Another example of classical conditioning can be seen in the development of conditioned taste aversions. Researchers John Garcia and Bob Koelling first noticed this phenomenon when they observed how rats that had been exposed to a nausea-causing radiation developed an aversion to flavored water after the radiation and the water were presented together. In this example, the radiation represents the unconditioned stimulus and the nausea represents the unconditioned response. After the pairing of the two, the flavored water is the conditioned stimulus, while the nausea that formed when exposed to the water alone is the conditioned response.
Later research demonstrated that such classically conditioned aversions could be produced through a single pairing of the conditioned stimulus and the unconditioned stimulus. Researchers also found that such aversions can even develop if the conditioned stimulus (the taste of the food) is presented several hours before the unconditioned stimulus (the nausea-causing stimulus). Why do such associations develop so quickly? Obviously, forming such associations can have survival benefits for the organism. If an animal eats something that makes it ill, it needs to avoid eating the same food in the future to avoid sickness or even death. This is a great example of what is known as biological preparedness. Some associations form more readily because they aid in survival.
In one famous field study, researchers injected sheep carcasses with a poison that would make coyotes sick but not kill them. The goal was help sheep ranchers reduce the number of sheep lost to coyote killings. Not only did the experiment work by lowering the number of sheep killed, it also caused some of the coyotes to develop such a strong aversion to sheep that they would actually run away at the scent or sight of a sheep.
In humans, a similar experience can be observed. Have you ever gotten sick relatively soon after eating a certain food? It’s likely you no longer choose to eat such food again, as you’ve associated that food with the unpleasant act of vomiting.