VISUAL PERCEPTION OF THE CHICK 75 



nations left a faint shadow which was regularly interrupted by 

 the flashing stimuli. This resulted in a slight but regular alterna- 

 tion of light and shadow on the side of the electric compartments 

 immediately above the exits. The interruption on each side, of 

 course, depends upon the rate of its respective source. This 

 indicates that the interruption of the flux was the basis of the 

 flicker discrimination. 



It thus appears that the chick readily discriminates, on some 

 basis, at least a one-two flicker difference. These preliminary 

 results convince me that here is a most promising field of investi- 

 gation, especially with birds. Interrupted illuminations seem to 

 have high stimulating value, making it relatively easy to direct 

 the attention of the subject to the movement detail. With such 

 stimuli the amount of aimless wandering seems to be considerably 

 less than that which occurs with size and form stimuli. 



It is hazardous to compare results obtained in this study from 

 spatial and moving stimuli on account of the improvement in 

 technique which clearly occurred during early stages of the inves- 

 tigation. Since flicker perception represents the last stage of the 

 study it is possible, yet doubtful, that indications of increased re- 

 sponsiveness to moving stimuli are due to improvement in experi- 

 mental technique. Possibility of individual differences should not 

 be overlooked because objective data on flicker perception have 

 been obtained from a single subject. Moreover, it is not possible 

 to analyze satisfactorily the visual factors that were operative in 

 the intermittent stimuli which were discriminated. On the other 

 hand, subjective judgments support these preliminary data. It 

 seems probable that we shall find the chick, and possibly the birds, 

 more responsive to movement than to spatial factors. At any 

 rate, these results indicate further possibilities of experimentation 

 in animal behavior which ought to receive consideration. 



