Pantomimed actions may be controlled by the ventral visual stream

Several studies have demonstrated that while perceptual judgements of object size can be biased by visual illusions, actions remain more closely scaled to true object properties. This dissociation is often cited in support of a two-stream model of visual processing, in which visual perception is thought to be mediated by a ventral stream, while goal-directed actions are controlled by a dorsal stream. Evidence suggests that pantomimed actions (i.e., actions directed toward remembered targets) are controlled differently to natural actions; indeed, it has been proposed that pantomimed actions are mediated by the ventral rather than the dorsal stream. To test this hypothesis, we examined the effect of a visual size illusion (a variation of the Müller-Lyer figure) on manual aperture formation during natural and pantomimed prehension (i.e., action) and aperture scaling (i.e., perception). As found in earlier studies, mean peak aperture (MPA) was significantly affected by the illusion in the perception task but not the natural action task. In the pantomime condition, action and perception were equally affected by the illusion as reflected by MPA. These results provide support for the hypothesis that pantomimed actions are mediated by the ventral visual processing stream, while natural actions depend on the dorsal stream.