Williard Small introduced the maze as a way to measure retention.
Edward Thorndike began the study of operant conditioning and gave us the law of effect which states that behaviors that bring about positive consequences are repeated.
B.F. Skinner continued Thorndike's Operant Conditioning studying. He invented the operant conditioning paradigm Skinner Box in which rats push a bar for food pellets.
He later wrote a behaviorists view book on language called Verbal Behavior, which was reviewed by Noam Chomsky. The review is said to have killed off Behaviorism as a viable school of Psychology.