Various - Harvard Psychological Studies, Volume 1

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TABLE I.

PRELIMINARY TRIALS WITH FROG NO. 2.

Trials. Red on Right. White on Left.
1 to 10 10 times to red 0

Red on Left. White on Right.
11 to 20 4 times to red 6

Red on Left. White on Right.
21 to 30 3 times to red 7

To Red. To White. To Right. To Left.
Totals. 17 13 23 7

This table indicates in trials 1 to 10 a strong tendency to the red
cardboard. Trials 21 to 30 prove that there was also a tendency to the
right.

Training was begun with the labyrinth arranged as shown in Fig. 1,
that is, with the left entrance passage and the right exit passage
open, and with red cardboard on the right (red was always on the side
to be avoided) and white on the left. Table II. contains the results
of 110 trials with No. 2, arranged according to right and wrong choice
at the entrance and exit. Examination of this table shows a gradual
and fairly regular increase in the number of right choices from the
first series to the last; after 100 experiences there were practically
no mistakes.

With another subject, No. _6a_, the results of Table III. were
obtained. In this instance the habit formed more slowly and to all
appearances less perfectly. Toward the end of the second week of work
_6a_ showed signs of sickness, and it died within a few weeks, so I do
not feel that the experiments with it are entirely trustworthy. During
the experiments it looked as if the animal would get a perfectly
formed habit very quickly, but when it came to the summing up of
results it was obvious that there had been little improvement.

[Illustration: FIG. 2. Labyrinth as arranged for experiments. _E_,
entrance; _R, R_, regions covered with red; _W, W_, regions covered
with white. The tracing represents the path taken by No. 2 on the
sixth trial. Dots mark jumps.]

TABLE II.

LABYRINTH HABIT. FROG NO. 2.

Entrance. Exit. Remarks.
Trials. Right. Wrong. Right. Wrong.
1- 10 1 9 4 6
One day rest.
11- 20 2 8 5 5
21- 30 4 6 7 3
31- 40 5 5 6 4
41- 50 5 5 6 2
(17) (33) (30) (20)
51- 60 9 1 8 2
61- 70 6 4 10 0
71- 80 7 3 9 1
81- 90 9 1 8 2
91-100 10(50) 0(10) 10(52) 0( 8)
--- --- --- ---
67 43 82 28

Other animals which were used gave results so similar to those for
frog No. 2 that I feel justified in presenting the latter as
representative of the rapidity with which the green frog profits by
experience.

TABLE III.

LABYRINTH HABIT. FROG NO. _6a_.

Entrance. Exit. Remarks.
Trials Right. Wrong. Right. Wrong.
1- 10 6 4 5 5
One day rest.
11- 20 7 3 4 6
21- 30 2 8 1 9
31- 40 6 4 1 9
41- 50 7 3 8 2
(28) (22) (19) (31)
51- 60 5 5 7 3
61- 70 6 4 4 6
71- 80 4 6 3 7
One day rest.
81- 90 5 5 7 3
91-100 10(30) 0(20) 8(29) 2(21)
---- ---- ---- ----
(58) (44) (48) (52)

Preliminary Trials.

Red on Left Partition at Exit on Right
1- 5 5 times to Red 4 times to Partition.

Red on Right Partition at Exit on Left
6-10 3 times to Red 5 times to Partition.

2. _Rapidity of Habit Formation_.--As compared with other vertebrates
whose rapidity of habit formation is known, the frog learns slowly.
Experimental studies on the dog, cat, mouse, chick and monkey furnish
excellent evidence of the ability of these animals to profit quickly
by experience through the adapting of their actions to new conditions.
They all show marked improvement after a few trials, and after from
ten to thirty most of them have acquired perfect habits. But the
comparison of the frog with animals which are structurally more
similar to it is of greater interest and value, and we have to inquire
concerning the relation of habit formation in the frog to that of
fishes and reptiles. Few experimental studies with these animals have
been made, and the material for comparison is therefore very
unsatisfactory. E.L. Thorndike[1] has demonstrated the ability of
fishes to learn a labyrinth path. In his report no statement of the
time required for the formation of habit is made, but from personal
observation I feel safe in saying that they did not learn more quickly
than did the frogs of these experiments. Norman Triplett[2] states
that the perch learns to avoid a glass partition in its aquarium after
repeatedly bumping against it. Triplett repeated Moebius' famous
experiment, and found that after a half hour's training three times a
week for about a month, the perch would not attempt to capture minnows
which during the training periods had been placed in the aquarium with
the perch, but separated from them by a glass partition. Triplett's
observations disprove the often repeated statement that fishes do not
have any associative processes, and at the same time they show that
the perch, at least, learns rapidly--not so rapidly, it is true, as
most animals, but more so in all probability than the amphibia.

[1] Thorndike, Edward: 'A Note on the Psychology of Fishes,'
_American Naturalist_. 1899, Vol. XXXIII., pp. 923-925.

[2] Triplett, Norman: 'The Educability of the Perch,' _Amer.
Jour. Psy._, 1901, Vol. XII., pp. 354-360.

The only quantitative study of the associative processes of reptiles
available is some work of mine on the formation of habits in the
turtle.[3] In the light of that study I can say that the turtle learns
much more rapidly than do fishes or frogs. Further observations on
other species of turtles, as yet unpublished, confirm this conclusion.

[3] Yerkes, Robert Mearns: 'The Formation of Habits in the
Turtle,' _Popular Science Monthly_, 1901, Vol. LVIII., pp.
519-535.

For the frog it is necessary to measure and calculate the improvement
in order to detect it at first, while with the turtle or chick the
most casual observer cannot fail to note the change after a few
trials. In connection with the quickness of the formation of
associations it is of interest to inquire concerning their permanency.
Do animals which learn slowly retain associations longer? is a
question to which no answer can as yet be given, but experiments may
readily be made to settle the matter. I have tested the frog for
permanency, and also the turtle, but have insufficient data for
comparison.

3. _Sensory Data Contributing to the Associations_.--Among the most
important of the sensory data concerned in the labyrinth habit are the
visual impressions received from the different colored walls, the
slight differences in brightness of illumination due to shadows from
the partitions and the contrast in form of the two sides of the
labyrinth resulting from the use of the partitions, and the muscular
sensations dependent upon the direction of turning. The experiments
proved beyond question that vision and the direction of turning were
the all-important factors in the establishment of the habit. At first
it seemed as if the direction of turning was the chief determinant,
and only by experimenting with colors under other conditions was I
able to satisfy myself that the animals did notice differences in the
appearance of their surroundings and act accordingly. In Table IV.
some results bearing on this point have been arranged. To begin with,
the habit of going to the left when the red was on the right at the
entrance had been established; then, in order to see whether the
colors influenced the choice, I reversed the conditions, placing the
red on the left, that is, on the open-passage side. The results as
tabulated in the upper part of Table IV. show that the animals were
very much confused by the reversal; at the entrance where there were
several guiding factors besides the colors there were 50 per cent. of
mistakes, while at the exit where there were fewer differences by
which the animal could be directed it failed every time. This work was
not continued long enough to break up the old habit and replace it by
a new one, because I wished to make use of the habit already formed
for further experiments, and also because the animals remained so long
in the labyrinth trying to find their way out that there was constant
danger of losing them from too prolonged exposure to the dry air.

TABLE IV.

INFLUENCE OF CHANCES OF CONDITIONS. FROG NO. 2.

Habit perfectly formed of going to Left (avoiding Red) at
entrance and to Right at exit. Conditions now reversed. Red on
Left. Partition at Exit on Right.

Trials. Entrance. Exit. Remarks.
Right. Wrong. Right. Wrong.
1- 5 3 2 0 5
6-10 2 3 0 5

Discontinued because animal remained so long in labyrinth that
there was danger of injuring it for further work. This shows
that the habit once formed is hard to change.

Given 20 trials with conditions as at first in order to
establish habit again.

1-10 9 1 8 2
11-20 10 0 9 1

Colors reversed, no other change. To test influence of colors.

1-10 6 4 10 0

INFLUENCE OF DISTURBANCE WHEN ANIMAL IS ENTERING BOX.

No Disturbance. Animal Touched.

To Red (Right). To White (Left). To Red. To White.
2 8 5 5

This was after the tendency to go to the Left at the entrance
had been established.

These experiments to test the effect of changing colors are also of
interest in that they show in a remarkable way the influence of the
direction of turning. The animal after succeeding in getting around
the first part of the labyrinth failed entirely to escape at the exit.
Here it should have turned to the left, instead of the right as it was
accustomed to, but it persisted in turning to the right. Fig. 3
represents approximately the path taken in the first trial; it shows
the way in which the animal persisted in trying to get out on the
right. From this it is clear that both vision and the complex
sensations of turning are important.

[Illustration: FIG. 3. Labyrinth with Conditions the Reverse of the
Usual. (Compare with FIG. 2.) The colors as well as the partitions
have been shifted. The path is, approximately, that taken by No. 2 in
the first trial after the reversal of conditions.]

The latter part of Table IV. presents further evidence in favor of
vision. For these tests the colors alone were reversed. Previous to
the change the animal had been making no mistakes whatever, thereafter
there were four mistakes at the entrance and none at the exit. Later,
another experiment under the same conditions was made with the same
animal, No. 2, with still more pronounced results. In this case the
animal went to the white, that is, in this instance, into the blind
alley, and failed to get out; several times it jumped over to the left
side (the open-passage side) of the box but each time it seemed to be
attracted back to the white or repelled by the red, more probably the
latter, as the animal had been trained for weeks to avoid the red.
Concerning the delicacy of visual discrimination I hope to have
something to present in a later paper.

The tactual stimuli given by contact with the series of wires used for
the electrical stimulus also served to guide the frogs. They were
accustomed to receive an electrical shock whenever they touched the
wires on the blocked side of the entrance, hence on this side the
tactual stimulus was the signal for a painful electrical stimulus.
When the animal chose the open passage it received the tactual
stimulus just the same, but no shock followed. After a few days'
experimentation it was noted that No. 2 frequently stopped as soon as
it touched the wires, whether on the open or the closed side. If on
the closed side, it would usually turn almost immediately and by
retracing its path escape by the open passage; if on the open side, it
would sometimes turn about, but instead of going back over the course
it had just taken, as on the other side, it would sit still for a few
seconds, as if taking in the surroundings, then turn again and go on
its way to the exit. This whole reaction pointed to the formation of
an association between the peculiar tactual sensation and the painful
shock which frequently followed it. Whenever the tactual stimulus came
it was sufficient to check the animal in its course until other
sensory data determined the next move. When the wrong passage had been
chosen the visual data gotten from the appearance of the partition
which blocked the path and other characteristics of this side of the
labyrinth determined that the organism should respond by turning back.
When, on the other hand, the open passage had been selected, a
moment's halt sufficed to give sensory data which determined the
continuation of the forward movement. Although this reaction did not
occur in more than one tenth of the trials, it was so definite in its
phases as to warrant the statements here made. Fig. 4 gives the path
taken by No. 2 in its 123d trial. In this experiment both choices were
correctly made, but when the frog touched the wires on the open side
it stopped short and wheeled around; after a moment it turned toward
the exit again, but only to reverse its position a second time. Soon
it turned to the exit again, and this time started forward, taking a
direct course to the tank. The usual course for animals which had
thoroughly learned the way to the tank is that chosen in Fig. 5.

[Illustration: FIG. 4. Path of No. 2 for 123d Trial. Showing the
response to the tactual stimulus from wires.]

An interesting instance of the repetition of a reaction occurred in
these experiments. A frog would sometimes, when it was first placed in
the box, by a strong jump get up to the edge; it seldom jumped over,
but instead caught hold of the edge and balanced itself there until
exhaustion caused it to fall or until it was taken away. Why an animal
should repeat an action of the nature of this is not clear, but almost
invariably the second trial resulted in the same kind of reaction. The
animal would stop at the same point in the box at which it had
previously jumped, and if it did not jump, it would look up as if
preparing to do so. Even after a frog had learned the way to the tank
such an action as this would now and then occur, and almost always
there would follow repetition in the manner described.

[Illustration: FIG. 5. Path Usually Taken by Animal Having
Perfectly-formed Habit.]

4. _The Effect of Fear upon Habit Formation._--A certain amount of
excitement undoubtedly promotes the formation of associations, but
when the animal is frightened the opposite is true. I have no
hesitation in stating that, in case of the green frog, any strong
disturbing stimulus retards the formation of associations. Although
the frogs gave little evidence of fear by movements after being kept
in the laboratory for a few weeks, they were really very timid, and
the presence of any strange object influenced all their reactions.
Quiescence, it is to be remembered, is as frequently a sign of fear as
is movement, and one is never safe in saying that the frog is not
disturbed just because it does not jump. The influence of the
experimenter's presence in the room with the frogs which were being
tried in the labyrinth became apparent when the animals were tried in
a room by themselves. They escaped much more quickly when alone. In
order to keep records of the experiments it was necessary for me to be
in the room, but by keeping perfectly quiet it was possible to do this
without in any objectionable way influencing the results. It may be,
however, that for this reason the learning is somewhat slower than it
would have been under perfectly natural conditions. Early in this
paper reference was made to the fact that the frog did not learn to
escape from a box with a small opening at some distance from the floor
if it was prodded with a stick. I do not mean to say that the animal
would never learn under such conditions, but that they are unfavorable
for the association of stimuli and retard the process. This conclusion
is supported by some experiments whose results are tabulated at the
bottom of Table IV. In these trials the animal had been trained to go
to the left and to avoid red. At first ten trials were given in which
the frog was in no way disturbed. The result was eight right choices
and two wrong ones. For the next ten trials the frog was touched with
a stick and thus made to enter the labyrinth from the box, _A_. This
gave five right and five wrong choices, apparently indicating that the
stimulus interfered with the choice of direction. Several other
observations of this nature point to the same conclusion, and it may
therefore be said that fright serves to confuse the frog and to
prevent it from responding to the stimuli which would ordinarily
determine its reaction.

5. _The Permanency of Associations._--After the labyrinth habit had
been perfectly formed by No. 2, tests for permanency were made, (1)
after six days' rest and (2) after thirty days. Table V. contains the
results of these tests. They show that for at least a month the
associations persist. And although there are several mistakes in the
first trials after the intervals of rest, the habit is soon perfected
again. After the thirty-day interval there were forty per cent. of
mistakes at the exit for the first series, and only 20 per cent. at
the entrance. This in all probability is explicable by the fact that
the colors acted as aids at the entrance, whereas at the exit there
was no such important associational material.

TABLE V.

PERMANENCY OF ASSOCIATIONS. FROG NO. 2.

Tests after six days' rest (following the results tabulated in Table
III.).

Trial. Entrance. Exit.
Right. Wrong. Right. Wrong
1-10 7 3 8 2
(110-120)
11-20 10 0 10 0

Tests after THIRTY days' rest.
1-10 8 2 6 4
10-20 10 0 10 0

D. Association of Stimuli.--In connection with reaction-time work an
attempt was made to form an association between a strong visual
stimulus and a painful electrical shock, with negative results. A
reaction box, having a series of interrupted circuits in the bottom
like those already described for other experiments, and an opening on
one side through which a light could be flashed upon the animal,
served for the experiments. The tests consisted in the placing of a
frog on the wires and then flashing an electric light upon it: if it
did not respond to the light by jumping off the wires, an electrical
stimulus was immediately given. I have arranged in Table VI. the
results of several weeks' work by this method. In no case is there
clear evidence of an association; one or two of the frogs reacted to
the light occasionally, but not often enough to indicate anything more
than chance responses. At one time it looked as if the reactions
became shorter with the continuation of the experiment, and it was
thought that this might be an indication of the beginning of an
association. Careful attention to this aspect of the results failed to
furnish any satisfactory proof of such a change, however, and although
in the table statements are given concerning the relative numbers of
short and long reactions I do not think they are significant.

TABLE VI.

ASSOCIATION OF ELECTRICAL AND VISUAL STIMULI. FROG No. 1a, 2a, 3a, 4a,
5a, A and Z.

Frog. Total No. Days. Result.
Trials.

No. 1a 180 18 Increase in number of long reaction
toward end. No evidence of association.

No. 2a 180 17 Increase in number of short reactions
toward end. No evidence of association.

No. 3a 180 17 Marked increase in the number of
short reactions toward end. No other evidence
of association.

No. 4a 200 19 Slight increase in the short reactions.
There were a few responses to the light on the
third day.

No. 5a 200 20 No increase in the number of short reactions.
Few possible responses to light on second and
third days.

Frog A 250 20 No evidence of association.

Frog Z 450 28 No evidence of association.

To all appearances this is the same kind of an association that was
formed, in the case of the labyrinth experiments, between the tactual
and the electrical stimuli. Why it should not have been formed in this
case is uncertain, but it seems not improbable that the light was too
strong an excitement and thus inhibited action. There is also the
probability that the frog was constrained by being placed in a small
box and having the experimenter near.

III. SUMMARY.

1. The green frog is very timid and does not respond normally to most
stimuli when in the presence of any strange object. Fright tends to
inhibit movement.

2. That it is able to profit by experience has been proved by testing
it in simple labyrinths. A few experiences suffice for the formation
of simple associations; but in case of a series of associations from
fifty to a hundred experiences are needed for the formation of a
perfect habit.

3. Experiment shows that the frog is able to associate two kinds of
stimuli, _e.g._, the peculiar tactual stimulus given by a wire and a
painful electric stimulus which in the experiments followed the
tactual. In this case the animal learns to jump away, upon receiving
the tactual stimulus, before the experimenter gives the electric
stimulus.

4. Vision, touch and the organic sensations (dependent upon direction
of turning) are the chief sensory factors in the associations. The
animals discriminate colors to some extent.

5. Perfectly formed habits are hard to change.

6. Fear interferes with the formation of associations.

7. Associations persist for at least a month.

PART II. REACTION TIME OF THE GREEN FROG TO ELECTRICAL AND TACTUAL
STIMULI.

IV. THE PROBLEMS AND POSSIBILITIES OF COMPARATIVE REACTION-TIME
STUDIES.

Animal reaction time is at present a new field of research of evident
importance and full of promise. A great deal of time and energy has
been devoted to the investigation of various aspects of the time
relations of human neural processes; a multitude of interesting facts
have been discovered and a few laws established, but the results seem
disproportionate to the amount of patient labor expended.
Physiologists have determined the rate of transmission of the neural
impulse for a few animals, and rough estimates of the time required
for certain changes in the nervous system have been made, but this is
all we have to represent comparative study. Just the path of approach
which would seem most direct, in case of the time of neural changes,
has been avoided. Something is known of the ontogenetic aspect of the
subject, practically nothing of the phylogenetic; yet, in the study of
function the comparative point of view is certainly as important as it
is in the study of structure. In calling attention to the importance
of the study of animal reaction time I would not detract from or
minimize the significance of human investigations. They are all of
value, but they need to be supplemented by comparative studies.

It is almost impossible to take up a discussion of the time relations
of neural processes without having to read of physiological and
psychological time. The time of nerve transmission, we are told, is
pure physiological time and has nothing whatever to do with psychic
processes; the time occupied by the changes in brain centers is, on
the contrary, psychological time. At the very beginning of my
discussion of this subject I wish to have it clearly understood that I
make no such distinction. If one phase of the neural process be called
physiological time, with as good reason may all be so named. I prefer,
therefore, to speak of the time relations of the neural process.