|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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