Since Ivan Pavlov's original experiments, many studies have examined the application of classical conditioning to human behavior. 

Watson's "Little Albert" Experiment

In the early 1900s, John B. Watson carried out a controversial classical conditioning experiment on an infant boy called "Little Albert." Watson was interested in examining the effects of conditioning on the fear response in humans, and he introduced Little Albert to a number of items such as a white rat, a bunny, and a dog. Albert was originally not fearful of any of the items. Watson then allowed Albert to play with the rat, but as Albert played, Watson suddenly banged a hammer on a metal bar. The sound startled Albert and caused him to cry. Each time Albert touched the rat, Watson again banged the hammer on the bar. Watson was able to successfully condition Albert to fear the rat because of its association with the loud noise. Eventually, Albert was conditioned to fear other similar furry items such as a rabbit and even a Santa Claus mask. While Watson’s research provided new insight into conditioning, it would be considered unethical by the current ethical standards set forth by the American Psychological Association.

The Little Albert experiment

Through stimulus generalization, Little Albert came to fear furry things, including Watson in a Santa Claus mask.

Classical Conditioning in Humans

The influence of classical conditioning can be seen in responses such as phobias, disgust, nausea, anger, and sexual arousal. A familiar example is conditioned nausea, in which the sight or smell of a particular food causes nausea because it caused stomach upset in the past. Similarly, when the sight of a dog has been associated with a memory of being bitten, the result may be a conditioned fear of dogs.

As an adaptive mechanism, conditioning helps shield an individual from harm or prepare them for important biological events, such as sexual activity. Thus, a stimulus that has occurred before sexual interaction comes to cause sexual arousal, which prepares the individual for sexual contact. For example, sexual arousal has been conditioned in human subjects by pairing a stimulus like a picture of a jar of pennies with views of an erotic film clip. Similar experiments involving blue gourami fish and domesticated quail have shown that such conditioning can increase the number of offspring. These results suggest that conditioning techniques might help to increase fertility rates in infertile individuals and endangered species.

Behavioral Therapies

Classical conditioning has been used as a successful form of treatment in changing or modifying behaviors, such as substance abuse and smoking. Some therapies associated with classical conditioning include aversion therapy, systematic desensitization, and flooding. Aversion therapy is a type of behavior therapy designed to encourage individuals to give up undesirable habits by causing them to associate the habit with an unpleasant effect. Systematic desensitization is a treatment for phobias in which the individual is trained to relax while being exposed to progressively more anxiety-provoking stimuli. Flooding is a form of desensitization that uses repeated exposure to highly distressing stimuli until the lack of reinforcement of the anxiety response causes its extinction. 

Classical Conditioning in Everyday Life

Classical conditioning is used not only in therapeutic interventions, but in everyday life as well. Advertising executives, for example, are adept at applying the principles of associative learning. Think about the car commercials you have seen on television: many of them feature an attractive model. By associating the model with the car being advertised, you come to see the car as being desirable (Cialdini, 2008). You may be asking yourself, does this advertising technique actually work? According to Cialdini (2008), men who viewed a car commercial that included an attractive model later rated the car as being faster, more appealing, and better designed than did men who viewed an advertisement for the same car without the model.