Taste Aversion Essay

This essay has a total of 1203 words and 6 pages.


Taste Aversion





Taste Aversion
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, Melanie,
Kittrell, Domjan & Amsel, 1978), where 12 and 15 day-old rats were conditioned by infusing
a .5% solution of saccharin into the oral cavity. This was then followed by an oral
infusion by the injection of lithium chloride. At both ages, subjects that had saccharin
exposure was followed by a lithium injection within 2 to 3 minutes drank less when the
saccharin solution was again presented by oral infusion 12 hours later. Ingestional
aversions were also learned by 12-day-olds when an interval as long as 30 minutes was
introduced between saccharin exposure and lithium toxicosis, however there was no sign of
aversion to the saccharin solution when the toxicosis was delayed by 120 minutes. In
contrast, the 15-day-olds were able to learn aversion with both the 30 minute and 120
minute delay intervals. Although the absence of 120 minute long-delay learning in 12 day
olds, further experiments show that ingestional aversion conditioned at 12 days of age
were retained for 2 weeks (Gregg, et al, 1978). These results provide more evidence to
support taste aversion.

To further test the validity of conditioned taste aversion, a study was done in the
generalization of conditioned taste aversion in rats (Richardson, Williams & Riccio,
1984). This study further investigates the effects of delayed testing (2, 7, 21 days), the
rats were given varying concentrations of sucrose (2.5%, 10%, 32%) and immediately
received lithium chloride. Subjects were then tested either 2, 7, or 21 days after
conditioning. Findings show that the rats show avoidance in all categories, this further
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