1000 25 weeks White-black 4 weeks Right 0 5 27 White-black 4 Right 5 7 210 15 White-black 8 Right 5 220 15 White-black 8 Right 4 230 15 White-black 8 Wrong 5 215 15 White-black 8 Right 5 225 15 White-black 8 Right 2 235 15 White-black 8 Right 7 410 15 White-black 8 Wrong 4 415 15 White-black 8 Wrong 6 420 15 White-black 8 Wrong 3 425 15 White-black 8 Right 3 2 28 Black-white 4 Wrong 9 7 17 Black-white 2 Wrong 1 7 21 Black-white 6 Right 1 7 27 Black-white 10 Right 1 6 998 18 Black-white 2 Wrong 3 998 22 Black-white 4 Right 0 998 28 Black-white 10 Right 5 5 13 10 Black-white 4 Right 3 14 10 Black-white 4 Right 3 15 10 Black-white 4 Right 2 16 10 Black-white 4 Right 4 1000 25 Light blue-orange 4 Right 4 2 28 Light blue-orange 2 Wrong 5 5 28 Light blue-orange 6 Wrong 4 6 3 25 Light blue-orange 4 Wrong 8 10 24 Light blue-orange 2 Right 8 10 26 Light blue-orange 2 Right 5 11 25 Light blue-orange 2 Right 6 11 27 Light blue-orange 2 Wrong 5 151 13 Green-red 2 Right 1 0 152 13 Green-red 2 Right 5 1

This quant.i.tative study of the duration of simple habits of choice showed that in the majority of cases a perfectly acquired habit persists for at least two weeks. To be perfectly fair to the animal I must restrict this statement to visual conditions other than colors, for the dancer exhibited little ability either to acquire or to retain a habit of distinguishing spectral colors. Altogether, I made a large number of white-black and black-white memory tests after rest intervals of four, six, eight, or ten weeks. The results for the four-week interval show extreme individual differences in memory. Number 1000, for example, was able to choose correctly every time in a series of white-black tests after a rest interval of four weeks, whereas No. 5 was wrong as often as she was right after the same interval. I have placed the results for these two individuals at the head of the table because they suggest the variations which render averages undesirable. Number 1000 had a perfect habit at the end of four weeks of disuse; No. 5 had no habit whatever. I shall reserve further discussion of age, s.e.x, and individual differences in the permanency of habits for the next chapter.

With Nos. 7 and 998 memory tests were made after three different rest intervals. At the end of two weeks the black-white habit was present in both individuals, although it was not perfect. After six and four weeks, respectively (see Table 48), it still persisted; in fact, it apparently had improved as the result of additional training after the earlier memory tests. At the expiration of ten weeks it had wholly disappeared. In her first series of memory tests after the ten-week interval No. 7 made only one error, but a chance choice of the black (right) in the first test and the subsequent choice of the box in which no shock had been received serve to account for results which at first appear to be indicative of memory.

That this explanation is correct is proved by the fact that a second memory series, in which the first choice happened to be wrong, resulted in six mistakes. Evidently she had lost the habit.

In no instance have memory tests definitely indicated the presence of a habit after a rest interval of more than eight weeks. It is safe, therefore, to conclude from the results which have been obtained that a white-black or black-white discrimination habit may persist during an interval of from two to eight weeks of disuse, but that such a habit is seldom perfect after more than four weeks.

The measurements of memory which were made in connection with color discrimination experiments are markedly different from those which were obtained in the brightness tests. As might have been antic.i.p.ated (?), in view of the extreme difficulty with which the dancer learns to discriminate colors, the habit of discriminating between qualitatively different visual conditions does not persist very long. I have never obtained evidence of a perfect habit after an interval of more than two weeks, and usually, as is apparent from Table 48, the tests indicated very imperfect memory at the end of that interval. It seems probable that even in these so-called color tests discrimination is partly by brightness difference, and that the imperfection of the habit and its short duration are due to the fact that the basis of discrimination is inadequate. This is the only explanation which I have to offer for the difference which has been demonstrated to exist between the duration of brightness discrimination habits and color discrimination habits.

The duration of a discrimination habit having been measured with a fair degree of accuracy, I undertook the task of ascertaining whether training whose results have wholly disappeared, so far as memory tests are in question, influences the re-acquisition of the same habit. Can a habit be re-acquired with greater facility than it was originally acquired? Is re- learning easier than learning? To obtain an answer to the question which may be asked in these different forms, ten individuals were experimented with in accordance with a method whose chief features are now to be stated. In each of these ten individuals a perfect white-black habit was established by the use of the standard series of tests the order of which is given in Table 12. At the expiration of a rest interval of eight weeks precisely the same series of tests were repeated as memory and re-training tests. In this repet.i.tion, the preliminary series, _A_ and _B_, served as memory tests, and the subsequent training series, as re-training series.

[Ill.u.s.tration: FIGURE 32.--Error curves plotted from the data given by ten dancers in white-black discrimination tests. The solid line ([Symbol: solid line]) is the error curve of the original learning process; the broken line (------) is that of the re-learning process, after an interval of eight weeks.]

The striking results of this investigation of re-learning are exhibited in the curves of learning and re-learning of Figure 32. These curves make it appear that the mice re-acquired the white-black discrimination habit much more readily than they had originally acquired it. But in addition to furnishing the basis for some such statement as the foregoing, the curves suggest a serious criticism of the experiment.

In the original tests, the preliminary series indicated a strong preference for black. In series _A_ it was chosen on the average 5.8 times in 10, and in series _B_, 5.7 times. This preference was rapidly overcome by the training series, and at the end of 130 tests discrimination was perfect. All this appears in the curve of learning (solid line of figure).

On the other hand, these preliminary series when repeated as memory tests, after a rest-interval of eight weeks, gave markedly different results.

Series _A_ indicated preference for white (5.6 times in 10) instead of black, and series _B_ indicated only a slight preference for black. In brief, series _A_ and _B_ show that the preference for black was considerably stronger at the beginning of the training than at the beginning of the re-training.

In the light of these facts it is fair to claim that the effects of the white-black training had not wholly disappeared as the result of eight weeks of rest, and that the experiment therefore fails to furnish satisfactory grounds for the statement that re-learning occurs more rapidly than learning. I accept this criticism as pertinent, although not necessarily valid, and at the same time I freely admit that the results have a significance which I had not antic.i.p.ated. But they are not less interesting or valuable on that account. Granting, then, that at least some of the ten individuals which took part in the experiment had not completely lost the memory of their white-black training at the end of eight weeks, it is still possible that an examination of the individual results may justify some conclusion concerning the question which was proposed at the outset of the investigation. Such an examination is made possible by Tables 49 and 50, in which I have arranged separately the results for the males and the females.

TABLE 49

WHITE-BLACK TRAINING. TEN TESTS PER DAY

Males TRAINING RETRAINING 210 220 230 410 420 AV. 210 220 230 410 420 AV.

A 6 5 6 6 6 5.8 5 4 5 4 3 4.2 B 6 8 8 5 1 5.6 8 4 5 4 6 5.4

1 6 7 6 2 4 5.0 3 3 4 7 3 4.0 2 4 3 1 2 3 2.6 2 4 2 5 3 3.2 3 3 1 4 3 4 3.0 1 4 1 4 1 2.2 4 5 0 3 3 2 2.6 0 1 0 1 2 0.8 5 3 0 4 1 4 2.4 0 2 0 2 0 0.8 6 2 1 4 0 1 1.6 0 1 0 0 2 0.6 7 1 0 3 1 0 1.0 0 0 0 0 8 0 0 1 0 0 0.2 0 0 1 0.2 9 0 0 0 1 0 0.2 0 0 0 10 0 0 0 0 1 0.2 11 0 0 0 0 0 12 0 0 0 0 13 0 0 14 15

Only three of the ten individuals failed to re-acquire the habit of white- black discrimination more quickly than it had originally been acquired, and, in the case of these exceptions, No. 220 required exactly the same number of tests in each case, and No. 420 was placed at a slight disadvantage in the re-learning series by an interruption of the training between the seventh and the eighth series. Had his training been completed by the sixth series he too would have had the same number of tests in training and re-training. Moreover, and this is of preeminent importance for a fair interpretation of the results, in several instances even those individuals which exhibited as strong a preference for the black in the memory series as in the preliminary series re-learned more quickly than they had learned. Number 210, for example, although he gave no evidence of memory, and, in fact, chose the black more frequently in the memory series than he did in the preliminary series, re-acquired the discrimination habit in less than half the number of tests which had been necessary for the establishment of the habit originally.

TABLE 50

WHITE-BLACK TRAINING. TEN TESTS PER DAY

Females

TRAINING RE-TRAINING 215 225 235 415 425 Av. 215 225 235 415 425 Av.

A 8 4 4 8 5 5.8 5 2 7 6 3 4.6 B 8 7 6 6 2 5.8 8 5 6 4 3 5.2 1 7 6 5 6 4 5.6 4 1 5 4 3 3.4 2 5 6 4 2 5 4.4 1 1 1 2 3 1.6 3 3 3 4 3 4 3.4 1 0 3 6 0 2.0 4 2 1 3 3 3 2.4 0 0 3 3 1 1.4 5 1 3 3 3 3 2.6 0 0 died 2 0 0.5 6 2 1 1 1 0 1.0 0 1 0 0.2 7 1 1 2 3 3 2.0 0 0 0 8 0 0 2 2 3 1.4 1 0.2 9 1 0 0 1 1 0.6 0 0 10 0 2 1 0 2 1.0 0 0 11 0 3 0 1 0 0.8 0 0 12 0 0 0 2 0 0.4 13 0 0 0 0 0 14 0 0 0 15 0 0

The facts which have been presented thus far become more significant when the indices of modifiability for the learning and the re-learning processes are compared.

INDICES OF MODIFIABILITY

LEARNING RE-LEARNING

Females . . . . . . . 104 42.5 Males . . . . . . . . 72 54

The behavior of the mice in the experiments, the detailed results of Tables 49 and 50, and the indices of modifiability together justify the following conclusions. Most of the ten dancers, at the end of a rest interval of eight weeks, had so far lost the habit of white-black discrimination that memory tests furnished no conclusive evidence of the influence of previous training; a few individuals seemed to possess traces of the habit after such an interval. In the case of each group of individuals re-training brought about the establishment of a perfect habit far more quickly than did the original training. This suggests the existence of two kinds or aspects of organic modification in connection with training; those which const.i.tute the basis of a definite form of motor activity, and those which const.i.tute the bases or dispositions for the acquirement of certain types of behavior. There are several indications that further study of the modifiability of behavior will furnish the facts which are necessary to render this suggestion meaningful.

Closely related to the facts which have been revealed by the re-training experiments are certain results of the labyrinth experiments. For the student of animal behavior, as for the human educator, it is of importance to learn whether one kind of training increases the efficiency of similar forms of training. Can a dancer learn a given labyrinth path the more readily because it has previously had experience in another form of labyrinth?

The answer to this question, which my experimental results furnish, is given in Table 51. In the upper half of the table have been arranged the results for six individuals which were trained first in labyrinth B, then in labyrinth C, and finally in labyrinth D. Below, in similar fashion, are given the results for six individuals which were trained in the same three labyrinths in the order C, B, D, instead of B, C, D. My purpose in giving the training in these two orders was to ascertain whether labyrinth C, which had proved to be rather difficult for most individuals, would be more easily learned if the training in it were preceded by training in labyrinth C.

TABLE 51

THE INFLUENCE OF ONE LABYRINTH HABIT UPON THE FORMATION OF ANOTHER LABYRINTH B LABYRINTH C LABYRINTH D NO. OF NO. OF NO. OF NO. OF NO. OF NO. OF NO. FIRST COR- LAST OF FIRST COR- LAST OF FIRST COR- LAST OF RECT TEST FIVE COR- RECT TEST FIVE COR- RECT TEST FIVE COR- RECT TESTS RECT TESTS RECT TESTS

76 8 14 3 19 4 7 78 5 20 6 14 4 5 86 13 22 5 12 3 9 75 4 15 8 19 4 13 77 7 11 11 29 11 12 87 12 22 9 20 4 9

AV. 8.2 17.3 7.0 18.8 5.0 9.2

LABYRINTH C LABYRINTH B LABYRINTH D

58 16 -- 2 14 7 10 60 17 -- 13 37 10 14 88 25 35 9 22 4 8 49 34 -- 1 5 7 8 57 15 -- 3 20 3 6 85 11 18 2 11 3 4

AV. 19.7 26.5 5.0 18.2 5.7 8.3

The results are sufficiently definite to warrant the conclusion that experience in B rendered the learning of C easier than it would have been had there been no previous labyrinth training. Those individuals whose first labyrinth training was in C made their first correct trip as the result of 19.7 trials, whereas those which had previously been trained in labyrinth B were able to make a correct trip as the result of only 7.0 trials. Similarly the table shows that training in C rendered the subsequent learning of B easier. To master B when it was the first labyrinth required 8.2 trials; to master it after C had been learned required only 5 trials. In addition to proving that the acquisition of one form of labyrinth habit may facilitate the acquisition of others, comparison of the averages of Table 51 furnishes evidence of the truth of the statement that no results of training can be properly interpreted in the absence of knowledge of the previous experience of the organism.

CHAPTER XVII