Watson, Color Vision in Monkeys. 3 



carefully made aud so satisfactory were the results obtained from 

 them that we find the author expressing himself somewhat extra- 

 vagantly as follows: 



"1. There can be no doubt that monkeys perceive colors. 



"2. Two grays having a given degree of difference in bright- 

 ness are not discriminated as well as two colors having an equal 

 diiference in brightness. 



''3. For accurate discrimination of diiference in brightness a 

 difference of about 35 degrees or 9 per, cent of the white constituent 

 of the gray is necessary. 



''4. The monkeys are able to distinguish colors from grays 

 though the brightnesses are the same. 



''5. The male appears to have a preference for bright colors, 

 but blue seems to be discriminated against.^ 



"6. In two instances there w^ere indications of at least a low 

 form of general notion." 



For detailed reasons, which can not be entered into here, the 

 assertion is ventured that the use of colored papers can never give 

 us a satisfactory test of color vision in animals.^ Certainly, the 

 writer has room for "doubt" both in Kinnaman's work and in his 

 own. The fact that there is a high jjercentage of correct choices 

 of the positive color in both investigations cannot be doubted, but 

 that the correct choices were made , upon basis of 'hue' and not 

 that of 'brightness' cannot be decided so easily as Kinnaman sup- 

 poses. It would not be at all ridiculous for one, skeptical of the 

 possibility of testing the color vision of animals, to assert that every 

 discrimination which has been made between two colored papers 

 by an animal could have been made if it had been totally color-blind. 



As a reason for such scepticism, a few of the defects of this method 

 as a whole may be mentioned noAv: 



1. The surfaces of the papers differ greatly, owing to accidents 



^Blue certainly was not discriminated against by tlie animals used by the 

 writer. See Table VI. 



^Tbe committee appointed by the American Psj'cbological Association at the 

 1907 meeting to report upon methods and apparatus for testing vision in 

 animals will take up in its report the defects and advantages of the various 

 ■ methods of testing color vision. 



