Taste Aversion

Modified: 2020-03-27

Garcia was studying classical conditioning in rats. Nausea was the UCR, and it was induced by two UCSs, either X-rays or LiCl (a salt). Both of the UCSs will cause nausea in the appropriate dosage. Other groups of rats were given electric shock as a UCS. The CSs were either bitter water or plain water associated with light and sound. So, some rats drank the bitter water and were made sick. Others drank the bitter water and received a shock. Still others drank the plain water and were made sick. Finally, some drank the plain water and received an electric shock.

Then all were allowed to choose between the bitter water and the plain water associated with the light and sound. Those that had been made sick would not drink the bitter water. One group would not drink even when the interval between the bitter water and the nausea had been 75 minutes! Talk about trace conditioning. The rats that had received the foot shock did not avoid the water in either form.

The main result of Garcia's research was to demonstrate that not all CS-UCS pairings are equivalent. This was a blow to established learning theory (More recent research has shown that nearly any CS can be made to act like the bitter water. However, the procedures to do so are different than Garcia's, so the effect of Garcia's research remains.)

In a practical sense, a new field emerged, one that studies taste aversions. For example, suppose you have never eaten oysters. You arrive in New Orleans, are persuaded to try a dozen raw ones, but one was bad. Your next three days are spent retching. What will you do if, three months later, someone offers you an oyster? What do you think of New Orleans? But, if you had eaten oysters for a long time, and ate a bad one, you will probably eat oysters again. This phenomenon is related to food neophobia, the fear of new foods. We are much more likely to become conditioned to the UCSs and UCRs associated with new foods than to old foods.

Another real example of food neophobia and taste aversion happened to me some 10 years ago. We stopped at a restaurant in Stamps, AR , late one hot August afternoon. I ordered chicken livers, ate them all. Much later that night, I was awakened from a sound sleep by gastrointestinal distress. Suffice it to say that I was sick for the next three days. I have never eaten at that restaurant in Stamps or at any of its franchises elsewhere again. Nor do I eat chicken livers. (So, I must not have eaten chicken livers very often before, and that was the case.) I still eat calves' liver however, so the avoidance did not generalize to all forms of liver.

Finally, a very real problem is the issue of pest control. Coyotes have thus far resisted all efforts at control, including poisoning. Poison baited carcasses have been set out in an attempt to reduce their numbers. The coyotes very quickly learn to avoid such baits. Why? If they only eat enough to become sick, they learn to avoid such new food sources. The same is true with rats. They will learn to avoid poison baits for the same reason.

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