The research on classical conditioning started with a number of experiments by Ivan Pavlov. He started with ringing the bell and after that giving some food to the dog. After some time the dogs start to salivate when they receive the food but do not actually salivate when they hear a bell. He repeated the experiment a number of times and observed that after some time the dogs started to salivate just after they heard the sound of the bell, even they did not get any food.
Classical conditioning works in the following way. Prior to the conditioning, when some subject is being presented with some stimulus that is unconditioned (UCS) normally, without former learning, the result of that is unconditioned response (UCR). A stimulus which has an outcome of a reflex that happens naturally and does not require to be learned, which is considered to unconditioned response is called unconditioned stimulus.
In the described above experiment the food and salivation can be called respectively UCS and UCR. At the same time, represented by the bell neutral stimulus in the experiment conducted by Pavlov does not have a result of in UCR, salivation.
For the duration of conditioning, a neutral stimulus is presented instantly foregoing unconditioned stimulus that in turn has a result of unconditioned response. This experiment is repeated a number of times, in dependence with the subject, the connection between neutral stimulus, UCS, and UCR, and preferred result. After the process of conditioning, the subject is given the originally neutral stimulus that in this case is conditioned stimulus (CS), avoiding unconditioned stimulus. The response of the subject is now directed to conditioned stimulus by making conditioned reaction, which was usually made by unconditioned stimulus. The conditioned response can be described as a response that was learned and the...