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Observation of a movement in the opposite direction when fixating a stationary object, after having looked at a waterfall for some time. This is an example of phenomena that are used to infer the existence of channels in the visual system. It is suggested that there are two opposed directionally sensitive neural channels (or neurons) which are normally in balance for stationary stimuli, but when the activity of one channel is fatigued by prolonged stimulation, the other one becomes the active one. The waterfall after-effect is a special case of motion or movement after-effect (or motion after-image). Syn. waterfall effect; waterfall illusion. See channel; Plateau's spiral.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann