The way the brain perceives stimuli says something about how taste, smell and touch affect behavior. Most stimuli that are perceived positively are, in fact, good for people; food tastes and smells "good" because without some kind of psychological inducement to eat, people would not survive. Stimuli that are perceived negatively are those that people need to avoid; the fact that rotting foods smell "bad" is the brain's way of keeping one from eating something that might make one sick.