The Dancing Mouse Part 16

Most mammals which have been experimentally studied have proved their eagerness and ability to learn the shortest, quickest, and simplest route to food without the additional spur of punishment for wandering. With the dancer it is different. It is content to be moving; whether the movement carries it directly towards the food is of secondary importance. On its way to the food-box, no matter whether the box be slightly or strikingly different from its companion box, the dancer may go by way of the wrong box, may take a few turns, cut some figure-eights, or even spin like a top for seconds almost within vibrissa-reach of the food-box, and all this even though it be very hungry. Activity is pre-eminently important in the dancer's life.

In pa.s.sing I may emphasize the importance of the fact that at no time did the brightness or color discrimination tests furnish evidence of attempts on the part of the dancers to choose by means of slight differences in the form of the cardboards or the cardboard carriers. Several times form differences, which were easily perceivable by the human subject, were introduced in order to discover whether the mice would detect them and learn to discriminate thereby instead of by the visual conditions of brightness or color. As these experiments failed to furnish evidences of form discrimination, the following special test in the discrimination box was devised.

[Ill.u.s.tration: FIGURE 22.--Cards used for tests of form discrimination.]

The color discrimination box of Chapter X was arranged so that the light at the entrance to each electric-box had a value of 20 candle meters, less the diminution caused by a piece of ground gla.s.s which was placed over the end of the electric-boxes to diffuse the light. The windows through which the light entered the electric-boxes were covered with pieces of black cardboard; in one of these cardboards I had cut a circular opening 4 cm.

in diameter, and in the other an opening of the same area but markedly different shape. These openings are shown in Figure 22. As the mouse approached the entrance to the electric-boxes, it was confronted by these two equally illuminated areas, whose chief difference was one of form.

Difference in the amount of light within the boxes was excluded so far as possible. The question which I asked was, can the dancer discriminate by means of this difference in visual form?

For the purpose of settling this point and of gaining additional knowledge of the role of vision, two individuals were tested in the discrimination box under the conditions which have just been described. During the first ten days of the experiment each of these mice, Nos. 420 and 425, was given a series of ten tests daily. At the end of this period experimentation with No. 425 had to be discontinued, and the number of daily tests given to No. 420 was increased to twenty.

Instead of taking s.p.a.ce for the presentation of the daily records, I may state the general results of the tests. Neither of the mice learned to choose the right box by means of form discrimination. In fact, there was absolutely no sign of discrimination at any time during the tests. This result is as surprising as it is interesting. I could not at first believe that the mice were unable to perceive the difference in the lighted areas, but a.s.sumed that they were prevented from getting the outlines of the areas by the blinding effect of the light. However, decreasing the intensity of the illumination did not alter the result. According to the indications of this experiment, the dancer's ability to perceive visual form is extremely poor.

Thus far the purpose of our experiments has been to ascertain what the dancer is enabled to do by sight. Suppose we now approach the problem of the role of this sense by trying to find out what it can do without sight.

[Ill.u.s.tration: FIGURE 23.--Labyrinth B. _I_, entrance; _O_, exit; 1, 2, 3, doorways between alleys.]

For the investigation of this matter the labyrinth method seemed eminently suitable. The first form of labyrinth which was used in these visual tests appears in ground plan in Figure 23. It was made of 1-1/2 cm. boards. The length was 52 cm., the width 17 cm., the depth 10 cm. Each of the doorways, _I_ (the entrance), 1, 2, 3, and _O_ (the exit), was 5 by 5 cm.

The alleys were 2-1/2 cm. wide. For this width the necessity is obvious from what has already been said of the animal's propensity to whirl on all occasions. As the mice almost never tried to climb up the walls, no cover for the labyrinth was needed. The direct route is indicated by the symbols _I_-1-2-3-_O_. If an error be defined as a choice of the wrong path as the animal progressed toward the exit, five mistakes were possible in the forward course: the first by turning to the left at the entrance; the second by failing to pa.s.s through doorway 1; the third by turning to the right after pa.s.sing through doorway 1; the fourth by failing to pa.s.s through doorway 3, and the fifth by turning to the left after pa.s.sing through 3. In case the mouse retraced its course, any mistakes made as it again progressed towards _O_ were counted, as at first, no matter how many times it went over the same ground. Thus an individual might make the same mistake several times in the course of a single test in the labyrinth.

With this labyrinth Nos. 7, 998, 15, 16, 151, and 152 were tested. At first a record was kept of the time which elapsed from the instant the animal entered _I_ to the instant it emerged at _O_, of the path which it followed, and of the number of errors which it made; but later only the number of errors was recorded.

TABLE 31

THE ROLE OF SIGHT

Labyrinth-B Experiments

NO. 7 NO. 998

TEST DATE TIME ERRORS TIME ERRORS 1 June 16 66" 8 127" 19 2 16 11 0 94 12 3 16 15 2 18 3 4 16 7 0 13 2 5 16 5 0 10 1 6 18 61 15 12 3 7 18 13 3 14 4 8 18 14 5 8 1 9 18 24 9 16 2 10 18 10 1 9 1 11 19 36 13 80 17 12 19 8 3 10 1 13 19 6 1 7 1 14 19 9 1 8 0 15 19 12 2 7 0 16 20 14 1 25 0 17 20 28 3 18 20 No efforts No efforts to escape to escape

TABLE 32

LABYRINTH-B EXPERIMENTS

with

Electric Shock given as Punishment for Mistakes

No. 7 No. 998 TEST DATE CONDITION ERRORS CONDITION ERRORS

1 June 29 Light 4 Light 9 2 29 Light 1 Light 3 3 29 Light 1 Light 2 4 29 Light 0 Light 0 5 29 Light 0 Light 0 6 29 Light 0 Light 0 7 29 Light 1 Light 0 8 29 Light 0 Light 0 9 29 Light 1 Darkness 0 10 29 Light 1 Light 0 11 29 Light 1 Darkness 0 12 29 Light 0 Light 0 13 29 Light 0 Light 0 14 29 Light 0 Light 0 15 29 Light 0 Light 0 16 29 Light 0 Light 0 17 29 Darkness 2 Darkness 0 18 29 Light 2 Light 0 with paper 19 29 Light 0 Light 0 20 29 Darkness 0 Light 0 with paper 21 29 Light 0 Light 0 22 29 Light 0 Darkness 0 23 29 Light 0 Odorless 0 24 June 29 Light 0 Darkness 0 25 29 Light 0 26 29 Darkness 4 27 29 Light with paper 1 28 29 Light 0 29 29 Light with paper 1 30 29 Darkness 0 31 29 Odorless 2 32 29 Darkness 4

As the results in Table 31 show, the time and number of errors rapidly diminished. Number 7, for example, made no errors in the second test. The chiefly significant fact which appeared in these preliminary experiments, however, was that the mice soon ceased to care whether they got out of the labyrinth or not. After they knew the path perfectly, they would enter the wrong pa.s.sages repeatedly and wander about indefinitely. It was obvious, therefore, that the labyrinth could not be used to reveal the role of sight unless some sufficiently strong motive for continuous effort to escape from it could be discovered. Naturally I looked to the electric shock for aid.

The labyrinth of Figure 23, which for convenience in distinguishing it from several other forms to be described later I have designated as labyrinth B, was placed upon a board 90 cm. long and 30 cm. wide about which had been wound two pieces of phosphor bronze wire after the manner described on p. 94. At _O_, Figure 24, there was an opening closed by a swinging door which led into a box 40 by 24 cm. In one corner of this box was a small nest-box. The significance of this rearrangement of the labyrinth is apparent. As in the preliminary tests, the dancer was started at I, but instead of being allowed to wander about without any other result than delay in escape, it was given a shock each time it made an error. The satisfaction of escaping from the narrow bounds of the labyrinth's pa.s.sages, which alone was not strong enough to impel a dancer constantly to do its best to escape, was thus supplemented by the powerful and all-controlling tendency to avoid the disagreeable stimulus which resulted from entering certain of the pa.s.sages. The result of this modification of method is strikingly exhibited by the data of Table 32.

[Ill.u.s.tration: Figure 24.--Labyrinth B on an interrupted circuit board.

_I_-1-2-3-_O_, labyrinth path; _B_, nest-box; _N_, nest; _EW_, board wound with phosphor bronze wire; _IC_, induction apparatus; _C_ electric cell; _K_, key.]

This table was constructed for the purpose of exhibiting the princ.i.p.al features of the results obtained with labyrinth _B_ in certain preliminary experiments in which the conditions were changed in various ways. Chief among the important facts which appear in the ill.u.s.trative data (for Nos.

7 and 998) which are presented, are the following. The dancers readily learn the path of labyrinth B so that they can follow it quickly and with perfect accuracy. After familiarity with the direct path from entrance to exit has been gained, they become indifferent about escaping and tend to wander aimlessly. The introduction of the electric shock as punishment for the choice of the wrong pa.s.sage impels them to do their best to avoid errors. The path once learned can be followed in total darkness with few or no errors. Table 32 indicates marked differences in the behavior of No.

7 and No. 998. The latter learned the path readily and was little disturbed by any of the changes in conditions. In total darkness he followed the path rapidly and accurately, as was indicated by the time of the trip and the path that he left on a sheet of smoked paper that had been placed on the floor of the labyrinth as a means of obtaining a record of the errors made. The presence of the smoked paper did not seem to interfere at all with his behavior, nor did the thorough washing of the labyrinth and the resultant removal of its odors. In the case of No. 7 the opposite was true. She did not learn the path readily, was confused by any change in conditions, had great difficulty in finding her way in darkness, made errors when the smoked paper was placed on the floor and after the odors of the labyrinth had been removed by washing. Of the six dancers which were observed in these preliminary tests, No. 7 alone gave convincing evidence of the importance of sight.

I think we may say in the light of the results of the table that such errors as appear in the darkness tests are due rather to the disturbing influence of a change in the conditions of the experiment than to the exclusion of visual data, for as many or more errors were sometimes caused simply by changing the position of the labyrinth, placing smoked paper on the floor, or by introducing a new odor at some point. The exclusion of the possibility of guidance by smell and touch did not seriously interfere with the animal's ability to follow the path.

The results which have just been considered seemed to be of sufficient interest and importance to justify the further use of the labyrinth method in the investigation of the role of vision. A series of experiments with labyrinth B was therefore planned so that the importance of sight, touch, and smell in connection with this form of habit should be more satisfactorily exhibited. Does the dancer follow the path by sight, touch, smell, by all, or by no one of them?

This series of tests with labyrinth B, whose several purposes may best be explained in connection with the various kinds of tests enumerated below, consisted of:

I. A preliminary test in which the dancer was permitted to wander about in the labyrinth, without being shocked, until it finally escaped to the nest-box by way of the exit. Thus the animal was given an opportunity to discover that escape from the maze was possible.

II. This was immediately followed by a series of tests at the rate of about one per minute, with an electric shock as punishment for every mistake. This was continued without interruption until the path had been followed without error five times in succession.

III. The labyrinth was now moved about 3 cm. to one side so that it covered a new floor area, and a test was given for the purpose of ascertaining whether the mouse had been following a trail on the floor.

IV. Tests with smoked paper on the floor were now alternated with tests in which the floor was plain. The alternation was rendered necessary by the fact that the paper was laid over the electric wires and therefore prevented the punishment of mistakes. The purpose of these tests was to discover whether the smoked paper, which was an essential condition for the next test, was itself a disturbing condition. These tests were continued until the animal had followed the path correctly, despite the smoked paper, twice in succession.

V. The electric lights were now turned out and tests were given in total darkness, with smoked paper on the floor as a means of obtaining a record of the number of errors. These tests were continued until the path had been followed once correctly.

VI. The labyrinth was now thoroughly washed with warm water, to which a little kerosene had been added, and quickly dried over a steam radiator.

This usually necessitated a delay of about five minutes. As soon as the labyrinth was dry, tests were given to discover whether the odors of the various pa.s.sages had been serving as important guiding conditions. These tests were continued until the path had been followed once without error.

VII. A final test in darkness completed the series.

As it was not possible for the observer to watch the animal and thus to count the number of mistakes which it made in total darkness, the simple method of placing a piece of smoked paper on the floor of the labyrinth was used. The mouse left a graphic record of its path on the paper and from this the number of errors could be ascertained. In the tests now to be described the smoked paper was placed upon the electric wires, but later a form of electric labyrinth was devised in which it was underneath and therefore did not interfere with the electric shock.

The above series of tests was given under the same external conditions in a dark-room to six pairs of dancers. In all cases, two individuals, a male and a female, which had been kept in the same cage, were experimented with at the same time, _i.e._ one was permitted to rest in the nest-box while the other was being put through a test. This was done in order that the comparison of the results for males and females should be perfectly fair.

The detailed results of this long series of tests may be presented for only two individuals, Nos. 210 and 215, Table 33. In this table lines separate the results of the seven different kinds of tests.

TABLE 33

THE ROLE OF SIGHT, TOUCH, AND SMELL IN LABYRINTH EXPERIMENTS

No. 210 No. 215