Taste aversion
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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).
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[edit] Garcia's study
Conditioned taste aversion is studied by Dr. John Garcia. Garcia "conditioned" rats to develop taste aversion to sweetened water, a substance that rats generally consume in higher quantities than tap water. In one study, Garcia had three main experimental conditions. In the control condition, rats were given access to sweetened water with no interference. In a second condition, the rats were given access to the sweetened water, then exposed to a mild dose of radiation some time after. In the third condition, the rats were given access to the sweetened water, then exposed to a higher dose of radiation. Radiation is an unconditioned stimulus that tends to induce nausea. Unlike humans, rats do not have the ability to vomit when they are nauseated.
All three groups of rats were then given a choice of sweetened water or unsweetened water, and Garcia measured the amount of each that the rats consumed. The rats in the control condition drank just over 80% sweetened water (20% unsweetened); those in the mild radiation condition drank nearly 40% sweetened water; those in the high radiation condition drank less than 10% sweetened water. Thus, especially for the high radiation rats, when associated with nausea the sweetened water became aversive.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 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.
