l6 :j 8 



I! VMlBI ic IK I 11 l'H\ S|i II i «,Y 



NEl'ROI'HYSIOLOOY III 



von Hoist & Mittelstaedl (505) and Sperry (4:58); 

 but the existence of such corollary discharges remains - 

 conjecture. It is certain, however, that neither 

 pattern nor depth perception can be studied without 

 an appreciation of perception of motion in the en- 

 vironment, of self-produced movement and of the 

 reafferent stimulation that results from the movement 

 of the perceiver himself. 



PERCEPTION OF APPARENT MOTION 



In classical psychophysics, with its assumption of 

 one-to-one 1 elation of stimulus and response, there 

 was no problem of perception of motion. Things were 

 seen to move because their "image" moved over the 

 retina, or felt as moving over the skin because the 

 stimulus did. Attention had to be directed to various 

 forms of motion perception in the absence of a mov- 

 ing object before the psychophysiologic problem of 

 motion could be discovered. There are four main 

 classes of apparent motion, viz. afterimages of motion, 

 induced motions, autokinetic effects and, most im- 

 portantly, stroboscopic motion. Each of these four 

 sets of phenomena has been considered an illusion 

 of motion, but the perceptions engendered are in- 

 discriminable for the observer from 'real' motion. 

 The physiologic basis of each of these apparent 

 motions, and of true motion, are likely to be the same. 



. Ifterimages of Motion 



Various aftereffects of seen and felt motion were 

 known to Purkinje (392) (who also described illusory 

 motions following vestibular stimulation). The most 

 familiar laboratory demonstrations are the waterfall 

 illusion and the rotating spiral. In the former, a 

 horizontally striped surface is moved vertically 

 upward or downward in the observer's frontal plane. 

 The pattern induces apparent motion, in reverse 

 direction, in its (stationary) surroundings; when the 

 pattern itself is slopped, there appears .m afterimage 

 11I movemenl th.it is negative, i.e. opposite in direc- 

 tion in the previous (objective) movement of the pat- 

 tern (545). In demonstrating the spiral aftereffect, 

 ..in rotates a disk with .1 spiral pattern in front of the 

 observer. During rotation at moderate speeds, the 



spiral pattern seems to expand or Contract, and these 

 Complex motions are transposed, temporarily, onto 



stationary patterns to which the observer shifis his 



The device, usually called Plateau's spiral 



after its inventor (383) also induces various subjective 



colors during rotation. Stationary patterns with high 



no. 29. Stationary visual pattern with high redundancy 

 which induces moving images. The radiating lines produce 

 shimmering effects on prolonged inspection and aftereffects of 

 wavy lines moving in circles at right angles to the stimulus 

 lines. This complementary aftereffect (following 10 see. in- 

 spection of the pattern) can be projected on a gray surface 

 where it is seen to rotate clockwise I predominantly I or counter- 

 clockwise. There is no simple correlation with handedness. 

 [From MacKay (3311 



redundancy, as those studied by MacKay (336), 

 likewise produce apparent motion during and after 

 inspection (see fig. 29). These motions are comple- 

 mentary, i.e. their direction is at right angles to tin- 

 static contours in the stimulus array. 



I ml lu id Motion 



Induced motion is familiar to anyone who has 



seen the moon 'race' through interrupted clouds. 

 Here the true motion of the surround (the clouds) 



is assigned to the (stationary) moon. Analogous 

 phenomena can be obtained in the laboratory e.g 

 Duncker (no)] when- .1 luminous rectangle and a 

 luminous dot within it can lie made to move, sepa- 

 rately or together, in .m otherw ise dark room Moving 

 the rectangle ordinarily leads to perception o) motion 

 for the enclosed dot; moving the rectangle and the 

 doi over a given distance, but in opposite directions, 

 leads to perceived motion of the dot within a (sub- 

 jectively) stationary rectangle over the combined 

 distance, etc. 



More complex motions can be generated 1>\ a de- 

 vice constructed by Johansson ' -■ 1 1 , -' |ji which 



permits analysis of resultant motion perception when 





