Effects of Voluntary Smooth Pursuit upon the Illusory “Snake Rotation”

Abstract

In order to examine how the voluntary smooth pursuit eye movement and other factors, such as retinal slip, which is caused by stimulus movement, affect the illusory snake rotation (Kitaoka, 2005), we conduced three experiments in which observer voluntarily pursuit a moving fixation point. Results of the experiments showed that the smooth pursuit, which is larger than 5.0 deg, facilitates the illusory rotation. However, because the afterimage could generate the substantial illusory rotation, the eye movement, or retinal slip which is caused by stimulus or eye movement, is not the necessary to obtain the illusory rotation. Based upon the results of the present study, we proposed an observation method that would enable to obtain a vivid illusory rotation even for the observer who had difficulty to obtain the illusory rotation in viewing the category of the Fraser–Wilcox illusion with the normal observation.