How do we grasp (virtual) objects in three-dimensional space?

Kerstin Stockmeier , Heinrich H. Bülthoff , Volker H. Franz ; email: kerstin.stockmeier@tuebingen.mpg.de Max Planck Institute for Biological Cybernetics, Tübingen, Germany; University of Gießen, Gießen, Germany Introduction Virtual realities can be a useful tool for psychophysical experiments. The experimenter is enabled to fully control the haptic and visual parameters of the simulated objects. For example, he is enabled to easily vary objects after movement onset and therefore to explore the mechanisms of online control in visually guided movements. While grasping real objects, a well studied parameter to quantify the grasp is the maximum grip aperture (MGA) (cf. Jeannerod, 1981, 1984). The MGA scales linearly with the object size and with a slope less than 1 (app. 0.82, Smeets & Brenner, 1999). In this Experiment, the size and position in 3D-space of a virtual disc was varied. We were interested in the question whether participants scale their MGA according to the object size and if the object position in 3D-space influences the MGA. Stimuli and Procedure