High-density thermal sensitivity of the hand under different thermal states and stimulus intensities.

Understanding how the human body senses small-scale heating and cooling stimuli can help researchers evaluate thermal comfort effects and health risks of thermal stimulus combinations under complex thermal exposure. Two experiments measured high-density thermal sensitivity on the hand to investigate whether the initial thermal states and stimulus intensities affect thermal sensitivity. After pilot tests, a 23°C cold-water bath and a 41°C hot-water bath were applied to create initial states deviating from thermal neutrality. The whole hand and part of the wrist with all test spots were immersed for 1 min and dried by a towel. Results showed that cold sensitivity and warmth sensitivity have a linear relationship with each other, but 16 of 20 subjects (80%) were more sensitive to cooling than to heating. The 1-min water-bath treatment significantly reduced hand thermal sensitivity. Compared with a thermally neutral state, a cold-water bath and hot-water bath reduced cold sensitivity by 22% and 61%, respectively, and reduced warmth sensitivity by 47% and 51%, respectively. Under a thermally neutral state, the perceptible thresholds for cooling and heating stimuli were -1.3°C and +1.8°C, respectively. Comfortable stimulating temperature ranges were 24°C-30°C for cooling and 34°C-39°C for heating. Thermal sensitivity differences among stimulus intensities were small, but differences among test spots and subjects were significant.