Tactile pattern discrimination at adjacent locations along the proximal-distal axis of the index finger

A discrimination task was used to examine how locations on the glabrous skin of the terminal and middle phalanges of the index finger affect the perceived shape of tactile patterns. On each trial, a pair of same-shape or different-shape patterns was presented successively on the distal half, on the proximal half, or on both halves of a phalanx. Observers responded "same" or "different" depending on the perceived pattern shape. Performance was compared between the two phalanges, with two different pattern sets. For patterns at separate locations, performance was uniformly poor. For patterns at the same location, performance was better on the distal halves than on the proximal halves of both phalanges for one pattern set but not for the other. Performance was best on the distal half of the terminal phalanx. The results are discussed in terms of the densities of innervation of first-order afferents.