Dynamics and Perception in the Thermal Grill Illusion

A basic challenge in perception research is to understand how sensory inputs from physical environments and the body are integrated in order to facilitate perceptual inferences. Thermal perception, which arises through heat transfer between extrinsic sources and body tissues, is an integral part of natural haptic experiences, and thermal feedback technologies have potential applications in wearable computing, virtual reality, and other areas. While physics dictates that thermal percepts can be slow, often unfolding over timescales measured in seconds, much faster perceptual responses can occur in the thermal grill illusion. The latter refers to a burning-like sensation that can be evoked when innocuous warm and cool stimuli are applied to the skin in juxtaposed fashion. Here, we show that perceptual response times to the thermal grill illusion decrease systematically with perceived intensity. Using results from behavioral experiments in combination with a physics-based description of tissue heating, we develop a simple model explaining the perception of the illusion through the evolution of internal tissue temperatures. The results suggest that improved understanding of the physical mechanisms of tissue heating may aid our understanding of thermal perception, as exemplified by the thermal grill illusion, and might point toward more efficient methods for thermal feedback.