The Motion Aftereffect

The aftereffect of motion is one of the oldest known illusions. It refers to the illusory motion of a stationary scene after some time of adaptation to real motion. While it is still unknown whether this adaptation effect has any functional value, it surely has served well as a tool to investigate the functional organization of the visual system. In this chapter some of the classic findings are discussed. More recent work using complex stimuli, attentional modulation, higher order motion, as well as modern neuro-imaging techniques has provided vision scientists with surprising new insights. Discussion of the related concepts of motion perception, motion transparency, and interocular transfer are included.

Adaptation-induced blindness is orientation-tuned and monocular

We examined the recently discovered phenomenon of Adaptation-Induced Blindness (AIB), in which highly visible gratings with gradual onset profiles become invisible after exposure to a rapidly flickering grating, even at very high contrasts. Using very similar stimuli to those in the original AIB experiment, we replicated the original effect across multiple contrast levels, with observers at chance in detecting the gradual onset stimuli at all contrasts. Then, using full-contrast target stimuli with either abrupt or gradual onsets, we tested both the orientation tuning and interocular transfer of AIB. If, as the original authors suggested, AIB were a high-level (perhaps parietally mediated) effect resulting from the ‘gating’ of awareness, we would not expect the effects of AIB to be tuned to the adapting orientation, and the effect should transfer interocularly. Instead, we find that AIB (which was present only for the gradual onset target stimuli) is both tightly orientation-tuned and shows absolutely no interocular transfer, suggesting a very early cortical locus.