360 ADAPTATIONS TO SPACE AND MOTION 



lights at zero distance would fuse into a single steady light. Many work- 

 ers have drawn the conclusion that our mechanism for apparent-move- 

 ment perception may be the only one we have with which to perceive 

 real movement. The 'laws of Korte', which express the interrelations of 

 the time interval, spatial separation, and intensity of stimuli for the 

 optimal ^-phenomenon, also hold very well for the perception of real 

 movements. That is, if a third light of the same intensity is really moved, 

 within the same time, parallel to the two lights used for the ^-phenome- 

 non, the real and apparent movements are seen alike. Speeded up to the 

 short interval of the simultaneous phase, the real movement becomes a 

 line of light without direction. Slowed down to simulate the successive 

 phase, the really-moving light loses its blur of movingness. 



Another common belief is that the movement of the movies is solely 

 created by projection at the speed of the critical frequency. Since both 

 the elimination of flicker and the optimal ^-phenomenon depend upon 

 this speed of projection, the conclusion that they are identical seems plaus- 

 ible. But it is easily possible to separate the conditions for the optimal 

 (^-phenomenon from the conditions for the elimination of flicker. Sup- 

 pose we print every twentieth frame of the negative on successive frames 

 of a positive film, and project it at the usual speed. There will be no 

 flicker — but the spatial separations in the images will be so great that 

 only jerky movements or successively new positions, with no smooth 

 movingness, will be seen. 



We need not produce such a film intentionally. It happened as an 

 unfortunate accident in the making of Walt Disney's Snow-White and 

 the Seven Dwarfs. The slow movements of the human characters seemed 

 unpleasantly jerky on the screen. The faster movements of the little 

 animals were just as jerky, but were quite acceptable to the onlooker; for 

 when we watch a real chipmunk skip about we do not actually see him 

 when he is in motion. Human movements are so much slower that the 

 loss of movingness, due to too great spatial separation of the successive 

 drawings of the animation, was 'unnatural'. Disney pushed the ^-phe- 

 nomenon a little too far; and to obtain any more satisfactory illusion of 

 human movements in animated cartoons, it is absolutely necessary to 

 draw just as many intermediate stages in each movement as there would 

 be on a motion-picture film of an actual human movement of the same 

 speed. While watching any ordinary movie, one can hold a finger in 

 front of the eyes and sweep it across the angle subtended by the screen 

 much faster than an object of the same apparent size would ever move 



