I once had an acquaintance who told a very vivid story about eating a chicken enchilada while on vacation. Hours after eating the enchilada, she became violently ill. For years after that incident, she was unable to bring herself to eat a chicken enchilada and even felt queasy when she smelled foods that reminded her of that particular dish. This was despite the fact that she knew that her illness was not connected to eating that particular item. In reality, she had picked up a nasty stomach virus from one of her traveling companions who had been ill just days before the trip.
These conditioned taste aversions are quite common and can last from a period of days to several years. Consider your own aversions to certain foods. Can you link your distaste for particular items to a period of illness, queasiness or nausea? In my own experience, I once avoided a very particular flavor of potato chip for years simply because ate them the day before I became ill.
Understanding Taste Aversions
Taste aversions can occur both consciously and unconsciously? In many cases, people may be completely unaware of the underlying reasons for their dislike of a type of food. Why do these taste aversions occur, especially when we consciously realize that the illness was not tied to a particular food? As you may have already realized, conditioned taste aversions are a great example of some of the fundamental mechanics of classical conditioning. The previously neutral stimulus (the food) is paired with an unconditioned stimulus (an illness), which leads to an unconditioned response (feeling sick). After this one-time pairing, the previously neutral stimulus (the food) is now a conditioned stimulus that elicits a conditioned response (avoiding the food).
Is that all there is to these conditioned taste aversions? As you may have already noticed, the scenario described above does not exactly fit with the standard expectations for classical conditioning. First of all, the conditioning occurred after just a single pairing of the neutral stimulus and unconditioned stimulus (UCS). As you may also remember from your studies of classical conditioning, the time span between the neutral stimulus and UCS is usually just a matter of seconds. In the case of a conditioned taste aversion, the time lapse often amounts to several hours.
While it may seem to violate the general principles of classical conditioning, researchers have been able to demonstrate the effects of conditioned taste aversions in experimental settings. In one such experiment, psychologist John Garcia fed flavored water (a previously neutral stimulus) to lab rats. Several hours later, the rats were injected with a substance (the UCS) that made them ill. Later, when the rats were offered the flavored water, they refused to drink it.1
Explaining Conditioned Taste Aversions
Because Garcia’s research contradicted much of what was previously understood about classical conditioning, many psychologists were unconvinced by the results. Pavlov had suggested that any neutral stimulus could elicit a conditioned response. If that were true, then why would the feelings of sickness be associated with the food that was eaten hours earlier? Wouldn't the illness be associated with something that had happened right before the symptoms occurred?
What Garcia and other researchers were able to demonstrate was that in some cases, the type of neutral stimulus used does have an influence on the conditioning process.2 So why does the type of stimulus matter so much in this particular case? One part of the explanation lies in the concept of biological preparedness. Essentially, virtually every organism is biologically predisposed to create certain associations between certain stimuli. If an animal eats a food and then becomes ill, it might be very important to the animal's continued existence to avoid such foods in the future. These associations are frequently essential for survival, so it is no wonder they form easily.
1Garcia, J., Ervin, F.R., & Koelling, R.A. (1966). Learning with prolonged delay of reinforcement. Psychonomic Science, 5, 121-122.
2Garcia, J. & Koelling, R.A. (1966). Relation of cue to consequence in avoidance learning. Psychomic Science, 4, 123-124.
3Riley, A.L., & Freeman, K.B. (n.d.). Conditioned taste aversion: An annotated biography. Found online at http://www.ctalearning.com/