Square that circle

It sounds simple: draw a circle with one hand, and a square with the other. But the circle usually has square sides, the square has curved sides, or you break the pencil in frustration.

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Bob Dylan can sing and strum. Brett Favre can (usually) run and throw. So why is it so hard to rub your tummy and pat your head, or draw a circle and a square simultaneously? David Rosenbaum, a professor of psychology at Penn State, says this is "a fundamental question: Why is it difficult to carry out two different movements at the same time? The joke says you can't walk and chew gum. You can do that, but there are certain pairs of activities that we can't do very well, like drawing a square and a circle."

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Rosenbaum, who directs Penn State's Laboratory for Cognition and Action, says, "It is a fundamental limitation that the nervous system seems to impose on the hands for reasons that are not fully understood."

It sounds plausible. Is it true?

To pinpoint the source of the limitation, Rosenbaum and associates Amanda Dawson, a recent Ph.D. recipient, and John Challis, associate professor of kinesiology, developed an apparatus that produced different movement patterns, and asked volunteers to track those patterns.

It turns that simultaneously outlining a square and a circle is easy -- if you can rely on your sense of touch to follow a moving object.

The blindfolded subjects tracked a disk located on a sheet of opaque glass, which followed a moving magnet behind the glass. If the volunteers leaned on the disk (indicating that they were using it to move their hands), the disk became detached and the trial was considered a failure.

But failures were rare: Guided by the sense of touch, the difficult square-and-circle movement was suddenly simple, Rosenbaum says. "We figured out that if we ask someone to gently touch an object that is moving in a circular way with one hand, and with the other, to gently touch one that's moving in a square fashion, they can do it lickety split. It was absolutely no problem. They needed no training."

Courtesy David Rosenbaum, Penn State University.

The experiment, published in the November/December Journal of Experimental Psychology, proved that the limitation is neither in the muscles nor in the part of nervous system that communicates directly with them, Rosenbaum says. "Instead, we have come to the idea that the source of the limitation is conceptual, it's not in the execution." When asked to draw a square and circle, "you need to keep those two forms in mind, and that's hard for us to do."

Touching better than thinking!

Touch input goes to a part of the brain called the somatosensory cortex, which is directly connected to the motor cortex, Rosenbaum explains. And apparently these two areas are happy to trace squares and circles without help (or hindrance!) from the brain's intellectual center, the prefrontal cortex, which makes plans and carries them out.

So how, for example, do musicians do two things at once? "It turns out that very, very few people can carry out two differently timed activities totally independently," says Rosenbaum. "If you sing while playing guitar, over time, you learn to think of them as a single task."

Learning to sidestep cognitive limitations on movement could have practical benefits, Rosenbaum says. "We are very interested in trying to use this with patients who have trouble moving in a coordinated fashion; clumsy children or people recovering from a stroke." By teaching patients to follow their sense of touch, and then gradually removing the touch stimulus, "maybe we could improve their coordination."

Courtesy David Rosenbaum, Penn State University.

The research is more proof of some basic limitations on multitasking, Rosenbaum adds. "It is dangerous to talk on the cell phone while driving because of the attention limits. In our research, those same attention limits are manifest in simple movement tasks. There are serious limits on how well we can multitask, whether it's for intellectual activities or even for simple motor acts."

-- David ("Type 'n Talk") Tenenbaum

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