Three-dimensional manual responses to unexpected target perturbations during rapid aiming.

The authors examined the execution of rapid aiming movements to targets that changed size and position. Participants viewed a medium-size target during movement preparation. The target became smaller or larger at movement initiation on size perturbation trials. The target moved closer or farther away from the home position on amplitude perturbation trials. The authors examined-in addition to several performance measures-the volume of 3-dimensional ellipsoids to quantify between-trials variability. In the size protocol, men executed movements in a similar manner irrespective of condition. In contrast, women exhibited less variability when target size increased. In the amplitude protocol, men moved inconsistently in the latter portion of the trajectory when targets became proximal. Men also failed to adjust for the perturbation on several trials. In comparison, women were more variable in the initial portions of the trajectory when the target became distal. Although men and women performed their movements in a similar duration, the trajectory and error analyses indicated different behaviors. Specifically, women made more rapid and efficient adjustments to their trajectories on the basis of concurrent visual information. In contrast, men executed movements on the basis of the visual information initially presented and then made adjustments, rather than gathering visual information and executing adjustments throughout the trajectory.