Sixteen Experimental Investigations from the Harvard Psychological Laboratory, Hugo Münsterberg [top fiction books of all time TXT] 📗
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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 cardboards 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
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