Hand aperture patterns in prehension

Although variations in the standard prehensile pattern can be found in the literature, these alternative patterns have never been studied systematically. This was the goal of the current paper. Ten participants picked up objects with a pincer grip. Objects (3, 5, or 7 cm in diameter) were placed at 30, 60, 90, or 120 cm from the hands’ starting location. Usually the hand was opened gradually to a maximum immediately followed by hand closing, called the standard hand opening pattern. In the alternative opening patterns the hand opening was bumpy, or the hand aperture stayed at a plateau before closing started. Two participants in particular delayed the start of grasping with respect to start of reaching, with the delay time increasing with object distance. For larger object distances and smaller object sizes, the bumpy and plateau hand opening patterns were used more often. We tentatively concluded that the alternative hand opening patterns extended the hand opening phase, to arrive at the appropriate hand aperture at the appropriate time to close the hand for grasping the object. Variations in hand opening patterns deserve attention because this might lead to new insights into the coordination of reaching and grasping.

► Different ways in which the hand can be opened in grasping an object are examined.
► Objects placed at large distances had to be picked up.
► The hand could open gradually, with bumps, or end in a plateau, before closing.
► Two participants delayed the start of hand opening with respect to start of reach.
► Alternative patterns might stall hand opening to coordinate reaching and grasping.