向“了解人类如何学习一项运动技能”迈出的重要一步

A significantstep toward understanding how we learn a motor skill

Usinga deceptively simple set of experiments, researchers at Johns Hopkins havelearned why people learn an identical or similar task faster the second, thirdand subsequent time around. The reason: They are aided not only by memories ofhow to perform the task, but also by memories of the errors made the firsttime.

"In learning a newmotor task, there appear to be two processes happening at once," says RezaShadmehr, Ph.D., a professor in the Department of Biomedical Engineering at theJohns Hopkins University School of Medicine. "One is the learning of themotor commands in the task, and the other is critiquing the learning, much theway a 'coach' behaves. Learning the next similar task goes faster, because thecoach knows which errors are most worthy of attention. In effect, this secondprocess leaves a memory of the errors that were experienced during thetraining, so the re-experience of those errors makes the learning gofaster."

Shadmehr says scientistswho study motor control - how the brain pilots body movement - have long knownthat as people perform a task, like opening a door, their brains note smalldifferences between how they expected the door to move and how it actuallymoved, and they use this information to perform the task more smoothly nexttime. Those small differences are scientifically termed "predictionerrors," and the process of learning from them is largely unconscious.

Thesurprise finding in the current study, described in ScienceExpress, is that not only do such errors train the brain to betterperform a specific task, but they also teach it how to learn faster fromerrors, even when those errors are encountered in a completely different task.In this way, the brain can generalize from one task to another by keeping amemory of the errors.

To study errors andlearning, Shadmehr's team put volunteers in front of a joystick that was undera screen. Volunteers couldn't see the joystick, but it was represented on thescreen as a blue dot. A target was represented by a red dot, and as volunteersmoved the joystick toward it, the blue dot could be programmed to move slightlyoff-kilter from where they pointed it, creating an error. Participants thenadjusted their movement to compensate for the off-kilter movement and, after afew more trials, smoothly guided the joystick to its target.

In the study, themovement of the blue dot was rotated to the left or the right by larger orsmaller amounts until it was a full 30 degrees off from the joystick'smovement. The research team found that volunteers responded more quickly tosmaller errors that pushed them consistently in one direction and less tolarger errors and those that went in the opposite direction of other feedback."They learned to give the frequent errors more weight as learning cues,while discounting those that seemed like flukes," says David Herzfeld, agraduate student in Shadmehr's laboratory who led the study.

The results also havegiven Shadmehr a new perspective on his after-work tennis hobby. "I'm muchbetter in my second five minutes of playing tennis than in my first fiveminutes, and I always assumed that was because my muscles had warmed up," hesays. "But now I wonder if warming up is really a chance for our brains tore-experience error."

"Thisstudy represents a significant step toward understanding how we learn a motorskill," says Daofen Chen, Ph.D., a program director at the NationalInstitute of Neurological Disorders and Stroke. "The results may improvemovement rehabilitation strategies for the many who have suffered strokes andother neuromotor injuries."

Thenext step in the research, Shadmehr says, will be to find out which part of thebrain is responsible for the "coaching" job of assigning weight to different types of error.