Classical conditioning was discovered, rather accidentally, by Ivan Pavlov. As mentioned before, Pavlov was studying the digestive processes in dogs. He inserted a tube into a dog's mouth in order to measure the amount of saliva the dog produced, using food to stimulate the flow of saliva. After visiting the lab several times for this procedure, Pavlov noticed something very interesting. The dog actually began to salivate before the food was in his mouth. The sight or smell of the food or even the sound of footsteps bringing the food stimulated the production of saliva. While Pavlov first considered this to be an obstacle to his experiment, he quickly realized that the dog's salivating was a conditioned response to its anticipation of being fed. As the dog had not done this before, he recognized that the response had been learned through experience. He dropped his study of the digestive system and turned to studying this response.
Though Pavlov is the one who first identified and studied classical conditioning as a form of learning and was awarded the Nobel Prize for his work in this field, some say that it was actually a student of his who pointed out that the dog was salivating before he had been given the food.
This is essentially the idea behind classical conditioning. By definition classical conditioning is the process by which a normally neutral stimulus becomes a conditioned stimulus, eliciting a response in an individual, or in this case a dog, due to its association with a stimulus that already elicits a similar response. Classical conditioning involves what are known as reflexive behaviors. A reflex is an automatic, involuntary response to an external stimulus.
How It Works
There are four components to classical conditioning. Breaking it down, the first two components are an unconditioned stimulus (US) and the unconditioned response (UR). The unconditioned stimulus in Pavlov's study was the dog's food. The food was the stimulus that automatically elicited the unconditioned response, salivation. Remember, these two factors are reflexive. In other words, they were automatic, not conditioned or learned.
The next two components make for an interesting study. In Pavlov's study, he paired the ringing of a bell with the distribution of the food, thus coupling a conditioned stimulus (CS) (bell) with an unconditioned stimulus (food). Eventually, he took away the US and only provided the CS. The CS by itself still produced the unconditioned response, thus making the UR a conditioned response (CR). In other words, the dog salivated when it heard the ringing of the bell even though there wasn't any food present. These two components were conditioned, or learned.
This process of a neutral stimulus becoming a conditioned stimulus is the basis for classical conditioning. Of course, you have to throw experience in there. A dog isn't likely to salivate after the bell is rung when paired with food just one time. The dog must experience this pairing regularly and repeatedly in order to make the association between the two stimuli.
Features of Classical Conditioning
Conditioned responses in classical conditioning aren't necessarily permanent responses. They can be unlearned, or extinguished. For instance, Pavlov's dog could have been reconditioned to have no response to the ringing of the bell. Had someone rung the bell regularly without following it with food over the course of several sessions, the dog would no longer have salivated in response to the ringing of the bell alone, as it did not signal the coming of food — in which case, the conditioned response would have been extinguished.
Classical conditioning can also produce stimulus generalization and stimulus discrimination. Stimulus generalization occurs when an individual has the same conditioned response to a stimulus that is similar though not the same as the conditioned stimulus. For example, if a child is bitten by a rottweiler, he may fear all dogs, not just rottweilers. Though not all dogs are the same, the stimuli are similar enough to elicit the same response. On the other hand, two similar stimuli may produce different responses, which is called stimulus discrimination. To use the previous example, another child may be bitten by a rottweiler but is able to distinguish the difference between a rottweiler and a poodle, and will therefore not produce the same response (fear) toward the poodle as she would toward a rottweiler.
Conditioned responses can sometimes reappear suddenly after being extinguished, a phenomenon known as spontaneous recovery. In Pavlov's experiment, for example, he found that if a dog was given a few hours of rest after a response was extinguished, the CR would suddenly reappear after the stimulus was presented. This suggests that while a response may disappear, it doesn't mean that it has been “unlearned.”