Dissociation of perception and action unmasked by the hollow-face illusion.

It has been suggested that there are two separate visual streams in the human cerebral cortex: a ventral pathway that provides perceptual representations of the world and serves as a platform for cognitive operations, and a dorsal pathway that transforms visual information for the control of motor acts. Evidence for this distinction comes from neuropsychology, neuroimaging, and neurophysiology. There is also evidence from experimental psychology, with normal observers experiencing an illusion-where perception and action can be dissociated, although much of this evidence is controversial. Here, we report an experiment aimed at demonstrating a large dissociation between perception and fast action using the hollow-face illusion, in which a hollow mask looks like a normal convex face. Participants estimated the positions of small targets placed on the actually hollow but apparently normal face and used their fingers to 'flick' the targets off. Despite the presence of a compelling illusion of a normal face, the flicking movements were directed at the real, not the illusory locations of the targets. These results show that the same visual stimulus can have completely opposite effects on conscious perception and visual control of fast action.