At around the same time, Clark Lewis Hull, an American psychologist, was a strong proponent of behaviorist stimulus-response theories, and headed a group at Yale University's Institute of Human Relations. Under him, Neil Miller and John Dollard aimed to come up with a reinterpretation of psychoanalytic theory in terms of stimulus-response. This led to their book, "Social Learning Theory", published in 1941, which posited that personality consisted of learned habits. They used Hull's drive theory, where a drive is a need that stimulates a behavioral response, crucially conceiving a drive of imitation, which was positively reinforced by social interaction and widespread as a result.