A chief concern of learning and memory researchers involves determining what is learned in a given situation. Edward L. Thorndike (1933) was an early proponent of the view that animals learn associations between stimuli and responses (i.e., S-R learning), and in his influential law of effect, Thorndike essentially proposed that S-R associations were strengthened by reinforcement (a satisfying event) and weakened by nonreinforcement (an annoying event). In Thorndike's laboratory investigation of the learning abilities of several animal species, the learning curves that he observed were gradual; he therefore argued that learning was not akin to intuition or the sudden illumination of a light bulb. Rather, learning appeared to be an incremental process of trial-and-error, resulting in the eventual acquisition of S-R associations. Thorndike's early S-R learning theory and the rise of James B. Watson's...