John Garcia identified a phenomenon that came to be known as the Garcia effect, also referred to as the Garcia theory. The Garcia effect is a term used to describe conditioned taste aversions that develop when food is associated with a negative reaction, such as nausea or vomiting.

A classic experiment by John Garcia in the 1960s demonstrated that a rat would associate a taste, but not a light or sound, with illness. In contrast, pain could be associated only with a visual or auditory cue, not a taste.

For example, rats more readily learn to associate an olfactory cue such as water sweetness than a visual cue such as pink water with illness. Birds, on the other hand, can associate visual cues with sickness with the ease that rats associate olfactory cues with nausea.

Originally reported by John Garcia in the 1950s, taste aversion is the rapidly acquired, robust, and selectively acquired avoidance of a novel and distinctive taste that has been associated with some aversive outcome.