Hand, eye, and head coordination while pointing to perturbed targets.

Normal human subjects were required to manually point to small visual targets that suddenly changed location upon finger movement initiation. They pointed either as fast or as accurately as possible. Movements of the eyes were measured by electrooculography, and the movements of the unrestrained limb and head were monitored by an optoelectric system (WATSMART), which allowed for the analysis of kinematic parameters in three-dimensional space. The temporal and kinematic reorganization of each body part in response to the target perturbations were variable, which indicated independent control for each part of the system. That is, the timing and nature of the reorganization varied for each body part. In addition, the pattern of reorganization depended upon the speed and accuracy demands of the movement task. As well, the movement termination patterns (eyes finished first, the finger reached the target, then the head stopped moving) were extremely consistent, indicating that movement termination may be a controlled variable. Finally, no evidence was found to suggest that visual information was used to amend arm movements early (before peak velocity) in the trajectory.