364 ADAPTATIONS TO SPACE AND MOTION 



as if they were witnessing the real movement. The real and apparent 

 movements were completely interchangeable for them. 



Moreover, Schiller was able to induce negative responses by lengthen- 

 ing or shortening the interval between the presentations of the two white 

 squares. When human observers were experiencing the successive or 

 simultaneous phases of the illusion, the fishes were negative. Within the 

 range of the optimal phase for humans, the fishes responded positively. 

 Schiller concluded that the three phases exist for Phoxinus and for man 

 under identical conditions. This would seem to imply that both species 

 have the same persistence time, at least under the adaptation-conditions 

 of the experiments. 



Mile. Gaffron and Schiller both stress the fact that the fishes have no 

 cerebral cortex, and that therefore they (and man?) must 'see' apparent 

 movement with some lower visual center. Schiller beUeves further that 

 the mechanisms for real- and apparent-movement perception must be 

 one and the same, and suggests that in apparent movement we "see 

 with unstimulated parts of the retina." Since intermediate parts of the 

 retina need not be stimulated in a real movement in order to perceive 

 the movement, Schiller goes so far as to say that it is incorrect to call 

 stroboscopic movement an apparent movement — it is as real as any other, 

 physiologically. But, though the movingness of this phenomenon is per- 

 haps registered in man somewhere below the visual cortex, it is the blurred 

 train of after-images — assuredly registered in the cortex — which puts mov- 

 ingness into the percept of a real movement of our 'medium' category.* 



The identity of persistence times in Phoxinus and man seems to be an 

 accident. In the Siamese fighting-fish, Betta splendens, Beniuc found a 

 much shorter period. He cleverly demonstrated both the biological 

 moment and the existence of complementary colors for this fish in a 

 single experiment. The fishes were trained positive to a gray disc and 

 negative to a slowly revolving disc whose six sectors were alternately of 

 two colors which are complementary for humans, yielding gray when 

 mixed by rapid rotation. 



When the disc rotated at a speed at which its sectors gave the fish 

 130 impressions per second, the fish responded to it as if it were the 

 motionless gray disc. Beniuc found that at 90 impressions per second 



*Pbtzl has described psychiatric cases in which the movingness of real movements was not 

 seen. A moving light was perceived as several lights in a series of positions — for all the 

 world like the appearance of a phi-phenomenon, in its successive phase, to a normal person. 

 It is impossible to say just what part of the normal equipment is lacking in such individuals. 



