REACTIONS OF CHICKS TO OPTICAL STIMULI 295 



(2) Chicks exhibit a qualitatively determined preference, such 

 as is apparent in some other animals. 



Brightness was found to be a controlling factor in the re- 

 sponses to optical stimuli. 



All four chicks after brief training formed the habit of select- 

 ing without error one of two colors at the brightness-indifference 

 point. 



This selective reaction was not determined by red or blue of 

 particular brightness values; neither was it determined by the 

 relative brightness of the two stimuli. 



Thus seemed verified a conclusion of our earlier work, namely, 

 that quality as well as quantity of the optical stimulus played a 

 determining part in the reactions of these animals. 



Positive reaction to a given stimulus as indicated in a table 

 of reactions did not necessarily imply specific reaction to that 

 stimulus. It sometimes meant merely a specific rejection of the 

 opposing stimulus. 



A chick learned to discriminate two optical stimuli on the 

 basis of difference in form. 



A chick learned to discriminate two optical stimuli on the 

 basis of difference in size. 



