Second-Order Conditioning

Second-order conditioning is a form of learning in which a first conditioned stimulus, already linked to an unconditioned stimulus through ordinary classical conditioning, is then used to condition a second stimulus, so that the second stimulus comes to produce a response even though it was never directly paired with the original unconditioned stimulus. In the classic laboratory sequence, an animal first learns to associate a bell with food, then learns to associate a light with the bell, and the light comes to be linked with food only through this intermediate step. The phenomenon has been demonstrated even in honeybees, whose proboscis-extension reflex can be second-order conditioned, with research showing that the resulting association can persist for weeks and suggesting that conditioning may be possible at even higher orders still.