Juggling Points to Better Prostheses & Tx for Ataxia

A study led by Johns Hopkins engineers has used the skill of juggling to gather critical clues about how vision and the sense of touch help control the way humans and animals move their limbs in a repetitive way, such as in running. The findings eventually may aid in the treatment of people with neurological diseases and could lead to prosthetic limbs and robots that move more efficiently. The study has been published online by the Journal of Neurophysiology and will be the cover article for the journal's March 2014 print edition.

In their paper, the team led by Johns Hopkins researchers detailed the unusual jump from juggling for fun to serious science. Jugglers, they explained, rely on repetitive rhythmic motions to keep multiple balls aloft. Similar forms of rhythmic movement are also common in the animal world, where effective locomotion is equally important to a swift-moving gazelle and to the cheetah that's chasing it.

A release from the university quotes Noah Cowan, an associate professor of mechanical engineering who supervised the research, as saying, "It turns out that the art of juggling provides an interesting window into many of the same questions that you try to answer when you study forms of locomotion, such as walking or running. Inn our study, we had participants stand still and use their hands in a rhythmic way. It's very much like watching them move their feet as they run. But we used juggling as a model for rhythmic motor coordination because it's a simpler system to study."

Specifically, Cowan and his colleagues wanted to look at how the brain uses vision and touch to control this type of behavior. To do so, they set up a simple virtual juggling scenario. Participants held a real-world paddle connected to a computer and were told to bounce an on-screen ball repeatedly up to a target area between two lines, also drawn on the monitor. In some trials, the participants had only their vision to guide them. In others experiments, whenever the digital ball hit the onscreen paddle the participants also received a brief impulse on their real-world paddle. This mimicked the sensation they would feel if a real ball had actually struck the paddle they were holding.

With the added touch sensation—called haptic feedback—the participants made about half as many errors, the researchers reported.

"We have a pretty good understanding as to why," said Cowan, who has been an amateur juggler since middle school. "One of the tricky challenges in juggling is catching a rhythm; that is, getting yourself entrained with the movement of the ball. It's about timing your own action with the action in the environment. When you get the pulse of haptic feedback at the exact moment the ball hits the paddle, it give you a precise sense of the timing for the juggling pattern that you're trying to achieve."