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MENTAL FATIGUE
BY
TSURU ARAI, Ph. D.
TEACHERS COLLEGE, COLUMBIA UNIVERSITY
CONTRIBUTIONS TO EDUCATION, No. 54
' - PUBLISHED BY
(ſearliera (Jullege, (Juluuthia littineraitu
NEW YORK CITY
1912
Copyright, 1912 by Tsuru Arai
CONTENTS
CHAPTER PAGE
I. INTRODUCTION AND HISTORICAL SURVEY . tº © I
II. PROBLEMS AND EXPERIMENTS OF THE PRESENT INVES-
TIGATION . ſº † e ge º tº • 29
ExPERIMENT I . º e { } e • 3 I
ExPERIMENT II . e cº e e • 42
ExPERIMENT III . e © e & . 48
ExPERIMENT IV . ſe e e & . 48
III. THE INFLUENCE OF MENTAL WoRK on PHYSIOLOGICAL
PROCESSES . . . e * ( ; o e . 61
IV. THE INFLUENCE OF MENTAL WORK ON THE FEELING
OF FATIGUE e ſº ſe º e • • 72
V. THE INFLUENCE OF MENTAL WORK ON THE EFFICIENCY
OF MENTAL FUNCTIONS ſº tº te e . 8o
VI. Con CLUSIONs . e * } e gº wº G • II.3
M E N T A L FAT I C, UE
CHAPTER I
INTRODUCTION AND HISTORICAL SURVEYºk
The facts of fatigue are conveniently divided into muscular
fatigue, sensory fatigue, and mental fatigue. That the division
is an artificial one does not need any explanation, for the indi-
vidual is an organic whole and a change in any part of the body
is more or less accompanied by a change of the whole. Mus-
'cular and sensory activities are, as a rule, connected in various
ways with the central nervous system. It is, moreover, very
difficult to get mental activity which is entirely free from mus-
cular and sensory accompaniments. Hence the division is made
for convenience. } When the terms “ mental activity ’ and ‘mental
fatigue are used in this monograph, it does not mean that they
are entirely independent of muscular and sensory activities or
fatigue. -
We have generally used mental multiplication as a type of
mental work, for the reason that its process contains hardly any
sensory and muscular elements.
Previous investigations of mental fatigue fall into four
classes, based on its influence on : Organic processes, motor
power and reaction time, sensibility of the skin, and the effi-
ciency of mental functions. -
I. The Investigations of Mental Fatigue Through Its Influence
on Organic Processes
Investigations have hitherto been confined to three processes:
namely, pulse, temperature, and metabolism.
*Acknowledgments are due to Professor E. L. Thorndike and Professor
R. S. Woodworth for their suggestions as to the general plan of the experi-
nients and to Professor J. McK. Cattell for his advice. The author’s grati-
tude should be expressed to Mr. T. Haraguchi for assistance in connection
with the form of presentation of the facts.
I
2 Mental Fatigue
I. Changes in the Pulse Rate
So far as the knowledge of the writer goes, the first attempt
to measure the relation between mental work and changes in
the pulse rate was made by John Davy" in the paper entitled
“On the Temperature of Man,” published in 1845. Davy
measured his pulse rate by the number of beats per minute on
eighteen nights soon after he completed strenuous mental work
lasting for from two to five hours and also on nights when no
mental work was done. As a result of these experiments, he
found that the average pulse rate at midnight after he had done
mental work was 57.0 per minute, while it was 54.6 at midnight
when none had been done.
In 1881,” Gley noted that the radial pulse rate is higher after
such mental work as reading and working at geometry than
after rest. Mosso" concluded that the circulation was not the
primary factor in psychological activity. In 1897, Vaschideº
published the result of his thoroughgoing investigations on the
subject. He measured the number of his radial pulse beats
per minute on resting days and on days when he devoted four-
teen hours to strict mental work. He reported the results of
forty resting days and seventy-two working days in Spring
and four resting days and nine working days in Summer. In the
first series, the average number of beats per minute was Zºot.&º
on the working days and 76.86 on the resting days. in the
second series, the average number of beats was 69.8 on the
working days and 74.44 on the resting days. Vaschide gives the
full data of the summer observations. By an investigation of
these the writer discovered that the average deviation was not
so great as the difference between the two averages given above;
therefore the difference can not easily be attributed to mere
chance.
In 1896, MacDougall" found that there is an acceleration of
the pulse in the first ten minutes of the attentive state, which is
* Phil. Trans., vol. CXXXV, pp. 319-349.
* Gley, E., Études de Psychologie, Paris, 1903.
* Mosso, A., Fatigue, trans. by Drummond.
* Vaschide, N., Influence du travail intellectuel prolongé sur la vitesse du
pouls, L’Année Psychol., vol. 4, pp. 356-378.
* MacDougall, The Physiological Characteristics of Attention, Psychol.
Rev., 1896, pp. I58–180.
Introduction and Historical Survey 3
followed by a decline/ In 1898, Binet" and Henri noted that the
pulse at the periphery is not necessarily changed by intellectual
work and that its change is not always accompanied by a change
of the cerebral pulse. In the same year, Larguier des Bancels"
reported measurements of his own pulse-rate during intellec-
tual work lasting from 8 p. m. to I2 p. m. and during periods
of rest covering the same hours of the day. As the results of
four days’ experiments he found that the pulse-rate during rest
fell rapidly to a certain point and remained practically with-
out change for the remaining hours, and that during intellectual
work it fell more gradually but lower than the lowest point in
the rest period. The average pulse rates in the four successive
hours in the work periods were 80.9, 72.2, 67. I5, and 62.9. The
corresponding figures for the rest period were 80.4, 69.8, 65.75,
and 65.25. From two series of experiments lasting from 8 a. m.
to 12.20 p. m. he obtained results in which the pulse-rates in
successive hours were 68.6, 64.5, 62.5 and 62.8 in the period of
mental work, while they were 69.1, 63, 62.8 and 63 in the rest
period.
In 1909, Benedict and Carpenter” reported the results of
measurements of the change in the radial pulse-rate caused by
mental work. During four hours of mental work such as
taking college examinations, the subjects were asked to count
the number of radial pulse beats per minute. As the result of
the experiments tried on twenty-two healthy young men, they
found that the average number of pulse beats per minute was
79 during the mental work, while it was 74 in the control ex-
periment. They were not inclined to attribute the difference to
the mental work itself, and said that it might be due to excitement
on the part of the subjects; for it was the first time that they
had gone into the respiration-calorimeter chamber. To the
writer, these averages seem to be unreliable, for each subject
measured his own pulse at any time that he wished during the
examination. The result would be that if they measured their
pulse oftener in the earlier hours of the mental-work experi-
* Binet, A. et Henri, V. La fatigue intellectuelle, Paris, 1898.
"J. Larguier des Bancels, Mesure de la fatigue, L’Année Psychol, vol. 5,
pp. IQI-I95.
* Benedict, F. G. and Carpenter, B. S., The Influence of Muscular and
Mental Work on Metabolism and the Efficiency of the Human Body as a
Machine, Washington, General Printing Office, Igog.
4 Mental Fatigue
ments than they did in the corresponding hours of the control
experiments, the average pulse-rate would be reported as rela-
tively higher; for in both mental work and control experiments,
the pulse-rate decreased gradually. From the complete reports
of these experiments the writer found that seventy-nine
measurements were taken in the first half of the experimental
period in the mental-work experiment, while only sixty-six
measurements were taken during the corresponding time in the
control experiment. Since the average number of pulse beats in
the earlier half of the experimental period was five and half
beats greater than that of the later part, and the number of sub-
jects tested was twenty-two, the difference in the number of
measurements in the first half of the experimental period alone
would make the average of the mental work test 3.I beats per
minute greater than the pulse rate of that of the control test.
To eliminate this source of error, the writer took the average
of the pulse-rate at the beginning and again at the end of the
mental work experiment and at the beginning and at the end
of the control experiment. The average rates are 87.4 and 76.3
respectively for the mental work test while for the control test
they are 82.4 and 69.9. Thus, the decrease during the period of
work is II. I ; during the period of rest it is 12.5.
In 1910, Billings and Shephard” made a careful study of “The
Change of Heart Rate with Attention,” performing their ex-
periments upon three subjects. They measured the changes in
the amplitude and rate of respiration and the pulse wave and
rate in connection with the degree of attention, auditory, visual,
and central. As the result of their experiments, the following
conclusion is reached: “With close visual attention the breath-
ing is uniformly decreased in amplitude. In rate it is sometimes
increased, sometimes decreased and sometimes not changed at
all. With auditory attention it is nearly always decreased in
rate, but changed irregularly in amplitude. The breathing in
the kind of central attention that we used is very little changed.
These changes are probably adaptive; they remove a source of
disturbance. Deep breathing, with its accompanying move-
ments, would interfere with looking; rapid breathing interferes
more with listening. With the effect of attention—the strain
"Billings, M. L. and Shephard, J. F., Psychol. Rev., vol. XVII, pp. 217-
228.
Introduction and Historical Survey 5
tends to increase the heart rate. Increased breathing, either in
rate or amplitude, tends to increase the heart rate. Restricted
breathing, either in rate or amplitude, tends to decrease the
heart rate. For the latter reason one often finds a decreased
heart rate with sensory attention, particularly at first. With
central attention the heart rate is regularly increased.”
2. Change of Temperature
Claude Barnard” reported a development of heat in the nerves
caused by mental work. Heidenhein, Helmholtz and Rollen-
ston,” according to Benedict and Carpenter, could not demon-
strate that heat is generated in the nerves. In 1844, Davy”
reported the results of eighteen series of experiments, several
of them control tests. He found that the average temperature
under his tongue at I2 p. m. was 98.4 F. on the mental work,
days, while it was 97.9 F. on the rest days. The most exhau
tive study on the subject is perhaps that of Lombard,” pub-
lished in 1879. Performing his experiments on the same sub-
ject, he first investigated the influence of four kinds of mental
work on the temperature of the three regions of the head, an-
terior, middle, and posterior. The result obtained was that the
mental work of four kinds caused a rise of temperature in all
three regions of the head and that the degree of the rise and
the rapidity of its appearance were different according to the
kind of work and the region of the head. Lombard's further
study of other individuals yielded similar results.
In 1881, Speck” reported that the average temperature on
three resting days was 35.73 C. and on three mental-work days,
35.77 C. (the work lasting for from two to three hours). In
.1884 Gley* made two series of experiments on himself. In the
first series, the temperature was taken every five minutes during
mental work of from one to three hours done between 5 p. m.
and 8 p. m. and also during a rest at about the same period of
* Vorlesungen über der Thierische Wärme. Cited by Benedict and Car-
penter, loc. cit., on their page 46.
* Ibid.
* Loc. cit., page 2.
* Experimental Researches on the Regional Temperature of the Head,
London, 1879. *
* Speck, Untersuch. tiber die Beziehungen der geistigen Thätigkeit zum
Stoffwechsels, Arch. Expt. Path. u. Pharmakol., vol. I5, pp. 87-88.
* Gley, E., Études de psychologie physiologique et pathologique, Paris,
IGO3, pp. IOI-II2. t k
6 Mental Fatigue
the day. It was found that temperature fell not only during
the mental-work, but during the rest also. This fall is attributed
by the observer to the immobile state which the subject was
forced to maintain during the experiment. In the second series,
a similar test was made while the subject was in bed, begin-
ning about an hour after awakening in the morning so as to
free the subject from the influence due to muscular inactivity.
In this test, unlike the results of the other, the temperature rose
more than one-half of a degree on the average during mental
work of about an hour. Gley concluded from the result of
these experiments that mental work raises the temperature. In
1898, Larguier des Bancels” noted that the fall of temperature
under his tongue after two or three hours of mental work was
O.325 C., while it was only O.23 C. after a rest for the same length
of time. In 1909, Benedict and Carpenter” found that, as the
result of the experiments tried on twenty-two individuals, the
average temperature under the tongue was 98.9 F. before, and
98.4 F. after, about four hours of mental work, such as taking
college examination. The average temperature under the tongue
was 98.3 F. before, and 98.O. F. after, the same number of hours
of rest.
3. Changes in Metabolism
The problem of the influence of mental fatigue on metabolism
has attracted the attention of such investigators as Hammond,
Oppenheim, Speck, Mosler, Luciani, Sherman, Bocker, and
Mairet. Their results, however, are of little value to us because
they did not report carefully the amount and nature of the
mental work done. Some of them compared the waste products
of the human body during the day with those during the night
both as to quantity and quality. But the method is questionable
inasmuch as they fail to take into consideration the fact that
more physical work is done in the day time as well as more,
mental work. The results which are important for us are quoted
below.
In 1881, Speck” reported the results of experiments tried on
himself and one other subject. Using a respiration apparatus,
* Loc. cit, on page 3.
* Loc. cit, on page 3. -
* Speck, Arch. Exper. Path, u. Pharmakoi., vol. 15, p. 128.
Introduction and Historical Survey 7
he concluded that mental activity has no influence on meta-
bolism.
In 1899, Atwater, Woods, and Benedict” attempted to study
this problem by the use of the respiration calorimeter. Their
subject led a very quiet life for three days. During the next
three days, he spent eight hours per day studying a German
treatise on Physics and making mathematical computations.
# They found that during the twenty-four hours of each mental-
{ work day, the average nitrogen output was 13. I grams; and the
\carbon output, 241 grams. The averages were 12.5 grams and
248.4 grams respectively for the rest days.
In 1909, Benedict and Carpenter” reported their careful in-
vestigations. They determined, by the aid of a respiration calori-
meter the amount of water vapor and carbon dioxide eliminated,
oxygen absorbed, and heat produced, by each subject during
four hours of mental work and during four hours of rest. Their
conclusions were: “From the results of the data accumulated
in this series of experiments on the effects of mental work on
metabolism it would appear that the pulse rate was slightly in-
creased, the body temperature somewhat higher, the water vapor
output increased by about 5 per cent, the carbon dioxide pro-
duction increased by about 2 per cent, the oxygen consumption
increased by about 6 per cent, and the heat production increased
by about one-half of I per cent as a result of sustained mental
effort such as obtains during a college examination. Of these
factors, those most accurately measured are undoubtedly the
carbon dioxide elimination and the heat production. On the
whole, however, the increase of both of these factors accom-
panying the mental exertion is so small and the exceptions are
so numerous that it would not be wise to say whether or not the
mental activity exercised a positive influence on metabolic pro-
cesses in general. Indeed, more than half of the subjects studied
produced more heat in the control than in the mental work test,
which might be considered as negative evidence. This is especi-
ally so when it is considered that although every precaution was
taken to eliminate all other extraneous influences it still remains
a fact that, with many of these subjects, the experiments during
the mental work period was their first experience inside of a
* U. S. Dept. Agric, Office of Experimentālsation Bull. 44.
* Loc. cit., p. 3. .” -

8 Mental Fatigue
$
complicated respiration chamber and they were more or less dis-
turbed by the novel experience, and perhaps more restless—that
is, made more muscular movements than during the control
period. In view of this fact, we are very strongly of the
opinion that the results obtained in these experiments do not
indicate that the mental effort has a positive influence on meta-
bolic activity.” -
II. Investigations of the Influence of Mental Work on Motor
Power and Reaction Time
I. Motor Efficiency
Mosso”, was the first investigator who tried to correlate ex-
perimentally mental fatigue with motor efficiency. Using the
ergograph he found, with himself as well as others, that mental
work resulted in a decrease of efficiency of muscular con-
traction.
In 1896, Kemsies” tested the motor power of school chil-
dren with Mosso's ergograph at different times during the
school day and reported a distinct correlation between the
amount of mental work done and decrease of the ability to lift
the weights. & &
In 1900, Thorndike” tested various individuals with Cattell's
spring ergograph. The subjects made one hundred, two hun-
dred, or three hundred contractions, at the rate of one contrac-
tion per second with a rest of one minute after each one hun-
dred contractions. They underwent the test in the morning
when no mental work had been done and after a day's class
work, study or office work. The comparison between the amount
of physical force at these different times indicated that mental
work effected no decided decrease in physical power. Thorn-
dike closes his report thus: “To say that mental work does
not necessarily decrease one's power to do physical work does
not imply that the latter is independent of mental conditions,
permanent or temporary, or that in individual cases whose
mental make-up is well known, dynamic tests might not be in-
dices of various mental conditions. Among these might be cer-
* Loc. cit., p. 2.
* Kemsies, Deutsche Medicinische Wochenschrift, July 2, 1896.
* Thorndike, Mental Fatigue, Psychol. Rev., vol. 7, pp. 576-578.
Introduction and Historical Survey 9
tain of the phenomena of fatigue. What is asserted is that the
difference between a mind before and after it has worked for
six or eight hours can not be detected by a record of physical
work.” *
Keller” tested a school boy with the ergograph at different
intervals during several days, giving him mental work between
the tests. The difference in motor power indicated in the ergo-
graph test is attributed to the mental work done. In 1903,
Ellis and Shipe” tested many persons for their reaction time
and their ability to lift a certain weight before and after con-
tinuous mental work, and found no uniform change either in
motor efficiency or in reaction time as the result of mental work.
In 1906, Marsh” wrote, “Where my own subjects noted mental
depression or even headache on their records, the figures rarely
failed to show a high grade of muscular performance at that
*** -
\
º
time. But the younger the individual, the more prone he is to
follow his feelings, in the quantity and quality of his work.”
2. Reaction Time
In 1877, Bernstein” found that the general fatigue from a
day’s work causes loss of speed of reaction. In 1896, Bett-
mann” found that one hour's mental work, such as adding
single-place numbers, caused a loss of Speed of reaction, but also
a decrease of the number of false reactions. The present writer
has not found any difference between the reaction time in the
morning before the day's mental work and in the afternoon
after a considerable amount of mental work has been done.
III. Investigations of Mental Fatigue Through Its Influence
on the Sensibility of the Skin
The first attempt to measure mental fatigue by changes in the
* Keller, Biologische Centralblatt, vol. I4, nos. I, 2, 3. Cited by Ellis and
Shipe in Psychol. Rev., vol. I4, p. 506.
* Ellis, A. C. and Shipe, M. M., A Study of the Accuracy of the Present
Method of Testing Fatigue, Psychol. Rev., vol. I4, pp. 496-509. -
* Marsh, H. D., The Diurnal Course of Efficiency, Arch. of Phil. Psychol.
and Sci. Method, Columbia Univ. Cont, to Philos. and Psychol., vol. XIV,
110. 3.
* Bernstein, J. A., Ueber die Ermiidung und Erholung der Nerven, 1877,
A.g. Phys., vol. I5, pp. 289-327. -
* Bettman, S., Ueber die Beeinflussung einfacher psychol. Vorgânge
durch körperl. und geist. Arbeit., Psycohl. Arbeit., vol. I, pp. I52-208.
IO Mental Fatigue
}.
sensibility of the skin was made by Griesbach” in 1895. He
tested School children and adults with an aesthesiometer at dif-
ferent times and obtained a decided decrease in the sensibility of
# the skin as the amount of mental work was increased. In 1898,
l
Wagner” and Vannod, following Griesbach’s method, found
that sensibility of the skin was weaker on the days of hard
mental labor than on the days of rest. Binet” and his collabora-
tors obtained results corresponding to Griesbach's.
In 1899, Leuba” published the results of his two series of ex-
periments, one made at Heidelberg with three subjects and the
other at Bryn Mawr College with six subjects. The method of in-
vestigation was that of Griesbach and Wagner: the threshold
for one point was sought by a gradual decrease and that for two
by a gradual increase of the distance of the points of the in-
strument. The results of both of these series agreed in showing
that mental work did not decrease the sensibility of the skin
and that the aesthesiometric method was not a fit method to
* measure mental fatigue.
Germann” used the aesthesiometer with a distance of a little
over two centimeters between the two points. He determined
the sensibility of the skin by the number of right judgments.
On twenty-seven out of the thirty days covered by the investiga-
tion, a total of forty-two tests was made. Of these forty-two
tests, twenty occurred in the morning previous to any study,
while the remaining tests were made in the evening. The re-
: sults of these tests showed that the errors were no more fre-
quent in the evening tests than in those made in the morning.
Germann concluded thus: “In at least one normal case, the
percentage of errors of cutaneous tactile discrimination bears no
constant, nor even relative, correspondence to the mental fatigue
experienced by the subject.”
In 1904, Bolton” made a careful study with one subject. He
followed closely the method used by Griesbach and measured
* Griesbach, H., Arch. f. Hygiene, vol. 24, pp. I24-212.
* Wagner, L., Unterricht u. Ermiidung, Berlin, 1898.
* Binet, A. and Henri, V., La fatigue intellectuelle, Paris, 1898.
* Leuba, J. H., On the Validity of the Griesbach Method of Determining
Fatigue, Psychol. Rev., vol. 6, pp. 573-598. -
* Germann, Geo. B., On the Invalidity of the Aesthesiometric Method
as a Measure of Mental Fatigue, Psychol. Rev., vol. 6, pp. 599–605.
* Bolton, T. L., Ueber die Beziehungen zwischen Ermädung, Raumsinn
der Haut und Muskelleistung., Psychol. Arb., vol. 4, pp. 175–234. w
Introduction and Historical Survey II
the threshold of discrimination of two points before and after
half an hour, an hour, and two hours of addition of one-place
numbers, and found no difference in the discrimination before
and after the mental work. Neither could he find a gradual de-
crease in the per cent of right judgments according to the in-
crease of the length of the mental work.
IV. Investigations of Mental Fatigue Through Its Influence on
the Efficiency of Mental Functions
For our present knowledge in regard to the problem, we are
most indebted to Professor Kraepelin and his pupils, and their
researches demand our special attention. In the present section,
we shall first present a brief account of the previous investiga-
tions made outside of Kraepelin's school; and second, gen-
eral outlines of the results obtained by Kraepelin and his
pupils.
I. A Brief Account of the Investigations Made Outside of
Kraepelin's Laboratory
One of the earliest attempts to study the subject was made
by Galton.” From the answers given by one hundred and six-
teen teachers to the questions respecting the symptoms of fatigue
of school children, Galton drew the following conclusions:
f First, mental fatigue causes worry and excitement. Second,
; fatigue occurs more often among those who work alone or are
* impelled to work hard through eagerness to excell.
In 1879, Sikorski” made experiments on the influence of
mental fatigue on voluntary movements like talking and writ-
ing. The results of his investigation showed that errors in these
movements increased after certain mental work and the amount
of increase was in proportion to the amount of work done. The
increase in the number of errors is attributed by him to a de-
crease in ability to distinguish Small psycho-physical differences,
weakening of memory and the appearance of mental excitement.
The increase of the number of errors in the course of work
* Galton, Fr., Remarks on Replies by Teachers to Questions Respecting
Mental Fatigue, Jour. Anthro. Institute, vol. 18, p. 157.
* Sikorski, Sur les effects de lassitude provoguées par les travaux intel-
lectuels chez enfants de l’āge scolaire. Annales d'hygiene publique, 1879,
vol. 2, pp. 458–467.
.
-:;
*ſ
T 2 Mental Fatigue
was observed by Burgerstein” in 1891, Laser” in 1894 and Eb-
binghaus” in 1897.
In 1895, Holmes” tested school children in regard to changes
in their ability to add as a result of continuous functioning.
Comparing the amount of work done and errors made in each
of the four successive work periods, each period lasting for nine
minutes, this writer found that both errors and the amount of
work increased from period to period. When gymnastics was in-
troduced between the two periods, the errors were reduced to a
considerable extent, while the amount of work done was unaffec-
ted. For this reason the author regards the increase in the num-
ber of errors as a result of fatigue; the increase in the amount of
5 work done, as the result of practice. Examination into the na-
iture of the errors revealed that the reproductive process, rather
than the perceptual and motor processes, is affected by fatigue.
It was also found that the children did no better work in the
last period.
In 1900, Thorndike published two articles reporting his two
series of investigations. In the beginning of the first article,”
^ he gives a brief account of the two theories of mental fatigue.
One of these, the mechanical theory, is that mental work causes
a gradual decrease of mental efficiency in proportion to the
amount of work done. The other, called the by-product theory,
is that mental fatigue is not a simple phenomenon. Just as
muscle is fatigued because of the fatigue substances produced
by its own activity, so mind produces as a result of its own ac-
tivity, various by-products such as feelings of weariness, head-
ache, and sleepiness. These products tend to weaken the ability
to do mental work. The effect of fatigue, according to the
theory, appears now and then suddenly in the course of work.
The purpose of these experiments was to determine the rela-
tive merits of these two theories. Four subjects underwent the
* Burgerstein, L., Die Arbeitscurve einer Schulstunde, Zeitsch. f. Schul-
gesundheitspflege, vol. 4, pp. 543-563.
* Laser, H., Ueber geistige Ermädung beinn Schulunterichte, Zeitsch.
f. Schulgesundheitspflege, vol. 7, pp. 2–22.
* Ebbinghaus, H., Ueber eine neue Methode zur Prüfung geistiger Fähig-
keiten und ihre Anwendung bei Schulkindern, Zeitsch. f. Psychol., vol. I3,
pp. 4OI-457. w
* Holmes, M. E., The Fatigue of the School Hour, Ped. Sem., vol. 3,
pp. 213–234. &
* Thorndike, Mental Fatigue, I, Psychol. Rev., vol. 7, pp. 466-489.
Introduction and Historical Survey I3
tests in the morning after a night's rest, and in the evening after
hard mental work. Tests were also made immediately before
and after continuous exercise of special mental functions. The
results showed that mental efficiency after mental work is not
necessarily less than that before the work, and that in the
course of two or three hours of mental work, the effect of
fatigue is not strong enough to outweigh the effect of practice.
His conclusions are as follows: “,
(I) “Mental energy, if it means anything, must mean a
Something which mental work uses up in regular proportion to
the work done. But incompetence, mental fatigue, does not come
in regular proportion to the work done.”
(2) According to introspection, there is no feeling of gen-
eral mental incompetence.
(3) The feeling of fatigue can not be a measure of mental
inability. On the whole, the results of the first series strongly
favor the by-product theory.
The second series of experiment, recorded in his second
article,” was made on school children, in order to determine the ;
influence of school work on their mental efficiency. The func-f
tions tested were written multiplication of four-place numbers
by four-place numbers, marking misspelled words, drawing cer-
tain figures from memory, writing certain numbers, nonsense
syllables and letters from memory, and also counting the number
of dots on a chart which was exposed five minutes. Every pre-
caution was taken to guard against such errors as would come
from testing a group of children specially selected, or with a
different degree of practice, etc. The children met all the tests
just as well after as before a day's school work except one:
i.e., memorizing nonsense syllables. In this experiment, their
records in the late test were slightly inferior to those made in
the early test. “A fair claim to make on the basis of the results
obtained,” says Thorndike in conclusion, “is that a regular |
day’s work in the grammar School does not decrease the ability #
of the child to do mental work. . . . The chief responsi-
bility for mental exhaustion in scholars falls, I should be in-
clined to think, not on a creator who made our minds so that
work hurt them, nor on the public opinion which demands
* Thorndike, Mental Fatigue, II, Psychol. Rev., vol. 7, pp. 547-579.
I4. Mental Fatigue
that children shall do a given amount of work, but upon the un-
wise choice of material for study, the unwise direction of effort,
the unwise inhibition of pleasurable activities, the unwise abuse
of sense-organs and unattractiveness of teachers and teach-
ing.” -
The results of tests made on an adult subject, W, agree with
the foregoing. In the first experiment, W marked every word
containing both e and t on one hundred and fifty-one pages of
a book, each page containing about seven hundred and twenty-
five words of text. He worked for eight hours without rest.
The number of words correctly marked was only a little less
in the later part than in the earlier part of the test. In the
second experiment in three hours of estimating the areas of
small parallelograms of paper, the accuracy of W’s judgment
was constant for the first two hours, but fell off seven per cent
in the last hour. In the third test, the results showed that
fatigue, if present, did not outweigh the practice effect. In the
fourth test, W measured the time it took him to correct ex-
amination papers for about six hours, and observed no sign
of fatigue. In the fifth experiment, W tested the change
in the time it took to go over three hundred and fifty cards,
on which were written titles of foreign books and articles, to
decide in each case to insert it in a certain bibliography. Here,
too, no fatigue effect was observable. The author asserts that the
results do not at all disprove the existence of fatigue. On the
contrary, mental incompetency is a fact. His conclusion is that
the causes of fatigue are not mere decrease of energy, but
highly complex by-products of mental work. a"
In 1903, Ellis and Shipe” investigated fatigue in special
mental functions resulting from general mental work. The
mental functions tested were (I) addition of numbers, (2) writ-
ing the cubes of numbers up to nine, and (3) memorizing non-
sense syllables. Five advanced students and a professor took
part in the first experiment. The subjects worked on adding,
cubing and memorizing for two minutes, each at about 8:30
a.m. and at 5:30 p.m. after severe, unremitting mental work with
rest for luncheon only. The results were divergent with dif-
ferent individuals and on different days, but they utterly failed
* Loc. cit.
Introduction and Historical Survey I 5
to show a difference in the amount of mental work done in the
two tests. The same kind of tests, made on the children be-
tween the ages of eleven and sixteen, yielded somewhat uni-
form results tending to show that mental efficiency was much
greater after the mental work.
In 1903, Pillsbury” studied the relation between the attention
wave and mental fatigue. The efficiency of attention was
meåSüFed by the ratio of the visibility to the invisibility of a
gray ring on a slightly different background. The number of
subjects was five, including the experimenter himself. He º
that the ratio was smallest after hard mental work, while it was;
greatest after rest. It was also found that the efficiency of at #
tention corresponded to the total length of the wave, and it under-
went diurnal periodicity like the Traube-Hering waves of blood
pressure. He gave the following explanation for the cause of
the inefficiency of attention: “We can explain our results if
we consider the fluctuations of the attention a resultant of two
physiological processes, of the degree of efficiency of the cortical
cells, on the one hand, and of the state of excitation of the vaso-
motor center on the other. The reinforcement from the medul-
lary center would have its effect in decreasing and increasing
the response of the cells, and would determine the ratio of fluc-
tuation, but the proportion of the cycle in which they would be
sufficiently effective to give rise to a sensation, would depend
primarily upon the freshness of the cells themselves. The de-
gree of efficiency of the cells, then, would be measured directly
by the ratio of the period of visibility to the period of invisi-
bility of our minimal stimuli, while the length of the total wave
would be a measure of the Traube-Hering wave.”
In 1910, Winch” published his experimental study of mental
fatigue in the eyening Schools. He took three classes which had
homogeneous groups of students, and divided each homogeneous
group into two equal groups, A and B, according to the results
of the previous tests. The group A did the given fatigue tests
at 8 p. m. and the group B at 9 p. m. The results of the tests
made on those classes showed that the work done by the group

* Pillsbury, W. B., Attention Waves as Means of Measuring Fatigue,
Anter. Jour. of Psychol., 1903, vol. I4, pp. 54I-552.
* Winch, W. H., Some Measurements of Mental Fatigue in Adolescent
Pupils, Jour. of Ed. Psychol., vol. I, no. 2, pp. 5-12 and 83-IOO.
I6 Mental Fatigue
B was much worse than the group A. He concluded that even-
ing school is of comparatively little profit and that a short period
of work after a day's labor is enough to produce low efficiency
of mental functions. -
In 1911, Thorndike” reported the results of an experiment
made on eighteen college students. The mental function tested
was mental multiplication of three-place numbers by three-place
numbers. The subjects worked for from two to twelve hours,
each choosing a convenient time, and again for a short time next
day. Efficiency was measured by the time taken to do each
example. The amount of fatigue was measured by the dif-
ference between the time taken at the end of the continuous
work period and that at the beginning of the test made next day.
The average ratio between the average time per example at the
end of the long work period and at the beginning of the brief
test on the following day, expressed as a percentage, was about
61 per cent for the group. He found that the number of errors
varied inversely as the degree of efficiency, and that the feel-
ing of fatigue bore little or no relation to mental efficiency.
2. The Important Investigations Made by Kraepelin and His
Pupils
It was by Axel Oehrn” in 1889 that the first attempt to de-
termine and analyse the work-curves of certain...mental-func-
tions was made, so far as the writer has been able to discover.
He measured the efficiency (I) of perception through ability to
count letters, to search for given letters, and to read proof;
(2) of memory through ability to memorize nonsense syllables
and lists of numbers; (3) of association through ability to add
one-place numbers; (4) of motor functions through writing
sentences from dictation and reading aloud. Each subject
marked his place on the stroke of a bell at the end of five-
minute periods so that the amount of work in each such period
might be computed. Ten professors and graduate students took
part in the tests, which yielded the following results:
* Thorndike, Mental Fatigue, Jour. of Ed. Psychol., vol. 2, no. 2, pp.
6I-80.
* Experimentelle Studien zur Individual psychologie, Psychol. Arbeit.,
vol. I, pp. 92-I5I. -
Introduction and Historical Survey I7
uſ (I) The predominant factors which determine the course of
efficiency of mental work lasting for one hour are practice and
fatigue. - -
~ (II) This course of efficiency is represented by a curve,
which rises at first, and falls toward the end of the test (show-
ing an increase of efficiency, followed by a falling off). The
effect of practice and fatigue on efficiency are matters of common
experience. Both are undoubtedly present throughout the tests.
The length and the height of the rise vary in different indi-
viduals and with different functions.
* (III) Individual curves are subject to other minor fluctua-
tions. Many of them show a sudden rise in the first ten or
twenty minutes followed by a sharp fall before they reach the
point of maximum efficiency. This sudden rise is explained by
Oehrn as resulting from strain of attention. *
* (IV) The point of maximum efficiency, or the point where
the fatigue effect begins to outweigh the effect of practice, comes
sooner in the curve of the function which is more automatic
than in that which is more purely mental. The average time
at which the maximum point is reached is as follows: At the
24th minute, in learning nonsense syllables; at the 26th minute,
in writing from dictation; at the 28th minute, in addition; at
the 38th minute, in reading; at the 39th minute, in counting let-
ters one by one; at the 59th minute, in counting letters three
by three; and at the 60th minute, in learning numbers.
(V). In measuring the effect of fatigue and practice, Oehrn
used the following formulae:
Practice = (M — m”) × IOO,
M
Fatigue = (M — mº) × Ioo,
M
M stands for the point of maximum efficiency, m” stands for
the first and m” stands for the second point of minimum effi-
ciency. The average amount of practice thus obtained in each
function is as follows: Writing, I.8; reading, 5.7; memory of
nonsense syllables, 6.2; counting letters one by one, 6.9; count-
ing letters three by three, II.I; memory of numbers, 28.O.
The average amount of fatigue is as follows: Reading, 5.9;
counting letters one by one, 6.2 ; counting letters three by three,
I 8 Mental Fatigue
6.9; writing, 8.4; addition, I5.4; memory of numbers, 22.3;
memory of nonsense syllables, 38.5. -
The effects of both practice and fatigue, in general, are less
in the less intellectual functions. The ability to memorize non-
Sense syllables is an apparent exception. Oehrn holds that the
Smaller net effect of practice is due to the far greater effect of
fatigue. *
In 1892, Bettmann” studied in himself the influences of phys-
ical and mental work on certain psychological functions. To
produce physical fatigue, he walked for two hours; for mental
work, he added numbers for one hour. The influence on psy-
chological functions was measured in the first series by 50 re-
actions, 30 minutes' work at memorizing numbers, 30 minutes’
work at addition, and by 3OO choice reactions (in the second
Series only). In both series of experiments, a day on which the
tests were taken after mental work was followed by a day of
physical work, then by a normal day when the tests were taken
after a period of rest, then by another day of mental work, and
so on in rotation. The first series covered twelve days; the
second, nine. The mental work was done from 7 to 8 a. m. ;
the walking, from 6 to 8 a.m. ; and the testing, from 8 to 9:Io
a. m. in the first series. In the second series, the mental work
was done from 7:30 to 8:30 a. m., the walking from 6:30 to
8:30 a. m., and the testing from 8:30 to 9:55 a. m. -
The results obtained were as follows: The reaction time was
decidedly affected by the work of both kinds. In the second
actions in each experiment was (in thousandths of a second)
as follows:

1 2 3 4. 5 Average
Normal day . . . . . . . . . . . . . . . . 312 || 381 284 || 285 299 292
Mental work day. . . . . . . . . . . . 376 || 391 386 388 377 384
Physical work day. . . . . . . . . . . . 296 || 254 246 || 234 || 254 257
The percentage of false reactions was: I per cent on normal
days, 2.9 per cent on mental work days, and 26.9 per cent on
physical work days.
* Bettmann, S., Ueber die Beeinflussung einfacher psychologischen Vor-
gänge durch körperlische und geistige Arbeit, Psychol. Arbeit., vol. I, pp.
I52-208.
Introduction and Historical Survey I 9
The results of the choice reaction-time test in the first series
were about the same. The average reaction time was 389 or with
no false reactions on the mental work days, 309 with 3.6 per cent
false reactions on the normal days and 340 or with IQ.5 per cent
false reactions on the physical work days. The influence of both
mental and physical fatigue increases the time of choice. The
quick reaction-time after the physical work is the result of ex-
citement which makes one react before the choice is made in-
tellectually. This is indicated by the large number of false re-
actions.
The tests of word reactions yielded the following results:
The average word reaction-time was 317 or on normal days, 391 or
On mental work days and 357 or on physical work days. Thus
continuous work of both mental and physical functions results
in increasing the time of word reaction. .*
The effect of practice is very great in memorizing lists of
numbers. The excess in the amount of work done on the last
normal day over that done on the first normal day was 38.5 per
cent of that done on the last normal day; on the last physical-
work day it was 2I.9 per cent; on the last mental-work day, II.2
per cent. These figures indicate also that the fatigue resulting
from both physical and mental work has an unfavorable effect
on the influence of practice. The average number of digits re-
membered in the first and second halves of the thirty-minute
period was:

First half | Second half
Mental work day. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 236
Normal work day. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 302
Physical work day . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 221
In the addition test, the average number of digits done in the
first and second halves of the thirty-minute periods was as
follows:
First half | Second half
Mental work day. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794 778
Normal work day. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 911 882
Physical work day. . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 771
2O Mental Fatigue
The two hours of walking and the one hour of adding, then,
result in reducing efficiency, both in the function of memorizing
and in that of adding.
The conclusions which Bettmann gives are, in substance, as
follows:
(I) Intellectual work of one hour and physical work of two
hours have an unfavorable influence on the efficiency of mental
functions.
(II) Decrease in mental efficiency after work of either sort
shows itself in the increased time taken for apprehension, choice,
and association, in the weakening of memory and in reducing
the effect of practice.
(III) Decrease in mental efficiency is as great after physical
work as after intellectual work. Therefore, gymnastics, walk-
ing, and many other forms of physical exercise are not suitable
recreation after mental work.
(IV) Motor inefficiency appears after mental work, and ex-
citement of the motor centers after physical work.
(V) Excitement in motor centers disappears sooner than
mental inability. Its disappearance is hastened by taking up in-
tellectual work.
(VI) The influence of fatigue such as results from the tests
described above disappears very soon, while that resulting from
work such as research throughout the night lasts for many
days. -
A Amberg” investigated the influence of periods of rest and
Awork of various length on mental ability and its variation with
A different individuals. The mental functions tested were ability
to add to one-place numbers and to memorize lists of numbers.
The addition research was of two kinds, a one-hour test and a
two-hour test. The one-hour test was made on the subject A,
(I) with a five-minute rest between two thirty-minute work
periods; (2) with five minutes’ work and five minutes’ rest
coming one after another; and (3) with fifteen minutes’ rest
between two thirty-minute work periods. The latter test was
made also on the subject B. The two-hour test was made on
the subject A and several others with a fifteen-minute rest be-
tween two one-hour work periods. The test of memory was
* Amberg, E., Ueber den Einfluss von Arbeitspausen auf die geistige
Leistungsfähigkeit, Psychol. Arbeit, vol. I, pp. 300-377.
Introduction and Historical Survey 2 I
made on two individuals, A and C, with a fifteen-minute rest
between two thirty-minute work periods.
The influence of rest was studied by noting the difference in
the amount of work done in the test with rest and that done
in the control test, in which the subject worked without rest.
Eight days were devoted to the experiment, with periods of
work and rest of varying length, the control test coming on the
first day, the rest test on the second day, and so forth on alter-
nate days.
Since the results of each rest test were affected by the prac-
tice gained in the control test of the preceding day, the follow-
ing method was used to make comparison possible. In the one-
hour test, half the average percentile gain in the amount of
work done in each control test over that done in the preceding
test two days before, was taken as a coefficient of daily practice
gain. A coefficient was likewise obtained in the two-hour test.
The influence of rest was measured by the difference between
the amount of work done in each rest test and that done in
the control test of the day before multiplied by one plus this
coefficient. By dividing the sum of these differences by four,
the average influence of a certain length of rest was gained.
\-The results thus obtained were:
(I) Different lengths of rest exercise different influences on
mental efficiency after rest.
(II) Favorable lengths of rest are determined by the dura-
tion of work preceding it. For instance, a fifteen-minute rest
was unfavorable after a half-hour of work, but it was favorable
after an hour of work. A five-minute rest is better after a
fifteen-minute work period than after a five-minute work period.
After thirty minutes of work, a five-minute rest was better than a
rest of longer duration. This is explained by the fact that,
during five minutes, the effect of “warming up * is retained,
while the effect of fatigue is largely offset. If the rest is longer
the effect of “warming up ’’ is also lost.
(III) Favorable lengths of rest are determined by the kind
of work preceding it. For example, after a thirty-minute work
period, a fifteen-minute rest was reported favorably in the mem-
ory test, while it was unfavorable in the case of the addition
teSt.
22 Mental Fatigue
Rivers and Kraepelin "" attempted to find the influence of
different rest periods after the same length of work. The
mental work used was addition of one-place numbers and only
one subject was observed. There were two series of experi-
ments. In the first series, there was a half-hour rest after each
half-hour of work; in the second there was an hour of rest be-
tween half-hour work periods. In both series of experiments,
‘long ' and ‘short ’ days alternated, the ‘long ' preceding. Eight
days were devoted to the first series, six to the second. On the
long days there were four work periods; on the short days,
but one. +.
The authors studied the four main factors which influence the
efficiency of mental function; “warming up ’’ (Anregung),
spurts (Antrieb), practice (Uebung) and fatigue (Ermädung).
The existence of “warming up ’’ effect was indicated by its loss
after the one-hour rest. Comparing the amount of work done
in the second half of each work period with that done in the
first half of the following period, it was found that the gain
was greater in the first series with the half-hour rest period;
a phenomenon attributed to the fact that the rest period of a full
hour in the second series caused a greater loss of “warming up ’’
effect. This is even more significant, since fatigue would be
more completely offset by the longer rest period. In comparing
the amount of work done in each successive five minutes, it was
discovered that there was a sudden increase here and there in the
amount done, which lasted but a few minutes. This was
attributed to the influence of spurts, which are defined by the
authors as follows: “We designate these brief periods of
greater accomplishment as ‘spurts' in order to distinguish the
special effort of the will from such ordinary influences as prac-
tice, fatigue, and ‘warming up effect.” The average amount of
practice effect resulting from thirty minutes of work, called, for
convenience, the average daily practice gain, was determined as
follows: The amount of work done in the first work period
of each long day was subtracted from that done on the succeed-
ing short day, and the difference, divided by four (the number
of the work periods on a long day), was assumed to represent
* Rivers, W. H. R. and Kraepelin, E., Ueber Ermädung und Erholung,
Psychol. Arbeit., vol. I, pp. 627-678.
Introduction and Historical Survey 23
the practice effect of a thirty-minute work period of a long day.
That of a short day was measured by the gross excess in the
amount of work done in the work period of the succeeding long
day over that done on the short day. These results were
averaged.
The amount of fatigue in each thirty-minute work period was
determined as follows: To the amount of work done in a given
period were added the “ daily practice gain '' as computed above,
and the “ daily practice loss,” also previously determined; from
this sum was subtracted the amount of work done in the period
immediately succeeding it. The average amount of fatigue is
given below expressed as a per cent of the reckoned amount.
Fatigue effect 30 minutes’ rest 60 minutes’ rest
First work period . . . . . . . . . . . . . . . . . . . . . . . 0.8% . . . . . .
Second work period . . . . . . . . . . . . . . . . . . . . . 4.6% 4.9%
Third work period. . . . . . . . . . . . . . . . . . . . . . . 14.8% 10.3%
The fatigue effect in the third period is smaller after the one-
hour rest than after the thirty-minute rest. The experimenters
conclude that the thirty-minute rest was not long enough to
eliminate all the fatigue effect which resulted from an equal
length of work.
The aim of the research by Weygandt" was to investigate the
relative influence of various changes of work on the recovery of
efficiency lost through fatigue. The method used was as follows.
The experimental days were of two kinds; namely, change-of-
work days and control days. During a test of an hour and
fifteen minutes, the subject did a certain kind of work during
the first thirty minutes, changed it to another kind in the next
thirty minutes and resumed the first kind for the last fifteen
minutes. On the control day, the subject did the same kind of
work as that done during the first thirty minutes on the change-
of-work day, for an hour and fifteen minutes without change.
The comparison was made between efficiency in the last fifteen
minutes on the change-of-work day, and on the control day.
In comparing the two, Weygandt used the same method as that
* Weygandt, W., Ueber den Einfluss des Arbeitswechsels auf forlaufende
geistige Arbeit., Psychol. Arbeit., vol. 2, pp. II8-202.
24 Mental Fatigue
of Amberg, to eliminate errors resulting from the order of the
test. The tests were varied by using the different kinds of work
in various combinations. Six subjects took part.
f The results obtained were, in substance, as follows:
f (I) Change of work has a different influence according to
the degree of difficulty of the work introduced for change.
If the work introduced is more difficult, its influence is unfavor-
able, and vice versa.
(II) Whether any given work is considered hard or easy,
depends on the individual and the degree of practice in the work
assigned.
sy (III) Fatigue in one function is transferable to another.
^ (IV) The insertion of a different kind of work has very
often a favorable influence in the form of a spurt due to the
change (Wechselsantrieb) which amounts to very little and dis-
appears Soon.
(V) A favorable influence due to spurts comes very often in
the state of fatigue; it depends on the motor excitement caused
by change of work.
Voss” studied the minor fluctuations of a work curve in
order to determine their causes. The author investigated the
problem by finding: first, the time taken for adding each two
succeeding figures; then, the extent of deviation of each single
addition time from the average; and finally, the frequency of
the occurrence of fluctuations of different lengths. Special ap-
paratus was arranged so that a record of the time could be taken
for each addition. The mental work employed was an hour of
addition. The number of subjects was three, including the ex-
perimenter himself. The results thus obtained were:
Ҽ
(I) The time taken for a single addition ranged, as a rule,
from O.4 sec. to I.2 sec., but there were a few cases in which it
took more than I.2 sec. A majority of the single addition times
fell between O.6 sec. and O.8 sec.
(II) In all the subjects, the effect of practice increased the
frequency of occurrence of a single addition time of O.6 sec. and
decreased the average deviation from it. It did not, however,
increase the frequency of occurrence of the shortest addition
time of O.4 sec.
* Georg von Voss, Ueber die Schwankungen der geistugen Arbeitsleis-
tung, Psychol. Arbeit., vol. 2, pp. 399–449.
Introduction and Histarical Survey 25
(III) The effect of fatigue, on the contrary, decreased the
frequency of occurrence of an addition time of O.6 sec. and in-
creased that of I.O sec.
(IV) The effect of the spurts tended to decrease the addi-
tion time to the minimum and made it very irregular.
(V) The fluctuations were most frequent at lengths of from
2 Sec. to 2 3/5 sec. This duration, according to other researches
made by the same author, was found to be about the same as
that of fluctuations of attention. Therefore he thinks that the
fluctuation of the addition time is probably due also to the same
change in the central nervous system. &
A very brief description of the investigation made by Lind-
ley” will be sufficient, as his methods are described in full in
Chapter V. The aim of the investigation was to find factors
entering into the work curve, such as: period of maximum rest,
gain by practice, persistency of practice effect, susceptibility to
fatigue (Ermädbarkeit), “warming up ’’ effect, spurts, and in-
dividual variation. -
The subjects were three in number, including the experi-
menter. The mental function tested was the addition of one-
place numbers. Experimental days of five kinds followed each
other in rotation for twenty-six days, as follows: a day on
which one hour's continuous work was done; four days on each
of which there were two thirty-minute work periods separated
respectively by rests of five, fifteen, thirty, and sixty minutes;
the one continuous hour work day again, and so forth.
The following conclusions were reached from the series of
experiments thus arranged:
(I) The influence of rest is threefold; elimination of fatigue
effect, loss of “warming up ’’ effect, and loss of practice effect.
(IT) The best period of rest varies with individuals. With
the three subjects tested, it lies between fifteen minutes and
sixty minutes or more, but, in case the “warming up ’’ effect is
great while fatigue is slight, work without rest amounts to
fully as much as work done after the period of maximum rest.
The absolute excess and the percentile excess of work done in
the work period before, over that done after, the different rest
periods with the three individuals are given below.
* Lindley, E. H., Ueber Arbeit und Ruhe, Psychol. Arbeit., vol. 3, pp.
482–534. *
26 Mental Fatigue

Subject. A Subject B Subject C
Rest
Absolute % Absolute % Absolute %
0. . . . . . . . . . . . . . . . 47 1 .. 8 96 4.2 186 11.3
5 minutes . . . . . . . . 23 0.8 29 1.2 118 7.0
15 minutes . . . . . . . . 135 4.8 63 2.7 109 6.4
30 minutes . . . . . . . . 132 4. 6 72 3.1 69 3.9
60 minutes . . . . . . . . 103 3.5 62 2.5 10 0. 5
(III) Capacity to gain by practice seems to go hand in hand
with weaker persistency of practice effect and greater suscepti-
bility to fatigue.
(IV) The greater part of the practice effect disappears
within twenty-four hours after the cessation of work. •,•'
Miesemer” investigated the same problem as Bettmann,
namely, the influence of physical and mental work on certain
simple mental and motor functions, using for physical work,
one hour's walking; for mental work, one hour's addition. Their
influence on mental functions was measured by the ability to
perceive nine letters exposed for .OI7 sec. and to reproduce
them after a half minute. A record was made of the number
of letters perceived and reproduced; of those rightly perceived
and reproduced ; of those wrongly perceived and reproduced.
Their influence on motor functions was measured by the ability
to write numbers from one to ten and from ten to one. Eighteen
days were spent on the investigation in the case of mental func-
tions; twenty-one days on the investigation in the case of motor
functions. The physical-work test, the control test and the
mental-work test came in rotation on successive days in the
order named. In the physical-work test, mental and motor effi-
ciencies were measured immediately after the walking; before
the control test, no work was done; and in the mental-work
test, measurements were made immediately after the hour of
adding.
The experiments yielded the following results:
(I) The number of letters perceived and the number rightly
perceived increased after both kinds of work, but more after
the mental work. The number of letters wrongly perceived was
* Miesemer, K., Ueber Psychische Wirkungen körperlicher und geistiger
Arbeit., Psychol. Arbeit., vol. 4, pp. 375-434.
Introduction and Historical Survey 27
greatest after the physical work. This was attributed to ex-
citement of the motor centers by the physical work.
(II) On the other hand, both walking and adding caused a
decrease of efficiency in reproducing letters perceived after a
half minute, and the decrease was greater after the adding. The
number of letters reproduced wrongly also increased after work
of both kinds and this decrease in efficiency was again greater
after the mental work.
(III) Speed in writing and the size of the figures written
increased after the physical work, and decreased after the
mental work. This corresponds with the result obtained by
Bettmann in which the speed of reaction and the number of the
false reactions increased after the physical work. This was ex-
plained by assuming that mental work exerts an inhibiting in-
fluence on the motor centers, while the physical work excites
them. -
The aim of the investigation made by Hylan and Kraepelin”
was to ascertain the effect of practice and fatigue. Long periods
of work and rest have hitherto been used by such investigators
as Amberg, Rivers and Lindley. Hylan and Kraepelin made
a new departure, by adopting short periods. An advantage of
using shorter periods is, in their opinion, that not only can ex-
periments be made on a greater number of individuals, but also
a greater number of measurements can be obtained from the
same individuals. A disadvantage is that the effect of work
and rest is sometimes so slight that it is not measurable.
The mental function used was the ability to add one-place
numbers. On each experimental day, there were four five-
minute work periods in groups of two, separated by a thirty-
minute rest. On the first day, the two periods of the former
group were separated by no pause; in the latter a twenty-minute
pause intervened between the two periods. On the second day,
the pauses were respectively one minute and fifteen minutes;
on the third day five and ten minutes. Three subjects under-
went the tests. *
The results of the experiments were:
(I) Mental work lasting only for five minutes produced an
appreciable amount of practice and fatigue. The ratio of these
* Hylan, J. P. and Kraepelin, E., Ueber die Wirkung kurzer Arbeits-
zeiten., Psychol. Arbeit., vol. 4, pp. 454-495.
28 Mental Fatigue
products determined efficiency. The amount differed with dif-
ferent individuals. For instance, W’s practice gain was 9.6 per
cent and H's was 3.5 per cent of his own average amount of
work, while K made progress only in the beginning and his
average daily gain was very small. -
(II) The fact that the amount of work done on one day
was greater than that done on the day before in spite of the
fact that efficiency at the end of one continuous work period
was lower than at the beginning, indicates that the effect of
practice outlasted that of fatigue.
(III) The influence of rest was favorable or unfavorable. It
eliminated, on the one hand, the effect of fatigue so that the
amount of work after rest was greater. But, on the other, it
tended to destroy the effect of “warming up * and practice.
“Warming up ’ effect was lost sooner than practice effect. The
most favorable length of rest was that which resulted in the
greatest ratio of favorable to unfavorable influence. The five-
minute rest was best after five-minute's work in all the individuals
tested. There lay an unfavorable length of rest between five
minutes and a certain period longer than five minutes, differing
with different individuals. For instance, with H the rests of
fifteen minutes and of twenty minutes were unfavorable, while
the thirty-minute rest was again favorable. With W, the un-
favorable length of rest lay between five minutes and twenty
minutes. With K, the longer the rest, the better the effect.
CHAPTER II
PROBLEMS AND EXPERIMENTS OF THE PRESENT
INVESTIGATION
To make the aim of the investigation clear, it is important
that we should define the term mental fatigue. By mental
fatigue, we mean the unfavorable and destructive effect which
continuous mental work produces on mental functions. In a
complete investigation, we should have to study at least its in-
fluence on the four large classes of mental and physical pro-
cesses mentioned in Chapter I. Lack of time for a more thor-
oughgoing examination of each problem, however, limits the
scope of the present investigation to its influence on (I) certain
physical processes; (2) the feelings of fatigue; (3) intellectual
efficiency. We shall, in the following pages, state more specific
phases of each problem and their relations to the results of the
previous investigations.
(I) In regard to the influence of mental fatigue on phy-
siological processes, we recorded the pulse and the body tem-
perature. In the matter of the influence of fatigue on the pulse,
previous investigators are not agreed. Davy, Gley, and Billings
and Shephard, for instance, found that mental work increased
the pulse rate, Vaschide and Larguier des Bancels have found
that it decreased it, while Benedict and Carpenter found no
change at all. These contradictory results may be due to the
difference in the subjects used, or in the duration of mental
work. We have no data on which to judge whether or not
there was a difference between their subjects, but in regard to
the different lengths of the work period, we do know that all of
the investigators who reported an increase of the pulse rate em-
ployed a working period of less than one hour while those who
obtained opposite results had a working period of more than
four hours. Consequently, if, as MacDougall states, mental
work increases the pulse rate at first but lowers it during the
later part of a work period, their obtaining contradictory results
29
3O Mental Fatigue
is perfectly natural. If the shorter period of work is used, it
is possibly only mental excitement that raises the pulse rate.
These considerations lead us to direct our labors to the investi-
gation of the following subjects: -
I. The direction and amount of change in pulse rate during
continuous mental work lasting long enough to produce enough
fatigue to decrease intellectual efficiency. {
2. The correlation between the change in the pulse rate an
that in mental efficiency. . . -
In regard to the bodily temperature, all the investigators agree
that mental work raises it. Here, again, a possible error may
come in from the effect of excitement. Therefore, we have
taken the same precautions as in the case of the pulse rate.
(II) In regard to the relation of mental fatigue to the feel-
ing of fatigue, Kraepelin, Thorndike and some others agree that
feelings of fatigue are not in any definite way related to de-
crease of mental efficiency. We have investigated the problem
by ascertaining:
I. The direction and the amount of the change in the feel-
ing of fatigue during continuous mental work. *
2. The correlation between the state of this feeling an
mental efficiency.
3. The correlations between the change in the feeling and
the change in mental efficiency during continuous mental work.
(III) The problem of the relation of mental fatigue to the
change in mental efficiency is divided into three parts. I. The
first concerns the factors having influence on the efficiency of
mental functions. The results of the previous investigations are
not uniform. Kraepelin and his pupils, for instance, found that
mental efficiency depends on practice, fatigue, “warming up,”
Gewöhnung, and spurts. But Thorndike found only the first
two of these factors playing important parts. It is, therefore,
necessary that a more careful investigation of the problem be
made before we can know how far the change in mental effi-
ciency is really due to fatigue itself. 2. The second con-
cerns the effect of mental fatigue on the efficiency of the special
mental function exercised. Kraepelin, Amberg and others dis-
covered that the longer the work lasts, the longer it takes to
eliminate the effect of fatigue resulting from the work. This
Problems and Experiments of the Present Investigation 31
they interpret as showing that decrease of mental efficiency is
in proportion to the increase of the duration of mental work.
But Thorndike, and Ellis and Shipe found that efficiency of
mental functions was not less after certain hours of mental work.
In the attempt to solve this problem, we have endeavored to
determine:
a. The amount of fatigue caused by continuous work.
b. The course of the change in efficiency during continuous
work.
3. The third concerns the transfer of fatigue. Kraepelin
states that the greatest difference between mental fatigue and
muscular fatigue is that mental fatigue has its effect on the
whole field of mental activity, while muscular fatigue affects
only the special muscles exercised. In short, Kraepelin holds
that fatigue is transferred almost in toto. Thorndike, on the
contrary, maintains that the effect of mental work is very largely
restricted to the special function exercised. Our investigation
of this problem was along the following lines:
a. The influence of such mental work as that of a school day
for a student upon the special mental functions, such as adding
or memorizing.
b. The influence of the exercise of the special mental func-
tions on other functions. º
c. The correlations between the fatigue in one function and
that in the other, both being affected by the same mental work.
d. Individual differences. sº
Experiment I
The first experiment was made during February and March,
1909, at Teachers College, Columbia University. The purpose
of the experiment was to ascertain : (I) the amount, rate and
the change of the rate of fatigue in the special mental function
exercised, and (2) the amount of the fatigue transferred to cer-
tain other functions. -
The particular function tested was that exercised in mental
multiplication of pairs of numbers like
2645 8324 7954 5438
} 5784, 7384, 3528 and 2347.
About one thousand different combinations of figures were used.
32 Mental Fatigue
The order of the examples being made by chance, the distribu-
tion of difficult and easy examples is random. The subject of
the experiment was the writer herself. But the danger that her
presuppositions affected the results was precluded by the fact
that the writer’s knowledge of mental fatigue at that time was
not enough to enable her to form any expectation of what form
the fatigue curve in mental work would take.
The experiment is divided into two parts by a slight difference
of method: each part consisting of two series, the practice
series and the fatigue series.
Earperiment I, Part 1
Practice series.—On February 2nd, the subject made the
first test in the following manner. Using an ordinary watch the
subject set a time for starting. When the hand of the watch
reached the point set, the subject looked at the first example and
multiplied mentally but with the original numbers in sight. The
answer was written down as soon as it was obtained and the
time recorded. Then the subject immediately took up the second
example and repeated the same procedure. Thus she worked
from 9:30 a.m. to 3:18 p. m. with a rest of forty-eight minutes
for luncheon, and obtained the answers of twenty-four ex-
amples. -
From the recorded results of the first test, the subject found
notable fluctuations in the time taken for doing an example, and
that these fluctuations were not due to the fatigue produced by
continuous exercise of the function, but were rather due to the
lack of training for this work. This is probably correct, for as
the subject became used to the experiment, the extraordinary ir-
regularity in time disappeared and the curve became smoother.
Also the fluctuations appeared more in the first part of a period
of continuous work in the first days of observation, while during
the latter days the fluctuations became greater in the latter part
of the continuous work, indicating that the former fluctuation
was due to lack of practice and adaptiveness, while the latter
was the result of continuous mental work. For this reason, it
is important that when fluctuations resulting from fatigue are
to be studied, the subject should be tested at or near the limit
Problems and Experiments of the Present Investigation 33
of practice and should be required to cooperate fully by always
achieving his maximum. Therefore, before any attempt to de-
termine changes in the rate of fatigue was made, the subject
practiced on mental multiplication until the daily effect of prac-
tice became very slight. The amount of work done in the prac-
tice series is given in Table I.
TABLE I
Time and errors in each successive mental multiplication of a four-place
number by a four-place number. both numbers being presented to percep-
tion. Feb. 2–15. Subject T. A. Times are in minutes and seconds.


Feb. 2, '09 Feb. 4, '09 Feb. 7, '09 Feb. 15, '09
9:30 A. M.– 9:30 A. M.– 10:40, 39, A. M.– 8:22 A. M.–
2:13 P. M. 1:40, 30 P.M. 12:14, 10 P. M. 12:15 P. M.
No. 1 Time | Er. | No. | Time Er. || No. | Time Er. || No. Time Er.
1 9.00 || 4 l 3. 55 || 4 1. 2. 16 || 3 1 4. 30 5
2 | 18.08 || 3 2 5.30 || 3 2 5. 50 2 2 7, 20 || 0
3 8. 20 || 0 3 6.30 3 3 5. 55 || 0 3 2.45 2
4 8.25 5 4 6. 50 | 5 4 3. 55 || 0 4 6.45 || 0
5 || 10.30 2 5 4. 55 | 1 5 6. 10 || 1 5 7.45 || 0
6 7. 15 2 6 7.20 2 6 4.20 | 5 6 5.45 || 4
7 7.30 4 7 6.05 i 2 7 4.40 || 3 7 4.50 || 4
8 9.00 | 1 8 2.55 || 4 8 18. 50 3 8 5.00 || 3
9 9. 30 || 1 9 || 14.00 || 3 9 9. 15 | 1 9 6.00 | 1
10 | 18. 10 || 5 || 10 | 16. 10 5 10 9. 50 || 0 10 6. 20 | 1
11 9. 30 || 2 || 11 5.00 || 4 11 || 10.55 || 4 11 | 12.20 || 0
12 || 13.20 || 2 || 12 5.00 || 3 12 || 12.00 || 0 12 8.25 || 0
13 9. 30 || 4 || 13 9. 35 | 3 13 9. 20 || 0
14 9. 55 | 1 14 4.08 || 5 14 6. 55 || 5
An hr. rest, lunch|| 15 9.00 || 0 15 | 10.10 || 3
15 5.00 || 1 16 12.15 || 0 16 5.25 | 3
16 3.55 || 2 || 17 5. 20 2 17 7.05 || 4
17 8. 10 || 3 || 18 || 10. 10 2 18 6. 50 || 0
18 7.20 | 1 ||34 m. rest, lunch 19 5.50 || 0
19 7. 50 | 1 19 || 10.05 || 2 20 4. 30 || 1
20 6.05 || 5 || 20 6. 55 5 21 11.20 || 5
21 4. 30 || 2 || 21 6. 10 2 22 9.25 2
22 || 14.30 || 1 || 22 7. 54 5 23 8.25 | 1
23 3. 50 || 5 || 23 13.07 || 0 24 8.00 || 0
24 | 16.00 || 4 || 24 5.05 || 5 25 || 13. 55 || 3
25 | 11.40 | 1 26 6. 55 || 0
26 14.15 || 0 27 | 4.45 || 3
28 11.20 2
29 || 17.30 || 0
30 || 10.45 || 3
:
:
.
gº
.
:
tº:
tº
34 Mental Fatigue
Fatigue series. After the practice series described above the
Subject made the experiment lasting from I :45,4O p. m. to
IO:O7,30 p. m. with a stop for dinner, the results of which are
given in Table II.
TABLE II
Time and errors in each successive mental multiplication of a four-place
number by a four-place number, both numbers being presented to percep-
tion. Feb. 22. Subject T. A. Times are in minutes and seconds.
Feb. 22, 1:45 P.M.–10:07 P. M.


Example Time Error Example Time Error Example Time Error
After dinner
No. 1 || 2.25 2 No. 22 || 6.10 2
2 4. 55 0 23 8.30 0 No. 41 || 6.00 2
3 6.05 3 24 6.00 O 42 | 8.00 2
4 || 4. 55 2 25 | 9.30 2 43 7.00 3
5 6.00 3 26 5.10 2 44 5.25 5
6 || 5, 20 2 27 6. 20 4 45 5.40 2
7 3.35 6 28 5.50 3 46 4. 20 3
8 || 4, 15 3 29 || 5. 10 3 47 | 6.40 1.
9 || 4, 30 4 30 7.00 3 48 6, 10 2
10 8, 10 5 31 || 7.30 2 49 || 7. 20 4
11 || 5.30 2 32 5.00 2 50 6.00 0
12 || 5.40 2 33 8.00 3 51 5.30 5
13 || 4. 20 3 34 5.40 3 52 j 5. 35 0
14 || 5.10 4 35 | 5.50 2 53 6.15 2
15 4.40 5 36 12.45 I 54 9.50 3
16 5.20 4 37 8.30 4 55 9.00 4
17 5.40 3 38 8.30 3 56 8.05 4
18 5.50 3 39 || 8.30 i 57 7.20 3
19 || 7.35 1 40 8.30 2 58 || 7. 20 4
20 4.15 2 59 5.40 1.
21 2.50 2 Dinner, 6:32–7:41 P. M. 60 6.45 3
The introspection recorded after the experiment is as follows:
“I have no feeling of fatigue but a little feeling of weariness
caused by the monotonous work. My consciousness is clear and
mood quiet. I was always guided by the hope of obtaining a
true result.”
Pulse record:
At the beginning of the experiment. . . . . . . . . . . . . . . . . . . . . . . . . 79
Immediately before the rest for dinner. . . . . . . . . . . . . . . . . . . . . . 82
Immediately after the rest for dinner . . . . . . . . . . . . . . . . . . . . . . . 9}
At the end of the experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
:
:
:
*
tº
Problems and Experiments of the Present Investigation 35
Earperiment I, Part 2
Practice series. From the experiment described above it was
discovered that the work was not difficult enough to produce
sufficient fatigue. In order to make the task harder, a new
condition was introduced; instead of multiplying with the
original figures in sight, the subject relied on memory for the
figures and multiplied them mentally with closed eyes. The
method was better than the earlier one, for it not only made the
task more difficult, but it helped to eliminate sensory fatigue.
When the subject forgot the original figures, she looked at them
again, but as the time was made longer on this account, the loss
of the original figures was counted against her. But this seldom
occurred as the subject was careful to commit the numbers to
memory. With this new method, six practice experiments were
performed. The results are given in Table III.
The introspections recorded by the subject after the experi-
ment were: Feb. 24, “The task is extraordinarily difficult. To
multiply mentally with the new method is many times more
difficult than it was by the other method.” Feb. 25, “I do not
feel well to-day; I studied hard all day before the experiment
and have great difficulty in concentrating my mind on the figures.
The work is very difficult.” Feb. 26, “No feeling of fatigue
after the hours of mental work.” Feb. 27, Lacking. Feb. 28,
“The work was so interesting that I forgot meals. No feeling
of fatigue.”
Fatigue series. Before going into the description of the ex-
periments in this series, a word is needed in reference to the
state of the subject’s mind. By this time, the subject was ac-
customed to the concentration of attention upon the work and
was little affected by fluctuations of feeling. She could do her
utmost in each example. The writer is more and more im-
pressed by the importance of this state of mind in the measure-
ment of mental fatigue. To her mind, the results of the ex-
periment made on one subject who can maintain an undisturbed
mental effort yield truer fatigue curves than those obtained from
carelessly conducted experiments made on hundreds of un-
trained subjects, for the errors in such experiment are not elimi-
nated by the number of tests. The experimenter found it more
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III (HISHWAL

Problems and Experiments of the Present Investigation 37
advantageous to use an ordinary watch instead of the stop
watch, for this made it easier to record the time when a cer-
tain example was done. The slight error of observation is of
no consequence in view of the long time required for a single
example and the great variation of examples in difficulty.
On March 3, 4, 5 and 6, the subject did the mental multiplica-
tion from II a. m. to II p. m. without any pauses except the
two or three seconds between the examples for recording time.
But the subject had taken a heavier, breakfast than usual at IO
a.m. and a light supper after II p. m. Her health was in good
condition and she slept soundly at night. The contents of her
consciousness during the experiments were very simple, all de-
sires being completely subjected to the one desire to get true
fatigue curves. The results of these experiments are sum-
marized in Table IV.
38
Mental Fatigue
3–6. Subject T. A.
The times are in minutes and seconds.
TABLE IV
Time and errors in each successive mental multiplication of a four-place
number by a four-place number, both numbers being held in memory. Mar.

Mar. 3 Mar. 4 Mar. 5 Mar. 6
No. of 11:01, 30 A.M.– 11:12 A.M.– 10:07, 30 A.M.– 11:15 A.M.–
º 11:07 P.M. 10:52 P.M. 10:55 P.M. 11:27, 40 P.M.
ple
Time Error! Time | Error Time Error Time Error
I 5.50 5 4. 30 0. 5. 10 0 5.00 0
2 5.50 1 7.20 2 4.50 2 4.40 1
3 5.25 O 4. 40 0 4. 20 2 4.45 2
4 6.30 2 6. 10 3 6. 10 2 4. 20 1.
5 6.00 3 4.40 I 4.50 2 5.00 2
6 6.45 5 6.05 2 4.40 0 5. 10 3
7 4.25 0 6. 20 4 3. 55 2 4. 30 I
8 5.05 0 6.00 3 4. 10 2 6.00 7
9 6. 20 O 6. 50 2 5.00 2 5.05 0.
10 5. 40 1. 5.40 I 5.40 2 4. 40 3
11 7. 10 4 10. 05 0 5.00 1. 5. 55 3
12 6. 20 0 6. I0 O 6.30 1 6, 15 4
13 7. 15 2 12.45 2 6.05 1. 6.30 2
14 8. 15 1 6. 10 0 4. 20 2 7.20 1.
15 6. 20 0 4.45 2 6.15 4 5.15 O
16 8.00 1. 6. 10 1 6. 10 1 6. 10 2.
17 8.05 O 7. 10 l 8.15 0 6.00 3
18 7.30 O 7.20 1. 7.30 2 5.25 O
19 8.55 2 6.50 2 4. 15 5 6. 20 0
20 6. 55 0 6. 20 3 8. 20 1. 6.00 0.
21 5. 50 0 7.05 4 12.40 3 9. 10 3
22 9.05 2 8. 30 2 6.00 2 4.25 l
23 6. 10 I 7.30 4 5. 20 0 5.05 0
24 8.50 I. 5.45 I 6.50 0 8. 20 3
25 9.40 O 10. 50 4. 5. 50 O 5. 50 1.
26 8. 50 O 10.30 2 6. 55 2 6. I5 2
27 7. 10 4 7.00 I 6. 40 I 9. 50 2
28 9.40 3 5.50 4 8. 50 O 6.35 6
29 8.00 I 6.00 2 8.05 1. 6.45 1.
30 9.00 l 5.40 I 8. 20 3 9.00 3
31 9. 30 O 9.00 0 8.00 0 10. 50 2
32 7. 40 3 5.40 3 6. 50 O 7. 10 2
33 8.00 1. 9.50 0 6.00 l 7.00 2
34 9.00 I 7.40 1. 4.00 0 6.30 0
35 10. 50 I 17. 10 3 3. 50 0 7.35 2
Problems and Experiments of the Present Investigation
39.
TABLE IV—Continued


Mar. 3 Mar. 4 Mar. 5 Mar. 6
No. of 11:01, 30 A.M.– || 11:12 A.M.– || 10:07, 30 A.M.– 11:15 A.M.–
Exam- 11:07 P.M. 10:52 P.M. 10:55 P.M. 11:27, 40 P.M.
pie
Time Error Time Error Time Error Time Error .
36 13. 20 4 7. 40 2 6. 55 2 8.15 1.
37 13. 50 0 12.50 5 8.15 4 7. 50 3
38 10.45 2 12. 10 0 9.05 1. 7. 10 l
39 10.15 5 11. 50 0 12.00 2 11.05 1.
40 15, 00 1. 7. 15 I 10.35 0 10. 20 5
41 11 : 00 5 9.00 2 8.25 0 6.00 0
42 13.05 2 11.00 1. 11. 10 I 11. 20 3
43 15, 40 I 13. 35 4 9. 10 4 10.35 2
44 19, 35 2 10. 55 2 12.50 1. 7. 40 3
45 10, 15 3 9 50 l 15. 20 1 12. 10 I
46 7, 50 2 10. 20 2 11.00 2 7.30 l
47 10, 20 3 13. 10 3 9. 30 3 7. 10 1
48 12.50 2 14.10 O 16.00 7 9. 30 3
49 8.05 I 9. 55 0 8. 20 2 10. 50 2
50 10, 00 0 12.00 2 12.40 3 9.40 O
51 15.00 0 12.00 2 10.00 3 9. 10 f
52 10, 00 3 10.40 2 10.00 0 14.40 7
53 9, 20 0 19. 50 0 9.00 3 8.40 I
54 12.05 1. 8. 50 0 8. 20 2 6. 10 2.
55 11 : 10 3 16. 10 3 8. 20 3 8.00 4
56 15, 10 1 6. 40 4. 8. IO 3 7.00 I
57 15. 20 3 9 : 00 5 8. 20 1 9.05 7.
58 9. O{} l 8.10 0 6.00 4 10.40 6
59 8.00 I 12.25 1 7.20 2 9. 30 6
60 11. 20 0 7.00 1 5. 50 2 6. 10 6
61 6. 55 1 7.00 4 8. 20 3 8. 50 6
62 12. 20 O 11.30 5 16.50 6 9.40 5
63 16. 20 2 10.00 2 10. 50 2 9.00 2
64 10. 20 O 14.30 4 7.30 2 7.35 5
65 16. 15 0 19. 10 4 10. I 0 4 8. 20 2
66 15.50 5 11. 20 2 8. 50 4 11. 10 1.
67 16. 30 l 12. 10 l 10. 20 3 7.40 1
4O Mental Fatigue
The introspective reports of the subject after each experi-
ment were: March 3, “In the morning I felt very well. I did
not have any special feeling of fatigue in the course of the ex-
periment. Towards the end of the test, however, it was hard
to keep the original figures and partial products in mind, and
I repeated the same products over and over again. Association
became very slow and my mind wandered very much.” March
4, “I feel excellent after the work and am not fatigued at all.”
March 5, “This morning, I did not feel so enthusiastic about my
experiments as I did yesterday. After work, I have a little
headache and feel very weak.” March 7, “After a week's con-
centrated mental work, I am as cheerful as usual. Physically
and mentally no effect of the hard work seems to remain this
morning.” *
Along with the multiplication test, the test for ‘transferred
fatigue’ was made. Before and after mental multiplication last-
ing for some time, the time taken for establishing connections
between English words and their corresponding German words
was measured. The procedure in the test was as follows: Two
sets of materials were prepared. One of them consisted of many
lists, each containing ten German words with their English
equivalents. The other set consisted of lists containing the
English words which were in the first set, but arranged in dif-
ferent order. The subject first learned the German equivalents
of the English words in the first set. When this was done, i.e.,
when the subject could call out the German words when the
English words were presented, she took the corresponding list
of the second set and wrote down as quickly as possible by the
English words their corresponding German equivalents. The
time spent in this process was measured from the instant of first
sight of the list with the German and English words to the com-
pletion of the task of writing down the German equivalents.
Before and after mental multiplication, four of these lists were
learned and the time taken for learning each one recorded. The
results of the experiment are given in Table V.
Problems and Experiments of the Present Investigation
4 I
TABLE V
Time for learning German equivalents of English words before and after
approximately eleven hours of continuous mental multiplication of four-
place Inumbers by four-place numbers.

Multiplication practice test
Association test
Time takenlTime taken
Num- for one for one
ber of | Rest group, group,
Date The time of day for exam- period before after
mental multiplication ples mental mental
done multipli- multipli-
cation cation
Feb. 24.7:37.20–11:24,45 P.M. . . . . . 20
m sº m Sº
Feb. 25.7:04–11:09 P.M. . . . . . . . . . . . 24 2.05 3.00
3.15 2. 15
2.40 2.25
2.10 3.00
Feb. 26.10:22.30 A.M.–2:46,45 P.M.. 30 1.50 2.35
1.20 3.30
2. 55 2.00
2.40 2. 15
Feb. 28|10:41,30 A.M.–9:14,45 P.M.. 51 90 m., 1.45 3.35
lunch 1.25 2.40
and 2.50 2. 20
dinner 4.30 3.05
March 210:22,30 A.M.–9:53,25 P.M.. 59
March 3|11:01,30 A.M.–10:50,30 P.M. 67 2. 15 2.40
1. 30 3.30
1.35 2.30
1.25 2.40
March 4.11:12 A.M.–10:40.30 P.M...] 67 2. 10 1.45
2.05 1. 40
2.00 2. 20
2.00 1.50
March 5||11:07,30 A.M.–10:44,30 P.M. 67 1. 10 2.10
1.50 2.00
1. 20 2. 20
l. 20 2.10
March 6||11:15 A.M.–11:20 P.M. . . . . . . 67 1.40 1. 20
- 1. 2.
2. 1.
2. 2.
* “m ” and ‘s’
equal minutes and seconds.
42 Mental Fatigue
Earperiment II
The purpose of this experiment was to investigate the in-
fluence of general mental work on the special mental and phy-
sical functions, and the relation of one function to the other.
For this purpose, the differences between the morning and
the evening efficiencies, (I) in memorizing German equivalents
of English words, (2) in doing mental multiplication, and (3)
in pulse and feeling were measured. Their direction and degree
according to the varying duration of mental work were then
worked out. The subject of the experiment was the writer her-
self. The experiment covered seventy-eight days between Feb-
ruary the first and the end of June.
The method of testing the efficiency of memory is the same
as that used in Experiment I, except that two lists of German
words instead of four were memorized. Efficiency in mental
multiplication of a three-place number by a three-place number
was measured, following the same method as in Experiment I.
States of feeling were classed as good, medium or tired. Pulse
rate was measured by the number of radial pulse beats per
minute.
In the morning at about IO o'clock before any mental work
was done and in the evening after a day's work, the subject
measured her pulse and her efficiency in memory and in multi-
plication, using different lists and examples on each occasion.
The state of feeling was recorded by introspection. With the
records of these measurements, there were carefully written
down the number of hours of sleep the night before and of
mental work during the days when the tests were made. Health
was recorded good when every physical function was normal,
not well when it was below the normal and bad when the sub-
ject was in any abnormal physiological condition.
In this investigation, the subject performed the tests on all
days when external circumstances made them possible. In order
to avoid errors which possibly might come from Suggestion or
interest of some kind, the records of experiments which were
Problems and Experiments of the Present Iuvestigation 43
obtained from day to day were kept out of sight. The subject
carefully guarded against speculating on the results of the ex-
periments. If there were errors at all in the results of the ex-
periments, they were beyond the control of the experimenter.
The results of Experiment II are given in Table VI.
TABLE VI
Efficiency in memorizing and in mental multiplication, pulse-rate, degree of fatigue felt, and state of physical well-being ob-
served before and after each day of general mental work.
f
Morning Evening
1 2 3 sº 6 7 8 9 12 13 14
--> s & | . Time, taken s
ºld # ‘ā Ś |formultiplying 3 ‘E Time taken 3
5 ‘E à à per example. 3 à for multiplying 3
§: Gº) 5.8 Ave. of 3 -Q §§ per example." 4
3 * +. 㺠examples § {e Subject's 5 § Ave. of 3 % Subject’s
#Tº & § 5 in seconds E. * | Subject's report of || 5 s examples TE Subject's report of
Date 3.3 || 3: º §: TÉ report of physical º à ...; report of physical
5. º - 3 3 – 8 a feeling condition $ 3 6 E | feeling condition
O o 2 | "… ºf ; : ‘à cº :- 'E
Ží || 3 || || || 4 5 | #5 * | 10 | 11 | #5
3 E | E ºf Q 3 ºf 9 35 Q)
3-3 || 3.5 | E 5, e E. P. 5 §. 5 Q4
T H: H Time | Error 2. É- Time Error || 2:
Feb. 4.30 & 20. 155.0 | 1. Fresh Good 22.9 288.0 | 1.0 $ tº Tired iMot well
{{ 0 & © . . . 157.5 | 1. Medium {4 {- ºr 175.0 0 . . . Medium | Good
{{ _0 tº e is º º tº tº Good {{ e & & ſº tº $ tº 76. Good {{
&t 8.50 | 9. 173.3 1.0 Medium 44 © tº 325.0 | 1. 86.5 Tired (4
{{ 6.45 || 7. 218.3 2. {{ {& 19.0 187.7 0 80.0 & Headache
& 5.30 7. 206. 7 | 1.0 & & 18.9 176.7 0 74. Good Good
“ 10| 8.20 | 7. 15 tº g g * > * Good {{ 33.3 . . . . . 79.0 | Tired &
“ 11| O 8.15 185.0 | 1. & & 20.5 || 258, 7 .7 | 84.5 | Good 44
* 12| 0 6. • . . © & (£ (4 e tº * tº tº tº & 84. Tired {&
“ 14. 4.30 7.20 tº e & * * {{ &&. tº tº e º º . & Cº. & (&
“ 15| 2.30 7.30 188.3 | 1.3 {{ Not well || 24.4 133.3 .3 || 79. {& {&
“ 16| 8.05 || 8.00 163. 3 .7 Medium & 20.8 169.0 | 1.7 77. Medium | Not Well
“ 17| 5.30 | 8.00 144.3 .7 {{ Good 28.8 213.3 || 1 , 7 || 91. Tired Good
“ 18| 4.03 || 7.00 175.0 .7 Tired £4 22.9 209.0 | 2.0 | 79. Good {{



Problems and Experiments of the Present Investigation
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Problems and Experiments of the Present Investigation
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48 Mental Fatigue
Ea:periment III
During November and December of 1910, the author trans-
lated into Japanese some chapters of Dewey’s “Influence of
Darwin on Philosophy and Other Essays,” the time taken for
translating each page being recorded. Before and after a period
of translation lasting for some time, the writer measured the tem-
perature under the tongue. Since the materials of the test were
not selected for the purpose of experiment and varied consider-
ably in difficulty, one could not expect to obtain accurate data
on the change in the rate of fatigue; but it will be seen that the
results are valuable when we come to discuss the relation of
body temperature to mental work. The results are summarized
in Table VII.
Experiment IV
This main series of experiments was performed during the
academic year of Iglo-'II at Teachers College, Columbia Uni-
versity."
The primary purposes of the experiment were to investigate,
(I) the work curve of a single mental function exercised for
two or three hours; (2) the influence of fatigue of one mental
function on the efficiency of another mental function; (3) the
relation of the amount of mental work done to the length of
rest period; and (4) the relation between mental fatigue and
certain physiological processes of the organism.
The function tested for this continuous work was that exer-
cised in multiplying mentally a two-place number by a two-
place number. For the test of transferred fatigue, the mental
functions tested were the ability to memorize nonsense syllables,
the ability to add 8 columns of Io one-place numbers, and the
ability to call up the opposite of each word of a list of words.
For the study of the relation of amount of work done to the
length of rest period, three different lengths of rest were used;
Io minutes, 60 minutes and 18O minutes. To test the relation
of mental fatigue to physiological processes, the pulse rate and
temperature were measured before and after the mental work.
Of the subjects of the experiments, all but seven were pro-
fessors and graduate students of psychology. Among the seven,
* The writer is indebted to the men and women who co-operated in this
experiment. Their zeal and care made the results especially valuable.
TABLE VII
Change of body temperature caused by mental labor as observed during the translation of English into Japanese, the speed
of work being measured by the average time per line for each page.
The speed of translation is given by the average time taken
for translating per line on each successive page, in seconds
1st, P. |2nd P. 3rd P.] 4th P. 5th P. 6th P. 7th P. 8th P. 9th P.
Date Before translation After translation
Time of day | Temp. | Time of day | Temp.
57.7 58.4 || 51.1 53.2 52.3 53. 55.4 || 48.5
Study of German.
51. 55.3 60. 56. 56.3 || 74.1 | 68.
69, 7 || 76. 63.7
Study of German.
85.2 69.6 | 66.0 58.2 | 67.2 | .
Translation for two hours, did not measure its speed.
75.0 64.2 | 61.8 ſ 61.8 |
74.4 62.4 60.0
94.2 97.8 || 79.0 55.8
69.2 101.4
94.2 || 51.6 | 72. 57.2 65.4 || 67.2
73, 8 || 71.2 --
42.6 58.2 54.0 | 57.6 || 48.0 56.4 || 53.4 || 51.6
50.4 60.0 58.2
59.4 58.8 63.6
54.6 56.4 57.6 || 48.0
*Here a new chapter, which is much harder than the old, was begun. The sudden rise of the time taken is due to the
Temperature under tongue measured
before and after translation
November 29 1:30 P. M. 98. 5: P. M. 97.8
{{ 30 | 10:37 A. M. 97.2 12: M. 97.6
(& 30 1:42 P. M. 97.7 4:55 P. M. 98.1
{{ 30 7:41. “ 97.9 9:20 “ 98.
December 2 | 10:59 A. M. 97.6 | 12: M. 97.
{{ 2 1:36 P. M. 98. 4:55 P. M. 97.8
({ 8 7: . “ 97.1 8: {{ 97.9
{{ 9 2:10 “ 96.6 4:15 “ 97.2
& 13 || 3:15 “ & © 5:28 “ tº º
{{ 13 7:20 “ 10:08 “
(ſ 14 | 11:08 A. M. 11:43 A. M.
tſ 14 || 2:19 P. M. e e 5:33 P. M.
{{ 15 | 10:56 A. M. 97.5 12:02 “
{{ 15 1:55 P. M. tº º 4:40 “ e tº
& 15 7:23 “ 8:50 “ 97.7
{{ 16 || 2:05 “ 3:28 “ tº º
(& 17 || 2:36 “ 4:21. “
change of materials.
Š
5 O - Mental Fatigue
the subject C. T. T. was a student in the Department of Polit-
ical Science and was taking graduate courses in Psychology;
the subject Sn. belonged to the Department of Philosophy and
was taking undergraduate work in the Department of Psy-
chology; the subjects, M. M., G. D. S. and P. E. R., were a pro-
fessor and graduate students in Education; C. T. R. and S. W.
were the mechanicians of the Psychological Department. All
except M. M., G. M. K. and P. E. R. were men. All but four
acted as subjects twice or more than twice.
These experiments can be divided into two kinds according
to the different materials used for the measurement of the trans-
ferred fatigue. We shall call the first kind memory-fatigue tests,
in which the ability to memorize nonsense syllables was tested
before and after continuous work in mental multiplication, and
the second kind, addition-and-association tests, in which the
ability to add numbers and the ability to associate the words
with their antonyms were tested.
Again the experiments can be divided into three kinds, ac-
cording to the different lengths of rest period, namely ten-
minute-rest-period tests, sixty-minute-rest-period tests and one
hundred-eighty-minute-rest-period tests. The procedure of the
tests was in the main, as follows: In memory-fatigue tests, the
subject was required to sit quietly for about ten minutes after
his entrance to the experiment room. The experimenter
measured the pulse rate of the subject by the number of the
radial pulse beats per minute and tested the temperature under
the tongue. The subject was then asked to memorize a list of
ten nonsense monosyllables. These syllables consisted of two
consonants with a vowel between them like gid, yat and sut. At
the end of two minutes, the signal was given and the subject
wrote down the syllables remembered. Then another list of the
ten nonsense syllables was given to the subject to repeat the
same process. The score was made by the number of letters re-
membered in their original order. For instance, if one remem-
bered all three letters in one syllable, the score I was given; if
he remembered only two letters in their right place, the score
.7 was given while for one letter remembered in its right place
the score .3 was given. When the memory test was completed,
the subject was asked to be ready for the mental multiplication.
Problems and Experiments of the Present Investigation 51
With the signal “go,' the subject looked at the first example,
and memorized the two-place numbers. With the eyes closed he
multiplied them mentally. As soon as the answer was obtained
it was written down. He immediately proceeded to the next
example. The experimenter recorded the time when the sub-
ject finished writing each answer. The work on mental multipli-
cation lasted for two hours with most of the subjects and
three hours with a few subjects. After this period of con-
tinuous mental work, the memory-fatigue-test was given with
different lists of nonsense syllables and by exactly the same
method. The pulse rate was measured here. A definite period
of rest followed this test. After the rest the subject did mental
multiplication again for ten minutes. In the addition-and-asso-
ciation-fatigue test, the whole process was the same as in the
memory-fatigue test, except that the time spent in adding eight
columns of ten single numbers, and writing the answer under
each column, and the time spent in associating antonyms with
the given words were taken before and after the mental multipli-
cation.
A word must be added to explain the use of the rest period.
In the ten-minute rest period, the subject remained in the ex-
perimental room and was allowed to do no mental work and
spent the time in conversation with the experimenter. In the
sixty-minute-rest-period test some subjects went to take
luncheon and others spent it just as they did with the ten-minute
rest. In the one-hundred-eighty-minute-rest-period test, it was
impossible to keep the subjects from doing Something. The sub-
jects who took this length of rest were a professor and an in-
structor who had to spend some part of the time for teaching.
Compared with the intense and most concentrated mental work
like mental multiplication, however, the time they spent in cus-
tomary class-room work was like a rest. The summary of the
results of Experiment IV is given in Table VIII.
TABLE VIII
Time spent per multiplication in each successive ten minutes, number of nonsense syllables held in memory correctly for
two minutes, time taken for adding eight columns of ten single numbers and writing down the answer under each column, and
time spent in associating antonyms before and after the mental multiplication—in each trial of each individual.
Subjects. . . . . . . . . . . . . . . . . . C. D. T, C. D. T. C. D. T. C. D. T. MS. MS. MS. MS.
Date. . . . . . . . . . . . . . . . . . . . . April 1 April 15 May 11 May 26 March 18 March 18 April 21 May 11
Time of day. . . . . . . . . . . . . . . 12:21–4:00 10:17–12:10 || 9:14–12:04 2:02–5:02 9:30–11:30 1:27–2:45 1:35–3:32 9:36–12:35
Temperature. . . . . . . . 970 F.
ºld
g Pulse . . . . . . . . . . . . . . 80 68 68 73
§ Memory. . . . . . . . . . . . 19 20 18 9
O
# Association . . . . . . . . . 95S 95S
Addition. . . . . . . . . . . 67S
Time I Error | Time Error | Time Error | Time | Error | Time I Error | Time Error | Time Error | Time | Error
1st 10 minutes. . . . || 44.3 .25 54.5 0 32.8 0 28.6 . 19 |144.2 2. 39.7 1.6 || 38.2 1.7 || 25.1 | 1.14
2nd {{ . . . . . . 37.7 . 12 || 41.1 0 29. 5 .05 || 23.9 0 130.8 .8 48. 3 1.3 || 46.7 1.7 26.2 | 1.17
3rd 6& 44.9 0 38.4 .06 || 26.9 .03 || 28.4 0 118.4 | 1. 62.6 1.0 || 45.8 1.4 27.6 .62
ſº 4th {& 41.3 . 14 || 37.5 . 13 || 28.0 0 29.3 . 13 | 80.3 | 1.4 50.3 1. 3 || 32.9 1.5 25.9 | 1.09
3 5th {{ 40. 5 .07 || 39.4 . 13 || 41.0 .0 26.3 .08 || 65.9 | 1.5 57.4 1.5 || 31.0 1.5 26.8 | 1.43
§ 6th {{ 36.5 . 13 || 33.3 .06 || 32.0 . 21 || 31.7 () 50. 5 | 1.6 55.7 1.1 || 42.9 1.5 24, 1 | 1.44
: 7th « 31.4 . 16 || 33.8 .06 28.6 .2 27.6 0 73.1 || 2. 54. 1 1.5 32.6 2. 1 || 29.6 | 1.45
.8 8th (t 36.2 .35 | 32.4 . 1 26.5 0 27.5 0 40.2 .9 57.5 1.0 31.7 1. 7 || 25.1 | 1.37
;: 9th {& 36.9 0 28. 1 .05 || 27.6 .05 || 31.1 . 21 55.0 | 1. 39.0 1.7 | 20.9 | 1.1
ă 10th {& 35.7 0 29.7 .05 || 36. () . 18 27, 1 .0 60.7 .4 48.8 1.2 22.4 | 1.4
11th {{ 27. 1 .03 || 31.7 .06 || 33.4 .06 59.7 .62 46.5 .7 22.3 | 1.1
Tº 12th {& 30.0 0 31.3 . 11 || 25.6 .04 || 46.6 | 1.5 40.6 1.3 24.8 | 1.3
† 13th {& 29.6 .0 30.3 0 23.1 : 1.15
Q) 14th 44 28.5 .09 || 29.5 0 26.3 | 1.26
A 15th & 28.6 || 0 26.6 || 0 24.8 | 1.29
16th (t 33.6 .06 || 21.7 O 24.3 | 1.12
17th & 26.1 30.0 0 22. 1 | 1.
18th {{ 25.9 O
Temperature. . . . . . . . 989 F.
# | Pulse . . . . . . . . . . . . . . 73 64 62 64
O
: Memory. . . . . . . . . . . . 19 20 19 10
# Association . . . . . . . . . 152S 105s
Addition . . . . . . . . . . . 78S
Rest. . . . . . . . . . . . . . . 10 m. 60 m., with 10 m. || 10 m. 60 m., with || TT | 60 m. 60 m., with
lunch lunch lunch
as 1st 10 minutes...|| 24.0 is 27.2 To T 25.6 TJ26 |317TToT 39.7 T16 21.8 1. 1 || 19.4| .92
# 2nd 4t 23.5 || 0 60 m. rest
> 24.4 | . 16
º
|

TABLE VIII—Continued
Subjects. . . . . . . . . . . . . . . . . . R. S. W. R. S. W. H. A. R. H. A. R. J. T. J. T. Pog. Pog.
Date. . . . . . . . . . . . . . . . . . . . . . April 7 April 28 April 8 May 5 March 22 April 5 April 10 April 23
Time of day. . . . . . . . . . . . . . 9:50– 9:43– 10:59– 10:28– 9:45– 9:50– 1:54– 1:27–.
11:59 A.M. 11:40 A.M. 11:42 A.M. 11:20 A M. 11:54 A.M. 11:50 A.M. 4:08 P.M. 3:36
Temperature. . . . . . . . 97.8 98.5° F.
*
g Pulse . . . . . . . . . . . . . . 66 62 75 90 92
£ Memory. . . . . . . . . . . . 16.7 19.7 13 15.7 18.1
O
§ Association . . . . . . . . . 57 S. 63 S 50 s.
Addition. . . . . . . . . . . 55 s. 54 S 45
Time I Error | Time I Error | Time I Error | Time I Error | Time I Error Time | Error | Time | Error | Time | Error
1st 10 minutes. . . . || 46.3 . 15 35.3 . 58 31.7 .25 || 48.8 .61 59.3 | 1.25 | 96.6 || 3.5 70. .3 53.2 .8
2nd {{ º 56.3 . 27 32.6 . 59 28.1 .35 || 41.8 . 59 || 86.0 | 3. 116. 1.4 77.5 .7 62.0 . 1
3rd &é 57.7 | 1.4 34.6 . 28 || 31.3 . 32 || 45.1 .49 |164.0 2 115.8 | 1.3 75.0 . 5 60.0 .7
C. 4th & 35.9 .75 || 42.3 | 1.27 | 40. 1 . 13 || 27.2 . 18 182.0 3.5 |136.2 | 1. 69. 3 | 1.29 51.3 .3
.9 5th &g 34.1 . 17 || 42.2 . 79 || 31.4 ... 5 30.8 .45 189.5 5 100.0 | 1.8 |110.8 . 17 | 51.4 ... 2
3 6th & 30.8 . 26 || 40.0 .67 28.3 .2 26, 3 . 43 |100.0 0 163. 3 | 1.7 81.3 .9 50.0 . 1
3 7th {& 37.5 .31 || 42.2 . 71 || 32.8 . 11 || 28.4 . 15 | 166.3 3. 138.8 . 25 || 77.5 ... 6 49.6 . 3
.8 8th 4& 29.8 .3 39.2 .75 26.5 . 1 22.6 . 38 |310.0 2. 176.0 | 1. 71. 1 .4 66.7 .7
;: 9th {& 26.3 .9 34.2 . 53 24.2 . 25 | 17.4 . 5 |227.0 | 2. 160.0 ... 5 76. 3 | 1. 57.2 .3
p 10th {{ 33.2 .44 || 29.8 . 15 24.3 . 13 17.7 . 26 || 117. 5 | 1.5 143.8 1.5 69.4 .4 46.9 . 5
8 11th 4& 31.1 . 26 || 32.1 .63 25.6 0 16.3 .6 |150.0 2. 183.3 .33 61.1 .6 52.3 .3
". 12th {& 29.0 .8 32.9 . 58 25.5 .2 16.0 .5 77.0 2.5 161.7 | 1.25 55. .8 55.4 .3
B 13th (g 32.6 , 24 31.2 . 5 - 162.5 2.0 54.5 .5 46.8 .5
Q 14th (£
F. 15th {&
16th 44
17th &g
18th 44
Temperature. . . . . . . . 97.2 970
* | Pulse . . . . . . . . . . . . . . 56 53 56 38 87
O
: Memory. . . . . . . . . . . . 16.7 19 8 9.7 19.7
Q
: Association . . . . . . . . . 63 s. 59 S. 60 S.
Addition . . . . . . . . . . . 55 s. 50 S. 43 s.
Rest. . . . . . . . . . . . . . . 60 m., with (50 m 180 m. 180 m. 180 m. 10 m. || 10 m.
UIHAC
M. M. 1st 10 minutes. . . . . . 28.5 .6 33.s . 15 || 32.6 .31 - 21.7 . 55 157.6 1.2 51. 1 .5 42. ... 1
ſ
g;

TABLE VIII—Continued
Subjects. . . . . . . . . . . . . . . . . . . Chs. Chs. M. M. M. M. G. M. R. G. M. K. C. T. R. C. T. R.
2-ovu . . . . . . . . . . . . . . . . . . . . . . May 19 May 20 March 20 May 6 May 2 May 5 May 8 May 15 CVI
Time of day . . . . . . . . . . . . . . . 10:32 A.M.– 9:22– 2:30– 2:16– 3:14– 12:56– 14:3— 2:34– -P-
12:22 P.M. 11:22 P.M. 4:28 P.M. 4:10 P.M. 5:05 P.M. 2:46 P.M. 3:40 P.M. 4:34 P.M.
Temperature. . . . . . . . 989 F. 88
24 Pulse . . . . . . . . . . . . . . 72 60 76 83
$-
§ | Memory. . . . . . . . . . . . 18 16
# | Association. . . . . . . . . 90 s. 80 s. 55 s. 74 s.
*4- -
Ä Addition . . . . . . . . . . . 110 s. 46 s. 50 s.
Time I Error | Time I Error | Time I Error | Time Error | Time Error Time I Error | Time I Error | Time Error
1st 10 minutes. . . . [103 . 15 55. .9 |160.0 O 100.8 0 60.0 | 1.5 52.7 . 8 177.7 | 1. 89.8 1.3
2nd & . . . . . . 90. 1. 1 52. 1 .8 ||149.5 | 1.25 | 92.5 17 | 68.8 | 1.1 41. 7 .4 |114.4 ... 6 58.8 1.3
3rd {{ . . . . || 87.8 .8 45.1 . 5 ||140.3 O 101.7 5 61.9 7 64.4 . 7 118. 1 0 79. O 1.5 s
C 4th & 70.3 ... 6 52.5 . 7 |165.8 5 108.2 | 1 102.0 w 50. 5 . 5 94. .3 87.1 2.8 OS
.9 5th {{ 70. 2 | 1.3 38.8 .4 |165.5 25 |114.8 || 1 54.7 . 36 || 42.1 .5 |138.4 ... 6 75.6 1. §
* 6th & 73.2 .9 62. 2 . 5 |114.7 178. 3 66.3 | 1.7 41.0 ... 2 99.0 .8 73.5 ... 6 Sºłº,
.# 7th & 71.2 .9 37.9 . 3 |173.3 0 125.0 17 | 66.7 . 67 || 53.2 . 5 103.3 . 17 | 75.0 1. S.
Q. 8th {{ 68.7 .4 42.7 .9 |146.3 . 75 151.3 O 64.4 .44 38.8 . 6 100.5 0 125.4 ... 8
£ 9th {{ 9.5 | 1. 35.9 . 7 |150.0 0 112.0 ... 2 55.9 . 36 || 38. 3 . 3 #101.4 || 1 118.8 .8 ‘r
5 10th {{ 121.0 .2 40.3 .4 180.3 | 1.3 77.3 | 1.4 42.2 0 61.1 . 3 |130.0 0 81.9 .5 S.
E 11th &&. 114.0 .4 55.0 | 1. 119.0 O 128.3 ... 5 43. 1 7 40.6 . 2 150.5 2 60.6 O CŞ'
": # 6& 122.0 .7 38.4 ... 3 92.5 5 112.0 .7 42.5 O 45.3 . 3 |117. 6 81.9 .8 Sº
<!--> 3t, {{ CS
5 | iº, {{
> 15th {{
16th {{
17th &
18th &
Temperature. . . . . . . . 989 F.
- Pulse . . . . . . . . . . . . . . 63 56 66 75 82
Ald
§ Memory. . . . . . . . . . . . 19 14
5 Association . . . . . . . . . 60 S. 63 s. 59 s.
<!-->
* | Addition. . . . . . . . . . . 90 s. 58 45 s. 70 s.
Rest. . . . . . . . . . . . . . . 60 m. 10 m. 10 m. 10 m. - 10 m. 10 m.
1st 10 minutes. . . . . 63.5 ! .6 || 34.7 | .6 69.4 .9 - - T sº.T. 2 T57.3 T 3
Tº s
# 60 m.
§ 5 30. .9

TABLE VIII—Continued
Subjects. . . . . . . . . . . . . . . . . . . P. E. R. P. E. R. P. E. R. S. W. S. W. S. W. H. L. H. A. J. C.
Date. . . . . . . . . . . . . . . . . . . . . . March 27 March 28 April 26 April 10 April 13 May 10 April 8 April 1
Time of day. . . . . . . . . . . . . . . 3:54– 4:08– 9:40– 9:42– 1:16, 15– 1:53– 10:25 A.M.– 9:25–
5:27 5:08 10:40 A.M. 11:50 A.M. 3:40 P.M. 3:48 P.M. 12:15 P.M. 12:04
Temperature. . . . . . . . 999 F. -
24 || Pulse . . . . . . . . . . . . . . 83 98 82 83 68 59 85
$–
§ | Memory. . . . . . . . . . . . 10.7 14.4 12 20 19
§ Association . . . . . . . . . 175 S. 57 S.
*4-3
à | Addition........... 120 s. 100 s.
Time Error | Time I Error Time I Error | Time Error | Time I Error | Time | Error | Time I Error | Time I Error
1st 10 minutes. . . . [1106. 72.8 1.1 49.6 .7 93.0 ... 6 74.3 . 14 | 69.0 | 1.2 44.1 0 39.2 .8
2nd £g . . . . $ 76.4 84.1 .9 52.5 .75 157.5 | 1. 85.0 . 14 || 54.9 | 1.5 88.0 | 1. 47.6 . 5
3rd {{ 110.8 56.5 .7 66.0 .7 84.2 | 1. 74. 4 . 5 #102.5 .7 39.6 . 07 46. 1 .5
4th {& 78.2 57.5 .2 47.8 . 5 |113.6 ... 6 87.4 | 1.9 |198.4 | 1. 45.8 . 15 33.1 .4
g 5th (g 66.9 67. 2 1.2 51.8 .4 122.0 ... 6 90.4 .6 | 186.3 1. 39.7 . 27 43.4 .2
3 6th & 83.7 52.7 .9 61.0 . 1 85.7 .4 63. 3 | 1. 166.0 | 1. 65.9 .44 || 36.4 . 13
.# 7th 4t 1.15, 0 68.9 . 7 |123.0 ... 6 66.7 | 1.3 |170.0 | 1. 50.0 . 16 || 30.6 .28
# | 8th & 66.9 50.4 .7 106.7 | .8 71.7 2.2 | Went to sleep 51.4 .09 30.4 .47
TE 9th {{ 59.3 52.1 . 2 104.1 | 1.7 70.9 .63 — 45.9 .01 26.6 . 34
E. 10th & 47.5 44.2 .5 |119.0 | 1.6 64.7 , 58 77.5 . 5 34.4 . 16 || 31.1 . 55
p- 11th (g 46.5 .2 |103.3 ) 1.8 |101.4 | 1.4 52. .8 36.0 . 27 | 26.5 . 22
§ | 12th ſt 46.3 | 1. 103.3 | . 8 71.3 | 1.1 39.0 || 0 22.7 .23
§ 13th {& 126.0 .2 98.7 ... 7 25.0 .21
> 14th {& 88.0 ... 6 62. 3 .5 28.0 .68
15th 4t 7. 0 | 1. 26. 5 , 69
16th {& 31.5 .47
17th £&
18th &
Temperature. . . . . . . . 989 F.
Pulse . . . . . . . . . . . . . . 85 81 65 65 61 49 66
ºld
§ Memory. . . . . . . . . . . . 10.7 10 8.7 20 14
§ Association . . . . . . . . . 60 S. 62 S.
+º
* | Addition. . . . . . . . . . . 90 s. 119 S.
Rest. . . . . . . . . . . . . . . 10 m. 60 m., with || 10 m. 60 m, 60 m., with 60 m., with
lunch lunch lunch
343 *- 44.3 .3 |100.0 .8 ſ 61 6 || 80. 1.4 32.6 .31 | 16. 7 | . 59
㺠71.9 || 1 , 3
# 5
§

56 Mental Fatigue
TABLE VIII—Continued
Subjects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sn. G. D. S.
Pate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 14 May 25
Time of day . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ºd
g Pulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 72
g Memory. . . . . . . . '• • * - - - - - - - - - - - - - - - - - - - - - - - - - - - 17.5
O
# Association . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 s.
Addition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 s.
Time Error Time Error
1st 10 minutes|| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76.3 .63 61.4 | 1.4
2nd “ . . . . . . . . . * * * * * * * * * * * * * * * * * * * * * * * 105.8 83 47.2 | 1.5
3rd " ||. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86.9 57 65. 7 .78
§ 4th " ll. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.4 8 54.8 .82
3 5th * ||. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122. 8 62. 7 | 1.3
§ 6th " ||. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86.7 67 47.3 .25
: 7th " ||. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127. 1 6 : 49.1 ! .. 77
.S. 8th * ||. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107.8 5 68. 1.
º 9th " ||. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117. 2 55.5 . 5
§ 10th " || . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153. 75 63. .4
11th * !!. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127.3 4. 48.2 .5
º 12th “ H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90.2 75 : 51.6 | 1. i
º 13th “ ll. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
J. 14th “ H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
rº 15th “ II. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16th “ ||. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17th * II. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1Sth “ II. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
# | Pulse. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 66
* Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.7
*: Association . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 S.
Addition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 s.
Rest. . . . . . . . . . . 60 I-- 10 m
1st 10 minutes! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114. 0} . 6 46.3 .72
":
# - 60 m.
#3 44.6 | 1.15



C. D. T. remembered all syllables in the second trial. So in the fourth
trial, only one and a half minutes was given instead of two minutes for
memorizing ten nonsense syllables; and yet the subject remembered all
syllables as easily as before. For the second list we shortened the time to
one minute. Therefore, the number of syllables in the table is that which
he memorized in only two minutes and a half.
Introspective reports of the subjects:
After the experiments each subject answered the following
questions: -
I. How did the subject feel after the long mental work?
2. What made the time taken for multiplying one example
any longer, than that for the other?
Problems and Experiments of the Present Investigation 57
Subject C. D. T.
After trial I, “A slight pain across the eyebrows. The fluctua-
tion of the time taken for multiplying one example is partly due
to the difference of difficulty of different examples and partly to
the disturbing thoughts.”
After trial 2, “I have a slight pain across eyebrows, feel fine
generally. I wondered sometimes whether I was doing well,
and forgot the numbers. Sometimes, I saw the table between
my eyelashes and was disturbed. Once, a voice outside made
me stop a moment. After about three-fourths of the test was
over, I found my hand was shaking, I have known it to do this
only occasionally when playing chess. I had to stop it by think-
ing hard.”
After trial 3, “I worked very hard to-day. The main diffi-
culty is lack of ability to concentrate the attention. I was dis-
turbed by what I saw whenever I opened my eyes.”
After trial 4, “The process became almost automatic. Some-
times I could get the answer by the first sight of the example.”
Subject MS.
After trial I, “I feel well in general but have pain in my eyes
which I never had in reading and studying. I can visualize the
numbers very easily. The process is very difficult, and the
length of the time is due to the inability to move. The mind
seemed perfectly blank. If I could only have moved across the
room, I could have done the work much easier.”
After trial 2, “I can not say that I am tired. I have severe
pain in my eyes and head. I got very angry when I could not
do the work so well as I wanted.” -
After trial 3, “ The sums of nines and eights confused me.
I felt so discouraged that I felt most of my answers were merely
guesses at those points. The smaller numbers seemed easy to
me and I felt no discomfort with the last sheet. I feel very un-
comfortable—I have no headache. I could visualize very easily,
I think much more easily than in the other test. Perhaps this
is due to the prolonged test I have been taking on imagery since
I took the last test.”
Subject R. S. W. -
After trial I, “(I) I feel well. (2) Some problems were
done by short cuts, e.g., 54 × 98 = 54 × IOO — 54 × 2 = 54OO —
IO8= 5292; or again 75 × 86 = % of 8600 or 4300 + 2 of
this. Other problems were difficult to remember; that seemed
the main difficulty. One or two distractions from noise out-
side; aside from these not much distraction. (3) Sometimes I
felt clearer-headed than at other times. I did not reduce the
58 Mental Fatigue
methods to automatic uniformity. It seemed to me thanſ con-
scious effort entered mostly when I was obstructed.”
After trial 2, “(I) Felt pretty good but yawned several times.
Felt rather dull and confused most of the time. (2) Used no
shortcut methods except near the start as noted. Hitherto, I
had always -- 4 instead of X 25, and X IOO — 2 instead of X 98.
But I decided it would be better to stick to a routine method.
(3) The great trouble seemed to be the remembering of
the given numbers, and I changed the method of retaining them.
Hitherto, I had repeated over 2, 4, 7, 3,' when the problem was
24 × 73; and Sometimes I had also said 2, 7; 2, 3; 4, 7; 4, 3;’
this being the order of my multiplications. But this did not
seem to work very well as a device for remembering the num-
bers; and I tried a new method which seemed to work better,
i.e., taking the 4 digits around in a circle. Thus for the pair
35
79
or three times before beginning to multiply. Then I multiplied
by 3, as in the usual way, viz., ‘3 × 9 = 27; 3 × 70 = 2 IO, + 27
= 237. Next added to the partial sum 5 X 7 ; then multiplied
by IO and added 5 × 9. This seemed to be more reliable than
previous methods of memorizing the numbers. (4) No visual
images. I tapped the table, locating the digits as it were, but
without going there with any writing movements.”
, I begin with three and said 3, 5, 9, 7; 3, 5, 9, 7;' two
Subject H. A. R.
“Conditions favoring rapidity: (a) Inhibition of external
stimuli. (b) Inhibition of (I) distracting or (2) inhibiting
ideas. (I) Irrelevant ideas—(not more than seventeen in this
case). (2) Especially unfavorable attitudes, self-conscious fears
of errors inhibiting from letting himself go—positive side, an
attitude of confidence or freedom. (c) Short-cut method, e.g.,
multiplying by 97 multiply by IOO and subtract the product of
3 × the no. (d) Apparently easier objective combinations.”
Subject J. T.
After trial I, “I feel pain behind the eyeball, dull and diffuse.
The greatest length of time is due to the inability to keep the
problem in mind and the partial products while arranging them
for the addition.”
Subject M. M.
After trial I, “I have no pain in my eyes. The length of time
is due to the number of repetitions without results.”
After trial 2, “It was very hard for me to remember the
figures. I had no headache.”
Problems and Experiments of the Present Investigation 59
Subject Pfg.
After trial 2, “I felt lazy when I was multiplying them. I
had pain in my eyes and cramp in my right arm.”
Subject C. T. R.
After trial I, “It became more and more easy to visualize the
numbers. The trouble is that I do not seem to have enough
energy to go on.”
Subject P. E. R.
After trial I, “I feel all right and have no pain in my eyes.”
Subject H. L. H.
“I. Feel well and in average shape mentally.
“2. Some problems are distinctly harder than others. The
difference seems chiefly due to the difficulty of adding the two
sums after the multiplication has been performed. I can only
image these two sums in their proper special position for adding
for a brief moment. If the numbers to be added combine quickly
enough, the addition can be made in this brief moment. If not
I have to start the adding all over again. I cannot hold the
two numbers in the form of visual imagery. I have to keep
saying either both of them or at least one of them (usually the
multiplier) to myself. The multiplying comes quickly. Then
I find that the original numbers are gone completely and I am
left alone with the two products. I frequently find myself hang-
ing on to these products, saying them over and over again, but
being unable to get a special picture so as to know which of
the digits to add together. If I lose one of these products, I
have to look at the paper again in order to learn what the
original numbers are.
“3. Was not conscious of a wave of attention, but the prob-
lems seemed to get easier toward the end of the series. In the
first part of the series, I did not have a perfectly comfortable
position. Felt rather formal and restrained. As the test went
on I began to slouch down in my chair in a position which I
frequently assume at my desk. Along with this change the
problems seemed to become easier. I can not say whether I felt
like assuming this attitude because the problems were not so
difficult and permitted a little relaxation, or whether the change
in position was what made the task easier.
“4. In the beginning, I was conscious of nothing but the num-
bers, but as the test progressed I found my mind wandering to
other things—to accidental and irrelevant characteristics of the
numbers (such as that the multiplier was just half or just one-
third of the multiplicand). During the latter part of the test
I once found myself in the midst of the problem, looking at a
6O Mental Fatigue
sparrow that has been playing on the window sill. Up to this
time I had ignored him.
“5. In the beginning, it was easy to confine my attention to
the problems. But toward the end it became more and more
difficult to keep outside thought out of my mind, although there
was, in spite of this tendency to distraction, the feeling that I
was making better time in the test than in the first part of the
series. I found myself wondering if this increased speed was
partly due to the fact that my mind wandered a little and
enabled me to approach each problem without so much feeling
of effort.”
CHAPTER III
THE INFLUENCE OF MENTAL WORK ON
PHYSIOLOGICAL PROCESSES
In Table IX, an attempt is made to find the difference in the
pulse rate of subject T. A. in the morning and in the evening
according to the different number of hours of mental work
during the day. The days are divided into ten different kinds
according to the different number of hours of mental work, and
under each kind there are given in pairs the morning and the
evening pulse rates. In the table, “O—I ‘’ means the days when
the duration of mental work was from zero to fifty-nine minutes
inclusive, “I–2,” from one hour to an hour and fifty-nine
minutes inclusive, and so on. The data came from Table VI.
TABLE IX
The relation between the degree of change in the pulse-rate and the num-
ber of hours of mental work.
0–1 Hours of work 1–2 Hours of work
Date Morning | Evening | Ratio Date Morning | Evening | Ratio
Feb. 5 79.5 77.0 96.8 Mar. 4 || 73.0 81.0 110.9
“ 10 || 88.0 79.5 90.3 May. 17 | 94.0 98.5 104.8
“ 27 | 85.0 84.0 98.8 “ 21 || 92.5 89.0 96.2
Mar. 6 79.5 83. 5 105.0 “ 23 94.5 90. 5 95.7
“ 8 || 78.0 70.0 89.7 “ 25 96.0 87.0 90.6
“ 28 || 100.0 92.0 92.0
Average 96. I 96.7
2–3 Hours of work 3–4 Hours of work
Date | Morning Evening | Ratio Date Morning Evening | Ratio
Feb. 15 | 73.0 79.0 108.2 || Mar. 7 82.0 80.0 97.6
“ 26 81.0 91.0 | 112.1 “ 9 || 79.0 70.0 88.6
Mar. 5 75.0 71.0 94.7 Apr. 22 93.0 90.0 96.9
June 7 || 101.0 92.5 91.6
Mar. 11 || 83.5 89.0 | 106.6
Average 102.6 94.4




6I
62 Mental Fatigue
4–5 Hours of work 5–6 Hours of work
Date | Morning | Evening Ratio Date | Morning | Evening Ratio
Feb. 4 81.5 83.5 | 102.4 Feb. 9 || 83.0 74.0 89.1
“ 18 || 86.0 79.0 91.8 “ 17 78.0 91.0 116. 7
Mar. 3 || 87.0 83.0 95.4 “ 21 87.0 86.5 99.4
Apr. 16 || 86.0 84.0 97.7 Apr. 23 83.0 84.0 101.2
May 18 100.0 96.0 96.0 May 9 91.0 79.0 86.8
“ 24 92.0 90.0 97.8 “ 10 | 84.0 90.0 107.1
“ 27 | 98.5 87.0 88.3 “ 11 || 95.0 88.5 93.2
“ 12 || 94.0 88.0 93. 6
Average 95.6 98.4
6–7 Hours of work 7–8 Hours of work
Date | Morning| Evening Ratio Date | Morning | Evening | Ratio
Mar. 8 93.0 80.0 86.0 Feb. 23 | 89.0 76.0 85.4
“ 18 90.0 82.5 91.7 “ 24 92.0 88.5 96.2
Apr. 5 85.5 74.5 87.1 Mar. 1 i 81.0 73.5 90.7
“ 18 100. 5 || 101.0 100.5 Apr. 12 87.5 78.0 89.1
June 20 98.5 90.0 91.3 “ 23 85.5 80.0 93. 6
“ 22 98.5 87.0 88.3 “ 14 | 82.5 78.0 94.6
“ 23 || 103.3 98.5 95.3
Average 91.5 91.6
8–9 Hours of work 9–10 Hours of work
Date Morning | Evening Ratio Date | Morning | Evening | Ratio
Feb. 7 | 85.0 86.5 | 101.8 || Apr. 7 | 92.5 | 87.5 95.7
“ 10 83.6 79.0 94.5 May 14 92.5 92.5 100.0
“ 16 86.0 77.0 89.5 “ 16 107.0 94.0 87.8
“ 22 84.0 , ; 80.5 95.8
“ 28 92.5 78.0 84.3
Mar. 16 || 86.0 84.0 97.7
Apr. 11 83.0 74.0 89.2
Average 93.2 94.5





If we examine the average ratios of the different kinds of
days on which observations were made, we find that the ratio
does not decrease regularly with the number of hours of mental
work (i.e., the pulse rate does not decrease in any strict arith-
metical ratio to the amount of increase in the time of mental
work). That the changes in the two factors in question are not
wholly independent of each other is, however, shown by the
Influence of Mental Work on Physiological Processes 63
following fact: If we take the average of the average per-
centages of decrease on the days of “O—I,” “ I—2 ” and
“2—3; ” that of the percentages on the days of “3—4,” “4—5”
and “5–6; ” and that of the percentages on the days “6—7,”
“7–8,” “8–9 ° and “9–IO,” we get respectively 98.5 with
A. D." of 6, and A. D. (t. av.–obt, av.) of I.5, 96.1 with A. D.
of 5.5 and “A. D. (t. av.–obt. av.) of I.3, and 92.7 with A. D.
of 3.2 and A. D. (t. av.–Obt. av.) of .6. This means, of course,
on the whole, that by evening the pulse rate has decreased least
compared with the morning rate when the subject has worked
mentally less than three hours during the day, the ratio of the
decrease being I.5 per cent, and that the decrease is greatest
when the hours of mental work are from six to ten, the ratio
of decrease being then 7.3 per cent of the morning rate. The
difference, however, might be greater if the pulse rates were
measured immediately before and after the mental work, for
the following reason: Since the time of day at which the mental
work was performed varies, the mental condition in the evening
cannot be expected to be the same on all the days when the same
number of hours were devoted to mental work. For instance,
if the subject did seven hours of mental work from Io a. m. to
6 p. m. and spent the evening in rest or recreation, the mental
condition at Io o'clock in the evening, when the pulse rate was
measured, might be only a little affected by the work of the
day. This state of mind cannot be the same as that at IO p. m.
after seven hours of mental work between 2 p. m. and IO p. m.
This tends to minimize the difference between the days of
greater and less mental work. If, therefore, 5.8 per cent (which
is the difference between the average percentage when the mental
work lasted for more than six hours and that of the days
when it lasted less than three hours) means a real difference due
to the greater amount of mental work, it would be still greater
if the pulse had been measured just at the close of a certain
amount of work.
A fair inference from the actual figures given above would
be that, so far as the particular subject tested goes, the average
decrease of pulse rate tends to become greater as the duration
of mental work increases. The chances are 8.9 to I that the
1. Average deviation.
* Reliability.
64 Mental Fatigue
true average percentile decrease of pulse rate during days of
o–3 hours of mental work will not exceed the average obtained
for decrease of pulse rate during the days of 3–6 hours’ mental
work; and the probability is 52 to I that the true average per-
centile decrease in pulse rate during a day of 4–6 hours’ mental
work will not exceed the decrease during a day of 7—IO hours
of mental work.
Let us now consider the correlations between change in pulse
rate and in efficiency of certain mental functions.
If the decrease of pulse rate can, to a certain extent, be a
measure of mental fatigue, there ought to be some correlation
between this and the decrease of efficiency in the mental func-
tions tested, provided that the latter is a true measure of mental
fatigue. Table X gives in full the relations of changes in the
two factors.
* 2 x. 3, * e tº
Using the formula, r=z- we obtain a correlation
of about —.II, between thºse of the pulse rate and the
decrease of the time taken for memorizing the German equiva-
lents of given English words, and a correlation of -.II, between
the decrease of the pulse rate and the decrease of the time taken
for doing mental multiplication. If we use the median ratio
method, using the formula,
ſº A/B ratio , Mid B/A ratio
r=} var. A var. B |
var. B var. A J
the former correlation becomes –.243; and the latter, —.2.193.
Since measurements of the mental abilities were made by the
times taken to do equal amounts, a greater decrease of mental
ability is indicated by a larger percentage. A greater decrease
of pulse rate is indicated by a smaller percentage. Therefore,
a negative correlation indicates that the greater the decrease in
the pulse rate the greater the decrease in the mental efficiency
of the function studied.
A fair conclusion from the figures obtained would be that in
the case of the individual T. A., the decrease of the pulse rate
is a little correlated with the decrease in efficiency of the func-
tion of memory and of mental multiplication.
TABLE X
Rate of pulse for morning and evening; rate of decrease and the divergence of the individual percentages from the average
percentage; average time taken to memorize a German word in the morning and in the evening; rate of decrease and the diver-
gence of the individual percentages from the average percentage; average time for mental multiplication in the morning and
in the evening; rate of decrease; and the divergence of the individual percentages from the average. Subject T. A.
Pulse Memory test Mental multiplication test
Day The The The
Morn- | Even- ratio of Devia- || Morn- | Even- ratio of Devia- || Morn- | Even- ratio of Devia-
ing ing |E. to M. tion ing ing |E. to M. tion ing ing |E. to M. tion
No. 1. . . . . . . . . . . . . 78. 91. 116. 7 || +21.7 21.3 28.8 || 133.8 +15.0 || 151.0 230.0 152.3 +34.5
“ 2. . . . . . . . . . . . . 73. 81. 111.0 | + 16.0 13. 3 13. 7 || 103. —15.8 || 141. 7 || 170.0 | 120.0 | +22,
“ 3. . . . . . . . . . . . . 73. 79. 108.2 | + 13.2 18, 8 24, 4 || 129. 7 || -- 10.9 || 201. 7 || 136. 7 || 67.6 —50.2
“ 4. . . . . . . . . . . . . 84. 90. 107.1 | + 12. I 9.5 10.5 110.5 —8. 3 || 123.3 87.6 | –30.0
“ 5. . . . . . . . . . . . . . . 83.5 | 89. 106.6 | + 11.6 10.6 11.6 109.4 —9. 4 || 153. 7 || 130.0 83.9 —33.9
“ 6. . . . . . . . . . . . . 79.5 83. 5 || 105.0 | + 10. 16.6 18.1 108.5 —10.3 97.5 132. 5 135.9 +18. 1
“ 7. . . . . . . . . . . . . 83. 84. 101.2 +6.2 11.7 12.8 || 109.4 —9.4 || 185.0 | 133.3 70.9 —46.9
“ 8. . . . . . . . . . . . . 82.5 92.5 100.0 +5.0 13.0 18.3 140.8 +22.0 iſ 100.0 | 163. 3 | 163.3 +45. 5
{{ 9. . . . . . . . . . . . . 85. 84. 98.8 +3.8 11. 10.6 96.4 —22.4 || 125.0 | 126.6 | 101.3 —16.5
“ 10. . . . . . . . . . . . . 47. 86. 98.3 +3.3 19.8 22. 5 || 113.0 —5.8 || 121. 7 | 163. 3 133.9 + 16.1
“ 11. . . . . . . . . . . . . 92. 90. 97.8 +2.8 10.5 13.6 108.8 —10. 0 || 113.3 | 1.49.0 | 123.6 +5.8
“ 12. . . . . . . . . . . . . 86. 84. 97.7 +2.7 11.3 12. 3 | 115.2 | –3.6 || 160.0 || 145.3 90.6 —27.2
“ 13. . . . . . . . . . . . . 86. 84. 97.1 +2.7 16.5 | 20.8 || 126.1 + 7.3 || 127.7 | 118.3 92.6 | —25.2
“ 14. . . . . . . . . . . . . 82. 80. 96.6 +2.6 11.5 15.0 | 130.5 | + 11. 7 || 148.3 150.0 | 101.1 —16. 7
“ 15. . . . . . . . . . . . . 75. 77. 96.7 + 1. 7 || 15.0 20.5 133.3 | + 14.5 || 153. 7 || 130.0 84.6 | —33.2
“ 16. . . . . . . . . . . . . 100. 96.5 96.3 +1.5 || 12.0 13.8 115.0 | —3.8 || 138. 3 | 111.8 80.9 —36.9
“ 17. . . . . . . . . . . . . 92.5 | 89. 96.2 + 1.2 13.7 13.0 99.3 —19.5 96. 7 || 130.0 134.4 + 16.6
“ 18. . . . . . . . . . . . . 92. 88. 96.2 + 1.2 14.5 21.5 || 148.3 | +29. 5 || 138. 3 | 196. 7 || 142.2 | +24.4
“ 19. . . . . . . . . . . . . 84 80. 5 95.8 + .8 18.5 21.9 || 118.4 —. 4 || 165.0 231. 7 140.4 +22.6
“ 20. . . . . . . . . . . . . 94.5 90. 5 95.8 + .8 12.2 10.5 | 85.2 —33.6 || 123.3 97.4 78.9 —38.9
“ 21. . . . . . . . . . . . . 7. 83. 95.4 + .4 20. 22.9 || 108.8 —10. 0 || 173.3 185.0 | 106.8 —11.0
* 22. . . . . . . . . . . . . 83.6 79. 95.2 + .2 30.3 25.3 116.6 —2.2 || 212.7 278.7 131.0 + 13.2
º




TABLE X—Continued
Pulse Memory test Mental multiplication test
Day The The The
Morn- | Even- ratio of Devia- || Morn- | Even- ratio of Devia- || Morn- | Even- ratio of Devia-
ing ing E. to M. tion ing ing |E. to M. tion ing ing |E. to M. tion
No. 23. . . . . . . . . . . . . 75. 71. 94.7 —. 3 11. 3 || 13.1 | 115.1 —3. 7 || 145.3 | 153.3 105.5 | –12. 3
“ 24. . . . . . . . . . . . . 92.5 87.5 94.6 —.4 13.8 || 14.0 | 101.5 —17.3 || 125.3 143. 3 | 114.3 | —13. 5
“ 25. . . . . . . . . . . . . 93. 90. 94.6 —.4 11.8 || 15.0 | 127, 1 +8.3 || 148.3 173.3 || 116.9 —.9
“ 26. . . . . . . . . . . . . 82.5 78. 94, 5 —. 5 10.3 || 14.5 140.8 +22.0 || 121.7 191. 7 157, 5 +39.7
“ 27. . . . . . . . . . . . . 85. 5 80. 93. —2.0 10.3 | 15.9 154.4 +35.6 || 162.5 | 162.5 100. —17.8
“ 28. . . . . . . . . . . . . 95.0 88.5 | 93. —2.0 10.9 14.3 || 131.2 | + 12.4 || 113. 3 || 135.0 | 1:19. 1 +1.3
T 29. . . . . . . . . . . . . 94.0 | 88. 93. —2.0 10. 12. 3 | 123.0 | +4.2 || 110.0 | 132.5 | 120.4 || --2, 6
“ 30. . . . . . . . . . . . . 100.0 92. 92. —3.0 10. 9.5 95.0 | +22.8 || 106.7 | 127.0 119.0 + 1.2
“ 31. . . . . . . . . . . . . 86. 79. 91.1 ! —3. 1 15.8 22.9 || 144.9 +26. 1 || 181. 7 || 229.0 | 110.9 —6.9
“ 32. . . . . . . . . . . . . 101. 92.5 91.6 —3.4 || 20.0 20.3 || 101.5 —17, 3 || 116.3 | 186.7 | 160. 5 || -- 42.7
“ 33. . . . . . . . . . . . . 98.5 | 90.0 91.4 —3.6 15.8 || 20.9 || 132. 3 | +13. 5 || 108.3 198.3 | 183. 1 || --65.3
“ 34. . . . . . . . . . . . . 81. 73.5 90.7 | —4.3 23. 3 || 26.4 || 113.3 —5. 5 || 126.3 170.0 135. 3 || -- 16.5
“ 35. . . . . . . . . . . . . 96. 87. 90.6 | —4.4 15, 0 || 10. 72.0 —46.8 || 130.0 | 138. 3 | 100.6 —17.2
“ 36. . . . . . . . . . . . . 88. 79. 90.4 —4.6 19.0 17.3 || 87.5 —31. 3 || 195.0 265. 5 || 136. 1 || +18. 3
“ 37. . . . . . . . . . . . . 90. 89. 90.3 —4. 7 14.2 | 18.0 | 126.7 | + 7.9 || 118.3 150.0 126.8 +9.1
“ 38. . . . . . . . . . . . . 78. 70. 89.7 | –5, 3 18.0 20.0 | 111.1 : —7. 7 || 143. 3 || 140.0 97.7 —20.1
“ 39. . . . . . . . . . . . . 86. 77. 89.2 —5.8 10. 0 || 20.0 123.8 +5.0 || 124.3 | 186.3 149.9 +32, 1
“ 40. . . . . . . . . . . . . 83. 74. 89.1 —5.9 17. 5 | 18.9 || 105.9 —12.9 || 153. 3 || 176. 7 | 115.3 –2, 5
“ 41. . . . . . . . . . . . . 83. 74. 89.1 —5.9 15.0 | 16.8 112.0 —6.8 || 216. 7 || 176. 7 || 81.5 —36, 3
“ 42. . . . . . . . . . . . . 87.5 78. 89.1 —5.9 20.0 22.8 112.9 —5.9 || 127.3 | 155.5 | 122.9 +5.1
“ 43. . . . . . . . . . . . . 79. 70. 88.6 —6.4 18.0 20. 5 || 113.9 —4.9 || 122. 5 | 187.5 153.9 || +36. 1 .
“ 44. . . . . . . . . . . . . 98.5 | 87. s 88.3 | –6, 7 8.0 | 10.5 | 131. 3 | +12. 5 || 131. 7 || 145.0 | 110. 1 || –7, 7
“ 45. . . . . . . . . . . . . 87. 0 || 76. 87.3 | —7.7 17. 5 || 19.8 || 113. 1 || –5, 7 || 145.0 || 173. 1 || 119, 5 || -- 1.7
“ 46. . . . . . . . . . . . . 107. 94. 87.2 —7.8 9. 18.4 204.0 +85.2 || 145.0 | 200.0 | 137.9 || +21. 1
“ 47. . . . . . . . . . . . . 85.5 74. 5 87.0 | —8. 12. 3 14.8 | 120.3 + 1.5 || 130.0 | 178.0 136.9 || -- 19.1
“ 48. . . . . . . . . . . . . 91. 79. 86.8 —8.2 11.5 | 13.3 115.7 —3. 1 || 125.0 | 168.3 135. 5 || + 17.7
“ 49. . . . . . . . . . . . . 93. 80. 85.9 || —9.1 15.0 | 19.0 | 126.7 | +7.9 || 238.3 190.7 | 82.5 —35.3
Average. . . . . . . . 95. 118.8 117.8
3.
|



Influence of Mental Work on Physiological Processes 67
In the case of the group of individuals (the materials are ob-
tained from the results of Experiment IV, given in Table VIII),
we find such differences of pulse rate before and after two hours
of mental multiplication as are shown in Table XI.
TABLE XI
The pulse rate before and after two hours of mental multiplication and
the percentage which the latter is of the former for each individual, and
for the average of the group.
Subjects Before After %
C. D. T. . . . . . . . . . . . . . . . . . . . . . . 72 66 91.7
MS. . . . . . . . . . . . . . . . . . . . . . . . . . . 73 64 87.7
R. S. W. . . . . . . . . . . . . . . . . . . . . . . 64 54.5 85.2
J. T. . . . . . . . . . . . . . . . . . . . . . . . . . . 75 56 74.7
Pog. . . . . . . . . . . . . . . . . . . . . . . . . . . 91 87.5 96.2
P. E. R. . . . . . . . . . . . . . . . . . . . . . . 98 81 82.6
S. W. . . . . . . . . . . . . . . . . . . . . . . . . . 82.5 65 78.8
H. L. H. . . . . . . . . . . . . . . . . . . . . . . 59 49 83. ].
A. G. C. . . . . . . . . . . . . . . . . . . . . . . 85 66 77.6
Chs. . . . . . . . . . . . . . . . . . . . . . . . . . . 68.5 59.5 86.8
M. M. . . . . . . . . . . . . . . . . . . . . . . . . . 79.5 70.5 88.7
G. M. K. . . . . . . . . . . . . . . . . . . . . . . 88 82 93.2
Su. . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 78 95. 1
G. D. S. . . . . . . . . . . . . . . . . . . . . . . 72 66 91.7
Average. . . . . . . . . . . . . . . . . . . 86.7
The figures in the table show that the pulse rate is invariably
lower after mental work, the difference being 13.3 per cent of
the pulse rate before mental work. This difference, however,
might be due to the fact that the subject sat for two hours
with very little muscular movement which invariably increases
the pulse rate. Indeed, experiments tried on the subjects R. S. W.
and C. H. S. showed that the pulse rate decreased during
a one-hour rest after two hours of mental work and that the
average rate of decrease is then about 5 per cent of the rate
immediately before rest.
Consider now the correlations between change in the pulse
rate and change in efficiency of certain mental functions, the
facts being given in Table XII. -
Relating the divergence of an individual from the average
change in the mental function to his divergence from the aver-
age gross change in pulse rate, we get a coefficient of correlation
68 Mental Fatigue
TABLE XII
The relation of change in pulse rate to change in efficiency in the process
of multiplication from the first to the last ten minutes of a two hour period.
Pulse Multiplication
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Gl) &4-4 st: Piº & 3 | g a $ $ $ * +º § 4, § §§
-Q -Q O *: º3 TE 33 ** E; e g: tº § 5 § *— ;
r; re: ° 33 3 || 3 & ă ă ă #35 | £3; C 35
CO Gł) $2 92 º g-c q) q} -c ‘P: 80 ºf 80 3 92 gº P-
§ § 3 & 55 g; #| 5: §§ gä3 || $º : § 3
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35 | 35 ; ##| # 33: #g | ###| ###| #| #
# #5 $35 | # ###| ###| ### ### ### | #
P- P+ ſº Q pd ſº <! . . . ~d ſd ſº
Pfg. . . . . 91.0 87.5 4. —5.5| 96.2 | +8.7 61.6 50.7 82.3 —9.6
Sn. . . . . . 82.0 78.0 4. —5. 5 95.1 + 7.6 76.3 90. 2 | 118.2 +26.3
C. D. T. . . 72.0 66.3 6. —3. 5 92.1 +4.6 42.5 27.0 62.5 —29.4
G. M. K. 88.0 82.0 6. —3. 5| 93.2 + 5. 7 60.0 43. 1 70. 2 —21.7
M. M. . . . . 71.5 # 65.5 6. —3.5| 91.6 + 4.1 130.4 97.3 74.6 —27.3
G. D. S. . . 72.0 66.0 6. —3.5| 91.7 +4.2 61.4 51.6 80.0 —11.9
P. E. R. 90.5 83.0 7. —2.5| 91.7 +4.2 61.8 49.5 80.9 —11.0
MS . . . . . 73.0 64.0 9. —0.5| 87.6 + ... 1 38.2 40. 6 || 106.2 + 14.3
Chs. . . . . 72.0 63.0 9. —0.5| 87.4 —. 1 || 103.0 | 114.0 110.7 +18.8
|R. S. W. 64.0 55.0 9. —0.5| 85.9 —1.6 40.8 32.8 80. 4 || –11. 5
H. L. H. 59.0 49.0 10 --0. 5| 83.0 —4.5 44.1 36.0 81.6 —10.3
S. W. . . . . 82.5 64.0 19 +9.5| 77.6 —9.9 83.8 77.5 92.5 + .. 6
A. G. C.. 85.0 | 66.0 19 +9. 5; 77.6 —9.9 39.2 21.5 80. 4 || –11. 5
J. T. . . . ] 75.0 ſ 56.0 19 +9.5| 74.7 –12.8 96.6 | 161. 7 | 167.4 || +75. 5
Central tendency... 9.5 . . . . . . 87.5 . . . . . . . . . . . . . . . . . . . . . 91.4



of about 4 (.442 by the Pearson method and .366 by the median
ratio method). Using the percentile change in pulse rate, we
get a coefficient of correlation of .42 (.429 by the Pearson and
.413 by the median ratio method). The individual who loses
most or gains least in the course of the work shows, to a con-
siderable extent, the greatest drop, absolute or relative, in pulse
rate.
The similar relation of loss in ability to memorize nonsense
syllables to lowering of pulse rate is shown in full in Table
XIII. -
Relating the divergence of an individual from the average in
one change to his divergence from the average in the other as
before, we get a coefficient of correlation of about .795 (.828
by the Pearson method and .75 by the median ratio method,
using gross changes in both traits; and, .76 by the Pearson
method and .84 by the median ratio method, using the percentile
changes).
Influence of Mental Work on Physiological Processes
69
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TABLE XIV
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The relation of decrease in the ability to perform the associa-
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decrease of pulse rate is shown in full in Table XIV.

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Relating the divergence of an individual from the average
change in the pulse rate to his divergence from the average
7o Mental Fatigue
change in the ability to associate opposites, we get a coefficient
of correlation of about .I4 (+ .32 by the Pearson method and
—.O4 by the median-ratio method). Since the ability of the
mental function is expressed by the time taken to do a certain
amount of work, a higher percentage indicates a greater de-
crease of mental efficiency, while it means in the case of pulse
rate a smaller degree of decrease. For this reason, a plus cor-
relation in the case described above means an inverse relation,
i.e., an individual whose pulse rate decreased most during two
hours of mental multiplication, did best in the association test
given after two hours of work.
Relating the divergence of an individual from the average
change in pulse rate to his divergence from the average in adding
single numbers as before, we get a coefficient of correlation of
about —. I34 (–.O69 by the Pearson method and —.I.99 by the
median ratio method). There is, thus, a correlation between
the decrease in the pulse rate and that in the ability to add. On
the whole, the facts from this small group of subjects favor
the existence of a slight correlation between lowered pulse and
lowered efficiency in intellectual work. Proof of its existence
and a reasonably accurate measure of its amount can be had only
by repeated tests with many more subjects.
The Influence of Mental Work on Body Temperature
Data obtained from Experiment III, given in Table V, give
the results of many different observations with one individual
on the difference of temperature before and after mental work.
These are summarized in Table XV.
On the average, according to the figures in the table, the tem-
perature rose only O.I per cent during 2 hours and 3 minutes of
translation work.
Experiment IV gives data on the changes of temperature in
six individuals during two hours of mental multiplication, which
are given in full in Table XVI. The average fall of tempera-
ture during two hours of mental multiplication is O.2 per cent
in terms of the temperature before the mental multiplication.
Influence of Mental Work on Physiological Processes 7I
TABLE XV
The temperature immediately before and after certain hours of translation
of English into Japanese, in each different test.
The
Before translation After translation percentage
Date which
* after”
Time of Temp- Time Of Temp- is of
day erature day erature | “before”
Nov. 29. . . . . . . 1:30 P. M. 98° F. 5: P. M. 97.8 99.8
“ 30. . . . . . . 10:37 A. M. 97.2° | 12: A. M. 97.6 100.4
“ 30. . . . . . . 1:42 P. M. 97.7° 4:55 P. M. 98.1 100.4
“ 30. . . . . . . 7:41. “ 97.99 9:20 “ 98.0 100. 1
Dec. 2. . . . . . . 10:59 A. M. 97.6° | 12:00 A. M. 97.0 99.2
“ 2. . . . . . . 1:36 P. M. 98.0° 4:55 P. M. 97.8 99.8
“ 8. . . . . . . 7: {{ 97. 19 8: & 97.9 100.8
“ 9. . . . . . ... 2:10 “ 96.6° 4:15 “ 97.2 100. 6
Average . . . 100. 1
Consider now the relation between change in temperature and
in efficiency of certain mental functions.
According to the results of Experiment IV, given in Table
VIII, a coefficient of correlation of .22 is found to exist between
the fall of temperature and the decrease of the ability to memo-
rize nonsense syllables. The figure, however, is unreliable, for
the number of cases is not sufficient.
TABLE XVI
Tempera- Tempera- || Percentage
ture , ture ratio of the
before after temperature
Subjects Time of day mental mental after to that
multipli- || multipli- before mental
cation cation | multiplication
R. S. W. . 9:50 —11:59 A. M. i. 99.8° F. 97.2° F. 99.5
J. T. ... . . 9:50 —11:50 “ 98.5 “ 97.0 “ 98.5
A. G. C. . 9:25 –12:04. “ 97.0 “ 98.0 “ 101.0
C. D. T. . . 10:17 A. M.–12:10 P. M. 97.0 “ 98.0 “ 101.0
M. M. . . . . . 2:30 – 4:28 “ 98.0 “ 98.0 “ 100.0
P. E. R. . . . 4:08 – 5:08 “ 99.0 “ 98.0 “ 98.9
Average. 99.8
CHAPTER IV
THE INFLUENCE OF MENTAL WORK ON THE FEEL-
ING OF FATIGUE
The writer has, by introspection, arrived at a conception of
the nature of the feeling of fatigue very similar to that pre-
sented by Professor Thorndike, which runs as follows:
“When I tried to analyse my feelings during states which in
accord with the social consciousness I called feelings of mental
fatigue, of inability to do mental work, I found in them emotions
of repugnance at the thought of certain forms of mental activ-
ity, amounting sometimes to a sort of mental nausea; feelings
of dullness or stupidity (by which names I mean a state of un-
suggestiveness, of insipidity), cravings for certain familiar
forms of mental relaxation, feelings of sleepiness, heavy feel-
ings in the head, pains in the chest or back (from leaning against
a table and sitting upright during work) and sometimes a feel-
ing best characterized by the awkward phrase ‘mental goneness,”
which reminds one of the feeling of physical faintness. This
last is most likely the supposed feeling of incompetency, but I
get it only very rarely and not necessarily after especially hard
mental work. I fancy that it has some direct physical cause. I
was constantly surprised to find myself when feeling, as I would
certainly have said, ‘mentally tired, unable to demonstrate in
the feeling anything more than emotional repugnance to the idea
of doing mental work. On at least half the occasions this
seemed to be all there was.”
Comparing the introspective reports of the subjects on the
feelings of fatigue with the actual efficiency of mental functions,
Thorndike drew the following conclusions, “Our third conclu-
sion was that the feelings of fatigue, such as they were, were
not measures of mental inability. Kraepelin has emphasized this
fact, but chiefly in connection with the claim that we can be
mentally fatigued without, feeling so. What I wish to emphasize
is that we can feel mentally fatigued without being so, that the
72
Influence of Mental Work on Feeling of Fatigue 73
feelings described above serve as a sign to us to stop working
long before our actual ability to work has suffered any impor-
tant decrease which an experimenting psychologist could
measure and use as a warning to us.”
In order to study the problem the writer used two methods.
One was to find whether the change in feeling is in any regular
relation to that in the actual decrease of efficiency.
We classify the feelings into three: ‘good,’ ‘medium ' and
‘tired,’ no finer distinction being practicable. The figures repre-
senting the degree of efficiency in mental and physical functions
were grouped under the different kinds of feelings accompany-
ing them. Comparing the averages of these three groups of
figures, we can find the average conditions of mental and phy-
sical efficiency accompanying these different feelings. In the
second method, comparison was made between the change in
feeling and change in mental efficiency produced by mental work
lasting for certain hours. In comparison, let I stand for the
feeling ‘good,' 2 for the feeling ‘medium' and 3 for the feel-
ing ‘tired.’ The change I–I signifies that the subject felt
well both before and after certain hours of work. The change
‘ 2–2 signifies that the subject felt no better and no worse
than usual before and after mental work. Thus, nine possible
changes are represented by the combinations of these figures;
namely, ‘ I–I (from good to good), 2–2 (from medium to
medium), 3–3 (from tired to tired), ‘ I–2 (from good to
medium), ‘2—3 (from medium to tired), 1–3" (from good
to tired), ‘3–2 (from tired to medium), ‘2—I (from medium
to good), and ‘3—I (from tired to good). We express change
in mental efficiency by the ratio which the time taken to do a
given amount of work, or the amount of work done in a given
length of time in a ‘late ’ test, bears to the time taken or the
amount of work in a given length of time in an ‘early ’ test.
The degree of change in pulse rate and temperature is indicated
by the percentage which the number of beats or the degrees
of temperature after is of that before, the continuous work.
We then group the percentages according to the different
changes in feeling which accompany them and compare these
groups. The third method is to obtain a coefficient of correla-
tion between the degree of change in feeling and that in phy-
74 Mental Fatigue
sical or mental efficiency. Since the classification of the feel-
ings is only approximate, getting coefficients of correlation may
not be a suitable method for the data. However, we shall use
this method simply to supplement others. In getting the co-
efficient of correlation, we count the number of like and unlike
signed pairs and calculate r by the formula, r = cosine ºr (per-
centage of unlike-signed pairs).
I shall report first the results obtained from the facts of Table
VI for subject T. A.
The degree of change in feeling from morning to evening is
recorded by the method described above. The minus sign is
used when the feeling in the evening is worse than that in the
morning, and the plus sign in the opposite case, e.g., the changes
‘ I—2 ° and ‘ I–3 are expressed respectively as —I and —2;
2—I and ‘3—I are expressed as + I and + 2. We classify
the differences into four groups according to the hours of mental
work performed during the day and obtain the average dif-
erence of each group. On the days of from O—2 hours of
mental work, the average difference in feeling from morning to
evening is o. On days when the work lasted between two and
four hours, it is —.44; on days when it lasted between four and
six hours, –.58; on days of from six to eight hours of mental
work, -75; and on days of from eight to ten hours of work,
—.87.
&
The feeling of fatigue and the pulse rate:
With the first method described above, we find that the aver-
age pulse rate accompanying the feeling ‘good is 87.2 with
A. D. 5.5 and A.D. (t. av.–obt. av.) O.8; the average pulse
rate accompanying the feeling ‘medium is also 87.2 with A. D.
6.5 and A. D. (t. av.–obt. av.) .9; and the average pulse rate
accompanying the feeling ‘tired ' is 85.2 with A. D. 5.4 and
A. D. (t. av.–obt. av.) I.I. The probability that the true
average pulse rate accompanying the feelings ‘good' and
‘medium ” will not drop lower than that accompanying the feel-
ing ‘tired is six to one.
With the second method, we find the following relations be-
tween the change in the feeling of fatigue and the percentage
which the evening pulse rate is of the morning pulse rate.
Influence of Mental Work on Feeling of Fatigue 75
Change in pulse rate
Change
in A. D. Number
feeling Average A. D. (t. av.– Of
obt. av.) days
‘2–1? 90.8 1.2 0.7 3
* 1–1? 93.4 3.9 1.2 11
* 2–22 97. I 3.1 0.9 11
‘3–3” 112.3 1
* 1–2? 92.9 3.5 1. 3 7
* 2–3” 97.2 10.3 2.5 17
* 1–3” 99.4 3.3 1.2 8

If there were any relation between the change in the feeling
of fatigue toward worse and the decrease of the pulse rate, it
would be expected that the change in the feeling from good to
tired would be accompanied by the greatest drop in the pulse
rate, and that the percentage would be near IOO when the change
in the feeling is ‘ I—I,’ ‘ 2–2 ° or ‘3—3.’ The actual results
are very different. The average percentage accompanying the
change of the feeling ‘ I—3' is 99.4 and is next to the highest.
The change ‘2—I’ has a percentage of 90.8. On the whole,
then, the pulse rate does not change in a regular relation with
the change in the feeling of fatigue in the particular subject
tested. *
With the third method, we find a coefficient of correlation of
zero existing between the change in the pulse rate and that in
the feeling.
The feeling of fatigue and efficiency in memorizing words:
With the first method, we find that, in 41 measurements, the
average time taken to memorize a German word is I5.7 sec. with
A.D. 4.I sec. and A. D. (t. av.–obt. av.) O.64 sec. when the
subject felt ‘good'; 16.9 sec. with A. D. 3.5 sec. and A. D.
(t. av.–obt. av.) O.56 sec. in 38 measurements when the subject
felt medium ”; and 18.8 sec. with A. D. 5.37 sec. and A. D.
(t. av.–obt. av.) I.I.8 sec. in 2I measurements when the sub-
ject felt “tired.’ Thus, the efficiency of the function of memory
is highest when the subject feels best and lowest when worst.
With the second method, the following relations are found
between the change in feeling and that in the speed of memory
during the day.
76 Mental Fatigue

Percentile change in time, required to memorize
Change
in A. D. Number
feeling Average A. D. (t. av.– of
- O obt. av.) C3SèS
* 3–1” 144.9 tº s e e 1.
* 2–12 108.8 0.8 0. 5 2
* 1–1” 113.6 16. 3 4. 7 12
* 2–22 115.9 10. I. 3. 6 8
* 1–22 100. 7 15.5 5.9 7
“2–3? 116.8 13.0 3, 6 13
* 1–3” 144.8 28.6 10.9 7
Grouping these facts we have:—
* 2–1”
| 120.8 3
‘3–1” J
& 1–1’ |
114.5 20
* 2–22 J
* 1–22
| 111.2 20
& 2–3? J
* 1–3? 144.8 7
If there is any relation between the two as in the results ob-
tained by the first method, it is to be expected that the change
of feeling ‘2—3 ° and ‘ I–2 will accompany higher percentages,
i.e., greater decrease of speed of memory than the changes
‘I—I and 2–2 '; and the change of feeling ‘I—3’ still higher
percentages than the other two. The actual figures given above
do not show much of this. Yet there is an indication that
changes in the two are not entirely independent. Percentages
accompanying ‘I—I and 2–2 are about the same as those
accompanying 1–2" and ‘I–3, but highest is the one accom-
panying ‘ I—3.’ The single case of ‘3—I is, however, also
very high.
With the third method, a coefficient of correlation of o.13 is
found between the change in one function and that in the other.
The feeling of fatigue and efficiency in mental multiplication:
By the first method, the average time taken to multiply men-
tally a three-place number by a three-place number is found to
be 138.8 sec. with A. D. 30.6 sec. and A. D. (t. av.–obt, av.)
Influence of Mental Work on Feeling of Fatigue 77
4.9 sec. when the subject feels “good'; I42.9 sec. with A. D.
20.6 Sec. and A. D. (t. av.–obt. av.) 3.3 sec. when ‘ medium ';
and I51.3 sec. with A. D. 28.8 sec. and A. D. (t. av.–obt. av.)
4.6 sec., when ‘tired.’ The average number of wrong digits in
each answer under these different conditions of feeling are re-
spectively I.O, I. I and I.I.
The chances are 7 to 3 that the true average time taken to
do an example accompanying the feeling ‘good will not be
greater than that which accompanies the feeling ‘medium.’
Chances are nearly 14 to I that the former will be smaller than
that which accompanies the feeling ‘tired.’
By the second method, we obtain the following relation be-
tween the change in feeling and that in the efficiency of the func-
tion exercised in mental multiplication.
Percentile change in time required for
Ch multiplication
ange
in A. D. Number
feeling Average A. D (t. av.– of
O abt. av.) C3 SeS
* 1–12 115.1 22.4 6.1 13
* 2–22 105.5 13.8 4.0 12
* 3–3? 70.5 tº gº tº ºs 1 .
* 1–22 114.5 23. 1 8, 2 8
* 2–3? 124.6 23.8 6.5 13
* 1–3? 108.6 36.7 2.6 7
“2–1? 89.4 24.3 14.3 3

According to the figures given above, we have a much smaller
percentage accompanying the change in feeling ‘ I–3 than that
accompanying the change in feeling ‘I—I,’ ‘I–2 ° or ‘2—3.’
This is quite contrary to what we would expect if there were
any regular relation between the two changes. That the per-
centages accompanying the changes in feeling ‘I—2 and
‘2—3' are greater than that accompanying the change of ‘2–2,'
and that the percentage accompanying the change in feeling of
‘2—I is the next to the smallest, might however serve as an
indication of some relation existing between the two changes
studied. -
By the third method, we get a coefficient of correlation of .31
between a decrease of mental efficiency and a change for the
worse in the feeling.
78 Mental Fatigue
The change in feeling as related to the duration of sleep the
night before:
By the third method, we find a coefficient of correlation of
zero between the change in the feeling toward the worse and the
decrease of the number of hours of sleep the night before. In
other words, the length of sleep the night before seems to have
nothing to do with the evening feelings on the next day. Such
results as this might not be obtained if the different durations of
sleep ranged from three to nine hours instead of from six to
nine as they did in our experiment.
The results so far in this chapter concern the subject T. A.
We next consider the relations of the feeling of fatigue to
changes in physical and mental functions in the case of a group
of individuals. Here we take the materials mainly from the
results of Experiment IV (given in Table VIII) and the intro-
spective reports of the subject. In this experiment, the intro-
spective reports were obtained only after the tests. Therefore,
we are able to study only the relations of the efficiency in mental
and physical traits to the feeling after continuous mental work.
A change in any trait is expressed by the percentage which the
efficiency after is of that before the work.
The change in the feeling and that in the pulse rate:
Of nine individuals whose pulse rate was measured before
and after the two hours of mental multiplication and whose
feelings were recorded after the work, five reported that they
felt ‘medium.” These had an average rate of late to early
pulse rate of 87.5 with A. D. 8.3 and A. D. (t. av.–obt. av.)
3.7. The remaining four reported that they felt “tired,’ and had
an average rate of late to early pulse rate of 79.6 with A. D.
3.6 and A. D. (t. av.–obt. av.) I.8. On the whole, those who
felt worse after the work were those whose pulse rate decreased
most. The chances are 19 to I that the true average decrease
in the pulse rate accompanying the feeling ‘medium ” will be less
than that accompanying the feeling ‘tired.’
By the third method, we find a coefficient of correlation of
o.77 between the change in the feeling and the decrease in pulse
rate.
Influence of Mental Work on Feeling of Fatigue 79
The changes in feeling and the efficiency of memorizing non-
sense syllables:
Of nine individuals, five reported that they felt ‘medium. For
these the average ratio which the average number of nonsense
syllables remembered after is to that before, the two hours of
mental multiplication, is IOI.2 with A. D. 3. I and A. D. (t. av.–
obt. av.) I.4. The remaining four reported that they felt ‘tired,’
their average ratio in the efficiency of memory being 80.6 with
A. D. I.4.9 and A. D. (t. av.–obt. av.) 6.8. On the whole, then,
those who felt worse had a greater decrease of efficiency of
nemory." The chances are 99 to I that those who report
that they feel ‘tired ' will have a greater decrease of efficiency
in memorizing than those who report that they feel ‘medium.’
By the third method, we obtain a coefficient of correlation of
.99 between the changes of feeling and of memory ability.
The feeling of fatigue and the decrease of efficiency in the
function exercised in mental multiplication of a two-place
number by a two-place number:
The decrease of ability is shown by the ratio of the average
time taken per example in the last ten minutes to that in the
first ten minutes. Of I2 individuals, six reported that they felt
‘medium ' and had the average percentage of 76.3 with A. D.
I5.3 and A. D. (t. av.–obt. av.) 6.3. The others, reported as
having felt ‘tired, had an average percentage of 97.3 with A. D.
35.0 and A. D. (t. av.–obt. av.) I4.6. There is a probability
of 6 to I that those who feel ‘medium ” will on the average show
less decrease of efficiency in the function.
By the third method, the coefficient of correlation is found to
be .37 between the change in the feeling and that in the efficiency
of the function of mental multiplication.
Since the efficiency of memory is measured by the number of syllables,
a higher percentage means less decrease of efficiency.
CHAPTER V
THE INFLUENCE OF MENTAL WORK ON THE EFFI-
CIENCY OF MENTAL FUNCTIONS
Methods of Measurement. A glance at the figures in the
tables of Chapter II will show that the subject does the work
with higher speed in the second than in the first test. The favor-
able influence which the continued exercise of a function exerts
on its own efficiency and which does not entirely disappear within
a few minutes is called the effect of practice.
A comparison between the speed of performance at the be-
ginning with that at the close of a course of work shown in
Table TV on page 38 shows that the former is much higher than
the latter. The unfavorable effect which continued exercise of a
function produces in its own efficiency is called fatigue. That
which it exerts on other functions is called transferred fatigue.
The amount of practice gain during a certain work-period is
measured by the excess of ability after a certain length of rest
immediately succeeding it over that at the beginning of the
work-period. It is, of course, impossible to measure the exact
amount of practice gain, for too long a rest causes a consider-
able loss of practice, while too short a rest does not completely
eliminate the effect of fatigue. The measure which I shall use
for the practice gain is obtained by taking the percentile gain
in efficiency of the function when tested under similar conditions
of rest.
The ideal method of investigating the fatigue is to test a sub-
ject who has approximately reached the limit of practice in the
work used. Under ordinary circumstances, however, it is not
easy to get such persons. In our investigations, the subject
T. A. was apparently in a very high stage of practice in mental
multiplication, (see Experiment I, Part 2). With these ma-
terials we measure fatigue by simply taking the difference be-
tween the efficiency at the beginning of the period and that at
the end.
8O
Influence of Mental Work on Efficiency of Functions 8 I
The coefficients of fatigue are obtained from these tables by
two different formulas according as different units of efficiency
are used. The formula A is used when efficiency is measured
by the time taken to do a given amount of work, and the formula
B when it is measured by the amount of work done in a given
time.
A. Coef. of fatigue =(T. — T,) × IOO
T.
B. Coef. of fatigue = (A → A,) X IOO
42 -
T, and A1 = time required and amount done at the beginning of
continuous work.
T, and A2 = time required and amount done at the end of con-
tinuous work.
In the case of transferred fatigue T, and A1, and T2 and A2
represent the efficiency before and after some hours of mental
work. We must use, however, a method slightly more complex
in dealing with figures including the influence of practice. There
are two different methods which were used by previous investi-
gators. One is the method used for the first time by Professor
Thorndike and the other that used by Kraepelin and his pupils.
The writer will summarize, according to her judgment, two
articles which represent the two methods and try to decide for
our investigation.
The first is “Mental Fatigue,” by E. L. Thorndike, published
in the Journal of Educational Psychology, Vol. II, No.2.
I. The function studied. The mental multiplication of a
three-place number by a three-place number, neither having any
o's or I's amongst the digits.
II. The subjects. Sixteen students (sex not stated).
III. The method employed for the test. Each measures the
time he takes for getting the answer of each example. He works
continuously on one day and on the next day for a half hour
or one hour.
IV, The method of calculating the amount of fatigue is
Aftured by the percentage which the time taken to multiply
ceſſain numbers of examples at the end of one period is of that
aft er certain hours of rest succeeding the work period.
"The second is “Ueber Arbeit und Ruhe,” by Ernest H. Lind-

82 Mental Fatigue
ley, published in Kraepelin's Psychologische Arbeiten, Vol. 3,
pp. 482–534.
I. The aim of the investigation is to ascertain the factors de-
terminating in work curves which are practice, fatigue, Gewóh-
nung, ‘warming up, and initial and final spurts.
II. The subjects. Two men and one woman.
III. The function studied. Adding one-place numbers.
IV. The method of measuring the efficiency of addition. By
the number of single additions.
V. The method of the test. Each subject works for one
hour continuously on the first day; for the two 30 m. periods,
with 5 m. rest between, on the second day; for the two 30 m.
periods, with I5 m. rest between, on the third day; for the two
3O m. periods, with 30 m. rest between, on the fourth day; for
the two 30 m. periods, with 60 m. rest between, on the fifth day.
The same program is repeated for the next five days. On the
eleventh day, the subject has a complete rest. The tests are
made on the next ten days following the same arrangement of
hours as in the first ten days. Another complete rest of a day
follows here. For the next five days, the same program as was
used for the first five days is employed, but is followed by a day
with one hour of continuous work. We shall call, for the sake
of convenience, the first ten working days group A; the second
ten, group B; and the last five, group C.
VI. The methods of measuring each factor, contained in the
results of the test described above.
(I) Finding the best rest period.
Take the length of rest which brings about the greatest excess
of the amount of work done in the second 30 m. over the amount
of work done in the first 30 m.
(2) Finding the practice effect.
Subtract the amount of work done in the first 30 m. on the
first day of each of the three groups from the amount of work
done in the first 30 m. on the last day of the same group. Divide
the answer by the number of the days between the two extreme
days of each. By getting the average of the three groups, is ob-
tained the amount of daily gain for each subject.
(3) Finding the amount of ‘Gewóhnung.’
It is defined by Lindley thus: “Die Gewóhnung zeight sich
Influence of Mental Work on Efficiency of Functions 83
in der Schnelligkeit, mit der man sich von innern and āussern
störenden Einflüssen unabhängig zu machen in Stande ist.” For
making a rough estimation of it, get the excess of work done in
the first 30 m. of the working period of the second day over
the work done in the same period on the first day of each
group.
(4) Measuring the rate of practice gain from 30 m. work.
The work after the best period of rest is held to contain a
minimum amount of loss of practice effect, fatigue effect and
warming up effect. Supposing this to be true, the excess of the
amount of work done after the best period of rest over the
amount of work done before it may be attributed to the amount
of gain due to the 30 m. work preceding. The ratio between
this excess and the amount of work done after the best period
of work is taken to be the rate of 30 m. practice gain.
(5) Measuring the persistency of the practice gain.
As the persistency of the practice gain relates to its loss in
an exactly inverse ratio, the latter is taken to be a measure of
the former. To find the loss of practice gain during a period
of rest, we must calculate first the amount of work which would
have been done after the rest, if there were no practice loss at
all. This is done by multiplying the amount of work done be-
fore the rest by I plus the rate of 30 m. practice. The difference
between the reckoned amount and the actual amount of work
done after the rest is attributed to the amount of loss of prac-
tice, for, as during the best period of rest the effects of fatigue
and warming up are supposed to have disappeared almost en-
tirely, what occurs during “a minus best" period is taken to be
the loss of practice gain.
(6) Measuring the effect of fatigue.
During 5 m. rest, according to Lindley, warming up effect is
almost all lost, while the effect of practice and that of fatigue
remain undiminished. Suppose that we can find the amount of
work done in the 30 m. containing the effect of practice, but
not that of fatigue resulting from the thirty minutes of work
preceding. Then the difference between this and the actual
amount of work done after the 5 m. rest may be attributed to
the amount of fatigue. The said amount of work, containing
practice effect only, is obtained by multiplying the actual amount
84 Mental Fatigue
of work done before the 5 m. rest by I plus the rate of the
thirty minute practice gain.
(7) Measuring warming up effect.
A comparison of the amount of work done in the sixth 5 m.,
i.e., the last 5 m. of the first work period with the amount of
work done in the seventh 5 m., i.e., the first 5 m. of the second
work period shows a certain decrease in the latter after a rest
of 5 m. or more, and the amount is more than the average
amount of loss of practice gain during the same length of rest
period.
Both methods are based on the supposition that the amount of
gain through rest can be a measure of fatigue resulting from the
work immediately before rest. The point of divergence of the
two methods lies in the further presuppositions. Lindley pre-
supposes that the best rest brings about the least loss of practice
gain and greatest recovery from fatigue, and naturally, that, if
there were no fatigue at all after 30 m. of work, the amount of
work done in the next 30 m., less the gain in warming up,
should be the same as that done in the 30 m. after the best
rest. Therefore, the greater part of excess of this reckoned
proportion is attributable to the amount of fatigue. But, from a
practical point of view, the validity of Lindley's presupposition
depends on the amount of practice gain lost during the best rest.
If it is a negligible quality, the problem is simply to find the
difference between efficiency in the next 30 m. and that im-
mediately after the best rest. But, if it is a considerable quan-
tity, the efficiency after the best rest will vary according to its
amount, provided that the fatigue effect remains the same. Ac-
cording to Tables III and V in Lindley's article (pp. 495-500),
in the case of subject B the amount of loss of practice gain in
the second 30 m. work period is II and the daily loss is 50.
Therefore, one-fifth of the whole amount of practice loss during
a day is lost during the second 30 m. The loss of the first 30 m.,
according to this rate of loss, should be approximately 20.
Since the amount of B's fatigue is found to be 42 according to
Lindley's method, the true amount of fatigue should be about
62, if the amount of recovery outweighing the negative influence
of practice loss is counted. Therefore, Lindley's method is justi-
fied only when there is a least amount of practice loss.
Influence of Mental Work on Efficiency of Functions 85
Thorndike's method disregards practice loss entirely. Its
validity depends on the length of rest. If the length of rest is
so much that it would cause a great amount of practice loss or
if it is so short as to leave a large amount of fatigue, the method
is inadequate. -
With our present materials, we can not use Lindley's method,
for our investigation was not carried out with so many varieties
of length of rest as Lindley’s. On the other hand, we shall not
always follow that of Thorndike exactly. He studied the amount
of fatigue by taking the ratio of the time taken before rest to
that after rest. But, in our investigation, we shall, when prac-
tice is not negligible, use the ratio of difference between the effi-
ciency before rest and that after rest to the latter. We shall,
for the sake of convenience, call the method of comparing effi-
ciency before and after the work period, Formula I; and that
of comparing efficiency after the work-period with that at the
beginning of the next work-period—i.e., after rest, Formula II.
Reducing accuracy and speed to one unit. Quantity and
quality are two essential elements which we must consider in
determining work done. Kraepelin and his colaborers, however,
attached great importance to the former, disregarding the latter.
Professor Thorndike attempted to do justice to both of these
elements by adding some amount of time for each error. In our
investigation, the question arises only in the case of mental
multiplication. If errors are distributed evenly in the course of
work, they may be due simply to chance and we may disregard
them in the study of fatigue. However, according to the results
obtained by Experiment I, the errors bear certain relations to
practice and fatigue, as will be seen in later pages. So it is not
justifiable to disregard them. For this reason we add ten seconds
for each wrong digit in the answers of all multiplications.
Fatigue in the special function exercised, in the case of indi-
vidual T. A. (The materials are obtained from Table I, II, III,
and IV): tº
I. The amount of fatigue.—In order to know which formula
to use in getting the amount of fatigue, we have to determine
the amount of practice involved in each observation. The re-
sults of the calculation run as follows:—
Mental Fatigue
Time taken (in minutes and seconds) and errors made per example in the
first five examples on each experimental day
Experiment I. Part 1 Experiment II. Part 2
Date Time Error Date Time Error
Feb. 2. . . . . . . . . . . 10. 53 2.8 Feb. 24. . . . . . . . . 9. 56 2.6
{{ 4. . . . . . . . . . . 5.30 3.2 “ 25. . . . . . . . . 8, 18 1.5
{& 7. . . . . . . . . . . 4. 49 1.2 “ 26. . . . . . . . . 6.30 1.5
“ 15. . . . . . . . . . . 5. 49 1.4 “ 27. . . . . . . . . 7. 22 2.8
“ 22. . . . . . . . . . . 4.52 2.0 “ 28. . . . . . . . . 7.42 3.2
Mar. 2. . . . . . . . . 6.45 1.6
{{ 3. . . . . . . . . 5. 55 2.2
{{ 4. . . . . . . . . 5. 28 1.2
& 5. . . . . . . . . 5.04 1.6
{{ 6. . . . . . . . . 4. 44 1.2
TABLE XVII


The sum of the times taken (plus 10 seconds for each error) for each five
examples at the end of each continuous work period, expressing the effi-
ciency before each rest; a similar record at the beginning of the succeeding
work period, expressing the efficiency after the rest; and the coefficient of
fatigue.
Length -
of test
before | Effi- Effi- || Coef.
Length of rest between each suc- rest. In ciency ciency Of
cessive test. In hours hours before after fatigue
and rest rest,
minutes
" | From Feb. 2, 12 A. M. to Feb. 2, 1 h.m.
ää ... P. M-1: ... . . . . . . . . . . . . . 2. 30 || 62.45 33.35 | 86.9
3 ſº | From Feb. 2 to Feb. 4=43. . . . . . . 1.30 || 47.45 29.80 57.4
‘. . . . From Feb. 4, 12:06 P. M. to Feb. A.
# = 4, 12:40 P.M.–4. . . . . . . . . . . . . 2. 30 42.23 46.31 —8.9
§ 3 | From Feb. 4 to Feb. 7=69.... . . . 2.00 53.51 25.06 || 114.5
pºſſi | From Feb. 7 to Feb. 15=173. . . . . 1. 20 62. 10 30. 15 105.5
From Feb. 15 to Feb. 22=169. . . . . 4. 17 | 52.35 | 26.00 | 102.3
From Feb. 24 to Feb. 25=26. . . . . 1. 32 || 51.50 42.40 21.4
H' From Feb. 25 to Feb. 26=11. . . . . 4.00 || 81.50 33.40 || 143.7
+5 From Feb. 26 to Feb. 27=19. . . . . 4. 24 58.00 39. 10 || 48.1
# | From Feb. 27 to Feb. 28–19..... 4. 34 45.45 43. 30 5.2
ſº From Feb. 28, 6:43 P. M. to Feb. /
F. 28, 7:32 P. M.–3. . . . . . . . . . . . . 6.00 70. 42 32.55 114.8.7"
g From Feb. 28 to Mar. 2=37. . . . . | 1.42 57.03 || 35.05 || 62.6
‘... 6." | From Mar. 2 to Mar. 3=13. . . . . . 11.00 65.00 || 31.25 | 106.9
# # | From Mar. 3 to Mar. 4=12. . . . . . 12.00 76.35 | 38. 20 | 99.8
§§§ | From Mar. 4 to Mar. 5=12. . . . . . 12.00 57.20 26.40 115.0
p: From Miar. 5 to Mar. 6=12. 12.00 || 50. 10 || 24.45 || 102.7

~"
ºf Influence of Mental Work on Efficiency of Functions 87
In the figures given above, two important facts are noted:, (I)
the gain in speed as a result of each test is greater in the be-
ginning and becomes slower as it approaches the end; (2) Some
practice gain is still observed in the tests of the last four days.
However, the average daily practice gain being thirty seconds in
these tests, the average practice gain per example in the course
of twelve hours of mental multiplication is only four hundredths
of a second. The gain per example is so small that in our study
of fatigue curves it may be disregarded. The coefficients of
fatigue are obtained by Formula II and given in Table XVII.
The figures given above indicate that mental multiplication
of four place numbers by four place numbers continued from
I.7 hours to I2 hours causes more or less decrease of efficiency
in the function exercised.
The amount of fatigue in the last four tests as determined by
Formula I is given in Table XVIII.
TABLE XVIII

With the With the
With the difference difference With the
difference between next between difference Average
between to the first 5 first 5 between next of the
Date first 5 examples examples to the first 5 four
and last 5 and next and next examples methods
examples to the last 5 to the last 5 and the last
examples examples 5 examples
Mar. 3 158. 8 64. 6 62.5 161.8 I 11.9 |
“ 4 144.7 43.0 66, 8 110.6 91.3
“ 5 90. 5 90.6 79. 1 106.7 91.4
“ 6 84.2 72. 3 88.5 68.3 78.3
93.2
Averaging the four tests, we find that twelve hours of mental
multiplication results in a reduction of speed to less than one-
half of the original speed. The average coefficient of fatigue
thus obtained is 93.2. The average coefficient of fatigue
measured by Formula II is IO6.I. Therefore, the true co-
efficient of fatigue (that is increase in time required as a result
of eleven hours of this work) would be near 99.6 per cent, the
average of the two. 4.
88 Mental Fatigue
2. The course of fatigue. The course of fatigue is repre-
sented by a curve made by the following method. A horizontal
scale line for the number of examples is drawn. The height of
the curve at any point represents the time taken for an example.
The rise of the curve, therefore, means decrease of speed or
increase of the time taken to do a given amount of work.
Curves I to V represent the courses of work according to Ex-
periment I, Part I. These curves bring out two important points.
20– 20-
ſº- CII?"Wé I !!- C//7"Vë ///
fº- * (7—
f $5– / 6–
45— f 5—
f 4.— Jº f 4—
(3– Q 43–
442— $2 4 2-
* f.- *J. º-
f *
:- S; {-
- $. –
7– Se 7–
S— § N :=
:- lc) 3—
32— 2–
f—- A—
cº cº
20– 20— sº
& 9— - #I
º– º Cº? We // (7— - C//7°Wę /V
First, the length of the curve increases in the later tests. Since
the subject ceased to work the very moment when she thought
it desirable to do so, the increase of the working period means
that the subject’s ability to continue the work increased. This
is either because the subject gained by practice a greater power
to resist the impulses to stop the work, or because the work be-
came actually easier as a result of practice, or both. Second,
the form of the curve varies according to the amount of prac-
tice. In general, the curve first falls and then rises; this shows
that the effect of practice is stronger than was that of fatigue




Influence of Mental Work on Efficiency of Functions 89
i

9d Mental Fatigue
at the beginning, and vice versa towards the end. In the
earlier tests, the fall and rise of the curve are more marked
than the later tests; this signifies that both gain by practice and
loss by fatigue become smaller as one's practice is greater.
Similar points are observed in the course of work in each
of the tests of the practice series of Experiment II, Part 2, which
are given below, in curves VI to XI.
/5–
cutºrve V, Aſ ºft- Cºlºrye V///
# 3–
curve V |
As was explained in Chapter II, the tests on the last four days
of Experiment I were performed when the subject was in a
very late stage of practice and the gain by practice in the course
of work is of a negligible quantity. Therefore, the results of
these tests may be considered as representing the course of fa-
tigue in a relatively pure form.
Curve XII shows (1) the four different curves representing
the course of work in the four different tests, and (2) the
curve representing the average of the four.








Influence of Mental Work on Efficiency of Functions9I
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92 Mental Fatigue
The divergencies of the separate curves from the average
curve are such that the true average curve obtained from an
infinite series of experiments will, on the average, not differ
from the average curve shown in Curve XII at any point by
more than twelve per cent. The chances are 8 to 2 that it will
not so differ in one direction. For the study of the fatigue
curve of individual T. A., the average curve will be used
throughout. It shows the following important characteristics:
(I) The curve does not fall at the beginning as do the other
curves already shown, but rises from the beginning.
(II) It rises gradually up to the 34th example, fluctuating
above and below the standard line. Then it takes on a different
aspect, the curve being above the standard line up to the 56th ex-
ample. The rise of the curve is due to decrease of speed. It falls
at the 56th example, and continues to be below the line until ex-
ample 61, it ends with another rise.
Many explanations can be given for the shape of the curve.
One explanation is to suppose that, at the point where the sudden
rise of the curve begins (example 35), the subject yields to the
feeling of fatigue, letting herself go for a while. During the
relaxation the subject is recovered from the effect of fatigue to
Some extent. As a result of this, efficiency again increases and
the increase of efficiency results in the fall of the curve (ex-
amples 44 to 60). Another way of interpreting the form of the
curve is to attribute it to the diurnal course of efficiency, i.e., to
Suppose that the subject accomplishes more at one time of the
day than at another. According to the curve given above, the
sudden rise occurs at 5 p. m. The fall of the curve occurs at
8 p.m. and lasts until IO p. m. This falls in with the subject's
habit. The subject is accustomed to spend the time between
5 p.m. and 8 p. m. in recreation, while the hours between 8 p.m.
and IO p. m. are reserved for intellectual work. The slope of
the curve may be due to this habit of mind. The examination
of curve V, for February 22, shows that the sudden decrease
of speed occurs at the 35th example, i.e., at 5 p. m., al-
though the subject had worked for only four hours instead of
six.
(III) Aside from the fluctuations noted above, the rise of
the curve seems on the whole to be gradual. Since these fluctua-
Influence of Mental Work on Efficiency of Functions 93
tions are explained by a fact other than the onset of fatigue, the
Onset of fatigue may be regarded as gradual.
(IV) The difference between the time taken for one example
and that for another is greater in the second half than in the
first half of the curve. This fact together with the evidence of
introspection of the subject suggests that fatigue not only causes
decrease of efficiency, but also loss of the subject’s control over
herself. For this reason, the subject tends to occasionally relax
her original standard of effort.
3. * Warming up effect. The results show little or no effect
of ‘warming up.” If there were any such effect, it would show
itself before being overcome by the fatigue effect and would
make itself manifest in the fall of the curve soon after the be-
ginning. There may be a slight effect of this kind, if so, it is
So Small that the effect of fatigue outweighs it from the be-
ginning.
4. Spurts or ‘Antriebe.’ There is nothing in our curves
which corresponds with “Anfang und Schluss-antriebe" or initial
and final spurt. The times taken for the first and second four
examples at the beginning as well as those taken for the first
and second four examples from the end are given below in
minutes and seconds. -

Number of examples | On Mar. 3 || On Mar. 4 || On Mar. 5 || On Mar. 6
1st 4 from the beginning 24. 55 23. 30 21.30 19.25
2nd 4 from the beginning 24.35 24.45 18.35 27.50
1st 4 from the end . . . . . 59. 55 49.00 39.00 30, 15
2nd 4 from the end. . . . . 47. 25 42. 55 44.00 36.50
The differences between the first and the second four examples
at the beginning and that between the first and second four from
the end are not regular in all our experiments.
5. Accuracy and fatigue. The average number of wrong
digits per answer in each successive ten examples in each test is
as follows: -
94 Mental Fatigue

Order of each ten examples
Date
lst 2nd 3rd 4th 5th 6th 7th
Mar. 3. . . . . . . . . 1.7 1.0 1. 3 2.3 1. 7 1. 3 l. 3
“ 4. . . . . . . . . 1.8 1.2 2.5 1.5 1.7 1.8 3. 1
“ 5. . . . . . . . . 1.6 1.8 1.2 1.0 2.4 2. 3 3. 1
“ 6. . . . . . . . . 2.0 1.5 2.2 1.9 1.6 4.1 3.1
Average . . . . 1.8 1.4 1.8 1.6 1.9 2.4 2.7

On the whole, accuracy decreases as the work progresses.
Fatigue in the special function earercised, in the case of the
group of individuals (the materials being obtained from Table
WIII).
The amount of fatigue. The effect of practice in each two
hours of mental multiplication is measured by comparing the
efficiency at the beginning of a two-hour period with that im-
mediately after rest succeeded it. The coefficients of practice
thus obtained (see page 80 for the formula used) are given in
Table XIX.
TABLE XIX
COEFFICIENTS OF PRACTICE
Subjects 1st Test 2nd Test 3rd Test 4th Test
C. D. T. . . . . . . . . . . 46. 6 53. 6 20.1 9.5
MS. . . . . . . . . . . . . . . 74.8 42.6 21.6
R. S. W. . . . . . . . . . 27.8 14.1
H. A. R. . . . . . . . . . . —4.4 50. 5
J. T. . 69.4
Pfg. . . . . . . . . . . . . . . 29.7
P. E. R. . . . . . . . . . . 16.4
S. W. . . . . . . . . . . . . 6.1 11.5
Chs . . . . . . . . . . . . . . 33.5 27.8
M. M. . . . . . . . . . . . . 22.2
C. T. R. . . . . . . . . . . 54.7 33.8
H. L. H. . . 19. I
Sn . . . . . . . . . . . . . . . —31.2
G. D. S. . . . . . . . . . . 25.6
A. G. C. . . . . . . . . . . 52. 1

The table shows that, in most cases, the amount of practice
effect is greater in the first test than in the second test. In both
cases, the course of fatigue is involved with the increasing prac-
Influence of Mental Work on Efficiency of Functions 95
tice effect.
Therefore, in measuring the amount of fatigue,
Formula II must be used. The coefficients of fatigue in the
two-hour work period are given in Table XX.
TABLE XX

Subjects
Coefficients of Fatigue
1st Test
2nd Test
3rd Test
4th Test
Average
A. The amount of fatigue measured by recovery during a ten
minute rest
C. D. T. . . . . . . . . 4.1.1 7.4 19.3 22.6
P. E. R. . . . . . . . . 8.7 8.7
S. W. . . . . . . . . . . 7.5 7.5
G. D. S. . . . . . . . . 7.3 7.3
Pfg. . . . . . . . . . . . 6.1 20. 2 13.2
Chs . . . . . . . . . . . . 30. 7 30. 7
M. M. . . . . . . . . . . 73. 2 73.2
C. T. R. . . . . . . . . 40. 5 49. 1 44.8
Average . . . . 26.
The amount of fatigue measured by recovery through a sixty
minute rest -
C. D. T 5.6 5. 6
MS. . . . 10.6 63. 7 72.2 48.8
S. W. . . . . . . . . . . 15.0 15.0
H. L. H. . . . . . . . 8.9 8.9
A. G. C 53.9 53.9
Sn. . . . . . . . . . . . . —4.6 —4.6
G. D. S. . . . . . . . . 11. 6 11.6
R. S. W. . . . . . . . 1.5 2.8 2.2
Chs . . . . . . . . . . . . 85. 6 6.2 45.9
Average . . . . 20.8
C. The amount of fatigue measured by recovery through a one hundred
eighty minute rest
H. A. R. . . . . . . . . —22.9 —22.8 —22.9
G. T. . . . . . . . . . . 2.7 2.7
Average. . . . 10.1

The fact that the average coefficient of fatigue is about the
same in both A and B (excluding C on account of its having
too small a number of cases) suggests that the fatigue caused
by two hours of mental work is very probably eliminated during
a ten-minute rest and that loss of practice effect during the next
96 Mental Fatigue
fifty minutes is insignificant. Therefore, the greater part of
the difference between efficiency immediately before and that im-
mediately after the rest is attributable to the whole amount of
fatigue caused during the work period. The average amount of
decrease of efficiency caused by the two hours of continuous
TABLE XXI
: Time taken per example in each ten minutes by each, and by the average
of all the individuals—also the average of all but the subject J. T. (J. T.’s
records are eliminated in the second average on account of their irregularity).
These averages are on the line of the starred average.
A. Results of the first test



Sub- Aye.
jects | Abil. 1 2 3 4 5 | 6 7 8 9 10 11 12
H. A. JR. 31.3| 34.2 31.6|| 34.5| 41.4| 36.4. 30.3. 33.9| 27.5| 26.7| 25.6|| 25.6; 27.5
C. D. T. 36.8 54.5, 41.1 ! 39. Of 38.8| 40.7| 33.9; 34.4| 33.4| 28.6|| 30.2| 27.4 30.0
R. S. W. 42.3| 47.8; 59.0; 71.7 43.4; 35.8; 33.3| 40. 6. 32.8| 35. 3; 37. 6. 33.7| 37.0
G. M. K. 67.8 W5.0} 79.8| 68.9|112.0] 58.3| 83.3| 73.4 68.8| 59.5 42.2 50.1| 42.5
Pfg. . . . . 80.9| 73.0| 84.5) 80.0} 82.2|127.8| 90.3 83.5 75.0 86.3| 73.4 67. 1; 63.0
MS . . 89.1|164. 3||138.8/128.4 94.2} 80.9| 66.5| 93.1 49.2| 56.0| 64.7| 65.9| 61.6
Chs. . 96.8||118.0/101.0| 95.8| 76.3| 83.2| 82.2| 80.2 72.7| 79.5|141.0|118.0|129.0
S. W. . . 116. 6| 99.0167.0| 94.0/119.6/128. Of 89.7|129.0|113.7|121.1||135. Of 121.3||111.3
C. T. R. 124.7|187.7|120.4|118.0| 97.0|144.4 107.0|105.0|100. 5||111.4|130.0|152.5||119.6
M. M... [150.8|160.0|162.0|140.3|120.8.190. 5|121.7|173.3|153.8|150.0|193.3|119.0| 97.5
J. T. . . . [171.4| 71.8 89.0|184. O217.0|194. 5: 100.0|196.3330.0|247.0||132.5|170.0|103.0
Ave. 91.7| 98.7; 97.7| 95.9| 99.3|101.4 76.2| 94.8| 96.4 92.2 95.9| 86.4| 74.7
Ave.* 83. 4101.4| 97.7 87.1 | 87.5| 92.1 | 73.8| 84.6|| 73.0| 76.7| 92.3| 78.0} 71.9
B. Results of the second test -
H. A. R. 32. 5: 54.9| 47.7. 50.0; 29.0) 35.3] 30. 6. 29.9; 26.4; 22.4; 20.3| 22.3| 21.0
C. D. T. 32.7; 32.8| 34.5| 29.9; 28.0|| 41. O|| 34.1 30.6; 20.5| 32.6; 37. S. 32.3| 32.4
R. S. W 42.7| 41. 1 38.5' 37.4 55.0| 50.1| 46.7| 49.3 46.7| 39.6, 31.3 38.4, 38.7
G. M. P.C. 51.9) 60.7; 45.7| 71.4 55.5| 47.1| 43.0l 58.2| 44.8 41.3| 64. 1 42.6|| 48.3
MS . . . . , 52.2| 39.9; 48.4 59.8; 47.9| 46.0 57.9 53. 6. 48.7| 56.0 60.8| 53.5| 53.6
Chs . . . . 52.5| 64.0} 60.4 50.1% 59.5| 42.8| 67.2| 40.9 51 .7| 42.9} 44.3| 65.0|| 41.4
Pfg. . 58.5 61.2| 63.0| 67.0 54.3| 53.4 51.0| 52.6] 73.7| 60.2| 51.9| 55.3i 58.4
S. W. 86. 4 W5.7| 86.4| 79.4106.4| 96.4 73.3 79.7 93.7| 77.2| 70.5||115.5| 82.8
C. T. R. 93. 5: 102.8, 71.8 94.04.115. 1 || 85.6; 79.5 76.0||133.4|126.8 86.9 || 60.0| 89.9
M. M. 124.3/100.8 94.2|106.7|118.2|124.8|178. 3|142.0|151.3||132.0| 91.3||133. 3:119.0
J. T. . . . 153.9||131.6}.130.0|128.84146.2|118.0|180.3|141.3;186.0|165.0|158. 8]186.6|174.0
Ave. 71.0| 69.9} 65.5| 70.4 74.1 || 67.3| 76.5| 68.5| 79.8 72.4] 65.3| 73.2| 69.4
Ave.* 62. 7| 63. 7, 59.0| 64. 5; 68.6| 62. 2 66. 1 ſ 61.2. 69.2| 63. 1; 56.5, 61.9; 59.9
C. Results of the two tests combined
H. A. R. 31.9l 44.6ſ 39.7| 42.3| 35.2 35.9} 30. 5. 31.9; 27.0] 24.6] 23.0| 24.0| 24.3
C. D. T. 34.8| 43.7| 37.8| 34.5 33.4 40.9; 34.0; 37. 5; 27.0) 30.6| 34.0| 29.9 31.2
R. S. W. 42.5| 44. 5; 48.8l 54.5, 49.2| 42.4 40. 1 || 45.0|| 39.8] 37.5| 34.5| 36. 1 || 39.9
G. M. P.C. 59.9| 67.9 62.8/ 63.9| 83.8 52.7 58.2| 65.5} 56.8, 50.4; 33.2; 42. 4 45.4
Pfg. . . . . 69.7 67. 1, 68.8 76.5| 68.3| 90.6 70.7| 68. 1 74.4| 73.3| 62.7| 66.2, 60.7
MS . . . . . 70.7|102.1| 93.6| 94.1 58. 1 || 63. 3| 62.2| 63.9| 49.0. 60.5| 62.8| 59.7 62.6
Chs . . . . 74.7| 91.0} 80.6| 75. O| 67.9|063. 0 || 70.7| 60.6|| 62.2| 51.2| 92.7| 91.5: 84.2
S. W. . . 101.5 87.4|127.0: 86.8||113.0|112. 2: 81.5|104.4|104. 2; 99.2|102.8||118.4| 96.8
C. T. R. 109. I 145.2 96.1|106.0|106. 1115.0 93.3 98.2|117.0|119. 1108.5||115.6||113.8
M. M. . . . 137.6|130.4|128. 1 |133. 5.144. 5|146.0|150.0|150.0|152.4|132.0|142. 2126, 2103.0
J. T. . . . [162.4 101.7|123.0/156.4|181. 6;156.3}140.2|168.8|256.0|228. 5; 145.7|178. 3.138. 1
Ave. 81.3| 84.3| 81.6| 83.2| 85.2| 84.41, 76.4 81.7| 88.1. 82.2 80. 6] 79.8| 72.1
Ave+ 73. 2 82.4| 78.4 75.8 78. 1 || 77. 2; 70.0|| 72.9| 71.1 69.9| 74.4 70,0; 65.9
Influence of Mental Work on Efficiency of Functions 97
work is then for this group 24.2 per cent of the efficiency after
reSt. -
The course of fatigue. In Experiment IV, all but four sub-
jects took part more than twice. As the tests were made at
different times and consequently in different stages of practice,
they contain varying amounts of practice effect. For instance,
the average time taken per example in each thirty minutes is, re-
spectively: for Subject MS., I31. I, 65.5, 56.1 and 55.7 in the first
test and 43.6, 35.6, 34.4 and 45.3 in the second test. There-
fore, the average of the two can not be taken as a typical curve
of the individual as is generally done. This holds true with the
average of the two tests of all individuals. We shall, therefore,
present separately the results of the first and the second test as
well as the average of the two in Table XXI. The records of
the first and second tests of eleven individuals out of sixteen are
given, because they worked two full hours at one time.
The following important points are to be observed in the
figures given above: First, the absolute speed is greater in the
second than in the first test, by 25 per cent. Second, the prac-
tice gain is much greater in the first test than in the second. The
percentage ratio of the average time taken in the last 30 minutes
to that in the first 30 minutes is 79.9 in the former, while it is
TABLE XXII
º average time taken to multiply per example in successive, 30-minute
periods -


Type Subjects 1st 30 m. | 2nd 30 m. 3rd 30 m. || 4th 30 m.
Pfg. . . . . . . . . . . . . . . . . . . 70, 8 76.5 71.8 63.2
I M. M. . . . . . . . . . . . . . . . . 130.7 146.8 144.8 123.8
J. T. . . . . . . . . . . . . . . . . . 127.0 159 .4 217.8 154.0
Average. . . . . . . . . . . 109.5 127.6 144.6 113.7
- Chs. . . . . . . . . . . . . . . . . . . 82.2 67.2 58.0 | 89.5
2" | S. W. . . . . . . . . . . . . . . . . . 100.4 102.2 102.6 106.0
C. T. R. . . . . . . . . . . . . . . . 115.8 104.8 111.4 112.6
Average. . . . . . . . . . . 99.5 91.4 90.7 102.7
H. A. R. . . . . . . . . . . . . . . 42.2 33.9 27.8 33.8
C. D. T. . . . . . . . . . . . . . . 38.7 36. 1 31.7 35.0
3 R. S. W. . . . . . . . . . . . . . . 49.3 43.9 40.8 36.8
G. M. K. . . . . . . . . . . . . . . 64.9 64.9 57.6 40.3
MS. . . . . . . . . . . . . . . . . . . 96.9 61.2 57.8 61.7
Average. . . . . . . . . . . 58.4 48.0 43.1 41.5
----------w
98 Mental Fatigue
96.4 in the latter case. Third, there are three types of fatigue
curves. The first type is represented by the curve which rises
first and then suddenly falls in the beginning of the last fourth
of the working period. To this type belong the curves M. M.,
J. T. and Pfg. The second type falls and then rises in the
second or third 30 minutes showing that the effect of fatigue out-
weighs the effect of practice within two hours. To this type, be-
long the curves of C. T. R., S. W., Sn. and Chs. The last type
falls gradually toward the end without showing clearly the point
of maximum efficiency from which the effect of fatigue out-
weighs the effect of practice. To this type, belong most of the
individual curves. Table XXII will show these three types by
the actual figures which show the average time taken to multiply
per example in each successive thirty minutes.
Oehrn' in his study of ten individual work curves of the four
different psycho-motor and mental functions remarks that the
maximum point is reached sooner in the more automatic func-
tions than in the purely mental functions, and that the average
point of maximum ability is reached in memorizing the numbers
(the most purely mental function) at the end of 60 minutes.
Thorndike” gives a detailed report of his investigation of
fatigue curves, from which the present writer calculated the time
when the maximum efficiency is reached in each individual curve
and obtained the following results.
THE TIME WHEN THE NUMBER OF
MAXIMUM EFFICIENCY INDIVIDUALS
Is REACHED
0–1 hrs.
1–2 {&
2–3 “
3–4. “
4–5 {&
5–6 “
(3–7 &
7–8 {&
8–9 (ſ
Our results, therefore, correspond with those obtained by
Thorndike.
There is a definite relation between the type of curve and
efficiency in the function. The average time taken per example
* Psychol Arbeit. vol. I. p. 136.
*Jour. of Ed. Psychol. vol. II. No. 2.
Influence of Mental Work on Efficiency of Functions 99
in the two-hour working period of the first type is I23 Sec. in
the case of three individuals; that of the four individuals belong-
ing to the second type is IO4.2 sec.; that of nine individuals be-
longing to the third type is 48 sec. Those who do not show the
points of maximum efficiency are the best performers of the
group. The types of the curves are, of course, determined by
the relation of fatigue to practice effect. The greater the ratio
the earlier the point of maximum efficiency occurs and the more
marked the slopes of the curve. Their relations depend either
on change in the absolute amount of one of the two factors, the
Other remaining the same in amount or on the change of both,
each in different amount. From this fact, an important question
arises, namely, which of the two, practice or fatigue, is the deter-
mining factor of the relation in our curves. In studying this
relation, we have chosen the records of eight individuals taken
under relatively uniform conditions. -
TABLE XXIII
Coefficients of fatigue and of practice of each individual and the average
coefficient of fatigue and of practice for each type, using the average of the
first and second trials of each individual.


Type Subjects Fatigue Coef. Practice Coef.
I Pig . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.3 26. 5
Average. . . . . . . . . . . . . . . . . . .
C. T. R. . . . . . . . . . . . . . . . . . . . . . . —30.8 48.
2 S. W. . . . . . . . . . . . . . . . . . . . . . . . . . 15.1 19.5
Chs. . . . . . . . . . . . . . . . . . . . . . . . . . . 45.9 36.3
Average. . . . . . . . . . . . . . . . . . . 30.6 34.6
H. A. R. . . . . . . . . . . . . . . . . . . . . . . —22.9 23. 1
3 C. D. T. . . . . . . . . . . . . . . . . . . . . . . 7.1 35.6
R. S. W. . . . . . . . . . . . . . . . . . . . . . . 1.3 19.7
MS. . . . . . . . . . . . . . . . . . . . . . . . . . . 39.0 53.4
Average. . . . . . . . . . . . . . . . . . . 5.6 33.0
According to the average coefficients of fatigue and those of
practice in the three types, the curves of the first and second
types contain a greater amount of fatigue than do the curves
of the third type, while the practice effect remains the same in
The difference in the form of the curves, then, is
Since
both cases.
due to a difference of absolute amount of fatigue effect.
tº º
* ºn
º “
ga
*
*
:
:
e &
º
:
º
:
;
:
gº
$' ºr , ,
“I OO Mental Fatigue
it is found that individuals of the third type are much more
competent in their work than those belonging to the first and the
second, it is probable that the most competent workers are af-
ected least by fatigue.
‘ Warming up ’ effect. As the result of study of the work
curves after rest, it is found that a curve falls after a rest of sixty
minutes, while it keeps practically the same level after a rest
of ten minutes. Table XXIV gives the time taken for the first,
second and third four examples after both periods of rest.
TABLE XXIV
Time taken in doing the first, second and third four examples after dif-
ferent lengths of rest.
A. After ten minutes of rest

Subjects Difference
1st 2nd 3rd between
1st and 2nd
C. D. T. . . . . . . . . . . . . . 135.0 133.0 120.3 —1.5
Pfg . . . . . . . . . . . . . . . . . 245.0 227.0 262.5 —7.3
Chs. . . . . . . . . . . . . . . . . 204. .0 211.0 215.0 +3.3
M. M. . . . . . . . . . . . . . . . 3.10.0 357.0 | . . . . . + 14.1
P. E. R. . . . . . . . . . . . . . 225.0 250.0 240.0 + 7.4
S. W. . . . . . . . . . . . . . . . 258.0 372 - 0 332.0 +3.9
Average . . . . 233.4 238.6 239.0 +3.3
B. After sixty minutes
R. S. W. . . . . . . . . . . . . 219.0 161.5 208.5 —29.3
MS. ... . . . . . . . . . . . . . . . 178.8 193.3 i.75.8 +2.5
Chs. . . . . . . . . . . . . . . . . 275.0 320.0 | . . . . . —22.6
S. W. . . . . . . . . . . . . . . . 585.0 425.0 535.0 —31.1
H. L. H. . . . . . . . . . . . . 180.0 145.0 170.0 —21.2
A. G. C. . . . . . . . . . . . . . 170.0 58.0 124.0 —95.8
Average. . . . . . . . . 266.6 196.6 242.7 —32.9
C. After one hundred and sixty minutes of rest
H. A. R. . . . . . . . . . . . . . | 180.0 | 135.0 | 110.0 | –45.

The difference between the form of the curve after the short
period of rest and that for the work after the longer period of
rest can not be explained without supposing that a ‘warming up ’
process acts in the course of work and disappears soon after the
cessation of work. This warming up process is more completely
neutralized during the sixty-minute rest than during the ten-
...!
* ," * *
:
.
:
*
º
&
*
:
Influence of Mental Work on Efficiency of Functions I of
minute rest, and, therefore, the efficiency immediately after the
longer rest is less than after the shorter rest.
Spurts. In our experiments, the subjects did not know when
the end of the work period was coming. Hence, it is not pos-
sible to study the effect of final spurts from our records. For
the study of initial spurts, the usual comparisons were made be-
tween the time taken for the first example and that for the
second, between the first four and the second four examples, and
also between the first and the second eight examples. The writer
did not find any uniform superiority of the first over the second
interval.
Accuracy and fatigue. According to the results of Experi-
ment IV, accuracy in work does not seem to be influenced either
by fatigue or practice. For eleven individuals who underwent
two tests, the average number of incorrect digits per answer in
each successive thirty minutes is .77, .72, .73 and .72 respectively,
in the first test, and .78, .80, .67 and .62 in the second. That the
absolute number of mistakes is not less in the second trial
than in the first suggests that practice has little to do with the
number of errors. That fatigue did not influence the accuracy
of the work is shown by the fact that in both trials, the number
of errors decreased in the course of work.
Supplementary data. An experiment was made on the subjects
T. A. and E. B. G. for the investigation of fatigue in the function
exercised in reading. T. A. read Dickens’ “Bleak House ’’ three
hours a day and repeated the process for five days in succession.
In this reading the time of beginning every other page and the
time spent in reading each two pages was computed. The re-
sults of this test are given in Table XXV.
According to the figures given above, the average time taken
for reading each ten pages on five days is (in minutes and
seconds) respectively 27.07; 26.44; 25.5I ; 26.27; 26.56 and 27.43.
The time decreases gradually to about the fortieth page, the time
increasing from then on to the end. It seems more reasonable
to attribute the cause of the increase of speed in the beginning
of the reading to the ‘warming up effect than to the effect of
practice, for its effect has no influence on the speed of the per-
formance of the next day. -
I O2
Mental Fatigue
TABLE XXV
Section of two pages and for each section of
Subject T. A.
Time in minutes and seconds.
Time spent in reading each
ten pages in both tests.



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Number
of page
The time for reading
E. B. G. read “Our Mutual Friend.”
was recorded in the same manner as before, except that the
Influence of Mental Work on Efficiency of Functions Iog
record was made by the experimenter, not by the subject herself.
The results are given in Table XXVI.
TABLE XXVI
Time spent in reading each two pages and for each ten pages.
Time in minutes and seconds.
Time Time Tilne Time
taken taken taken taken
Number for each for each Number for each for each
of page SUCCES- SUICCéS- of page SUICCGS- SUICCGS-
sive sive sive sive
2 pages 10 pages 2 pages 10 pages
1st 2 pages. . . 2. 10 21st 2 pages. . 3.00
2nd “ . . . 2. 30 22nd “ . . . 2. 30
3rd “ 2. 30 12.25 23rd “ 2.30 13. 30
4th “ 2.40 24th “ 2.40
5th “ 2.35 25th “ 2.50
6th “ 3. 10 26th. “ 3.10
7th “ 2. 10 27th “ 2.35
8th “ 2.05 12.25 28th “ 2.45 13. 55
9th “ 2.50 29th. “ 2.45
10th “ 2. 10 30th “ 2.40
11th “ 2.25 31st {{ 2. 40
12th “ 2.35 32nd “ 2 : 10
13th “ 2. 20 i2. 30 33rd “ 2. 30 12.35
4th “ 2. 30 34th “ 2.3
15th “ 2.40 35th “ 2.45
16th “ 2.30 36th “ 2. 20
17th “ 2.35 37th “ 3.00
18th “ 2. 55 13. 15 38th “
19th “ 2.40 39th “
20th “ 2.35 J 40th “
According to the figures given above, E. B. G. seems to have
no ‘warming up effect.
Another experiment was performed on the subject T. A. for
the purpose of investigating the effect of fatigue on the mental
function exercised in filling blanks in sentences where certain
words had to be supplied to make sense. This method was used,
for the first time, by Ebbinghaus who calls it ‘Combinations-
methode.” Professor Whipple" says concerning this: “The
author of the method says in substance: Mental ability demands
not merely retentive capacity, readiness of recall, or facile as-
Sociation of specific past experiences; it demands all this and
Something more, something more complex and, as it were, crea-
tive; namely, the ability to combine, into a coherent and signifi-
* Whipple, G. M., Manual of Mental and Physical Tests, pp. 446–447.
IO4 Mental Fatigue
cant whole, mutually independent and even seemingly a combina-
tive activity. To measure intelligence, therefore, we must em-
ploy a test that demands ability to combine fragments or isolated
sections into a meaningful whole. Such a test may be afforded
by mutilated prose, i.e., by eliding letters, syllables, words, or
even phrases, from a prose passage and requiring the examinee
to restore the passage, if not to its exact original form, at least
to a satisfactory equivalent of it.” Of the difficulty of deciding
the numbers and qualities of eliding words, the same author says:
“The completion method is peculiarly difficult to class psy-
chologically, for the simple reason that the nature of the mental
processes that it demands depends almost entirely upon the
number and kind of elisions that are made in the test. To take
extreme cases, if the elisions are numerous and sweeping, it may
become really a linguistic puzzle of a very difficult variety, and
it then belongs rather in the group of tests of active or creative
imagination of the literary type; if, on the other hand, the elisions
are but few and simple, it may degenerate into a simple test
of controlled association of any desired degree of ease.”
A careful attempt to eliminate the sources of error was made
in the preparation of the materials for the test. About 55 words
were elided on each page of the IQIO edition of Thorndike's
“Educational Psychology " in the manner shown below.
“The knowledge of human which psychology to
student of educational and may roughly
into . A body of knowledge about instincts, habits,
memory, attention, interest, reasoning, etc., find in the
ordinary books. Detailed of thoughts, feelings
and conduct of certain at different ages are available
in Of child ."
The difficulty of the work differs with different individuals.
Such materials as quoted above do not seem to be too difficult
or too easy to serve our purpose. The test was begun at about
noon and lasted to 9 p. m., with intermissions of a few seconds
now and then spent in recording the body temperature and pulse
rate, and with a fifty-minute rest for supper. The subject re-
Corded the time of beginning each page and the time spent on
each page was computed. The results are given in Table XXVII.
Influence of Mental Work on Efficiency of Functions
IO 5
TABLE XXVII
Time spent for each page and for each five pages, in completing passages;
together with the temperature and the pulse rate at irregular intervals.


Time Time Time Time
taken taken taken taken
Number per page for suc- Number per page for suc-
Of in min- cessive Of in min- cessive
page utes and 5 pages page utes and 5 pages
Seconds Seconds
Pulse . . . . . . . 98 27th page. . . . . 14.15
Temperature... |9.68°F. *º-
*- Pulse . . . . . . . . 74
1st page. . . 13. 10 Temperature... 98.9°F.
2nd “ . . . 13.00 *-
3rd “ 14. 21 69.41 Supper. . . . . . .
4th “ 13. 24
5th “ 15.46 Pulse . . . . . . . . 84
6th “ 13. 15 Temperature... 98.2° F.
7th “ 13. 30 ---
8th “ . . . . . 12.30 61.20 28th page. . . . . 14.30
9th “. . . . . 11.15 29th “ . . . . . 11.40
10th “ 10. 50 30th “ 12.10 73. 35
11th “ 12.50 3] St. “ 14.50
12th “. 12. 10 32nd “ . . . 20.25
13th “ 15. 20 65. 50 33rd “ . 15, 30
14th “ 11.15 *-*-
15th “ 14.15 Pulse . . . . . . . . 82
16th “ 10. 55 Temperature... 88.6°F.
17th “ 16.05 -
18th “ 13.00 66, 50 34th page. . . . . 11.01
. 19th “ 13. 15 35th “ . . . 14.54
20th “ 13.35 36th “ 12.40 75.35
21St. “ 11.15 37th “ 14.00
- 38th “ 15.00
Pulse . . . . . . 75 39th “ 14. 10
Temperature... 99°F. -
Pulse . . . . . . . . 80
22nd page . . 18.45 Temperature... 98.6°F.
23rd “ . . . 14.25 -
24th “ 13. 40 79.11 | Next morning.
25th “ 17. 15 *-
26th “ 15.06 40th page. . . . . 12.30
41st “ • 10. I0
The figures given in Table XXVII form another typical work
C111"Ve.
hours.
The speed increases in the beginning for about two
After that, it decreases gradually until the end. The
rest for supper restores the lost energy to some extent, the time
taken for the five pages after the rest being 92.7 per cent of that
spent for those before the rest. The fatigue effect appears again
in the second hour after rest.
Ioé Mental Fatigue
Tranferred Fatigue
I. The effect of fatigue from the continuous exercise of the
function of mental multiplication transferred to other functions:
According to the results of Experiment I, mental multiplica-
tion lasting for certain hours without rest brings about such
changes in efficiency in memorizing German words as are shown
in Table XXVIII.
TABLE XXVIII
Number of hours of mental multiplication; number of examples; time
taken to memorize 40 German words, 10 being memorized at one time, both
immediately before and after the mental multiplication; and coefficient
of fatigue. (The minus sign in the coefficient column means an increase
in efficiency as a result of continuous work.)

Time taken for memor-
Hours of Number izing 40 German words
mental Of before and after Coef. of
Date multipli- examples multiplication fatigue
cation done
Before After
Iſl. S. Iſl. S.
February 25. . 4 24 i{). 10 10.40 5.0
{& 26. . 5 30 8.45 10. 20 18.1
{{ 28. . 9 51 10.30 11. 40 11.1
March 3. . 12 67 6.45 11. 20 72.9
&& 4. . 12 67 8. 15 7.35 —8.1
& 5 . . 12 67 5.40 8.40 52.9
<& 6. . 12 67 7. 40 7.30 —2.2
Average. . 9.4 53 21.4
Table XXVIII shows that an average of 9.4 hours of mental
multiplication causes a 21.4 per cent increase in the time taken
to memorize. The time of memorizing does not, however, in-
crease in any exact proportion to the increase of the number of
hours of mental multiplication.
Eleven individuals (Experiment IV) memorized nonsense
syllables before and after two hours of mental multiplication.
The effect of fatigue caused by continuous mental multiplication
on the function of memory in each individual is given in Table
XXIX.
Table XXIX shows that, with all but five individuals, the
number of nonsense syllables remembered decreases during the
Influence of Mental Work on Efficiency of Functions Io'ſ
TABLE XXIX
Number of nonsense syllables remembered before and after two hours
of mental multiplication, and coefficients of fatigue.

Number of nonsense
syllables remembered Coef. of
Subjects fatigue
Before After
C. D. T. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.9 19. 3 —2.1
Chs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.0 19.0 —5.3
M. M. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.0 14.0 14.3
S. W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6 10.4 2] .. 2
H. L. H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.0 20.0 0
A. G. C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.0 14.0 35.7
R. S. W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.7 16, 7 0
H. A. R. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7 19.0 8.8
J. T. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.4 8.9 61.8
Pig. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.1 19.7 —8. 1
G. D. S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17. 5 13.7 7.7
Average. . . . . . . . . . . . . . . . . . . . . . . . . 13. 5
two hours of mental multiplication. For all the subjects, the
average decrease was I3.5 per cent.
Eleven individuals underwent the association test before and
after the two hours of mental multiplication. The effect of
fatigue caused by the mental multiplication on the speed in as-
sociating the antonyms with given words is, for each individual,
as follows:
TABLE XXX
Time of associating antonyms before and after two hours of mental mul-
tiplication, and coefficients of fatigue.

Time (in seconds) ||
taken for association | Coef."of
Subjects a fatigue
Before ter tº º,
C. D. T. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 152 0 60.0
MS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 105.0 10.5
M. M. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 60.0 —33.3
S. W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 62. 0 ; 8.8
R. S. W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 63.0 ; 10.5
H. A. R. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 59.0 —6.3
Pig. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 60.0 20.0
P. E. R. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 60.0 —65. 7
‘C. T. R. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 70. 0 —5.4
G. M. K. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67.5 61. 0 —9.6
Sn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 72.0 —25.0
Average. . . . . . . . . . . . . . . . . . . . . . . . . —2. 7
Io8 Mental Fatigue
The foregoing table shows that five subjects out of eleven lose
speed during the mental multiplication, while the rest give
opposite results. The individual differences are too great to draw
any general conclusion from the figures given above.
Nine individuals underwent the addition test before and after
two hours of mental multiplication. The effect of fatigue caused
by the work on efficiency in addition is given in Table XXXI.
TABLE XXXI
Time taken for addition as described in Experiment IV, before and after
mental work, and coefficients of fatigue. *
#Time (in seconds)
taken for addition Coef. of
Subjects fatigue
Before After
MS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . # 67 78 16.4
M. M. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 90 —18.2
S. W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 100 119 19.0
R. S. W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 55 55 0
H. A. R. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 50 —7.4
Pig. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 43 —4.5
P. E. R. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 90 —25.0
G. M. K. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 52 8. 3
Sn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 111 0
Average. . . . . . . . . . . . . . . . . . . . . . . . . — .2

Here, too, the effect of two hours of mental multiplication is
subject to great individual differences.
II. The effect of fatigue caused by general mental work
transferred to special mental functions:
The materials for the discussion are obtained from Experiment
II. One year elapsed between Experiments I and II. The prac-
tice effect in Experiment I might still be at work in the test of
mental multiplication in Experiment II. The results show that
practice has influence only on the first eight mornings.
In order to know clearly the effect of practice on the results of
the memory test of Experiment II, we must note the facts of
a short preliminary test. During April, I909, about ten months
before the beginning of Experiment II, the same subject made
a series of practice tests of the function exercised in memorizing
German words. Each day, the subject memorized five lists of
ten German words each and noted the time when she began to
Influence of Mental Work on Efficiency of Functions Io9
memorize each list and the time when she finished writing them
down in their original order. The same process was repeated
five times at each test. The average time taken for memorizing
a list on each day of the experiment is shown in Table XXXII.
TABLE XXXII
Day Time required Day Time required
1. 380 Sec. 11 180 sec.
2 222 “ 12 138 “
3 260 “ 13 280 “
4 212 “ 14 118 “
5 188 “ 15 120 “
6 182 “ 16 108 “
7 165 “ 17 105 “
8 200 “ 18 102 “
9 132 “ 19 100 “
10 145 “ 20 92 “
The figures of Table XXXII give a typical curve. The gain
by practice is greatest at the beginning and becomes smaller as
it approaches toward the end.
After this preliminary experiment, the memory test of Ex-
periment II was made. We find, in this test, the average daily
gain to be about .18 sec. and the gain observed in the morning
test only .09 sec. Therefore, in dealing with the observations
made in Experiment II, practice effect can be neglected without
causing any grave error. -
The fatigue caused by general mental work during the day is
measured by a direct comparison of the efficiency in the morning
with that of the evening. If the results of the comparison show
that fatigue through the day increases in proportion to the in-
crease in the amount of mental work, we are justified in suppos-
ing that the fatigue is caused directly by general mental work
during the day. The relations of these two factors are given in
Tables XXXIII and XXXIV.
According to Tables XXXIII and XXXIV, the transferred
fatigue increases with the number of hours of mental work for
both functions tested, at least from three hours on.
Relations of Fatigue in Different Mental Functions Caused by
the Same Cause
In the foregoing section it was found that fatigue in one func-
tion is, in part, transferred to some other mental function. The
question rises here, whether the transfer is equal for all func-
I IO Mental Fatigue
tions. We can answer this question by calculating the coefficient
of correlation between the fatigues of two functions. The cor-
relations are obtained between fatigue in the special function
exercised and its transferred fatigue, and also between the trans-
ferred fatigue in one function and that in another caused by the
same work. All the correlations which will be mentioned in this
section were obtained by the Pearson method.
In the case of fatigue from mental multiplication transferred
to the function of memorizing, the correlation is —.19 in the sub-
TABLE XXXIII
Ten different kinds of days according to different amounts of mental work
done (‘0–1’ meaning a day of zero to one hour of work, ‘1–2’ a day of one
to two hours, etc.); time taken to memorize per word in the morning and
in the evening; and coefficients of fatigue (i.e., the percentage which the
difference between the times taken in two cases is of the former).

Hours of work, 0–1 Hours of work, 1–2 Hours of work, 2–3
Coef. Coef. Coef.
Date Morn- Even- of Date Morn- Even- of Date Morn- Even- of
ing ing fatigue 1Ing ing fatigue ing ing fatigue
Feb.27 19.0 17.3 —8.9 Mar. 4 13.3 13.7 3.0 |Mar. 15 —11.3 —13. 1 15.9
Mar. 6 11.0 10.6 —3.7 |May 21 13.7 13.0 —5.5 “ 11 20.0 20.3 1, 5
“ 8 16. 6 18. 1 —9. 1 || “ 23 12.2 10.5 —13. 9 Jun. 6 10.6 11.6 9.
“ 10 18.8 “ 25 15.0 10.8 —28.0
“ 20 18.0 20.0 —11.1 : “ 28 10.0 9.5 —5.0
Ave. . . 1.9 —9.9 8.9
Hours of work, 3–4 Hours of work, 4–5 Hours of work, 5–6
Mar. 7 11.5 15.0 30.4 ||Feb. 19 20.0 22.9 14.5 Feb.17 21.3 28.8 35.2
44 9 18.0 20. 5 13.8 |Mar. 3 11. 3 12.0 6.2 || “ 21 19.8 22.5 13.6
Apr. 15 15.8 16.6 5. 1 Apr. 6 12.0 13.8 15.0 Apr. 23 11.7 12.8 9.4
“ 21 17. 1 16.8 –1.2 |May 19 10.5 16.9 60.9 May 9 11.5 13.3 15.7
May 13 10.8 13.3 23. 1 || “ 24 12.5 13.6 8.8 “ 10 9.5 10. 5 10.5
- “ 27 8.0 10. 5 13. 1 || “ 11 10.9 14.3 31.2
“ 12 10.0 12. 2 22.0
Ave. . . 14.2 19.8 19.7
Hours of work, 6–7 Hours of work, 7–8 Hours of work, 8–9
Mar.18 14.2 18.0 23.2 Feb.23 17.5 19.8 13.2 Feb.16 16.8 20.8 124.4
“ 21 25.6 30.3 18.4 “ 24 14.5 27.5 89.7 “ 22 18.5 21.9 118.4
Apr. 6 12.3 14.8 20.3 |Mar. 1 23.3 26.4 13.3 Mar. 16 16.5 20.8 126.7
“, 18 15.8 20.9 32.3 “ 15 17.8 22.2 24.7 Apr. 7 15.0 16.8 112.0
Feb.18 15.8 22.9 44.9 “ 22 16.3 23.9 48.4
Apr. 12 20.2 22.8 12.8
“ 13 10.3 15.9 54.4
“ 14 10.3 14.5 40.8
“ 20 17. 4. 22.2 27.6
Ave. . . 27.8 36. 1 20.4
Hours of work, 9–10
Apr. 7 13.8 14.4 4.3
May 14 13.0 18.3 40.8
“ 16 9.0 18.4 104.4
Ave... 49.8
Influence of Mental Work on Efficiency of Functions
III
This table is made on the s
TABLE XXXIV
ame plan as Table XXXIII, but with the time
taken to do mental multiplication of three-place numbers by three-place
numbers in place of the time of memorizing.
Hours of work, 0–1
Hours of work, 1–2
Hours of work, 2–3
Coef. Coef. Coef.
Date Morn- Even- of Date Morn- Even- of Date Morn- Even- of
Ing ing fatigue IIlg ing fatigue ing ing fatigue
Feb. 5 157.5 175.0 11.1 |Mar. 4 128.3 153. 3 19.5 Feb.15 188.3 133.3—29.2
“ 10 185.0 258.7 38.8 |May 17 161.7 126.7 —21. 1 || “ 26 156.7 141.7 —9.6
“ 27 115.0 120.0 4.4 || “ 21 96. 113.3 17.2 |Mar. 5 138. 3 140.0 1.3
Mar. 6 87. 5 132.5 51.4 “ 23 103.3 96.7 —4.4 || “ 11 6. 7 123.3—15.9
{{ 8 130.0 133.3 2.6 “ 25 120. O 125. O 4.2 Jun. 6 118.3 123.3 4.3
“ 10 126.7 126.3 —. 4 || “ 28 96.7 120.0 24.1 “ 7 103.3 156.7 52.7
Ave 18.1 6, 6 ... 6
Hours of work, 3–4
Hours of work, 4–5
Hours of work, 5–6
Mar. 7 131.7 140.0 6. Feb. 4 155.0 288.0 85.8 Feb. 9 206.7 176.7 —14.5
“ 9 153.3 128.3 —16.3 “ 18 175.0 209.0 19.4 || “ 17 144.3 213.3 47.8
Apr. 15 117. 5 177.5 51.1 |Mar. 3 160.0 165.0 3. 1 || “ 21 115.0 160.0 39.2
“ 21 142.5 115.0 —19. 3 Apr. 6 143.3 138. 3 –3.5 Apr. 23 175.0 123.3—29.5
May 13 118.3 133.3 12.7 |May 19 125.0 112.3 —10.5 May 9 118.3 148.3 25.4
“ 24 90.0 120.0 33.3 “ 10 113.3 101.7 —10.2
* 27 121.8 125.0 , 2.6 || “ 11 100.0 125. O 25.0
“ 12 105.0 117.0 11.4
“ 26 91.7 123.3 34.4
Ave. . . 6.8 18.6 14.3
Hours of work, 6–7 Hours of work, 7–8 Hours of work, 8–9
Feb. 8 218.3 187.7 — 14.0 ||Feb.23 141.7 163. 3 15.2 |Feb. 7 173.3 325.0 87.5
Mar, 18 118.3 150.0 27.0 “ 24 125.0 180.0 45.6 || “ 10 201.0 265.3 31.8
May 6 123.3 175.0 41.9 |Mar. 1 123.3 146.7 19.0 “ 16 163.0 109.0 —33. 1
“ 18 98.3 181.7 84.8 Apr. 12 120.0 125.0 4.2 “ 22 158.3 234.3 47.8
Jun. 18 220.0 153.3 —30.3 “ 13 137. 5 147.5 7.3 || “ 28 120.0 144.O 20.0
“ 20 118.3 150.0 27.7 “ #4 115.0 178.7 55.4 |Mar. 16 124.3 111.7 20.1
“ 22 101.7 121. 7 19.8 || “ 20 135.0 146.7 8.7 |Apr. 11 140.0 163.3 16.6
“ 23 120.0 138. 3 15.3
Feb.18 175.0 209.0 25.2
Ave. 21.9 22.2
Hours of work, 9–10
Apr. 7 138.0 156.7 113
May 14 100.0 163.3 163
“ 16 135.0 173.3 i28
Ave... + 35
8
3
4
O
—w
ject T. A., according to the results of Experiment I.” The cor-
relation is .21 in the group of ten individuals, according to Ex-
periment IV.”
In the case of fatigue from mental multiplication transferred
to the function of association, there is no correlation (.003) ac-
cording to the result of Experiment IV.”
* See Tables III, IV; and compare Tables XVII and XXVIII.
* See Table VIII; compare Tables XX and XXIX.
* See Table VIII; compare Tables XX and XXX.
II 2 Mental Fatigue
In the case of fatigue transferred to the function exercised
in adding, the correlation is +. I (.088) according to the results
of Experiment IV."
For correlations between the transferred fatigue in one func-
tion and that in some other function caused by the same work,
we have the following:
In the case of the subject T. A., according to Experiment II,
there is a correlation of .13 between the diminution in ability to
memorize and that in ability to do mental multiplication.”
In the group of individuals, according to Experiment IV, there
is a correlation of .77 between the fatigue in association and the
fatigue in addition.”
T. See Table VIII; compare Tables XX and XXXI.
* See Table X.
* Compare Tables XXX and XXXI.
CHAPTER VI
CONCLUSIONS
I. Mental Fatigue and Physiological Processes
In the case of the individual T. A., the morning to evening
decrease in pulse rate was on days of less than three hours of
mental work, I.5 per cent. On days of three to six hours of
mental work, it was 3.9 per cent and on days of more than six
hours of mental work, 7.3 per cent. This decrease in pulse rate is
correlated to decrease of efficiency in memory by a coefficient
by .18 and to decrease of efficiency in mental multiplication by a
coefficient of .17. In the group of individuals performing mental
multiplication for two hours there was a decrease in pulse rate
of 13.3 per cent, which decrease is correlated to loss of efficiency
in memory, multiplication, addition, and association by the co-
efficients, .73; .41; .24; and —.I4 respectively. We may, there-
fore conclude that there is a decrease of pulse rate as a result
of continuous mental work which decrease is positively, though
slightly, related to decreases in efficiency of the various mental
functions tested.
We are unable to draw any conclusions from the results ob-
tained from our observations on body temperature during mental
work. *
II. Fatigue and Feelings of Fatigue
In repeated measurements on the individual T. A., the direc-
tion and degree of change in feeling from morning to evening de-
pended somewhat on the hours of mental work during the day.
For instance, the feeling changed more toward the worse with
prolonged mental work and vice versa. These changes are
slightly correlated to the changes in pulse rate and in efficiency
in memory and in mental multiplication. These changes seem
to have no direct relation to the duration of sleep during the
previous night. In the case of the group of individuals, we find
similar relations between the degree of the feeling or fatigue, the
decrease in efficiency of mental functions and decrease in pulse
II3
II 4. Mental Fatigue
rate. From these facts, we conclude that the feeling of fatigue
is somewhat, though far from perfectly, correlated with the state
of mental inefficiency.
III. The Amount of Mental Work and Changes in Mental
Efficiency
I. Factors which influence the efficiency of mental functions.
In the course of several experiments on each individual, we
find that efficiency increases during continuous work and that this
increase affects efficiency during the next experiment. We al-
most invariably find this favorable effect—the effect of practice
—in the results of the experiment, except in the few cases where
the subject had already reached the limit of practice. But we do
not observe any regular ‘warming up effect. In the four twelve-
hour fatigue curves taken after the subject had reached the limit
of practice, there is no initial increase of efficiency. But the re-
sults of the two-hour experiment tried on the group of in-
dividuals, perhaps shows the existence of the factor in question.
In the reading experiment, the one who was less used to English
showed this effect, while the other who had read it much more
showed none. It seems then, to be a fact that ‘warming up is
not present in functions in which the subject has reached the limit
of practice. For this reason, the writer is inclined to conclude
that the ‘warming up effect is only a part of the effect of prac-
tice. In none of our fatigue curves are the spurts observable.
The unfavorable effect which is observed in our results is, of
course, attributable to fatigue. Besides these factors, it is prob-
able that habits of diurnal changes have some influence on the
efficiency in mental functions.
2. The effect of mental work on the efficiency of the special
mental function.
Difficult and disagreeable continued work brings about a de-
crease in the efficiency of the function exercised. In the case of
individual T. A., the time taken to do a certain number of ex-
amples is almost doubled during twelve hours of mental mul-
tiplication. In the case of the group of individuals (inexperi-
enced subjects), the increase in the time taken to do a certain
amount of work is 24 per cent during two hours of mental
multiplication.
Conclusions - II 5
3. Transferred mental fatigue.
Continuous exercise of a mental function not only causes
a decrease in the efficiency of the function tested, but may have
an unfavorable influence on other functions. For instance, in
the case of individual T. A., 9.4 hours of mental multiplication
increases the time taken to memorize words by 21.4 per cent.
After two hours of mental multiplication the group of in-
dividuals showed 13.5 per cent decrease in ability to memorize
nonsense syllables. But there was hardly any change in the
functions of addition and association. General mental work de-
creases the efficiency of special mental functions. Fatigue and
its transferred fatigue are, as a rule, correlated, though the cor-
relation is very low. There is also a very slight, but positive,
correlation between two transferred ‘fatigues' caused by the
same mental work. On the whole, then, we are led to con-
clude that fatigue in a special mental function as well as in
general is slightly transferrable to other functions and that the
greater the fatigue the greater the transferred fatigue.
IV. Individual Differences
We find great individual differences in the susceptibility to
fatigue. As a rule, the more competent people are less affected
by fatigue.
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