Juggling study leads to new revelations about human movement

A traditional circus act may shed new light on human movement, with implications for the treatment of neurological disorders or other scientific breakthroughs.

Researchers at the Johns Hopkins University are using juggling to study how touch, or haptic, feedback influences movement, and they’ve found that such feedback can help humans make fewer movement errors. The research could be beneficial to those studying how to create better prosthetic limbs or more nimble robots, they said.

Noah Cowan, a professor of mechanical engineering overseeing the research, and his team of graduate students designed and built a virtual juggling system with an acrylic paddle that study participants jiggled to bounce a ball on a screen, trying to keep the ball between two lines.

Some participants used only their vision for their exercise, but others got a tiny pulse when the virtual ball “struck” the paddle. Those who got the touch feedback, researchers found, made about half as many errors in the exercise as the group relying solely on vision.

The sense of touch influences movement in a way that is “very tiny compared to what we get from vision,” said M. Mert Ankarali, a mechanical engineering doctoral candidate and the study’s lead author. But “that little bit of timing information may be enough if you’re trying to catch a rhythm. If it’s something we’re uncertain about, it can make the difference.”

A number of researchers have studied haptic feedback in recent years. One German study last fall added haptic feedback to a touch-screen device in a car and found that it helped drivers keep their eyes on the road. Researchers in India are testing special shoes for the blind that use haptic feedback to help guide their movements. In 2011, researchers found that adding haptic feedback to electronic musical instruments might make it easier for musicians to play them.

“There’s a lot uncertain about how our brains control movements,” Cowan said.

Haptic feedback is key for movement, Cowan said. For example, runners may take clues about the type of terrain they are on — grass or hard pavement — from touch feedback and adjust their running style accordingly.

Cowan said older studies by other researchers have examined how haptic feedback affected the ability to fix movement errors as they were being made. Their new finding, Cowan said, was that haptic feedback helped the study participants “make fewer errors in the first place,” just as the sensation of a ball or other object touching a juggler’s hand can guide how they move in rhythm.

The study participants consisted of 18 Hopkins students, 15 of whom were successful in bouncing the virtual ball inside the two lines on the computer screen. Two others could not virtually juggle at all, with or without haptic feedback, and one person was able to juggle successfully with haptic feedback but unable without it.

The team built the virtual juggling system, with an acrylic and aluminum paddle attached to a special video game monitor by a cord, to eliminate any potential for the type of juggling balls used to influence the study’s outcome. Cowan took up juggling as a hobby as a teen, he said, which jump-started his interest in mechanics. He still juggles from time to time, and can do so using only haptic feedback with his eyes closed.

“Juggling has been a mainstay of the robotics and mechanics world for a long time,” he said. “It started out as kind of a fun project.”

The team members hope that their research will inform future studies into movement, which could benefit those suffering from Parkinson's disease or other neurological disorders. They also hope their findings can be used by those designing prosthetic limbs. Their work was supported in part by $741,000 in grants from the National Science Foundation, and was published as the cover feature for this month’s edition of the Journal of Neurophysiology.

In future studies, the researchers want to make the virtual juggling “more challenging,” perhaps by giving the participants less visual feedback.

So far, the researchers have not used real jugglers in their studies, but might explore that in the future. 



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