Influence of object weight and movement distance on grasp point selection V Paulun1, U Kleinholdermann1, K R Gegenfurtner1, J B Smeets2, E Brenner2 |
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1Department for General Psychology, Justus-Liebig University of Giessen, Germany |
| To effectively manipulate objects we need to choose appropriate grasp points. We brought two possible determinants of grasp point selection into conflict: minimizing torque versus minimizing movement costs. 21 right-handed subjects reached to grasp objects (10x3x1cm) of different mass from different distances to its left or right. Torque minimization predicts a grasp near the object center. Minimizing movement costs predicts a grasp nearer to where the movement started. As expected, the tendency to grasp off-center was larger for light objects, for which this produces less torque. However, the grasp axis was shifted to the right of the center, irrespective of where the movement started. The rightward bias was reduced when the required precision was increased in a second experiment (N=19) by having subjects balance the object on a small cylinder after grasping. Starting the movement above the object eliminated the bias, as did grasping with the left hand. In the latter case subjects tended to grasp the object to the left of its center. We conclude that grasp points are near the center to ensure stability, but tend towards the side of the acting hand to improve visibility. |
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