contrast; a profound difference and chiefly quantitative. The dog 
differs less from the frog than the monkey from the dog, while the mor- 
phological gap between the dog and monkey is much less than that be- 
tween the dog and frog." Spinal shock is much more severe in man than 
in the monkey. In man the tendon reflexes below the level of the injury 
are completely abolished for months and even years ; the reflexes above the 
level of the injury are not affected. This spinal shock — the elimination 
of reflex activity below the level of the injury — is not due to changes in 
blood pressure nor to long continued inhibition; nor is the degree of the 
trauma the causal factor. Spinal shock is purely a nervous phenomenon ; 
the essential factor is the rupture of the long conducting pathways in 
the spinal cord (Sherrington, 1, 2, 5; Pike; Hunter and Royle; Spie- 
gel; Magnus). 



CHAPTER III 

The Recording Apparatus; Is the Stimulus Constant? 
The Preliminary Set-up and Adjustments 

The subject sits in a chair at a table. The table is a heavy- 
one, but the legs are clamped to the floor to make sure that 
there is no movement. The subject's right leg rests in a 
wooden collar lined with leather and rubber to make sure of a 
maximum of comfort for the subject; the letter "a" on the dia- 
gram indicates this feature of the set-up. The frame which 
holds the collar is attached to the table. A screw attachment 
in the frame raises the subject's leg a suitable distance from 
the floor. The subject's sitting position is adjustable as to 
height; consequently the knee is horizontally level with the 
thigh. This adds to the subject's comfort and prevents any 
circulatory disturbances. The leg below the knee is held im- 
movable through attachments at three points. (1) A piece 
of wood screws down from the top of the table to meet the 
patellar bone — "b," in the diagram ; this prevents any upward 
movement of the leg. (2) Another attachment, "c," meets the 
front of the leg about half way between knee and foot. This is 
adjustable by means of a screw on either side of the leg; the 
screws are attached to the frame which supports the leg; this 
attachment prevents any forward movement of the leg. (3) 
Another attachment — "d" — meets the leg from the rear. A 
metal cup lined with a small bit of leather meets the enlarge- 
ment of the tibia at the ankle ; there is one cup on each side of 
the ankle at this enlargement. By means of a number of 
screw joints these cups are adjustable in several directions so 
that the cup is accurately and comfortably adjusted to the 
ankle. This attachment which thus meets the leg from the 
rear screws into the immovable frame supporting the leg. 
Thus the leg below the knee is firmly held in one position ; the 
tap on the tendon does not move the leg in any direction. The 
ankle joint alone is free to move in its customary extensor and 
flexor directions. In other words, the stimulus sets up action 
in the reflex mechanism only. 

The stimulus is delivered at the tendon by means of a pen- 
dulum, "e," which swings freely in a frame beneath the chair. 
This frame is firmly attached to the seat of the chair and is 
adjustable in a vertical direction. The pendulum begins the 

18 



A CRITERION OF SPEED IN MENTAL REACTIONS? 

^ 



19 




Figure I 



20 IS LATENT TIME IN ACHILLES TENDON REFLEX 

swing at the horizontal level. A magnet attached to the chair 
holds the pendulum at this horizontal position. The electric 
current which controls the magnet is made and broken at the 
myograph. During the experiment the current is closed. A 
pointer reaches out at the base of the drum and, pressing 
momentarily on a bit of spring, breaks the current and re- 
leases the pendulum. The stimulus is transmitted from the 
pendulum to the tendon by means of a small bar of light wood 
about one inch square, "f." A slender strip of hard wood, 
attached to one end of this bar, meets the tendon; a rubber 
band holds it firmly but lightly on the tendon. This trans- 
mission bar is about 8 inches long and is adjustable as to 
length. The other end of the bar rests in or is supported by a 
double swinging joint, as it may be called. A small pin, cone 
shaped at each end, supports the frame holding the bar; the 
cone-shaped pin fits into a similar-shaped socket ; a screw holds 
the pin in the socket firmly, but loosely enough to allow perfect 
freedom of movement. There are two of these joints; in com- 
bination, the joints allow free movement of the bar in a hori- 
zontal, backward and forward direction. A single joint tends 
to check this movement of the bar by pulling it up in a vertical 
direction. The combination of two joints eliminates this ver- 
tical pull and thus allows freedom of movement in response to 
the blow of the pendulum. The bar appears to respond to the 
blow as though it were resting in space. This transmission 
bar extends back such a distance that it meets the pendulum 
at exactly the vertical position of the swinging pendulum. 
Thus the pendulum "rests" — is held at the horizontal position 
— at the beginning of the quadrant, by the magnet. When the 
current is broken at the myograph, the pendulum falls through 
one quadrant, and striking the transmission bar when it 
reaches the vertical position — at the moment when the veloc- 
ity of the single quadrant swing is maximal — , delivers the 
blow to the tendon. 

The reflex response is taken directly from the Gastroc- 
nemius muscle — not from the extension movement of the foot. 
A small piece of light wood is held gently on the external skin 
surface of the muscle, at or near the heads of the muscle, by 
means of a rubber band, "g." At this spot, which is a few 
inches below the knee, the reflex response of the muscle is 
maximal ; the reflex requires a very limited number of muscle 



A CRITERION OF SPEED IN MENTAL REACTIONS? 21 

fibers.^ At the muscle this piece of wood is slightly hollow and 
is about 3 inches square; this large surface is for the muscle 
only. The piece of wood at each end is cut down to a small 
arm about one-half inch in width; this arm projects out at 
each side of the leg. When the muscle enlarges on contraction, 
the piece of wood moves in a backward and forward direction. 
A recording lever transmits this movement to the myograph 
drum, "h." Two limbs of this lever, one on each side of the 
leg, are attached to the projecting arms of the piece of wood 
which rests on the muscle. The connecting joint is a sort of 
universal joint; a rigid attachment at this point will not work. 
A strip of tin is tacked on each of the projecting arms and on 
each of the limbs of the lever. A notch is cut in each strip. 
The recording lever notch fits into the muscle attachment notch 
and is held securely but gently by a rubber band. Thus there 
is at least a minimum of restraint or resistance in the trans- 
mission of the total muscle movement to the recording lever. 

These two limbs meet the "body" of the recording lever in 
front of the leg. The size of the "limbs" and "body" of this 
lever is as small as is consistent with lightness and firmness in 
all parts of the lever. No matter how light these mechanical 
transmission parts may be, there is doubtless some lag in trans- 
mission of the reflex response. On the other hand, if the lever 
is too small and too weak, it is apt to buckle a bit and thereby 
interfere with the transmission of the muscle response. Bass- 
wood was used in all these mechanical recording and trans- 
mission parts ; this wood appears to supply a maximum in this 
combination of lightness and firmness. 

The external end of the lever — the myograph end — is at- 
tached to an L-square piece of bakolite. The short limb of this 
square holds a vertical position and is attached directly to the 
long limb of the recording lever. The long limb of the square 
narrows down to a small point in which fits a celluloid marker ; 

* According to Beritoff, contraction of a muscle is greatest at or near 
the entrance of the nerve and diminishes or may become zero at or near 
the distal or tendon end. It may be noted here that the stretch stimulus 
causes the recording lever to move in the same direction as does the con- 
traction of the muscle; in both cases the muscle enlarges. The fibers in 
this muscle are arranged diagonally; their attachments at the central 
end of the tendon make acute angles ; the fibers meet the tendon obliquely. 
These angles are small — 10° for example — at the distal end and larger at 
the proximal end of the muscle. On contraction these angles increase in 
size — as much as 3 times. The pull of the tendon or stretch of the 
muscle appears to produce a similar effect; it slightly increases the size 
of the angles w^hich the fibers make with the tendon attachments. (See 
P finger's Archiv., 205:475 and 209:763). 



22 IS LATENT TIME IN ACHILLES TENDON REFLEX 

this long limb holds a horizontal position. At the junction of 
the long and short limbs of this L-square, the bakolite rests on, 
is supported by, and moves freely in a cone-shaped pin-and- 
socket joint. A small pin or cylindrical bar is driven into a 
hole in the bakolite square ; the cone-shaped ends of the pin fit 
into sockets similar in shape ; a screv^ holds the pin snugly in 
the socket at both ends. At the same time, movement in the 
socket is perfectly free; friction is reduced to a minimum. 
Thus the slight backward and forward movement from the 
muscle is transmitted from the muscle to the marker. The 
marker moves in a vertical direction and records the amount 
of the muscle enlargement on the revolving drum. 

The myograph is a Starling-Sherrington model made by C. 
F. Palmer. It is driven by a Leeds and Northrup constant speed 
motor. A screw at the top of the vertical shaft on which the 
drum revolves enables one to raise and lower the drum any 
amount and at any time when the drum is moving. Gears and 
speed variation pulleys at the motor and at the myograph 
permit a wide range of speed. The time record is made by a 
marker of the tuning fork type; the time is recorded in 10 
sigma increments. The time record is made at the beginning, 
before any reflex records are recorded, and after the individual 
experiment is complete. The speed of the drum is naturally 
the same in making the time record as in making the reflex 
records. 

Is the external stretch stimulus constant? Two variations 
in the stimulating device might influence the constancy of the 
stimulus and, in consequence, might exercise some control over 
the latent time. (1) The velocity of the blow at the tendon. 
The essential factor in this stretch stimulus is the quickness 
and suddenness of the blow ; that is, the velocity of the blow as 
the pendulum hits the tendon. For example, if the pendulum 
falls through one-half quadrant instead of one quadrant, the 
velocity is diminished and the time-course of the muscle re- 
sponses is more or less disturbed. In all cases during the pres- 
ent experiment the pendulum fell from the horizontal to the 
vertical position ; that is, from the beginning to the end of one 
quadrant. Hence there is no chance for any change in the 
velocity of the blow ; it is uniformly the same for each individ- 
ual. (2) The weight of the pendulum. With a constant veloc- 
ity any change in the weight of the pendulum causes little if 
any change in the latency in any one individual subject. Dodge 



A CRITERION OF SPEED IN MENTAL REACTIONS? 23 

tested this factor with the following results. With a constant 
velocity the weight of the pendulum was progressively in- 
creased. The figures are for the same subject. 

TABLE 1 

The Relation of the Weight of the Pendulum to the Length of the Latent Time: 
Velocity of Pendulum is Constant. 

Weight of Pendulum Latent Time in Sigma 

25 grms. 31.5 

50 grms. 33. 

75- grms. 32 . 1 

100 grms. 31. 

125 grms. 30.7 

150 grms. 31.7 

(From Zeitschrift fiir allgemeine Physiologie, 12; 32.) 



In the present experiments the weight of the pendulum was 
adjustable by two 20 grm. and one 30 grm. increments. The 
aim was to make sure that the response was maximal — as 
much contraction of the muscle as the mechanism in response 
to the stretch stimulus was capable of setting in action. A 
stimulus of greater velocity — more nearly instantaneous — 
would very likely diminish the latent time ; but the velocity is 
constant. The addition of one 20 grm. and the 30 grm. weight 
was found to be ample for all the subjects. A minimum weight 
was ample for the most sensitive, most responsive subjects. 
In the case of these sensitive subjects, increasing the weight 
of the pendulum up to the regular level used with other sub- 
jects — as indicated above — did not appear to evoke any change 
in the latency. Usually the only variation in the response was 
a sort of rebound of the muscle at the end of the latent period. 
The blow appeared to be too heavy. As the lever described the 
small curve — the latency curve — it was jerked back beyond the 
base line. This made it difficult to measure the length of the 
latent period. Taking out the 30 grm. weight usually elimi- 
nated this. It appears reasonable to conclude, therefore, that 
the external stimulus in the present experiment is constant; 
it is not a factor in the individual variation in latency. In each 
individual the stimulus excited enough — very likely more than 
enough — muscle fibers to set off the muscle contraction. 

Several critical features in the set-up demand attention. 
(1) The reflex readiness to respond. This is a tonic condition. 
When the foot hangs limply extended there is no response, no 



24 IS LATENT TIME IN ACHILLES TENDON REFLEX 

matter what the stimulus may be ; there is too much slack to 
be taken up. When the foot is placed in such a position that 
the tendon and muscle are in a condition of slight tension, two 
results follow : (a) There is a heightened condition of excitabil- 
ity in the muscle fibers. The flexible support beneath the foot 
raises the foot and thereby stretches the muscle ; this support 
is a piece of tin and offers a minimum of resistance. The 
optimal position is midway between flexion and extension. In 
other words, the muscle is most or, at least, normally respon- 
sive when at or near its resting position in the body. The 
greatest change in responsiveness takes place with very small 
increments of increase in passive or resting stretch. The 
optimal condition of full responsiveness covers a rather wide 
range, (b) This initial passive stretch which is under the con- 
trol of the experimenter slightly excites muscle end organs 
and in consequence sets up a slight flow of nerve impulses 
along the reflex arc. This puts the other elements in the re- 
flex — other than the muscle — in a condition of readiness to 
respond. 

It is believed that, so far as the external controls are con- 
cerned, the tonic condition of the muscle and the other ele- 
ments in the reflex arc was constant for each individual. The 
initial stretch appeared to be optimal in each instance. There 
is no difficulty in making this adjustment for the muscle is very 
responsive over a wide range of change in the position of the 
foot. The reflex was set in action many times before any rec- 
ords were made. The reflex arc was thoroughly "warmed up." 
(2) In the individual set-up the knee ought to be on a 
horizontal level with the thigh. If the thigh is below the 
level of the knee ; that is, if the leg between the thigh and the 
knee tends to a vertical position, there is apt to be some circula- 
tory disturbance. The subject is also more or less uncomfort- 
able. Several cushions in the chair made the horizontal ad- 
justment possible and in consequence increased the comfort of 
the subject. (3) The adjustment at the ankle frequently 
causes some discomfort and demands more or less attention. 
It is essential that the metal cups meet the enlargements at the 
ankle and no more; they must not press tightly, for the sub- 
ject's comfort demands a minimum of pressure at these points. 
The apparatus at these points is adjustable in many different 
directions. Consequently it is possible to secure a maximum 
of comfortable adjustment for the subject and an accurate set- 



A CRITERION OF SPEED IN MENTAL REACTIONS? 25 

up for recording the reflex. Each subject was specially urged 
to insist on a comfortable position at all points. The attach- 
ment at the patellar bone offers no difficulty ; there is no pres- 
sure at this point. The apparatus merely meets the bone — no 
more — and thereby prevents any upward movement of the leg. 
(4) While the reflex record is being made the subject is 
reading an interesting story from Irving's Sketch Book. These 
stories appeared to serve the purpose best. The purpose is to 
make sure that the subject is perfectly calm and at rest, with 
attention on something external to himself. In many in- 
stances he forgot about the experiment; this is the ideal con- 
dition. The reflex then is free to respond in what may be called 
a "normal" manner — as free as possible from disturbances ex- 
ternal to the reflex arc itself. In many instances the subject 
did not read; he watched the procedure. His attention to the 
reflex appeared to make no difference in the response ; the re- 
sponse was uniform throughout the records. Other men pre- 
sented various difficulties. Some men were completely "in- 
hibitory" ; it was impossible to elicit any response at any time 
— not even with the reflex hammer. Some of the "inhibitions" 
were due to injuries at the ankle or in some other part of the 
foot or leg. Dodge found subjects who were completely in- 
hibitory. Some subjects exhibited a more or less erratic re- 
sponse ; at one time the response is good ; on the next trial there 
is no response ; the next trial may show a small response. Nat- 
urally such subjects cannot be used. The essential aim is to se- 
cure the records of about 40 successive reflex responses in each 
subject ; these responses must be very uniform. It is assumed 
that 40 consecutive individual records of uniform size present 
a good picture of a given individual's "normal" reaction when 
the Achilles Tendon is tapped. In some cases the experimenter 
had to use exceptional means to secure this number of records. 
In one case, for example, reading the story had no effect ; the 
subject's attention was on his reflex with consequent erratic 
reactions. It was found that when this man hummed a tune at 
certain intervals, the erratic reactions disappeared. The ex- 
perimenter gave the word ; at varying times after this signal 
the pendulum was released. In this way uniform re- 
sponses were obtained. When the man did not hum the tune 
there was complete or partial "inhibition." Apparently his 
reflex mechanism was very sensitive to the "inhibitory" im- 
pulses generated in the frontal lobe. In other cases an attempt 



26 IS LATENT TIME IN ACHILLES TENDON REFLEX 

was made to control attention by having the subject say "ah" 
as the tendon was tapped. This plan failed to give results.^ 

The subjects were college students. Some 20 were taken 
from the Summer Session students. One man, number 80, was 
taken from the Extension Department. One man, number 45, 
was a graduate student. The other subjects were Columbia 
College students. About 100 men were used; many of these 
were erratic, inhibitory, or presented some disturbance which 
made it impossible to secure the kind of records sought for. 
Eighty subjects presented satisfactory records; these records 
are the subject matter of this report. It is well to remember 
that these subjects are a highly selected group. The fact of 
admission to any college means selection. Students in Colum- 
bia are double-selected, as it were; the requirements for ad- 
mission to Columbia College are more severe than in many 
other colleges. Hence it is a group of superior men whose reflex 
reactions are here examined. In all cases the subjects were 
thoroughly cooperative ; they were students in the Department 
of Psychology and usually were taking their first course in 
Psychology. 



® It is doubtful if the erratic, inhibitory phenomena manifested in several 
of the subjects were due to volitional impulses. Some men, who did not 
exhibit the slightest trace of inhibitory behaviour, were told to block the 
reflex response — "don't let your foot move when I give the signal." In no 
case was the man able to block the reflex ; the reflex took place regardless 
of the efforts to block it when the pendulum hit the tendon. Presumably 
such an attempt to block the reflex consists chiefly in a voluntary contrac- 
tion of the flexor antagonist; such a volitional innervation must be inter- 
mittent — not a constant stimulus. Warner and Olmstead (Brain, 46:189) 
report an "inhibitory" center in the frontal lobes. Ablation of the 
frontal lobes immediately evokes extensor rigidity; the presence or ab- 
sence of the motor area has no influence on the rigidity. Stimulation of 
this frontal lobe area abolishes the rigidity. Thus, using Sherrington's 
theory of the inhibitory function as a basis, one may say that stimulation 
of the frontal area (1) shuts off or prevents a discharge of impulses 
into the extensor muscle or (2) sets up a discharge of impulses into the 
flexor antagonist or (3) both. In either case the discharge of impulses 
from the frontal lobes is constant. These frontal lobe impulses travel 
through the Cortico-ponto-cerebellar tract; thence through the superior 
peduncle and Red nucleus. 



CHAPTER IV 

The Latent Time in the Reflex; What it Consists of; 
How IT is Measured 

The reflex is essentially the contraction of the Gastrocne- 
mius muscle in response to a stimulus which originates in the 
muscle itself. The myograph record distinguishes these two 
factors; (1) the muscle contraction; when reflexly excited 
this contraction records a curve; this curve begins with the 
long downstroke of the recording lever. This stroke runs 
parallel with the quick downward movement or extension of 
the foot. Then follows a more or less flat plateau or crest; 
this plateau is shown only when the myograph is moving 
rapidly. This reflex contraction curve ends in a rather quick 
return to the base line. (2) The latent period of the reflex. 
During this period the mechanism which excites the contrac- 
tion is in action; that is to say, the stimulus or tendency to 
excite at the distant point — at the muscle fibers — is travelling 
around the reflex arc. The entire reflex arc is essentially an 
excitatory mechanism, for conduction means the rapid excita- 
tion of successive increments of nerve fibers and synaptic 
junctions. The present experiment is concerned only with the 
excitatory mechanism. How long does it take this mechanism 
to get the stimulus to the muscle fibers and thereby elicit a 
contraction of the muscle? One must isolate this period dur- 
ing which the stimulus is thus travelling to the muscle and 
establish a line beyond which the latent time does not run. 

This latent period in the reflex begins with the application 
of the stretch stimulus at the muscle end organs. It closes 
with the response of the muscle fibers. The record depicts 
only those changes which take place within the muscle. Be- 
fore the record begins, the pendulum has delivered the blow 
on the tendon. This blow has initiated the sudden change in 
the tension or stretch which is the normal or adequate stimu- 
lus. This sudden change in tension has been transmitted to 
the muscle. The initial downward movement or deflexion of 
the myograph lever records the moment when the stretch 
stimulus reaches the muscle end organs; at this moment the 
latent time begins. This initial deflexion exhibits three phases 
of the stretch: (1) The downward deflexion which is the 
stretch movement or period of sharply increasing tension; this 

27 



28 IS LATENT TIME IN ACHILLES TENDON REFLEX 

period covers about 15 sigma. (2) The period of maintained 
tension; in no case does the lever make a sharp return; 
in no case is the stretch stimulus instantaneous. The new, 
suddenly increased tension continues for an appreciable time. 
(3) The period of declining tension; the tension, for example, 
in the tendon, returns to the initial level ; the myograph lever 
returns to the base line. 

The effective or adequate stimulation takes place chiefly 
during the sudden change in tension — the stretch movement. 
It was just stressed that the stretch stimulus is never instan- 
taneous ; in fact, it is rather a continuous stimulus or state of 
tension. The muscle end organs are specially adapted to this 
kind of stimulus. An electrical stimulus does not reexcite the 
nerve, for the nerve immediately becomes adapted to the 
stimulus. This process of adaptation is much slower in the 
muscle end organs; a constant stimulus continues to excite 
these organs.^" This means that the state of excitation set 
up in the end organs outlasts the stimulus. The single tap 
on the tendon is able to send out a considerable number of 
impulse volleys or series of impulses into each nerve fiber. 

It should be noted that the time occupied by the sudden 
change in tension is independent of the latent time in the re- 
flex. In the quickest possible stretch — presumably about one 
sigma — this time is about one-quarter of the latent time. In 
the present series this stretch movement time is about one- 
third of the latent time. Stimuli which are more closely in- 
stantaneous — which deliver the blow at the tendon with in- 
creasingly greater velocity — excite a relatively greater num- 
ber of end organs and excite the greater number more or less 
simultaneously. But the muscle end organs have their own 
latency which depends on their own inherent excitability. 
Doubtless the tap on the tendon — a relatively slow stretch — 
excites many times more end organs than are actually essen- 
tial; the work which the muscle does in the reflex is very 
slight. When one remembers that this stretch stimulus is 
briefly continuous and continues to excite; that the stimulus 
is also recurrent in the sense that the tension movement in the 
taut tendon is repeated — the tendon does not immediately 



" For example ; at the end of one second the discharge of impulses 
from the end organs was at the rate of 145 per second; at the end of 10 
seconds this rate was 104 per second. The constant stretch stimulus 
continues to excite (Adrian). 



A CRITERION OF SPEED IN MENTAL REACTIONS? 29 

return to an equilibrium ; when one keeps these facts in mind, 
one is pretty sure that there is an ample discharge of impulses 
into the nerve fibers. In fact this discharge continues till 
the muscle responds. This is well illustrated in some of the 
records where there are two or at least one and a fraction of 
another deflexion during the latent period. The single oscilla- 
tion or wave of suddenly increasing tension is not enough to 
set off the contraction of the muscle. The muscle contraction 
appears to break into the discharging impulses at the moment 
when these discharging impulses are ample both in frequency 
and in the size of the volley — number of nerve fibers set in 
action — to start the contractile response. 

The latent time consists of a chain of interrelated events. 
In the first place there is the stimulation and response of the 
muscle receptors. The impulses generated in these organs 
stimulate afferent nerve fibers. The impulses set in action 
in these nerve fibers transmit the stimulus. It is to be expected 
that the conduction and transmission of this stimulus takes 
considerable time — relatively speaking- — for the arc is by no 
means a short one. There is, in the second place, the conduc- 
tion from the muscle to the dorsal horn synapse; thence 
through the spinal cord — lateral columns — to the prespinal 
center or centers. In animals this center appears to be Deiter's 
nucleus; in man other centers may be in the mid brain. 
In these prespinal centers the afferent impulses are trans- 
formed into efferent impulses. Then follows conduction along 
the efferent limb of the arc ; in animals this efferent path ap- 
pears to be the Vestibulo-spinal tract ; in man, there may be 
some other efferent pathway which conducts the stimulus to 
the ventral horn synapse; thence to the termination of the 
motor nerve fibers at the muscle. Another event is the pas- 
sage of the stimulus from the nerve fibers into the muscle 
fibers. There appears to be an intermediary something at 
this spot, between the nerve fibers and the muscle fibers. Per- 
haps it is best to follow Samojloff's recent conclusion that 
this something is a chemical process or mechanism. The im- 
pulses in the nerve fibers set in action some chemical process 
and thus elicit some stimulus substance ; the muscle fibers are 
specially adapted to respond to this stimulus thus produced. 
At any rate the stimulus which has been transmitted from 
the tap on the tendon passes over this "chemical bridge." The 
muscle fibers respond to this stimulus (1) after a brief period 



30 IS LATENT TIME IN ACHILLES TENDON REFLEX 

of latency during which an ionic interchange takes place — 
the preparation for the contraction; at any rate this is the 
assumption. (2) After a brief period of rigidity. For an 
appreciable length of time after the ionic response the muscle 
is rigid and markedly resistant to any change of form. The 
time or length of this period appears to differ in different in- 
dividuals; it is certainly part of the total latent time of the 
reflex. Very likely the underlying mechanism in this rigidity 
is the viscous-elastic acceleration which appears to be one of 
the preliminary components in every muscle contraction 
(Gasser and Hill). This initial rigidity may be a factor in 
determining the shape of the latent time curve in the second 
type of curves; the single impulse volley starts a response in 
the muscle but a very small one. When reinforcements arrive 
in the shape of other volleys of impulses, the muscle response 
is complete. The first volley elicits a small response because 
of the muscle resistance. The latent time is thus the sum of 
these different items in this closely interrelated chain of 
events. These events take place more or less simultaneously 
in each nerve and muscle fiber. The muscle responds as a 
unit. 

The latent time in a given individual is measured as follows : 
The myograph record is set under a small magnifying glass — 
9-power. A small sharp-pointed caliper "gets" the length of 
the latent period in the given reaction. This length which the 
caliper records is measured at the time scale on the myograph 
record which the tuning fork has already recorded twice; 
this time scale is in 10-sigma intervals. There is no doubt 
that the essential problem in this measurement is to fix the 
beginning and the end of the latent period. The latent time is 
indicated by the small wave or curve in the record. The be- 
ginning of this curve indicates the time when the stretch 
stimulus reaches the muscle. This beginning of the latency 
presents no difficulties. When does the latent period end? 
There are several types of latency curves. In the first place 
there is the single wave curve. This is illustrated in Figure 
2. In this type or record the recording lever responds with 
a small wave or curve and returns to the base line. The re- 
flex response may begin immediately on this return of the 
lever to the base line; this immediate response always takes 
place when the latent time is brief. In Figure 2 the latent 
time is relatively long — the record belongs to subject number 



A CRITERION OF SPEED IN MENTAL REACTIONS? 



31 



34; the lever returns to the base line and stays there briefly 
before the muscle contraction begins. The muscle contraction 
is exhibited in the long downward swing of the lever. 




Figure 2 

Usually the latent time in the slow individual is broken up 
into two full curves. The lever records one curve and returns 
to the base line. Immediately a second curve is recorded, the 
lever returning again to the base line; at this moment the 
muscle response begins. Then there is the type of latency 
curve which consists in one wave and part of another. The 
recording lever responds with a small curve; returns to the 
base line and starts on another wave. Just as the second wave 
reaches the end of the downstroke the response of the muscle 
breaks in; the length of the downstroke is the same in each 
wave — the whole wave and the part wave. In some cases 
there is a tendency for the second upstroke to begin — the up- 
stroke of the second wave. 



CHAPTER V 

The Mental Tests; Their Administration; What They 

Measure ; Are the Reactions in the Tests Comparable to 

the Reactions Which Take Place during the Latent 

Period in the Reflex? 

The mental tests employed are as follows: 
The first addition test in the Courtis series. 
A letter cross out test. 
A figure cross out test. 
A completion test. 

An easy word-object association test. 
An easy word-opposite association test. 
The Taylor recognition test. 

With one exception these tests are in common use; the par- 
ticular reaction in each test is relatively elementary. They 
are "speed" tests and not "power" tests. The Taylor test is 
not so well known; hence some account of what takes place 
in this test is in order. The numbers 1 to 50 are well mixed 
up and printed on a sheet of paper. No two consecutive num- 
bers are together; usually consecutive numbers are widely 
separated. The test consists in taking a pencil and connecting 
the numbers in consecutive order. That is, for example, the 
subject draws a line from 1 to 2 ; then to 3 ; then to 4 and so on 
up to 50. The score is the total time taken to make these 
consecutive connections. It is likely that there is a semblance 
of "power" in this test as opposed to "speed." This matter 
will be taken up later. 

These tests were given immediately after recording the re- 
flex reactions in each individual. The experimenter explained 
just what was wanted as each test was presented to the sub- 
ject. He then told the subject (1) to get ready for the test — 
pencil in hand; suitable position and suitable grip on the pa- 
per and pencil. (2) To begin at once at the signal "go." (3) 
That the time taken in doing the test would be measured by 
a stop watch. Nothing further was said after the signal was 
given except in some cases to set the subject going in the right 
direction. To some extent the experimenter watched the in- 
dividual reactions; he was careful to stand behind the subject 
so as not to interfere with the subject's performance. There 

32 



A CRITERION OF SPEED IN MENTAL REACTIONS? 33 

was no other person in the room while the tests were being 
given. 

The Tests Exhibit Speed of Reaction as their chief char- 
acteristic. At any rate this was the objective in selecting 
them. Speed of reaction is something tangible; it can be 
measured in terms of a definite unit — the time unit. But one 
must remember that these tests consist of acquired reactions. 
In all learning the speed of performance at the beginning is 
far different from the speed of performance at the end of 
learning. At the beginning, any learned reaction such as 
4 + 3 + 6 operates slowly. Such a reaction is functional in 
nature; like any other function it is the synthesis of various 
other active elements. At the beginning one discriminates, 
compares, recalls, recognizes and does a lot of other things. 
In particular, one is sharply conscious of these independent 
but cooperating reactions. One might call them the building 
material ; with this building material the individual constructs 
the new function — adding 4, 3, 6. As the learning proceeds 
these structural elements tend to fuse into a new unit-reaction. 
Then one becomes conscious of the new unit-reaction and it 
alone — ought to at any rate. With a single stroke of atten- 
tion one perceives the problem; this unit perception leads 
straight and immediately to the end result — ^the sum. Natu- 
rally the more perfect the learning, the more perfect the fusion 
of the structural elements and the more speedy the reaction; 
then one is dealing with a function in a relatively perfect state 
of responsiveness. In this ideal condition there is no count- 
ing ; one does not have to see 4 balls, for example, and 3 balls 
and 6 balls and then count up the total. Nor does one have 
to examine the outline of this figure to make sure it is a "4." 
In many of these 80 subjects this ideal does come to light, such 
as subjects 1, 2, 18, 45. On the other hand, many subjects de- 
part more or less widely from this ideal; their learning is 
relatively incomplete. 

Nevertheless in these tests Speed of performance is the sin- 
gle variable; the time score measures speed of performance 
only. In complete learning any other variable tends to ap- 
proach zero in value. Some of the men in this group — just 
mentioned — exhibit relatively complete learning. A score of 
69 or 77 on the addition test is pretty close to the very top 
notch; in such a performance there is practically no variable 
except the sheer time of reaction. In all the tests this single 



34 IS LATENT TIME IN ACHILLES TENDON REFLEX 

variable is measured and only this variable. It is doubtless 
true that other variables continue active ; the learning is often 
far from complete. Furthermore, the mental function or net- 
work of functions known as "intelligence" is in some degree 
a factor in varying the response of different individuals on 
the same test. Foresight is certainly a factor in intelligence ; 
it is a second variable for some of these 80 subjects in at least 
one of the tests — ^the Taylor Recognition Test. This second 
variable disturbs the results ; it is not a question of having or 
not having a particular ability ; rather is it a question of using 
or not using what one does have in potential form. 

Furthermore, in these tests, speed is usually, if not always, 
exhibited in operating different functions, one after the other. 
This means setting up action in one function ; stopping action ; 
passing on to another function and repeating the performance 
again and again. This sort of reaction is more or less intri- 
cate. It is pretty apt to involve something which is not speed 
at all. The subject may, for example, stop all action for a 
moment; some defect in his learning prevents his advance. 
This temporary block is not a constant factor for all the sub- 
jects. This or that man exhibits this block because he does not 
know all the combinations in addition. Other variables such 
as those just mentioned must be reckoned with in interpreting 
the individual performance; this problem will be taken up 
later. For the present, attention is directed to the single vari- 
able — speed of performance. It is assumed that, in adding 
4, 3, 6, the subject has been over the route so many times and 
knows the "road" so perfectly that the only item to be ex- 
amined is the time it takes him to make the "trip" — to perform 
the function. 

The measurement of this single variable is not an end in 
itself. The essential objective is the comparison of these speed 
measurements on the tests with the speed of reaction measured 
in the reflex latent time. Is it proper to make this comparison 
on the basis of the single variable — the speed of reaction? 
Speed of reaction may be the variable in two given types of 
reaction and yet the comparison between these types of reac- 
tion may be futile. Unlike structural and functional condi- 
tions may be far too numerous. This is notably true in the 
present inquiry where the essential problem is the possibility 
that one type of reaction, the latent time in the reflex, is a 
criterion of potential speed in the other type of reaction, the 



A CRITERION OF SPEED IN MENTAL REACTIONS? 35 

learned reactions in the tests. Hence one must know very 
precisely what is being compared. Are the things compared 
really comparable? What comparable elements are common 
to both types of reaction? What elements are present in one 
but not in the other type of reaction ? 

Suppose one examines the two types of reaction which are 
to be compared in this inquiry. Take the reflex latent time. 
It is an unlearned reaction. The transmission and conduction 
of the stimulus, or tendency to excite, around the reflex arc 
exhibits what may be called pure "speed." This speed of re- 
action in the latent time is exhibited in starting action at 
excitatory mechanisms; conducting nerve impulses in nerve 
fibers and transmitting these impulses at synaptic junctions. 
There are about 2i/| meters of nerve fibers, afferent and effer- 
ent; 2 spinal synaptic junctions and at least one large pre- 
spinal center or synaptic junction in the brain stem (these 
prespinal centers may be in the mid brain) ; the neuromyal 
junctions or transmission mechanisms between nerve fibers 
and muscle fibers. Speed or quickness in these elements cen- 
ters chiefly in the movement of nerve impulses ; these impulses 
are essentially conducted and transmitted tendencies to ex- 
cite at some distant point. The impulses carry the stimulus. 
There is a continuous forward movement of the stimulus along 
the reflex arc. This movement is slowed up at the synaptic 
junctions and at the neuromyal junctions; but this slowing up 
is present in every individual, differing, it is true, from one 
individual to another and due to the intrinsic speed condi- 
tions at these points. So far as one can see, there is nothing 
in the reflex latent time which cannot be classified as speed — 
the rapid or slow movement of the stimulus from one point 
to another point. Furthermore, this reflex mechanism is set 
in action hundreds of times every day during the life of the 
individual. It subserves the endless changes in posture de- 
pendent on the slight but changing amounts of contraction in 
the Gastrocnemius muscle. In this postural activity of this 
reflex there may be some relay action from one set of nerve 
fibers to another. Aside from this there are no alternative 
paths ; no semi-independent but closely allied functions which 
may be in action today but inactive for long periods of time. 
The reflex is a unit mechanism; essentially the same mecha- 
nism, the same neural path, is in action each and every time. 
Consequently the reflex mechanism is or ought to be in per- 



36 IS LATENT TIME IN ACHILLES TENDON REFLEX 

feet "running condition" so far as constant use can make it. 

On the other hand, consider the different learned reactions 
in the different tests. These learned reactions include struc- 
tural and functional elements similar to those in the reflex 
latent time. There are about 1% meters of nerve fibers, 
afferent fibers from the retina to the visual area and efferent 
fibers from the cerebral motor area to the arm, hand and 
fingers. There is the anterior horn synaptic junction and 
various neuromyal junctions. If one follows Sherrington 
(PRS., 97B: 519) and considers the synaptic junction as es- 
sentially an excitatory mechanism, then the excitatory mech- 
anism at the motor area comes v^ithin the limits of similar 
elements — to some extent at least. In these learned reactions, 
as w^ell as in the reflex, speed is exhibited in setting up action, 
conduction in nerve fibers and transmission at synaptic junc- 
tions. In both types of reaction, the fundamental basis of 
speed is the velocity of nerve impulses; at least this is true 
for the motor side of the learned reactions. Furthermore, 
these similar elements are constantly active — with this dif- 
ference. The reflex elements are active in the performance of 
one and the same function — the postural control of the Gas- 
trocnemius muscle. These similar elements in the learned re- 
actions are active in the performance of different functions. 
Each and every one of these functions is a unit, more or less 
independent of other functions. For example, adding 4, 8, 5 
is not the same as adding 2, 9, 6 and still less similar to cross- 
ing out 2's. It is expected that these elements, taken as a 
whole and regardless of the individual functions which are 
being performed at any one time, exhibit speed variations in 
different individuals. This must be true since individual dif- 
ferences in speed of performance on these same tests is an 
experimental fact. 

But these learned reactions include something which is not 
present in the reflex latent time reaction. There is the region 
between the terminus of the optic nerve fibers in the visual 
area and the reaction set up in the motor area. That part of 
any total reaction which takes place in this region is strictly 
mental or psychic in nature. Here are to be found such pure 
mental factors as volition, incentive, foresight. The greater 
part of learning is governed by these and other strictly mental 
factors. It is a fundamental part of this experiment that 
mental factors shall be present in one type of reaction. Com- 



A CRITERION OF SPEED IN MENTAL REACTIONS? 37 

parison is made between speed in reactions which have noth- 
ing particularly mental about them and speed in reactions 
which do contain strictly mental elements. These mental fac- 
tors are present in all reactions in the given tests; every in- 
dividual exhibits them and makes use of them. Consequently 
the mere presence of these mental factors does not disturb 
the validity of the experimental results. 

None the less, considerable disturbance does appear when 
one considers the Individual variations within the mental part 
of the total reaction. A mental factor, such as volition may be 
called "flexible" in the sense that the exercise of volition 
brings out a graded adjustment in terms of more or less speed. 
At the same time, any such mental factor or function tends 
to become hardened into habit and thereby loses much of its 
flexibility. The individual may settle into some definite speed 
level and stay there, no matter what the situation may be 
(Downey gives some illustrations, page 98). This habit or 
these habits are acquired reactions; they may or may not be 
the same in any two individuals. Take some illustrations: a 
stimulus which excites to action — acts as a stimulus or incen- 
tive — in one individual, may block or inhibit action in another 
individual. This or that individual may fail to use all his 
resources; he never looks ahead; never foresees the situation 
to come ; never prepares the way for the full use of some auto- 
matic speed mechanism. The individual can do this, but he 
habitually does not, while another individual habitually does 
look ahead. Both individuals may have the same potential 
ability to do this ; the one is using it ; the other is not. In the 
reflex latent time, the stimulus or conducted tendency to ex- 
cite at some distant point is always moving toward that point ; 
there are no in-between stops in some one or more individuals. 
On the other hand, at some part of the learned reaction, such 
as adding 4, 8, 7, there comes a temporary stop; something 
blocks. This total stop operates as a variable in This individ- 
ual. In another individual there is no such total block, but 
the reaction at some point and for some reason is slowed up. 
In still another individual or individuals, there is neither 
slowing up nor block. The man perceives with a single stroke 
of attention 4 + 8 + 7 and immediately writes 19. The fact 
that this or that variable is present in one individual but not 
in another individual is a serious matter when one attempts 
to compare speed in the two types of reaction. These Individ- 



38 IS LATENT TIME IN ACHILLES TENDON REFLEX 

ual variations must be reckoned with in the interpretation of 
results; they are so many uncontrolled variables. The sole 
variable ought to be the intrinsic conditioning factors whose 
speed of performance the time measurement is presumed to 
bring to light. It will presently be shown that the above and 
other individual variations have been acquired; they are de- 
fects in the individual learning. They operate to prevent the 
full manifestation of the individual speed of performance. 



CHAPTER VI 

The Scores on the Tests and Latent Time. Graphic 

Representation of the Measures. Central Tendencies. 

Measures of Dispersion 

The raw scores on the different tests are given in Table 2. 
The small figures directly beneath the given score indicates the 
quartile to which this score belongs. For example, in the case 
of number 45, all scores belong to the first quartile. The first 
quartile includes the smallest scores ; the men who make these 
small scores are the most speedy. The fourth quartile in- 
cludes the largest scores ; the men who make these large scores 
are relatively slow. Two rank orders are given : (1) The rank 
order of the 80 men according to the length of the individual 
latent time. For example, subject number 1 exhibits the short- 
est latent time; subject number 80 exhibits the longest latent 
time. (2) The rank order according to the size of the in- 
dividual's total score. For example, the smallest total score is 
510; this score belongs to the man whose latent time rank 
order is 45. When ranked according to the size of his total 
score this man's rank order is number 1. 

The frequency distributions and various relative data are 
given in the following figures. For the most part the different 
distributions take the "moderately asymmetrical form." The 
greater frequencies lie toward the lower end of the range. 
Yule calls this the most common of all smooth forms of fre- 
quency distributions. One might expect this type of distribu- 
tion since the group consists chiefly of extra selected, superior 
men; the slow men are relatively few and scattered over a 
relatively long range. Under each figure are given relative 
data concerning the distribution such as the average, median, 
standard deviation, skewness, probable error. The relation of 
Q to S. D. is also given. According to YuLE, Q, the semi-inter- 
quartile range, is usually about ^ of the standard deviation in 
distributions of the moderately asymmetrical type ; a range of 
10 points in this ratio does not indicate much displacement of 
this relationship. 

In the normal curve the mode, median and the average coin- 
cide. Actually a given distribution is usually pulled away from 
this symmetrical type. In the present measures the distribu- 
tions are usually distorted in the direction of the larger scores. 

39 * 



40 



IS LATENT TIME IN ACHILLES TENDON REFLEX 



The range in each quartile gives some clue to the spread or 
scatter at different parts of the distribution. In terms of sec- 
conds the range in the third quartile is the same as that in the 
second quartile ; this is true for the combined association tests 
and the latent time. In all other measures the range of the 
third quartile is slightly less than that of the second quartile. 
That is to say, the third quartile measures cluster more closely 
about the average — except in the latent time and association 
tests. The range of distribution in the first quartile is alv^^ays 
large, sometimes twice as large as the range in either the sec- 
ond or third quartile. The range of distribution in the fourth 
quartile is alw^ays much larger — 2 or 3 times larger — than the 
range in the first quartile. Consequently the measures on the 
large score end are considerably more spread out than the 
measures on the small score end of the distributions. In the 
latent time distribution the group is massed toward the small 
latent time values. The first three quartiles with a total range 
of 31 sigma include 80% of the cases. The fourth quartile 



Figure 3 
The Latent Time Distribution 




Score m sig^wvflu 



S.D. 

Average 
Median 

Qa 

Q 

A.D. 

P.E.dis 

Skewness 



2.67 
53.2 
52. 
43.25 
63.68 
10.22 
11.12 

9.004 
+.27 



X 5 = 
P.E.. 



13.35 
1.006 



QUARTILE RANGE 
I II III 



IV 



11 



10 



10 



33 



Q =.76 



S.D 



y-measures are the frequencies. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 



41 



with a range of 33 sigma contains the remaining 20% of the 
measures. 40 sigma include 93% of the cases; only 6 cases lie 
beyond the 72 sigma limit. It is noteworthy that in the latent 
time distribution, quartiles 1, 2, 3 are practically the same in 
range. 

Since the tests were given individually, once to each man, no 
measure of reliability was secured. The time taken to secure 
the different measures was relatively long — about one hour. In 
some cases it was possible to persuade the subject to return a 
second time. Usually this was very difficult to bring about and 
frequently impossible since the men had plenty of other work 
on their hands. Consequently the attempt was given up. 



Figure 4 
The Addition Test Distribution 




Scote. »Yv seconds 



S.D. 3.84 X 8 = 30.72 

Average 124.2 P.E.av 2.3 

Median 118. 

Qi 103. 

Qs 142. 

Q 19.5 

A.D. 24.4 

P.E.dis 20.72 

Skewness -J-.6 



QUARTILE RANGE 
I II III 



34 



21 

Q 



S.D. 



18 
.63 



IV 



63 



y-measures are the frequencies. 



42 IS LATENT TIME IN ACHILLES TENDON REFLEX 

TABLE 2 

THE RAW SCORES ON THE DIFFERENT TESTS AND 
LATENT TIME OF REFLEX 



Total 
Score 
Rank 


Latent 
Time 
Rank 


Latent 
Time 


A.D. 


Addi- 
tion 


Letter 
Cross 
Out 


Figure 
Cross 
Out 


Com- 
ple- 
tion 


Taylor 


Word 
Oppo- 
site 


Word 
Object 


Total 
Test 
Score 


9 


1 


32 


1.2 


78 
1 


86 

2 


150 

2 


84 
1 


204 

2 


26 

3 


30 

3 


658 


23 


2 


34 


1 


75 
1 


77 

1 


124 

1 


147 

4 


220 

3 


28 

4 


33 

3 


704 


15 


3 


34 


1.4 


88 

1 


93 

3 


169 

3 


105 

2 


165 

I 


22 

2 


36 

4 


678 


12 


4 


35 


1.6 


109 

2 


78 

1 


140 

1 


111 

2 


182 

2 


18 
1 


35 

3 


673 


37 


5 


36 


1 


129 

3 


75 
1 


139 
1 


106 

2 


250 

4 


19 

1 


42 

4 


760 


27 


6 


36 


1.5 


82 
1 


102 

3 


150 

2 


100 

1 


221 

3 


26 

3 


29 

2 


710 


47 


7 


36 


1.7 


122 

2 


84 

2 


155 

2 


120 

3 


230 

3 


27 

4 


40 

4 


778 


3 


8 


38 


2 


106 

2 


75 
1 


114 

1 


110 

2 


166 
1 


22 

2 


25 

1 


612 


5 


9 


38 


1.4 


69 

1 


79 

1 


123 

1 


100 

1 


215 

2 


16 

I 


33 

3 


635 


58 


10 


38 


0.8 


116 

2 


103 

4 


175 

3 


121 

3 


236 

3 


28 

4 


36 

4 


815 


2 


11 


38 


1.5 


111 

2 


77 
I 


132 


92 

1 


137 

1 


19 

1 


25 
1 


593 


42 


12 


38 


1.7 


118 

2 


80 

2 


185 

3 


127 

3 


210 

2 


19 

1 


30 

3 


769 


11 


13 


40 


2.1 


90 

1 


90 

2 


195 

4 


92 
1 


165 

1 


16 

1 


20 

1 


668 


59 


14 


40 


1.3 


146 

4 


110 

4 


196 

4 


127 

3 


198 

2 


22 

2 


27 

2 


816 


33 


15 


40 


1.8 


101 
1 


90 

2 


185 

3 


92 

1 


210 

2 


22 

2 


37 

4 


737 


44 


16 


40 


1 


145 

4 


80 

2 


140 

1 


106 

2 


246 

4 


20 

2 


37 

4 


774 


13 


17 


41 


1.5 


90 
1 


85 

2 


150 

2 


125 

3 


180 
1 


19 

1 


25 

1 


674 


14 


18 


41 


1.7 


107 

2 


74 
1 


125 

1 


96 
1 


226 

3 


21 

2 


28 

2 


676 


61 


19 


42 


2 


127 

3 


96 

3 


163 

2 


97 

1 


290 

4 


21 

2 


27 

2 


821 


16 


20 


42 


1.3 


73 

I 


82 

2 


165 

2 


95 

1 


225 

3 


19 

1 


20 
1 


679 


21 


21 


42 


1.5 


92 

1 


77 

1 


123 

1 


127 

3 


227 

3 


23 

2 


24 
1 


693 


10 


22 


42 


1.4 


92 

1 


72 
1 


154 

2 


80 
1 


218 

3 


28 

4 


23 

1 


667 


4 


23 


44 


2.3 


102 
1 


77 
1 


127 
1 


102 
1 


174 
1 


14 

1 


24 

1 


620 


34 


24 


44 


1.8 


114 

2 


67 


152 

2 


125 

3 


234 

3 


24 

3 


21 

1 


737 


36 


25 


45 


2.1 


191 

4 


84 

2 


126 
1 


115 

2 


191 

2 


23 

2 


25 
1 


755 


64 


26 


46 


1.5 


100 
1 


100 

3 


195 

4 


139 

4 


255 

4 


24 

3 


27 

2 


840 


57 


27 


47 


1.8 


106 

2 


80 

2 


171 

3 


140 

4 


264 

4 


18 
1 


35 

3 


814 



A CRITERION OF SPEED IN MENTAL REACTIONS? 43 
TABLE 2— CONTINUED 



Total 
Score 
Rank 


Latent 
Time 
Rank 


Latent 
Time 


A.D. 


Addi- 
tion 


LetUr 
Cross 
Out 


Figure 
Cross 
Out 


Com- 
ple- 
tion 


Taylor 


Word 
Oppo- 
site 


Word 
Object 


Total 
Test 
Score 


75 


28 


47 


2.4 


161 

4 


84 

2 


180 

3 


137 

4 


275 

4 


30 

4 


35 
a 


902 


31 


29 


47 


1.7 


90 
1 


78 
1 


139 

1 


134 

3 


230 

3 


20 

2 


30 

3 


721 


17 


30 


48 


1.2 


114 

2 


100 

3 


143 

2 


117 

2 


170 


17 

1 


18 
I 


679 


24 


31 


48 


1.4 


141 

3 


88 

2 


140 

1 


120 

3 


161 

1 


24 

3 


30 

3 


704 


53 


32 


48 


1.2 


177 

4 


87 

2 


135 

1 


113 

2 


234 

3 


24 

3 


26 

2 


796 


41 


33 


49 


1.6 


140 

3 


89 

2 


182 

3 


104 

2 


201 

2 


24 

3 


28 

2 


768 


30 


34 


50 


1.5 


102 
1 


99 

3 


160 

2 


140 

4 


156 

1 


27 

4 


34 

3 


718 


40 


35 


50 


1.2 


154 

4 


75 


140 

1 


120 

3 


225 

3 


22 

2 


29 

2 


765 


45 


36 


50 


1.8 


154 

4 


90 

2 


150 

2 


142 

4 


199 

2 


15 

1 


26 

2 


776 


49 


37 


50 


1.5 


113 

2 


99 

3 


170 

3 


145 

4 


220 

3 


18 

1 


26 

2 


791 


19 


38 


51 


2 


105 

2 


85 

2 


130 

1 


100 

1 


210 

2 


23 

2 


29 

2 


682 


20 


39 


51 


1.5 


120 

2 


96 

3 


140 
1 


128 

3 


165 

1 


18 
1 


24 
1 


691 


18 


40 


51 


1.6 


99 

1 


87 

2 


172 

3 


100 

1 


182 

2 


17 

1 


23 

1 


680 


74 


41 


52 


1.5 


185 

4 


98 

3 


197 

4 


131 

3 


235 

3 


26 

3 


25 

1 


897 


35 


42 


53 


1.2 


146 

4 


107 

4 


151 

2 


115 

2 


171 

1 


20 

2 


31 

3 


741 


38 


43 


53 


1.5 


82 

1 


105 

4 


165 

2 


106 

2 


257 

4 


19 

1 


26 

2 


760 


32 


44 


53 


1.5 


147 

4 


74 
1 


200 

4 


103 

1 


154 
1 


27 

4 


27 

2 


732 


1 


45 


53 


1.6 


77 
1 


65 
1 


106 
1 


82 
1 


140 

1 


15 

1 


25 
1 


510 


51 


46 


55 


2.5 


160 

4 


84 

2 


150 

2 


120 

3 


220 

3 


20 

2 


40 

4 


794 


22 


47 


57 


1.8 


104 

2 


112 

4 


159 

2 


114 

2 


150 
1 


29 

4 


25 

1 


693 


29 


48 


59 


1.5 


135 

3 


90 

2 


148 

2 


102 

1 


191 

2 


22 

2 


28 

2 


716 


60 


49 


60 


1.8 


122 

2 


85 

2 


176 

3 


135 

4 


250 

4 


18 
1 


33 

3 


819 


25 


60 


60 


1.3 


115 

2 


67 
1 


140 
1 


115 

2 


208 

2 


29 

4 


31 

3 


705 


48 


51 


60 


2.1 


124 

2 


85 

2 


205 

4 


115 

2 


220 

3 


20 

2 


21 

1 


790 


8 


52 


60 


1.3 


110 

2 


72 

1 


142 

2 


112 

2 


174 
1 


22 

2 


24 

I 


656 


6 


53 


60 


1.6 


130 

3 


69 

1 


129 

1 


94 

1 


169 


24 

3 


27 

2 


642 


63 


54 


60 


2.5 


144 

4 


105 

4 


190 

4 


129 

3 


198 

2 


26 
s 


43 

4 


835 


73 


55 


60 


1.5 


127 

3 


120 

4 


240 

4 


120 

3 


228 

3 


20 

2 


40 

4 


895 



44 IS LATENT TIME IN ACHILLES TENDON REFLEX 
TABLE 2— CONTINUED 



Total 
Score 
Rank 


Latent 
Time 
Rank 


Latent 
Time 


A.D. 


Addi- 
tion 


Letter 
Cross 
Out 


Figure 

Cross 

Out 


Com- 
ple- 
tion 


Taylor 


Word 
Oppo- 
site 


Word 
Object 


Total 
Test 

Score 


28 


56 


61 


1.7 


111 

2 


89 
2 


139 

1 


105 

2 


237 

3 


16 

1 


17 

1 


714 


52 


57 


61 


2.2 


182 

4 


67 
1 


142 

2 


125 

3 


230 

3 


20 

2 


29 

3 


795 


24 


58 


62 


1.5 


86 
1 


91 

2 


159 

2 


132 

3 


180 
1 


30 

4 


30 

3 


707 


67 


59 


62 


1.8 


118 

2 


102 

3 


190 

4 


141 

4 


271 

4 


24 

3 


23 

1 


869 


66 


60 


63 


1.5 


135 

3 


120 

4 


187 

3 


145 

4 


215 

2 


26 

3 


31 

3 


859 


70 


61 


63 


2.3 


119 

2 


105 

4 


213 

4 


121 

3 


285 

4 


18 

1 


24 

1 


885 


50 


62 


63 


1.5 


138 

3 


100 

3 


181 

3 


104 

2 


210 

2 


25 

3 


36 

4 


794 


55 


63 


63 


1.8 


174 

4 


106 

4 


182 

3 


98 

1 


166 

1 


31 

4 


43 

4 


800 


43 


64 


64 


1.3 


140 

3 


85 

2 


168 

3 


115 

2 


211 

2 


20 

2 


31 

3 


770 


78 


65 


65 


2.2 


164 

4 


96 

3 


200 

4 


137 

4 


300 

4 


22 

• 2 


40 

4 


959 


79 


66 


66 


1.5 


150 

4 


159 

4 


208 

4 


129 

3 


251 

4 


30 

4 


36 

4 


963 


72 


67 


69 


2 


195 

4 


77 
1 


157 

2 


154 

4 


240 

3 


37 

4 


35 

3 


895 


56 


68 


70 


2.4 


116 

2 


94 

3 


158 

2 


108 

2 


276 

4 


17 
1 


37 

4 


805 


62 


69 


70 


1.7 


127 

3 


95 

3 


200 

4 


124 

3 


231 

3 


18 
1 


32 

3 


827 


46 


70 


70 


1.8 


100 

1 


97 

3 


192 

4 


120 

3 


197 

2 


26 

3 


44 

4 


776 


54 


71 


70 


2.2 


90 

1 


119 

4 


224 

4 


118 

2 


195 

2 


25 

3 


27 

2 


798 


71 


72 


70 


2.5 


140 

3 


100 

3 


192 

4 


129 

3 


274 

4 


26 

3 


27 

2 


888 


65 


73 


71 


1.8 


142 

3 


104 

4 


167 

3 


118 

2 


264 

4 


28 

4 


32 

3 


855 


7 


74 


72 


2 


119 

2 


80 

2 


135 

1 


97 
1 


174 

1 


24 

3 


25 

1 


654 


39 


75 


74 


1.7 


114 

2 


91 

2 


153 

2 


112 

2 


238 

3 


20 

2 


33 

3 


761 


77 


76 


76 


1.5 


144 

4 


116 

4 


261 

4 


145 

4 


226 

3 


20 

2 


26 

2 


938 


76 


77 


80 


1.5 


160 

4 


126 

4 


193 

4 


142 

4 


265 

4 


23 

3 


25 
1 


934 


69 


78 


85 


1.6 


133 

3 


110 

4 


181 

3 


141 

4 


270 

4 


19 

1 


23 

1 


877 


68 


79 


85 


1.5 


154 

4 


107 

4 


169 

3 


145 

4 


211 

2 


34 

4 


50 

4 


870 


80 


90 


96 


1.8 


205 

4 


145 

4 


283 

4 


175 

4 


290 

4 


35 

4 


45 

4 


1168 



A CRITERION OF SPEED IN MENTAL REACTIONS? 45 



2o 
18* 

16. 
S. 

^. 



S.D. 

Average 
Median 

Qs 
Q 

A.D. 

P.E.dis 

Skewness 



Figure 5 
Letter Cross Out Distribution 



C3^ 



^ in 



CO 



^<^ 



J.' 

or O 



^~ Oft r- si) 
o - f< m 



r+ v> ^ 



1- 



OeoTC \nsecoA4s, 



92.35 
89. 
79.88 
102.57 
11.35 
13.72 
11.59 
+.55 



1.91 X 9 =17.19 



P.E.av 1.3 



quartile range 

I II III 



IV 



15 



43 



12 

Q_ - 

S.D. 
y-measures are the frequencies. 



10 
.66 



46 IS LATENT TIME IN ACHILLES TENDON REFLEX 



Figure 6 
Figure Cross Out Distribution 




tV~g- vIp- 






cc^Te \'A seconis 



S.D. 

Average 
Median 

Q3 
Q 
A.D. 

P.E.dIa 

Skewness 



2, 

165.4 

161. 

140.15 

188.5 
24.17 
25.5 
21.85 
-J-.38 



7 X 12 = 32.4 
P.E.aT 2.45 



QUARTILE RANGE 
I II III 



IV 



34 



95 



25 23 

-Q-=.74 
S.D. 
y-measures are the frequencies. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 47 



Figure 7 
Completion Test Distributions 




Score in secoivis 



S.D. 

Average 
Median 

A.D. 

P.E.dis 
Skewness 



2.63 X 7 = 18.41 
118.3 P.E.av 1.38 
118. 
103.8 
132. 

14.1 

14.52 

12.42 

+.048 



QUARTILE RANGE 
I II III 



IV 



24 



15 
Q 



14 
= .77 



43 



S.D. 
y-measures are the frequencies. 



48 



IS LATENT TIME IN ACHILLES TENDON REFLEX 



Figure 8 
Taylor Test Distributions 



14 






i 




It 




1 
1 


10* 




1 


s. 






1 






1 




i^ 






1 

1 




4" 






1 




Z r 


_r 


^ 




*-t, 


t— 


9- — «0 U 


n 


£, 


in r- «o ^ 
ScoTG \ 


S.D. 

Average 




3.17 X 12 = 

215.7 P.E.ay 


Median 




219. 


Qi 




181.5 


Qs 




240. 


Q 




29.25 


A.D. 




30.9 


P.E.dis 




25.65 


Skewness 






—.26 






<i :i. t<\ -zt G 
f* C^ ^<' 04 c* 



2.87 



QUARTILE RANGE 
I II III 



IV 



44 



85 



34 25 

S.D. 

y-measures are the frequencies. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 



49 



Figure 9 

Combined Association Tests- 



-DlSTRIBUTION 




-* id ■«< vj VI "# >*» 'VS 

5coTe \vv seconis. 



oo — r^ r- _ 

r* r- r* f)^ o» « 



S.D. 

Average 
Median 

Q3 
Q 

A.D. 

P.E.dis 

Skewness 



9.7 

53.15 

51. 

47.25 

59.33 

6.04 

7.2 

6.54 

+.66 



P.E. 



.73 



QUARTILE RANGE 
I II III 



IV 



14 



25 



6 6 

Q _ 

S.D. 
y-measures are the frequencies. 



= .62 



50 



IS LATENT TIME IN ACHILLES TENDON REFLEX 



(4. 
If 

10 

z 



Figure 10 
Total Raw Score Distribution 
I 



O 



-{ 









-sia 



£ (S 









Score \i\ secoTvos. 



2 ^ or m 

o- a* O* o 



rj- 






s "^ 



S.D. 

Average 

Median 

Qs 

Q 

A.D. 

P.E.dis 

Skewness 



2.53 X 40 



768. 
763. 
694. 
824.3 

65.15 

78. 

68.25 

+.148 



P.E.a 



101.20 
' 7.62 



QUARTILE RANGE 
I II III 



IV 



184 74 



56 



344 



Q =.64 



S.D 



y-measures are the frequencies. 



CHAPTER VII 

The Treatment of the Test Scores 

What is the best criterion of speed in the learned reactions? 
It is obvious that no one test is a safe criterion of the speed 
level to which these different men belong. In some instances 
an individual exhibits superior speed in all the tests; for ex- 
ample, numbers 23 and 45 achieve a first quartile rank in each 
of the different tests. Usually the superior speed is selective 
in each individual ; it appears in one test but not in another. 
For example, numbers 2, 9, 11, 13, 18 achieve the first quartile 
rank — superior speed — in three or four tests ; they fall to lower 
levels in the other tests. Frequently an individual exhibits 
marked inferior speed in some one test; for example, number 
25 falls to the fourth quartile rank in the Addition Test, Pre- 
sumably no one of these 80 men has reached his speed limit in 
any one of the tests or types of reaction. Practice invariably 
increases the individual speed. What these tests do is chiefly 
this : they bring to light the individual speed level in each of 
the tests at this particular time. They tell what the individual 
does now. Perhaps one can go further and say that a given 
test locates the individual at some point in his learning curve ; 
that one or more tests may locate him at the upper level of this 
curve while other tests locate the same man at lower levels. 
This statement is made in the light of the experimental facts 
of practice effects on the speed of an individual in a given func- 
tion. 

It is manifestly impossible to secure the absolute maximum 
speed of reaction for every individual in all the tests. One 
must take the speed conditions as the individual exhibits them 
at the present time. None the less must one keep in mind that 
what the individual does now may be a positive criterion of 
what he can and will do when given additional practice in any 
function or type of reaction. His rank order then after the 
period of practice may be about the same as his rank order 
now before such a period of practice. Consequently it is im- 
portant to determine rather precisely what the individual does 
now. No one test tells the whole story ; one must take account 
of several — the man's score in several tests. One must secure 
a composite score made up in some manner from the scores on 
the different tests. In the first place, one can add the raw scores 

51 



52 



IS LATENT TIME IN ACHILLES TENDON REFLEX 



of the different tests and get the total time taken to do all the 
tests. Is this a sound procedure? It may be that such a com- 
posite score contains an excess of some one type of reaction and 
thereby handicaps some men who excel not in this but in some 
other type of reaction. For example, such a composite score 
may contain an excess of the Cross Out reactions. Does this 
handicap any of the subjects? Again, such a composite score 
may contain rather new and only semi-learned functions. 
Speed in the mental sense is something learned and perfected 
through practice. At the beginning of practice in any one 
function achievement in that function is relatively slow ; speed 
in the function develops to higher levels with practice. 

In other words some tests may be already weighted. If these 
men had had but two weeks experience with addition — were 
mere beginners — but did possess a normal experience in the 
other tests, the Addition Test would be heavily weighted. The 
composite made up of the score of all the tests would be exces- 
sively burdened with this load of poor speed in addition. Per- 
haps one can get light on this problem in the following manner. 
Suppose one take as a composite the total score of different 
teams of tests and correlates these total scores with the latent 
time. For example, take a composite made up of the total scores 
of any two tests. The following table illustrates : 

TABLE 3 

Correlation Between the Latent Time and (1) Individual Tests 
and (2) Different Teams of Two Tests." 



.44 ± .06 Addition and Letter Cross Out .54 

Addition and Figure Cross Out . 67 

.49=t.057 Addition and Completion .51 

Addition and Taylor .43 

Addition and Association .47 

. 51 =t . 055 Letter Cross Out and Figure Cross Out.53 

Letter Cross Out and Completion . 52 

.44 =t .06 Letter Cross Out and Taylor .41 

.28 =t .069 Letter Cross Out and Association .47 

Figure Cross Out and Completion .55 

.21 ±.072 Figure Cross Out and Taylor .46 

Figure Cross Out and Association .54 

Completion and Taylor ,38 

Completion and Association .45 

Taylor and Association .32 



Addition 
Letter Cross Out 

Figure Cross Out 

Completion 
Taylor 

Association 



" In all cases, the value of "r" is calculated according to Pearson's prod- 
uct-moment formula. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 



53 



This shows that the sum of any two tests yields a larger 
value for "r" than either test taken singly — with one excep- 
tion. When the Taylor Test is added to another test, the value 
of "r" is reduced ; that is to say, when the team consists of the 
Taylor Test and one other test, one of the two tests in each 
team yields a larger value of "r" than the two tests taken to- 
gether. The correlation of the team consisting of the Taylor 
Test and the Association Tests is a possible exception to this 
rule. Again, suppose one takes a composite made up of any 
three tests: (1) When the Addition Test or the Figure Cross 
Out Test or the Completion Test is added to any two tests the 
value of "r" is always increased. The following table illus- 
trates : 

TABLE 4 

Changes in the Value of "r" (Correlation with the Latent Time) 

When the Addition Scores are Added to any Two Tests 



Letter and Figure Cross Out Tests . 53 

Letter and Completion Tests . 52 

Letter and Taylor Tests .41 

Letter and Association Tests .47 

Figure and Completion Tests . 55 

Figure and Taylor Tests . 46 

Figure and Association Tests .54 

Completion and Taylor Tests . 38 

Completion Association Tests .45 

Taylor and Association Tests . 32 



Add the Addition Scores . 58 

Add the Addition Scores . 58 

Add the Addition Scores . 50 

Add the Addition Scores . 53 

Add the Addition Scores .59 

Add the Addition Scores . 53 

Add the Addition Scores . 55 

Add the Addition Scores . 49 

Add the Addition Scores .52 

Add the Addition Scores .46 



(2) Precisely a similar increase in the value of "r" takes 
place when the Figure Cross Out or the Completion Test is 
added to a team of any two tests. The addition of the Letter 
Cross Out Test has a similar but less effect, especially when 
one member of the team of two is the Figure Cross Out Test. 

(3) On the other hand, when the Taylor Test is added to a 
team of any two tests the value of "r" is always diminished, 
the following table illustrates : 

TABLE 5 
Changes in the Value of "r" When the Taylor Test is added 
to a Team of any Two Tests 



Addition and Letter Cross Out . 54 

Addition and Figure Cross Out . 57 

Addition and Completion .51 

Addition and Association .47 

Letter and Figiu-e Cross Out . 53 

Letter and Completion .52 

Letter and Association .47 

Figure Cross Out and Completion . 55 

Figure Cross Out and Association .54 

Completion and Association .45 



Add the Taylor Test 
Add the Taylor Test 
Add the Taylor Test 
Add the Taylor Test 
Add the Taylor Test 
Add the Taylor Test 
Add the Taylor Test 
Add the Taylor Test 
Add the Taylor Test 
Add the Taylor Test 



.50 
.53 
.49 
.45 
.46 
.47 
.43 
.48 
.47 
.44 



54 IS LATENT TIME IN ACHILLES TENDON REFLEX 

The Taylor Test has this same effect — it reduces the value of 
"r" — no matter what the combination of tests is. That is, add 
the Taylor Test to any two tests, any three tests, any four 
tests, and five tests ; in any case the value of "r" is reduced. 

Furthermore these correlations bring to light more or less 
definitely the diminishing increment of yield as one test after 
another is added to a given team of tests. This appears to be a 
persistent characteristic of any team of tests (Hull). The fol- 
lowing figures illustrate this phenomenon : (1) The correlation 
of Latent Time and Addition is .44 ; Latent Time and Comple- 
tion is .44. (2) The correlation of the Latent Time and Addi- 
tion plus the Completion Test is .51. (3) The correlation of 
the Latent Time and Addition plus Completion plus Letter 
Cross Out Tests is .58. (4) The correlation of Latent Time 
and Addition plus Completion plus Letter Cross Out plus Fig- 
ure Cross Out Tests is .60. But the time soon comes when the 
addition of another test ceases to increase the value of "r." The 
increment of yield in the value of "r" is strikingly reduced 
when the third test is added. In fact the team of three tests 
consisting of Addition, Figure Cross Out and Completion 
Tests yields close to the maximum correlation of the tests with 
the Latent Time. When the Letter Cross Out Test is added, 
the value of "r" appears to increase from .59 to .60. 

So far as correlation can throw light on the matter these 
four tests exhibit a normal situation : (1) Each one adds some- 
thing to the value of "r" (when correlated with the latent 
time). (2) A diminishing increment of yield in the value of 
"r" takes place as the number of tests is increased. (3) "r" 
reaches a maximum value when the team consists of four 
tests — very close to the maximum when the team consists of 
three tests. The addition of the Taylor Test always reduces 
the value of "r." Hence this test must be heavily weighted at 
the outset — in the raw scores. The following is submitted as 
at least a partial explanation of this initial weighting. The 
directions for this test were perfectly clear; at any rate each 
man said he understood perfectly what to do. In every instance 
the resulting performance showed that the man had the direc- 
tions well in hand. Nothing was said in the directions about 
the method in doing the test. Speed in the test consists to a 
considerable degree in having several consecutive numbers 
always on hand — in mind so that the hand can be kept moving 
from one number to another in relatively quick succession. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 55 

Suppose, for example, this man makes a line to "2" ; then he 
stops and hunts for "3" ; then makes a line to "3" ; then stops 
and hunts for "4" ; draws a line to "4" — and so on. This is a 
very plodding, hand-to-mouth method. The long and numer- 
ous stops of the pencil take time and bring about more or less 
confusion. The subject becomes aware of delay and finds it 
increasingly difficult to locate the next number. 

Several subjects did this very thing — chiefly the men with 
the large scores on this test. They never discovered any plan 
to increase their speed. They habitually looked only for the 
next consecutive number. Other men discovered that they could 
just as well go in search of 2, 3, 4 or more consecutive num- 
bers and have them on hand. Thus the pencil was kept going 
rather steadily; there were few if any pauses. Other men 
started at the very beginning on this method ; they constantly 
had several numbers on hand ahead of the immediate pencil 
movement. They looked ahead and prepared the way well in ad- 
vance. All these men were well equipped with "intelligence," 
but the fact remains that they did not make full use of it. At 
least this is true for many of them. One might say that in 
some of these men the psychic factor of foresight has not be- 
come a working habit. Change the situation very slightly and 
there is little or no foresight. Probably they can use foresight 
but they habitually do not — at least not in the present situa- 
tion. 

Another individual variation comes to light in the perform- 
ance of this same test. The directions said clearly "take the 
shortest distance between two numbers." The men invariably 
asked about this. They distinctly understood — said they did 
— that they were to make a straight line from one number to 
another consecutive number. In a few cases some men did 
not do this ; they went from one number to another in a round- 
about way, and tried to escape passing through another num- 
ber. They were immediately set right. Thus in every instance 
the subject knew exactly what to do. But the speed of move- 
ment in passing from one number to another was notably dif- 
ferent in different men. Suppose one number is at the top of 
the sheet while the next consecutive number is at the bottom 
of the sheet. The subject knows exactly what to do and where 
to go and how to do it. Yet some men take as much as one sec- 
ond in making the line ; other men make the line in a flash. It is 
estimated that the time taken in this excessive slowness may 



56 IS LATENT TIME IN ACHILLES TENDON REFLEX 

be as much as a full minute during the performance of the test. 
Presumably this is a habitual matter. Perhaps there is exces- 
sive carefulness which may have spread beyond the limits of 
some other situation into this one. The man may fail to per- 
ceive that he can move fast in this particular instance. At any 
rate this factor must contribute considerably to the wide differ- 
ence in the individual's quartile location in this test. 

One can examine the problem of weighting from another 
angle. Different tests exhibit different amounts of scatter or 
dispersion. Consequently one test may influence the composite 
score more than another when the composite is made up of the 
raw scores. The composite score ought to be representative ; it 
ought therefore to be free from special stress and burden from 
any one test. When one adjusts this variability, it is presumed 
that each set of test scores has about the same weight or in- 
fluence on the composite score. Thus one weights the raw 
scores and gets a new composite ; is the weighted composite any 
more reliable than the raw composite score ? Anderson tested 
out several methods of weighting: (1) Sigma scoring method. 
(2) Correlation of the test with the composite — total score of 
all the tests. (3) Correlating the test with a criterion outside 
of the tests. (4) Multiple correlation weighting. She con- 
cludes that the raw scores have as high validity and reliability 
as the weighted scores. Even the "best possible method" — 
multiple correlation weighting — does not appear to add much 
of anything to the reliability of the raw scores. 

In spite of these conclusions it was deemed best to test out 
other methods of weighting. The following methods were 
used: 



1. WEIGHTING THE SCORES ACCORDING TO THE 
VARIABILITY OF THE DIFFERENT TESTS 

The purpose here is to equalise the spread or dispersion of 
the different test scores; the spread in one test ought to be 
about the same as the spread in another test. The evidence for 
this variability is found in the standard deviations of the dif- 
ferent tests. One makes the different standard deviations ap- 
proximately the same or similar in size; then uses the same 
multiplier or divisor with each of the scores on each test. The 
standard deviations of the present tests are treated as follows : 



18.41 


38.04 


9.7 


3 


6 


I'A 


6.15 


6.34 


6.47 



A CRITERION OF SPEED IN MENTAL REACTIONS? 57 

TABLE 6 

The Standard Deviations in the Different Tests; Corrections 
to Make the VariabiUty Constant in Each Test 

Letter Figure Combined 

Addition Cross Out Cross Out Completion Taylor Association 

30.72 17.19 32.64 

Divide each S. D. as follows: 

5 3 5 

Then one has a new set of S. D.'s 
6.14 5.73 6.53 



Thus the standard deviations are made approximately equal ; 
when the treatment is applied to the different tests — individual 
scores changed by the appropriate divisor — the spread or vari- 
ability is about the same in each test. Thus one divides each 
Addition Score by 5 ; each Letter Cross Out Score by 3 and so 
on. 



2. CONVERT THE DIFFERENT TESTS INTO A 

COMPARABLE SERIES 

(Hull's method) 

According to this method one converts the different scores 
into a standard normal distribution in which the scores shall 
range from to 100 with the mean at 50. 3.5 sigma usually 
takes care of all spread or variability above or below the aver- 

50 

age; hence -5-^ =14 which is the standard deviation of the 
0.0 

new distribution. The new individual scores are computed ac- 
cording to the formula X = K + SXi. S is a ratio between 
the S.D. of the new distribution and the S.D. of the given test; 

14 
S = ^ — K is a constant found by the formula 50 — (Average 

of the distribution X S) in the given test. The values for S 
and K in each test are as follows : 

TABLE 7 
Figures Used in Converting the Raw Scores into a Comparable Series 

Letter Figure 

Addition Cross Out Cross Out Completion Taylor Association 

S .45 .81 .43 .76 .368 1.44 

K —6.6 —24.8 —21.1 —39.9 +29.38 —26.53 



58 IS LATENT TIME IN ACHILLES TENDON REFLEX 

The results of using these two methods of weighting and 
comparison with the raw scores are as follows : 

TABLE 8 

Correlation of the Latent Time With the Individual Tests 
When Different Methods of Weighting are Used 







Scores Adjusted 


Scores Converted 






According to 


into 


Comparable 




Raw Scores 


Variability 




Series 


Addition 


.44 


.43 




.45 


Letter Cross Out 


.47 


.49 




.44 


Figure Cross Out 


.51 


.46 




.55 


Completion 


.44 


.42 




.50 


Taylor 


.28 


.29 




.29 


Association 


.21 


.26 




.25 



The correlation between the raw scores and the scores adjusted 
according to variability is .96 ; between the raw scores and the 
scores converted into comparable series the correlation is .97. 
The correlation between the two weighted scores is .999. 

According to this examination of the problem of weighting, 
the composite secured by adding the raw scores has about the 
same relation to the latent time as either of the weighted 
scores. Very considerable labor is involved in the weighting 
and nothing is gained in terms of accuracy and soundness of 
the composite score. Hence the raw score composite is adopted 
as giving a satisfactory "picture" of the individual's speed of 
performance in the learned reactions. The relation between 
the total raw score — all tests — and the latent time is, "r" = 
.59 ± .049. Since the Taylor Test tends to pull down this value 
of "r," the use of a team of 3 or 4 tests tends to slightly raise 
this correlation — up to .60 or .61. The fact that a team of 3 
or 4 of these tests yields practically the same value for "r" and 
the fact that weighting the tests according to variability 
and according to Hull's method does not materially alter 
the relationship between the test scores and the latent time — 
these facts are made use of in the construction of the Regres- 
sion line. 



CHAPTER VIII 

Certain Physical Speed Mechanisms are Active During 
THE Latent Time of the Reflex. These Mechanisms 
Transmit a Stimulus from One Point to Another Point 
Within the Nervous System. Relative Importance of 
THESE Physical Mechanisms in Determining the Quick- 
ness OF Performance in the Tests. Relative Importance 
OF Mental Speed Factors in Determining This Quickness 
OF Performance on the Tests 

The latent time in this particular stretch reflex — the Gas- 
trocnemius muscle — differs in different individuals. So far 
as these 80 men are concerned, this appears to be an estab- 
lished fact. This latent time is consumed in transmitting a 
stimulus from one point to another point within a section of 
the nervous system of these different individuals. In many 
ways this section is a representative sample of the individual 
nervous system. It includes muscle end organs, afferent and 
efferent nerve fibers, synaptic junctions, neuromyal junctions 
and prespinal centers. The fact of difference in latency means 
that this section of the nervous system transmits a stimulus 
at a different velocity in different individuals.^^ ^ brief latency 

^ This conclusion is supported by evidence from other courses. (1) 
There is the experimental work of Carlson culminating in the conclusion 
that the most rapidly contracting muscle is attached to the most rapidly 
conducting nerve. This fact comes to light in the present experiment. 
At the beginning of the inquiry the myograph was driven at a high 
speed. This speed recorded some reflexes perfectly; in these cases, the 
latent time was brief. In other cases the reflex record was much spread 
out; the angles at the junction of the latent time period and the beginning 
of the muscle response were so large that accurate measurements were 
very difficult or impossible; these cases exhibited a long latency. It is 
likely that, with the myograph running at a high speed, the reflex record 
of a slow individual would tend to approach a straight line. (2) There is 
the experimental work of Lucas, Hill, Lapicque and Nernst, culminat- 
ing in the exact measurement of the time factor in excitability — chron- 
axie — and the expression of the excitatory process in mathematical terms. 
The chronaxie, in this gastrocnemius nerve-muscle unit, differs in differ- 
ent individuals. Therefore the velocity of conduction differs. (3) There 
is the recent conclusion of Sherrington (PRS, 100B:448 — 1926) that the 
dominant factor, in individual variability in nerve muscle reaction, is 
functional. The source of this functional variability is chiefly in the 
nerve centers. Excitability is a functional factor. When the excitability 
is increased — chronaxie reduced — the reaction to a constant stimulus is 
greatly increased. (4) Since the present report went to press, additional 
support of the above results has appeared. Tuttle, Travis & Hunter 
(AJP, 82:99) using a stretch stimulus and action current, measured 
the latent time — from response of the muscle to the stretch stimulus to 
the beginning of the electrical change in the muscle — in the Achilles 

59 



60 IS LATENT TIME IN ACHILLES TENDON REFLEX 

means a high velocity or superior quickness; a long latency- 
means a low velocity or slowness. These different levels of 
speed in different individuals characterise a native, unlearned 
reaction — the reflex. Presumably the latent time brings to 
light the individual's intrinsic speed capacity in this partic- 
ular section of his nervous system. The question of im- 
mediate interest is this: is this individual intrinsic speed ca- 
pacity in this section of the nervous system a purely local 
phenomenon? Is the same or closely similar speed also in- 
trinsic for other parts, perhaps for all parts of the individual 
nervous system ? Can one, on the basis of the latent time, lo- 
cate an individual in a more or less definite speed level? In 
particular, what does the latent time tell about speed condi- 
tions in reactions which the individual has learned? 

Suppose we set forth this problem in the following manner : 
A. A totality of factors is active in producing the varying 
length of the latent time in different individuals. This latent 
time is consumed, chiefly, in the movement of the stimulus 
from one point to another point within the nervous system. 
Quickness or slowness in this movement — brief or long latent 
time — centers primarily (1) in the velocity of the nerve im- 
pulse; (2) in the number of nerve fibers in action. The stim- 

Tendon reflex in 8 subjects; this latent time ranged from 25 to 38 sigma. 
L. E. Travis (Science, Jan. 13, 1928) measured the latent time in the 
Patellar reflex in 40 subjects. He used a stretch stimulus and the action 
current; the latent time is the period between the response of the muscle 
end organs to the stretch stimulus and the moment of the electrical 
change in the muscle. He made 8 records for each subject; the latent 
period ranged from 11 to 27 sigma. He compared this latency with in- 
telligence as measured by the Otis Higher Examination form A and 
found a correlation of .87. 

There is considerable evidence that electrical response in the muscle 
takes place before the change of form. Fulton (Quarterly Journal of 
Experimental Physiology, 15:349) stresses the period of "true latency." 
The action current reaches the muscle, but for about 2 sigma the muscle 
remains unaff'ected by this stimulus from the motor nerve. Further- 
more, there appears to be a period of rigidity; the muscle does respond 
to the motor nerve stimulus, but for about 4 sigma it is unable to 
change its form owing to the excessive rigidity which sets in immediately. 
Sanderson (JP, 17:117) found that the mechanical thickening of a 
given point in a muscle occurs about 3 sigma after the stimulus is ap- 
plied to that point. In all voluntary action this period of "true latency" 
and initial rigidity ought to be reckoned with; such items are essential 
■components in the speed of reaction in such functions as addition with 
pencil and paper. Suppose one adds 4 sigma to the figures which Tra- 
vis reports. Then the latency in the Achilles reflex in his 8 subjects 
ranges from 29 to 43; in the Patellar reflex, from 15 to 31. It is well 
"known (Dodge) that the latent time in Patellar reflex is briefer than that 
in the Achilles. The figures which Travis reports for the Achilles reflex 
harmonize well with the figures in the present report. It is noteworthy 
that Travis found in his 40 subjects that the slowest latent time was 
21/^ times larger than the most rapid. In the present report the slowest 
latent time is 3 times larger than the most rapid. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 61 

ulus must be adequate ; a single active nerve fiber has no special 
value no matter how fast the nerve impulse travels; there 
must be a certain number of nerve fibers in action in order to 
set off any response. Under accurately controlled conditions, 
where the external stimulus is instantaneous, an increasing 
number of active nerve fibers means diminishing length of 
the latent time (Sherrington 7, 8). (3) In the frequency of 
nerve impulses ; how many pass a given point within a given 
time? This frequency subserves the phenomenon of summa- 
tion at synaptic junctions, at neuromyal junctions and at the 
muscle fibers. A high frequency is associated with a brief 
latency; low frequency with a long latency (Fulton 2; Sher- 
rington 7). 

B. A totality of factors is active in determining the time 
which each individual consumes in doing each test. 

C. Some factor or factors are active only in the learned re- 
actions — the various tests. Perhaps one can say also that 
some factors or factor is active only in the unlearned reactions 
— the reflex latent time. 

D. Some factor or factors are active in both types of reac- 
tion, learned and unlearned. Examine the figures in Table 2 ; 
fluctuation in the speed of performance in the tests runs more 
or less parallel with fluctuation in the length of the latent time 
or speed of movement in the reflex arc. The value of "r" in 
the correlation is a measure of these concomitant speed 
changes. In Chapter V, attention was directed to the fact of 
similar elements in the two types of reaction, learned and un- 
learned. These elements are (a) Structural; excitatory mech- 
anisms, nerve fibers and synaptic junctions. In the tests as 
well as in the reflex arc, a stimulus is transmitted from one 
point to another point within the nervous system. At least, 
this is true for the motor side of the learned reactions where 
the stimulus is transmitted from the cerebral cortex to the 
arms, hands and fingers, (b) Functional; this includes the 
velocity and frequency of nerve impulses and the number of 
nerve fibers in action, in which these impulses are travelling 
at any one moment. Doubtless these physical speed mechan- 
isms in the nervous system are chiefly responsible for the 
length of the latent time in the reflex. The essential objective in 
this research is to throw some light on the value of this latent 
time as a criterion of what the individual can do in strictly 
mental reactions. Hence the questions : How important is the 
influence of these physical speed factors in determining the 
time an individual consumes in his performance of the tests? 
How much do the physical factors contribute? How much do 
the strictly mental factors contribute ? 

In the first place, the sphere of influence of the physical 
mechanisms centers in the single reaction, movement or mo- 



62 75 LATENT TIME IN ACHILLES TENDON REFLEX 

tion. In the reflex the nerve impulses and allied mechanisms 
determine the time consumed in transmitting a stimulus, or 
tendency to excite, to some distant point ; that is, from receptor 
to effector organs. A similar transmission takes place in the 
test. For example, how soon after a given signal does the in- 
dividual write the figure "9"? A large part — perhaps the 
greater part — of this time is consumed in the transmission of 
the stimulus, which is set in action at the signal, from one 
point to another point within the nervous system. Velocity of 
nerve impulses goes far to determine the quickness or slowness 
of such a reaction. It is to be expected that when the nerve 
impulses travel from one point to another point at a high veloc- 
ity, the individual reacts quickly; his movement is "quick"; 
the stimulus reaches the muscle or effector organ in a very 
brief space of time. The intensity of the stimulus within the 
nervous system also influences the quickness of reaction. For 
example, summation at synaptic junctions in reaction time — 
light and sound stimuli — greatly augments the quickness of 
reaction. Light alone elicits a conducted tendency to excite or 
set in action some effector organ. The union of light and 
sound stimuli makes this conducted tendency much more in- 
tense ; the frequency of nerve impulses is increased ; the num- 
ber of active nerve fibers is greater. In other words, one can 
make this reaction or movement — write the figure "9" — 
rapidly or slowly according to the intensity of effort or concen- 
tration of attention. The physical speed mechanisms possess 
a certain range of capacity for speed. At the same time this 
range has rather strict limits. In spite of the summation of 
light and sound stimuli, one man's reaction continues to be 
relatively slow, while another man's reaction continues to be 
relatively fast (Jenkins). 

This transmission of the stimulus, or tendency to excite, 
from one point to another point within the nervous system 
takes place in each reaction, movement or motion; for ex- 
ample, a single movement in the process of laying a brick, the 
movement or movements in writing the figure "9" and crossing 
out a "2." Furthermore, these physical speed mechanisms are 
active and perhaps chiefly responsible for the quickness or 
slowness of a single stroke of attention. Crossing out a "2" 
involves a stroke of attention, but the strictly motor element 
stands out pretty prominent. The fixation pause in reading 
language units and numerals is a single stroke of attention. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 63 

The strictly motor element may not always be so prominent in 
the fixation pause as it is in crossing out a "2." Nevertheless 
there appears to be more or less overt response of motor speech 
mechanisms. In reading numerals the fixation pause may be 
of long or short duration ; long, for example, when the fixation 
covers 3 or 4 numerals, and short when the fixation covers a 
single numeral. Apparently also the duration of any fixation 
pause may be greatly reduced through practice (Terry). 
When one reacts to a single letter, there is a single stroke of 
attention or fixation pause ; when one reacts to a single word, 
there is a single stroke of attention or fixation pause. But the 
reaction time to a single letter appears to be the same as the 
reaction time to a single word (Cattell). The fact of the 
matter is this ; these physical speech mechanisms influence the 
speed or quickness of a single movement, motion, stroke of at- 
tention. This stroke of attention may consist in copying "9" 
or in adding 7 and 2 or in multiplying 3 and 3. In each case the 
end result is the same — writing "9." In each case there is a 
reaction to a stimulus. Presumably the stimulus to the effector 
organ travels just as far in copying "9" as in multiplying 3 and 
3 ; the stimulus to the effector organ travels just as far and the 
time consumed is just the same when the reaction is to a single 
letter as when the reaction is to a word. In reading, a word is 
of greater value than a letter ; the word accomplishes more — 
enables one to read more rapidly. These physical mechanisms 
are not concerned with what the stroke of attention accom- 
plishes. So far as they are concerned one stroke of attention 
is the same as any other; for example, from the physical 
mechanism standpoint a stroke of attention to a letter is ex- 
actly the same as a stroke of attention to a word, for in each 
case the stroke of attention consumes exactly the same time. 

On the other hand, the sphere of mental quickness centers in 
(1) accomplishments, purposes, ends and (2) means for 
achieving the end. "Means" here is essentially a time factor ; 
different types of "means" accomplish a result in different 
amounts of time. Quickness in accomplishment depends on the 
means which the individual uses. From the point of view of 
physical movement the child takes short steps ; the adult takes 
long steps. Hence the adult moves faster; he covers more 
space in a given time; he covers the same space in less time. 
But the limit to the length of the step or stride in these phys- 
ical movements is soon reached. In mental quickness the limit 



64 IS LATENT TIME IN ACHILLES TENDON REFLEX 

to the length of the stride is scarcely ever reached. One can 
express a given idea tersely in 5 words or verbosely in several 
hundred words. One handles numbers by counting, by adding 
and by multiplying. In counting one moves along with "baby" 
steps or strides; in multiplying one takes "league" steps. When 
one uses multiplication he achieves the desired result hun- 
dreds of times more quickly. 

Hence come two fundamental questions in mental quickness. 
Given the purpose, end or result to be accomplished; what 
means or tools are on hand for achieving this end? (1) How 
many movements? Suppose, for example, that the end result is 
the laying of a single brick in the vocation of bricklaying. One 
man (A) uses 18 movements; another man (B) uses 4 move- 
ments. Each man accomplishes exactly the same result — lay- 
ing one brick. The speed or quickness of a single movement is 
a minor factor in speed of bricklaying. It is chiefly the num- 
ber of movements which determines the speed of accomplish- 
ment. In fact, (A's) latent time may be considerably less 
than (B's) and yet (A) vdll consume much more time in laying 
the one brick. In (A's) case nerve impulses transmit the stim- 
ulus to the effector organs — the muscles — in each movement; 
this same transmission is repeated 18 times. In (B's) case 
this stimulus^ transmission is repeated 4 times. It is as though 
(A) runs 18 miles while (B) runs 4 miles to reach exactly the 
same destination. ^^ 

(2) Mental speed or quickness is concerned not so much 
with a reaction per se (movement, motion, stroke of attention) 
as with what may be called, the value of the reaction. What 
does the reaction yield or accomplish in relation to the desired 
end? What is the length of the stride? In bricklaying, 13-15 
movements were found to be useless ; they contributed nothing 
to the end result. But, in the sphere of mental quickness, a 
given result may be accomplished by several reactions of one 
type or by one or two reactions of another type. In each case 
all the reactions are essential. The time taken to accomplish 
the result depends on the nature of the reaction. Take this 
sentence : "Put the book on the table." One can spell out each 



^* This illustration depicts Gilbreth's experimental findings. Speed in 
bricklaying depends not so much on quickness of motion as on the number 
of motions. He found that men were using 12-18 movements in laying a 
single brick; two-thirds of these movements were useless. These men 
were Slow bricklayers although quick in making a single motion. 2, 3, 
or 4 movements accomplished the Same result many times more quickly. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 65 

word and eventually reach the meaning of the sentence ; one re- 
acts or gives a stroke of attention to each of the 20 letters; 
reacts to each word after spelling it and finally reacts to the 
sentence as a unit. On the other hand, one can react to the 
sentence as a unit immediately; one or two or possibly three 
fixation pauses reach the direction which the sentence contains. 
The end result is the same in each case. One can reach this end 
result by reacting 27 times or by reacting 3 times. The time 
of the individual reaction is about the same ; at any rate, the 
reaction time to a letter is the same as the reaction time to a 
word. But the reaction to the larger unit has greater value ; it 
accomplishes more ; it reaches the end result more quickly. 

These questions — How many reactions (movements, motions, 
strokes of attention) ? What is the value of the reaction? — are 
of prime importance in determining the individual speed in 
addition. Addition itself is a "higher" tjrpe of reaction. One 
can handle numbers by counting ; one can count with consider- 
able speed. But necessarily counting is a slow method, no 
matter how fast one counts. When one counts, he uses a large 
number of reactions to achieve a given result. Be his latent 
time ever so brief, his quickness in each of 8 individual reac- 
tions cannot reach the end result as quickly as a single reaction 
in 6 -f 2. In addition, the distinctly mental speed factors are 
(1) span of perception. With a single stroke of attention one 
can fixate 1 or 2 or 3 or even more figures. Terry reports that 
in reading numbers in a row — saying them aloud, the average 
span is 2.38 figures with a range of 1.88 to 3.40. In language 
the same observer reports an average of 6.47 words per span 
with a range of 5.18 to 7.90. Cattell reports that after a very 
brief exposure a subject recognizes 3-6 figures; 2-5 letters; 1-4 
words. Evidently the recognition span — presumably a single 
stroke of attention — is pretty large. Warren has additional 
evidence in support of the proposition that subjects such as the 
men in the present experiment can readily grasp, recognize, ap- 
prehend as many as 3 figures in a single stroke of attention. 
Warren is studying reaction time in perceptive counting ; that 
is, given 1, 2, 3 or more dots on a card, expose the card for a 
very short time ; how long does it take to apprehend that there 
is one dot, that there are two dots, that there are three dots, 
and so on? The following reaction time figures illustrate — 
figures are in terms of sigma : 



66 IS LATENT TIME IN ACHILLES TENDON REFLEX 

TABLE 9 
Reaction Time in Perceptive Counting 





Subjects: 








Number of dots 


A 


B 


C 


D 


1 


407 


523 


429 


497 


2 


415 


532 


419 


416 


3 


481 


575 


466 


514 


4 


620 


652 


600 


613 



(1) Three subjects apprehend 1 or 2 dots in about the 
same time. For example, a single stroke of attention con- 
sumes 429 sigma in apprehending "1"; the same man appre- 
hends "2" in 419 sigma. One subject — Warren (D) — appre- 
hends "2" in much less time than he consumes in apprehending 
"1." (2) Three subjects consume longer time in apprehending 
"3" — longer than they consume in apprehending "1" or "2." 
Subject D consumes 98 sigma more in apprehending "3" than 
he consumes in apprehending "2" but it takes him about the 
same time to apprehend "3" or "1." Ordinarily, according to 
Warren, perceptive counting is limited to 1, 2, or 3; these are 
the limits of a single mental act or stroke of attention. (3) 
Reaction to "4" is a more complex act; the subject apprehends 
"3" as a unit and then reacts to the extra unit; apparently 
there is no additional eye movement. (4) the limit of pro- 
gressive counting — by successive units — without eye move- 
ments is "5" ; that is, one can apprehend that there are 5 dots 
with no eye movements but with more than one mental act or 
stroke of attention. 

The subjects in Warren's experiment were intellectually 
superior — perhaps not unlike some of the 80 men in the present 
experiment. It is likely, therefore, that some of these 80 men 
can apprehend 3 figures in a single stroke of attention as 
quickly as they can apprehend one figure ; this apprehension of 
1 or 2 or 3 figures takes place in a single mental act and there 
are no eye movements. This capacity is part of their original 
nature. Some of these 80 men can apprehend 2 figures as 
quickly as they can apprehend 1 figure ; their apprehension of 1 
or 2 figures takes place in a single mental act or stroke of at- 
tention ; to apprehend 3 figures they may use no eye movements 
but they do use an additional mental act. Likewise this capac- 
ity to apprehend 2 and no more in a single mental act is a part 
of their original nature. Perhaps, also, some of these 80 men 
are limited by original nature to the apprehension of a single 



A CRITERION OF SPEED IN MENTAL REACTIONS? 67 

figure in a single mental act. In the presence of 3 figures they 
react to one figure and then to each additional figure with addi- 
tional mental acts; there may or may not be additional eye 
movements. 

Suppose one assume (1) that the quickness of a single men- 
tal act or stroke of attention has a physical basis in the velocity 
of nerve impulses; (2) the velocity of nerve impulses in cer- 
tain 3 individuals is the same. If in one of these three in- 
dividuals a single mental act can apprehend 3 figures, in an- 
other individual 2 figures, and in the third individual one 
figure only, one has a variable which is relatively independent 
of any physical speed mechanism such as conditions the length 
of the latent time. The mental act which apprehends 3 figures, 
in adding the three single place figures, has greater accom- 
plishment value; it reaches the end result — the sum — more 
quickly than the mental act which apprehends one figure only. 
It seems very likely that these different speed capacities — ^to 
apprehend different numbers of figures in a single mental act 
— actually characterise original nature of these 80 men. 

(2) Duration of the Individtuil Pause. The span of per- 
ception varies the speed in adding because, for example, the 
single stroke of attention which apprehends 3 figures contains 
more, has greater accomplishment value, reaches the end result 
more quickly than the single stroke of attention which appre- 
hends 1 figure. The length of the individual fixation pause or 
stroke of attention also varies the speed in adding. The in- 
dividual stroke of attention may be long or short in duration. 
To a considerable extent the duration of the individual pause 
is independent of the number of figures which the individual 
pause apprehends. The results in Warren's experiment illus- 
trate this. The following illustration is taken from studies in 
reading (language) but it is applicable to numbers and aptly 
illustrates the present point : 

TABLE 10 

The Number of Fixation Pauses; The Duration of the 
Individual Pause in Reading (Terry) 

Pauses per Line Duration of Reading Time 

Each Pause per Line 

Group A (5 adults) 6.05 5.37 32.52 

Group B (45 adults) 6.50 7.70 50.08 

Time umt=V26 of a second 



68 



IS LATENT TIME IN ACHILLES TENDON REFLEX 



The subjects in "A" read much faster than the subjects in the 
other group ; "faster," in the sense of achieving a result very 
quickly — much more quickly than group B. This "result" con- 
sists in getting the thought from the printed line, sentence or 
paragraph. 

Another illustration throws light on individual methods in 
adding : 

TABLE 11 

Number of Fixation Pauses and Length of Each Pause in 
Adding 12 Singles Place Figures. (Buswell) 



Range in Total Time 

Number of Duration of Average Spent in Adding 

Pauses Each Pause Duration the Problem 

Time Unit = ^/25 sec. 



Subject A 


11 


6 to 24 


14 


Subject B 


10 


7 to 18 


9.8 


Subject C 


11 


6 to 18 


12.2 


Subject D 


9 


12 to 69 


35. 


Subject E 


17 


4 to 59 


25. 



In another but more difficult problem — more difficult 
number of single place figures — the record for the first three 
Subject A 10 10 to 88 38.2 

Subject B 9 7 to 28 16. 

Subject C 14 7 to 56 22.1 



6Vi5 seconds 

3 2^/25 seconds 

5^/5 seconds 

I218/25 seconds 

17 V25 seconds 

combinations — same 

subjects is as follows; 

15^/26 seconds 

6 seconds 

12^/5 seconds 



Subjects A, B, C are college students; subjects D, E are 
elementary school students. According to the above superior 
speed in adding consists in (1) Few fixation pauses; the single 
span of preception covers more "ground" — has greater accom- 
plishment value. (2) Brief duration of the individual pause. 
(3) Regularity in the duration of the different pauses. All 
these factors must be in action. Subject B uses few pauses, 
brief duration in each pause, and regularity in the duration; 
in the first problem, 9 pauses ranged in duration from 7 to 11 ; 
one pause only was larger. Subject D used few fixations but 
the fixations were very long ; this is to be expected, for this sub- 
ject, being an elementary school student, has not developed his 
speed ; further practice will doubtless reduce the length of the 
fixation pause. 

Many of the men in the present experiment are making use 
of these higher types of reaction ; the individual fixation pause 
includes more, has greater accomplishment value and its dura- 
tion is brief. The time taken in the performance of the Addi- 
tion Test is frequently less than 90 seconds. If one takes ac- 
count of the time spent in moving the hand from one problem 



A CRITERION OF SPEED IN MENTAL REACTIONS? 69 

to another and from the end of one row to the beginning of 
another row of problems, the actual time spent on each prob- 
lem is short — about one second. Other men exhibit excep- 
tional slowness. This is due among other things to (1) The 
small accomplishment value of the individual fixation pause; 
there may be several pauses on a single figure. (2) The in- 
dividual pause occupies a relatively long space of time. (3) 
Adding 3 single place figures is frequently honeycombed with 
a number of perfectly useless habits ; when a man adds he goes 
through all these habits ; this takes time. 

Some examples will illustrate. One man, number 41, was 
observed to be very slow in his addition. He was questioned 
about it. He admitted that he always verified each result even 
in such an elementary problem as adding 3 -j- 4 -(- 1. Doubt- 
less a long and involved problem or a long column of figures 
does demand some verification. But in these simple additions 
on this Addition Test this verification is a time-consuming habit 
— a useless habit. It makes the man distinctly slow while his 
nervous system is competent to do rapid work. Take number 
25 ; he admitted that he did not know some of the combinations. 
This means that he broke up some combination into smaller 
units or he paused an exceptionally long time at the "hard" 
combination; perhaps also he used other strictly individual 
methods. Thus a single function such as 9 -{-1 -\-5, becomes 
literally honeycombed with a lot of useless movements.^"* 

What are the mental speed factors in the Cross Out Tests? It 
is significant that there appears to be less opportunity for im- 
provement on such tests than on Addition Tests (Race) . In 
terms of product per unit of time one reaches an upper limit of 
speed more quickly. Recent experiments (Book) show that 
the champion typists in the world are notably superior in vol- 
untary motor ability such as the rate per second at which one 
can move the hand using the wrist as a hinge. Practice ap- 
pears to have but slight influence in perfecting this movement. 
Likewise in tapping there appears to be a minimum of im- 
provability. The reaction on the Cross Out Tests is not unlike 
these types of motor ability. When one crosses out "A" he 



" BuswELL quotes individual methods actually used in managing diffi- 
cult combinations. One boy was slow in adding 9, 7, 5. "In working this 
problem he said to himself: '9 + 2 + 2 + 2+1 = 16 and 21.' Another 
boy in adding 9, 7, 5 said: *9 and 3 is 12 and 4 is 16 and 2 is 18 and 2 — 
20 and 1 — 21.' Another pupil in adding 4, 9, 6 explained thus : take the 
6, then add 3 out of the 4. Then 9 and 9 are 18 and 1 are 19." 



70 IS LATENT TIME IN ACHILLES TENDON REFLEX 

makes a downward movement with the pencil ; from one point 
of view high speed in crossing out a letter or figure consists in 
rapid down and back movements. The intrinsic speed in the 
motor part of the cross out reaction is doubtless a prominent 
factor in determining the individual variations. The value of 
"r" is larger in the correlation of the latent time and the Cross 
Out Tests than in the correlation of the latent time and the 
other tests. 

None the less, improvement in speed does take place as the 
result of practice. Very likely "technique" is a factor in such 
improvement ; this consists in such items as grip on the pencil 
and paper; adjustment of the arm and elbow; attention to the 
movement or to the stimulus. It appears likely, however, that 
speed factors of a distinctly mental nature are fundamental in 
determining the performance time of these 80 men. These 
mental factors appear to center in the span of attention ; per- 
haps it is best to call it a certain "flexibility" of attention. In 
crossing out "A" one can fixate each letter one at a time and 
cross it out or not ; then move attention to the next letter. This 
is a sort of "hand-to-mouth" method ; attention does not move 
beyond the letter immediately present. With this method cross- 
ing out takes place slowly for the hand is doing nothing most 
of the time. (2) One can send attention on ahead and isolate 
"A's" in advance. That is to say, attention covers both the ac- 
tual crossing out of a letter and keeping a constant supply on 
hand to be crossed out. Perhaps it is not so much a span of 
attention as the rapid movement of attention. It is possible 
that one could keep the hand crossing out the letter in quick 
succession when the attention is skilled in keeping a supply of 
letters on hand — isolated and ready for the "operation." This 
situation is not unlike the eye-voice span in reading. In a rapid 
reader the eye moves at a relatively long distance ahead of the 
voice ; that is to say, at any one moment of time the point on 
the line which the eye is fixating is as much as 8 words ahead of 
the point on the line which the voice is speaking. BuswELL 
reports that "the rate of reading and the width of eye-voice 
span increase together. There is a high positive correlation 
between these two factors in reading." 

This examination of addition and crossing out letters or 
figures at least illustrates the nature of the strictly mental fac- 
tors in adding and in the Cross Out Tests. Very likely the 
same or similar mental factors are active in the Completion 



A CRITERION OF SPEED IN MENTAL REACTIONS? 71 

Test. The team of tests, consisting of the Addition, Figure 
Cross Out and Completion Test, yields a maximum correlation 
with the latent time. Some reasons for the failure of the Taylor 
Test to contribute to the correlation yield have already been 
given. Can one measure the relative importance of the two 
factors, physical and mental, in determining the performance 
time on the tests? However this may be, one must take ac- 
count of the following situation: (1) The physical speed 
mechanism determines the time of a single reaction, motion, 
movement, or stroke attention. It governs such items as set- 
ting up action in some excitatory mechanism and sending out 
nerve impulses ; transmitting nerve impulses or the tendency to 
excite to another point within the nervous system ; setting up 
action in some effector organ such as the muscles of the hand 
and fingers and the speech mechanisms. This physical speed 
mechanism is a part of original nature which is the foundation 
of speed of performance in the tests. (2) If other things were 
equal, this physical speed mechanism might govern the in- 
dividual performance time in the tests. But these other things 
are never equal. Mental speed factors operate more or less 
independent of the physical speed mechanisms. Original na- 
ture enables one to climb up through a hierarchy of reactions. 
Handling numbers by counting stands at a low level in this 
hierarchy; one must use a large number of this type of reac- 
tion to achieve a given result. A single "high" reaction such 
as associating 13 with 8 + 3 + 2 with a single stroke of atten- 
tion handles the same situation with great economy of time. 
It is likely that these 80 men differ to some extent in ability to 
develop the "high" reactions ; for example, they may differ in 
ability to apprehend 1 or 2 or 3 figures in a single stroke of 
attention. 

These mental speed factors must be learned. Undoubtedly 
learning exercises a marked influence on the individual per- 
formance time. Different men stand at different levels in the 
hierarchy of reactions; perhaps they can reach a higher level 
but have not done so. Speed in any one type of reaction — be 
it counting or associating 3 figures with their sum — is an effect 
of practice or learning. It seems likely that each man, in the 
type of reaction which he uses, stands at a different speed level. 
For example, one man may count very rapidly; another man 
may react to 3 figures very slowly because he has not developed 
his speed in this type of reaction. Furthermore it may be said 



72 IS LATENT TIME IN ACHILLES TENDON REFLEX 

that the "intellect" perceives that certain movements are use- 
less; perceives that one can move fast at this or that place; 
perceives that one can move his eyes ahead and keep a supply 
of letters ready for the hand to cross out. But this perception 
may or may not take place. Useless movements persist and 
slow up this or that man. Vestiges of counting hang over into 
the strictly "addition" types of reaction. In fact, the mental 
speed factors present a veritable conglomerate of acquired 
speed abilities, each one of which is relatively independent of 
the physical mechanism. When one compares the latent time 
with this conglomerate, it is as though one were comparing the 
latent time with the performance time of a group of bricklay- 
ers in laying a single brick where one man uses 3 movements, 
another 5, another 7, and so on up to 18. 



CHAPTER IX 

The Regression Line in the Present Problem. Signifi- 
cance OF ITS Limited Prediction Value. How Much the 
Test Scores Depart from a Perfect Correlation with the 
Latent Time Measures. The Effects of Practice on the 
Correlation. Conclusions. 

The primary purpose at work in examining the regression 
line is to secure evidence on the question — how much does the 
physical speed mechanism contribute to the performance time 
on the tests. In the preceding chapter it was emphasized that 
the mental speed factors are more or less independent varia- 
bles — independent, that is, of the physical mechanism in speed 
of action. These mental factors in speed must be learned. 
Wide variations in the amount and quality of the learning 
greatly augment the capacity of the mental factors to vary 
the individual independent of the physical mechanism. The 
net result is that the individual quickness on the tests does 
not always have much in common with the intrinsic capacity 
for speed which the latent time is presumed to depict. Bryan 
stresses a similar fact when he says "no reaction time test 
will surely show whether a given individual has or has not 
effective speed in his work ; very slow rates may point to slow- 
ness in all things ; but rapid rates by no means show that the 
subject has effective speed." 

In constructing the regression line in Figure 11 three tests 
only are used; these are the Addition Test; the Figure Cross 
Out Test and the Completion Test. The scores on these tests 
were corrected for variability on the basis of the standard 
deviation. The correlation of these corrected scores with the 
latent time is the same as the correlation of the raw scores 
with the latent time — "r" = .59. Furthermore these three 
tests yield a correlation value which is the same as the corre- 
lation of the sum of all the test scores and the latent time. The 
corrected scores of the three tests are small in numerical size ; 
this makes it possible to use a class interval of 5 in both x- 
and y-measures. The standard deviation of the test scores 
is but slightly different from the standard deviation of the 
latent time scores. Thus one has an excellent condition for 
the construction of an understandable regression line. 

73 



74 IS LATENT TIME IN ACHILLES TENDON REFLEX 



FIGURE 11 

The Scatter Diagram. Regression Line. Graphic Representation 

OF the Probable Error of Estimate and the Amount of Departure 

OF THE Measures from a Perfect Correlation 




x-measures = test scores 
<Tx= 14.40 
Qi=: 87.5 
Q3= 106.3 
Average = 98. 



A-B = Regression line 
/ 14.40 \ 

^ ^ '^^ \ 13:35/ y — -^^y 

X = .65 (y — 53.2 ) +98- 
P.E.est z= .6745 (14.40 VI — r^) 



.65y + 63 
= 7.76 



y-measures = latent time 
ay = 13.35 
Qi — 43.25 
Q3 = 63.7 
Average =^ 53.2 

The x-measures are the test scores of a team of three tests; this 
team consists of the Addition Test; Figxire Cross Out Test, and the 
Completion Test. The raw scores are weighted according to their vari- 
ability. The raw scores are about four times larger than the weighted 
scores. The diagonal broken lines represent 1 P.E., 2 P.E., 3 P.E., and 
4 P.E. on each side of the regression line. 

One can draw this line immediately by means of the equa- 

/14 40\ 
tion, X == .59 f ..„', ) y. Solving this equation, x = .65y. 

When one computes the new or estimated test scores on the 
basis of the equation, X = .65y + 63 — ^the score form of the 
regression equation — one gets a pair of test and latent time 
measures, each of which lies on the regression line. Each of 



A CRITERION OF SPEED IN MENTAL REACTIONS? 75 

the 80 pairs of measures, the given latent time measures and 
the estimated test measures, lies on this line. The new or 
estimated test measures correlate perfectly with the old or 
given latent time measures. 

Thus one has two sets of test measures; the one set corre- 
lates perfectly with the given latent time measures ; the other 
set correlates with the same latent time measures with a ratio 
of 0.59. Thus one has the facts for determining how much 
the true test scores depart from a perfect correlation with 
the latent time measures. One can readily compute these 
differences. The differences are strictly individual ; some new 
or estimated measures are larger than the old while others are 
small and still others are about the same size. One can take 
the group as a whole and compute the departure of the group 
from a perfect correlation with the latent time measures by 
means of the equation, P.E.e^tx = .6745 i\/l — r^) ; this gives 
a value of 7.76. This probable error of estimate as a single 
quantity takes account of all the individual departures from a 
perfect correlation with the latent time measures; it is the 
median amount of shift or change in the size of the test meas- 
ures which one must make in order to secure a perfect corre- 
lation. It must be stressed that this estimated or perfect 
correlation "line-up," as it were, is specific to this group; it 
is based on what these men do now. 

Do these regression line figures offer a basis for accurate 
prediction? Can one take a definite latent time measure and 
predict what the corresponding test score will be? A reli- 
able prediction must locate the test measures in a rather pre- 
cise spot. Every prediction is subject to change according to 
the size of the probable error of estimate. In the case of 50% 
of the given pairs of measures there is a departure from a 
perfect correlation which equals or exceeds 7.76 ; this is equiv- 
alent to about 31 in terms of the raw scores. A single prob- 
able error includes only 50% of the cases. If the value of the 
probable error is small, a distance of 2, 3, 4 P.E. is relatively 
small. When the probable error is large, these distances in 
terms of the raw score units of measurement are very large. 
Suppose one take the latent time of 34 ; the predicted or esti- 
mated score on the tests is 85. Let this estimated score read 
"plus or minus 2 P.E." The estimated test scores may be as 
much as 15 points larger or 15 points smaller than 85. The 



76 IS LATENT TIME IN ACHILLES TENDON REFLEX 

raw scores are about four times larger than the corrected 
scores. Hence the estimated score is 340 plus or minus 60 
seconds. But 2 P.E. include only 82.26% of the cases. When 
one takes account of 3 P.E. and 4 P.E., the limits within which 
the estimated score may lie become very great when the size 
of the single P.E. is large. 

Why should one expect to predict? The fact that the mental 
speed factors operate as variables relatively independent of 
the physical speed mechanisms; the fact that amount and 
quality of learning in these mental factors differ enormously 
from one individual to another and in the same individual 
from one type of function to another — these facts ought to re- 
duce the possibilities of prediction to a low level. Suppose 
one examine subjects 42, 43, 44, 45. In each case the length 
of the latent time is 53 sigma; thus there is no difference in 
the capacity of the physical mechanisms. The scores on the 
three tests — total scores of Addition, Figure Cross Out, and 
Completion Tests — are as follows : 



45 


265 


43 


352 


42 


412 


44 


450 



These scores are widely scattered, covering a range of 185 
seconds. Subject number 45 has first quartile rank in each of 
the tests used in the present experiment. Number 43 has first 
quartile rank in Addition. In fact his score of 82 in Addition 
is very superior ; number 45's Addition Score is 77. Evidently 
these two men have made ample use of their mental speed 
factors in Addition; they have developed reactions to large 
units and have eliminated all useless movements. For pupils 
in the 8th grade the fixed accomplishment time on this Addi- 
tion Test is 180 seconds. These two men — several other men 
also — accomplish this same task in considerably less than one- 
half this time. Number 42 has a score of 146 on the Addition 
Test ; this is very slow. But the same man has a very superior 
score on the Taylor Test — 171. This man has no small speed 
ability; he must be quick in a single reaction. In performing 
this test in 171 seconds he must have eliminated useless move- 
ments; must have looked ahead and located several numbers 
in advance; must have moved fast when he saw the chance 



A CRITERION OF SPEED IN MENTAL REACTIONS? 77 

and must have perceived the chance. Number 44 has a large 
score in Addition — 147; a large score in Figure Cross Out — 
200. At the same time he has a superior score in the Letter 
Cross Out — 74 ; a superior score in the Completion Test — 103, 
and his score on the Taylor Test is exceptionally speedy — 154. 
Hence he is not a slow man. On the contrary he must be quick 
in a single reaction and in some types of function has devel- 
oped his mental speed factors to a high level of speed. 

Thus these 4 men exhibit about the same degree of quick- 
ness in a single reaction. Their latent time is the same; each 
man exhibits superior quickness in some one or two or three 
tests. Their total scores are scattered over a wide area because 
this or that man is slow in some one or more tests. Presumably 
these men have the ability to make quick time in these tests 
also. The trouble is that they are not making full use of their 
mental speed factors ; they are, for example, reacting to small 
units and are making useless movements or, if they do react 
to large units, they have not developed their speed in this type 
of reaction. When one tries to predict on the basis of these 
men's total scores, this prediction cannot fix on any one spot; 
the predicted score may be, for example, 265 or 352 or 412 or 
450 or some other score. The predicted score must be labelled 
"plus or minus 5 P.E." Number 45's true score lies 5 P.E. 
distance from the predicted score; number 44's score is lo- 
cated a distance of 2 P.E. on the other side of the regression 
line. Prediction here is not unlike predicting speed in brick- 
laying when (1) the quickness of a single movement is the 
same in each man; (2) one man uses 3 movements, another 
man 7 movements, another man 12 movements, and another 
man 19 movements; and (3) with these different movements 
each man lays just one brick. 

Suppose one examine number 45 in some detail. His true 
score on the three tests is 63 — corrected for variability. The 
estimated score which makes a perfect correlation with the 
latent time measure is 98. Thus beginning with the point of 
perfect correlation with the latent time measures one must 
move out a distance of 5 P.E. in order to reach this man's 
actual score. 4 P.E, includes 99.3% of the cases. The chances 
are 142 to 1 that a measure chosen at random will fall within 
this distance. Number 45 is this One man who belongs 
beyond this limit. 5 P.E. includes 99.92% of the cases; 
the chances are 1310 to 1 that a measure chosen at 



78 IS LATENT TIME IN ACHILLES TENDON REFLEX 

random will fall within this distance. One may say that num- 
ber 45 is one man in a thousand who takes up a position so 
far out in the speed end of the distribution. In quickness of 
a single movement this man does not appear to be superior 
to the other men — 42, 43, 44 ; they have the same latent time ; 
each of the three men exhibits a speed of performance in some 
one of the tests which is fully as superior as that of number 
45. Number 45 exhibits a superior development of his mental 
speed factors. He perceives useless movements and eliminates 
them and thereby augments his speed of performance. He per- 
ceives that he can move fast when making a line from one 
figure to another and actually moves fast. He looks ahead 
in crossing out figures so that his hand is crossing out a fig- 
ure in rather quick succession. He has developed higher 
types of reaction to numbers. His physical speed mechanism 
does participate in determining his superior performance. 
But his superior mental habits have greatly reduced his ac- 
complishment time. His physical mechanism is no more rapid 
than that of number 44, but his performance time is fully 
75% quicker. His physical mechanism is only 50% as rapid 
as that of number 1, while his speed of performance is 40% 
greater. 

Improvement through practice in functions which the tests 
represent is a fundamental fact. The present true test scores 
correlate with the latent time measures with a ratio of 0.59. 
Suppose these 80 men were practiced on these diiferent func- 
tions — Addition, Cross Out and Completion, for example; one 
would have at the end of the practice period 80 new and true 
scores in each of the tests. What would be the relation of the 
two sets of true scores? What would be the relation of the 
present regression line and the new regression line? Would 
the new scores exhibit a Trior e perfect correlation with the 
latent time? Is the present correlation ratio relatively stable? 

At the present time there is considerable positive evidence 
on the actual effects of a period of practice in such functions 
as are used in the present experiment. Several observers con- 
clude that improvement through practice is rooted in original 
nature (Kirby, Pyle, Ruch, Thorndike, Wells). The bright 
improve more than the dull. Changing time allowance does 
not alter the relative position of the subjects; that is, the 
extra time does not permit the dull to equal the score of the 
bright; a correlation of .965 between single and double time 



A CRITERION OF SPEED IN MENTAL REACTIONS? 79 

allowance is reported (Ruch). Thorndike is pretty in- 
sistent that original nature is the governing factor in im- 
provability. Those who are ahead at the start maintain and 
increase their lead. "The status which an individual has at- 
tained in a function from a given amount of practice is highly 
prophetic of the status which he will attain from any given 
amount of additional practice" (Thorndike 4). The fol- 
lowing figures illustrate: 

5 initially lowest gain 4.7 (amount per unit of time) 

7 initially next gain 9.4 
4 initially next gain 13.6 

8 initially highest gain 15.2 

Thus the 8 whose initial score (score at the beginning of prac- 
tice) was the highest, whose speed was greatest, gain 3.23 
times more than the 5 whose initial score was the lowest. 
Again, given 670 college students who are practiced in add- 
ing 10 single place numbers; "the highest initial levels made 
the greatest absolute gain (Thorndike 6). 

Furthermore, speed and level of intelligence (power) ap- 
pear to be related (L. S. Hollingworth, Hunsicker, Race, 
Peak and Boring). Given, for example (1) a speed or rate 
test — the first two sheets of the I.E.R.^^ completions and the 
first two sheets of the I.E.R. arithmetical problems; (2) a 
power or ability test — the highest difficulty level in which 
50% of the elements of that level are done correctly. The 
correlations between rate and level in arithmetic, between 
rate and level in completion, range from .39 to .61. According 
to the experimenter, this indicates "a consistent relationship 
between rate of mental work and level of intelligence" (Hun- 
sicker). Race found that subjects of superior intelligence 
(above the 75 percentile) make a greater gain through prac- 
tice in adding 10 single place numbers than the subjects of 
average ability (below the 25 percentile). Within the su- 
perior intelligence group those above the 75 percentile make 
the greatest gain. Within the average ability group those 
above the 75 percentile make the greatest gain. For example, 
in a group of college students : 

Below 25 percentile ; initial score 13.875 (amount done in 

gain 16.0 ""i<^ o^ ^^^^> 

Above 75 percentile; initial score 38.25 

gain 26.75 



" I.E.R. = Institute of Educational Research. 



80 IS LATENT TIME IN ACHILLES TENDON REFLEX 

These studies measure improvability by means of a definite 
but limited amount of practice; they follow the subjects 
through the "first quarter" and perhaps into the "first half." 
What will happen in the "third and fourth quarters"? Ordi- 
narily the experiments make no pretence of reaching the limits 
of ability. Besides, to more or less extent they are concerned 
with averages. The group or that part of the group which 
exhibits the superior initial scores will exhibit the largest 
average gain. But some in the group will show a large gain 
while others will show a small gain. On the other hand, some 
in the slow group will make large gains while others will make 
small gains. The classification on the basis of the initial score 
is more or less arbitrary. The experiments are "trial heats," 
as it were. Various facts come to light in these trials. Will 
the same facts continue to dominate up to the limits of maxi- 
mal improvement? For example, on the basis of what the 
subjects do in the "first quarter," one may assume that the 
initial score is a sort of coefficient of original nature. Will 
the subjects with the largest initial scores finish the "fourth 
quarter" — maximum ability — with largest scores? 

If one expects to practice a group of subjects through to 
maximum ability, several controlling factors must be reckoned 
with. With a few exceptions, one of which will be mentioned 
later, experiments on improvability make no attempt to meas- 
ure or otherwise utilise these factors. An individual may make 
large gains for more than one reason. There are gains due 
to the high level of mental speed ability; there are gains due 
to the low level of practice at the time the initial score was 
made. (1) It is possible to get some light on the subjects' 
original nature and thereby form a criterion as to what they 
may be expected to do when perfecting their speed of perform- 
ance in different types of materials. In the first place the 
length of the latent time in the Achilles tendon reflex measures 
the intrinsic speed with which physical mechanisms transmit 
a stimulus from one point to another point within one section 
of the nervous system; this measure points to a similar in- 
trinsic speed in other parts of the nervous system of the same 
individual, (b) The I.Q. tells something about intrinsic speed 
conditions; children whose average I.Q. is about 150 exhibit 
a considerably higher rate of tapping than children whose 
average I.Q. is about 100 (Hollingworth). (c) The rate of 
to and fro movements of the forefinger, wrist, forearm and 



A CRITERION OF SPEED IN MENTAL REACTIONS? 81 

upper arm bring to light intrinsic speed conditions (Book). 
Such measures bring to light the individual quickness in a 
single movement. Original nature in the mental speed factors 
is much more difficult to "reach." One can measure the in- 
dividual span of attention and span of perception, assuming 
that these may not be precisely the same thing. Foresight ap- 
pears to be a factor in many of the tests such as the Cross 
Out Tests, but it defies any sort of measurement. 

(2) What is the state of the subjects' learning in this or 
that type of material at the time of the initial score? The 
initial score may be considered as a point on a line; this line 
or curve measures the distance from zero ability to the maxi- 
mum ability in the given type of material or function. The 
amount of the individual improvability is the distance from 
this point to the limits of his ability in the given function. The 
size of the initial score is, in some respects, a measure of the 
relative position of this score on a scale of increasing quickness 
on the one hand and increasing slowness on the other hand. 
For example, in the Addition Test, a score of 140 and beyond 
may be set down as characterizing slowness ; a score of 45-50- 
60 indicates superior speed. At any rate the variable condi- 
tion at the time of the initial score ought to be measured and 
controlled in some manner. Ordinarily the studies in im- 
provability make no attempt to measure this relative position 
of the initial score (Buswell, 3 — page 112). 

(3) How much unlearning? For example, the man who 
habitually breaks up various combination^ in addition must 
unlearn these useless habits before he can forge ahead in his 
positive improvement in speed. Many subjects may make no 
improvement because of these accumulated parasitic habits. 
Buswell (1) gives a list of 28 such habits. Such initial con- 
ditions of learning differ in different individuals. The fact 
that a man has a superior score in some one or more tests 
but a poor score in other tests is evidence that the poor score 
is due chiefly to defects in learning. This is illustrated in the 
discussion of subjects number 42, 43, 44, 45. A study of fixa- 
tion pauses, their number and duration, would throw a lot of 
light on the state of the individual's learning at the time of the 
initial score. 

(4) The type of mental function which the individual uses 
in his experiment also cooperates in determining the amount 
of improvement which the subjects will make. When the 



82 IS LATENT TIME IN ACHILLES TENDON REFLEX 

function is chiefly motor, such as the rapid to and fro move- 
ments of the arm, the effect of practice is close to zero 
(Book). When the function is relatively simple, such as 
crossing out letters and figures, the improvement is larger 
than in the motor functions but still relatively small. Com- 
plex functions such as adding several single place figures offer 
the greatest opportunity for augmenting the speed of per- 
formance (Race). The ability to improve and increase speed 
appears to consist chiefly in the ability to set in action higher 
types of reaction; these are the distinctly mental speed fac- 
tors. 

(5) The most important factor in securing improvement 
through practice is incentive or drive. Phillips gives sound 
evidence that subjects whose initial ability is high make the 
greatest gain only when the practice or drill is very intense. 
When the drill is that of the daily work of the class, the group 
whose initial ability is the lowest makes the best gain; the gain 
of the low ability group may be two or three times greater 
than the gain of the superior group. In other words, the su- 
perior group has the intrinsic capacity; but having capacity 
is one thing ; setting the capacity in action is another and dif- 
ferent thing. Only when the drive is very severe — the com- 
petition intense — only then is the superior capacity set in 
action. Bryan stresses a similar idea when he insists that, 
in rising to high level types of reaction in telegraphy, it is the 
supreme effort that brings the results. The problem is how 
to enlist the supreme effort. It is entirely possible that ten 
men may have the same potential capacity; yet the actual 
scores at the beginning of a period of practice will be dis- 
tinctly "jagged"; that is, the scores will be ten peaks of dif- 
ferent heights. After a period of practice there will be the 
same ten peaks but two or three men, very likely those whose 
initial scores are superior, will rise to superior heights. 
Banker develops the point of view that competition exercises 
a differential effect. Under its influence speed variations de- 
part from the normal probability type in that the skew from 
symmetry may be as much as 8 times the probable error — 
beyond the range of chance errors. Within limits competition 
stimulates to greater effort. But some men give up trying and 
fall behind; that is, a reversal takes place when they do not 
secure and maintain the lead. On the other hand, the stimulus 
to competition acts on other men in only one way; the su- 



A CRITERION OF SPEED IN MENTAL REACTIONS? 83 

preme effort to surpass is always active; there is no reversal. 
The situation may be a losing one ; none the less the incentive 
to surpass is always present in full force. In consequence of 
this individual action of incentive (motivation, interest, drive, 
ambition) different men will exhibit different amounts of im- 
provement at the close of any period of practice — even when 
all other things are equal. 

HoLLiNGWORTH practiced 13 subjects to the absolute limits 
of capacity. Progress up to the limit is illustrated by the 
relation of the Addition Score at different points in the prac- 
tice period with the final score — in this experiment, the 175th 
trial : 

TABLE 12 

Correlation of the Addition Score, at Different Points 
in the Practice Period, with the Final Score 
in Addition. (Hollingworth) 



Initial 


5 Trials 


25 Trials 


50 Trials 


80 Trials 


130 Trials 


.154 


.193 


.874 


.869 


.873 


.962 



Thus the initial ability is a long distance from the final abil- 
ity. In color naming and cancellation the distance is not so 
great ; the correlation of the initial score with the final score 
in color naming is .68; in cancellation the correlation is .67. 
In the Addition Test there is a marked jump in the relation 
of the final score at the 25th trial ; 20 trials raise the correla- 
tion from .193 to .874. The next 150 trials raise the correla- 
tion 13 points. There is no doubt that it is much more diffi- 
cult to secure this 13-point gain than to secure a 50-point gain 
in the lower end of the practice period. A gain of one second 
in a 50-yard dash is enormously difficult to secure. 

Hollingworth suggests that there may have been a change 
in the nature of the response. "The opposite test after many 
repetitions comes to resemble color naming; that is, the re- 
sponse becomes more and more intimately associated with the 
stimulus word." Be this as it may, increase of speed in add- 
ing 2 single place digits consists chiefly in (a) using a sin- 
gle fixation pause; the subject perceives the two figures in a 
single stroke of attention; (b) reducing the duration of the 
fixation pause; (c) associating these two numbers with one 
and only one other number — the sum. For example, high 
speed in adding 5 and 2 consists in perceiving the two figures 



84 75 LATENT TIME IN ACHILLES TENDON REFLEX 

in a single fixation pause and immediately calling up 7. The 
"7" must be most intimately associated with 5 -f 2 — so close 
and permanent that the response is immediate. It is possible 
that some of the 13 subjects, at the beginning of the practice 
period, fussed and fumbled among several candidates for the 
sum of this or that group of two digits. Such fumbling among 
several figures is a sort of pathological condition. If the fum- 
bling does take place, and it undoubtdely does in many in- 
dividuals, the individual has not learned how to add; for he 
can never be certain that the sum he selects is the right one. 
One must associate one figure and only one figure with 5 + 2 ; 
the association must be so intimate that the response on per- 
ceiving the two figures is instant. 

Perhaps some of the 13 subjects, at the beginning of the 
practice period, used two fixation pauses, one on the 5, for 
example, and one on the 2. At the end of the practice period 
they had advanced to a higher level; they perceived the two 
figures with a single fixation. Given a single fixation pause 
and one and only one number — ^the sum — associated with 
5 + 2, for example, advance in speed consists in reducing the 
length of the fixation pause. Buswell gives some figures on 
the duration of the fixation pause in adding several single 
place numbers. In one case the duration of the pauses ranged 
from 7 to 11 ; in terms of sigma this is 280 to 440 sigma. One 
may venture the conclusion that when subjects reach a high 
level of speed in adding two single place numbers, the response 
is not unlike a reaction time response. 

Thus a varied group of more or less interacting factors de- 
termines how far any one individual will actually travel on 
the road from his initial score to maximum ability in speed 
of performance. Incentive appears to be the most significant 
factor. In Hollingworth's experiment incentive was given 
adequate attention. In the present group of 80 men many 
were eager to show what they could do; in them no reversal 
would ever take place. The stimulus of competition either 
with themselves or with another acts in only way — a su- 
preme effort to surpass. Other men exhibited a distinct 
"what's the use" attitude and the "don't care" attitude. Doubt- 
less in other men a reversal would take place during the prac- 
tice; that is, they would give up all effort; incentive would 
cease to have any influence. What will happen when these 
same men are practiced to the limit of their capacity, with ade- 



A CRITERION OF SPEED IN MENTAL REACTIONS? 85 

quate attention to the various factors mentioned above? The 
following is submitted as a tentative conclusion. It seems very 
likely that after such a period of practice, up to 200 trials or 
more, the relative position of these men on a scale of speed 
would be about the same as the present position. Some would 
rise to new heights; others would occupy a middle position; 
others would either make no effort at all or after a period of 
more or less vigorous effort would get discouraged and fall , 
behind. 

Is there a general speed capacity? Hollingworth suggests 
this. The correlation between addition and color naming at 
the first trial was .26 ; at the 205th trial it was .76. The cor- 
relation between addition and opposites at the first trial was 
.23; at the 205th trial, .76. Perhaps these final correlations 
point to the setting up of a sort of reflexlike movement from 
receptor organs to effector organs in the different types of 
functions. In the present experiment, subject number 45 is a 
good example in support of the notion of a general speed ca- 
pacity ; this man is superior in every test ; his superior speed 
ability is associated with a superior level of intelligence. 

If there is such a thing as general speed capacity, it must 
consist of two more or less independent factors. (1) There 
is the intrinsic physical speed mechanism ; this centers chiefly 
in the velocity of the nerve impulses. But this intrinsic speed 
mechanism is and must be the average speed capacity of dif- 
ferent parts of the nervous system. For example, the flexor 
nerve-muscle unit is as much as 4 times more rapid than the 
extensor nerve-muscle unit — in the same individual. It is 
possible on the basis of the chronaxie (Bourguignon) to se- 
cure the average intrinsic speed capacity in any one individ- 
ual. (2) There are the various distinctly mental speed fac- 
tors. These mental factors are not concerned with the slow 
or rapid transmission of a stimulus from one point to another 
point within the nervous system ; they operate in terms of how 
long it takes to accomplish a given task. Span of perception 
is an illustration of a strictly mental speed factor. How far 
up can this or that individual go in the ability to perceive in a 
single stroke of attention, or at least in a very limited num- 
ber of strokes of attention, single letters or single words or 
single phrases or single sentences or even paragraphs? How 
far up can he go in perceiving a single figure or two figures 
or three figures, or even more, in a single stroke of attention ? 



86 IS LATENT TIME IN ACHILLES TENDON REFLEX 

Is the intrinsic span of perception the same in this individual 
for different types of material or functions? Does his span 
of perception differ for different types of function? That is, 
the individual may vary in his capacity to reach a high level 
type of reaction ; he may have a relatively large span of per- 
ception for language units and a relatively small span of per- 
ception for numerals. However this may be, it is certainly 
true that a potential general speed capacity does become dif- 
ferential in a single individual and in different individuals; 
defects in the amount and quality of the learning appear to 
be the chief disturbing factor. 



CONCLUSIONS 

1. An apparatus has been devised which records the latent 

time in the Achilles tendon reflex. 

2. This latent time in the reflex differs in these 80 men, rang- 

ing from 32 to 96 sigma. 

3. This latent time is the expression of a physical speed mech- 

anism — the velocity of nerve impulses and allied mech- 
anisms; the mechanism governs the time it takes the 
nervous system to transmit a stimulus from one point 
to another point. 

4. The latent time reveals a certain level of speed in that part 

of the nervous system which subserves the reflex. The 
correlation ratio points to a similar level of speed of 
transmission in other parts of the nervous system of the 
given individual. 

5. In the correlation, the comparison is between a single in- 

trinsic speed mechanism on the one hand and a conglom- 
erate of strictly mental speed factors on the other hand. 
The physical mechanism governs the quickness of a sin- 
gle movement ; the influence of the mental factors centers 
in the quickness of achievement or performance. 

6. These mental speed factors differ in these 80 men; (1) in 

original endowment ; for example, the span of perception 
may be 3 figures in some men ; two figures in other men ; 
and one figure only in some men. (2) These mental speed 
abilities must be acquired through learning; the present 
functional efficiency of these mental factors differs very 
greatly in the different men in consequence of the differ- 
ent amounts of learning and the different qualities of 
the learning. 

7. It appears likely that a period of practice, even a prolonged 

period with the purpose of reaching the limits of speed 
in each man, will not greatly alter the present correla- 
tion ratio. The relative position of the 80 men on a scale 
of speed will be about the same as it is at present. The 
strictly differential effect of incentive appears to be the 
chief factor in maintaining this same relative position. 

87 



88 IS LATENT TIME IN ACHILLES TENDON REFLEX 

8. It seems likely that there is a general speed ability which 
is more or less intimately associated with the level of in- 
telligence. But the potential ability is one thing ; actually 
setting this ability into action is another thing. The 
most challenging problem is how to make incentive actu- 
ally stimulate the given individual so that he eventually 
does rise to a maximum level of speed. 



A CRITERION OF SPEED IN MENTAL REACTIONS? 89 
BIBLIOGRAPHY 

ABBREVIATIONS 

AJP: American Journal of Physiology. 

AJPsy: American Journal of Psychology. 

JEdPsy: Journal of Educational Psychology. 

JExPsy: Journal of Experimental Psychology. 

JAPsy: Journal of Applied Psychology. 

PR: Psychological Review, 

PRS: Proceedings of Royal Society of London. 

TC : Teachers College Contributions to Education. 

AP: Archives of Psychology. 

JP: Journal of Physiology. 

Pfliiger: Pfliiger's Archiv fiir die gesamte Physiologic. 

Anderson, Rose G. A Critical Examination of Test Scoring Methods, 

AP, No. 80. 
Adrian, E. D. The Impulses Produced by Sensory Nerve Endings. JP, 

60:49 and 151. 1926. 
Bernstein, E. Quickness and Intelligence. British Journal of Psychology 

Monographs, No. 7, 1924. 
Book, W. F. Voluntary Motor Ability of the World's Champion Typists. 

JAPsy, S:2S3. 1924. 
Bourguignon, G. Chronaxie chez I'homme. Paris, 1923. 
Bryan, W. L. and Harter. Studies in the Telegraphic Language: The 

Acquisition of a Hierarchy of Habits. PR, 6:345. 1899. 
Bremer, Frederick. Contribution a I'etude de la Physiologie du Cervelet; 

la fonction inhibitrice du paleo-cerebellum. Archives Internation- 
ales de Physiologie, 19:189. 1923. 
Banker, H. J. The Competitive Factor in Skewness. Journal of Ameri^ 

can Statistical Association, March, 1927. 
Beritoff, J. Kontraktionsfahigkeit der verschiedenen Telle des Skelett- 

muskels. Pfliiger, 205; 475. 

Uber der Physiologische Bedeutung des gefiederten Baues dea 

Muskeln. Pfliiger, 209, 763. 
Buswell, G. T. (1) Diagnostic Studies in Arithmetic. 1926. 

(2) An Experimental Study of Eye- Voice Span in Reading. 1920. 

(3) Summary of Educational Investigations relating to Arith- 
metic. 1925. 

Cathcart, E. P. (and others). The Influence of Speed on Mechanical EflS- 
ciency. JP, 57:355. 1924. 

Chaney, W. C. Tendon Reflexes in Myxedema. Journal of American 
Medical Association, 82:2013. 

Chapman, J. C. Individual Differences in Ability and Improvement and 
their Correlation. TC, No. 63. 

Cattel, J. M. Uber die Zeit der Erkennung und Benennung von Schrift- 
zeicher, Bilder und Farber. Philos Studien II, 4:635. 

Dodge, Raymond. A Systematic Exploration of a Normal Knee Jerk^ 
Its Technique and the Form of the Muscle Contraction; Its Am- 
plitude; Its Latent Time and Its Theory. Zeit.f.allg. Physiologie. 
12:2. 1910. 

(and Benedict). Psychological Effect of Alkohol. Carnegie In- 
stitution, No. 232. 1915. 

Downey, June E. The Will Temperament and its Testing. 1923. 

Evans, J. E. The EflPect of Distractions on Reaction Time. AP No. 37. 

Fulton, J. F. (and Liddell). Electrical Responses of Extensor Muscles 
During Postural (Myotatic) Contraction. PRS, 98B:577. 1925. 
(2) On the Summation of Contractions in Skeletal Muscle. AJP,. 
75:235. 

Garrett, Henry E. A Study of the Relation of Accuracy to Speed. AP, 
No. 56. 

Gasser and Hill. The Dynamics of Muscle Contraction. P/?S, 96B:398.. 
1924. 



90 IS LATENT TIME IN ACHILLES TENDON REFLEX 

Gilbreth, F. B. Bricklaying Systems. 

Hunter & Royle. The Symptomatology of Complete Transverse Lesions 

of the Spinal Cord. Aust7'alian Journal of Experimental Biology. 

1:17. 1924. 
Highsmith, J. A. Relation of the Rate of Response to Intelligence. 

Psychological Monographs, 34 : No. 3. 1925. 
Hull, C. I. The Joint Yield from a Team of Tests. JEdPsy, U:S96. 
Hill, A. V. The Maximum Work and Mechanical Efficiency of Human 

Muscles and Their Most Economical Speed. JP, 56:19. 1922. 
Hollingworth, L. S. Tapping Rate of Children Who Test Above 135 I. Q. 

JEdPsy, 17:505. 1926. 
Hollingworth, H. L. Individual Differences Before, During and After 

Practice. Pi?, 21:1. 

Correlation of Abilities as Affected by Practice. JEdPsy, 4:405. 

1913. 
Hunsicker, L. M. A Study of the Relationship Between Rate and Ability. 

TC, No. 185. 1925. 
Jenkins, T. N. Facilitation and Inhibition. AP, No. 86. 1926. 
Johanson, Albert M. The Influence of Incentive and Punishment upon 

Reaction Time. AP, No. 54. 
Kirby, T. J. Practice in the Case of School Children. TC, No. 58. 1913. 
Lankes, W. Perseveration. British Journal of Psychology, 7: 387. 1915. 
Minkowski, M. Zur Entwicklungsgeschicte, Lokalisation und Klinik des 

Fussohlenreflexes. Schweizer Archiv fiir Neurologic und Psy- 
chiatric, 13:475. 

Sur les Modalites et la localisation du reflexe plantar au cours de 

son evolution du foetus a I'adulte. L'Encephale, 21:729. 
Pike, F. H. The General Phenomenon of Spinal Shock. ^JP, 24:124. 
Pyle, W. H. Is Individual Learning Capacity Constant for Different 

Types of Materials? JEdPsy, 10:121. 1919. 
Peak, Helen and Boring, E. G. The Factor of Speed in Intelligence. 

JExPsy, 9:71. 1926. 
Phillips, F. M. Relation of Initial Ability to the Extent of Improvement 

in Certain Mathematical Traits. Pedagogical Seminary, 26:330. 

1919. 
Ruch, G. M. (1) The Influence of the Factor of Intelligence on the Form 

of the Learning Curve. Psychological Review Monographs, 34 : No. 

7. 

(2) "Power" vs. "Speed" in the Army Alpha. JEdPsy, 14:193. 
1923. 

(3) Correlation of Initial and Final Capacity in Learning. JExPsy, 
6:344. 

Riddock, G. The Reflex Functions of the Completely Divided Spinal 
Cord in Man. Brain, 40:264. 1917. 

Rothmann, H. Zusammenfassender Berichte iiber den Rothmanischen 
grosshirnlosen Hund nach klinischer und anatomischer Unter- 
suchung. Zeit.f.g. Neurologie und Psychiatrie, 87:248. 

Race, H. V. Improvalibity : Its Intercorrelation and Its Relation to Men- 
tal Ability. TC, No. 124. 1922. 

Spiegel, E. A. Der zentrale Mechanismus der statischen Innervation. 
Klinische Wochenschrift, Feb. 12, 1926. 

Streifenhugel und Korperhaltung. Klinische Wochenschrift, 
Aug. 26, 1924. 

Samoljloff. Zur Frage des tjberganges der Erregung vom notorischen 
Nerven auf den quergestreiften Muskel. Pfliiger, 208:508. 1925. 

Sherrington, C. S. (1) Reflexes in Response to Stretch (Myotatic Re- 
flexes). PRS, 96B:212. 

(2) Further Observations on Myotatic Reflexes. PRS, 97B:267. 

(3) Remarks on Some Aspects of Reflex Inhibition. PRS, 97B:519. 

(4) Observations on the Excitable Cortex of the Chimpanzee, 
Orang-utan and Gorilla. Quarterly Journal of Experimental 
Pysiology, 11:135. 

(5) Peripheral Distribution of the Fibers of the Posterior Roots 



A CRITERION OF SPEED IN MENTAL REACTIONS? 91 

of the Spinal Nerve. Philosophical Transactions of the Royal 
Society, 190B. 

(6) Decerebrate Rigidity and Reflex Coordination of Movement. 
JP, 22, 

(7) Stimulus Rhj^hm in Reflex Tetanic Contraction. PRS, 95B: 
142. 

(8) Break-shock Reflexes and "Supermaximal" Contraction 
Response of Mammalian Nerve-Muscle to Single Shock Stimuli. 
PRS, 92B:245. 

Terry, P. W, How Numerals are Read. 1922. 

Thorndike, E. L. (1) Improvement in a Practice Experiment under 
School Conditions. AJPsy, 24:426. 1913. 

(2) Some Results of Practice in Addition under School Conditions. 
JEdPsy, 5:65. 1914. 

(3) The Effect of Practice in the Case of a Purely Intellectual 
Function. ^JPsi/, 19:374. 1908. 

(4) Notes on Practice and Improvability. AJPsy, 27:550. 1915. 

(5) Practice in the Case of Addition. A JPs?/, 21:483. 1910. 

(6) The Relation Between Initial Ability and Improvement in a 
Substitution Test. School and Society, 1:429. 1915. 

(7) On the Relation between Speed and Accuracy in Addition. 
JEdPsy, 5:537. 1914. 

Wells, F. L. Relation of Practice to Individual Differences. AJPsy, 23: 

75. 1912. 
Warren, H. C. The Reaction Time in Counting. P/2, 4:569. 
Witty and Lehman. Drive; a Neglected Trait in the Study of the Gifted. 

PR, 34:364. 1927. 



Classification number 




Accession number 




Date Due: 



5-7"^/ 



BP 21 A7 no.9S k09hh 
a criterion of speed.. 



Issued to 



^^ 



6-/^ 



OX*iui.t^'- 



0/?i 



AL 



6c, 



PSYCH 


BF21 
A7 
no* 95 



KounciSf George Baydent 1884— 

Is the latent tiuie in the Achilies 

tendon reflex a criterion o± speed in 

mental reactions? hy George fi« Rounds* 

New Yorky 1928* 

91 p* 1 illus*t diagrs* 24 cm* 

(Archives of psychology ••* no* 95) 

40944 



PSYCH 



( 



3 158 583 MiiDZhp 



28-19085 



ARCHIVES OF PSYCHOLOGY 

SIS West 116th St., New York City 



List of numbers, continued 

63. Race Differences in Inhibition: Albert 

L. Crane. $1.50. 

64. Individual Differences in Incidental 
Memory: Sadie Myers Shellow. $1.25. 

65. Character Traits as Factors in Intelli- 
gence Test Performance: William M. 
Brown. $1.25. 

66. A Study of the Sexual Interest of 
Young Women: F. I. Davenport. 
$1.25, 

67. The Psychology of ' Confidence : Wm. 
Clark Trow. $1.25. 

68. Experimental Studies of College Teach- 
ing: Harold E. Jones. $1.25. 

69. The Influence of Treatment for In- 
testinal Toxemia on Mental and Motor 
Efficiency: Alice E. Paulsen. $1.00. 

70. A Study of Suggestibility of Children: 
Margaret Otis. $1.50. 

71. The Value of Praise and Reproof as In- 
centives for Children : Elizabeth B. 
HURLOCK. $1.00. 

72. Attention and Interest In Advertising: 
Howard E. Nixon. $1.25. 

73. An Experimental Study of Thinking: 
Edna Heidbreder. $1.75. 

74. Estimation of Time: Robert Axel. 
$1.00. 

76. Measurement of Emotional Reactions: 
David Wechsler. $1.75. 

77. Tested Mentality as Related to Success 
in Skilled Trade Training: Theodora 
M. Abel. $1.25. 

78. Aggressive Behavior in a Small Social 
Group: E. M. Riddle. $1.75. 

79. The Memory Value of Advertisements: 
Edith R. Brandt. $1.25. 



from inside front cover 

80. A Critical Examination of Test-Scor- 
ing Methods: Rose G. Anderson. 
$1.00. 

81. Thermal Discrimination and Weber** 
Law: Elmer A. K. Culler. $1.75. 

82. A Correlational Analysis of Typing 
Proficiency: Luton Ackerson. $1.50. 

83. Recall as a Function of Perceived Re- 
lations: Cora B. Key. $1.25. 

85. An Experimental Investigation of Recov- 
ery from Work: S. L. Crawley. $1.25. 

86. Facilitation and Inhibition: Thomas N. 
.Jenkins. $1.00. 

87. Variability of Performance in the Curve 
of Work: James D. Weinland. $1.00. 

88. A Mental Hygiene Inventory: S. Daniel 
House. $1.50 

89. Mental Set and Shift: Arthur T. Jbr- 
SILD. $1.25. 

90. An Experimental Investigation of Rest 
Pauses: Charles W. Manzer. $1.25. 

91. Routine and Varying Procedure as Prep- 
aration for Adjustment to a New Situa- 
tion. Leland W. Crafts. $1.00. 

92. The Development of a Standardized An- 
imal Maze. L. H. Warner and C. J. 
Warden. $1.25. 

93. An Experimental Study of Speed and 
Other Factors in "Racial" Differences. 
Otto Klineberg. $1.50. 

94. The Relation of Reaction Time to Mea- 
sures of Intelligence, Memory, and Learn- 
ing. Vernon W. Lemmon. 80 cents. 

95. Is the Latent Time in the Achilles Ten- 
don Reflex a Criterion of Speed in Mental 
Reactions? George H. Rounds. $1.25. 



In addition to the numbers of the Archives, the following monographs 
are to be obtained from us: 

The Psychology of Association : Felix Arnold. 50 cents. 

The Measurement of Variable Quantities : Franz Boas. 50 cents. 

Linguistic Lapses: Frederic Lyman Wells. $1.00. 

The Diurnal Course of Efficiency: Howard D. Marsh. 90 cents. 

The Time of Perception as a Measure of Differences in Sensations: Vivian 

Allen Charles Henmon. 60 cents. 
Interests in Relation to Intelligence: Louise E. Poull, $1.00. Reprinted 

from Ungraded. 
The Conditioned Pupillary and Eyelid Reactions: Hulsey Gabon. $1.00. 

Reprinted from the Journal of Experimental Psychology. 



THE JOURNAL OF PHILOSOPHY 
515 W. 116th St., New York City 

Published on alternate Thursdays 
$4 PER ANNUM, 26 NUMBERS 20 CENTS PER COPY 

Edited by Professors F. J. E. Woodbridge, Wendell T. Bush 
and H. W. Schneider of Columbia University. 



ARCHIVES OF PHILOSOPHY 

Edited by the Department of Philosophy 

Columbia University, New York City 



American J( 
Subse 
E. G- 

The Pedago_ 
Subsc 
board 

Psychologic 
Subsc_ 
Bi-mc 

PSYCHOLOGIC- 

Subsc 
Publii_ 

Psychologic 
Subsc- 
An ai 

Psychologic" 
Subsc 
MontL 

Journal of 
Subsc- 
Bi-we 

Training Sc 
Subsc 
Montl- 

Archives of_ 
Subsc 
Publii 

Journal of 
Sub. 
Quart" 



PSYCHOLOGIC- 

Subsc 
With( 



Date Due 



JU^ 



L J 



T99r 




ICALS 



>allenbach, M. Bentley and 
nded 1887. 



Mass. ; Clark University, 
intertintinnal cooperating 
funded 1891. 



John 3. Watson. 
[. Franz. 



RARY BUREAU FORM 1197,3 



Schneider. 



ed 1904. 



Toodworth. 



m with Floyd H. Allport. 



)07. 



Comparative Psychology Monographs — Baltimore : Williams and Wilkins Co, 
Subscription $5.00. 500 pages per volume. Edited by W. S. Hunter. 

Published without fixed dates, each number a single research. 

Psychoanalytic Revifw — Wnshington, D. C. ; 3617 10th St., N. W. 
Subscription $6.00. 600 pages annually. Psychoanalysis. 
Quarterly. Founded 1913. Edited by W. A. White and S. E. Jelliffe. 

Journal of Experimental Psychology — ^Princeton, N. J. ; Psychological Review Company. 
Subscription $5.00. 480 pages annually. Experimental. 
Bi-monthly. Founded 1916. Edited by Madison Bentley. 

Journal op Applied Psychology — Bloomlngrton, Ind. ; Indiana University Press, 
Subscription $4.00. 400 pages annually. Founded 1917. 
Quarterly. Edited by James P. Porter and William F. Book. 

Journal op Oomparativb Psychology — Baltimore; Williams and Wilkins Company. 
Subscription $5.00. 500 pages annually. Founded 1921. 
Bi-monthly. Edited by Knight Dunlap and Robert M. Yerkes. 

Genetic Psychology Monographs — Worcester, Mass. ; Clark University. 
Subscription $7.00. 600 pp. ann. Edited by Carl Murchison. 

Bi-iiio;ithly. Each number a complete research. Child behavior, differential and genetic psvcholoev. 
Founded 1925. f j sj 



Psychological Abstracts- — Princeton, N. J. ; American Psychological Association. 
Subscription $0.00. GOO pages annually. Edited by W. S. Hunter. 
Monthly. Abstracts of Psychological literature. Founded 1927. 

The Personnel Journal — Baltimore; WilUam and Wilkins Co. 
Subscription $.').00. 500 pp. Founded 1922. 
Bi-monthly. Edited by Walter V. Binghan. 



BF21.A7no95 



3 9358 00040944 8 

0) 



This book may be kept .U.L...^^v.-.r -weeks. 

A fine of two cents will be charged for each day- 
books or magazines are kept overtime. 

Two books may be borrowed from the Library at 

one time. 

Any book injured or lost shall be paid for by the 
person to whom it is charged. 

No member shall transfer his right to use the 
Library to any other person. 




STHAPFLEX CO.. Medford. Mass. 



BF21.A7no95 



3 9358 00040944 8