16 



K. S. LASHLEY 



TABLE 4 

 Reactions to Red and Green Lights of Estimated Threshold Value 



The second group of tests, made with Chicks D and E gives 

 additional evidence against a reaction to the relative brightness 

 of the stimulus patches. A very intense white light (the image 

 of a Nernst glower directed upon the stimulus patch by a 2 -inch 

 lens of 6-inch focus) was first substituted for the red light, the 

 green light being left at full intensity somewhat diluted by 

 light reflected from the white stimulus patch. Under these 

 conditions Chick E (positive to red) chose — ■ 



White 

 11 



Chick D (positive to green) chose — 



White 

 3 



Green 

 1 



Green 

 13 



The white was then substituted for the green and the red was 

 restored at full energy. The records of the birds were — 



Chick E. 

 Chick D. 



White 

 1 

 4 



Red 

 9 



1 



The intensity of the white light was many times that of the 

 monochromatic so that the brightness relations of the stimulus 

 patches were certainly reversed in the two tests. The prob- 

 ability of reaction to absolute brightness is also reduced by the 

 dilution of the monochromatic lights by light reflected from 

 the white patch. For me this reflected light had greater bright- 

 ness than either of the monochromatic lights. 



To avoid a reaction to secondary criteria given by the shifting 



