Haptic exploration of spheres: Techniques and initial experiments

Haptic perception of properties of objects in the hand is not fully understood. One aspect is the precision with which subjects can detect geometrical features. In this experiment, subjects discriminated between pairs of steel spheres in which one was a precisely manufactured ball bearing and the other was distorted by various degrees. Precise distortions of spheres provide a very sensitive but practical way to create controlled experiments. In one experiment, we reduced the diameter along a single axis and smoothed and polished the resulting shape. In another, the reduced diameter was held constant, and local curvature was varied. Using these spheres, subjects were able to detect subtle changes in sphere diameter along one axis, but were not as sensitive to changes in local curvature. For diameter, a just-noticable-difference (JND) between 2% and 5% was measured.