An automatic, stereotyped response to a stimulus; the conditioned reflex (Pavlov) is the simplest form of learning and memory.
Young uses the eye-blink and hand-withdrawal to introduce the reflex arc, then distinguishes fixed reflexes and tropisms from genuine learning.
George illustrates conditioning with Grey Walter's machine CORA, whose neon tube learns to flash to a whistle that has been paired with a light — “Pavlov's dogs” in hardware.