Grasping movement plans.

Despite the great amount of research that has been done regarding the time it takes to move the hand to targets of varying distances and widths, it is unclear whether target distance and width are both represented in movement plans prior to movement initiation. We addressed this question by studying performance in an object manipulation task. Our participants reached out and took hold of a familiar object (a bathroom plunger) to move it to wide or narrow targets of varying heights. Grasp heights on the plunger were additively affected by target height and target width, suggesting that both factors were taken into account by participants prior to moving the plunger from its initial position. Another factor we manipulated was the width of the base from which the plunger was lifted on its way to its next position. This factor also affected grasp heights, but no more so than target widths. The latter result contradicts the view that movement starts are planned in moredetail than movement ends, as might be expected from the fact that movement starts come sooner. Together, our results suggest that forthcoming movements are planned in considerable detail. A surprising methodological implication of this study is that recording how people prepare to move can reveal as much--or in some cases more--about what they have planned than can recording their subsequent movements.