Eye movements and decrement in the Muller-Lyer illusion.

Abstract

Two experiments are reported in which a decrement in the magnitude of the Muller-Lyer illusion was found if free eye movements were allowed. Little or no decrement was obtained if Ss fixated one point of the figure during inspection. In one experiment eye movements were recorded. Saccades across the perceptually short side of the Muller-Lyer figure were found to be shorter than across the perceptually long side. After inspection with free eye movements, the saccades became more nearly equal on the two sides. Such changes in eye movements did not occur if Ss fixated one point during the inspection period. The data are interpreted in terms of perception being determined by the efferent readiness activated by visual input. According to this interpretation, the decrement in the magnitude of the illusion results from recalibration of the efferent programs.