The Dancing Mouse by Robert M. Yerkes (page 4)

3 Oct. 1 3 7 4 6
4 2 5 5 3 7
5 3 3 7 5 5
6 4 6 4 5 5
7 5 5 5 5 5
8 6 — — 3 7
9 7 — — 6 4
10 8 — — 4 6

Averages 4.7 5.3 4.5 5.5

The account of my color vision experiments is finished. If it be objected that other than visual conditions may account for whatever measure of discriminating ability, apart from brightness discrimination, appears in some of the series, the results of the series of Table 29, in which all conceivable visual means of discrimination were purposely excluded, and those of the several check tests which have been described from time to time in the foregoing account, should furnish a satisfactory and definite answer. I am satisfied that whatever discrimination occurred was due to vision; whether we are justified in calling it color vision is quite another question.

I conclude from my experimental study of vision that although the dancer does not possess a color sense like ours, it probably discriminates the colors of the red end of the spectrum from those of other regions by difference in the stimulating value of light of different wave lengths, that such specific stimulating value is radically different in nature from the value of different wave lengths for the human eye, and that the red of the spectrum has a very low stimulating value for the dancer. In the light of these experiments we may safely conclude that many, if not most, of the tests of color vision in animals which have been made heretofore by other investigators have failed to touch the real problem because the possibility of brightness discrimination was not excluded.

Under the direction of Professor G. H. Parker, Doctor Karl Waugh has examined the structure of the retina of the dancing mouse for me, with the result that only a single type of retinal element was discovered. Apparently the animals possess rod-like cells, but nothing closely similar to the cones of the typical mammalian retina. This is of peculiar interest and importance in connection with the results which I have reported in the foregoing pages, because the rods are supposed to have to do with brightness or luminosity vision and the cones with color vision. In fact, it is usually supposed that the absence of cones in the mammalian retina indicates the lack of color vision. That this inference of functional facts from structural conditions is correct I am by no means certain, but at any rate all of the experiments which I have made to determine the visual ability of the dancer go to show that color vision, if it exists at all, is extremely poor. It is gratifying indeed to learn, after such a study of behavior as has just been described, that the structural conditions, so far as we are able to judge at present, justify the conclusions which have been drawn.

CHAPTER XI

THE ROLE OF SIGHT IN THE DAILY LIFE OF THE DANCER

Darting hither and thither in its cage, whirling rapidly, now to the left, now to the right, running in circles, passing through holes in the nest box quickly and neatly, the dancer, it would seem, must have excellent sight. But careful observation of its behavior modifies this inference. For it appears that a pair of mice dancing together, or near one another, sometimes collide, and that it is only those holes with which the animal is familiar that are entered skillfully. In fact, the longer one observes the behavior of the dancer under natural conditions, the more he comes to believe in the importance of touch, and motor tendencies. Sight, which at first appears to be the chief guiding sense, comes to take a secondary place. In this chapter it is my purpose to show by means of simple experiments what part sight plays in the dancer’s life of habit formation.

The evidence on this subject has been obtained from four sources: (1) observation of the behavior of dancers in their cages; (2) observation of their behavior when blinded; (3) observation of their behavior in a great variety of discrimination experiments, many of which have already been described; and (4) observation of their behavior in labyrinth experiments which were especially planned to exhibit the importance of the several kinds of vision which the dancer might be supposed to possess. The evidence from the first three of these sources may be presented summarily, for much of it has already appeared in earlier chapters. That from the fourth source will constitute the bulk of the material of this chapter.

My observation of the behavior of the mice has furnished conclusive evidence of their ability to see moving objects. But that they do not see very distinctly, and that they do not have accurate perception of the form of objects, are conclusions which are supported by observations that I have made under both natural and experimental conditions. In Chapters VII, VIII, IX, and X, I have presented an abundance of evidence of brightness vision and, in addition, indications of a specific sensitiveness to wave length which may be said to correspond to our color vision. It is noteworthy, however, that all of the experimental proofs of visual ability were obtained as the result of long periods of training. Seldom, indeed, in my experience with them, have the dancers under natural conditions exhibited forms of activity which were unquestionably guided by vision.

It is claimed by those who have experimented with blinded dancers that the loss of sight decreases the amount and rapidity of movement, and the ability of the animals to avoid obstacles.

By means of the discrimination method previously used in the preliminary experiments on color vision, a full description of which may be found in Chapter IX, p. 133, the dancers’ ability to perceive form was tested. Immediately after the two males _A_ and _B_ had been given the “food-box” tests, whose results appear in Table 15, they were tested in the same apparatus and by the same method for their ability to discriminate a rectangular food-box from a round one. In the case of the color discrimination tests, it will be remembered that the circular tin boxes 5 cm. in diameter by 1.5 cm. in depth, one of which was covered with blue paper, the other with orange, were used. For the form discrimination tests I used instead one of the circular boxes of the dimensions given above and a rectangular box 8.5 cm. long, 5.5 cm. wide and 2.5 cm. deep. “Force” was placed in the circular box. The tests were given, in series of 20, daily.

TABLE 30

VISUAL FORM TESTS

SERIES DATE MOUSE A MOUSE B RIGHT WRONG RIGHT WRONG (CIRCULAR (RECTANGU- (CIRCULAR (RECTANGU- BOX) LAR BOX) BOX) LAR BOX) 1 Jan. 5 10 10 9 11
2 7 12 8 13 7
3 10 6 14 10 10 4 11 7 13 10 10
5 12 9 11 10 10 6 13 11 9 11 9
7 14 13 7 9 11 8 15 10 10 11 9
9 16 10 10 11 9 10 17 11 9 9 11
11 18 11 9 12 8 12 19 12 8 10 10
13 20 10 10 12 8 14 21 10 10 8 12
15 22 10 10 10 10

Totals 152 148 155 145

The results of 15 series of these tests, as may be seen by the examination of Table 30, are about as definitely negative, so far as form discrimination is in question, as they possibly could be. From the first series to the last there is not one which justifies the inference that either of the dancers depended upon the form of the boxes in making its choice. In view of the general criticisms I have made concerning the use of hunger as a motive in experiments on animal behavior, and in view of the particular criticisms of this very method of testing the discriminating powers of the mouse, it may seem strange that space should be given to a report of these tests. I sympathize with the feeling, if any one has it, but, at the same time, I wish to call attention to the fact that almost any mammal which is capable of profiting by experience, and which, under the same conditions, could distinguish the rectangular box from the circular one, would have chosen the right box with increasing accuracy as the result of such experience. The results are important in my opinion, not because they either prove or disprove the ability of the dancer to discriminate these particular forms, the discrimination of which might fairly be expected of any animal with an image-forming eye, but because they demonstrate an important characteristic of the dancing mouse, namely, its indifference to the straightforward or direct way of doing things.

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 passing 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.

[Illustration: 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 glass 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 space 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 assumed 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.

[Illustration: 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 pass through doorway 1; the third by turning to the right after passing through doorway 1; the fourth by failing to pass through doorway 3, and the fifth by turning to the left after passing 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 passages 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 passages, 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 passages. The result of this modification of method is strikingly exhibited by the data of Table 32.

[Illustration: 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 principal 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 illustrative 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 passage 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 passages 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

TEST CONDITION ERRORS CONDITION ERRORS

I. 1 No shock 9 I. No shock 2

II. 2 Shock 5 II. Shock 3 3 Shock 4 Shock 1
4 Shock 2 Shock 0 5 Shock 3 Shock 0
6 Shock 0 Shock 0 7 Shock 0 Shock 0
8 Shock 0 Shock 0

9 Shock 0 III. Labyrinth 0 moved

10 Shock 0 IV. Paper on floor 4

III. 11 Labyrinth 0 No paper (shock) 0 moved

IV. 12 Paper on 0 0 floor
13 No paper 0 No paper 0 (shock)
14 Paper 1 Paper 1 15 No paper 0 No paper 0 16 Paper 7 Paper 4
17 No paper 0 No paper 0 18 Paper 0 Paper 0
19 No paper 0 No paper 0 20 Paper 4 Paper 0
21 No paper 0 No paper 0 22 Paper 2 V. Darkness 0 23 No paper 2 VI. Labyrinth 2 24 Paper 1 washed 0
25 No paper 0 VII. Darkness 2 26 Paper 0
27 No paper 0
28 Paper 0
29 No paper 0
V. 30 Darkness 0
VI. 31 Labyrinth 2
washed
32 0
VII. 33 Darkness 0

The average results for the twelve individuals (six of each sex) which were subjected to the tests, I have arranged in Table 34. The Roman numerals at the top of the table designate the seven groups of tests, and the figures under each, the numerical results of the tests. I may explain and comment upon the averages of the several columns of this table in turn.

Column I gives the number of errors made in the preliminary test. Curiously enough, the males made many more errors than the females.

For the second group of tests (II) two results have been tabulated: the number of the first correct test, and the total number of tests before the path was followed correctly five times in succession. The first correct trip came usually after not more than five or six tests, but five successive correct trips demanded on the average at least fourteen training tests.

Destruction of the floor path by movement of the labyrinth to one side, without changing its relations to the points of the compass, disturbed the mice very little. Only four of the twelve individuals made any mistakes as a result of the change in the tactual conditions, and the average error as it appears in Column III is only .3.

TABLE 34

ROLE OF SIGHT, TOUCH, AND SMELL IN LABYRINTH EXPERIMENTS

II. IV.
TRAINING TESTS SMOKED I. NO OF TESTS BEFORE III. PAPER ON MALES PRELIMINARY CORRECT LABYRINTH FLOOR TEST. _____________________ MOVED. NO OF TIMES ERRORS FIRST TIME FIVE TIMES ERRORS BEFORE COR- RECT TWICE

210 9 5 9 0 9 212 2 3 8 1 3
214 6 10 28 0 22 220 25 4 8 0 14
410 11 6 20 0 10 420 14 6 14 1 7

AVERAGES 11.2 5.7 14.5 .3 10.8

FEMALES

211 16 6 10 1 5 213 7 5 14 1 21 215 2 3 7 0 6
225 14 6 18 0 14 415 6 6 13 0 3
425 10 7 13 0 8

AVERAGES 9.2 5.5 12.5 .3 9.5

V.
DARKNESS VI.
MALES LABYRINTH VII. ERRORS IN NO. OF TESTS WASHED. DARKNESS. FIRST TEST BEFORE COR’CT ERRORS ERRORS

210 0 1 2 0
212 2 2 0 0 214 0 1 — 0
220 2 4 2 0 410 1 3 2 1
420 2 4 1 4

Averages 1.2 2.5 1.2 0.8

FEMALES

211 2 2 0 0
213 2 2 — 3 215 0 1 2 2
225 3 2 0 0 415 1 3 2 1
425 1 7 0 0

Averages 1.5 2.8 0.7 1.0

That covering the floor with smoked paper forced the mice to relearn the path, in large measure, is evident from the results of Column IV. An average of ten tests was necessary to enable the mice to follow the path correctly. It is almost certain, however, that the interference with the perfectly formed labyrinth habit which this change in the condition of the floor caused was not due to the removal of important tactual sense data.

As Column V shows, the number of errors in total darkness is very small. Some individuals gave no sign of being disturbed by the absence of visual guidance, others at first seemed confused. I have given in the table the number of errors in the first darkness test and the number of the first test in which no mistakes occurred.

No more disturbance of the dancer’s ability to follow the path which it had learned resulted from washing the labyrinth thoroughly than from darkening the room. Indeed it is clear from Column VI that the path was not followed by the use of smell. However, the test in darkness, after the odor of the box had been removed, proved conclusively that in most cases the mice could follow the path correctly without visual or olfactory guidance.

The behavior of 18 individuals as it was observed in labyrinth B makes perfectly evident three important facts, (1) In following the path which it has learned, the dancer in most instances is not guided to any considerable extent by a trail (odor or touch) which has been formed by its previous journeys over the route; (2) sight is quite unnecessary for the easy and perfect execution of the labyrinth habit, for even those individuals which are at first confused by the darkening of the experiment room are able after a few tests to follow the path correctly; (3) and, finally, smell, which according to current opinion is the chiefly important sense of mice and rats, is not needful for the performance of this habitual act.

At this point we may very fittingly ask, what sense data are necessary for the guidance of the series of acts which constitutes the labyrinth habit? I answer, probably none. A habit once formed, the senses have done their part; henceforth it is a motor process, whose initiation is conditioned by the activity of a receptive organ (at times a sense receptor), but whose form is not necessarily dependent upon immediate impressions from eye, nose, vibrissae, or even from internal receptors. These are statements of my opinion; whether they express the truth, either wholly or in part, only further experimentation can decide.

In considering the results of these labyrinth tests it is important that we distinguish clearly those which have to do with the conditions of habit formation from those which instead have to do with the conditions of habit performance. Sense data which are absolutely necessary for the learning of a labyrinth path may be of little or no importance for the execution of the act of following the path after the learning process has been completed. Thus far in connection with the labyrinth tests we have discussed only the relations of sight, touch, and smell to what I have called habit performance. We may now ask what part these senses play in the formation of a labyrinth habit.

A very definite answer to this question is furnished by observation of the behavior of the dancers in the tests. Most of them continuously made use of their eyes, their noses, and their vibrissae. Some individuals used one form of receptive organ almost exclusively. I frequently noticed that those individuals which touched and smelled of the labyrinth passages most carefully gave least evidence of the use of sight. It is safe to say, then, that under ordinary conditions habit formation in the dancer is conditioned by the use of sight, touch, and smell, but that these senses are of extremely different degrees of importance in different individuals. And further, that, although in the case of some individuals the loss of sight would not noticeably delay habit formation, in the case of others it would seriously interfere with the process. When deprived of one sense, the dancer depends upon its remaining channels of communication with environment. Indeed there are many reasons for inferring that if deprived of sight, touch, and smell it would still be able to learn a labyrinth path; and there are reasonable grounds for the belief that a habit once formed can be executed in the absence of all special sense data. Apparently the various receptive organs of the body furnish the dancer with impressions which serve as guides to action and facilitate habit formation, although they are not necessary for habit performance.

The reader may wonder why I have not carried out systematic experiments to determine accurately and quantitatively the part which each sense plays in the formation of a labyrinth habit instead of basing my inferences upon incidental observation of the behavior of the dancers. The reason is simply this: the number and variety of experiments which were suggested by the several directions in which this investigation developed rendered the performance of all of them impossible. I have chosen to devote my time to other lines of experimentation because a very thorough study of the conditions of habit formation has recently been made by Doctor Watson.[1]

[Footnote 1: Watson, J. B., _Psychological Review_, Monograph Supplement, Vol. 8, No. 2, 1907.]

What is the role of sight in the dancing mouse? How shall we answer the question? The evidence which has been obtained in the course of my study of the animal indicates that brightness vision is fairly acute, that color vision is poor, that although form is not clearly perceived, movement is readily perceived. My observations under natural conditions justify the conclusion that sight is not of very great importance in the daily life of the dancer, and my observations under experimental conditions strongly suggest the further conclusion that movement and changes in brightness are the only visual conditions which to any considerable extent control the activity of the animal.

CHAPTER XII

EDUCABILITY: METHODS OF LEARNING

Nearly all of the experiments described in earlier chapters have revealed facts concerning the educability of the dancer. In order to supplement the knowledge of this subject thus incidentally gained and to discover the principles of educability, the specially devised experiments whose results appear in this and succeeding chapters were arranged and carried out with a large number of mice. In the work on the modifiability of behavior I have attempted to determine (1) by what methods the dancer is capable of profiting by experience, (2) the degree of rapidity of learning, (3) the permanency of changes wrought in behavior, (4) the effect of one kind of training upon others, (5) the relation of re-training to training, and (6) the relation of all these matters to age, sex, and individuality.

As it is obvious that knowledge of these subjects is a necessary condition for the intelligent appreciation of the capacities of an animal, as well as of the choice of methods by which it may be trained advantageously, perhaps it is not too much to expect that this investigation of the nature and conditions of educability in the dancing mouse may give us some new insight into the significance of certain aspects of human education and may serve to suggest ways in which we may measure and increase the efficiency of our educational methods.

Merely for the sake of convenience of description I shall classify the methods which have been employed as problem methods, labyrinth methods, and discrimination methods. That these names are not wholly appropriate is suggested by the fact that discrimination necessarily occurs in connection with each of them. As problem methods we may designate those tests of initiative and modifiability which involve the opening of doors by pushing or pulling them, and the climbing of an inclined ladder. An example of the labyrinth method has been presented in Chapter XI. The name discrimination method I have applied to those tests which involve the choice of one of two visual, tactual, or olfactory conditions. The white-black discrimination tests, for example, served to reveal the rapidity and permanency of learning as well as the presence of brightness vision.

In the case of most mammals whose educability has been studied experimentally, problem methods have proved to be excellent tests of docility and initiative. The cat, the raccoon, the monkey, in their attempts to obtain food, learn to pull strings, turn buttons, press latches, slide bolts, pull plugs, step on levers. The dancer does none of these things readily. Are we therefore to infer that it is less intelligent, that it is less docile, than the cat, the raccoon, or the monkey? Not necessarily, for it is possible that these methods do not suit the capacity of the animal. As a matter of fact, all of the tests which are now to be described in their relation to the educability of the dancer bear witness to the importance of the selection of methods in the light of the motor equipment and the habits of the animal which is to be tested. Judged by ordinary standards, on the basis of results which it yields in problem and labyrinth tests, the dancer is extremely stupid. But that this conclusion is not justified is apparent when it is judged in the light of tests which are especially adapted to its peculiarities.

Problems which are easy for other mammals because of their energetic and persistent efforts to secure food in any way which their motor capacity makes possible are useless as tests of the dancer’s abilities, because it is not accustomed to obtain its food as the result of strenuous and varied activities. There are problems and problems; a condition or situation which presents a problem to one organism may utterly lack interest for an organism of different structure and behavior. What is a problem test in the case of the cat or even of the common mouse, is not necessarily a problem for the dancer. Similarly, in connection with the labyrinth method, it is clear that the value of the test depends upon the desire of the organism to escape from the maze. The cat, the rat, the tortoise do their best to escape; the dancer is indifferent. Clearly, then, methods of training should be chosen on the basis of a knowledge of the characteristics of the animal whose educability is to be investigated.

The simplest possible test of the intelligence of the dancer which I could devise was the following. Beside the cage in which the mice were kept I placed a wooden box 26 cm. long, 23 cm. wide, and 12 cm. deep. Neither this box nor the cage was covered, for the animals did not attempt to climb out. As a way of passing from one of these boxes to the other I arranged a ladder made of wire fly-screen netting. This ladder was about 8 cm. broad and it extended from the middle of one side of the wooden box upward at an angle of about 30 deg. to the edge of the box and then descended at the same angle into the cage.

A dancer when taken from the nest-box and placed in the wooden box could return to its cage and thus find warmth, food, and company by climbing the ladder. It was my aim to determine, by means of this apparatus, whether the dancers can learn such a simple way of escape and whether they learn by watching one another. As it turned out, a third value belonged to the tests, in that they were used also to test the influence of putting the mice through the act.

In the first experiment three dancers, Nos. 1000, 2, and 6, were together placed in the wooden box. At the end of 15 minutes not one of them had succeeded in returning to the cage. They were then driven to the bottom of the ladder and started upward by the experimenter; with this assistance all escaped to the nest-box. At the expiration of 5 minutes they were again placed in the wooden box, whence the chilly temperature (about 60 deg. F.) and the lack of food made them eager to return to their cage. No attempt to climb up the ladder was made by any of them within 15 minutes, so the experimenter directed them to the ladder and started them upward as in the first test. This completed the experiment for the day. The following day two tests were given in the same way. In the second of these tests, that is, on its fourth trial, No. 1000 climbed over of his own initiative in 5 minutes. The others had to be assisted as formerly. On the third day No. 1000 found his way back to the nest-box quickly and fairly directly, but neither No. 2 or No. 6 climbed of its own initiative in the first test. When their movements were restricted to the region of the box about the base of the ladder, both of them returned to the cage quickly. And on the second test of the third day all the mice climbed the ladder directly.

In Table 35 I have given the time required for escape in the case of 40 tests which were given to these 3 individuals at the rate of 2 tests per day.

When the time exceeded 15 minutes the mice were helped out by the experimenter; a record of 15 minutes, therefore, indicates failure. Naturally enough the motives for escape were not sufficiently strong or constant to bring about the most rapid learning of which the dancer is capable. Sometimes they would remain in the wooden box washing themselves for several minutes before attempting to find a way of escape. On this account I made it a rule to begin the time record with the appearance of active running about. The daily average time of escape as indicated in the table does not decrease regularly and rapidly. On the fourth day, which was the first on which all three of the dancers returned to the cage by way of the ladder of their own initiative in both tests, the average is 214 seconds. In contrast with this, on the twentieth day the time was only 5 seconds. It is quite evident that the dancers had learned to climb the ladder.

At the end of the twentieth day the experiment was discontinued with Nos. 2 and 6, and after two weeks they were given memory tests, which showed that they remembered perfectly the ladder-climbing act, for when placed in the wooden box, with Nos. 4 and 5 as controls, they returned to the cage by way of the ladder immediately and directly.

TABLE 35

LADDER CLIMBING TEST

Time in Minutes and Seconds

No. of Date No. 1000 No. 2 No. 6 Average Daily Av. Exp. 1905 For All For All

1 Nov. 14 15′ 15′ 15′ — — 2 15′ 15′ 15′ — —

3 15 15′ 15′ 15′ — — 4 300″ 15′ 15′ — —

5 16 480″ 15′ 15′ — — 6 180″ 300″ 420″ 300″ 300″

7 17 450″ 240″ 540″ 410″ 8 20″ 15″ 18″ 18″ 214″

9 18 90″ 180″ 135″ 135″ 10 135″ 105″ 165″ 135″ 135″

11 19 480″ 240″ 330″ 350″ 12 30″ 120″ 90″ 80″ 143″

13 20 360″ 75″ 120″ 185″ 14 5″ 6″ 8″ 6″ 95″

15 21 105″ 450″ 120″ 192″ 16 8″ 80″ 20″ 54″ 123″

17 22 255″ 300″ 180″ 245″ 18 10″ 30″ 270″ 103″ 174″

19 23 300″ 660″ 450″ 470″ 20 90″ 120″ 150″ 120″ 295″

21 24 240″ 125″ 225″ 197″ 22 4″ 6″ 168″ 59″ 128″

23 Nov. 25 305″ 85″ 130″ 173″ 24 5″ 6″ 118″ 43″ 108″

25 26 3″ 8″ 44″ 18″
26 19″ 1″ 176″ 98″ 58″

27 27 150″ 79″ 269″ 166″ 28 26″ 3″ 31″ 20″ 93″

29 28 214″ 18″ 267″ 166″ 30 40″ 3″ 4″ 16″ 91″

31 29 130″ 45″ 250″ 142″ 32 12″ 3″ 25″ 13″ 77″

33 Dec. 2 61″ 35″ 44″ 47″ 34 50″ 5″ 24″ 26″ 36″

35 3 66″ 18″ 2″ 29″ 36 8″ 5″ 10″ 8″ 19″

37 4 9″ 4″ 3″ 5″
38 10″ 5″ 6″ 7″ 6″

39 5 5″ 3″ 5″ 4″
40 10″ 4″ 3″ 6″ 5″

One of the most interesting and important features of the behavior of the dancer in the ladder experiment was a halt at a certain point on the ladder. It occurred just at the edge of the wooden box at the point where the ladder took a horizontal position, and led over into the cage. Every individual from the first test to the last made this halt. Although from the point of view of the experimenter the act was valueless, it may have originated as an attempt to find a way to escape from the uncomfortable position in which the animal found itself on reaching the top of the ladder. Its persistence after a way of escape had been found is an indication of the nature of habit. Day after day the halt became shorter until finally it was little more than a pause and a turn of the head toward one side of the ladder. I think we may say that in this act we have evidence of the persistence of a particular resolution of physiological states which is neither advantageous nor disadvantageous to the organism. Had the act resulted in any gain, it would have become more marked and elaborate; had it resulted in injury or discomfort, it would have disappeared entirely. I have observed the same kind of behavior in the frog and in other animals. What the animal begins to do it persists in unless the act is positively harmful or conflicts with some beneficial activity. The only explanation of certain features of behavior is to be found in the conditions of their original occurrence. They persist by sheer force of conservatism. They have value only in the light of the circumstances under which they first appeared. Although this is merely a fact of habit formation, it suggests that many of the problems which have puzzled students of behavior for ages may be solved by a study of the history of activity.

That there are marked individual differences in intelligence in the dancing mice is apparent from the results of the ladder-climbing experiment. No. 1000 learned to climb quickly, and largely by his own initiative; Nos. 2 and 6, on the contrary, learned only by reason of tuition (being put through the required act by the experimenter). It occurred to me that this experiment, since it was difficult for some individuals and easy for others, might be used to advantage as a test of imitation. If a dancer which knows how to escape to the cage by way of the ladder be placed in the wooden box with one which, despite abundant opportunity, has proved unable to form the habit on his own initiative, will the latter profit by the activity of the former and thus learn the method of escape?

On November 20, Nos. 4 and 5 were placed in the wooden box and left there for half an hour. As they had failed to escape at the end of this interval, they were taken out of the box by the experimenter and returned to the nest-box. November 21 and 22 this test of their ability to learn to climb the ladder was repeated with the same result. On November 23 they were placed in the box with the three mice which had previously been trained to climb the ladder. The latter escaped at once. Apparently the attention of Nos. 4 and 5 was drawn to the ladder by the disappearance of their companions, for they approached its foot and No. 5 climbed up a short distance. Neither succeeded in escaping, however, and they made no further efforts that day. On the 24th, and daily thereafter until the 29th, these two dancers were placed in the box for half an hour, with negative results. At the end of the half hour on the 29th, Nos. 2 and 6 were placed in the box and permitted to go back and forth from one box to the other repeatedly within sight of Nos. 4 and 5. The latter made no attempts to follow them, although at times they seemed to be watching their movements as they ascended the ladder.

To render the results of this test of imitation still more conclusive No. 5 was given further opportunity to learn from No. 1000. Beginning December 2, the following method of experimentation was employed with these two individuals. They were placed in the wooden box together. No. 1000 usually climbed out almost immediately. Sometimes No. 5 apparently saw him disappear up the ladder; sometimes she paid no attention whatever either to the presence or absence of her companion. After he had been in the nest-box for a few seconds, No. 1000 was returned to the wooden box by the experimenter and again permitted to climb out for the benefit of No. 5. This mode of procedure was kept up until No. 1000 had made from three to ten trips. No. 5 was left in the box for half an hour each day. This test was repeated on 18 days within a period of 3 weeks. No. 5 showed no signs of an imitative tendency, and she did not learn to climb the ladder.

To this evidence of a lack of an imitative tendency in the dancer I may here add the results of my observations in other experiments. In the discrimination tests and in the labyrinth tests I purposely so arranged conditions, in certain instances, that one individual should have an opportunity to imitate another. In no case did this occur. Seldom indeed did the animals so much as follow one another with any considerable degree of persistence. They did not profit by one another’s acts.

Excellent evidence in support of this conclusion was furnished by the behavior of the mice in the discrimination experiments. Some individuals learned to pull as well as to push the swinging wire doors of the apparatus and were thus enabled to pass through the doorways in either direction; other individuals learned only to pass through in the direction in which the doors could be pushed open. Naturally I was interested to discover whether those which knew only the trick of opening the doors by pushing would learn to pull the doors or would be stimulated to try by seeing other individuals do so. At first I arranged special tests of imitation in the discrimination box; later I observed the influence of the behavior of one mouse upon that of its companion in connection with visual discrimination experiments. This was made possible by the fact that usually a pair of individuals was placed in the discrimination box and the tests given alternately to the male and to the female. Both individuals had the freedom of the nest-box and each frequently saw the other pass through the doorway between the nest-box, _A_, and the entrance chamber, _B_ (Figure 14), either from _A_ to _B_ by pushing the swing door or from _B_ to _A_ by pulling the door.

Although abundant opportunity for imitation in connection with the opening of the doors in the discrimination box was given to twenty-five individuals, I obtained no evidence of ability to learn by imitation. The dancers did not watch the acts which were performed by their companions, and in most instances they did not attempt to follow a mate from nest-box to entrance chamber.

These problem tests, simple as they are, have revealed two important facts concerning the educability of the dancer. First, that it does not learn by imitation to any considerable extent, and, second, that it is aided by being put through an act. Our general conclusion from the results of the experiments which have been described in this chapter, if any general conclusion is to be drawn thus prematurely, must be that the dancing mouse in its methods of learning differs markedly from other mice and from rats.

CHAPTER XIII

HABIT FORMATION: THE LABYRINTH HABIT

The problem method, of which the ladder and door-opening tests of the preceding chapter are examples, has yielded interesting results concerning the individual initiative, ingenuity, motor ability, and ways of learning of the dancer; but it has not furnished us with accurate measurements of the rapidity of learning or of the permanency of the effects of training. In this chapter I shall therefore present the results of labyrinth experiments which were planned as means of measuring the intelligence of the dancer.

The four labyrinths which have been used in the investigation may be designated as _A, B, C,_ and _D_. They differ from one another in the character of their errors, as well as in the number of wrong choices of a path which the animal might make on its way from entrance to exit. In the use of the labyrinth method, as in the case of the discrimination method of earlier chapters, the steps by which a satisfactory form of labyrinth for testing the dancer was discovered are quite as interesting and important for those who have an intelligent appreciation of the problems and methods of animal psychology as are the particular results which were obtained. For this reason, I shall describe the various forms of labyrinth in the order in which they were used, whether they proved satisfactory or not. At the outset of this part of my investigation, it was my purpose to compare directly the capacity for habit formation in the dancer with that of the common mouse. This proved impracticable because the same labyrinth is not suited to the motor tendencies of both kinds of mice.

[Illustration: FIGURE 25.–Labyrinth A. _I_. entrance; _O_, exit; 1, 2, 3, 4, blind alleys.]

The first of the four labyrinths, A, appears in ground plan in Figure 25. It was constructed of wood, as were the other labyrinths also, and measured 60 cm. in length and width, and 10 cm. in depth. The outside alleys were 5 cm. wide. In the figure, _I_ marks the starting point or entrance to the maze, and _O_ the exit through which the mouse was permitted to pass into its nest-box. Any turn in the wrong direction which the animal made in its progress from entrance to exit was recorded as an error. The four errors, exclusive of the mistake of turning back, which were possible in this labyrinth, are indicated in the figure by the numerals 1, 2, 3, and 4. By retracing its steps a mouse might repeat any one or all of these errors, and add to them the error of turning back.

In the experiments a mouse was permitted to enter the maze from a small box which had been placed by the experimenter at _I_, and an accurate record was kept of the number of errors which it made in finding its way from entrance to exit, and of the time occupied. Each of five dancers was given 31 tests in this labyrinth. The number of tests per day varied, as is indicated in Table 36, from 1 to 4. The results of the tests, so far as errors and times are in question, appear in the table. _T_ at the head of a column is an abbreviation for time, _E_ for errors.

The dancers did not learn to escape from this labyrinth easily and quickly. In fact, the average time of the thirty-first test (198″) is considerably longer than that of the first (130″). The number of errors decreased, it is true, but even for the last test it was 6.6 as compared with only a little more than twice that number for the first test. The last column of the table furnishes convincing proof of the truth of the statement that the animals did not acquire a perfect labyrinth-A habit. Was this due to inability to learn so complex a path, or to the fact that the method is not adapted to their nature? Observation of the behavior of the mice in the experiments enables me to say with certainty that there was no motive for escape sufficiently strong to establish a habit of following the direct path. Often, especially after a few experiences in the maze, a dancer would wander back and forth in the alleys and central courts, dancing much of the time and apparently exploring its surroundings instead of persistently trying to escape. This behavior, and the time and error results of the accompanying table, lead me to conclude that the labyrinth method, as it has been employed in the study of the intelligence of several other mammals, is not a satisfactory test of the ability of the dancer to profit by experience. That the fault is not in the labyrinth itself is proved by the results which I obtained with common mice.

TABLE 36

RESULTS OF LABYRINTH A TESTS WITH DANCERS

AVERAGE TEST DATE No. 1000 No. 2 No. 6 No. 4 No. 5 FOR ALL 1905
T E T E T E T E T E T E

1 Nov 23 130″ 14 100″ 8 170″ 13 60″ 6 190″ 26 130″ 13.4 2 24 140 19 78 7 60 8 149 6 211 25 128 13.0 3 25 392 31 87 1 98 5 185 13 120 9 176 11.8 4 26 448 38 38 3 47 2 50 3 121 12 141 11.3 5 27 142 8 21 2 27 3 27 2 17 1 47 3.2 6 28 45 2 61 7 63 5 102 8 33 4 61 5.2 7 29 303 17 64 7 36 3 42 2 57 4 100 6.6 8 30 222 15 26 2 37 5 42 3 7 0 67 5.0 9 Dec 1 185 9 36 5 48 3 63 3 94 8 85 5.6 10 2 52 2 71 4 19 0 196 5 95 11 87 4.4 11 3 180 8 32 2 107 4 52 3 38 4 82 4.2 12 4 310 10 133 11 65 3 242 6 125 6 175 7.2 13 4 153 9 335 55 130 10 195 15 154 18 193 21.4 14 5 330 7 69 2 42 2 201 6 130 10 154 5.4 15 5 287 7 34 4 61 4 136 7 25 2 109 4.8 16 5 455 15 65 4 25 0 110 8 160 15 183 8.4 17 6 120 15 280 9 33 0 168 4 39 2 128 6.0 18 6 120 4 164 10 81 4 101 5 85 4 110 5.4 19 6 132 12 78 7 110 6 40 2 151 12 102 7.8 20 7 258 10 223 16 33 1 92 5 37 1 129 6.6 21 7 110 7 23 3 44 4 20 4 305 23 100 8.2 22 7 100 4 60 8 167 15 44 7 58 4 86 7.6 23 8 43 1 179 7 356 6 34 3 65 3 135 4.0 24 8 92 5 56 5 42 3 17 1 23 1 46 3.0 25 9 85 5 114 3 62 3 129 8 31 0 84 3.8 26 9 30 2 36 4 109 15 12 1 34 2 44 4.8 27 9 69 5 40 4 85 6 36 3 16 1 49 3.8 28 10 169 7 80 3 28 0 142 5 35 2 89 3.4 29 10 155 5 266 8 91 5 27 0 37 2 115 4.0 30 10 29 1 25 2 124 14 83 6 111 12 74 7.0 31 10 465 6 208 8 95 3 65 3 159 13 198 6.6

On the basis of two tests per day, two common mice, a white one and a gray one, quickly learned to escape from labyrinth _A_ by the shortest path. The time of escape for the gray individual (Table 37) decreased from 180″ in the first test to 21″ in the tenth, and the number of errors from 6 to 1. Similarly in the case of the white individual, the time decreased from 122″ to 8″, and the errors from 5 to 1. A fraction of the number of tests to which the dancer had been subjected sufficed to establish a habit of escape in the common mouse. It is evident, therefore, that the dancer differs radically from the common mouse in its behavior in a maze, and it is also clear that the labyrinth method, if it is to be used to advantage, must be adapted to the motor tendencies of the animal which is to be tested.

TABLE 37

RESULTS OF LABYRINTH A TESTS WITH COMMON MICE

GREY MOUSE WHITE MOUSE
TEST T E T E

1 180″ 6 122″ 5
2 26 2 80 6
3 37 1 56 4
4 18 0 27 1
5 68 2 33 2
6 10 1 19 1
7 11 1 17 1
8 13 1 17 1
9 10 0 8 1
10 21 1 8 1

The behavior of the dancer made obvious two defects in labyrinth A. Its passages are so large that the mouse is constantly tempted to dance, and it lacks the basis for a strong and constant motive of escape by the direct path. To obviate these shortcomings labyrinth B was constructed, as is shown in Figures 23 and 24, with very narrow passages, and a floor which was covered with the wires of an interrupted electric circuit so that errors might be punished. The length of this labyrinth was 52 cm. and the passages were 2.5 cm. wide and 10 cm. deep. Dancing in these narrow alleys was practically impossible, for the mice could barely turn around in them. In the case of all except the common mice and two dancers, a depth of 10 cm. was sufficient to keep the animals in the maze without the use of a cover.

As an account of the behavior of the dancer in labyrinth B has already been given in Chapter XI, I may now state the general results of the experiments. In all, thirty individuals were trained in this labyrinth. Each individual was given tests at the rate of one per minute until it had succeeded in following the correct path five times in succession. The weak electric shock, which was given as a punishment for mistakes, provided an activity-impelling motive for escape to the nest-box.

An idea of the extreme individual difference in the rapidity with which the labyrinth-B path was learned by these dancers may be obtained by an examination of Table 38, from which it appears that the smallest number of training tests necessary for a successful or errorless trip through the maze was one and the largest number fourteen. It is to be remembered that each mouse was given an opportunity to pass through the labyrinth once without punishment for errors, and thus to discover, before the training tests were begun, that a way of escape existed. This first test we may designate as the preliminary trial. Table 38 further indicates that the females acquired the labyrinth habit more quickly than did the males.

TABLE 38

RESULTS OF LABYRINTH-B EXPERIMENTS, WITH TWENTY DANCERS

MALES FEMALES

NO. OF NO. OF FIRST NO. OF LAST OF NO. OF NO. OF FIRST NO. OF LAST OF MOUSE CORRECT FIVE CORRECT MOUSE CORRECT FIVE CORRECT TEST TESTS TEST TESTS

76 8 14 75 4 15 78 5 20 77 7 11 86 13 22 87 12 22 58 2 14 49 1 5 50 6 23 57 3 20 60 13 37 59 14 28 410 6 20 415 4 13 220 4 8 225 6 18 212 3 7 211 6 10 214 10 28 213 5 14

AV. 7.0 19.3 AV. 6.2 15.6

A graphic representation of certain of the important features of the process of formation of the labyrinth-B habit is furnished by Figure 26 in which the solid line is the curve of learning for the ten males of Table 38, and the broken line for the ten females. These two curves were plotted from the number of errors made in the preliminary trial (P in the figure) and in each of the subsequent tests up to the sixteenth. In the case of both the males and the females, for example, the average number of errors in the preliminary trial was 11.3, as is indicated by the fact that the curves start at a point whose value is given in the left margin as 11.3. In the second training test the number of errors fell to 3.3 for the males and 2.7 for the females. The number of the test is to be found on the base line; the number of errors in the left margin. If these two curves of learning were carried to their completion, that for the males would end with the thirty-seventh test, and that for the females with the twenty- eighth.

[Illustration: FIGURE 26.–Curves of habit formation, plotted from the data of labyrinth-B tests with ten males and ten females. The figures in the left margin indicate the number of errors; those below the base line the number of the test. _P_ designates the preliminary test. Males ____[solid line]; Females —-[broken line].]

Time records are not reported for these and subsequent labyrinth tests because they proved to be almost valueless as measures of the rapidity of habit formation. At any point in its progress through a labyrinth, the dancer may suddenly stop to wash its face, look about or otherwise examine its surroundings; if a shock be given to hurry it along it may be surprised into an error. It is my experience, and this is true of other animals as well as of the dancing mouse, that a long trip, as measured in time units, does not necessarily indicate the lack of ability to follow the labyrinth path correctly and rapidly. Hence, whenever it is possible (and the experimenter can always plan his tests so that it shall be possible), the number of errors should be given first importance and the time of the test second place. I have presented in Table 38 the number of the first correct test, and the number of the last of five successive correct tests. Space cannot be spared for records of the errors made in the several tests by each individual.

In general, labyrinth B proved very satisfactory as a means of testing the ability of the dancer to learn a simple path. The narrow passages effectively prevented dancing, and the introduction of the electric shock as a punishment for mistakes developed a motive for escape which was uniform, constant, and so strong that the animals clearly did their best to escape from the labyrinth quickly and without errors. This maze was so simple that it did not tend to discourage them as did the one which is next to be described. It must be admitted, however, that, though labyrinth B is perfectly satisfactory as a test of the dancer’s ability to learn to follow a simple path, it is not an ideal means of measuring the rapidity of habit formation. This is due to the fact that the preliminary trial and the first training test play extremely different roles in the case of different individuals. A dancer which happens to follow the correct path from entrance to exit in the preliminary trial may continue to do so, with only an occasional error, during several of the early training tests, and it may therefore fail for a considerable time to discover that there are errors which should be avoided. The learning process is delayed by its accidental success. On the other hand, an individual which happens to make many mistakes to begin with immediately attempts to avoid the points in the maze at which it receives the electric shock. I was led to conclude, as a result of the labyrinth-B experiments, that the path was too easy, and that a more complex labyrinth would, in all probability, furnish a more satisfactory means of measuring the rapidity of habit formation.

[Illustration: FIGURE 27–A record sheet, showing the plan of labyrinth C (as made on the sheet by means of a rubber stamp) on which the experimenter recorded the path followed by the mouse. This sample sheet presents the path records for the first, fifth, tenth, and eleventh tests of No. 2 in labyrinth C. 1, 2, 3, 4, 5 designate the several errors of the labyrinth.]

On the basis of the supposition that a maze whose path was so complex that the animal would not be likely to follow it correctly in the early trials would be more to the purpose than either A or B, labyrinth C was devised. As is shown in the plan of this maze, Figure 27, five mistakes in choice of path were possible on the forward trip. These errors, as a rule, were more difficult for the dancers to avoid than those of labyrinths A and B. Those which are designated by the numerals 2, 3, and 4 were especially difficult. Error 4 was much more troublesome for left whirlers than for right whirlers because, after turning around abruptly at the entrance to the blind alley, the former type of dancer almost always followed the side wall of the maze so far that it missed the correct path. Undoubtedly the various errors are not of the same value for different individuals; but it would be extremely difficult, if not impossible, to devise a maze which should be equally difficult for several normal individuals.

In order that records of the path followed by a mouse in test after test might be kept with ease and accuracy by the experimenter, the plan of this labyrinth, and also that of labyrinth D, were cast in rubber. The outlines of labyrinths C and D which appear in Figures 27 and 28 respectively were made with the rubber stamps which were thus obtained. Figure 27 is the reproduction of a record sheet which presents the results of the first, the fifth, the tenth, and the eleventh tests of No. 2 in labyrinth C. The path followed by this individual in the first test was far too complex to be traced accurately on the record sheet. The record therefore represents merely the number of errors which was made in each region of the maze. For the fifth test, and again for the tenth and the eleventh, the path was recorded accurately. This simple device for making record blanks which can readily be filled in at the time of the experiment should recommend itself to all students of animal behavior.

In labyrinth C ten pairs of dancers were given continuous training tests at the rate of one test per minute until they were able to follow the direct path correctly. Because of the difficulty in learning this maze perfectly, it was not demanded of the mice that they should follow the path correctly several times in succession, but instead the training was terminated after the first successful trip.

TABLE 39

RESULTS OF LABYRINTH-C EXPERIMENTS, WITH TWENTY DANCERS

MALES FEMALES

NO. OF NO. OF FIRST NO. OF NO. OF FIRST MOUSE CORRECT TEST MOUSE CORRECT TEST

2 11 29 15
30 33 49 34
50 49 57 15
52 22 59 15
58 16 215 10
60 17 415 10
76 3 75 8
78 6 77 11
86 5 87 9
88 25 85 11

AV. 18.7 AV. 13.8

The results of the experiments with this labyrinth as they are presented in Table 39 indicate that its path is considerably more difficult for the dancer to learn than that of labyrinth B, that the females learn more quickly than the males, and finally, that individual differences are just as marked as they were in the case of the simpler forms of labyrinth. It therefore appears that increasing the complexity of a labyrinth does not, as I had supposed it might, diminish the variability of the results. Certain of the individual differences which appear in Table 39 are due, however, to the fact that in some cases training in labyrinth B had preceded training in labyrinth C, whereas in the other cases C was the first labyrinth in which the animals were tested. But even this does not serve to account for the wide divergence of the results given by No. 2 and No. 50, for the latter had been trained in B previous to his training in C, and the former had not been so trained. Yet, despite the advantage which previous labyrinth experience gave No. 50, he did not learn the path of C as well in fifty tests as No. 2 did in eleven. The facts concerning the value of training in one form of labyrinth for the learning of another, as they were revealed by these experiments, may more fittingly be discussed in a later chapter in connection with the facts of memory and re-learning.

[Illustration: FIGURE 28.–Plan of Labyrinth _D_, as reproduced from a print made with a rubber stamp. _I_, entrance; _O_, exit; numerals 1 to 13, errors.]

Labyrinth C is a type of maze which might properly be described as irregular, since the several possible errors are extremely different in nature. In view of the results which this labyrinth yielded, it seemed important that the dancer be tested in a perfectly regular maze of the labyrinth-D type. The plan which I designed as a regular labyrinth has been reproduced, from a rubber stamp print, in Figure 28. As is true also of the mazes previously described, it provides four kinds of possible mistakes: namely, by turning to the left (errors 1, 5, 9, and 13), by turning to the right (errors 3, 7, and 11), by moving straight ahead (errors 2, 4, 6, 8, 10, and 12), and by turning back and retracing the path just followed. The formula for the correct path of _D_ is simple in the extreme, in spite of the large number of mistakes which are possible, for it is merely “a turn to the right at the entrance, to the left at the first doorway, and thereafter alternately to the right and to the left until the exit is reached.” This concise description would enable a man to find his way out of such a maze with ease. Labyrinth D had been constructed with an exit at 10 so that it might be used as a nine-error maze if the experimenter saw fit, or as a thirteen-error maze by the closing of the opening at 10. In the experiments which are now to be described only the latter form was used.

Can the dancer learn a regular labyrinth path more quickly than an irregular one? Again, I may give only a brief statement of results. Each of the twenty dancers, of Table 40, which were trained in labyrinth D had previously been given opportunity to learn the path of C, and most of them had been trained also in labyrinth B. All of them learned this regular path with surprising rapidity. The numerical results of the tests with labyrinths B, C, and D, as well as the behavior of the mice in these several mazes, prove conclusively that the nature of the errors is far more important than their number. Labyrinth D with its thirteen chances of error on the forward trip was not nearly as difficult for the dancer to learn to escape from as labyrinth C with its five errors. That the facility with which the twenty individuals whose records are given in Table 40 learned the path of D was not due to their previous labyrinth experience rather than to the regularity of the maze is proved by the results which I obtained by testing in D individuals which were new to labyrinth experiments. Even in this case, the number of tests necessary for a successful trip was seldom greater than ten. If further evidence of the ease with which a regular labyrinth path may be followed by the dancer were desired, it might be obtained by observation of the behavior of an individual in labyrinths C and D. In the former, even after it has learned the path perfectly, the mouse hesitates at the doorways from time to time as if uncertain whether to turn to one side or go forward; in the latter there is seldom any hesitation at the turning points. The irregular labyrinth is followed carefully, as by choice of the path from point to point; the regular labyrinth is followed in machine fashion,–once started, the animal dashes through it.

TABLE 40

RESULTS OF LABYRINTH-D EXPERIMENTS, WITH TWENTY DANCERS

MALES FEMALES

NO. OF NO. OF FIRST NO. OF LAST OF NO. OF NO. OF FIRST NO. OF LAST OF MOUSE CORRECT TWO CORRECT MOUSE CORRECT TWO CORRECT TEST TESTS TEST TESTS

2 3 7 29 10 11 58 7 10 49 7 8
30 9 10 57 3 6 60 10 14 215 6 10 402 10 11 415 7 8 76 4 7 75 4 13
78 4 5 77 11 12 86 3 9 87 4 9
88 4 8 85 3 4 90 7 8 83 4 7

Av. 6.1 8.9 Av. 5.9 8.8

From the results of these labyrinth experiments with dancers I am led to conclude that a standard maze for testing the modifiability of behavior of different kinds of animals should be constructed in conformity with the following suggestions. Errors by turning to the right, to the left, and by moving forward should occur with equal frequency, and in such order that no particular kind of error occurs repeatedly in succession. If we should designate these three types of mistake by the letters _r, l_, and _s_ respectively, the error series of labyrinth C would read _l-l-r-s-l_. It therefore violates the rule of construction which I have just formulated. In the case of labyrinth D the series would read _l-s-r-s-l-s-r-s-l-s-r-s- l_. This also fails to conform with the requirement, for there are three errors of the first type, four of the second, and six of the third. Again, in a standard maze, the blind alleys should all be of the same length, and care should be taken to provide a sufficiently strong and uniform motive for escape. In the case of one animal the desire to escape from confinement may prove a satisfactory motive; in the case of another, the desire for food may conveniently supplement the dislike of confinement; and in still other cases it may appear that some form of punishment for errors is the only satisfactory basis of a motive for escape. Readers of this account of the behavior of the dancing mouse must not infer from my experimental results that the electric shock as a means of forcing discrimination will prove satisfactory in work with other animals or even with all other mammals. As a matter of fact it has already been proved by Doctor G. van T. Hamilton that the use of an electric shock may so intimidate a dog that experimentation is rendered difficult and of little value. And finally, in connection with this discussion of a standard Labyrinth, I wish to emphasize the importance of so recording the results of experiments that they may be interpreted in terms of an animal’s tendency to turn to the right or to the left. My work with the dancer has clearly shown that the avoidance of a particular error may be extremely difficult for left whirlers and very easy for right whirlers.

I hope I have succeeded in making clear by the foregoing account of my experiments that the labyrinth method is more satisfactory in general than the problem method as a means of measuring the rapidity of habit formation in the dancer, and I hope that I have made equally clear the fact that it is very valuable as a means of discovering the roles of the various senses in the acquirement of a habit (Chapter XI). From my own experience in the use of the labyrinth with the dancer and with other animals, I am forced to conclude that its chief value lies in the fact that it enables the experimenter so to control the factors of a complex situation that he may readily determine the importance of a given kind of sense data for the formation or the execution of a particular habit. As a means of measuring the intelligence of an animal, of determining the facility with which it is capable of adjusting itself to new environmental conditions, and of measuring the permanency of modifications which are wrought in its behavior by experimental conditions, I value the labyrinth method much less highly now than I did previous to my study of the dancer. It is necessarily too complex for the convenient and reasonably certain interpretation of results. Precisely what is meant by this statement will be evident in the light of the results of the application of the discrimination method to the dancer, which are to be presented in the next chapter. The labyrinth method is an admirable means of getting certain kinds of qualitative results; it is almost ideal as a revealer of the role of the senses, and it may be used to advantage in certain instances for the quantitative study of habit formation and memory. Nevertheless, I think it may safely be said that the problem method and the discrimination method are likely to do more to advance our knowledge of animal behavior than the labyrinth method.

CHAPTER XIV

HABIT FORMATION: THE DISCRIMINATION METHOD

Discrimination is demanded of an animal in almost all forms of the problem and labyrinth methods, as well as in what I have chosen to call the discrimination method. In the latter, however, discrimination as the basis of a correct choice of an electric-box is so obviously important that it has seemed appropriate to distinguish this particular method of measuring the intelligence of the dancer from the others which have been used, by naming it the discrimination method.

It has been shown that neither the problem nor the labyrinth method proves wholly satisfactory as a means of measuring the rapidity of learning, or the duration of the effects of training, in the case of the dancer. The former type of test serves to reveal to the experimenter the general nature of the animal’s capacity for profiting by experience; the latter serves equally well to indicate the parts which various receptors (some of which are sense organs) play in the formation and execution of habits. But neither of them is sufficiently simple, easy of control, uniform as to conditions which constitute bases for activity, and productive of interpretable quantitative results to render it satisfactory. The problem method is distinctly a qualitative method, and, in the case of the dancing mouse, my experiments have proved that the labyrinth method also yields results which are more valuable qualitatively than quantitatively. I had anticipated that various forms of the labyrinth method would enable me to measure the modifiability of behavior in the dancer with great accuracy, but, as will now be made apparent, the discrimination method proved to be a far more accurate method for this purpose.

Once more I should emphasize the fact that my statements concerning the value of methods apply especially to the dancing mouse. Certain of the tests which have proved to be almost ideal in my study of this peculiar little rodent would be useless in the study of many other mammals. An experimenter must work out his methods step by step in the light of the daily results of patient and intelligent observation of the motor capacity, habits, instincts, temperament, imitative tendency, intelligence, hardihood, and life-span of the animal which he is studying. The fact that punishment has proved to be more satisfactory than reward in experiments with the dancer does not justify the inference that it is more satisfactory in the case of the rat, cat, dog, or monkey. Methods which yielded me only qualitative results, if applied to other mammals might give accurate quantitative results; and, on the other hand, the discrimination method, which has proved invaluable for my quantitative work, might yield only qualitative results when applied to another kind of animal.

The form of the discrimination method whose results are to be presented in this chapter has already been described as white-black discrimination. In the discrimination box (Figures 14 and 15, p. 92) the two electric-boxes which were otherwise exactly alike in appearance were rendered discriminable for the mouse by the presence of white cardboards in one and black cardboards in the other. In order to escape from the narrow space before the entrances to the two electric-boxes, the dancer was required to enter the white box. If it entered the black box a weak electric shock was experienced. After two series of ten tests each, during which the animal was permitted to choose either the white or the black box without shock or hindrance, the training was begun. These two preliminary series serve to indicate the natural preference of the animal for white or black previous to the training. An individual which very strongly preferred the white might enter, from the first, the box thus distinguished, whereas another individual whose preference was for the black might persistently enter the black box in spite of the disagreeable shocks. First of all, therefore, the preliminary tests furnish a basis for the evaluation of the results of the subsequent training tests. On the day succeeding the last series of preliminary tests, and daily thereafter until the animal had acquired a perfect habit of choosing the white box, a series of training tests was given. These experiments were usually made in the morning between nine and twelve o’clock, in a room with south-east windows. The entrances to the electric-boxes faced the windows, consequently the mouse did not have to look toward the light when it was trying to discriminate white from black. All the conditions of the experiment, including the strength of the current for the shock, were kept as constant as possible.

Choice by position was effectively prevented, as a rule, by shifting the cardboards so that now the left now the right box was white. The order of these shifts for the white-black series whose results are quantitatively valuable appear in Table 12 (p. III). That the order of these changes in position may be criticised in the light of the results which the tests gave, I propose to show hereafter in connection with certain other facts. The significant point is that the defects which are indicated by the averages of thousands of tests could not have been predicted with certainty even by the most experienced investigator in this field.

In Table 41 are to be found the average number of errors in each series of ten white-black discrimination tests for five males and for five females which were trained by being given ten tests per day, and similarly for the same number of individuals of each sex, trained by being given twenty tests per day. Since the results for these two conditions of training are very similar, the averages for the twenty individuals are presented in the last column of the table. For the present we may neglect the interesting individual, sex, and age differences which these experiments revealed and examine the significant features of the general averages, and of the white-black discrimination curve (Figure 29).

TABLE 41

WHITE BLACK DISCRIMINATION TESTS. NUMBER OF ERRORS IN THE VARIOUS SERIES

MALES FEMALES

AVERAGES AVERAGES GENERAL AVERAGES AVERAGES GENERAL AVERAGES SERIES FOR 5, FOR 5, AVERAGES FOR 5, FOR 5, AVERAGES FOR ALL 10 TESTS 20 TESTS FOR 10 10 TESTS 20 TESTS FOR 10 (20) MALES PER DAY PER DAY PER DAY PER DAY AND FEMALES

A 5.8 6.0 5.9 5.8 5.8 5.8 5.85 B 5.6 6.2 5.9 5.8 5.6 5.7 5.8 1 5.0 5.0 5.0 5.6 4.6 5.1 5.05 2 2.6 4.6 3.6 4.4 5.0 4.7 4.15 3 3.0 3.4 3.2 3.4 3.4 3.4 3.3 4 2.6 3.8 3.2 2.4 2.2 2.3 2.75 5 2.4 2.0 2.2 2.6 1.8 2.2 2.2 6 1.6 1.6 1.6 1.0 2.2 1.6 1.6 7 1.0 1.4 1.2 2.0 0.4 1.2 1.2 8 0.2 0.6 .4 1.4 1.6 1.5 .95 9 0.2 1.0 .6 0.6 0.8 .7 .65 10 0 .8 .4 1.0 0.8 .9 .65 11 0 .8 .4 0.8 0 .4 .40 12 0 .6 .3 0.4 0 .2 .25 13 0 0 0 0 0 0 0
14 0 0 0 0 0 0 15 0 0 0 0 0 0

[Illustration: FIGURE 29.–Error curve plotted from the data given by twenty dancers in white-black discrimination tests. The figures in the left margin indicate the number of errors; those below the base line, the number of the series. _A_ and _B_ designate the preference series.]

The preference series, _A_ and _B_, reveal a constant tendency to choose the black box, whose strength as compared with the tendency to choose the white box is as 5.8 is to 4.2. In other words, the dancer on the average chooses the black box almost six times in ten. The first series of training tests reduced this preference for black to zero, and succeeding series brought about a rapid and fairly regular decrease in the number of errors, until, in the thirteenth series, the white was chosen every time. Since I arbitrarily define a perfect habit of discrimination as the ability to choose the right box in three successive series of ten tests each, the tests ended with the fifteenth series.

The discrimination curve, Figure 29, is a graphic representation of the general averages of Table 41.–It is an error curve, therefore. Starting at 5.85 for the first preliminary series, it descends to 5.8 for the second series, and thence abruptly to 5.05 for the first training series. This series of ten tests therefore served to reduce the black preference very considerably. The curve continues to descend constantly until the tenth series, for which the number of errors was the same as for the preceding series, .65. This irregularity in the curve, indicative, as it would appear, of a sudden cessation in the learning process, demands an explanation. My first thought was that an error in computation on my part might account for the shape of the curve. The error did not exist, but in my search for it I discovered what I now believe to be the cause of the interruption in the fall of the error curve. In all of the training series up to the tenth the white cardboard had been on the right and the left alternately or on one side two or three times in succession, whereas in the tenth series, as may be seen by referring to Table 12 (p.111), it was on the left for the first four tests, then on the right four times, and, finally, on the left for the ninth test and on the right for the tenth. This series was therefore a decidedly more severe test of the animal’s ability to discriminate white from black and to choose the white box without error than were any that had preceded it. If my interpretation of the results is correct, it was so much more severe than the ninth series that the process of habit formation was obscured. It would not be fair to say that the mouse temporarily ceased to profit by its experience; instead it profited even more than usually, in all probability, but the unavoidably abrupt increase in the difficultness of the tests was just sufficient to hide the improvement.

As I have suggested, the plan of experimentation may be criticised adversely in the light of this irregularity in the error curve. Had the conditions been perfectly satisfactory the curve would not have taken this form. I admit this, but at the same time I am glad that I chose that series of shifts in the position of the cardboards which, as it happens, served to exhibit an important aspect of quantitative measures of the modifiability of behavior that otherwise would not have been revealed. Our mistakes in method often teach us more than our successes. I have taken pains, therefore, to describe the unsatisfactory as well as the satisfactory steps in my study of the dancer.

[Illustration: FIGURE 30.–Error curve plotted from the data given by thirty dancers, of different ages and under different conditions of training, in white-black discrimination tests.]

The form of the white-black discrimination curve of Figure 29 is more surprising than disappointing to me, for I had anticipated many more irregularities than appear. What I had expected, as the result of training five or even ten pairs of mice, was the kind of curve which is presented, for contrast with the one already discussed, in Figure 30. This also is an error curve, but, unlike the previous one, it is based upon results which were got from individuals of different ages which were trained according to the following different methods. Ten of these individuals were given two or five tests daily, ten were given ten tests daily, and ten were given twenty tests daily. The form of the curve serves to call attention to the importance of uniform conditions of training, in case the results are to be used as accurate measures of the rapidity of learning.

Examination of the detailed results of the white-black discrimination tests as they appear in the tables of Chapter VII will reveal the fact that some individuals succeeded in choosing correctly in a series of ten tests after not more than five series, whereas others required at least twice as many tests as the basis of a perfect series. In very few instances, however, was a perfect habit of discrimination established by fewer than one hundred tests. As the averages just presented in Table 41 indicate, fifteen series, or one hundred and fifty tests, were required for the completion of the experiment. One might search a long time, possibly, for another mammal whose curve of error in a simple discrimination test would fall as gradually as that of the dancer. It is fair to say that this animal learns very slowly as compared with most mammals which have been carefully studied. It is to be remembered, however, that quantitative results such as are here presented for the dancer are available for few if any other animals except the white rat. Neither in the form of the curve of learning nor in the behavior of the animal as it makes its choice of an electric-box is there evidence of anything which might be described as a sudden understanding of the situation. The dancer apparently learns by rote. It exhibits neither intelligent insight into an experimental situation nor ability to profit by the experience of its companions. That the selection of the white box occurs in various ways in different individuals, and even in the same individual at different periods in the training process, is the only indication of anything suggestive of implicit reasoning. Naturally enough comparison of the two boxes is the first method of selection. It takes the dancers a surprisingly long time to reach the point of making this comparison as soon as they are confronted by the entrances to the two electric-boxes. The habit of running from entrance to entrance repeatedly before either is entered, once having been acquired, is retained often throughout the training experiments. But in other cases, an individual finally comes to the point of choosing by what appears to be the immediate recognition of the right or the wrong box. In the former case the mouse enters the white box immediately; in the latter, it rushes from the black box into the white one without hesitation. So much evidence the discrimination tests furnish of forms of behavior which in our fellow-men we should interpret as rational.

[Illustration: FIGURE 31.–Curve of habit formation, plotted from the data of labyrinth-D tests with ten males and ten females.]

Comparison of the error curves for the labyrinth tests (Figures 26 and 31) with those for the discrimination tests (Figures 29 and 30) reveals several interesting points of difference. The former fall very abruptly at first, then with decreasing rapidity, to the base line; the latter, on the contrary, fall gradually throughout their course. Evidently the labyrinth habit is more readily acquired by the dancer than is the visual discrimination habit. Certain motor tendencies can be established quickly, it would seem, whereas others, and especially those which depend for their guidance upon visual stimuli, are acquired with extreme slowness. From this it might be inferred that the labyrinth method is naturally far better suited to the nature of the dancer than is any form of the discrimination method. I believe that this inference is correct, but at the same time I am of the opinion that the discrimination method is of even greater value than the labyrinth method as a means of discovering the capacity of the animal for modification of behavior.

Inasmuch as my first purpose in the repetition of white-black discrimination tests with a number of individuals was to obtain quantitative results which should accurately indicate individual, age, and sex differences in the rapidity of learning, it is important to consider the reliability of the averages with which we have been dealing. Possibly two groups of five male dancers each, chosen at random, would yield very different results in discrimination tests. This would almost certainly be true if the animals were selected from different lots, or were kept before and during the tests under different environmental conditions. But from my experiments it has become apparent that the average of the results given by five individuals of the same sex, age, and condition of health, when kept in the same environment and subjected to the same experimental tests, is sufficiently constant from group to group to warrant its use as an index of modifiability for the race. This expression, index of modifiability, is a convenient mode of designating the average number of tests necessary for the establishment of a perfect habit of white-black discrimination. Hereafter I shall use it instead of a more lengthy descriptive phrase.

As an indication of the degree of accuracy of measurements of the rapidity of learning which are obtained by the use of 5 individuals I may offer the following figures. For one of two directly comparable groups of 5 male dancers which were chosen from 16 individuals which had been trained, the number of tests which resulted in a perfect habit of white-black discrimination was 92; for the other group it was 96. These indices for strictly comparable groups of 5 individuals each differ from one another by less than 5 per cent. Similarly, in the case of two groups of females, the indices of modifiability were 94 and 104. These figures designate the number of tests up to the point at which errors ceased for at least three successive series (30 tests).

The determination of the probable error of the index of modifiability further aids us in judging of the reliability of the measure of the rapidity of learning which is obtained by averaging the results for 5 individuals. For a group of 5 males (Table 43, p. 243) the index was 72 +- 3.5; and for a group of 5 females of the same age as the males and strictly comparable with respect to conditions of white-black training, it was 104 +- 2.9. A probable error of +- 3.5 indicates the reliability of the first of these indices of modifiability; one of +- 2.9, that of the second.

I do not doubt that 10 individuals would furnish a more reliable average than 5, but I do doubt whether the purposes of my experiments would have justified the great increase in work which the use of averages based upon so large a group would have necessitated.

Further discussion of the index of modifiability may be postponed until the several indices which serve as measures of the efficiency of different methods of training have been presented in the next chapter.

From the data which constitute the materials of the present chapter it is apparent that the results of the discrimination method are amenable to much more accurate quantitative treatment than are those of the problem method or the labyrinth method. But I have done little more as yet than describe the method by which it is possible to measure certain dimensions of the intelligence of the dancer, and to state some general results of its application. In the remaining chapters it will be our task to discover the value of this method and of the results which it has yielded.

CHAPTER XV

THE EFFICIENCY OF TRAINING METHODS

The nature of the modifications which are wrought in the behavior of an organism varies with the method of training. This fact is recognized by human educators, as well as by students of animal behavior (makers of the science of comparative pedagogy), but unfortunately accurate measurements of the efficiency of our educational methods are rare.

Whatever the subject of investigation, there are two preeminently important aspects of the educative process which may be taken as indications of the value of the method of training by which it was initiated and stimulated. I refer to the rapidity of the learning process and its degree of permanency, or, in terms of habit formation, to the rapidity with which a habit is acquired, and to its duration. Of these two easily measurable aspects of the modifications in which training results, I have chosen the first as a means to the special study of the efficiency of the training to which the dancing mouse has been subjected in my experiments.

The reader who has followed my account of the behavior of the dancer up to this point will recall that in practically all of the discrimination experiments the number of tests in a series was ten. Some readers doubtless have wondered why ten rather than five or twenty tests was selected as the number in each continuous series. I shall now attempt to answer the question. It was simply because the efficiency of that number of tests, given daily, when taken in connection with the amount of time which the conduct of the experiments required, rendered it the most satisfactory number. But this statement demands elaboration and explanation.

Very early in my study of the dancer, I learned that a single experience in a given experiment day after day had so little effect upon the animal that a perfect habit could not be established short of several weeks or months. Similarly, experiments in which two tests per day were given proved that even a simple discrimination habit cannot be acquired by the animal under this condition of training with sufficient rapidity to enable the experimenter to study the formation of the habit advantageously. Next, ten tests in succession each day were given. The results proved satisfactory, consequently I proceeded to carry out my investigation on the basis of a ten-test series. After this method had been thoroughly tried, I decided to investigate the efficiency of other methods for the purpose of instituting comparisons of efficiency and discovering the number of tests per day whose efficiency, as measured by the rapidity of the formation of a white-black discrimination habit, is highest.

For this purpose I carefully selected five pairs of dancers of the same age, descent, and previous experience, and gave them white-black tests in series of two tests per day (after the twentieth day the number was increased to five) until they had acquired a perfect habit of discriminating. Similarly other dancers were trained by means of series of ten tests, twenty tests, or one hundred tests per day. Since it was my aim to make the results of these various tests strictly comparable, I spared no pains in selecting the individuals, and in maintaining constancy of experimental conditions. The order of the changes in the position of the cardboards which was adhered to in these efficiency tests was that given in Table 12.

At the beginning of the two-test training I thought it possible that the animals might acquire a perfect habit with only a few more days’ training than is required by the ten-test method. This did not prove to be the case, for at the end of the twentieth day (after forty tests in all) the average number of mistakes, as Table 42 shows, was 3.2 for the males and 3.0 for the females. Up to this time there had been clear evidence of the formation of a habit of discriminating white from black, but, on the other hand, the method had proved very unsatisfactory because the first test each day usually appeared to be of very different value from the second. On account of the imminent danger of the interruption of the experiment by the rapid spread of an epidemic among my mice, I decided to increase the number of tests in each series to five in order to complete the experiment if possible before the disease could destroy the animals. On the twenty- first day and thereafter, five-test series were given instead of two-test. Unfortunately I was able to complete the experiment up to the point of thirty successive correct tests with only six of the ten individuals whose numbers appear at the top of Table 42. That the results of this table are reliable, despite the fact that some of the individuals had to be taken out of the experiment on account of bad condition, is indicated by the fact that all the mice continued to do their best to discriminate so long as they were used. Possibly the habit would have been acquired a little more quickly by some of the individuals had they been stronger and more active.

It should be explained at this point that the results in all the efficiency-of-training tables of this chapter are arranged, as in the previous white-black discrimination tables, in tens, that is, each figure in the tables indicates the number of errors in a series of ten tests. In all cases _A_ and _B_ mark preliminary series of tests which were given at the rate of ten tests per series. The numbers in the first column of these tables designate groups of ten tests each, and not necessarily daily series. In Table 42, for example, 1 includes the results of the first five days of training, 2, of the next five days, and so on. The table shows that No. 80 made seven wrong choices in the first five series of two tests each. This method of grouping results serves to make the data for the different methods directly comparable, and at the same time it saves space at the sacrifice of very little valuable information concerning the nature of the daily results. It is to be noted, with emphasis, that the two-five tests per day training established a perfect habit after four weeks of training. This method is therefore costly of the experimenter’s time.

TABLE 42

EFFICIENCY OF TRAINING. WHITE-BLACK TESTS AT THE RATE OF 2 OR 5 PER DAY