Sixteen Experimental Investigations from the Harvard Psychological Laboratory by Hugo Münsterberg (100 books to read .txt) 📕

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