Force Shading for Haptic Shape Perception

Abstract This paper proposes a novel haptic rendering algorithm and describes a perceptual experiment that demonstrates its effectiveness in causing humans to perceive shapes during manual interactions with virtual environments. The algorithm, called “Force Shading” (analogous to Phong Shading for visual displays), refers to a controlled variation in the direction of the force vector displayed by the haptic renderer for the purpose of creating the illusion of a non-flat shape on a nominally flat surface. Experiments on shape perception were done on 5 subjects using the Phantom as the haptic interface device. In these experiments, subjects manually explored the haptic display of various virtual polyhedral approximations of a circular cylindrical bump, with or without force shading. They then indicated the perceived shape by selecting one from a menu of shapes displayed on a computer monitor. Without force shading, the subjects accurately identified the polyhedral nature of the virtual bumps. With force shading, however, the subjects identified the polyhedral approximations as feeling closer to that of a smooth cylinder. The higher the number of polygons, the higher was the percentage of trials in which the shape was identified with a smooth cylinder.