Variability appears critical to motor learning

Anyone who has ever stepped on a tennis court understands all too well the frustration that comes with trying to master the serve, and instead seeing ball after ball go sailing out of bounds in different directions.

Rather than cursing these double-faults, Harvard researchers say errors resulting from variability in motor function can play a critical role in learning.

Though variability is often portrayed as a flaw to be overcome, a new study suggests that variability in motor function is a key feature of the nervous system that helps lead to better ways to perform a particular action. The study, conducted by Maurice Smith, Thomas D. Cabot Associate Professor of Bioengineering at the Harvard School of Engineering and Applied Sciences (SEAS), and Bence Ölveczky, John L. Loeb Associate Professor of the Natural Sciences in Harvard's Department of Organismic and Evolutionary Biology, is described in a Jan. 12 paper published in the journal Nature Neuroscience.

“I think this changes the paradigm of how we think about motor variability and performance,” Ölveczky said. “In human performance, variability is usually thought of as a consequence of noise in the nervous system — it’s something we’re trying to overcome. What we’re trying to understand is whether variability might be useful. The question is: Does the nervous system perhaps use that variability as a feature to improve learning?”

In the case of the tennis serve, Ölveczky explained, variability would prove useful by allowing a player to see the effect of subtle changes — slightly altering the toss of the ball, the swing of the racket, or the angle of the serve — that might improve performance.

“In general, we think that most tasks are best performed with high precision,” Smith said. “It’s clear that as you practice a task, and go from a novice to someone who is more accomplished, your variability goes down and your performance goes up.

“The question is: Is your performance improving because your variability is going down? Was the high variability you originally had standing in the way of good performance?” he continued. “That’s what many people believed, but what this paper is showing is the other possibility — that the high variability you display early on actually improves your ability to learn and is thus responsible for the expertise you develop.”

The notion that variability can play a role in learning came in part from Ölveczky’s study of zebra finches.

While studying how birds learn their individual songs, Ölveczky and colleagues identified a neural circuit that allows male finches to alter the variability in their singing, depending on circumstance. Birds that are still learning their song can have high vocal variability. But if females — who value precisely repeated songs — are nearby, they can suddenly turn off that variability and produce highly stereotyped songs.

“That was a clue to us that variability is something the animal uses to improve learning, and improve his song,” Ölveczky said.

Read the entire article in the Harvard Gazette