from the article. Classical conditioning is the process by which a particular stimulus (the conditioned stimulus or CS) causes an unconditional response (the unconditioned response or UR) in a subje

In classical conditioning, the unconditioned stimulus (UCS) causes an unconditioned response (UCR). The UCS is an uncontrolled, naturally occurring stimulus that does not require learning. It is usually a biologically significant stimulus, such as a tasty food or sound of a bell, which elicits an innate, automatic response. An example would be a ringing bell causing a dog to salivate. In this example, the bell is the UCS and the salivating response is the UCR. Evidence of this can be found in the work done by Ivan Pavlov and his experiments with conditioning dogs.