waterfall illusion

Quick Reference

A visual illusion of apparent movement created by gazing for a period of time at a fixed point in a waterfall and then looking at a stationary object, which appears to move upwards. It is usually produced in the laboratory by means of an endless belt of horizontal stripes or dots at which a viewer is instructed to stare fixedly. If the belt is stopped after about 30 seconds, the vivid illusion is created that it is drifting backwards, but in a strange manner, appearing to move without changing position. The illusion was first discussed in print by the Greek philosopher Aristotle (384–322 bc) in the Parva Naturalia in the essay On Dreams, although Aristotle did not mention waterfalls: ‘When people turn away from looking at objects in motion, for example rivers, and especially those that flow very rapidly, things really at rest are then seen as moving’ (Chapter 2, Bekker edition, p. 459b). Also called the waterfall effect. See also motion aftereffect. Compare Plateau spiral.

Subjects: Psychology.

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