1890: William James publishes "The Principles of Psychology"
1896: Lightner Witmer opens the first psychological clinic at the University of Pennsylvania
1913: John B. Watson publishes "Psychology as the Behaviorist Views It"
1920: Hermann Rorschach introduces the Rorschach inkblot test
1938: B.F. Skinner introduces the concept of operant conditioning
1967: Ulric Neisser publishes "Cognitive Psychology", marking the beginning of the cognitive revolution
1971: Albert Bandura publishes "Social Learning Theory", introducing the concept of observational learning
1980: The third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III) is published, introducing a new classification system for mental disorders