Directional sensitivity to a tactile point stimulus moving across the fingerpad.

The ability of subjects to discriminate between directions of a point contact moving across the fingerpad was examined. Subjects were required to report, using an adaptive two-interval, two-alternative forced-choice procedure, whether in two sequential stimuli the direction of motion changed in a clockwise or counterclockwise direction. The overall mean orientation-change threshold across eight stimulus orientations was approximately 14 degrees, with the lowest threshold for the point motion toward the wrist. This observed lower threshold in the distal-to-proximal direction is thought to be due to stretching of the skin at the tip of the fingernail, to which one may be particularly sensitive. For all orientations, thresholds were generally more uniform and higher than those reported on vibrotactile linear contactor arrays for horizontal and vertical orientations.