Illusions of time and extent when the Müller-Lyer figure moves in an aperture.

Abstract

Following informal observations, three experiments confirmed that the Müller-Lyer illusion occurs when the composite figure consisting of angles-outward and angles-inward components is progressively exposed in a narrow slit, as in the Zöllner-Parks demonstrations. The illusion of extent was consistent over subjects and about half that with the figure stationary and moving in full view. The experiments showed also that there is a parallel illusion of time, with one of the two equal extents taking apparently longer than the other to pass the slit. The illusion of extent was enhanced or canceled by manipulating the relative velocities of the two components and, therefore, the time taken by them to pass the slit. It is argued that time of exposure in the slit serves as the reference for extent. The illusions of time and extent are attributed to a perceptual compromise between the time taken by an extent to pass the aperture and that of the component itself to do so. The role of time in perceived extent and its possible involvement in visual scanning are considered.