Hockenbury Discovering Psychology 5th txtbk

Contemporary Views of Classical Conditioning197Such learned taste aversions are relatively common. Our students have told usabout episodes of motion sickness, morning sickness, or illness that resulted in tasteaversions to foods as varied as cotton candy, strawberries, and chicken soup. In somecases, a taste aversion can persist for years.At first glance, it seems as if taste aversions can be explained by classical conditioning.In Don’s case, a neutral stimulus (spaghetti) was paired with an unconditionedstimulus (a stomach virus), which produced an unconditioned response(nausea). Now a conditioned stimulus, the spaghetti sauce by itself elicited the conditionedresponse of nausea.But notice that this explanation seems to violate two basic principles of classicalconditioning. First, the conditioning did not require repeated pairings. Conditioningoccurred in a single pairing of the conditioned stimulus and the unconditioned stimulus.Second, the time span between these two stimuli was several hours, not a matterof seconds. Is this possible? The anecdotal reports of people who develop specific tasteaversions seem to suggest it is. But such reports lack the objectivity and systematiccontrol that a scientific explanation of behavior requires.Enter psychologist John Garcia, who demonstrated that taste aversions could beproduced in laboratory rats under controlled conditions (Garcia & others, 1966).Garcia’s procedure was straightforward. Rats first drank saccharin-flavored water(the neutral stimulus). Hours later, the rats were injected with a drug (the unconditionedstimulus) that produced gastrointestinal distress (the unconditioned response).After the rats recovered from their illness, they refused to drink the flavoredwater again. The rats had developed a taste aversion to the saccharin-flavored water,which had become a conditioned stimulus.At first, many psychologists were skeptical of Garcia’s findings because theyseemed to violate the basic principles of classical conditioning. Several leadingpsychological journals refused to publish Garcia’s research, saying the results wereunconvincing or downright impossible (Garcia, 1981, 2003). But Garcia’s resultshave been replicated many times. In fact, later research showed that taste aversionscould develop even when a full 24 hours separated the presentation of the flavoredwater and the drug that produced illness (Etscorn & Stephens, 1973).Conditioned taste aversions also challenged the notion that virtually any stimuluscan become a conditioned stimulus. As Pavlov (1928) wrote, “Any natural phenomenonchosen at will may be converted into a conditioned stimulus . . . any visual stimulus,any desired sound, any odor, and the stimulation of any part of the skin.” Afterall, Pavlov had demonstrated that dogs could be classically conditioned to salivate toa ringing bell, a ticking metronome, and even the sight of geometric figures.But if this were the case, then why didn’t Don develop an aversion to other stimulihe encountered between the time he ate the spaghetti and when he got sick? Whywas it that only the spaghetti sauce became a conditioned stimulus that triggered nausea,not the dinner table, the silverware—or even Sandy, for that matter?Contrary to what Pavlov suggested, Garcia and his colleagues demonstratedthat the particular conditioned stimulus that is used does make a difference in classicalconditioning (Garcia & Koelling, 1966). In another series of experiments,Garcia found that rats did not learn to associate a taste with a painful event, suchas a shock. Nor did they learn to associate a flashing light and noise with illness.Instead, rats were much more likely to associate a painful stimulus, such as ashock, with external stimuli, such as flashing lights and noise. And rats were muchmore likely to associate a taste stimulus with internal stimuli—the physical discomfortof illness. Garcia and Koelling (1966) humorously suggested that a sickrat, like a sick person, speculates, “It must have been something I ate.”Why is it that certain stimuli are more easy to associate than others? One factorthat helps explain Garcia’s results is biological preparedness—the idea that anorganism is innately predisposed to form associations between certain stimuli andresponses. If the particular stimulus and response combination is not one that ananimal is biologically prepared to associate, then the association may not occur ormay occur only with great difficulty (see the In Focus box, “Evolution, BiologicalPreparedness, and Conditioned Fears: What Gives You the Creeps?”).taste aversionA classically conditioned dislike for andavoidance of a particular food that developswhen an organism becomes ill after eatingthe food.biological preparednessIn learning theory, the idea that an organismis innately predisposed to form associationsbetween certain stimuli and responses.John Garcia (b. 1917) John Garcia grew upworking on farms in northern California.In his late 20s, Garcia enrolled at a communitycollege. At the age of 48, Garciaearned his Ph.D. in psychology from theUniversity of California, Berkeley(Garcia, 1997). Garcia was one of the firstresearchers to experimentally demonstratethe existence of taste aversions and other“exceptions” to the general laws of classicalconditioning. His research emphasizedthe importance of the evolutionary forcesthat shape the learning process.