| MadSci Network: Neuroscience |
Hmmmm, this is an interesting question. I'll try to deal with it
directly before I get to the peripheral issues. As far as I can tell, if a
person develops normal binocular vision, then it will not matter which eye
is presented what information. Duke-Elder, in his 'System of
Ophthalmology,' refers to experiments in which one eye is trained in any
given monocular visual task, and then is asked to repeat the task
monocularly with the other eye. In humans, there is an instant transfer of
ability from one eye to the other, i.e. the other eye performs the task
equally well as the trained eye on the first try.
This experiment suggests that there is a transfer of information from
the parts of the cortex that receive input from one eye and the other.
Since about 50% of the nerve fibers from one retina cross to the
contraleteral visual cortex, this isn't surprising. For an interesting and
very recent reference on interhemispherical transfer of visual information,
see the current issue of Science magazine.
Another interesting experiment by Leat and Woodhouse ('Perception,'
1984; vol. 13(3):351-357) shows that not only do people have a dominant
eye, but we have a dominant visual half of the cortex.
Unfortunately, I can't give you a definitive answer to your question,
but I doubt that in a person who has normal binocular vision that there is
a significant difference between visual abilities in the dominant and
non-dominant eyes. Of course, if you really wanted to know, you
could always do the experiment yourself...
The big question, at least in my mind, would be how these visual
systems you speak of would work. When each eye is presented a different
stimulus, as in ocular dominance experiments, the phenomenon of binocular
rivalry arises. Binocular rivalry means that when you sense two different
images on your different retinas, you perceive both, but in alternating
fashion. Your brain suppresses one of the images automatically. In
younger people with strabismus in which their eyes don't line up, their
brains begin to ignore one of the images it receives, and eventually, their
ability to see out of the ignored eye deteriorates. This corresponds to
degeneration of areas in the visual cortex which receive input from the
ignored eye. It seems to me that we are wired to concentrate on one thing
at a time.
There are other possible problems to be surmounted. For instance, the
lenses of both eyes are wired to accommodate together. If you were to
attempt to look at two different things at two different distances, one or
both of them would be out of focus as your eyes struggled to focus on both
at the same time. Also, the muscles of both eyes are neurologically
'yolked,' i.e. they are wired to move in the same direction at the same
time. Try moving your eyes in two different directions at once. Of
course, you can move them both toward each other, but that's just so you
can look at a very close object. The eyes won't go in opposite directions
in any other case.
This isn't to say that such a system to see two things at once may not
someday be invented. I just think it might be a long time before one is.
Tom Stickel
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