Department of Psychology
Colloquium
John P. Zubek Memorial Lecture
““Acting without thinking: When do visually-guided actions escape conscious control?”
Melvyn A. Goodale
Centre for Brain and Mind, University of Western Ontario
Abstract
Human beings are capable of reaching out and grasping objects with great accuracy and precision – and vision plays a critical role in the control of this ability. The visual guidance of these skilled movements, however, requires transformations of incoming visual information that are quite different from those required for visual perception. For us to grasp an object successfully, our brain must compute the actual (absolute) size of the goal object, and its orientation and position with respect to our hand and fingers – and must ignore the relative size or distance of the object with respect to other elements in the visual array. These differences in the required computations have led to the emergence of dedicated visuomotor modules in the dorsal visual stream 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 on-line control systems in the dorsal stream and associated motor areas. But even though the dorsal stream may allow an observer to reach out and grasp objects with exquisite ease, it is trapped in the present. By itself, the dorsal stream can deal only with objects that are visible when the action is being programmed. The ventral stream, however, allows an observer to escape the present and bring to bear information from the past – including information about the function of objects, their intrinsic properties, and their location with reference to other objects in the world. Ultimately then, both streams contribute to the production of goal-directed actions.
Friday, September 25, 2009
3:00 pm – 4:30 pm in 343 Drake Centre
Wine and Cheese to follow in Room 543, University Centre
Everyone welcome!
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