The effect of optically induced blur on the magnitude of the Mueller-Lyer illusion

Abstract

The magnitude of the Mueller-Lyerillusion was measured under conditions of high and low image blur. Blur was manipulated by altering the focus of an image projected on a screen. Elusion magnitude increased under high blur conditions. This supports the theory that blur-inducing optical imperfections of the eye are partially responsible for illusory effects in figures with converging lines. The data also indicate the importance of testing the acuity of observers in such experiments, since poor refraction can result in artifactual overestimation of illusion magnitude. © 1976, The Psychonomic Society, Inc.. All rights reserved.