Illusion of rotary motion reversal in a sphere is facilitated by increased rotational speed

A rotating sphere with an artistically painted surface may appear to reverse its direction of rotation and at the same time reverse its curvature from convex to concave (the Termes Illusion). This study tested the effects of 4 rotational speeds (stationary, 1 rpm, 2.5 rpm, and 3.75 rpm) in producing this illusion. Analysis indicated that the number and duration of reversals increased with speed of rotation and successive viewing sessions. Latency of reversal decreased with successive sessions. Explanations in terms of satiation theory, learning theory, instructions, and perceptual bias were discussed.