Changes in motor planning during the acquisition of movement patterns in a continuous task.

Changes in the planning and execution of movements were studied as a function of practice on a continuous motor task. Twelve subjects learned to move a pen through a cut-out square and maze patterns with their eyes closed. Maze patterns consisted of six, eight, ten, or twelve segments that were connected by intersections. Task performance was studied during six blocks. Although the mazes could be traced continuously in a clockwise direction, selecting a wrong turn at an intersection resulted in coming to a dead end. Performance at intersections was analyzed by determining the number of correct (and incorrect) turns following mechanically forced stops and the number of correctly planned and executed turns without any halt. In addition, movement time and pause duration were analyzed. With practice an increase in the number of correctly executed turns indicated that subjects gradually learned to group segments into chunks of increasing size. It was found that up to eight segments could be organized and executed as a single unit. Finally, with practice a non-linear performance improvement was found, suggesting that the learning process proceeded through qualitatively different learning stages. It is concluded that within five minutes subjects gradually changed their movement strategy from a sequential, trial-and-error mode in which planning and execution occurred segment by segment, to a mode in which concurrent planning was realized, i.e. in which the planning of oncoming segments occurred concurrently with the execution of segments.