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. Computer-controlled manufacturing techniques have made it possible to produce stimuli with sufficient accuracy to explore the gamut of haptic scales. We used stimuli with a convex or concave Gaussian-shaped profile running over the middle of a strip. The width of the Gaussian profile was varied between 150 microns 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 threshold between a flat surface and a Gaussian surface was investigated in a series of two alternative forced choice experiments on human subjects. The thresholds run from 1 micron for the narrowest Gaussian profiles to 8 mm for the broadest profile. The same thresholds were found for convex and concave shapes. 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 found to be a power function with an exponent of about 1.3.