|We use the term "classical conditioning" to describe
one type of associative learning in which there is no contingency between
response and reinforcer. This situation resembles most closely the archetypic
experiment from I. Pavlov in the 1920s, where he trained dogs to associate
a tone with a food-reward (see figure). In such experiments, the subject
initially shows weak or no response to a conditioned stimulus (CS,
e.g. a tone), but a measurable unconditioned response (UR, e.g.
saliva production) to a unconditioned stimulus (US, e.g. food).
In the course of the training, the CS is repeatedly presented together
with the US; eventually the subject forms an association between the US
and the CS. In a subsequent test-phase, the subject will show the conditioned
response (CR, e.g. saliva production) to the CS alone, if such an association
has been established and memorized. Such "Pavlovian" conditioning is opposed
to instrumental or "operant conditioning", where
producing a CR controls the US presentations.
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