Tracking the decay of the after-effect of seen rotary movement.

Abstract

It is not certain whether the after-effect of seen movement should be classified as a figural after-effect. Smith (1945, 1952) assumes that it should, and criticises the Koehler-Wallach and Osgood-Heyer theories of figural after-effects because they do not predict the movement after-effect. According both to the physiological theory hinted at by Sutherland (1961) and to the psychophysical theory proposed by Taylor ( 1962 ) , the movemenc after-effect should behave in the same way as static f i g ~ ~ r a l fter-effects. On the other hand, Day, et al. (1959) conclude thac the movemenc after-effect may nor behave in the same way as the static figural after-effects. In making their generalizations, however, Day, et dl . did not take into account many Japanese studies on figural aftereffects, for example, those of Ikeda and Obonai (1953a; 1953b; 1955a; 1955b), Nozawa (1953), Oyama (1953; 1956), Suro and Ikeda (1957). The Japanese studies yield certain generalizations at variance with the usual Western description of the time course of figural after-effects. The apparent contradiction between them and the Western description has been shown to be due to misinterpretation of the Western data (Taylor, 1962). For inspection periods longer than 100 msec., the amount of after-effect immediately following the end of the inspeccion period is independent of the length of the inspeccion period. For shorter inspection periods, the immediate after-effect increases with inspeccion time. According to the psychophysical theory (Taylor, 1962) the critical period of 100 msec. represents the time over which acuity continues to increase. So long as acuity increases with inspection time, so should the immediate after-effect. For inspection periods longer than 1 sec., the decay of the after-effect is exponential, with a time constant proportional to the square root of the inspection time. The decay has not been studied for shorter inspection periods, but according to the psychophysical theory the square root law should hold down to an inspection time of 100 msec. The Western idea that the amount of immediate after-effect increases with inspection time up to as much as 90 sec. is due to the fact thac the determination of the after-effect was delayed by 6 to 8 sec. in the two Western studies chat have attempted to invescigace the question (Gibson & Radner, 1937; Hammer, 1949). A further generalization, in which Japanese and Western descriptions