Taste Aversion

Taste aversion—learning to avoid a food that makes you sick—is an intriguing form of classical conditioning. The signal or CS is the taste of a food. The reflex that follows it is sickness. Organisms quickly learn to associate taste with sickness. Taste aversion is interesting to researchers because it appears to violate several rules of classical conditioning.

What is taste aversion and how is it unusual among examples of classical conditioning?

1. It emerges in full strength after only one CS-UCS pairing.

2. The CS-UCS gap is very long—up to six hours or more—yet the conditioning is strong.

3. The association is very selective. People associate the sickness with the odor or taste of a food, not with sights or sounds or other stimuli in the environment.

4. The learned response resists unlearning.

Taste aversion can occur even though a person knows that an illness occurred because of a virus, not because of food. It does not matter; the body jumps to the conclusion that the food was bad, and the food becomes repulsive to us. In ancient times, that was a good thing. Food was often the cause of illness, and it was important to learn quickly to avoid ingesting the same poison twice. In modern times, we might know intellectually that a virus was responsible for our illness...but that does not matter. The heart (or gut) overrules the head, and the innocent food repels us. This illustrates again how classical conditioning involves automatic, involuntary, primtive processes in the human brain.

How did John Garcia achieve fame?

The tendency to blame food for illness, even if the food had nothing to do with the illness, is called the Garcia Effect. John Garcia gave rats a radiation treatment that made them sick after they drank sweetened water in a red-lighted room. He found that after getting sick the rats would then avoid sweetened water, but they would not avoid red light.

This made sense to Garcia (food or water can make animals sick, light normally cannot). However, the idea that animals would naturally associate sickness with one stimulus instead of another flew in the face of established wisdom in the 1960s. Most psychologists at that time believed that all stimuli should be equally easy to associate. Garcia's articles were initially rejected by prestigious publications like Science, but he did not give up. He published in lesser journals and continued to replicate his experiment in several variations. Eventually his evidence convinced the scientific establishment, and Garcia's name was attached to the new phenomenon.

What is tumor anorexia? How might it be explained?

Bernstein (1978) reported that children receiving chemotherapy, which causes extreme nausea, develop taste aversions for foods consumed before treatment. Tumor anorexia is a generalized loss of appetite experienced by cancer patients who are not necessarily receiving chemotherapy. Bernstein and Sigmundi (1980) suggest tumor anorexia may be due to a generalized conditional aversion to the entire diet. In effect, all foods are associated with feelings of illness, so the patient develops an aversion to all eating.

What is bait shyness? How did psychologists make it work in favor of ranchers?

Taste aversion can work against attempts to control predation with poison bait. Perhaps you have heard the term bait shyness Ranchers in the western United States put poison bait in their fields to kill coyotes that preyed on herds of sheep. After the coyotes sampled the bait and got sick from it, they became "bait shy" and would not touch it, so the bait no longer worked. This is a form of taste-aversion conditioning.

Psychologists (including Garcia) suggested a different strategy that would make taste aversion work in the rancher's favor. The ranchers put out poisoned bait that was mutton (sheep meat). Again the coyotes sampled it and got sick. However, this time the "bait shyness" worked to the ranchers' advantage. The coyotes developed an aversion to mutton and left the sheep alone (Gustafson, Kelly, Sweeny, and Garcia, 1976).

How did Nicolaus and colleagues combat egg predation in crows?

Nicolaus and colleagues (1983) showed that taste aversion could be used to control crow predation on eggs-a problem for bird sanctuaries and farmers with outdoor chickens. The researchers put a sickness-causing agent in several eggs, and then left them where crows could get them. This eliminated the egg-eating habit in a population of crows. A therapy called sensitization attempts to do the same thing with humans, conditioning them against drinking or smoking cigarettes by deliberately making them sick when they indulge.


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Copyright © 2007 Russ Dewey