In classical conditioning, a neutral (conditioned) stimulus is paired with—that is, immediately precedes—an unconditioned sthnulus a number of times until it is capable of bringing about a previously unconditioned response, now called the conditioned response. The shnplest examples include reflexive behavior. Light shined hi the eye stimulates the pupil to contract; food placed on the tongue brings about salivation; and pepper in the nostrils results in the sneezing reflex. With reflexive behavior, responses are unlearned involuntary, and common not only to the species but across species as well. Classical conditioning, however, is not lhnited to simple reflexes. It can also be responsible for more complex human learning like phobias, fears, and anxieties.
An early example of classical conditioning with humans was described by John Watson and Rosalie Rayner hi 1920 and involved a young boy—Albert B., usually referred to as Little Albert. Albert was a normal, healthy child who, at 9 months of age, showed no fear of such objects as a white rat, a rabbit, a dog, a monkey with masks, and so forth. When Albert was 11 months old the experimenters presented him with a white rat. Just as Albert was beginning to touch the rat, one of the experimenters struck a bar behind Albert's head. The little boy immediately showed signs of fear, although he did not cry. Then, just as he touched the rat with his other hand an experimenter struck the bar again. Once more Albert showed fear and began to whimper. A week later, Watson and Rayner repeated the procedure several thnes and finally presented the white rat without the loud sudden sound. By this time, Albert had learned to fear the rat by itself and quickly began to crawl away from it. A few days later, the experimenters presented Albert with some blocks. He showed no fear. Next, they showed him the rat by itself. Albert showed fear. Then, they offered him the blocks again. No fear. They followed this part of the experiment by showing Albert a rabbit by itself. Albert immediately began to cry and crawl away from the rabbit. Watson and Rayner then showed Albert the blocks again, then a dog, then blocks again, then a fur coat, and then a package of wool. For all objects except the blocks, Albert showed some fear. Finally, Watson brought in a Santa Claus mask, to which Albert showed signs of fear. This experiment, which was never completed because Albert's mother intervened demonstrated at least four points. First, infants have few, if any, innate fears of animals; second they can learn to fear an animal if it is presented in association with an aversive sthnulus; third, infants can discriminate between a furry white rat and a hard wooden block, so that fear of a rat does not generalize to fear of a block; and fourth, fear of a furry white rat can generalize to other animals as well as to other white hairy or furry objects.
The key to this classical conditioning experiment was the pairmg of a conditioned stimulus (the white rat) with an unconditioned stimulus (fear of a loud sudden sound) until the presence of the conditioned sthnulus (the white rat ) was sufficient to elicit the unconditioned sthnulus (fear).
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