Subjective magnitude of tactile roughness

The subjective experience of tactile roughness was judged by subjects using the method of absolute magnitude estimation (AME). The stimuli were 11 gra des of sandpaper having particle diameters ranging from 16 to 905 mu m All of the estimates resulted in power functions when assigned numbers were plo tted as a function of particle diameter. It was determined that on the fing er pad of the index finger and the thumb there was no difference between th e active and passive modes of stimulation and that there was no difference in roughness estimates made on the finger and on the thumb. When the finger and thumb were stimulated simultaneously, higher numbers were assigned for a given stimulus indicating the presence of a form of spatial summation at these sites. The pleasantness of the tactile sensation, as assessed using AME, was inversely related to the roughness estimates. Furthermore, hydrati on of the stratum corneum with water and three concentrations of surfactant solutions reduced the sensation of roughness below that of normally hydrat ed skin.