Abstract
Recent theories of sensorimotor control propose that complex movements are constructed by combining simpler output-generating neural processes. Composing together reusable elements allows a rich variety of movements to be generated using a limited set of neural representations, but it may also impose limits on how new sensorimotor skills can be learned. If skill learning requires modification of existing compositional units, then other skills using the same components may be harmed when the new one is learned. Alternatively, if new skills simply reuse existing units, the repertoire of available units may impose limits on what skills can be learned. In this study, we used a myoelectric interface to explore whether learning a novel coordinated control task requires modification of the existing repertoire of output-generating components. Over five sessions on five consecutive days, participants learned to trace a series of trajectories using a computer cursor controlled by coordinated activation of two muscles. The timing of the generated cursor trajectory and its shape relative to the target improved for conditions trained with post-trial visual feedback. Improvements in timing transferred to all untrained conditions, but improvements in shape transferred only to untrained conditions requiring the trained order of muscle activation. Notably, all muscle outputs in the final session could already be generated during the first session. These results suggest that participants learned the new task by independently improving the selection and timing of existing output-generating components. This tendency toward reuse may help to protect existing skills from interference during learning of new skills.
Significance Statement Complex movements may be generated by selecting and combining elements from a repertoire of movement-generating neural processes. It remains unclear if these processes are reused or modified when learning entirely new motor skills. In this study, we used a novel human-computer interface task to test this. Over five sessions, participants learned to trace a series of cursor trajectories by coordinating the activation of two muscles. We found that participants tended to reuse the same muscle contractions for different variants of the task, and that performance improvements were attributable to improvements in the choice and timing of muscle contractions. Our results demonstrate that learning of new complex movements does not necessarily require changes to the neural motor repertoire.
Competing Interest Statement
The authors have declared no competing interest.