The effects of practice on movement reproduction: Implications for models of motor control

This study investigated how consistently and accurately subjects could reproduce final movement position when performing three different movement tasks over four experimental sessions. Task 1 involved moving five different inertial loads over one movement distance. Task 2 involved performing movements over five different distances against a constant inertial load. Task 3 involved moving five distances against five inertial loads that were adjusted to keep movement time relatively constant. Subjects who had practised Task 1 demonstrated the largest decrease in variable error over experimental sessions but little change in constant error. Subjects who had practised Task 2 showed a smaller improvement in variable error and no improvement in constant error. Subjects who had practised Task 3 demonstrated a small change in variable error and an improvement in constant error. The largest reduction in variable error in the first group is consistent with the equilibrium-point hypothesis of motor control but not with force-control models. The improvement in constant error in the third group is discussed with respect to a possible role of noise in practising simple movements.