The purpose of this project is to study psychophysically the sensitivity of the skin to non-caustic chemicals. Although human skin is generally considered to be an effective barrier against environmental chemicals, numerous natural substances are capable of penetrating the skin and producing sensations ranging from coolness or warmth to irritation and pain. The incorporation of many of these chemicals into items such as personal hygiene products (e.g., deodorants and toothpastes) and topical medicaments (e.g., liniments and balms) has made chemical stimultion of the skin commonplace. However, the perceptual characteristics of cutaneous chemical stimulation have never been systematically analyzed, hence little is known about the sensory consequences or medicinal efficacy of topical treatments. The proposed research will therefore employ proven psychophysical techniques (e.g., the method of limits, magnitude estimation, cross-modality matching) in novel experimental paradigms to obtain germinal data on the sensory effects of five of the most common chemical stimul (menthol, capsaicin, mehtyl salicylate and ethanol). Studies will evaluate the qualitative and quantitative properties of cutaneous chemosensation (e.g., spatial summantion and localization) and the possible sensory interactions that result from concurrent chemical-thermal, chemical-mechanical and chemical-chemical stimulation. The results will help establish (l) the psychophysical properties of chemical stimulation, (2) which sensory system or systems mediate cutaneous chemical sensation, (3) which cutaneous receptor mechanisms (e.g., mechano-sensitive or thermo-sensitive) are most vulnerable to particular topical chemicals, and (4) the kinds of sensory interactions that occur during multi-modal cutaneous stimulation. It is anticipated that a greater understanding of these issues will contribute significantly to our knowledge of cutaneous sensitivity and impact upon the frequency and manner of use of sensorially-active substances on the skin.
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