Surely it has happened to you at some time, that after ingesting some kind of food and feeling a gut pain, you end up refusing (consciously or unconsciously) to eat that food again, at least for a while.

But why is this happening? It can be explained through the Garcia effect , a phenomenon of classical conditioning.

This phenomenon, discovered by the American psychologist John Garcia in the 1950s, consists of a type of taste aversion conditioning, which was first studied with rats. In this article we will know how this effect was discovered, what it consists of and why it occurs.

Garcia Effect: What is it?

The Garcia effect is a phenomenon that we find within classical conditioning, and that alludes to the fact that an exteroceptive Conditioned Stimulus (EC) (for example a light or a sound) is more easily associated with an exteroceptive Unconditioned Stimulus (EI) , and that an interoceptive EC (for example a type of food) is more easily associated with an interoceptive EI.

An example of this effect would be when we feel a stomach ache, or nausea, and then relate it to something we have eaten; it doesn’t matter if the pain or nausea is caused by any other external reason, which most of the time we will relate it to food.

This occurs because a selective conditioning according to the type of stimulus ; that is, we associate the nature of the stimulus with the nature of the response, which must be the same (in this case, an internal origin). But, how did we arrive at the discovery of the Garcia effect? Let’s go to the origin.

Origin of aversive conditioning

The origin of the study of taste aversion conditioning is found around the 1940s. To carry out these studies, poison was used to eradicate pests of rats and mice. Remember that aversive conditioning involves learning a rejection response to some type of stimulus.

Specifically, this type of conditioning we are talking about is associated with the taste or smell of certain foods (which would be the aversive stimulus).

Ten years later, around the 1950s, John García, an American psychologist, became interested in studying aversive conditioning . He was the creator of the so-called “Garcia Effect”. This psychologist and researcher studied at the University of California (Berkeley) and later began working in San Francisco for the Navy.

Experiments by John Garcia

It was in San Francisco where, through his experiments with rats, J. Garcia applied the same ionizing radiation to them to cause them gastric pain. He then observed how they stopped drinking water from the plastic bottle, since they had associated tummy ache (internal conditioned response) with the plastic of the water bottles (internal conditioned stimulus) .


He also studied it with food, and the effect was the same. This was even if the cause of the tummy ache was someone else. According to him, and what defines the Garcia effect itself, the rats associated these two stimuli (which in reality, had nothing to do with each other, because the tummy ache was caused by another stimulus, ionization), because they had the same internal nature.

Thus, the Garcia effect refers to a type of conditioned reflex of rejection of certain foods and flavors. In this case, the rejection stimulus would be the water contained in the plastic bottles.

Variations in experiments

John Garcia used another technique to demonstrate the Garcia effect; what he did was to change the taste of the water in the plastic bottles by adding saccharin to the container. This was a new flavour for the rats . J. García incorporated a red light in the container with the water+saccharin.

He saw how the rats kept rejecting the water (in this case, with a new taste), but did not reject the red light in the container. This last phenomenon reinforces the fundamental idea of the Garcia effect, which alludes to the nature of the stimuli, considering that it must be the same for the conditioning to occur (in this case, the light is an external stimulus, and the gut pain is internal).

Rejection of your research

At first, John García’s research was rejected by the scientific community because it did not follow the basic principles of classical conditioning, considered to be true. This is why prestigious scientific journals, such as Science, refused to publish his findings.

Characteristics of the psychological phenomenon

It is interesting to explain the novel contributions that John García made to the field of classical conditioning, based on the phenomenon of the Garcia effect. These also allude to the characteristics of this effect, and were as follows:

On the one hand, he determined that conditioning could be achieved through only one exposure, and that it was not always necessary for many exposures to occur in order to achieve conditioning or learning . He also argued that conditioning was selective; in the case of rats, they associated tummy ache (internal response) with food or drink (internal stimulus).

On the other hand, they did not associate pain with external stimuli (for example a red light), even if they were paired in time; this is because the Garcia effect defends the association of stimuli of the same nature.

Furthermore, another novelty proposed by J. García was that the time interval that occurred between the conditioned stimuli (in this case, the taste and smell of the food) and the unconditioned response (gut pain) that ends up conditioning (to rejection of the food), was prolonged.

This interval could be as long as six hours. That is, it could take up to 6 hours from the time the animal ate until it suffered from the tummy ache, and that anyway the conditioning and learning that “the food has caused me this pain, therefore I reject the food” took place. Finally, the Garcia effect is a phenomenon that is resistant to unlearning, that is, it is difficult to extinguish (it is difficult for it to disappear).

Examples in everyday life

Another characteristic in the J. Garcia phenomenon is that the fact that the animal (or person) knows that the reaction or discomfort (tummy ache) is caused by an illness (e.g. flu or cancer), does not prevent him from continuing to reject such food.

This is also observed in cancer patients , who end up developing a rejection of the food they have eaten prior to a chemotherapy session if the latter has caused nausea or vomiting; thus, although the person “knows” that the food has not caused the nausea and vomiting, their body continues to reject it because it is associated with these symptoms.

Other animals

The Garcia effect was also demonstrated in other animals such as coyotes. J. Garcia observed how they generated a conditioned response of rejection to poisoned food. To achieve this conditioning, as in the case of rats, a single exposure was sufficient .

It was even possible to get the coyotes to reject the sheep meat by injecting poison into it. In this way, these animals ended up associating the gastric discomfort with the taste of the meat and therefore, they finally refused to eat this type of meat. The Garcia effect was also demonstrated in the crows, which, using the same mechanism, were made to refuse to eat the birds’ eggs.

Bibliographic references:

  • Bayes, R. y Pinillos, J.L. (1989). Aprendizaje y condicionamiento. Alhambra: Madrid.
  • García, J. y R. A. Koelling. (1966). Relación de la pista con la consecuencia en el aprendizaje de la evitación. Psychonomic Science, 4: 123 – 124.
  • García, J., Ervin, F. R. y Koelling, R. A. (1966). Aprendizaje con retraso prolongado de refuerzo. Psychonomic Science, 5:121 – 122.