Size discrimination on the skin.

Reasons are given for rejecting the two-point threshold as the standard measure of spatiotactile resolution. As alternative techniques, thresholds were obtained for disc-size and disc-annulus discriminations. Disc-annulus thresholds are comparable to two-point values, but disc-size thresholds are smaller by a factor of 10. Thus, at least part of the cutaneous system is better organized for localization and sizing of a stimulus than for detection of discontinuities in it.