In order to test the quickness of the members of the Hospital
Corps Detachment, and to determine whether the changes in
diet affected in any way their ability to respond promptly to
sensory stimulation, each man was carried through a series of
reaction experiments at the Yale Psychological Laboratory.
The method of the experiments was that regularly employed in
simple reaction time experiments. The person whose reaction
time is to be measured is seated in a comfortable position
with his finger pressing on an electric key. He is told that
he is to lift his finger from the key as quickly as possible
when he hears a given sound-signal. The sounder which produces
this signal and the electric key are placed in a circuit with
a standard time-measuring apparatus—the Hipp Chronoscope. This
chronoscope is arranged so that it begins to record the instant
the sound is given and stops the instant the reactor lifts his
finger. The dial of the chronoscope shows in thousandths of a
second (hereafter designated by the technical term _sigmas_)
the time that elapses between the sound to which the reactor is
to respond and the movement of response. The chronoscope was
tested at frequent intervals by means of a standard pendulum
and errors in the record are well under two sigmas.
The time which is measured by this method is occupied chiefly
by nervous processes. The following factors may be specified:
First, the auditory organ is aroused by the sound; second,
the afferent nerve transmits the stimulation to the central
nervous system; third, the central nervous system carries
the energy to the motor nerves; fourth, the efferent motor
nerves transmit the stimulus to the muscles; and finally, some
time is required by the muscle for its contraction. It will
be seen, accordingly, that the chief factors of a reaction
are nervous processes, and since the external conditions
of successive reactions are in all respects uniform, any
variations in the time of a given person’s reactions may be
regarded as indicating variations in the nervous condition of
the reactor. In view of the instability of nervous conditions,
it is necessary to eliminate any slight or merely temporary
fluctuations by taking each time a given reactor is tested a
series of reactions. For this reason, a series of ten reactions
was taken with each of the men every two weeks during November,
December, and January. After an interval of two months, namely,
on March 30, 31, and April 1, two final series were made with
each man.
The results are presented in tables 1 to 5. The dates in the
first column indicate the day on which each individual set
of ten reactions was taken. The second column presents the
averages of each ten reactions in sigmas. The third column
gives the mean variations of the various single reaction times
from the average. The fourth column gives the variations of the
day’s average, recorded in column 2, from the general average
of that individual for all his experiments. These general
averages are presented in table 6. At the bottom of each
complete column of averages will be found the group average.
This quantity is obtained by averaging the results from all the
members of the squad for periods of, approximately, two weeks.
The mean variations in the third column make it clear that the
subjects did not settle down into what could be regarded as
trained subjects. Trained subjects are expected to give mean
variations which are consistently within the limits of 10 per
cent of the average. While there are, of course, instances in
which the mean variation falls within this limit, there is no
consistent exhibition of the regularity indicative of thorough
practice. This fact is further confirmed by a comparison of
the results of March 30, 31, and April 1 with those of the
earlier months. At the end of March, all effects of practice
in November, December, and January, except the most general,
may be regarded as having disappeared; and yet the averages
and variations for the March and April dates resemble closely
those of the month immediately preceding and also those of
November. The effects of practice may, accordingly, be regarded
as insignificant.
This lack of special training accounts for the large
variations which appear in some cases. As is usual in reaction
experiments, the signal to which the reactors were to respond
was in each case preceded by about two seconds by a bell signal
to arouse attention. Conditions were thus rendered as nearly
uniform as possible, but the variations indicate in three or
four cases exceptional lapses of attention. Such exceptional
cases can be eliminated without prejudicing the final validity
of the results by substituting the median for the averages. In
table 7, the medians are grouped together and show even more
than the tables of average the absence of any general variation
during the period of the tests.
The obvious conclusion from these tests is that the quickness
of the members of the squad underwent no general change during
the whole period covered by the test. Individual members showed
variations from time to time, but these variations are clearly
accidental in character, for they show no regular tendencies
and are in no way related to the changes in the character and
amount of the diet.
(Signed) CHARLES H. JUDD.
April 12, 1904.
The following tables give all the data upon which the foregoing
conclusions are based, being furnished by Dr. Judd and Mr. Warren M.
Steele, Assistant in Psychology, by whom the observations were made. Dr.
Cloyd N. McAllister, Instructor in Psychology, was also associated in the
making of these observations.