Classical Conditioning

Classical (Pavlovian) conditioning, first studied by Ivan Pavlov, is a four‐step learning procedure involving reflexes. Pavlov became curious about the fact that some of his laboratory dogs began salivating before food actually was in their mouths. He then found that if he used the appropriate sequence of events, a dog would salivate at the sound of a buzzer or the appearance of a light. Further experimentation established the conditions essential in producing such a phenomenon.

Classical conditioning requires the existence of an unconditioned stimulus (UCS) that elicits an unconditioned response (UCR), that is, that reliably elicits an unlearned response, in the experimental subject. UCRs (unlearned responses) are also known as reflexes. The UCR is usually a physiological response that can reliably be elicited by a UCS, for example, salivation (the UCR) in response to the smell or sight of food (the UCS), particularly if one is hungry, or an eye blink (the UCR) in response to a puff of air (the UCS) blown into the eye. The classical conditioning procedure also requires a conditioned stimulus (CS), a stimulus of which the subject can be made aware but which initially does not cause the UCR, followed by a conditioned response, the same response as the UCR, but eventually in reaction to a different stimulus. For example, the CS in the puff of air example might be simply the sound of a buzzer, resulting, after conditioning is complete, in a blink (CR) caused by the CS alone.

Classical conditioning, then, would proceed as follows, using the four components and four steps.

  • CS: The CS (conditioned stimulus)—for example, the sound of a buzzer—is presented in several trials.

  • UCS: Each presentation of the CS is followed closely by presentation of the UCS (unconditioned stimulus)—for example, the puff of air.

  • UCR: Presentation of the UCS causes a UCR (an eye blink).

  • CR: After a sufficient number of presentations of the CS followed by the UCS, the experimenter presents the CS without the UCS. If a response, an eye blink, occurs, the UCR is now called a conditioned response (CR). The eye blink response to the buzzer has been conditioned (learned).

Shown graphically, the sequence is



If the CS now produces a CR, with no presentation of the UCS, it can be said that conditioning (learning) has occurred and



Higher order conditioning. Higher order conditioning, that based upon previous learning, may also occur in the classical conditioning paradigm. In higher order conditioning, what was the CS comes to serve as a UCS. For example, if the experimenter always turned on a desk light before sounding the buzzer to begin classical conditioning (to produce an eye blink at the sound of the buzzer), the turning on of the light may eventually itself produce the eye blink, independent of the buzzer. In this case, the buzzer has become a UCS, and the turning on of the light has become a CS. Consequently, although initially (light) → CS(buzzer) → UCS(air puff) → UCR(eye blink) → CR(eye blink) higher order conditioning proceeds



And higher order conditioning (learning) occurs:



Classical conditioning terminology. Specific terminology is used to describe the classical conditioning procedure.

  • The process of learning a conditioned response is called acquisition. Usually, conditioning is faster if only a short time elapses between the presentation of the CS and the UCS.

  • The reverse process—that is, unlearning—can occur also and is called extinction. If the CS is presented for a time without the UCS, the CR will eventually cease (be extinguished).

  • If the CS is again presented later, however, the CR will sometimes return temporarily (this temporary return is called spontaneous recovery). But the CR will disappear unless the UCS is at times reinstated