Taste aversion conditioning

Conditioned Taste Aversion is an example of classical conditioning, also called Pavlovian conditioning. Conditioned taste aversion occurs when a subject associates the taste of a certain food with symptoms caused by a toxic, spoiled, or poisonous substance. Generally, taste aversion is caused after ingestion of the food causes nausea, sickness, or vomiting. The ability to develop a taste aversion is considered an adaptive trait or survival mechanism that trains the body to avoid poisonous substances (e.g., poisonous berries) before they can cause harm. This association is meant to prevent the consumption of the same substance (or something that tastes similar) in the future, thus avoiding further poisoning. However, conditioned taste aversion sometimes occurs in subjects when sickness was merely coincidental and not related to the food (for example, a subject who gets a cold or the flu shortly after eating bananas might develop an aversion to the taste of bananas).

Garcia's study
While studying the effects of radiation on various behaviours during the 1950s, Dr. John Garcia noticed that rats developed an aversion to substances consumed prior to being irradiated. To examine this, Garcia put together a study in which three groups of rats were given sweetened water followed by either no radiation, mild radiation, or strong radiation. When the rats were subsequently given a choice between sweetened water and regular tap water, rats who had been exposed to radiation drank much less sweetened water than those who hadn't. Specifically, the total consumption of sweetened water for the no-radiation, mild radiation and strong radiation rats was 80%, 40% and 10% respectively.

This finding ran contrary to much of the learning literature of the time in that the aversion could occurr after just a single trial and over a long delay. Garcia proposed that the sweetened water became dispreferred because of the nausea inducing effects of the radiation, and so began the study of conditioned taste aversion.

Interesting notes concerning taste aversion
Taste aversion does not require cognitive awareness to develop--that is, the subject does not have to think, "Wow, this tastes like the stuff that got me sick." In fact, the subject may hope to enjoy the substance, but the body handles it reflexively. Conditioned taste aversion illustrates the argument that in classical conditioning, a response is elicited.

Also, taste aversion generally only requires one trial. The experiments of Ivan Pavlov required several pairings of the neutral stimulus (e.g., a tuning fork) with the unconditioned stimulus (i.e., meat powder) before the neutral stimulus elicited a response. With taste aversion, after one association between sickness and a certain food, the food may thereafter elicit the response. In addition, lab experiments generally require very brief (less than a second) intervals between a neutral stimulus and an unconditioned stimulus. With taste aversion, however, the bratwurst a person eats at lunch may be associated with the vomiting that person has in the evening.

If the flavor has been encountered before the subject becomes ill, the effect will not be as strong or will not be present. This quality is called latent inhibition. Conditioned taste aversion is often used in laboratories to study gustation and learning in rats.

Aversions can also be developed to odors as well as to tastes.

Taste aversion in humans
Taste aversion is fairly common in humans. When humans eat bad food (e.g., spoiled meat) and get sick, they may find that food aversive until extinction occurs, if ever. Also, as in nature, a food does not have to cause the sickness for it to become aversive. A human who eats sushi for the first time and who happens to come down with an unrelated stomach virus or influenza may still develop a taste aversion to sushi.

Taste aversion is a common problem with chemotherapy patients, who become nauseated because of the drug therapy but associate the nausea with consumption of food.

Applications of taste aversion
Taste aversion has been demonstrated in a wide variety of both captive and free-ranging predators. In these studies, animals that consume a bait laced with an undetectable dose of an aversion agent avoid both baits and live prey with the same taste and scent as the baits. When predators detect the aversion agent in the baits, they quickly form aversions to the baits, but discriminate between these and different-tasting live prey. The use of conditioned taste aversion in wildlife management has so far been resisted by governmental wildlife managers, mainly because of a lack of understanding of the process.

Stimulus generalization
Stimulus generalization is another learning phenomenon that can be illustrated by CTA. This phenomenon demonstrates that we tend to develop aversions even to types of food that resemble the foods which cause us illness. For example, if one eats an orange and gets sick, one might also avoid eating tangerines and clementines because they look similar to oranges, and might lead one to think that they are also dangerous.