A combined psychophysical and peripheral neural study of cutaneous texture perception is proposed. Textured surfaces that are 3-D replicas of computer generated patterns (with elements that could be made as small as 10 micrometers) will be rubbed against the finger pad. The lateral and vertical displacements of the skin and the associated compressional and shear forces will be controlled or measured. In psychophysical experiments, human subjects will either actively rub (or be passively rubbed with) textures made of arrays of either nodes or bars that vary in shape, height, and in spatial frequency. The sensory capacities to detect, discriminate and judge the roughness of these textures will be determined as a function of spatial frequency and compressional force. These measurements will be obtained under varied conditions of stimulation in order to determine the constancies and limits of cutaneous texture perception. The nature of any sensory channels responsive to selected regions of the spatial-frequency spectrum will be examined; sensitivity will be measured following adaptation, induced by rubbing with certain patterns, or following local cutaneous anesthesia of mechanoreceptors sensitive to low frequencies of vibration. In neurophysiological experiments, the same textures will be applied to the finger pad of the anesthetized monkey while the evoked activity in single rapidly- and slowly-adapting mechanoreceptive afferents is recorded. The range of spatial frequencies (bandwidth) which excites each type of mechanoreceptor will be determined under physical conditions found important in the psychophysical experiments. The peripheral neural mechanism for coding a spatial pattern as opposed to that coding surface roughness will be investigated. The goal is to characterize the primary afferent data base on which central spatiotemporal processing mechanisms must operate during cutaneous texture perception.
