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Why some can't tell left from right

At some point most of us confuse left and right like we’re in a scene from an old Three Stooges one-reeler: “The one in your left hand!” “No, your other left!” Bonk!

It seems silly. After all, it’s not like we’re new to the concept; we’ve been using our left and right hands all our lives. Yet we sometimes flub -- some of us more often than others.

I’m not referring to people who’ve had strokes or suffered some other injury or illness. Then there’s often a clear explanation for what neuroscientists call “left-right confusion.”

But in 1978, researchers polled 364 university faculty, none of whom had any known neurological problems, and all of whom would seem to be smarter than the Three Stooges. It turned out that left-right confusion was common, especially among the women. The question was, why?

It’s now 34 years later and, said Eric Chudler, director of the Center for Sensorimotor Neural Engineering at the University of Washington, whose work depends on knowing left from right, “that’s a difficult question. I don’t know if any answer exists.”

According to M.K. Holder, executive director of the Handedness Research Institute, and an adjunct assistant professor of psychological and brain sciences at Indiana University, the link between brain “lateralization” -- the way specific functions appear to reside in left or right sides of our brains -- and handedness (or even what we mean when we say “handedness”) is still unclear.

But there does appear to be a link between degree of lateralization and confusion.

For example, left-right confusion may be related to spatial reasoning. If so, it might help explain why it’s more common in women than men; as a group, women tend to underperform on a critical test of spatial reasoning, called mental rotation, that requires subjects to mentally rotate images to tell if they’re identical or mirror images of each other.

In 2011, though, a team of German scientists disputed that connection by testing men and women who were matched in mental rotation ability before subjecting them to two standard tests of left-right confusion. (The tests require people to make a quick decision in response to directional words or symbols.) Their report, which appeared in Brain and Cognition, found that “matched participants showed robust sex differences in favor of men in all [left-right confusion] measurements. This suggests that pronounced sex differences…are a genuine phenomenon that exists independently of sex differences in mental rotation.”

The degree of asymmetry of one’s brain hemispheres, or the degree of lateralization, may be important. In 2009, British scientists found that those whose hearing was more biased toward one ear over another, a sign of asymmetry, were more likely to display confusion. Still, there’s no definitive answer yet.

Meanwhile, if you’d like to test your own degree of left-right confusion, Chudler has a test on his website.  

Brian Alexander (www.BrianRAlexander.com) is co-author, with Larry Young PhD., of "The Chemistry Between Us: Love Sex and the Science of Attraction," to be published Sept. 13.

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