Recall an experience in which you consumed a meal that was fresh from the oven and served too [Page 594]hot. Your mouth may have felt like it was burning; you may have even begun to sweat. Now recall an experience in which, on a dare, you ate a raw chili pepper. In that situation, you may also have experienced a burning mouth and a sweaty forehead. Interestingly, these same responses are evoked by physically different stimuli. In the case of the meal being served too hot, the stimulus is one of a thermal nature—heat. In the case of the chili pepper, the stimulus is a chemical. How can these two, disparate stimuli evoke the same burning perception and the same physiological response (sweating)? The answer ...