SPEED AND SEQUENTIAL EFFECTS IN REACHING

To investigate the impact of future task demands on reaching, particip ants performed repetitive sagittal-plane reaches at low and high speed s. In a control condition, they reached from a start location to a tar get and back. In the experimental conditions, they reached from the st art to the target, then to a second target (the location of which vari ed between trials), then back to the first target, and finally back to the start. Contributions of the hip, shoulder, and elbow to reaches m ade to the first target depended on the second target's location, on m ovement speed, and on repetition. Participants combined sustained and transient postural adjustments to minimize effort. The results support the knowledge model of movement selection (D. A. Rosenbaum, L. D. Lou kopoulos, R. G. M. Meulenbroek, J. Vaughan, & S. E. Engelbrecht, 1995) but also call for its elaboration. Variants of the model are explored through simulations of the above study.