Haptic detection thresholds of Gaussian profiles over the whole range of spatial scales

In the literature only a small subset of the broad range of scales of human haptic perception has been explored. In this experiment, haptic detection thresholds have been investigated over a wide range of spatial scales. Comp uter-controlled manufacturing techniques have made it possible to produce s timuli with sufficient accuracy to explore the gamut of haptic scales. We u sed stimuli with a convex or concave Gaussian-shaped profile running over t he middle of a strip. The width of the Gaussian profile was varied between 150 mu m and 240 mm. In this range of spatial scales a number of mechanisms , ranging from cutaneous mechanoreception to proprioception in fingers, arm and shoulder, contribute to haptic perception. The discrimination threshol d between a flat surface and a Gaussian surface was investigated in a serie s of two alternative forced choice experiments on human subjects. The thres holds run from 1 mu m for the narrowest Gaussian profiles to 8 mm for the b roadest profile. The same thresholds were found for convex and concave shap es. Over the range of spatial scales, from 1 mm width on, the dependence of the detection threshold on the spatial width of the Gaussian profile was f ound to be a power function with an exponent of about 1.3.