288 FREDERICK S. BREED 



brightness for the chicks, provided brightness alone was the 

 determining factor in the preference. The readiness, however, 

 with which the chicks came to discriminate these two stimuli leads 

 one to suspect that the basis of the discrimination was not differ- 

 ence in brightness. But this result alone is not proof conclusive 

 that color was a factor. A point of brightness indifference may not 

 mean brightness equality, nor need brightness equality for the 

 chick in advance of training mean brightness equality after 

 training. The selective reaction might therefore have been based 

 on difference in brightness. But the evidence that color was a 

 factor in these reactions does not rest on the fact alone that the 

 indifference stimuli were discriminated. The fact that blue of 

 different brightness value from that used in the training was 

 rejected consistently when appearing with red that was not the 

 same in brightness as the original red, ruled out the probability 

 of specific reaction to specific brightness values. And more 

 important still was control test 5. When red was increased 

 in brightness from 70 to 10 and the accompanying blue de- 

 creased from 10 to 100, blue was rejected. When red was 

 decreased from 70 to 100 and used with blue 10, blue was 

 again rejected. Alternations of these combinations failed to 

 interrupt the specific rejection of blue. It should be borne in 

 mind that red 10 was brighter than blue 100 both for the chick 

 (see preference test C) and the human ; and red 100 was less bright 

 than blue 10 both for the chick (see preference test F) and the 

 human. Finally, in the control test on white-blue, the rejec- 

 tion of blue continued perfectly when white was much brighter 

 and when it was much less bright than blue. Thus it seems 

 almost certain that the quality of the stimulus as well as quantity 

 played a determining part in the reactions of these animals. 



An attempt was made to photometer the stimuli with a 

 Lummer-Brodhun photometer and a Hefner amyl acetate lamp, 

 but without success, primarily on account of the very low inten- 

 sities of the weaker stimuli. But even had the intensities of the 

 colored lights been sufficiently high for examination by this 

 method, limited progress would have been made toward an 

 objective measurement of the color values, for this method 

 depends upon a human judgment such as we have already given. 

 Radiometry is the hope of the experimenter in this difficulty. 



