Classical conditioning, a form of associative learning. It requires an unconditioned reflex, where an unconditioned stimulus (US)brings about an automatic, unlearned (unconditioned) response (UR). If a neutral stimulus (NS) tends to precede it, an association is made and the conditioned response (CR) becomes transferred onto the (previously neutral) conditioned strimulus (CS); a conditioned reflex has been learned. For instance, food (US) elicits salivation (UR) in a dog as a natural response. If the sound of a bell (NS) frequently occurs before the food (US) is presented then the mere sound of the bell (CS) will elicit salivation (CR).