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NUMBER VI.
THE

TIME-RELATIONS OF MENTAL PHENOMENA

BY PROF. JOSEPH JASTROW

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THE TIME-RELATIONS OF
MENTAL PHENOMENA

JOSEPH JASTROW,

Professor of Psychology at the University of Wisconsin.

NEW YORK :

N. D. C. HODGES, PUBLISHER

47 LAFAYETTE PLACE

1890

THE TIME-KELATIONS OF
MENTAL PHENOMENA.

THE study of the time relations of mental phenomena is
important from several points of view: it serves as an index
of mental complexity, giving the sanction of objective
demonstration to the results of subjective observation ; it
indicates a mode of analysis of the simpler mental acts, as
well as the relation of these laboratory products to the pro-
cesses of daily life; it demonstrates the close inter-relation
of psychological with physiological facts, an analysis of the
former being indispensable to the right comprehension of the
latter; it suggests means of lightening and shortening men-
tal operations, and thus offers a mode of improving educa-
tional methods; and it promises in various directions to
deepen and widen our knowledge of those processes by the
complication and elaboration of which our mental life is so
wonderfully built up. It is only within very recent years
that this department of research has been cultivated ; and it
is natural that the results of different workers, involving
variations in method and design, should show points of

2 THE TIME-RELATIONS OF

difference. In spite of these it seems possible to present a
systematic sketch of what has been don?, with due reference
to the ultimate goal as well as to the many gaps still to be
filled. It is with the object of furnishing such a general
view that the following exposition has been attempted.
Rate of Nervous Impulses.

While it follows, as a very natural consequence of the
modern view of the relation between body and mind, that
mental processes, however simple, should occupy time, it
must be remembered that the very opposite opinion has
been held by serious thinkers. It has been argued as a proof
of the immateriality of thought that its operations were out
of relation to time, and the expression "quick as thought"
has come to indicate a maximum -of speed. It being estab-
lished thr-t so comparatively simple a process as sensation
involves the passage of an impulse along nerve-fibres, it is
plain that the rate of travelling of this impulse sets a limit
to the time of the entire process, as well as of all more com-
plicated mental operations in which sensations are involved.
The physiologist Johannes Muller, writing in 1844, despaired
of our ever being able to measure the time of so excessively
rapid and short a movement; but before the close of the same
decade, Helmholtz measured the rate in the nerve of the frog,
finding it to be about 86 feet per second. Though somewhat
greater in man. 110 feet per second, this movement is ex-
tremely slow compared with the velocity of light or even
sound: indeed, it is only slightly faster than the fastest ex-
press train.

Mi'iller writes: '" We shall probably never secure the means
of ascertaining the speed of nerve activity, because we lack
the comparison of enormous distances from which the speed
of a movement, in this respect analogous to light, could be
calculated;" and again: "The time in which a sensation
proceeds from the periphery to the brain and the spinal cord,
and is followed by a re-action at the periphery by means of
muscular contractions, is infinitely small and immeasura-

MENTAL PHENOMENA. 3

ble." It is interesting to note how very crude were the con-
ceptions of the older physiologists upon this point. Haller
(1762) tells us of one who, following the view that the ner-
vous impulse was a fluid, and its action analagous to that of
the blood, fourd the " nerve tubes" of the heart to be 2,880
million times as narrow as the aorta, and concluded that the
nervous impulse travelled proportionately faster than the
blood, thus making its rate 57,600 million feet per second.
Haller himself measured the maximum rapidity of short
rhythmical movements, and (falsely), assuming that the im-
pulse travelled to and from muscle and brain between each
contraction, found an (accidentally not very erroneous)
speed of 9,000 feet per second. The method introduced by
Helmholtz, and improved by himself and others, consists in
excising a muscle with a long stretch of nerve attached,
and connecting the muscle with a lever, so that every con-
traction of it is registered upon the quickly moving surface
of a revolving drum or a swinging pendulum. By electrically
stimulating the nerve first at a point near to and then at a
point far off from the muscle, two curves are recorded, the
latter of which is found to leave the base line a trifle after
the former. A tuning-fork writes its vibrations beneath
these records, and enables us to measure how much later
the second contraction began, while the distance travelled
in this time is that between the two points of stimula-
tion on the nerve. It has been attempted to measure this
rate in man by having the subject re-act once to a stimulus
applied to the foot, and again to a stimulus at the hip, or
some point nearer the spinal cord, and counting the differ-
ence in time as due to the difference in length of nerve
traversed. While the method is necessarily inaccurate, and
other factors contribute to the difference in time, the majority
of the determinations indicate a rate of between 30 and 40
metres (100 to 130 feet) per second. These determinations
apply to sensory nerves: for the motor nerves of man, Helm-
holtz has found, by a method closely similar to that employed
upon the frog, a rate of 110 teet per second. The most in-
fluential of the conditions affecting this rate is temperature:
cold decreases and heat increases it. the extremes of varia-
tion being 30 to 90 metres. Under normal conditions it
seems fait- to regard the rate for both motor and sensory
nerves of man as about 110 feet per second.

THE TIME-RELATIONS OF

Analysis of Re-actions.

A great variety of actions may be viewed as responses to
stimuli. There is a flash of light, and we wink; a burning
cinder falls upon the hand, and we draw it away; a bell
rings, and the engineer starts his train, or the servant opens
the door, or we go down to dinner; the clock strikes, and
we stop work, or go to meet an appointment. Again, in
such an occupation as copying, every letter or word seen
acts as a stimulus, to which the written letter or word is the
response; in piano playing, and the guidance of complicated
machinery, we see more elaborate instances of similar pro-
cesses. The printer distributing "pi." the post-office clerk
sorting the mails, are illustrations of quick forms of re-action,
in which the different letters of the alphabet or the different
addresses of the mail matter act as the stimuli, and the plac-
ing them in their appropriate places follows as the response.
In many games, such as tennis or cricket, the various ways
in which the ball is seen to come to the striker ai'e the
stimuli, for each variation of which there is a precise and
complex form of response in the mode of returning the ball.
In military drill the various words of command are the
stimuli, and the actions thus induced the responses; and such
illustrations could be multiplied indefinitely. In all these
actions the time-relations are more or less definite and im-
portant, but a useful study of them presupposes a careful
and systematic analysis of the processes therein involved.
We recognize that certain of the above actions are more
complicated than others, and we must inquire in what this
complication consists. In the process as usually presented
the nature of the re-action depends upon the nature of the
stimulus, a variation in the one being concomitant with a
variation in the other. The piano player, seeing a certain
mark on the page, strikes a certain key on the key-board,
but strikes a different key if this mark be differently placed ;
the soldier varies his movement according to the word of

MENTAL PHENOMENA. 5

command, aud so on with most of the others. All such
actions in volve at least three processes: (1) the recognition
of the sense impression, (2) the performance of the appro-
priate action, and (3) the association of the one with the
other. The recognition involves the appreciation of the
presence together with the appreciation of the nature of the
sense-impression; and the movement involves the contrac-
tion of muscles together with the initiation of the impulse.
We obtain the simplest form of re-action by limiting the
stimulus to a single definite one, and having one and the
same response irrespective of the nature of the stimulus.
The subject expects the stimulus the nature of which he
knows, and is ready to signal, by a simple movement agreed
upon in advance, merely that the impression has bsen re-
ceived. This we shall speak of as a "simple re-action." It
occurs whenever a certain sense-impression is agreed upon
as a signal for the execution of a simple movement. Tlie
lime-keeper pressing the spring of the stop-watch, or the
racer starting off as soon as the pistol is fired or the word
is given, are instances of simple re-actions. It should be
noted that the simplicity of the act refers primarily to the
subject's fore-knowledge of what is to occur; the nature of
the sense-impression, as of the motion, is known in advance,
the association between the two being in the main artificial.
Inasmuch as the more elaborate mental processes involve
those of the simple re-action, our first step must be to deter-
mine its elements and their time-relations.

The Elements of a Simple Re action.

The several elements of a simple re-action have been
variously analyzed by different observers, but all recognize
the physiological and the specially psychological portions
of the process. The physiological time-elements include,
(a) the time for the sense-organ to respond to an impression,
i.e., to overcome its inertia; (b) the time for the passage of
the impulse inward along nerves (and spinal cord), with the

6 THE TIME-RELATIONS OF

various delays whenever the impulse eaters or passes through
ceils; (c) the return passage of the motor impulse from the
brain to (spinal chord and) nerve and muscle; and (d) the
time for the contraction of the muscle. The time thus left
unaccounted for is that taken up by the psychological pro-
cess, the transformation of the sensory into the motor im-
pulse,— a process taking place in the brain, but as to the
precise nature of which we have no definite information.
The separate determination of each of the physiological fac-
tors enables us to find approximately the duration of the
central process As a sufficiently typical case we may accept
the estimate of Cattell, that, in re-acting to a light by press-
ing the key with the finger, the time needed by the impulse
to travel from eye to brain and from brain to spinal cord
and finger is about 507 ;* the latent time in the muscle, dur-
ing which it overcomes its inertia, is judged from experi-
ments upon the frog to be about 5(7 to 10(7; and experiment
gives a value of 15(7 to 20(7 for stimulating the retina and
initiating the impulse. As the entire re-action occupied
about 150(7 we conclude that in this case the physiological
and the psychological portions of the process occupy about
equal times. One may obtain a fair notion of the rate of
these processes by the following simple experiment. A
score or so of persons form a chain by joining hands, and at a
given signal a certain member of the group sharply presses
the hand of Ids neighbor, who in turn imparts the pressure
as quickly as possible to his neighbor, and so on until the
impression has gone the rounds. An outsider keeps the
time (which may be done with sufficient accuracy by count-
ing the ticks of a watch, usually fifths of a second) from the
moment of giving the signal to start to the moment of re-
ceiving the signal from the last member of the group that
the impression has been circulated. The entire time divided
by the number of persons in the group (or better, by that

1 The sign <r indicates one one-thousandth of a second.

MENTAL PHENOMENA. 7

number plus two to include the re-actions at starting and
stopping) gives an average simple re-action time, which,
though long at first, is reduced after a lii/cle practice to a
sixth or a seventh of a second. On this basis one may cal-
culate that if a number of men, stretching out their arms
and grasping one another's hands, were stationed in a
straight line, it would take three minutes to send a message in
the manner just described along a mile of this human telegraph.

(a) The inertia of sense-organs has been variously deter-
mined. One method measures how closely impressions may
follow one another without fusing. The time thus measured
is the minimum time during which the sense-organ may he
stimulated and recover sufficiently to receive a second stim-
ulation. This process thus includes something more than
the one we desire to measure, and may perhaps be regarded
as furnishing a maximum time of the sensory inertia. Here
again various circumstances influence the determinations,
the chief ones being the sense-organ in question and the
clearness and intensity of the impression. Sectors of black
and white upon a disc revolving in daylight at the rate of
about 25 times a second fuse into a uniform gray, making
the inertia of the retina under these conditions about 40(7.
In weak light (moonlight) the time lengthens to about lOOff.
The same experiment has been made with sectors of different
colors, with the disc stationary and the light reflected from
a rotating mirror, with a vibrating point of light; and, while
all these variations somewhat affect the result, the majority
of the determinations indicate a fusion at 30 to 40 impressions
a second, or a duration of S3ff to 25O". For sound, different
observers have chosen different points for measurement.
The slowest rate of impressions fusing into a musical sound
has been fixed at between 30 and 40 per second ; but Helmholtz
has shown that the interi'erence of sound-waves perceptible
as beats does not escape detection when recurring as rapidly
as 132 per second. For non-musical sounds, such as electric
clicks, a still higher rate has been found. In touch we dis-
tinguish differences of feeling when impressions are rapid
enough to fuse but not rapid enough to fuse perfectly. The
smoothness of a polished surface is not obtained until the
impressions occur 480 to 640 times a second (Valentin). For
taste and smell the period, though not accurately determined,

THE TIME-RELATIONS OP

is undoubtedly very long. Here the time needed to reach
the somewhat concealed sense-organs is considerable, and the
chemical processes involved are relatively slow in action.
The influence of the mode of activity of the sense-organ upon
its period of stimulation is further illustrated in the long
inertia period of the probably chemical action of vision com-
pared with the short period of the mechanical senses of hear-
ing and touch. This view is also supported by the fact that
the period for the retina is shortened if the eye be directly
stimulated electrically. Another mode of experimenting
consists in applying a stimulus for the minimum time during
which it can be recognized. The time thus measured will be
shorter than the other, for it tells us only how long is needed
for initiating the process of recognition sufficiently to have
it continue to completion (probably after the stimulus ceases).
This is indeed a surprisingly short time. Cattell and San-
ford independently found that a color or a letter could be
recognized when visible for only from Iff to 5ff, while less
recently Baxt recognized 6 to 7 letters when exposed for only
5<7. Others have calculated that the maximum effect of an
impression is not reached until from 50 ff to 150(7, but these
determinations seem to involve some mental process of recog-
nition. Whether or not some such process of recognition is
involved is not quite clear. Unless specially prevented, the
recognition will take place on the basis of the after-image, a
few thousandths of a second being sufficient to initiate the
process. By following the impression by a strong flash of
light, and thus nullifying the afterimage, Baxt found a
longer time needed to recognize a more complicated impres-
sion. Within 10(7 to 15(7, one letter : within 24(7, three letters ;
within 34(7, four letters, could be recognized. This only
partially excludes the effect of the after-image, so that per-
haps the results with complicated impressions are minimum
"recognition times," and those with simple impressions
'' inertia times.'' Another method, that of Exner, is similar
to the method of fusion. It consists in finding how closely
two impressions, stimulating slightly different portions of
the sense-organ, may follow one another and yet be recog-
nized as successive. Optical impressions were so recognized
when falling at an interval of 44(7 on two points of the retina
near the centre .011 millimetres apart, a longer time being
necessary if the points are away from the centre of the ret-
ina, It seems probable that this process is more complicated

MENTAL PHENOMENA. 9

than the one we are attempting to study. While the data
thus at our disposal do not allow us to fix accurately the
time of sensory inertia, the estimate provisionally accepted
in the text cannot be far from the truth, being rather over
than under estimated. The methods of measuring the rate
of nervous impulses (6) and (c) have already been described.
The inertia of the muscle and the time of its contraction are
determined upon the same apparatus by observing how much
;:fter the shock is given the curve leaves the base-line.

Reflex, Automatic, and Voluntary Re-actions.
The term " re-action " as here used is not intended to in-
clude all responses to stimuli. The above instanced forms
of re actions present various grades of naturalness, utility,
and habituation; that is, the association between motion and
stimulus has by practice become more or less close and easy.
Copying, for example, may become so entirely automatic
that it runs on of itself without the need of renewed voli-
tional effort. The actions recognized as reflex take place in
spile of all volition. The re-actions here considered are
limited to those requiring some degree of voluntary effort for
their execution, though this may be almost indefinitely re-
duced by practice. The reflex act takes very much less time
for its execution than the voluntary: the time for winking
has been determined by Exner to be something over 50(7.
In other words, it takes about three times as long to signal
by a voluntary closure of the eye-lid that an impression has
been received as to perform the same act reflexly when
the eye is threatened. The utility of this quick action for
the protection of the eye is evident; and other useful re-ac-
tions, such as those of flight and escape in timid animals,
seem to be of a similar nature. The quick movements of
defence when attacked, of regaining one's balance when slip-
ping, are so immediately useful and so well inculcated in
the organism as often to surprise us by their quickness.
Most of these actions can also be performed voluntarily, but
neither so well nor so quickly; it is therefore difficult to

10 THE TIME-RELATIONS OF

subject them to experiment. As already indicated, in the
oi'dinary re-action there is little naturalness in the connec-
tion of stimulus and movement, the same type of movement
being1 used for all. The experienced re-actor becomes accus-
tomed to signal by the finger movement that the operation
required of him has been accomplished, but hardly associ-
ates this movement with any particular stimulus.

It is perhaps well to add that the great saving of time in
actions that have become automatic (such as is seen in the
experienced piano player or post-office clerk as compared
with the beginner), is in great part due to the increased
facility of doing several things at once and not serially, a
factor that enters only in a small degree into the simple re-
action. The processes we should be most interested in
measuring are those most closely approaching the operations
of daily thought, so that the inference from experiment to
practice shall be as direct as possible. This, however, it is
difficult to do, because every-day mental processes do not
present the simplicity of conditions required by experiment.
Accordingly the method has been to study the simplest re-
actions, and then take into account the circumstances in
which our usual mental operations differ from them.

Conditions Affecting Simple Re-action Times.

Referring to the accompanying tab'e for a general view
of the time-relations of simple re-actions, we may pass at once
to the topic of greatest interest, viz., the influences by which
they are quickened or retarded. These maybe considered as
(A) objective, or affecting the conditions of the experiment,
and (B) subjective, affecting the attitude of the re-actor.

(A, 1) The Nature of the Impression. The distinctive
characteristics of a simple re-action being in the attitude of
the re-actor, it would seem that its time could be little af-
fected by the nature of the impression. The motor signal-
ling process is the same, the connection between the im.

BIENTAL PHENOMENA.

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Normal.

Intensity of sound unknown. \
Attention directed to sensation.
" " movement.

Intensity of sound known.

Preparatory signal irregularly varied with-
lu 15 seconds.

Preparatory signal at regular intervals.

Ou the hand.
Ou the foot.
With preparato-y signal.
Without " "

The intensity in terms of a common unit
were as 7, 23, 123, 315, 1000, the two high-
est intensities not being determluable.

Average of all parts of body.

Remarks.

12 THE TIME-RELATIONS OF

pression and movement is about equally artificial in all
cases, so that the chief variability must be in the time needed
for receiving the impression. For the different senses this
time is different. Taking the general average of all the
observations accessible to me, I find, for hearing, 1380";
for touch, 148(7; for sight, 185(7. This order is quite con-
stant with the different observers, the long time of visual
re-actions being referable to the long inertia period of that
sense, as well as to the small perceptive area of the retina,
necessitating a precise accommodation, — a condition not
always supplied in the above experiments. This view is
strengthened by the shortening in the re-action time (by 36(7
for Exner, by 24(7 for v. Wittich) when the eye is stimu-
lated electrically. In re-acting to a temperature sensation,
care must be taken not to re-act to the sensation of contact
with the skin. Where this has been done it has been found
that the re-action to the sensations of temperature is longer
than to contact, and I hat the re-action to heat is longer than
to cold. Thus, Vintschgau and Steinach re-act to a pressure
on various points of the head in 109(7, to a sensation of cold
in 135(7, of heat in 146(7, similar values for various points of
the hand being 121(7, 188(7, 209(7. The researches of Gold-
scheider agree with these in the main, but make the differ-
ence between the re action times to heat and to cold much
greater. The senses of taste and smell clearly illustrate the
effect of the kind of stimulation, for here the relative inac-
cessibility of the sense organs and the slowly acting cLemi
cal processes involved lead to a long re-action time. Though
experimentation is difficult and uncertain in these senses, we
may cite for smell the results of Moldenhauer on the odors
of various oils, centring about 300(7 (oil of roses 273(7, cam-
phor 321(7, musk 319(7, ether 255(7, etc.), and for taste, of
Honigschmied, who re-acts to various tastes on the tip of the
tongue in 182(7, though other subjects require about 300(7.
On the back of the tongue the time is much longer, and it

MENTAL PHENOMENA. 13

varies for different tastes, being longest for bitter, shortest
for salt, and about equal for sweet and sour. Within the
same sense the re-action time will var}' according to the na-
ture and place of the stimulus. The above cited differences
for tastes and smells show this; and for different visual im-
pressions, for different tones, for contact at different parts of
the body, different results have been obtained, referable to
slight variations in sensibility, length of nerve traversed,
clearness of the impression, and the like. These minor dif-
ferences are not easily established, but the following may be
cited. Exner re-acts to an electric shock on the hand in
132(7, on the forehead in 137(7, on the foot in 175(7; v. Wit-
tich re-acts to a point 011 the back of the finger in a longer
time than to one on the front, 144(7 and 156(7, and regards
the difference as due to a difference of sensibility. Hall
and Kries clearly show that the re-action to a point looked
at in indirect vision is longer than to one in direct vision,
195(7 and 235(7, and find further differences according as the
point is above or below, inside or outside, the retinal centre.
A high tone is re-acted to more quickly than a low one, and
so on.

It is easier to demonstrate the influence of (2) the inten-
sity of the stimulus. Within limits, intense stimuli affect
sense-organs more quickly than weak ones, and, roughly
speaking, an increase in the intensity of the stimulus is con-
comitant with a decrease in the re-action time. According
to Wuudt, the noise of a hammer falling respectively from
heights of 1, 4, 8, and 16 millimetres was re-acted to in 217(7,
146(7, 132(7, and 135(7, and the sound of a ball falling from
heights of 2, 5, 25, and 55 centimetres in 176(7, 161(7, 159(7,
and 94(7 respectively. Exner varied the length and there-
fore the brilliancy of an electric spark from 0.5 to 7 milli-
metres and obtained a steadily decreasing re-action time of
158(7 to 123(7. More complete are the observations of Ber-
ger and Cattell, who found that as the light increased from

14 THE TIME-RELATIONS OF

7 to 23, to 123, to 315, to 1.000, and to two greater but not
deterrniuable degrees of intensity (as compared with a small
unit of light), the re-action *,imes fell (average of two ob-
servers) from 210(5- to 184(7, to 174(7, to 1707, to 169(7, to
156(7, to 148(7. For sound, as the ball fell from heights of
60, 160, 300, and 560 millimetres the re-action times were
151 (7, 146(7, 1270", and 123 ff. For electrical touch excitations,
re-actions to four grades of stimuli separated by equally
perceptible differences were made (average of two observers)
in 173(7, 159(7, 145(7, and 145(7. Wundt regards the differ-
ence in re-action times of the different senses as in part

•

referable to differences in intensity, and, when re-acting to
just perceptible intensities of sensation in various senses,
finds about the same long time for each, 330(7.

3. The Mode of Re-action. The various movements by
which we may signal that a sensation has been received may
differ in the ease of their execution, in the length of nerve
traversed, as well as in the naturalness of association with
the impression. Such differences, however, seem to be
small ; when once the movement is understood and antici-
pated, the difference in the times of its execution is slight.
Thus, Miinsterberg found, in testing the re-action of each of
the five fingers, that while at first the thumb and little finger
re-acted more slowly than the others, after some practice the
times of all were substantially the same. Fere, however,
has some results suggesting that the fingers making the
strongest movements re-act in the shortest times. Very in-
teresting, too, is the experiment of Ewald in which the
stimulus, an electric shock, is given to the finger in the very
key by which the re-action is signalled, the re-action consist-
ing in the very natural movement of drawing the finger
away. Under these circumstances he found a brief and
constant time of 90(7. Both Vintschgau and Cattell have
compared the time of re-acting by closing a key with the
finger and by speaking a word, and find the vocal method

MENTAL PHENOMENA. 15

the longer by about 16 0" and 30(7 respectively. Differences
in re-acting from the two sides of the body have been ob-
served by some, the right side showing the shorter re-action,
but this difference can hardly be considered as constant.
Orchansky has shown in one case that the movements of
inhibition take about the same time as those of excitation of
a muscle, and it would be possible to study the relative ease
of various movements by this method. A practical exam pie
is furnished by the commands of military drill, the words,
"carry," "present," etc., announcing the mode of re-action
for the performance of which the following word, "arms,"
is the signal.

(B) We pass next to the more important subjective fac-
tors, referring in the main to the expectation and the atten-
tion. While nothing has been definitely said upon tins
point, the implication has been that the subject tries his ut-
most to re-act as quickly as possible, and that he knows the
nature of the experiment. While the influences now to
be discussed seem to be general in their effect, making the
nervous system at one time a better and again a worse re-
acting apparatus, they may, in certain respects, be subjected
to a more definite analysis. We begin with (1) the subject's
fore-knowledge of what is to take place. We may antici-
pate the outcome of experimentation on this point by for-
mulating the law that the more definite the fore-knowledge
of the subject the quicker the re-action. Apparently there
is a process that must be gone through with in each re action,
and the better prepared the subject is for this, — that is, the
more of this process gone through with before the giving of
the stimulus, — the less of it falls within the measured inter-
val. The precise nature of this process is a difficult and
much discussed problem. It may be sufficient to note at
present that the re action to a certain stimulus cannot but
imply in some sense the distinction of that stimulus from the
many others by which we are constantly surrounded. If

16 THE TIME-RELATIONS OF

the subject be re-acting to a visual impression, he will prob
ably not press the key should a noise occur in the room or
something accidentally come in contact with his hand. To
re-act to a visual impression thus implies the distinction of
that from other impressions. It implies the identification
of the expected with the existing impression. Just as we
recognize an appearance in the heavens or under the micro-
scope more readily when we know where and what to look
for, or as we immediately recognize an almost forgotten ac-
quaintance when expecting him, though at a chance mealing
W3 might have passed him without recognition, so we re-act
to an impression most quickly when it is most definitely ex-
pected, with regard to its nature, its time, place of ap-
pearance, and the like. This expectation may be more or
less specific, and an interesting series of experiments consists
in varying the fore-knowledge of the subject while still leav-
ing it definite enough to call the result a simple re-action,
(a) We may leave the precise time of the appearance of the
stimulus undetermined. This may be done by experiment-
ing with and without a preparatory .signal, preceding the
stimulus by a regular interval. Wundt re-acted to the sound
of a ball falling from a height of 25 centimetres in 76(7 with
a preparatory signal, but in 253(7 if no such signal preceded ;
to a ball falling five centimetres, in 175(7 in the first case, and
266(7 in the second. Marti us re-acts to the sound of a falling
hammer in 127(7 when preceded at a regular interval by a
signal, but in 178(7 without the signal. Dwelshauvers re-acts
in 193(7 in the former case, in 236(7 in the latter (average of
"sensory" and "motor" re-actions). The time between
the signal and stimulus is here regular, and the most favora-
ble time seems to be about two seconds. Lange found the
time with an interval of two seconds less than with one of
one or three seconds. Dwelshauvers varied the interval from a
second and a half to three, and then to six seconds, and finds
the shortest re-actions at a second and a half. Martius has

MENTAL PHENOMENA. 17

experimented with intervals from about one second to one-
sixth of a second, and finds the one-second interval the most
favorable. If the interval be irregularly varied within two
seconds the effect is hardly noticeable, but if irregularly
varied within fifteen seconds the time is increased (Cattell).
With a normal re-action to sight of 1490" and to sound of
124(7, the re-action to sight with the interval varying within
two seconds was 148(7; when varying within fifteen seconds,
to sight 174(7, to sound 165(7 (average of two observers).
Similarly Martius finds that re-actions with an irregular
interval between signal and stimulus result in a time inter-
mediate between that with a regular interval and that with-
out a signal at all. (6) If the time and nature of the stimulus
be known, but its intensity be varied, the time is increased.
When re-acting to a uniform change between a feeble and a
loud sound, the re-action time to the former was 127(7, to the
latter, 116(7; but when these changes were made in an irregu-
lar and unexpected manner, the times were lengthened to
208(7 and 19S<7.

In a similar manner the attention, which we have sup-
posed hitherto to be focused upon the matter in hand with
a maximum of effort, may be prevented from being ef-
fectually directed to the making of the re-action by a variety
of circumstances. Some of these we may group under the
term (2) distraction. By a constant noise or other means
we may be creating a stimulus to which the attention is in-
voluntarily drawn, and thus withdrawn from the process of
re-action. Wundt re-acted to a sound of mean intensity in
189(7, to a strong sound in 158(7, but when a disturbing
sound was going on in the room these re-actions required
313(7 and 203(7. On the other hand, with Cattell, when in
good practice, so that the re-action became almost automatic,
the effect of a disturbing sound both upon sight and sound
re-actions was insignificant, — normal for sight 149(7, with
disturbing noise 155(7; normal for sound 124(7, with dis-

18 THE TIME-RELATIONS OP

turbing noise 124(7. Dwelshauvers finds a longer re-action
time when a minimum of attention is paid to the re-action.
It is quite probable that what acts as a disturbance to one
person hardly affects another. In some individuals the re-
action time seems to be extremely sensitive to any mental
disturbance. One of Obersteiner's subjects, with an average
re-action time of about 100(7, requires 142(7 to re-act when
music is heard, and another's re action time is lengthened by
100(7 when talking is going on in the room.

A more general and thorough form of distraction may be
effected by imposing a task requiring distinct mental effort
at the same time that the re-action is to take place. Thus
Cattell attempted to add 17 consecutively to a series of num-
bers, and found that re actions taken while this was going
on were longer by 28(7 (average of two observers). All such
effects seem to be much more marked when the re-action in
question is new than when it has become familiar and partly
automatic. The disturbance seems to act by delaying the
association between stimulus and movement.

(3) We have now to notice a distinction which, though
but recently brought to light (by N. Lange, 1888), is of fun-
damental importance. A re-action may be made in two
ways. In the one form of re-action the attention is directed
to the expected impression: it is identified as the expected
impression, and thereupon is initiated the impulse resulting
in the re- acting movement. The several processes are per-
formed serially, the attention being concentrated upon the
sensory part of the process. In the other form of re-action
the attention is directed to the movement: the impulse is
ready, and is set off by the appearance of the signal almost
automatically, the identification of the actual with the ex-
pected impression being omitted. The first is spoken of as
the "complete" or "sensory" mode of re-action ; the second,
as the " shoi'tened "or " motor " form. In the experiments
of Lange the simple sensory re-action time to a sound (aver-

MENTAL PHENOMENA. Ill

age of three persons) was 227(7, motor 123(7; to a visual im-
pression (average of two persons), sensory 290(7, motor 113d;
to a tactile impression (one person), sensory 213(7, motor
108(7.

These differences, however, seem to be rather extreme.
Miinsterberg finds for sound, sensory 162(7, motor 120(7.
Martius finds (average of various experiments) for a "sen-
sory " re action to a sound 161(7, for a " motor" 141(7, but in
two subjects not practised in re-acting 210<T and 111(7.
Dwelshauvers finds a difference as great as between 279(7 and
137(7 for three subjects. It should be noted that this differ-
ence in the attitude of the subject is not always easy to
maintain, and that it is at times equally difficult to decide
whether a re-action has been "sensory" or " motor." Un-
doubtedly transitional modes of re-action occur in which the
attention is not sharply focused on either stimulus or move-
ment, but rather divided between the two; and it maybe
that this is the most usual mode of re-action when the distinc-
tion is not taken in to account. Both Martius and Dwelshauvers
have recorded the subject's own opinion of the quickness of
each re-action, and the state of his attention at the moment
of re-acting. The estimate of the relative speed of re-action
seems to be fairly accurate, and those re actions seem to be
shortest in which the attention of the subject was sharply
focused upon the matter in hand. A further characteristic
of the motor form of re-action is that its average varia-
tion is smaller, i.e., the process is more regular; and that
false re-actions occur, either anticipations of stimulus or
re-actions to some accidental disturbance. The distinc-
tion is important as aiding in the explanation of individ-
ual differences, as well as of the path of practice. The
somewhat conflicting results obtained before this distinc-
tion was taken into account might very well be due to
the fact that the one observer re-acted in the one way,
and the other in the other. Thus the re-action times of

20 THE TIME-RELATIONS OF

Kries and Auerbach are motor; for they are brief, false re-
actions occur, and it is noted that the simple re-actions fol-
lowing re-actions involving distinctions were longer by 410"
and Biff than before,— a change probably due to a return to
a partially sensory mode of re-action. Again, there are
doubtless transitional modes between the two, and there are
reasons for believing that the path of practice is from the
sensory to the motor form of re-action.

The influences that remain to be discussed may be consid-
ered under the heads of "practice," "fatigue," 'individual
differences," and "abnormal variations." (4) Practice. As
just noticed, the effect of practice is intimately connected
with the mode of re-action. It is noticed by almost all
writers, but the extent to which it influences the time is very
various. The observations make it probable that the effect
of practice is most marked at first, and that when once the
initial stages are over, the effect of continued practice is small.
It is greatest in those persons whose time is longest at first,
and seems most influential in acts that are complicated and
lie somewhat beyond the realm of daily experience.

When the action is once thoroughly learned, an interval
of disuse seems not to affect the time seriously. After not
re-acting for three months, Cattell found no essential differ-
ence in the time. On the other hand, with some there is a
slight newness on beginning each day's work, making the
first re-actions of a series rather long (Trautschoklt).

(5) A similar statement may be made of fatigue: it has
greatest effect upon the complicated, less thoroughly learned
processes, and varies with the individual and the mode of
re action. With an automatic simple process its effect is
very slow to appear (Cattell. It may enter at any stage of
the process, sensory, motor, or central ; but the last seems to
be the most serious. It appears as a difficulty in keeping
one's attention upon the experiment, and thus lengthens the
time, and especially the average variation of the experi-

MENTAL PHENOMENA. 21

mrnts. By fatigue is meant the fatigue brought about by
the experimenting itself. The time is also affected by gen-
eral fatigue preceding tbe experiment. Some individuals
are extremely sensitive to influences of this kind.

(6) Individual Variations. The fact here to be investi-
gated is the general one that different persons require differ-
ent times for the performance of the same operations. The
difficulty of drilling a company of men to act in concert,
whether in military drill or otherwise, springs in part from
this difference. It was from this point of view, too, that
the time of mental processes was first studied. So long ago
as 1795 Maskelyne, the astronomer i-oyal, discharged his as-
sistant because the latter recorded the transit of a star across
the wire of the telescope half a second or more later than he
himself. Some twenty-five years later Bessel, another as-
tronomer, had his attention called to the point, and upon in-
vestigation established the fact that no two observers re-
corded such ti-ansits at precisely the same time. The differ-
ence in time between any two observers was usually
expressed as an equation, and hence the term "personal
equation," which, though strictly applicable only to the
differences so found, has assumed a much wider meaning.
The individual differences become greater as the process to
be performed increases in complexity, and this explains in
part why the personal equations as determined by the com-
plicated eye and ear method were so large: with the simpler
method of electrical record these d ifferences are much reduced .
Besides the differences due to practice and the mode of re-
action, there are a large number of minor sources of varia-
tion, which as yet are not sufficiently understood to justify
a correlation of quick or slow re-action times with definite
individual qualities. We may, however, note (a) that the
time is longer in children than in adults, as has been shown,
amongst others, by Binet, who found that children from 3^
to 7 years re-acted in from 440(7 to 6600", when adults required

22 THE TIME-RELATIONS OP

but 140(7. In the very old the time is longer than in the
prime of life. Under the influence of mental or physical
fatigue, worry, or slight indisposition, the time has been in-
creased. Obersteiner, Vintschgau, Goldscheider, and others,
have incidentally observed these effects, showing an increase
of 30i to 40(7. These variations are related to others, shad-
ing over into the abnormal. Under this head may be con-
sidered (7) the action of drugs and re-action times in the
insane. Several of the earlier experimenters made a few
observations concerning the effect of drugs. Exner found
quite a marked lengthening of the time after drinking wine.
Vintschgau and Dietl found that the effect of coffee was to
decrease and of morphium to increase the time for a consid-
erable period. The more elaborate researches of Kraepelin
show that the effect of amyl, ether, and chloroform is a
sudden lengthening of the re-action times, reaching a maxi-
mum in a very few minutes, and followed by a rather long
period of times slightly shorter than the normal. If a strong
dose of the drug be used the lengthening is more considera-
ble and the secondary shortening slighter. Thus Kraepelin,
whose normal re-action was 183(7, after a strong inhalation
of ether re-acted in 298(7, and in the period of shortening in
170(7; while with a light narcosis the maximum re-action
was 223(7, and the shortened re-action 150(7. The effect of
alcohol, however, is a brief period of shortened times fol-
lowed by a long period of lengthened times. This is also
found by Orchansky, who, with a normal re-action of 155(7,
re-acts in 105(7 eight minutes after taking a dose of alcohol,
and in 225(7 after thirty minutes. The observations of War-
ren do not yield equally positive results, but do not conflict
with those of Kraepelin. Changes in the extent of the aver-
age variation have also been observed. On what psycho-
logical factors these differences depend it is difficult to say,
but the subjective feelings accompanying the lengthened
times are a difficulty in keeping the attention upon the mat-

MENTAL PHENOMENA.

ter iu hand, and an unwillingness to exert one's self. The
evidence afforded by the action of drugs upon these pro-
cesses is important as indicating the dependence of the
re-actions upon physiological conditions. A change of re-
action times in insanity has been frequently observed, but
the field for individual variation is here very large. It
seems probable that in most forms of mental disease, and
particularly in melancholia, there is a considerable length-
ening of the re-action time, amounting in extreme cases to
one half or three-quarters of a second. In the excited forms
of disease, such as mania, a shortening has been observed.
Obersteiner cites a case of general paralysis in the incipient
stages of which the thne was 1660", in a more advanced
stage 2810", in a most advanced stage 451<T. Stanley Hall
has found a marked shortening of the time iu the hypnotic
condition, but his result is not corroborated by others.

Methods of Experimentation.

The chief requisite in these experiments is an apparatus
for accurately measuring small intervals of time. The ear-
liest method, still in use, records the vibrations of a tuning-
fork upon the quickly-moving smoked surface of a rotating
drum, and beneath this the moment of giving the signal and
making the response. If a fork making one hundred vibra-
tions per second be used, whole hundredths can be directly
counted and smaller fractions estimated. Wundt has con-
structed a more accurate and specialized instrument in which
a fork making five hundred vibrations per second is used.
A very much simplified form of apparatus has been devised
by Obersteiner, in which the slide holding the record is
moved by hand, and the movement of re-action draws the
fork off the record; and by Bowditch, in which the fork it-
self carries the record, and the signal and re-action are indi-
cated by a shifting of the writing point. In the astronomical
records clock-work takes the place of a tuning fork. The
objection to these methods is that they necessitate te.lious
counting of curves. If the rate of the rotating-apparalus is
very uniform and frequently tested, one may substitute

24 THE TIME-RELATIONS OF

measuring- for counting-, but the most convenient apparatus
for the purpose is the Hipp chronoscope. This instrument
contains a fine clock-work, set iu motion by releasing a
spring and running for about half a minute. The hands of
the two dials, the one indicating tenths and the other thou-
sandths of a second, do not move until drawn away from a
set of cogs by the opening or closure of a magnetic circuit,
and are stopped again in the same way. By making- the
usual arrangement whereby the production of the stimulus
sets the hands in motion and the re-acting movement brings
them to a stand-still, we can read off directly the interval of
the re-action time. Unless we can afford to sacrifice accu-
racy for convenience, a means of controlling the chrono-
scope is indispensable. This may be done by timing the fall
of a ball from a given height and comparing it with the theo-
retical time. In the apparatus for this purpose supplied
with the chronoscope the ball is mechanically released, and
the mode of making the circuit is equally defective, so that
the error of the control apparatus is probably greater than
that of the chronoscope. To obviate this difficulty I make
use of a ball held in position by a magnet, and failing from
any height up to seven feet, upon the arm of a well-balanced
lever, thus securing an instantaneous release. By setting the
magnet and ball at different distances we are also enabled to
decide whether the error is absolute or relative. It is here
necessary to break the current by which the ball falls, and
to make the current by which the chronoscope starts at the
same moment; this is effected by a key specially devised for
the purpose. The chronoscope possesses a regulation for
altering its rate when too slow or too fast, but I find it
most convenient to make sparing use of this, and apply a
correction for each day's determinations as found with the
•'fall apparatus." Another form of control makes use of a
falling hammer, the record being also made with a tuning-
fork. A recent device of Ewald combines the two methods
by mechanically counting the vibrations of a tuning-fork: a
delicate armature is drawn to and released by a magnet with
each vibration of the fork, moving the hand of a dial over
one of its divisions as it does so. The fork is vibrating con-
stantly, but the making of the signal sends the current into
the u interruption-counter," while the re-acting movement
again diverts the current away from it. It will record at

IUKNTAL PHEXOMFXA. 25

the rate of one hundred per second. Galton has constructed
for ordinary uses a machine in which the signal is given by
the release of a rod or pendulum, and the re-acting move-
ment mechanically arrests the fall or swing, a scale of in-
terval being determined for the apparatus empirically. San-
ford has devised a simple but not expeditious chronoscope,
in which the signal and the response separately set in mo-
tion two pendulums of slightly different periods, the re-act-
ing interval being calculated from the number of oscillations
occurring before the two are in unison.

The methods of indicating the moment at which the
signal appeared and the moment at which the re-acting
movement was made are simple. When the record is writ-
ten on a rotating surface, a point connected with a magnet,
and writing a straight line beneath the vibrations of the
fork, writes that line at a different level when the signal is
given, and returns to the same level when the re-acting
movement is made; or the tuning-fork itself may be made
to write at a different level during the interval measured.
The arrangement by which the level is changed on the rec-
ord, or the hands are set in motion in the chronoscope at
the same instant that the stimulus appears, is equally sim-
ple. For sound, the noise of the key by which the circuit
is made is generally sufficient, or other sound may be pro-
duced by bodies falling upon various surfaces and thereby
opening or closing a key. For sight, the impression to
which a re-action is to bo made may be concealed behind a
screen, and the drawing away of this screen at the same
time makes or breaks an electric circuit. Frequently the
re-actor sits in the dark, and the impression becomes visible
only when an electric spark appears, or the spark itself may
be the stimulus. For touch, temperature, and taste, a typi-
cal device is that of Vintschgau, in which the end of a rod
touches the sensitive surface, and the pressure so exerted
makes a contact with a delicate metallic blade inserted in
the same apparatus. For smell, the movement by which
the odor is set free is similarly utilized. The re-acting
movement is usually that of pressing an ordinary telegraphic
key. Devices have been constructed by which movements
of the foot, of the jaw, of the voice and lip, may be similarly
noted. For more detailed descriptions consult the references
under this head at the end.

»b THE TIME-RELATIONS OF

Having- thus considered the time-relations of a simple re-
action, we may proceed, on the line of analysis there laid
down, to the consideration of the more complex forms of
re-action.

Adaptive Re-actions.

It has been noted that the prominent characteristic
of a useful re-action is the adaptation of the response
to the excitation by which it was called out. This
adaptation involves a recognition of the stimulus, and
its association with the movement in question. In this
recognition we found it convenient to distinguish between
the recognition of the presence and that of the nature of the
stimulus ; but it may be questioned whether we can recognize
the presence except by noting some point of the nature of
the stimulus, and whether the noting of this point does not
involve its distinction from others. If, in re-acting to a
sound, I recognize that it is the stimulus to which I am to
re-act, and press the key, does this mean that I know that
the stimulus is not a visual or a tactile one, that it is not a
higher or a lower, a louder or a feebler, sound ? Here, as
still more in the analysis to follow, our experimental basis
is defective.

Experiment has naturally followed the lines of conven-
ience and ready analysis; and as there has been little har-
mony in these analyses, and as the one here adopted differs
somewhat from those adopted by other writers, it will be
difficult to maintain the parallelism between theoretical
discussion and the obtained results. If we understand by
the simple re-action the mere signalling that a definite, pre
designated, and expected stimulus is present, and by an
"adaptive" re-action one in which the mode of response
depends upon and varies with the nature of the stimulus, we
may distinguish several stages of connection between the
two. as shown in the schedule at the top of the following
page.

MENTAL PHENOMENA. 27

I. A single stimulus with a single mode of re-action.
II. Several stimuli with a single mode of re-act inn.
(a) The subject foreknows the stimulus.
(6) The subject does not foreknow the stimulus.
III. A single stimulus icith several modes of re-action.

SIMPI.K UK-

IV. Several stimuli with several modes of re-action. ACTIONS.

(a) The subject foreknows the stimulus and al o he
re-action.

(b) The subject foreknows the re- action, but not the
stimulus

(O The subject foreknows neither stimulus ) ADAPTIVE RE.ACTION.
nor re-action. (

Or, more simply, if the re-action is foreknown, the pro-
cess is a simple re-action ; if not, it is an adaptive re-action.
In addition, in the simple re-action the foreknowledge of the
stimulus may be entirely definite, the stimulus always being
the same, or there may be a known range of variation or an
unknown range of variation ; while in the adaptive re-action
the possibilities are limited to the latter t\vo.

I. has been fully considered. In IT. (a) we have a num-
ber of different simple re-actions; but, instead of investigat-
ing them in separate series, we have different kinds in one
series: e.g.. a sound, a light, or a touch may appear, it being
announced to the subject which it is to be; and he in each
case re-acts by pressing the key. The impressions may be
more homogeneous, as a series of colors; but in all cases the
subject need not appreciate the nature of the stimulus, but
simply that a stimulus has appeared. In II. (6) the subject
knows the possible stimuli, but does not know which is to
come next; otherwise the conditions are precisely the same
as above. Wuiidt's experiment with the irregular change
between two intensities of sound would belong here, and
would indicate that this is an essential factor. In III. the
several modes of re-action are necessarily known in advance.
Instead of testing the different forms of re-actions in separate
series, we have several in one series. For example : we re.
act to a sound now with the thumb, then with the I'oivlinger,
the subject always knowing in advance what he is to do. In

28 THE TIME-RELATIONS OF

IV. (a) we are combining into one series different forms of
simple re-actions, differing both in stimulus and form of re-
action: but the complete reaction (e.g., red color to be
re-acted to by middle finger) is announced beforehand. In
IV. (6) the subject is told in advance how to re-act, but not
what the stimulus is to be. However, in both this and the
foregoing case he need not wait to recognize the nature of
the stimulus, but re acts as soon as he detects its presence.
All these are variations of simple re-action times. When we
pass to IV. (c), we have a different, namely, an adaptive,
re-action. The subject is not told any thing in advance ex-
cept the association upon which he is to re- act: e.g., if a blue
light, with the right hand ; if a red light, with the left hand ;
and so on. The essential difference here is that the subject
must first distinguish a certain feature of the nature of the
stimulus, in this case the color; then call up the appropriate
movement and perform it. A re-action of this kind, there-
fore, involves a definite distinction of stimuli, and a choice of

movements.

Distinction and Choice.

The mental processes involved in an adaptive re-action,
in addition to those involved in the simple re action,
are thus a more specific recognition of the stimulus,
and a choice between movements. By maintaining all
other factors alike, the difference of time of the two
modes of re-action measures the combined time of distinction
and choice. The first determinations of this nature were
made by Donders and his pupils (1865-68^. A simple re-
action to a light, white or red, was made in 201(7 (average
of five observers) ; but an adaptive re-action with the right
hand for the one light, and the left hand for the other, in
355o-,_a difference of 154(7. Cattell makes a simple adap-
tive re-action to two colors in 340(7, his simple re-action time
being 146(7, or a difference of 194(7 (XL). Miinsterberg re-
acts simply with any of the five fingers in 141(7, but re-acts

MENTAL 1'HKNOMEXA. 2!t

willi M definite finger (according as the numbers of the fin-
gers "one," "two,"' "three," etc., are called) in 195(7 longer
(XXIV.). Accepting these as values for the combined dis-
tinction and choice time under simple conditions, our next
step would naturally be to determine how much of the time
is due to distinction, how much to choice. This is a diffi-
cult step; for we cannot readily determine that a distinction
has been made, except by indicating it in the mode of re-
action, and we cannot execute a choice except upon the basis
of some distinction. The most usual experiment by which
it has been attempted to overcome this difficulty consists in
re-acting to only a designated one of a group of stimuli, allow-
ing all others to pass without re-action. To take a simple
case, let red and blue be the possible stimuli: if red appears,
re-act; if blue, do nothing. While this form of experiment
is interesting and useful, the inferences from it are not as
clear as could be wished. It may be termed the "incomplete
adaptive re-action," or briefly the "incomplete re-action."
It involves a distinction of the stimulus to be re acted to,
from those not to be re-acted to, and a choice between
motion and refraining from action. It seems probable that
these processes are respectively easier than a distinction that
cannot be anticipated and a choice between two movements;
but it seems equally probable that the extent of these differ-
ences will vary considerably under different circumstances.
If the simple re- action is of the quick, motor form, and the
incomplete re-action involves an additional distinction of
the stimulus, as well as the choice between motion and rest,
the additional time above the simple re-action would be long,
and the difference between it and the adaptive re-action
short. This is evidently the case with Cattell and Berger,
who, with a simple re action of 146 ff and 150(7, perform the
incomplete re-action in 306(7 and 277(7, the adaptive in 340(7
and 295(7 (IV. and XL). On the other hand, Dondrrs, with
an evidently sensory mode of re-action, has a simple re-

30 THE TIME-RELATIONS OF

action of 201(7, an incomplete of 237 (7, and an adaptive of
284(7. A second method attempts to deal with the difficulty
by delaying the re-action until the precise nature of the
stimulus has been appreciated, and regards the difference in
time between this and the simple re action as ' he time needed
for the distinction of the stimulus. There is nothing but the
subjective guaranty that the moment of re-action is coinci-
dent with the process of recognition, and we have no reason
to regard this guaranty as valid. There may be a tendency
to make the distinction on the basis of the after-image, and
thus signal the appreciation of it too soon; or, again, an
extreme desire not to re-act before the distinction is made
may delay reaction to an unusual length. Friederich's
investigations show for colors a simple re-action time of 175(T,
and a "subjective distinction" time of 267(7 (XXXIX.);
while Tigerstedt, and also Tischer, find only about half this
difference for nearly the same re-action.. It seems wisest,
under these circumstances, not to decide the relative shares of
the distinction and choice in the adaptive re action, but to
study the combined time as a whole, and the influences by
which it is affected. We can thus utilize the results of all
the methods for comparative purposes; and, in addition, we
can vary the complexity of the distinction while leaving the
choice the same (and to a more limited extent can vary the
choice without the distinction), and thus can in many cases
distinguish whether an increased complexity of an adaptive
re action is to be referred to an increase in the difficulty of
the choice or to an increase in the difficulty of the distinc-
tion.

It is desirable to analyze more particularly the nature of
the difference between the simple re-action and the "sub-
jective," and between the simple and the incomplete. An
essential point relates to the mode of re action, whether motor
or sensory ; nor is it necessary that the same mode of re-action
be followed in all cases. A few points here relevant are
illustrated in Tischer's results upon nine subjects with sound

MKNTAL PHENOMENA 31

re-actions and distinctions. The average of the nine gives a
distinction time of 159(T, and a simple time of I18o". Four
of the subjects evidently make vise of the motor re-action,
their simple time being 107(7, and their subjective distinction
116(7; i.e., the re-action takes place upon the appearance of the
stimulus, its distinction taking place later. Berger and Cat-
tell express the same difficulty, and for this reason discarded
the method. Their simple re-action to weak liyht was 198(7,
with distinction of intensity 208(7. Two of the subjects
evidently 7-e-act according to the "sensory" method, their sim-
ple re-action being 141(7, and the subjective distinction 246(7.
That these are not individual differences is shown by the
fact that the adaptive re-actions are about alike in all.
Similarly with regard to the difference between the simple
and the incomplete re action times. Dondeis, and those of
Tischer's subjects who re-act by the "sensory" method, show a
relatively small difference, though this is not true of Friede-
rich's subjects. While Tischer's "motor" subjects show a
difference of 159(7 between the simple and the incomplete,
the " sensory " subjects show one of only 61(7. Again, when
the re-action is " motor," the expectation is entirely directed
to the stimulus upon which re-action is to follow, and the
fact that other stimuli may appear hardly enters into the
experiment. This seems to he the case with Kries and Auer-
bach, who, with clearly "motor" re-actions, find a difference
of 30-40(7 for (XXX.-XXXYJ.) a variety of incomplete re-
actions. It may be added that the change from the simple to
the incomplete form of re-action will often bring with it an at-
tention to the sensory part of the process, and thus make the
difference between it and the simple time long. This seems
to be the case with Berger and Oattell, who. witli a simple re-
action time of 147(7 and 150 >. have an incomplete re-action
time of SOQ'J and 277o~. The difference between the incom-
plete and the adaptive re-action seems to be uniformly small
(many of the differences being not far from 40(7), though
the individual variations are considerable. It is likely that
the effects attributed to practice and fatigue may really be
due to a change from the sensory to the motor form of re-
action. Thus Kries and Auerbach mention that their incom-
plete times were at first very long, but that they became very
small, the reduction continuing long after the effect of pi tc-
tice upon the simple re-action had ceased. Again, the i'a<-t

THE TIME-RELATIONS OP

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34 THE TIME-RELATIONS OF

that simple re-action times are long when following complex
ones, or that subjective times are longer when following
adaptive re-actions, seems to be not so much the effect of
fatigue as of a continuance of a sensory mode of re-action.
It should also be mentioned that Tigerstedt ingeniously
proposes to measure the distinction time by taking the differ-
ence between two incomplete re-actions, in one of which we
re-act to a definite simple impression, and in the other to the
impression requiring distinction (e.g., in one series I re-act
to white, but not to a color; in the other, to a color, but not
to white); and the difference in time will be needed for
distinguishing a color from white. The general fact re
mains, then, that while the combined distinction and choice
times exhibit only such individual and other variations as
seem explicable by the differences in the conditions of ex-
periment (the adaptive re action times of eight of Tischer's
nine subjects fall between 293 and 3205"), the estimates that
have been attempted of the portions of the time due to dis-
tinction and to choice separately, show such large variations
as to force the conviction that the different experimenters
were not measuring the same processes.

Conditions affecting Distinction and Choice.
Bearing in mind that we are dealing with comparative re-
sults only, and comparisons restricted mainly to the results
of the same observer, obtained by the same method, we pro-
ceed to investigate the conditions by which these processes
involving distinction and choice are affected. It will be
convenient to begin with the effect of (1) the number of dis-
tinctions and of choices. The effect of the number of ob-
jects among which distinction is to take place, upon the time
needed to make the distinction, is best shown in the "incom-
plete" and subjective methods, in which the range of dis-
tinction may be varied without affecting that of choice.
For example: Cattell makes an incomplete re-action to a
certain color when either that or one other color may appear in
306o", when either that or any one of nine other colors may
appear (IV and V.) in 3130". Friederich's subjects make a
subjective distinction bet ween two colors in 267<J, between four

MENTAL IMIKNOMENA.

in 296<7 (XXXIX. and X I,.). Six of Tischer's subjects make
a subjective distinction between two sounds of different inten-
sity in 146(7 (simple re-action, 114 (7) ; between three sounds,
in 1640"; four sounds, in 178(7; five sounds, in 194(7 (XLIV.-
XLVII.). Other experiments cited in the table (p. 32) show
the same slight increase of distinction time with the increase of
the range of impressions, but complicated with other factors
as well. With regard to the effect upon the choice time
when the number of possible choices increases, we have the
results of Merkel, who found for the simple re-action time of
ten subjects to visual impressions 1883"; for an adaptive re-
action between two impressions, 2760"; between three, 3300";
between four. 3940"; between five, 4450"; between six, 489(7;
between seven, 526(7; between eight, 562(7; between nine,
581(7; and between ten, 588(7 (partially cited in XL VIII.-
L1I.). The impressions were the numbers 1, 2, 3, 4, 5, and I.,
II., III., IV., and V. The re-actions to movements of the ten
fingers naturally associated with these impressions, and the
naturalness of this association doubtlessly contributes to the
small increase in time. Miinsterberg called these numbers
and re-acted in the same way, finding for a choice between
five movements 383(7. and between ten 478(7 (simple re-action
being 162(7). Martins finds for the same re-actions 474(7
and 552(7 (average of three observers). It being established
that but a small share of the increase is due to the
distinction (Merkel has experimentally shown this for
his subjects), we may conclude, that, with an increase
in number, the difficulty of choice increases rr.ore
rapidly than the difficulty of distinction. In addition, we
have reason to believe that the increase would be still more
marked in case the association between impression and
motion is artificial. When this association reaches the
maximum of natutalness, in naming objects, the increase
with the number of impressions is slight Thus it may !><•
calculated from Cattell's results that it takes him but a

36 THE TIME-RELATIONS OF

100" longer to name 26 letters or short words than to name
one of two, but QQff longer to name one of 26 than one of
two pictures, and 163(7 longer to name one of ten than one
of two colors; the action of naming being more closely re-
lated to letters and words than to pictures and colors.

It is the ability to deal promptly and correctly with a large
and varying number of impressions, disposing of each in its
appropriate way, that we recognize as evidence of mental
power, and it is this that experiment shows to be a factor
of great influence upon the time of an adaptive re-action.
It is the skill in disposing of so large a number of adaptive
re-actions that we admire in the post-office clerk, and in many
other exhibitions of manual dexterity. It is this that necessi-
tates the division of labor, there being a limit to the number
of adaptive re-actions that can be economically controlled.
Again: the fact that a large number of distinctions does not
complicate the process as much as a large number of choices,
finds its analogue in the observation that our power of re-
production falls below our powers of appreciation. This
plays a part in the fact that we learn to understand a lan-
guage long before we learn to speak it, and in many similar
processes. The development of mental power reveals itself
as an increasing facility in performing a large number of
complicated adaptive re-actions; and here, too, the power
of appreciating distinctions develops earlier than the power of
choosing. This result was illustrated experimentally in a
brief study of the re-action times of a ten-year-old child as
compared with those of an adult. While the pure distinc-
tion time rose from 58 ff to 250(7 as the impressions to be
distinguished increased from two to five 'subjective method,
with colors), as compared with 44(f and 78(7 for adults, for
the adaptive re-action for two impressions the time was 120(7,
for five impressions 603(7, as compared with 79(7 and 210 ff
for adults.

We may conveniently introduce the general topic of the

MENTAL PHENOMENA. 37

effect of the nature of the distinction and the choice upon
the time of its performance with ths consideration of a few
points affecting th'e distinction alone. (2) The similarity
of the impressions. The endowment of the various sense-
organs varies considerably (e.g., the sense of musical pitch is
finer than that of sound intensity) ; but, in the absence of a
standard of comparison of sense-differences in disparate types
of sensation, we can only illustrate the point in question by
varying the difficulty of distinction within the same sense.
Thus Kries and Auerbach find that it takes much longer to
tell whether a sound is to the right or to the left, according
as the two points at which the sound is produced are closer
together. When they form an angle of 35°-120° with the
centre of the face, the additional time (by the incomplete
method) was 17 ff; when varied between 35° and 26°, the
time was 78ff; when within 26° and 11°, it was 137(7. The
ease of distinction is largely a function of practice. We
readily seize the slight optical differences furnished by the
different letters of a known language, but constantly con-
fuse much greater sense differences with which we are less
familiar. (3) The specific nature of the impression. Very
many of the results cited in the table may be said to illus-
trate the effect of a change in the nature of the distinction ;
but it is difficult to show this, uncomplicated with other
variations. The determinations of Kries and Auerbach
(XXX.-XXXVIII.) show the result of distinctions of vari-
ous kinds, though an analysis of the causes of these differ-
ences is hardly practicable. It is quite clear that in re-act-
ing by the incomplete method the re action is shorter when
the stimulus is the stronger of t\vo intensities than when it
is the weaker of the two (XXXVI and XXXVIII.). Berger
has also shown that the intensity of the stimulus has some
influence upon the distinction time beyond what would be
due to the effect upon the simple re-action time therein con-
tained. The difference between the corresponding simple

;!S THE TIME-RELATIONS OF

and the incomplete re-action to a bright light is 85tf; to a
medium light, 119(J; to a weak light, 114(T; while similar
differences for adaptive re-actions are 167<7, 179 ff, 1925"; the
inference being that the intensity of the stimulus affects the
distinction rather than the choice. Again (in the series
VI. -X.), we find that Cattell recognized most quickly that
an expected one of 26 pictures was present, then that one of
26 letters, next one of 28 short English words, next one of
26 short German words. The differences between the time
for recognizing letters and short words is very slight com-
pared to the increase in complexity of the impression, and
thus shows the effect of practice in recognizing words as a
whole. Furthermore, in the series of experiments (partly
cited in XLT.-XLIIF.) in which one to six place numbers
were recognized, while there is a concomitant increase in the
number of possible impressions, it seems fair to refer the
main increase in time to the increasing complexity of the
impression. In passing from the recognition of one to two
or of two to three place numbers, the increase in time is
slight; but from there on, the increase itself increases with
the increase of the number of numerals (53 ff, 147 ff, 322<r),—
a fact probably related to the practice in grasping numbers
in groups of threes. Another series (XXIV. -XXIX ) may
be mentioned here, and is interesting as indicating that it is
more difficult to tell to which of five categories (a city, a
river, etc.) a word belongs than what part of speech it is;
and this is in turn easier than to tell the sphere of activity
of a noted man. It should be noted that the choice, the
range of impressions, the connection between impression
and movement, the method of re-action, are equivalent hi all
three experiments; so that the difference is fairly referable
to the distinction process involved. We may finally notice
as here pertinent the observations of Vintschgau upon the
distinguishability of different tastes. He found that by the
incomplete method it took longest to re-act to bitter when

MENTAL PHENOMENA. :>>!)

the alternative \vas distilled water, next long to sweet, next
to sour, and shortest to salt. Similarly, in adaptive re-ac-
tions with the two hands to all possible combinations of .two
of the four tastes, salt was most quickly re-acted to (384(7),
sour next (397(7), sweet next (409(7), and bitter last (456(7).

(4) The Foreknowledge of the Subject. Within the re-
striction that the foreknowledge of the subject shall be
limited to the knowledge of the associative boud between
stimulus and movement, there is room for variation. The
simplest case would present but one stimulus re-acted to,
and but one not re-acted to, or, in the adaptive re-action, but
one stimulus for each mode of re-action. In all such cases
(I., II., IV., XI., XXXVIII., may be cited as instances)
the foreknowledge of the subject presents the maximum of
definiteness. Any departure from these conditions brings
with it an increase in the time of re action. Cattell finds
but a very slight increase (5-7(7) in the incomplete re-action
when the stimulus not re-acted fo, instead of being but a
single one, is any one of ten colors, but finds a greater in-
crease (15(7, difference of II. and III.) when the stimulus
re-acted to, instead of being a single one, is one of ten
colors, though the particular kind of color need not be recog-
nized. Both the stimulus re-acted to and the one not re-
acted to might be one of a larger or smaller, a more or less
homogeneous group; but I am unable to find a rrcoid of
such an experiment. The somewhat modified form of ex-
periment adopted by Tigerstedt and Bergqvist shows a similar
result. They re-acted to a light, when either the light or a
one to three place number might appear, in 297<T, and to the
number (including its recognition) in 318(7. If the number
of digits of the numbers that may appear is foreknown, the
time is considerably reduced; and when either the light or a
foreknown letter might appear, the time for recognizing the
light was still further shortened (190(7). The same scries <>f
variations could be applied to adaptive reactions (i.e., one

THE TIME-RELATIONS OF

or more, or all, of the modes of re-action might be associated

with any member of a variable group of stimuli), but experi-

ments designed to show the effect of such variations are

lacking. Mention should be made, however, of the experi-

ments of Miinsterberg, in which he first re-acts witb the five

fingers to five categories, each limited to one term (XXIV.

and XXV.); then to five categories, each comprising three

terms (XXVI.); and then to five categories, each com-

prising a practically indefinite number of terms (XXVII.,

XXVIII., XXIX.); and finds an increase of time in making

these steps (Martius has repeated experiments XXV.,

XXVI., and XXVII., finding the times to be 551ef, 644ff,

and 804ff). Although other factors contribute to this in-

crease in time, part of it may be referred to the decreasing

definiteness of the foreknowledge of the subject. It may be

added, that the mechanism by which an increase in the

number of possible re-actions increases the re-action time

is allied to that by which a decrease in the foreknowledge of

the subject does so.

The effect of the mode of re-action upon the re-action
time is the same here as in the simple re-action. Re-acting
by the voice in the incomplete form of re-action has been
found to be longer than re-acting by the finger; and when-
ever the re-action takes the form of speaHng or naming, it
takes some time to place the organs in position and speak
the word. But a very special and important effect in adap-
tive re-actions is that of (5) the association between move-
ment and stimulus.

As the effect of a special or a general practice, certain
modes of re-acting to certain types of stimuli have become
natural, easy, and familiar, while in other cases (e.g., the
re-acting by pressing a key, —a process learned only for the
purposes of the experiment) the association is extremely
artificial If we compare, in Miinsterberg's series, the ex-
periment in which the five fingers re act to the numbers

MENTAL PHENOMENA. 41

"one," "two," "three,'1 "four," "five" (XXIV.), with
that in which they re-act to the declensional forms of a Latin
noun (XXV.), we recognize that the former is a more natu-
ral association than the latter, and seem justified in at-
tributing a good share of the increase in time to this differ-
ence. Again: to re-act by naming is a process in which we
have had considerable training, and it is quite evident that
the time needed for naming one of 26 different impressions
(XV.-XVJIL, and XX.) is much shorter than would be
needed for re acting by 26 artificial and irregular movements
of the hand. The difficulty in learning a foreign language,
or a telegraphic code, or a shorthand system of writing, is
largely the difficulty of forming associations between com-
plex stimuli and movements; and the great decrease in time
that is brought about when such associations have been
mastered emphasizes the importance of the factor now under
discussion, which, in turn, may be regarded as an expression
of the effect of practice.

We may push the analysis a step farther. The process of
naming is much more closely associated with a word or a
letter than with a picture or a color; for the former are
artificial symbols, becoming significant only when so
interpreted, while the latter reveal their meaning directly
without needing to be named or read. Accordingly, we find
that it takes longer to name a color (6010") or a picture
(545(7) than to name a letter (4240") or a word (409(7), though
the recognition of a color or a picture is a quicker process
than the recognition of a letter or a word (compare XV.,
XVII.. XIX., XX., and V., VI., VII., X ). Furthermore,
if the time of naming or reading is thus mainly conditioned
by the strength of association involved, we may in turn
utilize this process as an index of familiarity with the nam-
ing or reading, or, more briefly, with the language. Thus
Cattell, an American, reads English words more quickly
than German (XVII. and XVIIT. t, while with Berger, a

42 THE TIME-RELATIONS OF

German, this relation is reversed. To name a picture in
German occupies Cattell for 614(7; in English, 588 ff. It
occupies Berger in German for 501(7; in English. 580(7. The
inference is the same (though the absolute time is much
shorter) if we read words in construction instead of isolated.
By this method Cattell finds that he can read an English
word in 138(7, a French in 167(7, a German in 250(7, an
Italian in 327(7, a Latin in 434(7, and a Greek word in 484(7,
this being the order of his familiarity with these languages.
The particular nature of the association may be revealed in
the study of these time-relations. Thus, while in all cases
it takes longer to read words from right to left than from
left to right, this difference is relatively least in the least
familiar languages; i.e., in those in which the bond of asso-
ciation between the words is least significant. For a like
reason letters are read much more quickly from above down-
wards (102(7) than from below upwards (264(7).

(6) The Overlapping of Mental Processes. We pass
now to a point of critical importance in the application of
results gained in the laboratory, to the mental operations of
daily life. While in the former case we are performing a
set task, isolated for purposes of investigation, in the lat-
ter case (i.e., in such operations as reading, copying, play-
ing upon instruments, and the like) we are performing a
continuous, more or less extended, series of re-actions, bound
together by bonds of common purpose and associations of
habit. It is not a mere aggregate, but an organization of
mental processes ; and this makes possible the performance
of the several factors of the process in part at the same time.
It leads to an "overlapping" of the mental elements. It is a
proficiency in thus doing several things at once that consti-
tutes much of the difference between the expert and the
novice; and it is this "telescoping" process that seems to be
the method by which complicated operations are at length
performed in short times. It is for this reason that the time

MENTAL PHENOMENA. (:',

per word of reading 100 words is shorter than the time of
reading a single word. Cattell reads a short word in 4090",
a long one in 4510", but 100 such in 255(7 per word, and, if
the words are in construction, in 125(T per word ; thus indicat-
ing how much of the difference between ordinary reading, and
reading single words, is due to the continuity of the experi-
ment, how much to the association between the words. So,
also, Cattell reads a single letter in 424<7, but 100 such in
224(7 (compare XVII., XV., with LIIL, LIV.). When the
series is too long continued, fatigue sets in, and the time is
again longer; it is longer for 500 than for 100 words and
letters; and for colors and pictures there is no saving in
naming 100 above naming a single color or picture.

A special study of this power of grasping several things at
once was made by Cattell by having letters move along on
the surface of a rotating drum, and varying the width of a
slit in a screen through which they were read. When the
slit just allowed one letter to be seen at a time, they could
be read at the rate of one letter in 228(7; and as the slit was
widened to admit two, three, four, five, and six letters at
once, the rate increased to one letter in 200(7, 178 (7, 166 ff,
160(7, and 160<7. As it takes 424(7 to name a letter singly
("XV.), it would seem that the whole of a letter need not be
seen at once to be recognized, — an inference corroborated bv
the fact, that, when the slit admils only one-tenth of a let-
ter at a time, the letters can be read at 4000" per letter. The
result also indicates that there is a limit to the power in
question. M. Paulhan finds similar results in more complex
operations. He multiplies numbers and recites a verse or
two at the same time ; and the time needed for this is shorter
than the sum of the times required to do each separately.
In very simple cases the time of doing both together is not longer
than the time for doing the more difficult of the two separately.
The mind should accordingly not be likened to a point at
which but a single object can impinge at our time, but

44 THE TIME-RELATIONS OF

rather to a surface of variable extension. It should like-
wise be noted that the performance of a complex and ex-
tended mental task is not the same thing as the separate
performance of the several elements into which that task
may be analyzed.

Mtinsterberg has applied the distinction between the
sensory and motor form of re-action to complicated adaptive
re-actions, and regards it as there involving the overlap-
ping of mental processes. The times cited in the table
(XXIV.-XXIX.) in Munsterberg's experiments refer to
sensory re-actions. In these the attention is directed
to the word about to be uttered. It is recognized, and re-
ferred to its group. The corresponding movement is then
aroused and performed, the several processes being succes-
sive in time. In the motor form the word is thought of as a
"forefinger-moving" word; and the movement upon which
the attention is kept fixed is expectantly kept ready to be
set off at the slightest notice. The several processes thus
play into one another, some perhaps entirely falling away.
Both anticipatory movements and errors (moving the finger
next to the correct one) are not infrequent. The motor
times for the series XX IV. -XXIX. are 289, 355, 430, 432, 432,
and 437 6; the differences between motor and sensory times,
94, 110, 258, 280, 461, 6850". Until these very important and
striking results are better understood, it would be unwise to
enter into a discussion of them. Martius has very recently
repeated some of Munsterberg's results (XXLV.-XXVII.),
and not only fails to corroborate them, but finds that the
attention to the movement about to be made lengthens the
time. He holds that the distinction between motor and
sensory re-actions is applicable only to simple re-actions,
and, while unable to explain Munsterberg's results, does not
believe the difference there involved to be the same as that
involved in simple re-actions. It remains for future research
to shed light upon the problem.

(7) Practice and Fatigue. What was said under these
headings of simple re-actions applies with equal force to
complex ones. Various experimenters notice the decrease
in time as the experiments proceed. They note that this

MENTAL PHENOMENA. C,

decrease is relatively greatest at first, and in those individu-
als and processes whose time is relatively longest at the out-
set; also that it soon reaches a limit, and, when once thor-
oughly acquired, is not liable to be lost after a moderate
degree of disuse; and that it at times seems to be confused
with a transition from a sensory to a motor form of re-ac-
tion. As illustrative of one or other of these points, it may
be mentioned that Tischer finds as a rather typical case the
decrease of a distinction time from 1600" in the first set to
95(7 in the second, and 860" in the third, all reduction ceas-
ing on the average after 5.5 sets; that Trautscholdt, in re-
actions consisting of repeating a word, finds times of 299,
273, and 258, and in another case of 205, 176, and 155 G, in
three successive periods of fourteen days each; that Ber-
ger and Cattell, beginning with some practice in experi-
ments of this kind, find the time for incomplete re-actions
reduced by 30 and 20(7 after four months' experimentation;
and, finally, that the great decrease in the incomplete re-
actions of Kries and Auerbach (from 64 and 117 to 21(7,
from 153 and 109 to 36 ff, from 104 and 97 to 49 and 54(7, in
various experiments) strongly suggests a radical change in the
mode of re-action. Another aspect of the effect of practice
appears in a study by Berger of the times required by the
boys of the nine classes of a German Gymnasium, and of
the class preparatory to the Gymnasium, to read 100 and
500 words in construction in German and in Latin at a
maximum and at a normal rate. There is a constant de-
crease in time as the boys advance in age. In Latin the several
times per word were 262, 135, 100, 84, 79, 57, 54, 49, 48, 43(7 ;
in German 72, 55, 43, 37, 39, 28, 27, 26, 25, 23(7; the great
difference between the first two times in Latin being due to
the fact that the boys who required 262(7 to read a Latin
word had never learned Latin at all. That these differences
are to be referred to specific practice rather than to general
mental maturity, appears from a comparison of the above

40 THE TIME-RELATIONS OF

times with the times required by those boys to name colors;
viz., 135, 99, 119, 123, 100, 91, 112, 99, 86 ff.

The results regarding fatigue are not equally definite.
Many mention the general fact of fatigue, and to avoid it
perform but few experiments in a series. We have already
seen that it takes relatively longer to read 500 letters, words,
colors, pictures, than to read 100. On the other hand, Cat-
tell, after a very long series of re-actions, found no serious
or constant increase in the time, but seemed to feel the ef-
fects of fatigue on the following day. Both practice and
fatigue are subject to large individual variations. Oehrn
has studied the minor variations of practice and fatigue in a
session of two hours1 work, finding first a stage in which
practice outweighs fatigue, and then a stage in which the
reverse is true.

(8) Miscellaneous and Individual Variations. The
complex re-actions, just as the simple ones are subject to the
influences of distraction, vary under the action of drugs, in
morbid conditions, and present large individual variations.
These points, though frequently noticed incidentally, have
not been subjected to special study, so that briefly citable
and conclusive figures are lacking. Regarding the action of
drugs, Kraepelin is inclined to believe that the distinction
is, under their influence, almost always rendered more diffi-
cult, being only slightly subject to the period of shortened
times, while the choice factor very readily becomes shorter
than the normal. Marie Walitzkaja finds that the complex
re-action times in the insane differ more from the normal
than do their simple times. __ An adaptive re-action for the
two hands which for the normal required 351-406(7, required
707-9435" in cases of general paralysis, and 1085 ff in a case
of mania. These should, however, be regarded as individ-
ual rather than general results. The individual variations
may be regarded as increasing with the complexity of the
re-action. Men differ more from one another in the time

MENTAL PHKNOMKXA. 47

needed for doing difficult things than in the time needed for
simple things. Systematic experimentation upon this point
is lacking: but a suggestion of the truth may be obtained by
calculating the average deviation from their mean, of Mer-
kel's ten subjects in their simple re-action times, their sub-
jective distinction times, and their adaptive re-action times;
the result being 2.23 per cent, 3.35 per cent, and 6.79 per

cent.

Association Times.

While the effect of the association between stimulus and
movement upon the time of the re-action has been already
discussed, the process of association forms so important a.
factor in our mental life, that it requires a more specialized
and independent investigation.

(1) Questions ivith but a Single Ansiver. We may
view an adaptive re-action under the aspect of a "question
and answer;" the stimulus being equivalent to the question,
'What, with regard to certain points, is this impression?"
and the answer, whether indicated by a name, or word, or
movement, is given in the re-action. Our problem is to in-
vestigate the time-relations of these questions and answers,
as an index of the readiness of the association between the
two. The processes intervening between the appreciation of
the question and the formulation of the answer may vary
greatly in complexity and character. A common character-
istic of the re-actions hitherto regarded consisted in the fact
that the material for forming the answer is simply and di-
rectly supplied by the stimulus itself: it is in the main a
verdict regarding the particular nature of sensation then
present. The re-actions to which we now pass all include
something more than this; and the formulation of the an-
swer involves to a greater or less extent more complicat>-:l
forms of mental activity, and depends more or less upon the
past experiences, the special habits and tendencies of mind,
of the individual.

48 THE TIME -RELATIONS OF

While the line of division between the direct appreciation
and the indirect interpretation of a sense-impression cannot
be rigidly drawn, and while it is no less difficult to decide
what processes are involved in this interpretation and elabo-
ration of the sense-impression, yet we may with sufficient
precision mark out as the first class of associations (a) those
in which a simple act of memory plays the chief role.
Thus, when Cattell, instead of naming a picture in his own
language (which he does in 545(7), names it in German (in
6940"), the difference in time is needed for calling to mind
the German name, and measures the strength of this asso-
ciation. Berger's acquaintance with English is less than
CattelTs with German, and accordingly with him the differ-
ence between naming a picture in the vernacular and in a
foreign language is greater (477 ff and 649(7). The transla-
tion of a short familiar word from English to German occu-
pies Cattell 686(7; from German to English, but 5SO<J; the
time for long and less familiar words being much longer.
(We may obtain the portion of the time required for the act
of translation alone by subtracting from this the time to see
and name a word, 428(7.) Such operations as addition and
multiplication, when confined to numbers of one place, can
hardly be more than acts of memory. Cattell adds such
numbers in 336(7; Berger, who is a mathematician, in 221 ff.
The former multiplies them in 544^7; the latter, in 389(7.
Vmtschgau's three subjects multiply such numbers (though
under different conditions) in 233(7. More complicated types
of "memory re-actions" have been performed by Cattell and
by Miinsterberg. The former determined in separate series
the time necessary, when given a city, to name the country
in which it was situated (462(7); when given a month, to
name the season to which it belongs (310(7), to name the fol-
lowing month (389(7), to name the preceding month (832(7);
given an author, to name the language in which he wrote
(350(7) ; given an eminent man, to name his sphere of activity

MENTAL PHENOMENA. 49

(368(7). Miinsterberg constantly varied the type of question
including suck as the above, the position of cities, the quali-
ties of objects, the relations of men, and many others, find-
ing an average time of 848(7 (average of two subjects).
While many of these determinations are doubtless of more
individual than general value, we may stop to note a few
points that are presumably typical. The re-actions here
grouped under one class vary considerably in difficulty, and
a few instances may be cited to indicate the range of this
variation. In giving a country in which a given city is
situated, the shortest time is for Paris (278ff) ; the longest,
for Geneva (4850"). In giving the language in which an au-
thor wrote, Berger requires least time for Luther (227(7) and
Goethe (265(7), most for Bacon (565(7); Cattell, least for
Plato (224(7) and Shakspeare (258(7), most for Plautus
(478(7). In giving the calling of an eminent man, the least
time is required for poets (291(7), the longest for men of
science (421(7). Miinsterberg mentions as quickly answered
questions (400(7 to 600(7), "On what river is Cologne?" " In
what season is June?" "In what continent is India?" as
questions requiring a long time (1100(7 -1300(7), "Who is
the author of Hamlet?" "What is the color of ice?" "Who
was the teacher of Plato?" An influence which we have
found of great significance hitherto is equally important
here; viz., the foreknowledge of the subject of what is to
occur. In Cattell's experiments the general question is vir-
tually asked once for the entire series, the special terms be-
ing given in each experiment, while in Miinsterberg's results
the entire question changes with each observation; and this
difference in the expectancy of the subject cannot but be an
important factor in the longer times found by the latter. A
somewhat different phase of this influence appears in the
results of Vintschgau. In multiplying the numbers from
1X1 to 9X9, the smaller number was always announced
first. Accordingly, when the first nine was announced, the

50 THE TIME-RELATIONS OF

subject practically anticipated the result, and had the prod-
uct ready; when eight was announced, he knew that it was
one of two results; when seven, one of three; and so on.
Accordingly we find these to be the shortest processes (9x9,
only 160(5") but there is another factor at work counteract-
ing this effect, viz., the familiarity of certain multiplications,
making the products by one short, and those by four and
five long.

(b) The next type of "question and answer11 will be one
in which, in addition to the act of memory, a comparison,
or a judgment, is involved. The result of the comparison,
thougb not always the same for all individuals (and in this
sense the question is not limited to a single answer), will
probably always be the same in the same individual. The only
experiment of Cattail's that seems properly to belong here is
that in which the subject decided which was the greater of
two eminent men (558(7). Munsterberg finds the average
time for answering a miscellaneous group of such compari-
sons 947(7, or 99(7 longer than the process without compari-
son: comparisons rapidly made (600(7-800(7) being, "Which
has the more agreeable odor, — cloves or violets?'' "Who is
greater, — Virgil or Ovid?" "What is more beautiful, — woods
or mountain?" and difficult questions (1200(7-1500(7) being,
"Which is healthier, — swimming or dancing?" "Which do
you like better, — Goethe's drama or his lyric?" "Which is
more difficult, — physics or chemistry?" The comparison
may be among more than two objects. Thus, in asking which
is the finest of Goethe's dramas, the process of formulating
the reply may include the calling to mind what the various
dramas are, and a choice among them; not, of course, a con-
siderate judgment, but the selection, under the necessity of
an immediate answer, of one deciding motive. On the other
hand, among the several possibilities, a certain one may, by
habitual association or for other reasons, have become &o
prominent that virtually no comparison ensues; and the

MENTAL PHENOMENA. 51

relatively slight excess in time of this type of association
above the former ones (1049<7) suggests that this was often
the case. To decide which is the pleasantest odor (rose), or
which the most important German river (Rhine), required
only between 6000" and 700(7; to decide which was the most
difficult Greek author (Pindar), or your favorite French
writer (Corneille), from 14000- to 1600(7.

Miinsterberg has ingeniously modified this form of experi-
ment to show the influence of the foreknowledge or pre-
paredness of the subject. He precedes the asking of the
question by a dozen or so words of the category within
which the comparison is to be made. Thus, ''Apples, pears,
cherries, peaches, plums, grapes, strawberries, dates, figs,
raisins: which do you like better, — grapes or cherries?"
Although the comparison cannot be begun until the last
word is heard, still the subject has in a way anticipated the
general nature of the question, as well as the scope of the
comparison, and has reduced the time considerably (676(7, as
compared with 947(7), — certainly a striking result.

(2) Questions with More than a Single Answer. In the
class of re-actions to which we now pass, the question ad-
mits of several answers. The answer at one time may
not be the same as at another time; and the determining
factors in the particular character of the answer are the
peculiar mental habits and tendencies of the individual.
The question thus changes from a specific to a general one,
the answer being any member of a more or less extended
class answering to such and such a description. In some
the choice may be somewhat limited. This is true of Cat-
telFs experiments in which, given a country, we are to name
a city in it (346(7); given a season, to name a month in it
(435ff); given a language, to name an author writing in
that language (519(?) ; or, given an author, to name any work
of his (763(7). In all these cases we are apt to have in mind
only a very few prominent instances under each head among

52 THE TIME-RELATIONS OF

which individual preference is exercised. In the following
series the classes are more general, and accordingly the
scope for individual preference much larger: given a general
term to name a particular instance under that term (537 ff) ;
given a picture to name some detail of it (447 ff) ; given the
word instead of the picture, to make a similar association
(439(7) ; given the picture or the name to mention some prop-
erty of it (372(7 and 337(7) ; given a quality to name an ob-
ject to which it can be applied (351(7); given an intransitive
verb to find an appropriate subject (527(7), or a transitive
verb to find an appropriate object (379<J). Miinsterberg has
a series including a miscellaneous collection of such re-ac-
tions, and finds a time of 1036(7. Trautscholdt has investi-
gated a similar series in which a specific instance of a gen-
eral term had to be given, and finds a time of 1020(7 (average
of three subjects), 155(7 of which must be deducted to get the
pure association time.

Here, again, we may stop to consider a few generalizations
which these results seem to sustain. The processes involved
vary very considerably in the different experiments. Miin-
sterberg cites as quick responses (450(7-600(7) the instancing
of ' a German wine (Rudesheimer)," "of a number between
ten and four (six),' "of a Greek poet (Homer);" as slow
ones (1200(7-1500(7), "a beast of the desert (lion),1' " a French
author (Voltaire)." Trautscholdt names " mast "as "a part
of a ship" in 391(7, but requires 1899(7 to name "art" as
' an aesthetic activity of man." These differences should ap-
pear in the average variations: that is, the average divergence
of the re-action times from their mean. When the process
is simple and constant, the average variation is small ; when
the processes are complicated and variable, the average
variation is large. While in simple re-actions it is often less
than 10 per cent of the re-action time, it is not infrequently as
high as 30 per cent in the re-actions just considered. It may
have been noticed that in certain cases the process in (2) was

MENTAL PHENOMENA. 53

the reverse of that in (1). The one was a step from the
whole to the part, the general to the special; while the other
was from the part to the whole, the special to the general.
In CattelTs case 'the former is the longer (433(7 and 374(7).
In Trautscholdt's results the conclusion comes out more
clearly, the pure association time of an association of part to
whole is 608(7; of whole to part, 901<7; of special to general,
754(7; of general to special, 947(7. It is thus easier to refer
an individual ohject or quality to its class than to give an
instance of a general concept. A similar result (namely,
that the bond of association between two concepts is not
equally strong in both directions) is derived from observing
that it takes longer to recall that May precedes June than
that June follows May, longer to go back and find a subject
for a verb than to go forward and find an object for it, longer
when given a quality to find an object possessing that quality
than to recall a quality for an object, and so on.

We may here also conveniently consider the overlapping
of mental processes, which we have found takes place when-
ever a series of simple processes, or a complex process in-
volving many simple ones, is performed. The general truth
that the time of a complex mental operation is less than the
sum of the times needed for the performance of the separate
factors into which the former may be resolved, will be again
illustrated. Thus Mtinsterberg finds that it takes 103(7 to
name a specific instance of a class (e.g., to name a German
river), 992(7 to make a comparison, (e.g.. Which is more im-
portant,— this river or that?) but only 1049(7 to decide
both questions together (e.g.. Which is the most important
German river ?) In this case we clearly recognize that the
last pi'ocesses are not the sum of the preceding two, but that
the category "most important German river" is already
formed in the mind. The following comparisons are more
illustrative. Instead of asking first, "Which is the most
important German river ?" (1049(7,) and then, " Which lies

54 THE TIME-RELATIONS OF

more westerly, -- Berlin, or the Rhine?1' (992(7,) we ask
at once, "Which lies more westerly, -- Berlin, or
the most important German river ? " and find the time
18550", or 176 ff less than the sum of the two foregoing
processes. Similarly, if instead of asking first, "On what
river is Cologne situated?" (848 ff,) and then, "Which is
more westerly, — the Rhine or Berlin ?" (992(7,) we ask at
once, "Which is more westerly, — Berlin, or the river on
which Cologne is situated ? " we find a more remarkable
saving of time (1314(7, or 526(7 less than the sum of the two
questions). This time was still further reduced to 1149<T
when the question was preceded by a list of a dozen cities.

(3) Unlimited Associations. When we pass to the re-
action of naming as rapidly as possible any word whatever,
that is suggested by a given word, we are drawing entirely
upon the natural associative habits of the individual, and
accordingly this method has been most useful in studying
psychological habits and tendencies. Our present purpose,
however, is only with the time-relations of this unrestricted
association. This has been the type of association first and
most frequently investigated, and it is customary to speak of
the " pure association time " as the total time minus the time
needed to repeat a word. Thus Miinsterberg repeats a word
in 3820", and calls out a word in association with the given
word in 896 ff. Trautscholdt, however, who experimented
upon Wundt, Stanley Hall, and two other subjects, finds an
average time of 1024(7, 727(7 of which is regarded as the
pure association time. Galton and others have made esti-
mates, by rougher methods, of the rapidity with which
trains of ideas pass through the mind, and the result is a
rate not differing much in either direction from one associa-
tion per second. It will be recognized at once that this pro-
cess will be very different in different individuals and with
different words. Miinsterberg's shortest association was
"gold-silver" (390(7); the longest, "sing-dance," "moun-

MENTAL PHENOMENA. -Vi

tain-level'' (1100(7-14000-). Trautscholdt also found " gold-
silver " a very quick re-action (4020-), " storm-wind " (368(7),
" duty-right" (415(7). Long re-actions were " God-fearing "
(1132(7), "throne-king" (1437(7), " Karl- August" (1662(/).
Some interesting inferences result from the consideration of
the times of different types of these unrestricted associations
Trautscholdt divides these into " word associations," or those
suggested hy the word rather than by the thing; "outer
associations," or those relating to the sense-qualities of the
object; and "inner" or logical associations. The results
were 1033;7, 1028(7, 989(7, though this order may be liable to
individual differences. Cattell and Berger have also com-
pared the re-action times to concrete nouns (374(7, pure asso-
ciation time), to less concrete nouns (462(7), to abstract nouns
(570(7), and to verbs (501(7), clearly showing that concrete
terms are more readily suggestive than abstractions, and
concrete objects more so than actions. Trautscholdt finds
for associations to concrete nouns, 710(7; to actions, 837(7; to
abstractions, 871(7.

Many of the influences to which we found simpler forms
of re-action times open, are doubtless true of association
times, but the great variability of the latter makes these diffi-
cult to establish. The effect of practice is noticed by Traut-
scholdt; and Cattell has shown that in students from thirteen
to eighteen years of age a distinct shortening of the associa-
tion time accompanies growth and education, while the
students ranking higher in class have a somewhat shorter
time than those standing low in class. Fatigue very readily
enters, the accessible associations are easily exhausted, ;m<l
the mind repeats itself very markedly. Changes under the
action of drugs and in morbid mental states have been inci-
dentally noticed, but still await systematic investigation.

The various processes, the times of which we have been
studying, by no means exhaust the possibilities in this field.
As our knowledge of mental operations becomes more per-

56 THE TIME-RELATIONS OF MENTAL PHENOMENA.

feet and more capable of experimental study, and as our
power of analysis makes similar progress, the study of the
time-relations of mental phenomena, already fertile in sug-
gestions and results, will increase in interest and impor-
tance.

BIBLIOGRAPHY.

(This bibliography, though intended to be fairly complete, is by no
means exhaustive. It is furthermore Limited to the points discussed in the
text, and the classification corresponds in the main with the order of topics
in the text. Each article is cited in full under the topic to which it is more
especially devoted, and referred to by number under other topics to which it
contributes to a greater or less extent. While the general articles are fre-
quently cited under the special topics, it will be well to consult them even
when not so cited. Specially important articles have their numbers printed
in bold type.)

A. GENERAL.

I. Expository.

I. WUNDT. Physiologische Psychologic, 3d ed., 1887, vol. ii. pp. 261-364.
2. SERGI. La Psychologic Physiologique. 1888, pp. 272-296.

3. BUCCOLA. La legge del tempo nei fenomeni del pensiero, 1883.
4. LADD. Elements of Physiological Psychology, 1887, pp. 468-497.

5. KRAEPELIN. BiolofjischesCentralblatt. vol. i. (several articles).

6. KRAEPELIX. Die Neueste Literatur auf dem Gebiete der psychischen

Zeitmessung, Idem, Hi. 53-63.

7. FRICKE. Ueber psychische Zeitmessung, Idem, viii. 673-690; ix. 234-256,

437-448, 467-469.
8. BIBOT. German Psychology of To-day (translation), 1886, pp. 250-287.

9. EXNER. Herrmann's Handbuch der Physiologic, ii. 2, part ii. chap. iv.

pp. 252-283.

ii. Experimental.

10. DONDERS. Die Schnellegkeit Psychischer Processe(DuBois-Reymond^

Archiv, 1868, pp. 657-681).

II. DE JAAGER. De physiologische Tigo bij psychische Processen, Thesis,

1865.

12. KRIES and AUERBACH. Die Zeitdauer einfachster psychische Vor-

gange (Du Bois-Reymond's Archiv, 1877, pp. 297-378).

13. CATTELL. Psychometrische Untersuchungen (Wundfs Studien, iii.

pp. 2, 3; also as thesis, 1886).

14. JASTROW. An Easy Method of Measuring the Time of Mental Processes
(Science, Sept. 10, 1886).

B. SIMPLE RE-ACTIONS.

i. General.

15. EXNER. Experimentelle Untersuchungen der einfachsten psychischen

Processe (Pfliif/ci-'x Anitir, vii. 601-060, viii. 520-537, xi. in:! I :.'

58 THE TIME-RELATIONS OF

ii. Inertia of Sense-Organs.

16. CATTELL. The Inertia of the Eye and Brain (Brain, 1885).

17. PEEYER. Grenzen des Empfindungsvermogens, etc., 1868.

18. SANFORD. The Relative Legibility of the Small Letters (American

Journal of Psychology, i. pp. 402-436).

19 EUNKEL. Ueber die Abhangigkeit der Farbenempflndung von der Zeit
(Pfluger"s Archiv, ix. pp. 197-220).

20. V. WITTICH. Bemerkungen zu Preyer's Abhandlung (Idem, ii. pp. 329-

350).

21. BAXT. Ueber die Zeit, welche nothig ist damit ein Gesichtseindruck

zum Bewusstsein kommt, etc. (Idem, iv. pp 325-336).

22. EXNER. Ueber die zu einer Gesichtswahrnehmung nothige Zeit (Wie-

ner Sitzungsberichte, 58, pp. 601-631).
47.

in. Be actions to Impressions of Sight.
10, 11, 13, 15, 29, 31, 48.

23. VINTSCHGAU and LUSTIG. Zeitmessende Beobachtungen iiber die

Wahrnehinung des sich entwickelnden positiven Nachbildes eines
electrischen Funkens (Pfliiger's Archiv, xxxiii. pp. 494-512).

IV. Re-actions to Impressions of Sound.
10, 13, 15, 33, 45, 49.

v. Re-actions to Impressions of Touch.

24. VINTSCHGAU. Die physiologische Reactionszeit und der Ortsinn der

Haut (Pfluger's Archiv, xxii. pp. 87-110).
10, 11, 12, 15, 26, 27, 31, 32, 37.

v. (a) Temperature.

25. GOLDSCHEIDER. Du Bois-Reymond's Archiv, 1887. p. 469.

26. VINTSCHGAU and STEINACH. Zeitmessende Versuche iiber den Tem-

peratur- und Drucksinn (Pfliiger^s Archiv, xliii. pp. 152-195).

vi. Re-actions to Taste.

27. VINTSCHGAU and HONIGSCHMIED. Versuche iiber die Reactionszeit

einer Geschmacksempfindung (Pfl tiger's Archiv, x. pp. 1^18, xiv. pp.
529-592).

vn. 3e actions to Smell.

28. MOLDENHAUER. Ueber die einfache Reactionszeit einer Geruchsem-

pflndung (Wundfs Studien, i. pp. 606-614).

vni. Influence of Intensity of Stimulus.

29. BERGER. Ueber den Einfluss der Reizstiirke auf die Dauer einfacher
psychischer Vorgange, etc. (WundVs Studien, iii. pp. 38-93).

30. CATTELL. Influence of the Intensity of the Stimulus on the Length of

the Re-action Time (Brain, 1886, pp. 512-516).
12, 15, 32, 49.

ix. Variation of Stimulus within the Same Sense.

31. HALL and KRIES. Ueber die Abhangigkeit der Reactionszeit, etc. (Du

Bois-Reymond's Archiv, 1879, supplement, pp. 1-10).
2, 10, 11. 12, 15, 20, 24, 25, 26, 27, 28.
x. Mode of Re-actions; Analysis of Re-actions.

32. ORCHANSKY (reported by Gad). Du Bois-Reymnnd's Archiv, 1887, p.

369.

10, 13, 15, 24.

xi. Effect of Disturbance, Expectation, Practice, and Fatigue.

11, 12, 13, 34, 35, 49.

MENTAL PHENOMENA. oil

xii. Distinction betireen S'DI.SW// and Motor.

33. LANGE. Neue Experimeute Qber den Vorganjj der eiufarhm Reaction

auf Sinneseindriicke (Wundt's Studien, iv. pp. 479-511;.

34. MARTIUS. Die muskuliire Reaction und die Aufmerksamkeit

(Idem, vi. pp. 167-'-!17).
35. DWELSHAUVERS. Untersuchungen zur Mechanik der activen Auf

merksainkeit (Idem, pp. 217-249).
45.

xni. Individual Variations: Personal Equations.

36. SANFORD. Personal Equation (American Journal of Psycltolor/y, it.
pp. 3-38. 271-298, 403-430. Consult bibliography there given for de-
tailed references).
15,38.

xiv. Abnormal Variations.

37. DIETL and VINTSCHGAU. Das Verhalten dor pbysiologischen Reac-

tionszeit unter den Einfluss von Morphium, Caffee und Wein
(Pfliiger's Archiv, xvi. pp. 316-4061.

38. OBERSTEINER. Experimental Researches on Attention (Brain, i. pp.

439-453).

39. OBERSTEINER. Ueber eine neue einfache Methode zur Bestimmung

des psychischen Leitungsfahigkeit des Gehirns Geisteskranker
(Virchow's Archiv, lix. pp. 427^58).

40. KRAEPELIN. Ueber die Einwirkung einiger medicamentoser Stoffe auf
die Dauer einfacher psychischer Vorgiinge (Wundt's Studien, i.
pp. 417^62, 573-605).

41. WARREN. The Effect of Pure Alcohol on the Re- action Time, etc.

(Journal of Physiology, viii. No. 6, pp. 311-348).
15, 26, 32.

42. STANLEY HALL. Re-action Time in the Hypnotic State (Mind, viii.).

43. JAMES. Re-action Time in the Hypnotic Trance (Proceedings of the

American Society for Psychical Research, i. 3, pp. 246-248).
xv. Appliances and Methods.

44. SANFORD. A Simple and Inexpensive Chronoscope (American Journal

of Psychology, iii. pp. 174-182).
1, 11, 13, 14, 39, 41.

C. ADAPTIVE RE-ACTIONS.

(Distinction and Choice.)
i. General and Theoretical.
45. MUNSTERBERG. Beitrage zur Experimentellen Psychologic, i. pp. 64-

188.
1, 4,5,6,7,9. 10. I:.'. 13, 4!).

46. KRIES. Ueber Uuterseheidungszeiten (Vierteljahrsschrift fiir wissen-

schaftliche Philosophic, xi. pp. 1-23).

47. CATTELL. Ueber die Zeit der Erkeunung und Benennung von Schrift-

zeichen, Bildern, und Parbeu i M"ini</f .s Studien, ii. 4, pp. 635-650).
. n. Effect of Number of Distinctions and of Choices.

48. TIGERSTEDT and BERGQVIST. Zur Kenntniss der Apperceptionsdauer

zusammengesetzter Gesichtsvorstellungen (Zeitschrift fiir Bio-
logic. xix. pp. 5-44).

49. TISCHER. Ueber die Unterscheiduug von Schallstiirken (Wundr*

Studien, i. pp. 495-542).
50. MERKEL. Die zeitlichen Verhaltnisse der Willcusthatigkeit (Idem. ii.

PP. 73-127).
1, 10, 13, 14,34.

CO THE TIME-RELATIONS OF MENTAL PHENOMENA.

in. Specific Nature of Impression.

1, 4, 5, 6, 7, 9, 10, 11, 12, 13, 15, 27, 29, 30.

iv. Foreknowledge of Subject.

1, 13, 54.

v. Mode of Re-action: Association of Stimulus and Movement.
13, 34.

vi. Overlapping of Mental Processes: Sensory and Motor Re-actions.
13, 44, 35, 52.

51. PAULHAN. Revue Scientifique, 1887.

VII. Practice and Fatigue.

52. BERGER. Ueber den Einfluss der Uebung auf geistige Processe

(WundVs Studien, v. pp. 170-178).
1, 12, 13, 27, 50.

vni. Miscellaneous and Individual Variations.
1, 9, 13, 39, 40, 49, 50.

D. ASSOCIATION TIMES.

i. General.

53. CATTELL. Experiments on the Association ot Ideas (Mind, xii. pp.

68-74).
1, 4, 45.
II. Questions limited to a Single Answer, involving Acts of Memory.

54. VINTSCHGAU. Die physiologische Zeit einer Kopfmultiplication vou

zwei einziffrigen Zahleii (Pliiger's Archiv, xxxvii. pp 187-202).

45, 53.
in. Questions limited to a Single Answer, involving Comparison.

45, 53.
iv. Questions admitting of Various Answers.

45, 53, 56.

v. Unrestricted Associations.

55. CATTELL and BRYANT. Mental Association investigated by Experiment

(Mind, xiv. pp. 230-250).

56. TRAUTSCHOLDT. Experimentelle Untersuchungen iiber die Associa-
tion der Vorstellungen ( Wundfa Studien, i. pp. 213-250).
1, 14, 45.
57. GALTON. Inquiries into Human Faculty, pp. 182-203.

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