The control of discrete and reciprocal target-aiming responses: Evidence for the exploitation of mechanics

The purpose of this study was to examine the target impact constraint hypothesis of the one-target advantage. This phenomenon reflects the finding that a movement toward a single target is executed faster than the same movement followed by a second movement toward a second target. According to the target impact constraint hypothesis, the one-target advantage results from a motor control strategy in which one-target movements are characterized by relatively shorter deceleration phases and smaller peak velocities than the corresponding movement in a two-target response because the former rely to a greater extent on passive deceleration through target impact. Employing discrete and reciprocal sliding movements and manipulating target impact constraints, kinematic analyses supported the impact constraint hypothesis of the one-target advantage for movements toward small targets. However, for sliding movements toward large targets, a two-target advantage was found. We argue that a reciprocal response toward large targets might not require a movement stop but rather a movement reversal on the first target and therefore is characterized by a two-burst instead of a three-burst pattern of EMG activity.