The influence of obstacles on the speed of grasping.

The movement time of a reach-to-grasp movement increases when obstacles are placed close to the target object. We investigated whether this increase can best be explained by limits on the grip aperture or by limits on the paths of the individual digits. In our experiment subjects were instructed to pick up an object with their index finger and thumb. There was an obstacle at either side of the object. The increase in movement time when either obstacle was placed closer to the object was best described by a model in which the movement amplitude and the distance between each obstacle and the target object are independent factors. We conclude that the way that obstacles influence the movement time in reach-to-grasp movements is determined by the extent to which they limit the digits' paths.