Time course and temporal order of changes in movement kinematics during motor learning: Effect of joint and instruction

Learning a motor task is associated with specific changes in movement kinematics. Recently, it has been shown that changes in different kinematic parameters occurred with different time courses for subjects who practiced simple, single-joint elbow movements. For example, movement time was seen to decrease and level off in a shorter time than peak velocity, which increased and plateaued later. What is not known, however, is whether the time course and temporal order of these learning-related changes seen at the elbow are similar for movements learned at other joints and with different instructions. In this study, neurologically normal subjects practiced 50°-flexion movements made at the wrist, with the instruction to be both "fast and accurate" (same instruction used in the earlier elbow study). A different group of subjects practiced wrist movements of the same amplitude, but with instructions to make movements that were "always accurate;" only as movement skill developed could subjects increase their speed (but without ever sacrificing accuracy). We measured time-related parameters (duration of acceleration, duration of deceleration, and total movement duration) and magnitude-related parameters (peak velocity, peak acceleration, and peak deceleration). We found that the time course of changes in kinematic parameters for subjects instructed to be "fast and accurate" was similar to that reported at the elbow. When the instruction was changed to be "always accurate," the time for changes in kinematic parameters to level off was found to be longer. However, regardless of instruction, time-related parameters plateaued before magnitude-related parameters. Thus, our results indicate that motor learning mechanisms may operate in a similar way at different joints.