Pseudo-haptics for rigid tool/soft surface interaction feedback in virtual environments

This paper proposes a novel pseudo-haptic soft surface stiffness simulation technique achieved by displaying the deformation of the soft surface and maneuvering an indenter avatar over a virtual soft surface by means of a touch-sensitive tablet. The visual feedback of the surface deformation and the alterations to the indenter avatar behavior produced by the proposed technique create the illusion of interaction with a hard inclusion embedded in the virtual soft surface. The proposed pseudo-haptics technique is validated with a series of experiments conducted by employing a tablet computer with an S-pen input and a tablet computer with a bare finger input. Tablet computers provide unique opportunities for presenting the pseudo-haptic (indenter avatar speed), haptic (contact reaction force from the device surface) and visual cues (surface information) at the same active point of interaction which facilitates information fusion. Hence, here, we evaluate the performance of tablet computers in identification of hard inclusions within virtual soft objects and compare it with the performance of a touchpad input device. A direct hand-soft surface interaction is used for benchmarking of this study. We found that compared with using a touchpad, both the sensitivity and the positive predictive value of the hard inclusion detection can be significantly improved by 33.3% and 13.9%, respectively, by employing tablet computers. Using tablet computers could produce results comparable to the direct hand-soft surface interaction in detecting hard inclusions in a soft object. The experimental results presented here confirm the potential of the proposed technique for conveying haptic information in rigid tool/soft surface interaction in virtual environments.