Separate visual systems for perception and action: a framework for understanding cortical visual impairment

The visual control of skilled goal-directed movements requires transformations of incoming visual information that are quite different from those required for visual perception. These differences in the required computations have led to the emergence of dedicated visuomotor modules in the dorsal visual stream of the cerebral cortex that are quite separate from the networks in the ventral visual stream that mediate our conscious perception of the world. Although the identification and selection of goal objects and an appropriate course of action depends on the perceptual machinery of the ventral stream and associated cognitive modules in the temporal and frontal lobes, the execution of the subsequent goal-directed action is mediated by dedicated online control systems in the dorsal stream and associated motor areas. This functional distinction can provide a useful framework for interpreting the range of perceptual and visuomotor deficits observed in children with cortical visual impairment.