Mutual referral of thermal sensation between two thermal-tactile stimuli

When thermal stimulation is applied to one location on the skin and tactile stimulation is presented to another, we perceive the thermal sensation on the latter location as well. While this illusion, known as thermal referral, has been well studied, there is little knowledge on the mutual interaction among multiple thermal-tactile stimuli. We conducted an experiment for verifying the mutual interaction of thermal referral between two thermal-tactile stimuli on forearm and found that there are strong asymmetry between the stimuli locations and between the thermal conditions. The elbow side perceives more thermal referral and synthetic heat (thermal grill illusion) than the wrist side. The warm sensation tends to spread from the periphery toward the center, whereas the cool sensation tends to spread from the center toward the periphery.