The role of visual-haptic discrepancy in virtual reality environments

Visual-haptic interactions are of utmost importance for VR surgical simulators. We investigate the role of spatial visual-haptic discrepancy by manipulating the presentation order of visual and force feedback. Participants were asked to indicate the nearer wall between a visual and an pliable haptic virtual surface. We factorially manipulated the discrepancy levels (±5, 15, 25 mm) and the stiffness values of the pliable haptic wall, 83 (human fat) and 331 N/m (human skin). Psychophysical curves over depth penetration and latency time inside the wall were estimated. Results showed that haptic and visual walls were indistinguishable among the discrepancy range of 10.57±23.12 mm for 83N/m and -3.07±9.11 mm for 331 N/m. The trend of psychophysical curves show as, in presence of discrepancies or errors between an haptic and a visual surface, the overall perception is influenced by the stiffness of the haptic surface, in according with a weighted summation model, showing a direct relation between the stiffness factor and the weight of the haptic component in the model.