ABSTRACT
This chapter describes historic evidence for a motor theory explanation of visual illusions and new insights into their cause, like the compelling aspects of the length of wings on the familiar Mueller-Lyer illusion. Van Biervliet and Binet, Lipps, and Judd, each separately proposed that the Mueller-Lyer illusion could be explained by the fact that the eyes tend to be drawn outward into the wings of the perceptually longer segment of the figure causing an inappropriately long eye movement. There is a version of a motor theory of visual illusions, which might be called the underground theory. The chapter measures eye movements during the occurrence of that perceptual distortion. It examines an experiment which sought to see if the magnitude of the distortion varied as the distance between the extraneous stimulus and the target varied. The experiment indicates that one can predict a set of perceptual distortions on the basis of knowledge of some simple biases in the eye movement system.
