Perceiving the World and Grasping It: Dissociations Between Conscious and Unconscious Visual Processing

Visual systems. first evolved not to enable organisms to see, but to provide sensory control of their movements. Vision as "sight" is a relative newcomer on the evolutionary landscape, but its emergence has enabled animals to carry out complex cognitive operations on internal representations of the world in which they live. In the more ancient visuomotor systems, there is a basic isomorphism between visual input and motor output. In representational vision, there are many cognitive "buffers" between input and output. Thus, the relationship between what is on the retina and the behavior of the organism cannot be understood without reference to other mental states, including those typically described as "conscious." The duplex nature of vision is reflected in the organization of the visual pathways in the primate cerebral cortex. The dorsal "action" stream projecting from primary visual cortex to the posterior parietal cortex provides. flexible control of more ancient subcortical visuomotor modules for the control of motor acts. The ventral "perceptual" stream projecting from the primary visual cortex to the temporal lobe provides the rich and detailed representation of the world required for cognitive operations. Both streams work together in the production of goal-directed behavior. The ventral stream identifies goals and together with prefrontal cortical areas plans an appropriate action; the dorsal stream (in conjunction with related circuitry in premotor cortex, basal ganglia, and brainstem) programs and controls those actions.