Prof. Melvyn A Goodale

时间： 2007-09-07 15:00 - 17:00

地点： Room 103 of Department of Psychology

Visual systems first evolved not to enable animals to see, but to provide distal 
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 representations of the world. 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, in this system, the relationship between what 
is on the retina and the behaviour 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.
This might sound rather like Cartesian dualism—the existence of a conscious 
mind separate from a reflexive machine. But the division of labour between the 
two streams has nothing to do with the kind of dualism that Descartes 
proposed. Although the two kinds of visual processing are separate, both are 
embodied in the hardware of the brain. Moreover, there is a complex but 
seamless interaction between the ventral and the dorsal streams in the 
production of adaptive behavior. The selection of appropriate goal objects 
depends on the perceptual machinery of the ventral stream, while the 
execution of a goal-directed action is mediated by dedicated on-line control 
systems in the dorsal stream and associated motor areas. Ultimately then, 
both streams contribute to the production of goal-directed actions.

2007-09-07

2007-09-07