Pavlov was a Russian physiologist who experimented with conditioning responses. He rang a bell every time that he fed a dog to the point that whenever he rang this bell, the dog would salivate, thinking he would be fed. Thus, Pavlov began the study of conditioned responses and their implications for psychology; this study is termed classical conditioning.
In "Brave New World," the castes are conditioned to think in certain ways through hypnopaedia, sleep-conditioning. For example, Betas are taught to dislike Deltas so that they will not associate with them. This process can also be used for counter-conditioning to get rid of unwanted behavior. Of course, this conditioning works better in "Brave New World" because the individual differences of humans have been eliminated by the genetic engineering in the Hatchery.