NeuroQuest: How Left and Right Hands Cooperate

Grab a pen or pencil and quickly make a list of things you couldn't do if you suddenly lost your right hand (or left hand if, like one in 10 people, you're a southpaw). Next, taking the same amount of time, write down what you couldn't do if you still had the use of your dominant hand but your other hand abruptly vanished. In all likelihood, your first list is longer than the second.

Conventional wisdom would suggest that your dominant hand does all the really important stuff (like preparing lists of what it couldn't accomplish without itself), leaving your nondominant hand to watch helplessly from the sidelines. But conventional wisdom doesn't take into account the subtle role your brain plays in completing manual tasks, as you'll soon discover.

Photograph by Zeke Berman

With the same pen or pencil you just used, make a note of whatever random thoughts pop into your head. If you've got writer's block, perhaps you could start by describing how you'd feel if the world lost the IRS or telemarketers. As your pencil flies across the page, notice what your nondominant hand is doing. Odds are it's holding down the page and occasionally repositioning it to keep your dominant hand from having to wander too far from its comfort zone. To appreciate fully the contribution of your nondominant appendage, keep it in your lap as you continue to write. Awkward, isn't it?

It turns out that virtually everything your dominant hand does is helped by the largely unconscious—and unappreciated—cooperation of its nondominant counterpart. For instance, right-handers write 20 percent faster when allowed to hold the page with their left hand than when forced to keep that hand at their side. Similarly, keeping two hands on the steering wheel while driving a car will give you much better control.

Sometimes cooperation between two hands can improve performance even when you wouldn't expect it. For example, it seems logical to assume that hitting a stationary target is easier than hitting a moving one. So try this: Plant a sewing needle in a piece of cardboard and attempt to thread the needle, holding your nondominant hand behind your back. Now take the needle out of the cardboard and thread it while holding it in your unsteady, nondominant hand.

Your left hand does know what your right hand is doing (thanks to rich communication between the right and left cerebral hemispheres, which control the left and right hands, respectively), enabling your left hand to move the needle to the thread even as your right hand is bringing the thread to the needle.

Interesting things can happen when cooperation between hands is interrupted. Ask a friend to hold a glass in his outstretched palm. Then have him remove the glass with his other hand. Your friend's outstretched palm should move very little because it "knows" to decrease steadily the force applied against the glass as it is removed.

Now replace the glass in your friend's palm, then take it away yourself. This time, his outstretched palm should lift up. This is because your friend's brain did not expect the hand's load to be lightened and commanded it to exert force against the weight of the glass.

Psychologists hope that a deeper understanding of how our left and right hands cooperate will lead to the development of intuitive two-handed user interfaces that give us more control over computers than the mouse we use with one hand today. If these researchers succeed, we'll gain a much-needed ally in our uneven battle against computers, and our nondominant hands may finally get the recognition they deserve.