Classical Conditioning Introduction
Like many great scientific advances, classical conditioning was discovered accidentally.
The nineteenth-century Russian physiologist Ivan Pavlov was looking at salivation in dogs in response to being fed, when he noticed that his dogs would begin to salivate whenever he entered the room, even when he was not bringing them food. At first this was something of a nuisance (not to mention messy!).
However, when Pavlov discovered that any object or event which the dogs learnt to associate with food (such as the food bowl) would trigger the same response, he realised that he had made an important scientific discovery, and he devoted the rest of his career to studying this type of learning.
Behaviourism as a movement in psychology appeared in 1913 when John Broadus Watson published the classic article 'Psychology as the behaviourist views it'. Watson believed that all individual differences in behaviour were due to different experiences of learning. He famously said:
“Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I'll guarantee to take any one at random and train him to become any type of specialist I might select - doctor, lawyer, artist, merchant-chief and, yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations and the race of his ancestors”. (Watson, 1924, p. 104)
Watson proposed that the process of classical conditioning (based on Pavlov’s observations) was able to explain all aspects of human psychology. Everything from speech to emotional responses were simply patterns of stimulus and response. Watson denied completely the existence of the mind or consciousness.
Classical conditioning involves learning to associate an unconditioned stimulus that already brings about a particular response (i.e. a reflex) with a new (conditioned) stimulus, so that the new stimulus brings about the same response. Pavlov developed some rather unfriendly technical terms to describe this process. The unconditioned stimulus (or UCS) is the object or event that originally produces the reflexive / natural response. The response to this is called the unconditioned response (or UCR). The neutral stimulus (NS) is a new stimulus that does not produce a response. Once the neutral stimulus has become associated with the unconditioned stimulus, it becomes a conditioned stimulus (CS). The conditioned response (CR) is the response to the conditioned stimulus.
Pavlov and Classical Conditioning
Ivan Pavlov and his studies of "classical conditioning" have become famous since his early work between 1890-1930. Classical conditioning is "classical" in that it is the first systematic study of basic laws of learning / conditioning.
1. When Pavlov provided food (UCS) to a dog, the dog's salivary reflex was triggered, and the dog drooled (UCR).
2. Pavlov found that when he rang a bell (NS) next to the dog, no drooling happened, and who would expect any?3. Next, he rang a bell (CS) a brief time before giving the food (UCS), and paired the bell and the food many times.
4. Then, on a "test trial" he only rang the bell (CS). Lo and behold, the animal began to drool (CR) to the sound of the bell almost as much as the dog had drooled when presented with the food.Here is the big point: As far as the dog was concerned, the dog had learned to associate the bell with food, so that the bell functioned just like the food--it caused drooling.
To summarise what had happened: Before, only the food had been connected to the drooling response. With repeated pairings, a circuit in the brain had connected the bell (formerly a "neutral" stimulus) to the drooling response. This connection (or association) between the two is what is called learning.
Watson and Raynor (1920) Little Albert
Ivan Pavlov showed that classical conditioning applied to animals. Did it also apply to humans? In a famous (though ethically dubious) experiment Watson and Raynor (1920) showed that it did "Little Albert" was a 9-month-old infant who was tested on his reactions to various stimuli. He was shown a white rat, a rabbit, a monkey and various masks. Albert described as "on the whole stolid and unemotional" showed no fear of any of these stimuli. However what did startle him and cause him to be afraid was if a hammer was struck against a steel bar behind his head. The sudden loud noise would cause "little Albert to burst into tears.When "Little Albert" was just over 11 months old the white rat was presented and seconds later the hammer was struck against the steel bar. This was done 7 times over the next 7 weeks and each time "little Albert" burst into tears. By now "little Albert only had to see the rat and he immediately showed every sign of fear. He would cry (whether or not the hammer was hit against the steel bar) and he would attempt to crawl away. Watson and Raynor had shown that classical conditioning could be used to create a phobia. A phobia is an irrational fear, i.e. a fear that is out of proportion to the danger. Over the next few weeks and months "Little Albert" was observed and 10 days after conditioning his fear of the rat was much less marked. This dying out of a learned response is called extinction. However even after a full month it was still evident
Classical Conditioning Downloads
Listen to a MIT undergraduate lecture on Conditioning 
