Preparation and execution of manual sequential aiming movements under conditions of response uncertainty

When moving from a starting position to a single target, movement time is faster than when you must continue the movement on to a second target (i.e., one-target advantage). Processes underlying both the movement integration and constraint hypotheses account for the preparation and control of sequential aiming movements. In the present experiments, we investigate the time course of these processes by varying the number of targets and target size during movement preparation and execution. Aiming movements with a stylus to one or two targets on a horizontally positioned touch screen were performed. Results revealed the emergence of the OTA only when participants knew the number of targets in advance of target presentation. It appears that the integration between the first and second segments and the constraining of limb trajectories was determined in advance of movement initiation. Implications for the results to the movement integration and movement constraint hypotheses are discussed