the process of forming a conditioned reflex based on a combination of a neutral stimulus with an unconditioned one. An unconditioned stimulus evokes an unconditioned response, and a neutral stimulus acquires the ability to elicit the same response after several combinations with an unconditioned stimulus. Classical conditioning underlies many forms of learning and behavior in animals and humans. The most famous and most detailed early work on classical conditioning was done by the Russian scientist Ivan Petrovich Pavlov during experiments with dogs and published in 1897. Together with operant conditioning, respondent (classical) conditioning became the basis of behaviorism (see Behaviorism in Chapter 5 Famous Scientists, Their Scientific Schools and Organizations in Psychological Science).