Pantomimed actions may be controlled by the ventral visual stream

Several studies have demonstrated that while perceptual judgements of objec t size can be biased by visual illusions, actions remain more closely scale d to true object properties. This dissociation is often cited in support of a two-stream model of visual processing, in which visual perception is tho ught to be mediated by a ventral stream, while goal-directed actions are co ntrolled by a dorsal stream. Evidence suggests that pantomimed actions (i.e ., actions directed toward remembered targets) are controlled differently t o natural actions; indeed, it has been proposed that pantomimed actions are mediated by the ventral rather than the dorsal stream. To test this hypoth esis, we examined the effect of a visual size illusion (a variation of the Muller-Lyer figure) on manual aperture formation during natural and pantomi med prehension (i.e., action) and aperture scaling (i.e., perception). As f ound in earlier studies, mean peak aperture (MPA) was significantly affecte d by the illusion in the perception task but not the natural action task. I n the pantomime condition, action and perception were equally affected by t he illusion as reflected by MPA. These results provide support for the hypo thesis that pantomimed actions are mediated by the ventral visual processin g stream, while natural actions depend on the dorsal stream.