VISUAL PERCEPTION OF THE CHICK 



15 



serving as the discriminable factor. The conditions of control 

 leave the rectangular tunnel constant but wholly change, if not 

 destroy, the perceptibility of the environment. 



That the animals could not see the environment is attested by the fact that they 

 were frequently observed to walk bHndly into the confining walls. Not all of the 

 time was the environment "darkened," but the control tests were always made to 

 determine whether, among other factors, setting was a factor in discrimination. 



Figure 1, as presented by Hunter, does not accurately illus- 

 trate the condition of the stimulus areas. With the intro- 

 duction of a screen as a means of control between the general 

 illumination and the electric boxes and with the reduction of 

 the intensity of the source lights, a similar condition to that 

 illustrated in figure 2 appears. In the compartment where the 

 triangle appears, the source light fails to illuminate the corners 



Fig. 1. 

 Reprinted from Jour. Animal BeJmvior, vol. 3, no. 5, p. 331. 



of the tunnel, and so the perceptible portion of the setting 

 changes to a sort of circular form as in diagram 1. About the 

 circular stimulus, the visible setting is more nearly a perfect 

 circle as is shown in diagram 2. Even if my apparatus offered 

 a possibility of pattern discrimination, my plan of control 

 (2 : p. 98) would have made so variable the patterns confronting 

 the animal that they never could have served as a basis of 

 discrimination. 



Hunter has apparently overlooked one of the essential fea- 

 tures of the apparatus used in my study. The dark-room ap- 

 paratus allows the experimenter to control the visibility of sur- 

 roundings by means of artificial illumination. His criticism 



