Time requirements of changes in program and parameter variables in rapid ongoing movements

Two experiments investigated the differences in processing time requirements of two types of modifications of a rapid ongoing movement. In response to a signal presented at either 0, 100, or 200 msec after initiation of a 400-msec horizontal arm movement, subjects attempted to either increase the speed of the movement or to reverse it. EMG modification latencies were shorter in the former condition than in the latter indicating a difference in processing-time requirement between modification types. The results support the generalized motor program hypothesis of Pew (1974) and Schmidt (1976) in that increasing the speed of an ongoing movement may require modification of a parameter variable while reversing movement direction requires the implementation of a new motor program.