Chapter 20 Different spaces and different times for perception and action

Abstract

Separate, but interacting, visual systems have evolved in the primate brain for the perception of objects on the one hand and the control of actions directed at those objects on the other. This 'duplex' account of high-level vision suggests that 'reconstructive' approaches and 'purposive-animate-behaviorist' approaches need not be seen as mutually exclusive, but as complementary in their emphases on different aspects of visual function. Indeed, the limitations of one system are the strengths of the other. Perception (which is mediated by the ventral stream of visual projections in primate cortex) delivers a rich and detailed representation of the world, but does not compute the detailed metrics of the scene with respect to the observer. In contrast, the action system (which depends heavily on dorsal-stream projections) delivers accurate metrical information about an object in the required egocentric coordinates for action, but these computations are fleeting and are for the most part limited to the particular goal object that has been selected. Both systems work together in the production of purposive behavior--one system selects the goal object from the visual array, the other carries out the required metrical computations for the goal-directed action.