Why is conditioned taste aversion an example of classical conditioning (rather than operant)?

Question

The internet seems to be in complete agreement that conditioned taste aversion is an example of classical (Pavlovian) conditioning. My (admittedly limited) understanding of classical conditioning is that it's a process in which two stimuli are paired in such a way that the response to one of the stimuli changes. I'm having trouble spotting what those stimuli are in this case. This seems more like operant conditioning, in which unpleasant consequences (the symptoms) mold behavior by causing us to associate the taste of that food with those symptoms.

Am I misunderstanding operant/classical conditioning? Am I overcomplicating things?

Answer 1

This is an excellent question. The difference between Classical conditioning (also called Pavlovian conditioning) and operant (instrumental) conditioning is subtle for the new student, but can be quite profound when fully appreciated.

Pavlovian conditioning is learning a response that you have no control over. In this context, a conditioned taste aversion (CTA) might be produced by mildly poisoning a rat after it eats watermelon for the first time. Or you might suffer food poisoning after eating a watermelon. The CS is the watermelon. The usual response to watermelon is licking lips and paws, and savouring the sweet flavour - any rat version of yum you can think of. However after poisoning (where the US is usually denoted by the poisoning method, e.g. weak lithium chloride injections), the new response is gaping, retching and avoiding the now yucky flavour. In people who get food poisoning, we know the actual flavour of the food changes from pleasant to revolting, and can even elicit retching and vomiting. This response won't change even if you tell the person the next watermelon is fresh and sweet. In other words, the subject of the CTA cannot change their response (yucky flavour/retching) to the CS at will. This obviously creates a problem when a CTA is produced as a side-effect of medical treatment such as chemotherapy. Which is why people on chemo will often only be fed very bland and boring foods (to reduce the chance of a CTA). Even telling the person the chemo is causing the nausea is not sufficient to change their opinion of the foods they ate shortly before they felt sick.

By contrast, instrumental conditioning is learning a response you have control over. E.g., training a rat to press a lever for watermelon (or a person buying watermelon from the grocer). In this case you or the rat has control over the action (lever pressing or shopping at the grocer). So after a rat is convinced to press a lever for sweet juicy watermelon, if the rat gets poisoned by the watermelon then it will simply stop pressing the lever. Here the instrumental response to a CTA is 'avoidance'. Just as you would stop shopping at a grocer who previously sold you a bad watermelon. If however the owner of the grocery changed, you might be happy to resume shopping for watermelon there. Note that while you may no longer avoid shopping for watermelon, your Pavlovian response to the bad watermelon might still be intact - i.e., you might retch when you first bite into the fresh watermelon you just bought. This can obviously create odd situations where animals will work for food they do not want.

Whenever experimental psychologists are faced with a learned response they don't understand, one of the first things they will do is ask whether the response is Pavlovian or instrumental. The classic way to test this is with an omission schedule. Under an omission schedule, the reward is removed if the animal makes the response. If the animal continues to make the response, then the response is clearly not under instrumental control. If you look up some of Anthony Dickinson's work on this subject, you will discover many weird and wondrous examples of this distinction, especially in his incentive learning research. A lot of behaviour we think of as instrumental, is probably Pavlovian - e.g., a dog approaching a food bowl when he hears the can opener. One place to start is Dickinson, 1981, Conditioning and associative learning, British Medical Journal, 37 (2), 165-168

Answer 2

The conditioning of aversion to taste is part of learning studies in which there is an association between food and flavors with positive reactions such as food preferences or satiety and negative reactions such as lack of appetite, gastric discomfort, etc.

For example, it has been shown that patients with gastric discomfort acquire aversion to food, or patients (who have received prior chemotherapy) are averse to food when going to receive new sessions (chemotherapy usually causes nausea).

It is usually considered a classic conditioning learning. For example, foods that are neutral or independent stimuli before learning, produce conditioned responses (after the learning process), for example nausea, so foods are conditioned stimuli that produce conditioned responses (conditioned responses never they are exactly the same as the responses of the absolute stimulus).

Not only stimuli (foods or flavors) can produce a conditioned response but also events (such as being close to another session of chemotherapy).

Stimuli > CR

Events > CR

This is why in general it is considered classic conditioning, since the person (or animal) can not control the consequences with their behavior as it occurs in instrumental learning.

If for example you are thinking about the learning process of a person who tastes a food (with control over being able to try that food for the first time) and the food does not like it, in that case it is evidently instrumental learning. Of course, in relation to food learning, not everything is classical conditioning. The fundamental thing is to handle the concepts of analysis of the types of conditioning.

It is essential to read the section on Learning to taste aversion in the book by Michael Domjan. Principles of learning and behavior. Pages 72 to 74 in the 3 edition. It is interesting to review the studies indicated in this section.