MadSci Network: Neuroscience

Re: Do people respond more accurately when info is given to their dominant eye

Date: Mon Aug 17 16:24:25 1998
Posted By: Tom Stickel, Grad student, Optometry, Indiana University School of Optometry
Area of science: Neuroscience
ID: 899066858.Ns

     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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