JOURNAL OF ANIMAL BEHAVIOR 



Vol. 2 MAY-JUNE, 1912. No. 3 



EXPERIMENTS ON THE BRIGHTNESS VALUE OF RED 

 FOR THE LIGHT-ADAPTED EYE OF THE RABBIT 



M. F. WASHBURN AND EDWINA ABBOTT 

 From the Psychological Laboratory of Vassar College 



I. METHOD 



The most fundamental source of error in experiments on color 

 discrimination in animals lies in the possibility that the animals 

 tested, while they discriminate successfully between objects which 

 appear to the human eye of different colors, are in reality seeing 

 the colors as different shades of gray, which would be the case 

 with a color-blind human being. It used to be considered a 

 sufficient precaution against this possibility if the color used were 

 matched with the gray that a color-blind human being would see 

 in its place, and if it were then shown that the animal tested was 

 able to distinguish between the color and its equivalent bright- 

 ness to the human eye. The work of Yerkes on the dancing 

 mouse ! and that of Watson on the color-sense of the monkey 2 

 have made us realize, however, that the brightness value of a 

 color to the eye of an animal may possibly be quite different 

 from its brightness value to the human eye, so that the animal 

 may successfully discriminate between a color and its equivalent 

 gray to the human eye and still see the color merely as a gray. 

 For the same reason, it is no longer sufficient proof of color vision 

 to show that an animal's choice of a given color is unaffected 

 by such wide variations in its saturation as would to the human 

 color-blind subject cause great differences in the grays seen: 

 though a very dark red and a very light red are equally chosen 

 when presented with a medium green, it is possible that to the 

 eye of the animal even the light red may look darker than the 

 green, so that the discrimination may be based on brightness 

 alone. Evidently, an important step in the investigation of 

 color vision in an animal is to find the brightness equivalent of 

 a given color to the eye of that animal. If it proves to be the 



1 Yerkes, R. M. The Dancing' Mouse. New York. 1907. 



2 Watson, J. B. Some Experiments Bearing Upon Color Vision in Monkeys. 

 Jour. Comp. New. and Psych., vol. 19, pp. 1-28. 1909. 



