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.