Discusses how the human brain processes vision. How different brain
areas tackle particular aspects of the job; Comments from Carol Colby, a
cognitive neuroscientist at the National Eye Institute; How the task of
tracking spatial locations is divided up in the brain; Comparison of
vision to a multiplex movie theater where each screen shows a slightly
different version of the same film.
By
PT Staff, published on May 01, 1995
Experience suggests that the things we see are somehow projected
onto asingle mental movie screen. But vision is more like a multiplex
theater where each screen shows a slightly different version of the same
flick.
That's because vision is a modular process: Different brain areas
tackle particular aspects of the job. Some regions, for example,
specialize in detecting moving objects, a division of labor vividly
demonstrated by certain stroke victims who can see shapes and colors but
have trouble seeing objects in motion.
Similarly, the task of tracking spatial locations may also be
divvied up in the brain, reports Carol Colby, Ph.D., a cognitive
neuroscientist at the National Eye Institute. An object's location in
three-dimensional space seems to be represented many times over in the
cerebral cortex, with specific regions keeping tabs on where objects are
in relationship to specific parts of our anatomy.
For example, circuits in the parietal lobe--a region in the upper
rear of our brain that concerns itself with sensory information--monitor
the location of objects relative to our head; they signal their neuronal
colleagues if we suddenly need to duck. Another brain area helps perceive
where things are in relationship to our mouth, allowing us to bite into a
hot dog without chomping on air.
"We have the sense that we see the world directly," observes Colby.
But vision is a furiously active process in which our brain constructs
reality for us. Interpreting the patterns of light that strike our retina
requires integrating signals from billions of disparate neurons. Given
the complexity of the job, she says, "it is remarkable how easily we do
this."
Images seem to be represented in the brains of rhesus monkeys in as
many as 20 places--and our own brains may contain even more sites.
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