Programming Sequences of Hand Postures

The extent to which complex skills are programmed before movement is a concern for research in motor control. This study investigates a model which maintains that after a motor program is constructed, only the first response in a sequence is programmed prior to movement (Sternberg, Monsell, Knoll, & Wright, 1978). In a simple reaction time paradigm, subjects executed sequences of hand postures that varied in length, the number of different hand postures, and the location of a hand posture transition. For sequences containing repetitions of the same hand posture, sequence length had a small effect on RT when the number of responses ranged between two and five (Experiment 1) and no effect when the number of responses ranged between three and five (Experiment 2). For sequences containing clearly different hand postures, Experiment 2 showed that RT was influenced by the type of hand posture beyond the first response. The analysis of interresponse times suggested that the first two responses were completely preprogrammed before movement. These results were consistent with a model in which responses are hierarchically organized and some but not all information about each response in the sequence is preprogrammed before movement execution.