In a series of theoretical articles, my colleague, David Milner, and I have proposed that separate, but interacting visual systems, have evolved 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. Evidence from both humans and monkeys has shown that this distinction between vision for perception and vision for action is reflected in the organization of the visual pathways in primate cerebral cortex. Two broad "streams" of projections from primary visual cortex have been identified: a ventral stream projecting to the inferotemporal cortex and a dorsal stream projecting to the posterior parietal cortex. Both streams process information about the structure of objects and about their spatial locations – and both are subject to the modulatory influences of attention. Each stream, however, uses this visual information in different ways. The ventral stream transforms the visual information into perceptual representations that embody the enduring characteristics of objects and their relations. Such representations enable us to identify objects, to attach meaning and significance to them, and to establish their causal relations – operations that are essential for accumulating knowledge about the world. In contrast, the transformations carried out by the dorsal stream deal with moment-to-moment information about the location and disposition of objects with respect to the effector being used and thereby mediate the visual control of skilled actions directed at those objects. Both streams work together in the production of adaptive behavior. The selection of appropriate goal objects and the action to be performed depends on the perceptual machinery of the ventral stream, but the execution of a goal-directed action is carried out by dedicated on-line control systems in the dorsal stream.
Milner, A. D. & Goodale, M.A. (1995). The Visual Brain in Action. Oxford: Oxford University Press, 248 pp. (paperback 1996).
Goodale, M.A. & Milner, M.A. (2004). Sight Unseen: An Exploration of Conscious and Unconscious Vision. Oxford: Oxford University Press, 140 pp.
A precis of The Visual Brain in Action is available in Psyche, a web-based journal.
See also: Goodale, M.A. & Humphrey, G.K. (1998). The objects of action and perception. Cognition, 67, 179-205. Download pdf