Copyright © 2007-2017 Russ Dewey
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 biological event that follows is sickness.
Organisms quickly learn to associate taste with sickness. Taste aversion is interesting to researchers because it is unusual in several ways.
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.
What is taste aversion and how is it unusual among examples of classical conditioning?
Taste aversion can occur even when a person knows that an illness was caused by a virus, not food. That modern knowledge does not interact with the classical conditioning of taste aversion.
The body jumps to the conclusion that the food was bad. So the food becomes repulsive.
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 sometimes know that a virus caused our illness. But the heart (or gut) overrules the head, and an innocent food may repel us. This illustrates again how classical conditioning involves automatic, involuntary, primitive processes in the human brain.
The tendency to blame food for illness, even if the food had nothing to do with the illness, is called the Garcia Effect. In a famous series of experiments, John Garcia gave rats radiation treatments that made them sick.
The rats drank sweetened water in a red-lighted room. Garcia found that rats would avoid sweetened water after getting sick. However, to his surprise, they would NOT avoid red light.
This made evolutionary sense (food or tainted water can make animals sick, light cannot). However, the idea that animals would associate sickness with one type of stimulus rather than another went against long-established dogma in behavioral psychology.
Most behaviorists believed, at the time, in the equivalence of associations assumption. All stimuli should be equally easy to associate.
Garcia's articles were initially rejected by prestigious publications like Science. He did not give up. He published in lesser journals and continued to replicate his experiment with variations.
Eventually Garcia's evidence convinced the scientific establishment. His reward? Garcia's name was attached to the phenomenon of food aversion blamed on food instead of radiation or some other cause.
This shows, incidentally, sometimes it is true that the scientific establishment resists innovation when a new idea contradicts established wisdom. However, it also shows that patience and accumulation of relevant evidence can win the day.
How did John Garcia achieve fame?
Bernstein (1978) reported that children receiving chemotherapy, which causes nausea, develop taste aversions for foods consumed before treatment. That is easy to explain because chemotherapy can make people very sick.
More puzzling is the phenomenon of tumor anorexia. This is a loss of interest in food by cancer patients who are not necessarily receiving chemotherapy.
Bernstein and Sigmundi (1980) suggested tumor anorexia might be due to a generalized conditional aversion to the entire diet. In effect, all foods are associated with illness, so the patient develops an aversion to eating.
What is tumor anorexia? How might it be explained?
Taste aversion can defeat attempts to control predators with poison bait. You may have heard the term bait shyness.
Ranchers in the western United States put poison bait in their fields to kill coyotes preying 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. Make taste aversion work in the rancher's favor.
The ranchers put lithium, which would sicken coyotes but not kill them, into bait that was mutton (sheep meat). The coyotes sampled it and got sick.
However, this time the bait shyness helped the ranchers. The coyotes developed an aversion to mutton and left the sheep alone (Gustafson, Kelly, Sweeny, and Garcia, 1976).
What is bait shyness? How did psychologists make it work in favor of ranchers?
Nicolaus and colleagues (1983) showed taste aversion could be used to control crow predation on eggs, which is a problem for bird sanctuaries and farmers with outdoor chickens. The researchers put a sickness-causing agent in several eggs, 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.
How did Nicolaus and colleagues combat egg predation in crows?
Bernstein, I. L. (1978). Learned taste aversions in children receiving chemotherapy. Science, 200, 1302-1304.
Bernstein, I. L. & Sigmundi, R. A. (1980). Tumor anorexia: A learned food aversion? Science, 209, 416-418.
Gustavson, C. R., Kelly, D. J., Sweeney, M., & Garcia, J. (1976). Prey lithium aversion I: Coyotes and wolves. Behavioral Biology, 17, 61-72.
Nicolaus, L. K., Cassel, J. F., Carlson, R. B., Gustavson, C. R. (1983). Taste-aversion conditioning of crows to control predation on eggs. Science, 220, p.212.
Write to Dr. Dewey at firstname.lastname@example.org.
Copyright © 2007-2017 Russ Dewey