Virtual surfaces and the influence of visual cues on grasp

This research compared grasps to real surfaces with grasps to virtual surfaces, and used virtual surfaces to examine the role of cues to surface shape in grasp. The first experiment investigated the kinematics of overhand grasps to real and virtual objects. The results showed that compared to grasps to real surfaces, grasps to virtual objects were different in the deceleration phase and were more variable in their endpoint position. The second experiment examined how, for several real and virtual surface conditions, the decision to use either an over or underhand grasp switched as a function of object orientation and compared these results with data obtained for visual matching of orientation to the same stimuli. The decision to switch between types of grasp showed no difference between actual grasp movements and verbal reports of grasp choice that were not accompanied by arm movement. It was also found that variability in the decision to switch between over and under hand grasps was correlated to variability in visual matching of orientation. The third experiment used virtual surfaces to examine how the removal of visual cues to shape affected the decision to switch from over to underhand grasp. Results showed that the orientation at which the decision switched was dependent on the visual information content. In summary, it was shown that grasps were affected by the information available in virtual surfaces and that, compared with real surfaces, grasps to virtual surfaces appear identical in choice of a grasp type, but differ in the kinematics of the execution of the grasp