Analysis of Medium Wrap Freehand Virtual Object Grasping in Exocentric Mixed Reality

This article presents an analysis into the accuracy and problems of freehand grasping in exocentric Mixed Reality (MR). We report on two experiments (1710 grasps) which quantify the influence different virtual object shape, size and position has on the most common physical grasp, a medium wrap. We propose two methods for grasp measurement, namely, the Grasp Aperture (GAp) and Grasp Displacement (GDisp). Controlled laboratory conditions are used where 30 right-handed participants attempt to recreate a medium wrap grasp. We present a comprehensive statistical analysis of the results giving pairwise comparisons of all conditions under test. The results illustrate that user Grasp Aperture varies less than expected in comparison to the variation of virtual object size, with common aperture sizes found. Regarding the position of the virtual object, depth estimation is often mismatched due to under judgement of the z position and x, y displacement has common patterns. Results from this work can be applied to aid in the development of freehand grasping and considered as the first study into accuracy of freehand grasping in MR, provide a starting point for future interaction design.