Sensitivity to edges of mechanoreceptive afferent units innervating the glabrous skin of the human hand

One type of rapidly adapting (RA) and one type of slowly adapting (SA I) mechanoreceptive unit innervating the glabrous skin area of the human hand have small and well defined receptive fields. Their responses to perpendicular sinusoidal skin displacements were measured when the field was completely covered by a flat contact surface and when the edge of the contact surface was placed over the field. It was found that the majority of the RA and SA I units exhibited stronger responses when the edge of the contactor was placed over the receptive field. This edge sensitivity, which was greatest for the SA I units, may be of particular importance in improving the spatial analysis of the edges of objects in contact with the skin during manual manipulation and exploration.