Learning

In the early twentieth century, Ivan Pavlov, a Russian scientist, unwittingly stumbled upon an important discovery for the field of behavioral psychology. While studying digestion in dogs, he discovered that after being fed a few times, the animals would salivate before actually receiving food. The dogs were associating external cues such as the sound of the food cabinet being opened with being fed, so they would salivate upon hearing these sounds before they saw the food.

This phenomenon is called classical conditioning or respondent conditioning. Pavlov found that by pairing a previously neutral stimulus, such as the sound of a cabinet being opened, with a stimulus that generates an automatic response, such as presenting meat, which automatically causes dogs to salivate, a dog will come to associate the neutral stimulus with the automatic response. After many pairings of the neutral stimulus (sound) with the automatic stimulus (meat), the response to the neutral stimulus, without the presence of the automatic or unconditional stimulus, produced salivation on its own. So, eventually, just hearing the cabinet being opened was sufficient for Pavlov's dogs to begin salivating.

Under natural circumstances, food causes a dog to salivate. This response is not learned or conditioned so the food is called an unconditioned stimulus while salivation is called an unconditioned response because it occurs without any prior conditioning or learning. After multiple pairings of the sound with food, however, the sound alone would cause the dogs to salivate. The sound has now become a conditioned stimulus and the salivation is the conditioned response because the dogs have been conditioned to salivate to the sound.

Pavlov later found that he did not even need to pair the conditioned stimulus (sound) directly with the unconditioned stimulus (food) in order to cause a conditioned response. He found that if he first conditioned the dogs to salivate at the sound, and then paired the sound with a wooden block, the dogs would eventually salivate at the sight of the block alone even though the block itself was never paired with the food. This is called second-order conditioning; a second neutral stimulus is paired with the conditioned stimulus and eventually becomes a conditioned stimulus as well.

In the 1920s John Watson, an American psychologist, applied the principles of classical conditioning to human beings. He conducted an experiment on an eleven-month-old baby, "Little Albert," in which a startling noise occurred as Albert was presented with a white rat. Startling noises are unconditionally upsetting to infants, causing them to cry and crawl away, while young children are not afraid of white rats. After multiple pairings of the rat and the startling noise, however, Little Albert developed a fear of the rat, crying and crawling away even if the loud noise did not occur. Watson thus showed that classical conditioning also works with humans and that it works for spontaneous emotional responses as well as physiological ones.