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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
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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
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A CRITERION OF SPEED IN MENTAL REACTIONS? 91
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Classification number
Accession number
Date Due:
5-7"^/
BP 21 A7 no.9S k09hh
a criterion of speed..
Issued to
^^
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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
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