Analysis of Paradoxical Phenomenon Caused by Presenting Thermal Stimulation on Three Spots

Thermal referral (TR) and thermal grill illusion (TGI), known as illusions of thermal sensation, have been well studied. In a previous study, an experiment using two thermal-tactile stimulations to the forearm revealed that these illusions simultaneously occurred. In this experiment result, a few subjects perceived a hot stimulation as a cold sensation and/or a cold stimulation as a hot sensation. This paradoxical phenomenon of thermal sensation, which is not discussed specifically in the previous study, could be a fatal problem in the case presenting thermal stimulation on multiple spots intentionally. Therefore, we decided to analyze this paradoxical phenomenon. In this paper, we confirmed that this phenomenon occurs when we present thermal stimulation on two spots and three spots. In comparing the results of thermal stimulation on two spots and three spots, the occurred probability increased on three spots.