Easy-to-Recognize Bump Shapes using only Lateral Force Cues for Real and Virtual Surfaces

Friction-variable-type surface texture displays can present macroscopic bumps and dents on flat touch panels. In this study, bumps and dents of different shapes were identified only when frictional or lateral resistance forces were presented. Shapes that were easy to recognize were then investigated. The tested surfaces varied in height and width, whereas their maximum gradients were the same; those with greater widths also exhibited greater heights or depths. We conducted experiments with these surfaces under virtual conditions using an electrostatic friction display (Experiment 1) and under real conditions, where actual bumps and dents were explored using a lateral force presenter (Experiment 2). The experimental results were not consistent between the virtual and real conditions. In the virtual condition, bumps and dents with moderate heights/depths and widths were most likely to be recognized as bumps and dents. This suggests that adjusting the heights and widths of the bumps and dents increases their perceptual clarity when the maximally applicable voltages are limited owing to safety regulations. Under real conditions, we did not observe significant differences among the different bump shapes. Pursuing the incongruency between virtual and real conditions will lead to a better understanding of the haptic perception for macroscopic surface shapes.