The ebbinghaus illusion affects visual size perception but not pointing movement

Ebbinghaus illusion is commonly used as an example of a visual size-contrast effect. The aim of present study was to examine the effects of visual illusion performance on pointing movements. Twenty healthy subjects performed two pointing movement experiments with different visual illusion conditions. Central circular targets of five different sizes were presented on a large semitransparent screen. In experiment 1, subjects were asked to look at the visual targets first and adjust the size of the right central circle to match the left central circle. Next, subjects were asked to point to the right central circle as quickly and as accurately as possible. In experiment 2, all subjects were asked only to point to the right central circle in the same manner as in experiment 1 but without the previous size adjustment. The findings of the present study suggest that the Ebbinghaus illusion affects visual size perception but does not affect pointing movements. This result suggests that visual size illusion changes only the perceived size of visual stimuli during the movement-planning period but not online control processes.