Sixteen Experimental Investigations from the Harvard Psychological Laboratory by Hugo Münsterberg (good novels to read in english TXT) 📖

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 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