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