Investigating the Illusion of Wetness: Cold Dry Stimuli in Sensory Perception

Abstract

Humans lack specialized receptors for perceiving wetness and so it is a compound sensation based on changes in skin temperature and contact pressure that are sensed by thermoreceptors and mechanoreceptors in the skin. In addition to perceiving the wetness of damp fabrics in contact with the skin or the presence of sweat on the skin, humans can perceive wetness in the absence of any moisture, a phenomenon known as illusory wetness. The illusion has been shown to arise when the skin is in contact with a surface and is cooled. This thesis is focused on understanding the variables that contribute to illusory wetness by first determining the difference threshold for perceiving the rate of skin cooling and relating this to perceived wetness. The results from the first two experiments showed that the difference threshold averaged 0.9 °C/s -1.06 °C/s at a reference value of 0. 5 °C/s. For perceiving wetness, the threshold averaged 1.08 °C/s - 1.41 °C/s. The latter finding indicates that the rate the skin cools exceeds some threshold value before it is perceived as being wet. A third experiment explored the role of temperature and surface material in the perception of illusory wetness. The results showed that temperature was the more critical valuable, with ratings of perceived wetness increasing as the temperature decreased further below the baseline skin temperature. These experiments have demonstrated the effect that rates of cooling have on perceiving illusory wetness and have contributed to a better understanding of the role of surface material and temperature on perceiving wetness during static contact. These findings are relevant to simulating wetness in prosthetic devices and virtual reality environments.