Juggling: Not Just Fun and Games

Winter 2014

Eye On The Ball: By analyzing juggling, researchers hope to find clues to improving prosthetics and physical  rehabilitation programs, says Noah Cowan.
Eye On The Ball: By analyzing juggling, researchers hope to find clues to improving prosthetics and physical
rehabilitation programs, says Noah Cowan.

Juggling is usually viewed as little more than a fun pastime.

But now, researchers at the Whiting School, armed with a portion of a three-year $600,000 National Science Foundation grant, are taking a serious look at that avocation.

The aim of the study isn’t to produce more skilled circus performers or street-corner entertainers. It’s to tease apart the mechanisms that human nervous systems and brains use to constantly make adjustments when we engage in rhythmic behaviors, from juggling to walking and running.

“The beauty of juggling as a system of study is that it is a mathematically simplified version of human locomotion,” says Noah Cowan, an associate professor of mechanical engineering and director of the Locomotion in Mechanical and Biological Systems (LIMBS) laboratory. “When we walk down the street we have to constantly adjust what we are doing to avoid falling. How do we do that? Looking at juggling lets us examine how our
nervous systems perform this task; it might seem simple, but it is really astonishingly complex.”

The study’s results hold important implications for improving prosthetics, designing more effective physical rehabilitation programs, and enhancing the design of bioinspired robots.

Though Cowan—an accomplished juggler who can deftly handle everything from balls to clubs to chainsaws—believes most people can learn to juggle, he isn’t asking study subjects to do the real thing. Instead, they juggle “virtually.”

“What they do in the study is similar to playing a video game. Subjects hold a ‘paddle’ that is specially designed to give them tactile feedback, and then we ask them to ‘juggle’ using that paddle to hit a virtual ball that appears on a screen in front of them,” explains Cowan. “The paddle and ball physics are simulated in on a computer, and the people in the study can see, hear, and feel the ball.”

By carefully manipulating the virtual reality environment (including varying the amount of haptic feedback the juggler gets), Cowan’s graduate students Mert Ankarali and Robert Nickl are examining the neuromechanical
components involved in the juggler’s ability to control the ball.

“For example, we have a motor in the paddle that provides an impulse to simulate touch feedback when the ball hits the paddle. We can virtually ‘numb’ the study subjects’ hands by not providing the impulse to the paddle when they hit the ball, so they have visual feedback on the screen but no feeling in the hand,” Cowan says. “We can also do things like simulate a gust of wind, and then we study how people recover and maintain control of what they are doing.”

The team is analyzing this data using a theoretical and computational framework being developed in collaboration with Tim Kiemel and Norman Wereley at the University of Maryland, College Park, and John Jeka at Temple University. Cowan’s team will combine its juggling data with data being generated by Kiemel, Wereley, and Jeka, who are using the same tools to study walking.

“Understanding how animals control rhythmic behavior—such as walking, running, playing music, and juggling—is one of the grand challenges in neuroscience,” Cowan says, adding, “We hope that this study will help take us one step closer, metaphorically speaking!”