Ramp After-effect


In 1967 Stuart Anstis reported that after adaptation to a spatially uniform field that grows gradually brighter, a subsequently viewed steady grey field appears to grow gradually dimmer. The effect can be seen on the right. After viewing the brightening light for about 20 seconds, use the playback control to pause the movie, and observe the after-effect.
Stuart Anstis considered the ramp after-effect as evidence that the visual system contains neurons which respond selectively to the sign of luminance change over time - brightening or dimming. Adaptation to brightening can selectively reduce the responsiveness of neurons that signal brightening, so the test field appears to grow dimmer. What functions might such neurons serve? Movement of contours across the retina always causes the light received at each retinal position to change over time. For example, a bright bar moving across a dark background causes a transitory brightening at each location it passes over. Change in luminance over time thus provides important information relating to movement, if it is combined with information about spatial contours.
In a later paper, Stuart Anstis reported that adaptation to brightening or dimming lights can actually induce the appearance of motion in static test patterns that contain spatial luminance variation, supporting his contention that the neurons responsible for the ramp after-effect play a role in motion perception. This effect can be observed on the right. After a short time the brightening field is replaced by a test field that contains steady luminance ramps of opposite sign (one is brighter on the left and the other is brighter on the right). Notice that adaptation to the brightening field causes the two ramps apparently to move in opposite directions. Motion after-effects from motionless stimuli present a challenge to theories of neural motion detection. Surprisingly, to date relatively little attention has been paid to the theoretical implications of the ramp after-effect.
Anstis, S. M. (1967). Visual adaptation to gradual change of intensity. Science, 155(3763), 710-712.
Anstis, S. (1990). Motion aftereffects from a motionless stimulus. Perception, 19(3), 301-306.
Arnold, K., & Anstis, S. (1993). Properties of the visual channels that underlie adaptation to gradual change of luminance. Vision Research, 33(1), 47-54.