Wheels: a new illusion in the perception of rolling objects.

A new illusory effect is described which consists of a conspicuous perceptual overestimation of the speed at which a wheel rolling across an observer's visual field appears to be rotating. Wheels appear to revolve much faster than is compatible with their linear displacement. Experimental verification of the genuineness and magnitude of the effect is reported, along with a discussion of some of the variables upon which it may depend.