Has coincidence ever made you sick to your stomach after eating a favorite food?
Perhaps you got seasick on a boat shortly after gobbling some blueberry pie. Even weeks after the vomiting is over, what happens when you try to eat that once-favorite dessert again? Chances are, you may find the taste downright disgusting. Years later, you might still dislike blueberries, even after you've forgotten the incident completely.
You've developed a food aversion.
Food aversions are always triggered by nausea, and they seem to bypass the slow trial-and-error of ordinary learning. They may be annoying, but they're an important survival trait that helps most animals, including humans, avoid poisonous foods. What's more, food aversions tend to err on the side of caution. That's why one bout of coincidental nausea can change our taste preferences for life, even about a safe food.
Food aversions are interesting to scientists that study learning. In one study, rats were injected with nausea producing drugs shortly after drinking sweetened water. This caused the rats to permanently avoid sweetened water thereafter. In contrast, rats that got a different unpleasant stimulus, electric shocks to their feet, for example, continued to enjoy the sweet water taste. This suggests that nausea induces a special type of super-efficient learning that other unpleasant stimuli can't touch.
This education of the palate occurs automatically, and has nothing to do with whether we consciously remember the nausea. Indeed, food aversions can develop if a nauseating injection is given when the animal is unconscious or asleep, hours after the meal.