Influence of Cooling Rates and Contact Material on Illusory Wetness

It has been known for some time that a perception of wetness can be elicited when the skin is in contact with a cold, dry surface, a phenomenon called illusory wetness. The critical feature of the illusion is the rate at which the skin cools. This paper focuses on understanding the variables that contribute to illusory wetness by initially determining the sensitivity of participants to the rate with which the skin is cooled and then examining how the perception of illusory wetness is affected by the thermal and material properties of the contact surface. In the first experiment, the method of constant stimuli was used to measure the difference threshold for the rate of cooling on the hand. The results showed that the threshold averaged 0.90 $^{\circ }$C/s at a reference value of 0.5 $^{\circ }$C/s and that wetness was perceived at an average cooling rate of 1.09 $^{\circ }$C/s. In the second experiment, participants rated the perceived wetness of five contact materials presented at four different surface temperatures. The results showed that temperature was the more critical variable in determining perceived wetness, and that the influence of material properties in this experiment related primarily to their effects on the heat transfer process.