John B. Watson
Behaviorism developed in the 1920s, and behavior modification as a therapy became popularized in the 1950s and 1960s. Notable contributors were Joseph Wolpe in South Africa, M.B. Shipiro and Hans Eysenck in Britain, and John B. Watson and B.F. Skinner in the United States. Behavioral therapy approaches relied on principles of operant conditioning, classical conditioning and social learning theory to bring about therapeutic change in observable symptoms. The approach became commonly used for phobias, as well as other disorders.