Bumps and Dents are Not Perceptually Opposite When Exploring With Lateral Force Cues

Virtual tactile bumps and dents are presented by controlling frictional forces on a surface tactile display, a flat touch screen with tactile feedback functions. This technology enables users to touch and feel three-dimensional objects. The resistive force against a sliding finger is increased and then decreased compared to a base level to present a bump. The order of increase and decrease is inverted for a dent. Thus, the difference between bump and dent presentations lies in the change order of the resistive force. However, bumps and dents are not simply opposite when investigating psychophysical functions with only lateral force cues available, without height and depth information. The results demonstrate that bumps are more easily detected with high surface gradients or resultant force changes and small widths. In contrast, these parameters do not influence the detection of dents among different participants. These findings contribute to a deeper understanding of tactile perception of surface shapes.