Displaying Pain Sensation in Midair by Thermal Grill Illusion

In this study, we propose a method to display a pain sensation by thermal grill illusion in a noncontact manner. An ultrasound-driven cold air flow using mist vaporization cools a spot on a skin while a light beam irradiation produces a hot spot near the cooled spot. The cold and hot stimuli presented simultaneously produce a pain sensation without damage of the skin. We clarify the relationship between the pain sensation and the temperature change on the skin observed by a thermography camera. Since it is a noncontact method, we can evaluate the precise condition of the skin temperature distribution for the thermal grill illusion. This study provides a scientific tool to clarify the thermal grill illusion as well as a practical pain display.