The relation between experimental psychology and second language acquisition research has gone through at least two major swings of the pendulum. During the heyday of behaviorism, the pendulum swung strongly toward psychology. The behaviorist psychologists advised us to think of language learning as nothing more than habit formation (Mowrer, 1960), and second language learning materials reflected an emphasis on repetition, drill, rewards, practice, and conditioning. During the early years of the cognitive revolution, Chomsky (1959) argued that viewing language as a conditioned response (Skinner, 1957) ignores the complexities of both language structure and cognition. Persuaded by these arguments, second language researchers turned away from behaviorist psychology and sought the explanation for language acquisition in universals of language structure (Dulay & Burt, 1974).