Each new example of classical conditioning can be analyzed in three steps. This three steps analysis is illustrated below with salivary conditioning in dogs.
First, find a stimulus which reliably lead to a response before conditioning. Before salivary conditioning with a dog, food(a stimulus) leads to salivation(a response). When the stimulus and response have been found, they may be labelled the US (food) and UR (salivation).
During Conditioning Trials
Second, find a neutral stimulus that is paired with the US. During salivary conditioning with a dog, a tone(a neutral stimulus) may be paired with food (the US). When these two stimuli have been found, they may be labelled the CS (tone) and US(food).
When conditioning has occurred
Third, find a response that is made to the CS. Once salivary conditioning has occurred, the dog makes a salivation response to the tone. Label this new response as the CR.
A Modern View Of Classical Conditioning
Robert Rescorla is a modern scientist producing important research and theory regarding classical conditioning. He views classical conditioning from an information-processing perspective. According to Rescorla, a subject in classical conditioning attempts to learn patterns of stimuli. The goal is to learn about predictive relationships in the environment.
Rescorla has shown that pairing a CS with a US is necessary but not sufficient for classical conditioning to occur. In one of Rescorla's experiments a group of subjects experienced a CS paired with a US. The CS and the US always occurred in this paired predictive relationship and strong CRs occurred. Another group of subjects experienced as many CS-US pairings, but they also experienced presentations of the US alone. This group lacked the important predictive relationship between the CS and the US and did not develp strong CRs.