What neuroimaging tells us about the division of labour in the visual system

propose that the visual system is able to accomodate two distinct functions: vision for action and vision for perception. These functions are proposed to rely respectively on the dorsal and the ventral streams. This functional dissociation emphasizes the output rather than the input side of the visual analysis. Progress in neuroimaging offers various ways to investigate this model. There is now evidence from studies using positron emission tomography on the study of brain activity in the perception of human movement that the roles of the two pathways are more easily understood when considered from the point of view of the output side of visual processing as suggested by Milner and Goodale. A well established general framework indicates that the visual cortex is organized into two distinct pathways both originating in the primary visual cortex. The ventral stream which reaches the inferotemporal cortex is involved in the identification of objects, whereas the dorsal stream which projects into the parietal cortex is engaged in the visual spatial localization of objects (Ungerleider & Mishkin, 1982). In their book, Milner and Goodale (1995) substantially reinterpreted these functions on the basis of certain neuropsychological dissociations. They postulate that both streams process informatio