The Influence of Object Height on Maximum Grip Aperture in Empirical and Modeled Data

During a grasping movement, the maximum grip aperture (MGA) is almost linearly scaled to the dimension of the target along which it is grasped. There is still a surprising uncertainty concerning the influence of the other target dimensions on the MGA. We asked healthy participants to grasp cuboids always along the object's width with their thumb and index finger. Independent from variations of object width, we systematically varied height and depth of these target objects. We found that taller objects were generally grasped with a larger MGA. At the same time, the slope of the regression of MGA on object width decreased with increasing target height. In contrast, we found no effect of varying target depth on the MGA. Simulating these movements with a grasping model in which the objective to avoid contact of the digits with the target object at positions other than the goal positions was implemented yielded larger effects of target height than of target depth on MGA. We concluded that MGA does not only depend on the dimension of the target object along which it is grasped. Furthermore, the effects of the other 2 dimensions are considerably different. This pattern of results can partially be explained by the aim to avoid contacting the target object at positions other than the goal positions.