Part 11 (1/2)
With colored cardboards inside the electric-boxes as well as at their entrances (see Figure 14 for position of cardboards) blue-orange tests were given to Nos. 2 and 3 until they discriminated perfectly. The papers were Bradley's blue tint No. 1 and orange. Number 2 was perfect in the twelfth series (Table 17), No 3 in the fourteenth and again in the sixteenth. They were then tested with a special brightness check series which was intended by the experimenter to reveal any dependence upon a possible brightness difference rather than upon the color difference of the boxes.
TABLE 17
LIGHT BLUE-ORANGE TESTS IN COLOR DISCRIMINATION BOX
SERIES DATE NO. 2 NO. 3 1906 RIGHT WRONG RIGHT WRONG (LIGHT (ORANGE) (LIGHT (ORANGE) BLUE) BLUE)
1 Jan. 26 7 3 1 9 2 27 7 3 5 5 3 28 7 3 6 4 4 29 7 3 7 3 5 30 7 3 4 6 6 31 10 0 7 3 7 Feb. 1 9 1 7 3 8 2 8 2 6 4 9 3 9 1 9 1 10 5 7 3 5 5 11 6 8 2 5 5 12 7 10 0 5 5 Special brightness check series (see Table 18) 13 8 10 0 7 3 Special light blue-dark blue series 14 9 8 2 10 0 15 10 9 1 9 1 Special light blue-dark blue series 16 11 9 1 10 0 Special brightness check series 17 12 10 0 9 1
TABLE 18
LIGHT BLUE-ORANGE
Brightness check series Mouse No. 2, Series 13 Feb. 8, 1906
TEST CONDITION RIGHT WRONG
1 Light blue on right Orange on left Right ____
2 Light blue on left Orange on right Right ____
3 Light blue on right Red subst.i.tuted for orange Right ____
4 Light blur on left Red subst.i.tuted for orange Right ____
5 Dark blue on right Orange on left Right ____
6 Dark blue on left Orange on right Right ____
7 Dark blue on left Orange on right Right ____
8 Dark blue on right Red subst.i.tuted for orange Right ____
9 Dark blue on left Red subst.i.tuted for orange Right ____
10 Dark blue on left Red subst.i.tuted for orange Right ____
Totals 10 0
The nature of this brightness check series, as well as the results which No. 2 gave when tested by it, may be appreciated readily by reference to Table 18. Tint No. 1 of the blue, which is considerably brighter, in my judgment, than the Bradley blue, was replaced at intervals in this series by the latter. For it was thought that in case the mouse were choosing the blue of the series because it seemed brighter than the orange, this subst.i.tution might mislead it into choosing the orange. These blues are referred to in the table as light blue (tint No. 1) and dark blue (standard blue). Again a change in the opposite direction was made by subst.i.tuting Bradley red for orange. As this was for the human eye the subst.i.tution of a color whose brightness was considerably less than that of the orange, it seemed possible that the mouse, if it had formed the habit of choosing the box which seemed the darker, might by this change be misled into choosing the red instead of the light blue. In a word, changes in the conditions of the experiments were made in such a way that now one color, now the other, appeared to be the brighter. But I did not attempt to exclude brightness discrimination on the part of the mouse by dependence upon the human judgment of brightness equality, for it is manifestly unsafe to a.s.sume that two colors which are of the same brightness for the human eye have a like relation for the eye of the dancer or of any other animal. My tests of color vision have been conducted without other reference to human standards of judgment or comparisons than was necessary for the description of the experimental conditions. In planning the experiments I a.s.sumed neither likeness nor difference between the human retinal processes and those of the dancer. It was my purpose to discover the nature of the mouse's visual discriminative ability.
As is indicated in the tables, neither the subst.i.tution of dark blue for light blue, nor the replacement of the orange by red or dark blue rendered correct choice impossible, although certain of the combinations did render choice extremely difficult. In other words, despite all of the changes which were made in the brightness of the cardboards in connection with the light blue-orange tests, the mice continued to make almost perfect records. What are we to conclude from this? Either that the ability to discriminate certain colors is possessed by the dancer, or that for some reason the tests are unsatisfactory. If it be granted that the possibility of brightness discrimination was excluded in the check series, the first of these alternatives apparently is forced upon us. That such a possibility was not excluded, later experiments make perfectly clear. The fact was that not even in the check series was the brightness value of the orange as great as that of the blue. Consequently the mice may have chosen the brighter box each time while apparently choosing the blue.
Although conclusive proof of the truth of this statement is furnished only by later experiments, the results of the light blue-orange series, as given in Table 17, strongly suggest such a possibility. Mouse No. 3 had not been experimented with previous to these color discrimination tests.
Her preference for the orange, which in the case of the first series was 9 to 1, consequently demands an explanation. If she had been trained previously to choose the white instead of the black, as was true of No. 2, it might be inferred that she went to the orange box because it appeared brighter than the blue. As this explanation is not available, we are driven back upon the results of the white-black preference tests in Chapter VII, which proved that many dancers prefer the black to the white.