ABSTRACT
Following inspection of a slowly rotating disc, a stationary test disc appears to rotate in the opposite direction. Also, following adaptation to a light that grows gradually brighter (or dimmer), a steady test light appears to be growing gradually dimmer (or brighter). These aftereffects are probably caused by adaptation of neural channels sensitive to motion and to gradual luminance change, respectively. The nature and physiological site of these aftereffects was investigated. It was found that motion aftereffects could be made contingent on color, intensity and pattern.
Other studies explored spatial and temporal interactions between colored patterns. A grey spot on a green background looked faintly pink; but after prolonged fixation its afterimage was a brilliant green. Where did the green come from? We found that it had two independent sources; (1) the apparent pink induced into the adapting spot by simultaneous contrast led to a green afterimage, and (2) the pink afterimage of the surround spatially induced an apparent green into the spot's afterimage.
We also examined the spatio-temporal interactions between a pair of similar, overlapping patterns which were exposed in rapid succession to give apparent motion, like two successive frames of a movie. We asked how similar the successive pictures must be in order to give apparent motion. We found that the visual system could detect local, point-by-point correlations between the pictures to give local apparent motion. More subtle global correlations could also give rise to apparent motion, by means of a second, long-range perceptual mechanism. Various new illusions of motion illustrate these findings.
