Classical conditioning (also Pavlovian conditioning or
respondent conditioning) is a form of learning in which the
conditioned stimulus or CS, comes to signal the occurrence of a
second stimulus, the unconditioned stimulus or US. (A stimulus
is a factor that causes a response in an organism.) The
conditioned response is the learned response to the previously
neutral stimulus. The US is usually a biologically significant
stimulus such as food or pain that elicits a response from the
start; this is called the unconditioned response or UR. The CS
usually produces no particular response at first, but after
conditioning it elicits the conditioned response or CR.
Classical conditioning differs from operant or instrumental
conditioning, in which behavior emitted by the subject is
strengthened or weakened by its consequences (i.e. reward or
punishment). There are many examples of these innate
(unconditioned) reflexes (corneal, coughing, swallowing,
withdrawal reflexes etc.) or learned (conditioned) reflexes.:p.
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