The Sense of Sight: Color Vision 143 



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 assume 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 de- 

 scription of the experimental conditions. In planning the 

 experiments I assumed neither likeness nor difference be- 

 tween 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 substitution of 

 dark blue for light blue, nor the replacement of the orange 

 by red or dark blue rendered correct choice impossible, al- 

 though certain of the combinations did render choice ex- 

 tremely 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 con- 

 tinued 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. 



