Age-related differences in prehension: the influence of task goals.

A single study is reported in which the influence of age and task goal on reaching and grasping movements were examined. Ten young and 10 elderly subjects reached and grasped a disk (4.5-cm diameter) and then either (a) placed it in a well, (b) placed It in a box, or (c) threw it in a box, all located 30 cm to the left of the disk. The reach-to-grasp movements were analyzed over two phases: the approach to capture the disk and the transporting of the disk. Differential effects were observed over the two phases as a function of age. Over the approach, the movement times of the elderly subjects were comparable with those of the young subjects, but their relative deceleration and hand enclosing times took longer. During object transport, however, the elderly subjects moved more slowly than the young subjects did, but there were no differences in relative timing. In both phases, the precision required of the task influenced the duration of movement and the relative timing of arm deceleration, suggesting that subjects accurately anticipated the demands of the task. Those results, which are discussed in relation to hardware and software limitations on performance, suggest that the age-related differences reflect changes in the use of software strategies over the two phases of movement.