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Coordination of what and where in visual attention.
Duncan, J.D.
Perception, 22, 1261-1270.
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Performance often suffers when two visual discriminations must be made concurrently ("divided attention"). In the modular primate visual system, different cortical areas analyze different kinds of visual information. Especially important is a distinction between an occipitoparietal "where?" system, analyzing spatial relations, and an occipitotemporal "what?" system responsible for object recognition. Though such visual subsystems are anatomically parallel, however, their functional relationship in divided attention is unknown. In the present experiments, human subjects made two simultaneous discriminations concerning a brief visual display. If discriminations concerned different objects, they showed strong mutual interference, which was equally severe whether the two were similar (two "what?" or two "where?") or dissimilar (one of each). If "what?" and "where?" discriminations concerned the same object, however, all interference disappeared. Such results suggest that "what?" and "where?" systems are coordinated in visual attention: their separate outputs can be used simultaneously without cost, but only when they concern one object.