What do juggling and running have in common?

Both use repetitive motion. But when a person juggles, his or her feet are usually fairly stationary — which is why researchers at Johns Hopkins University are using juggling to study the way a person moves in a repetitive way. They wanted to see how vision and touch helps accomplish a repetitive task.

The Johns Hopkins engineers used a sort of virtual juggling game, in which participants used a real-life paddle that was represented by an on-screen paddle. The participants used the paddles to bat a virtual ball and hit a virtual target area. Some participants could only see whether they hit the paddle. Other participants received a small buzz on their real-life paddle when the on-screen ball hit the on-screen paddle.

They found participants who got the bump on their real-life paddle made half as many errors as the participants who felt nothing.

The researchers think they know why. They say juggling is about lining up your action with the environment’s action. In other words, you have to line up when you toss the ball with when that ball comes back down and hits your hand. That gives you a sense of timing. Toss ball, wait a beat, catch ball. Feel ball in hand. Repeat.

Same goes for when humans or animals walk or run. They see the ground approach their foot and feel it as their foot touches the ground. All the while, their body adjusts to the constantly changing dynamics of walking or running.

The researchers hope understanding how sight and touch interact can help clinicians study how neurological disorders might affect walking and running. They also hope their work can aid the making of touch-sensitive artificial limbs and touch-sensitive robots.

Maybe someday you’ll see a cheetah-bot galloping gracefully through a grassland … all because of a few researchers watching a juggler.