The Spinning Ellipse Speed Illusion

The Spinning Ellipse Speed Illusion is an illusion of perceived speed in which a low-aspect ratio “fat” ellipse will appear to rotate more slowly than a higher-aspect ratio “skinny” ellipse that is rotating at the same speed. This illusory percept can be observed when the ellipses are defined by luminance, color, relative motion, and dotted contours and across a wide range of rotational speeds and eccentricities. The illusion is not limited to rotating ellipses and can be observed with different-shaped contours as well. The Spinning Ellipse Speed Illusion illustrates that the perceived speed of a rotating object depends in part on the form and form features of the object. Objects without characteristic form features such as regions of high or discontinuous contour curvature will appear to rotate more slowly than objects that have these features.