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Conditioned Stimulus (CS)
An originally neutral stimulus that is classically conditioned to induce a response. Ivan Pavlov (1849–1936), a Russian physiologist, first coined this term after incidentally discovering classical conditioning while studying the digestive system. He trained his dogs to salivate to the sound of a bell. The bell was originally a neutral stimulus because it did not evoke any response. However, after pairing it with food several times, the dogs began to salivate to the sound of the bell. The bell is then called a CS because it evokes the conditioned response of salivation. A large number of neutral stimuli can, through association with unconditioned stimuli, eventually become a CS in both animals and humans. For more information, see Pavlov (1927/1960).