Motor skill learning by increasing the movement planning horizon

Motor skill is usually understood as a capability to perform faster and more accurate movements than other, unskilled, individuals. In this study we investigated motor skill learning using a path tracking task, where subjects had to track various curved paths as fast as possible, in the absence of any external perturbations. We found that subjects become better with practice, producing faster and smoother movements even when tracking novel untrained paths. Using a “searchlight” paradigm, where only a short segment of the path ahead of the cursor was shown, we found that subjects with a higher tracking skill demonstrated larger planning horizon, i.e. took a longer chunk of the future path into account when computing the control policy for the upcoming movement segment. This suggests that the motor system uses receding horizon control, and its horizon length can increase with practice, resulting in an increased accuracy of the movement controller.