Pavlovian conditioning, also known as respondent conditioning and classical conditioning (to distinguish
it from instrumental or operant conditioning), is an elementary learning process and has been of major
interest to psychologists ever since the Russian physiologist Ivan Petrovich Pavlov discovered that a
dog could learn to salivate to a neutral stimulus after the stimulus was paired repeatedly with food.
Pavlov’s early career focused on the study of heart circulation and
digestion in animals (usually dogs), for which he received the
Nobel Prize in Physiology or Medicine in 1904. However, by that
time Pavlov had already turned his attention to experiments on
conditioned reflexes, from which flowed a new psychological
The core of Pavlovian conditioning is the pairing (association) of
stimuli to elicit responses. Food (meat powder) placed in a dog’s
mouth naturally produces salivation. Pavlov called the food an
unconditioned stimulus (US) and salivation, elicited by the food,
the unconditioned response (UR). When a neutral stimulus—for
example, a tone that does not naturally elicit salivation—is
repeatedly followed by food, the tone alone eventually evokes
salivation. Pavlov labeled the tone a conditioned stimulus (CS) and
the response (