510 ADAPTATIONS TO PHOTIC QUALITY 



Walton, however, has insisted that the rat has color vision. In 1933, 

 he trained rats to large patches of filtered colors, the two members of 

 each pair of stimuli being matched in brightness for the human eye at 

 first. The animals readily learned to discriminate red from green, blue, 

 and yellow, and to tell blue from yellow. Their discriminations of green 

 from blue, and of yellow from green, were not high but were better than 

 chance. When one member of a pair was increased in brightness, the 

 animals continued to make the proper choice. Walton concluded that 

 the rat has hue sensations; but the Watsons had shown that the rat's 

 brightness curve is enormously different from man's, and Walton made 

 insufficient efforts to find a point of matched brightness for any pair of 

 stimuli. With Bomemeier in 1938, Walton used red and blue stimuli and 

 satisfied himself that the rat discriminated them solely on a basis of hue. 

 His animals also discriminated red versus darkness; but, far from the 

 red's being all but invisible to them, they behaved as if they were 'rather 

 sensitive' to it when in a condition of semi-dark-adaptation. 



Walton's methods are not sufficiently different from those of other 

 students to make it at all easy to see why he gets such unique results. 

 Majority opinion seems to be that until his work has been abundantly 

 confirmed, it must be held to conceal some unknown errors of procedure. 



For the house mouse, as for the laboratory rat, the great weight of 

 evidence is negative; yet here again a single investigator has claimed 

 positive results with what seems to be adequate technique. In his classical 

 study of the dancing mouse in 1907, Yerkes reported that the mouse 

 could discriminate between filtered green and blue lights only when they 

 differed greatly in intensity. Green versus red, and blue versus red dis- 

 criminations were easily learned; but when any colored light was replaced 

 by colorless, the mouse went to the less bright of the two stimuli. Red 

 light was only responded to as the brighter of two lights when it was of 

 very high intensity. As in the case of the rat, the spectrum of the mouse 

 appears to be shortened at the long-wave end. 



The preference for dim lights is in interesting contrast to the mouse's 

 strong preference for white and bright-colored papers (as nest-building 

 material), as reported in 1934 by Kolosvary. This worker's animals pre- 

 ferred blue paper to red however, which would be expected from his 

 other results since the invisibility of the redness of red papers would 

 naturally make such papers appear dark to the mouse. 



Hopkins, rejecting the work of Yerkes and the later, also negative, 

 findings of Waugh and Roth, described in 1927 some experiments on 



