A cup of coffee in Mixed Reality: analysis of movements' smoothness from real to virtual

Mixed Reality (MR) is promising to fuse the visualization potentialities of Virtual Reality (VR) with the physical properties of the real world, thus allowing a more natural interaction in virtual environments and preserving visuo-motor coordination and tactile perception. In this work, we perform an interaction task, taking a cup of coffee, which involves hand movements and grasping. We consider three scenarios: an MR environment implementing an ecological object substitution technique, in which the user touches real objects tracked in real-time and sees a virtual counterpart; a classical VR environment, in which virtual objects do not have any real counterpart; the corresponding real scenario. In MR, the tracked real object can be either with a shape like the virtual one or a simpler real object. We compute the Minimum Jerk Cost function as a metric to compare movements in the different modalities, assuming that a major goal of motor coordination is producing the smoothest possible movement of the hand. From a pilot study, movements cost in VR is 5.1 times higher than the cost of the movements in the real world. This could be due to the lack of physicality when grabbing virtual objects without a real counterpart. Furthermore, the cost of movements obtained in MR is only 2.8 times higher than the one obtained in the real scenario, indicating that such a system could lead to more realistic and efficient human movements with respect to a VR system.