THE PERCEPTION OF SPACE 



703 



a bird such as the gannet, Sula hassana, which is provided only with 

 laterally directed central foveae, and feeds by diving for fish. Portier 

 (1923) found that if he fastened fish to floating pieces of wood the 

 birds dived for them with great directional accuracy but, misjudging 

 the distance, impaled their open beaks in the wood, a lack of precision 

 which would bear no penalty were the fish swimming freely in the 

 yielding water. 



Fig. 



848. — Visual Illusions with Cikculak Figures used in Training 



or Fish. 



The black circle surrounded by small circles appears larger than a circle 

 of the same size surrounded by larger circles (after Herter, 1930). 



It is interesting that the visual judgment of birds is subject to 

 the same illusions as ours, showing its basic similarity on the perceptual 

 level. Thus Revesz (192-4-25) showed that hens and chicks trained to 

 peck for the smaller of two figures (rectangles, squares, circles, etc.) 

 when presented with two drawings illustrating the Jastrow illusion, 

 pecked preferentially from the upper (Fig. 849). Similarly in 

 experiments with doves (Warden and Baar, 1929) and with chicks 



Gannet 



Fig. 



849. — The " Jastrow " Illu- 

 sion. 



Fig. 



850. — The " Muller-Lyer 

 Illusion. 



(Winslow, 1933) it has been shown that their response to the Muller- 

 Lyer illusion was comparable with that of the human being (Fig. 850). 

 It would seem, therefore, that the form as a whole impresses itself on 

 the consciousness of the bird, thus providing evidence for the Gestalt 

 theory of perception. The rapid assessment and recognition of a 

 territory of the homing bird seems to be another example of the same 

 process (Thorpe, 1944 ; von Haartmami, 1949 ; Fabricius, 1951 ; 

 Wilkinson, 1952 ; and others) ; so also is the curious phenomenon of 



