Russian physiologist Ivan Pavlov was the first to describe classical conditioning. In classical conditioning, also called “respondent conditioning” or “Pavlovian conditioning,” a subject comes to respond to a neutral stimulus as he would to another, nonneutral stimulus by learning to associate the two stimuli.

Pavlov’s contribution to learning began with his study of dogs. Not surprisingly, his dogs drooled every time he gave them food. Then he noticed that if he sounded a tone every time he fed them, the dogs soon started to drool at the sound of the tone, even if no food followed it. The dogs had come to associate the tone, a neutral stimulus, with food, a nonneutral stimulus.

Conditioned and Unconditioned Stimuli and Responses

Psychologists use several terms to talk about classical conditioning. In Pavlov’s experiment, salivation was the unconditioned response, which is a response that occurs naturally. Food was the unconditioned stimulus, the stimulus that naturally evoked salivation. The tone was the conditioned stimulus, the stimulus that the dogs learned to associate with food. The conditioned response to the tone was salivation. The conditioned response is usually the same as, or similar to, the unconditioned response.

Example: Suppose Adam has a psychology class with Professor Smith, who is determined to teach him about classical conditioning. In the first class, Professor Smith whips out a revolver and shoots it into the air. The revolver is loaded with blanks, but when Adam hears the loud bang, he cringes out of surprise. Professor Smith repeats this action several times during the class. By the end of the hour, Adam cringes as soon as she whips out the revolver, expecting a bang. He cringes even if she doesn’t shoot. In this scenario, the unconditioned stimulus is the bang, the unconditioned response is cringing, the conditioned stimulus is the revolver, and the conditioned response is cringing.

Acquisition of Conditioned Responses

Subjects acquire a conditioned response when a conditioned stimulus is paired with an unconditioned stimulus. Conditioning works best if the conditioned stimulus appears just before the unconditioned stimulus and both stimuli end at about the same time. In the above example, Professor Smith’s conditioning will work best if she displays the revolver right before firing and puts it away after shooting.

Extinction

After Adam has been conditioned to cringe at the sight of the revolver, Professor Smith comes into the next class and pulls out the revolver again. He cringes, but she doesn’t shoot. If she pulls it out again and again on several occasions without shooting, Adam will soon stop cringing when she pulls it out. This process called extinction is the gradual weakening and disappearance of a conditioned response. Extinction happens when the conditioned stimulus appears repeatedly without the unconditioned stimulus.

Spontaneous Recovery

Suppose that by the end of the second class, Adam has completely stopped cringing when Professor Smith pulls out the revolver. His conditioned response has been extinguished. However, if Professor Smith comes into class later in the semester and pulls out the revolver again, Adam may still cringe, though maybe a little less than before. This is called spontaneous recovery. Spontaneous recovery is the reappearance of an extinguished conditioned response when the conditioned stimulus returns after a period of absence.

Stimulus Generalization

Now suppose Professor Smith conditions Adam again to respond to the revolver as she did in the first class. Soon he cringes every time she pulls out the revolver. While Adam is in this conditioned state, the professor pulls out a cell phone. Adam is likely to cringe at that too because of stimulus generalization—the tendency to respond to a new stimulus as if it were the original conditioned stimulus. Stimulus generalization happens most often when the new stimulus resembles