Taste Aversion through Classical Conditioning
Classical conditioning states that learning is a gradual process, that it is not possible for a subject to be classically condition in only one trial. However, if you eat something and become sick from it, there is a very good probability that you will develop a strong distaste for that food. This effect is known as taste aversion, which has brought up many questions about classical conditioning.
It was Garcia and Koelling (1966) who studied the level of conditioning in rats using two conditioned stimulus (CS), an audiovisual stimulus and a salty flavor added to drinking water. The two unconditioned stimulus (UCS), a mild foot-shock and a nausea-producing drug. In the conditioning phase of this experiment, the two CSs (salty flavored and the audiovisual stimulus) always occurred at the same time and were presented to the rats equally. One group of rats received a UCS with a nausea-producing substance in the drinking water (lithium chloride). Another group of rats were shocked in the foot as a UCS 2 seconds after drinking the water (Garcia & Koelling as sited Walker 1995).
After many conditioning trials, each rat was tested with each of the two CSs taken separately. In one trial the rats were given access to tasty water, salty flavored water with out the audiovisual CS. In another trial, the rats were given access to "bright noisy water" as stated by Garcia and Koelling: unflavored drinking water that had the audiovisual CS present. If there is an aversion to the stimulus of the foot-shock of the nausea-producing drug then the rats will have become conditioned to the CS. Both UCSs produced an aversion a particular CS; the foot-shock produced a strong aversion to the audiovisual CS but showed little or no avoidance to the salty flavored water. However the group of rats that were given lithium chloride, resulting nausea-produced taste aversion to the salty flavored water, but no aversion to the audiovisual CS. It is seen that the rats promptly learned to associate a taste CS with a UCS of nausea but not with the foot-shock, where the audiovisual CS was conditioned to the foot-shock but not to nausea (Walker 1995).
Taste aversion has violated three principles of classical conditioning, the first is that equal associability of stimuli: any CS can be paired with any UCS. This has proven to be untrue because if it were, the rats that became sick would have avoided both the salty water CS and the audiovisual CS. The second principle violated is temporal contiguity: CS and UCS have to be presented close together in time. Again untrue in this case because of such a long delay between drinking the salty water and becoming sick. The third and final principle is that learning is gradual, but in this case only one trial was enough.
The studies done by Garcia and Koelling have had much support from many other experiments done in similar or the same situations. A study of ingestional aversion (Gregg,...