The principle of classical conditioning was discovered by the Russian physiologist, I.P. Pavlov (1849-1936), while he was investigating the way the body digests food. Pavlov won Nobel Prize for his work on digestive system. Yet he is remembered not for his physiological research, but for his experiments on the basic learning processes.
Pavlov was studying secretion of stomach acids and salivation in dogs in response to varying amounts of food. He implanted a tube in dog’s salivary gland in order to measure the amount of saliva secreted by the dog. While doing so, he observed a very curious phenomenon. One day, as Pavlov approached the dog with a tray of powdered meat, the dog began to salivate. Pavlov (1927) wondered, “Why did the dog salivate before eating the meat powder?” Pavlov thought that salivation at the sight of the meat powder was the result of learning or as it came to be called, classical conditioning.
In classical conditioning, an organism learns to respond to a neutral stimulus that normally does not bring about that response. Pavlov’s curiosity prompted him to begin formal experimentation (Pavlov, 1927). A hungry dog was made to stand on a pedestal in a soundproof room. A tube was attached to the salivary gland of the dog to precisely measure the amount of salivation. He sounded a bell, and just a few seconds later, presented the dog with meat powder, in response to the sound of the bell, the dog pricked its ears and made some exploratory movements. When the food was presented, the dog salivated and ate the food. The pairing of the bell and food was repeated for several trials with exactly the same amount of time elapsing between the presentation of the bell and food.
At first, the dog was salivating only to the food. But as the trials proceeded, the dog began t salivate at the sound of the bell. Even when Pavlov stopped presenting food, the dog still salivated after hearing the sound. Salivation is a natural biological response to food. There is no natural connection between the sound of the bell and salivation. Because bell and food repeatedly came together in the experiment, bell acquired the potentiality of evoking salivation. A new learning took place. In course of the experiment, the dog learn to associate the response of salivation to the sound of the bell. The dog had been classically conditioned to salivate to the bell.
Classical conditioning involves establishing a connection between a stimulus (bell) and a response (salivation), which are not naturally linked.