Perceived warmth and skin temperature as functions of the duration and level of thermal irradiation!

This study examined the correlations among the degree of perceived warmth. the level and duration of irradiant flux. and the thermal response of the skin. For any constant duration. perceived warmth grew as a power function of the difference between the irradiant flux of the stimulus and the flux that approximates the absolute threshold for warmth. The exponent of the power function was about 0.87 for the shortest durations (2—6 sec). but rose to 1.04 for the longest duration of exposure (12 sec). For any constant level of flux. perceived warmth changed only slightly with duration. In contrast, superficial skin temperature. and inferred temperatures of deeper layers of the skin, rose continuously and markedly with duration. Neither the change in tissue temperature. nor the rate of change of tissue temperature, nor thermal gradient correlated consistently with level of perceived warmth. The change in the difference between the temperature 0.2 mm and that 1.0 mm below the skin surface provided a fairly good but not perfect correlate to perceived warmth. The findings suggest the possibility that sensory adaptation at the site of the receptor system mediating warmth could act in such a way as nearly to offset the effect of rising skin temperature with increased duration ofstimulation.