Motor learning without movement

Fascinating work from Kim et al. on the influence of the prediction errors that are essential in calibrating actions of our predictive minds:

Significance

Our brains control aspects of our movements without conscious awareness, allowing many of us to effortlessly pick up a glass of water or wave hello. Here, we demonstrate that this implicit motor system can learn to refine movements that we plan but ultimately decide not to perform. Participants planned to reach to a target but sometimes withheld these reaches while an animation simulated missing the target. Afterward, participants unknowingly reached opposite the direction of the apparent mistake, indicating that the implicit motor system had learned from the animated error. These findings indicate that movement is not strictly necessary for motor adaptation, and we can learn to update our actions without physically performing them.

Abstract

Prediction errors guide many forms of learning, providing teaching signals that help us improve our performance. Implicit motor adaptation, for instance, is thought to be driven by sensory prediction errors (SPEs), which occur when the expected and observed consequences of a movement differ. Traditionally, SPE computation is thought to require movement execution. However, recent work suggesting that the brain can generate sensory predictions based on motor imagery or planning alone calls this assumption into question. Here, by measuring implicit motor adaptation during a visuomotor task, we tested whether motor planning and well-timed sensory feedback are sufficient for adaptation. Human participants were cued to reach to a target and were, on a subset of trials, rapidly cued to withhold these movements. Errors displayed both on trials with and without movements induced single-trial adaptation. Learning following trials without movements persisted even when movement trials had never been paired with errors and when the direction of movement and sensory feedback trajectories were decoupled. These observations indicate that the brain can compute errors that drive implicit adaptation without generating overt movements, leading to the adaptation of motor commands that are not overtly produced.