Dominant myth?

By Bob Fancher

Scientists don't seem to care about dominant eyes. Maybe there's a reason.

Something happens-that's one thing. Why it happens, and what it amounts to, are different things entirely. People easily misinterpret obvious facts-like that lipstick on your collar after the office Christmas party.

I suspect "the dominant eye" falls into that category. The phenomenon has been known for several hundred years-if memory serves, da Vinci gets credit for first noting it. Golf, pool, archery, and shooting instructors get a lot of mileage, or sell a lot of snake oil, from the fact that many people have a dominant eye.

I'm sure you've done a test to discern your dominant. It's a cute trick.

Over the years, though, I've noticed something: I've never read a scientific account of vision that even mentions any functional significance of dominant eyes. And I've read a lot of scientific accounts of vision.

I got curious about this. Maybe I just hadn't read the right books, I thought. I went looking at more science books on vision-and found nothing. Nowhere could I find any scientific account of vision that ascribed any function to the dominant eye.

I did a search on MEDline-and found nothing. Searches of the databases at the National Eye Institute, National Institutes of Health, and the American Academy of Ophthalmology. Again, nothing, except for some tragic pathologies.

So far as I can discover, scientists don't consider dominant eyes important to understanding normal vision.

I did find one study of eye dominance and sports performance published in a reputable research journal, Ophthalmology, in 1998. A team of UCLA researchers studied the Dodgers for the 1992-95 seasons, to look for relationships between handedness, eye dominance, and performance, either for hitting or pitching. The conclusion: "Our data, based solely on professional baseball players ... show no statistically significant difference between dominance patterns and [earned run average] or batting average," according to Daniel M. Laby, MD, and colleagues. They also say, "In addition, no consistent pattern of dominance . . . was found in the best or worst groups of hitters or pitchers."

These researchers disproved the idea that a left-handed batter needs to be right-eye dominant, a righty left-eye dominant, a left-handed pitcher left-eye dominant, etc. It simply doesn't matter which eye faces the pitcher, or the batter, relative to your swing or pitch-and that's with the ball moving ninety feet at ninety miles an hour! Can anyone, then, really believe that where you hold your cue stick in relation to your dominant eye, while looking at balls that sit still, only a few feet from each other, really matters?

Having discovered all this, I began thinking through the issue more carefully.

To start with, those cute tests really tell us nothing at all about real vision. That one eye working alone is "more accurate" than the other eye, also working alone, tells us nothing about what happens when the two work together.

Eyes play only a supporting role in constructing visual images. They feed data to your brain, a bit like a carburetor or fuel injector feeds gas to your car engine. The data from the eyes resemble visual images about as much as gas resembles a moving car-namely, not at all. The brain, not the eyes, constructs visual images. What your brain does with data from one eye doesn't tell us much about what it does with data from two.

Normal vision, for most people, is stereoscopic, not monocular-that is, the brain uses data from both eyes to construct each visual image. If dominant eyes had any significance, the brain would normally give more weight to data from one eye than the other. There's no evidence of that, that I can find.

Furthermore, brains don't depend entirely on which eye data comes from. About half the nerves from each eye go to the opposite side of the brain. The two sides of the brain exchange information. Once the brain knows something, it's quite agile in adapting to whatever information it has available. In controlled experiments, you can train a person to do a task with one eye blindfolded, then change the blindfold to the other eye, and the person can do the task just as well.

And why suppose that the "dominant eye" is more accurate? People generally don't see entirely straight-we can prove this with all manner of tests. To the degree that one eye dominates, that may impose inaccuracy. Since our eyes are roughly equidistant from our bodies' axes, one eye dominating would mean we gave too much weight to its perspective. However, so long as this dominance-and the resultant inaccuracy-is small, it just doesn't matter. Brains don't execute actions by vision alone. Brains use information from all our senses and from memory. Each of us learns, through feedback from all our senses, how to coordinate an action-and we remember. What matters is the whole sensory/memory complex, not just your eyes.

Having thought about all this, I tried an experiment. I know I'm right-eye dominant, so I went to the pool table and blindfolded my right eye. Instinctively, I lined up differently over my stick-moving my chin farther to the right-and amazed myself by shooting quite well immediately. I was stunned. I tried this for several days running, with the same results each time.

Maybe the myth of the dominant eye got started by someone who misinterpreted the idea of "ocular dominance." Within the brain, each cell in the visual cortex responds to one eye but not the other, to both equally, or to one more than the other-and cells of like response patterns line up in "dominance columns." Dominance refers only to the responsiveness of cells, not to the construction of the entire visual image. For one eye to dominate construction of visual images, the brain would have to contain a greater number of dominance columns for that eye. I know of no evidence of this, except in certain tragic pathologies.

I suppose that there could be something to the "dominant eye" nostrums, but I can't imagine any reason to believe it. After all, scientists have known of the phenomenon for hundreds of years, yet-so far as I can discover-have not discovered it to be of great significance. I rather suspect that eye dominance is fairly trivial. Human bodies just aren't precisely symmetrical. If your body has two of something, chances are good they aren't equal. That rarely matters. With most people, one foot is bigger than the other-usually the foot opposite your handedness. That's a fact, but a fact of no importance. I rather suspect that dominant eyes mean about as much as unequal feet.

When was the last time you heard a pool instructor tell you to put most of your weight on your bigger foot?

 

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