Effects of hydration on tactile sensation.

The routine tasks of washing usually necessitates the immersion of parts of the body in water, which causes hydration and changes in the mechanical properties of the superficial layer of skin. To determine how hydration affects tactile sensations, the hydration and skin-surface temperature of glabrous and hairy skin was first measured under normal conditions (air), after submersion in distilled water alone and after submersion in a surfactant-water solution. In these experiments, measurements were made of the time to achieve complete hydration and the recovery time to normal levels. The uptake of water in hairy skin was found to be considerably greater than in glabrous skin, and retention was significantly prolonged by the surfactant additive. Subsequent experiments on glabrous skin, based on the results of the preceding hydration studies, measured in-air and hydrated tactile thresholds and sensation magnitudes to vibratory stimuli and to the roughness of textured surfaces. Vibrotactile detection thresholds were not affected by skin hydration, nor were sensation magnitudes to suprathreshold vibratory stimuli. However, suprathreshold perceptions of roughness were substantially altered by hydration. It is concluded that hydration and the mechanics of the skin play a major role in the perception of spatiotemporal (i.e., textured) surfaces and, thus, must be taken into account in any physiological/psychophysical model based on using such stimuli. This may not be required for models based on predominantly temporal (i.e., vibratory) stimuli.