Series 23 to 27 of Table 24 were given as final and crucial tests of the relation of brightness discrimination to color discrimination. As it is not possible to express in a simple formula the conditions of the tests, a sample series which indicates the brightness of the colors in each of the twenty tests of a series, and in addition the results given by No. 151 in the first of these final series, is reproduced in Table 25. For an animal which had presumably learned perfectly to choose green in preference to red, the record of 8 mistakes in 20 choices as a result of changes in relative brightness is rather bad, and it renders doubtful the existence of color discrimination in any of these experiments. No. 152 showed no ability whatever to choose the green in the first of the series (series 23 of Table 24) of which that of Table 25 is a sample. His record, 10 mistakes in 20 choices, was even poorer than that of No. 151. That both of these mice learned to choose fairly accurately in these final tests is shown by the results of series 24, 25, 26, and 27. I must admit, however, that these records indicate little ability on the part of the animals to discriminate colors.
Brightnesses Extremely Different for Human Eye Intensities are given in candle meters (c.m.)
NO. 151 NO. 152 SERIES DATE CONDITIONS RIGHT WRONG RIGHT WRONG (GREEN) (RED) (GREEN) (RED)
1 April 26 18 c.m. on left 1800 c.m. on right 11 9 7 13 2 27 Same 16 4 16 4 3 28 Same 20 0 17 3 4 29 Same 19 1 19 1 5 30 Green 18 c.m. Red 18 c.m. 9 1 10 0 6 30 Green 64 c.m. Red 18 c.m. 9 1 8 2 7 May 1 Green 6 c.m. Red 1500 c.m. 7 3 9 1 8 1 Green 4 c.m. Red 1500 c.m. 8 2 7 3 9 2 Both varied from 4 to 1500 c.m. 18 2 18 2 10 3 Green 2 c.m. Red 1800 c.m. 6 4 7 3 11 3 Same 10 0 10 0 12 4 Same 7 3 8 2 13 4 Same 8 2 6 4 14 5 Green 1 c.m. Red 1800 c.m. 19 1 19 1
Filters were now removed. An illumination of 15 c.m. was established on one side and an illumination of 0 on the other side, in order to ascertain whether the mice would choose the brighter box. This was done to test the assumption that the green in the previous tests had always appeared brighter to the mice than did the red, and that in consequence they had chosen the brighter box instead of the green box.