The coding of roughness.

This review examines the way information about textures is captured, encoded, and processed by the somatosensory system to produce sensations of roughness/smoothness. Textures with spatial periods exceeding about 200 microm are encoded spatially, so roughness is nearly independent of the speed and direction of their movement across the skin. The information consists of spatial variations in activity among slowly adapting (SA1) mechanoreceptors, and appears to be extracted by specialized cortical neurons. Perception of the roughness of finer surfaces is mediated by detection, primarily by Pacinian afferents, of cutaneous vibrations generated when textures move across the skin. Movement is necessary to the perception of these textures, and vibrotactile adaptation interferes with it. The code is an intensitive one (i.e., the amount of activity in Pacinian afferents).