Various - Harvard Psychological Studies, Volume 1

V >> Various >> Harvard Psychological Studies, Volume 1

Pages:
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55

[Illustration: FIG. 3. Path taken by crawfish while being trained to
avoid the left passage. Marks along the glass plate and partition
indicate contact by the antennae and chelae.]

Of the significance of the sensations due to the 'direction of
turning' in these habits the best evidence that is furnished by this
work is that of the following observations. In case of the tests of
Table II. the subject was, after 100 preliminary tests, trained by 250
experiences to escape by the Right-hand passage. Now, in Groups III.
to VII., the subject's usual manner of getting out of the closed
passage, when by a wrong choice it happened to get into it, was to
draw back on the curled abdomen, after the antennae and chelae had
touched the glass plate, and then move the chelae slowly along the
Right wall of the partition until it came to the upper end; it would
then walk around the partition and out by the open passage. Fig. 3
represents such a course. In Group VIII. the Right passage was closed,
instead of the Left as previously. The first time the animal tried to
get out of the box after this change in the conditions it walked
directly into the Right passage. Finding this closed it at once turned
to the Right, _as it had been accustomed to do when it came in contact
with the glass plate_, and moved along the side of the box just as it
did in trying to get around the end of the partition. The path taken
by the crawfish in this experiment is represented in Fig. 4. It is
very complex, for the animal wandered about more than fifteen minutes
before escaping.

The experiment just described to show the importance of the tendency
to turn in a certain direction was the first one of the first series
after the change in conditions. When given its second chance in this
series the subject escaped directly by the Left passage in 33 seconds,
and for the three following trips the time was respectively 25, 25 and
30 seconds.

Upon the experimental evidence presented we base the conclusion that
crawfish are able to profit by experience in much the same way that
insects do, but far more slowly.

[Illustration: FIG. 4. Path taken by crawfish which had been trained
to avoid the Left passage, when the Right passage was closed. Showing
turning to the right as in Fig. 3.]

It was thought that a study of the way in which crawfish right
themselves when placed upon their backs on a smooth surface might
furnish further evidence concerning the ability of the animals to
profit by experience.

Dearborn[3] from some observations of his concludes that there is no
one method by which an individual usually rights itself, and,
furthermore, that the animals cannot be trained to any one method. His
experiments, like Bethe's, are too few to warrant any conclusions as
to the possibility of habit formation.

[3] Dearborn, G.V.N.: 'Notes on the Individual Psychophysiology
of the Crayfish,' _Amer. Jour. Physiol._, Vol. 3, 1900, pp.
404-433.

For the following experiments the subject was placed on its back on a
smooth surface in the air and permitted to turn over in any way it
could. Our purpose was to determine (1) whether there was any marked
tendency to turn in a certain way, (2) whether if such was not the
case a tendency could be developed by changing the conditions, and (3)
how alteration in the conditions of the test would affect the turning.

A great many records were taken, but we shall give in detail only a
representative series. In Table III., 557 tests made upon four
subjects have been arranged in four groups for convenience of
comparison of the conditions at different periods of the training
process. Each of these groups, if perfect, would contain 40 tests for
each of the four subjects, but as a result of accidents II., III., and
IV. are incomplete.

TABLE III.

RE-TURNING OF CRAWFISH.

Group. Number of L. R. Time in Tests.
Animal. Per cent. Seconds.
I. 2 22.5 77.5 14.6 40
3 42.5 57.5 2.6 40
4 52.8 47.2 4.3 38
16 44.5 55.5 22.5 45
-- ---- ---- ---- ---
40.6 59.4 10.8 163

Group. Number of L. R. Time in Tests.
Animal. Per cent. Seconds.
II 2 28 72 50 43
3 32 68 6.2 50
4 -- 100 6.8 40
16 31.3 68.7 39.3 42
-- ---- ---- ---- ---
22.8 77.2 25.6 175

Group. Number of L. R. Time in Tests.
Animal. Per cent. Seconds.
III 2 2.5 97.5 46.5 40
-- -- -- -- --
4 20 80 5.5 40
16 41 59 15 49
-- ---- ---- ---- ---
21.2 78.8 22 129

Group. Number of L. R. Time in Tests.
Animal. Per cent. Seconds.
IV. 2 2 98 41 50
-- -- -- -- --
4 32.5 67.5 7.3 40
-- ---- ---- ---- ---
17 83 24 90

Group I., representing 163 tests, shows 59 per cent. to the right,
with a time interval of 10.8 seconds (_i.e._, the time occupied in
turning). Group II. shows 77 per cent. to the right; and so throughout
the table there is an increase in the number of returnings to the
right. These figures at first sight seem to indicate the formation of
a habit, but in such case we would expect, also, a shortening of the
time of turning. It may be, however, that the animals were gradually
developing a tendency to turn in the easiest manner, and that at the
same time they were becoming more accustomed to the unusual position
and were no longer so strongly stimulated, when placed on their backs,
to attempt to right themselves.

All the subjects were measured and weighed in order to discover
whether there were inequalities of the two sides of the body which
would make it easier to turn to the one side than to the other. The
chelae were measured from the inner angle of the joint of the
protopodite to the angle of articulation with the dactylopodite. The
carapace was measured on each side, from the anterior margin of the
cephalic groove to the posterior extremity of the lateral edge. The
median length of the carapace was taken, from the tip of the rostrum
to the posterior edge, and the length of the abdomen was taken from
this point to the edge of the telson. These measurements, together
with the weights of three of the subjects, are given in the
accompanying table.

TABLE IV.

MEASUREMENTS OF CRAWFISH.

Chelae. Carapace. Abdomen. Weight.
Left. Right. Left. Right. Median.

No. 2, 9.8 10.0 38.2 38.7 47.3 48.1 29.7
No. 4, 7.7 7.7 33.6 33.8 39.4 42.3 17.7
No. 16, 12.5 12.4 37.6 37.6 46.4 53.2 36.2

Since these measurements indicate slightly greater size on the right
it is very probable that we have in this fact an explanation of the
tendency to turn to that side.

To test the effect of a change in the conditions, No. 16 was tried on
a surface slanted at an angle of 1 deg. 12'. Upon this surface the subject
was each time so placed that the slant would favor turning to the
right. Under these conditions No. 16 gave the following results in two
series of tests. In the first series, consisting of 46 turns, 82.6 per
cent. were to the right, and the average time for turning was 17.4
seconds; in the second series, of 41 tests, there were 97.5 per cent,
to the right, with an average time of 2.5 seconds. We have here an
immediate change in the animal's method of re-turning caused by a
slight change in the conditions. The subject was now tested again on
a level surface, with the result that in 49 tests only 59 per cent.
were toward the right, and the time was 15 seconds.

SUMMARY.

1. Experiments with crawfish prove that they are able to learn simple
labyrinth habits. They profit by experience rather slowly, from fifty
to one hundred experiences being necessary to cause a perfect
association.

2. In the crawfish the chief factors in the formation of such habits
are the chemical sense (probably both smell and taste), touch, sight
and the muscular sensations resulting from the direction of turning.
The animals are able to learn a path when the possibility of following
a scent is excluded.

3. The ease with which a simple labyrinth habit may be modified
depends upon the number of experiences the animal has had; the more
familiar the animal is with the situation, the more quickly it changes
its habits. If the habit is one involving the choice of one of two
passages, reversal of the conditions confuses the subject much more
the first time than in subsequent cases.

4. Crawfish right themselves, when placed on their backs, by the
easiest method; and this is found to depend usually upon the relative
weight of the two sides of the body. When placed upon a surface which
is not level they take advantage, after a few experiences, of the
inclination by turning toward the lower side.

* * * * *

THE INSTINCTS, HABITS, AND REACTIONS OF THE FROG.

BY ROBERT MEARNS YERKES.

PART I. THE ASSOCIATIVE PROCESSES OF THE GREEN FROG.

I. SOME CHARACTERISTICS OF THE GREEN FROG.

The common green frog, _Rana clamitans_, is greenish or brownish in
color, usually mottled with darker spots. It is much smaller than the
bull frog, being from two to four inches in length ordinarily, and may
readily be distinguished from it by the presence of prominent
glandular folds on the sides of the back. In the bull frog, _Rana
catesbeana_, these folds are very small and indistinct. The green frog
is found in large numbers in many of the ponds and streams of the
eastern United States, and its peculiar rattling croak may be heard
from early spring until fall. It is more active, and apparently
quicker in its reactions, than the bull frog, but they are in many
respects similar in their habits. Like the other water frogs it feeds
on small water animals, insects which chance to come within reach and,
in times of famine, on its own and other species of frogs. The prey is
captured by a sudden spring and the thrusting out of the tongue, which
is covered with a viscid secretion. Only moving objects are noticed
and seized; the frog may starve to death in the presence of an
abundance of food if there is no movement to attract its attention.
Most green frogs can be fed in captivity by swinging pieces of meat in
front of them, and those that will not take food in this way can be
kept in good condition by placing meat in their mouths, for as soon as
the substance has been tasted swallowing follows.

The animals used for these experiments were kept in the laboratory
during the whole year in a small wooden tank. The bottom of this tank
was covered with sand and small stones, and a few plants helped to
purify the water. An inch or two of water sufficed; as it was not
convenient to have a constant stream, it was changed at least every
other day. There was no difficulty whatever in keeping the animals in
excellent condition.

Of the protective instincts of the green frog which have come to my
notice during these studies two are of special interest: The
instinctive inhibition of movement under certain circumstances, and
the guarding against attack or attempt to escape by 'crouching' and
'puffing.' In nature the frog ordinarily jumps as soon as a strange or
startling object comes within its field of vision, but under certain
conditions of excitement induced by strong stimuli it remains
perfectly quiet, as do many animals which feign death, until forced to
move. Whether this is a genuine instinctive reaction, or the result of
a sort of hypnotic condition produced by strong stimuli, I am not
prepared to say. The fact that the inhibition of movement is most
frequently noticed after strong stimulation, would seem to indicate
that it is due to the action of stimuli upon the nervous system.

What appears to be an instinctive mode of guarding against attack and
escaping an enemy, is shown whenever the frog is touched about the
head suddenly, and sometimes when strong stimuli are applied to other
parts of the body. The animal presses its head to the ground as if
trying to dive or dodge something, and inflates its body. This kind of
action is supposed to be a method of guarding against the attack of
snakes and other enemies which most frequently seize their prey from
the front. It is obvious that by pressing its head to the ground the
frog tends to prevent any animal from getting it into its mouth, and
in the few instants' delay thus gained it is able to jump. This is
just the movement necessary for diving, and it is probable that the
action should be interpreted in the light of that instinctive reflex.
The 'puffing' also would seem to make seizure more difficult. Another
fact which favors this interpretation is that the response is most
commonly given to stimuli which seem to come from the front and which
for this reason could not easily be escaped by a forward jump, while
if the stimulus is so given that it appears to be from the rear the
animal usually jumps away immediately. We have here a complex
protective reaction which may be called a forced movement. It is, so
far as one can see, very much like many reflexes, although it does not
occur quite so regularly.

The machine-like accuracy of many of the frog's actions gives a basis
for the belief that the animal is merely an automaton. Certain it is
that one is safe in calling almost all the frog's actions reflex or
instinctive. During months of study of the reaction-time of the frog I
was constantly impressed with the uniformity of action and surprised
at the absence of evidences of profiting by experience. In order to
supplement the casual observations on the associations of the green
frog made in the course of reaction-time experiments, the tests
described in this paper were made. They do not give a complete view of
the associative processes, but rather such a glimpse as will enable us
to form some conception of the relation of the mental life of the frog
to that of other animals. This paper presents the outlines of work the
details of which I hope to give later.

II. EXPERIMENTAL STUDY OF HABITS.

A. The Chief Problems for which solutions were sought in the following
experimental study were: (1) Those of associability in general, its
characteristics, and the rapidity of learning; (2) of discrimination,
including the parts played in associative processes by the different
senses, and the delicacy of discrimination in each; (3) of the
modifiability of associational reactions and general adaptation in the
frog, and (4) of the permanency of associations.

B. Simple Associations, as studied in connection with reaction-time
work, show that the green frog profits by experience very slowly as
compared with most vertebrates. The animals have individual
peculiarities in reaction which enable one in a short time to
recognize any individual. To these characteristic peculiarities they
stick tenaciously. One, for instance, always jumps upward when
strongly stimulated; another has a certain corner of the tank in which
it prefers to sit. Their habits are remarkably strong and invariable,
and new ones are slowly formed. While using a large reaction box I
noticed that the frogs, after having once escaped from an opening
which could be made by pushing aside a curtain at a certain point in
the box, tended to return to that place as soon as they were again put
into the box. This appeared to be evidence of an association; but the
fact that such stimuli as light and the relation of the opening to the
place at which the animals were put into the box might in themselves
be sufficient to direct the animals to this point without the help of
any associations which had resulted from previous experience, makes it
unsatisfactory. In addition to the possibility of the action being due
to specific sensory stimuli of inherent directive value, there is the
chance of its being nothing more than the well-known phenomenon of
repetition. Frogs, for some reason, tend to repeat any action which
has not proved harmful or unpleasant.

For the purpose of more carefully testing this kind of association, a
small box with an opening 15 cm. by 10 cm. was arranged so that the
animal could escape from confinement in it through the upper part of
the opening, the lower portion being closed by a plate of glass 10 cm.
by 10 cm., leaving a space 5 cm. by 10 cm. at the top. One subject
placed in this box escaped in 5 minutes 42 seconds. After 5 minutes'
rest it was given another trial, and this time got out in 2 minutes 40
seconds. The times for a few subsequent trials were: Third, 1 minute
22 seconds; fourth, 4 minutes 35 seconds; fifth, 2 minutes 38 seconds;
sixth, 3 minutes 16 seconds. Although this seems to indicate some
improvement, later experiments served to prove that the frogs did not
readily form any associations which helped them to escape. They tended
to jump toward the opening because it was light, but they did not
learn with twenty or thirty experiences that there was a glass at the
bottom to be avoided. Thinking that there might be an insufficient
motive for escape to effect the formation of an association, I tried
stimulating the subject with a stick as soon as it was placed in the
box. This frightened it and caused violent struggles to escape, but
instead of shortening the time required for escape it greatly
lengthened it. Here was a case in which the formation of an
association between the appearance of the upper part of the clear
space and the satisfaction of escape from danger would have been of
value to the frog, yet there was no evidence of adaptation to the new
conditions within a reasonably short time. There can be little doubt
that continuation of the training would have served to establish the
habit. This very clearly shows the slowness of adaptation in the frog,
in contrast with the rapidity of habit formation in the cat or chick;
and at the same time it lends additional weight to the statement that
instinctive actions are all-important in the frog's life. A few things
it is able to do with extreme accuracy and rapidity, but to this list
new reactions are not readily added. When put within the box
described, an animal after having once escaped would sometimes make
for the opening as if it knew perfectly the meaning of the whole
situation, and yet the very next trial it would wander about for half
an hour vainly struggling to escape.

A considerable number of simple experiments of this kind were tried
with results similar to those just given. The frog apparently examines
its surroundings carefully, and just when the observer thinks it has
made itself familiar with the situation it reacts in such a way as to
prove beyond doubt the absence of all adaptation. In all these
experiments it should be said, for the benefit of any who may be
trying similar work, that only animals of exceptional activity were
used. Most green frogs when placed in the experiment box either sit
still a great part of the time or jump about for only a short time. It
is very important for studies of this kind, both on account of time
saving and the obtaining of satisfactory records, to have animals
which are full of energy and eager to escape when in confinement. By
choosing such subjects one may pretty certainly avoid all unhealthy
individuals, and this, it seems to me, counterbalances the
disadvantage of taking animals which may be unusually quick in
learning.

C. Complex Associations.

1. _Labyrinth Habits_.--A more thorough investigation of the
associative processes, sensory discrimination and the permanency of
impressions has been made by the labyrinth method. A wooden box, 72
cm. long, 28 cm. wide and 28 cm. deep, whose ground plan is
represented by Fig. 1, served as the framework for a simple labyrinth.
At one end was a small covered box, _A_, from which the frog was
allowed to enter the labyrinth. This entrance passage was used in
order that the animal might not be directed to either side by the
disturbance caused by placing it in the box. _E_, the entrance, marks
a point at which a choice of directions was necessary. _P_ is a
movable partition which could be used to close either the right or the
left passage. In the figure the right is closed, and in this case if
the animal went to the right it had to turn back and take the left
passage in order to get out of the box. A series of interrupted
electrical circuits, _IC_, covered the bottom of a portion of the
labyrinth; by closing the key, _K_, the circuit could be made whenever
a frog rested upon any two wires of the series. When the frog happened
to get into the wrong passage the key was closed and the animal
stimulated. This facilitated the experiment by forcing the animal to
seek some other way of escape, and it also furnished material for an
association. Having passed through the first open passage, which for
convenience we may know as the entrance passage, the animal had to
choose again at the exit. Here one of the passages was closed by a
plate of glass (in the figure the left) and the other opened into a
tank containing water. The box was symmetrical and the two sides were
in all respects the same except for the following variable conditions.
At the entrance the partition on one side changed the appearance, as
it was a piece of board which cut off the light. On either side of the
entrance there were grooves for holding card-boards of any desired
color. The letters _R, R_ mark sides which in this case were covered
with red; _W, W_ mark white spaces. These pieces of cardboard could
easily be removed or shifted at any time. At the exit the glass plate
alone distinguished the sides, and it is not likely that the animals
were able to see it clearly. We have thus at the entrance widely
differing appearances on the two sides, and at the exit similarity.
The opening from _A_ into the large box was provided with a slide door
so that the animal could be prevented from returning to _A_ after
entering the labyrinth. The partitions and the triangular division at
the entrance extended to the top of the box, 28 cm., so that the
animals could not readily jump over them.

[Illustration: FIG. 1. Ground Plan of Labyrinth. _A_, small box
opening into labyrinth; _E_, entrance of labyrinth; _T_, tank
containing water; _G_, glass plate closing one passage of exit; _P_,
partition closing one passage at entrance; _IC_, interrupted
electrical circuit; _C_, cells; _K_, key in circuit; _RR_, red
cardboard; _WW_, white cardboard. Scale 1/12.]

The experiments were made in series of ten, with ten-minute intervals
between trials. In no case was more than one series a day taken, and
wherever a day was missed the fact has been indicated in the tables.
The only motive of escape from the box depended upon was the animal's
desire to return to the water of the tank and to escape from
confinement in the bright light of the room. The tank was one in which
the frogs had been kept for several months so that they were familiar
with it, and it was as comfortable a habitat as could conveniently be
arranged. Usually the animals moved about almost constantly until they
succeeded in getting out, but now and then one would remain inactive
for long intervals; for this reason no record of the time taken for
escape was kept. On account of the great amount of time required by
experiments of this kind I have been unable to repeat this series of
experiments _in toto_ on several animals in order to get averages, but
what is described for a representative individual has been proved
normal by test observations on other animals. There are very large
individual differences, and it may well be that the subject of the
series of experiments herein described was above the average in
ability to profit by experience. But, however that may be, what is
demonstrated for one normal frog is thereby proved a racial
characteristic, although it may be far from the mean condition.

Before beginning training in the labyrinth, preliminary observations
were made to discover whether the animals had any tendencies to go
either to the right or to the left. When the colored cardboards were
removed it was found that there was usually no preference for right or
left. In Table I. the results of a few preliminary trials with No. 2
are presented. For these the colors were used, but a tendency to the
right shows clearly. Trials 1 to 10 show choice of either the right or
the red throughout; that it was partly both is shown by trials 11 to
30, for which the colors were reversed. This individual has therefore,
to begin with, a tendency to the right at the entrance. At the exit it
went to the right the first time and continued so to do for several
trials, but later it learned by failure that there was a blocked
passage as well as an open one. In the tables the records refer to
choices. It was useless to record time or to lay much stress upon the
course taken, as it was sometimes very complicated; all that is given,
therefore, is the action in reference to the passages. _Right_ in
every case refers to the choice of the open way, and _wrong_ to the
choice of the blocked passage. The paths taken improved steadily in
that they became straighter. A few representative courses are given in
this report. Usually if the animal was not disturbed a few jumps
served to get it out of the labyrinth.