The American psychologist Clark Leonard Hull (1884-1952) was a primary representative of the neobehaviorist school. He was also the first known psychologist to apply quantitative experimental methods to the phenomena of hypnosis.
Clark L. Hull was born in a country farmhouse near Akron, N.Y., on May 24, 1884. He attended high school for a year in West Saginaw, Mich., and the academy of Alma College. His education was interrupted by bouts of typhoid fever and poliomyelitis, giving him pause to consider possible vocational choices; he decided upon psychology. He then matriculated at the University of Michigan, took his bachelor's degree, and went on to the University of Wisconsin, receiving his doctorate in 1918. Staying on at Wisconsin to teach, Hull was at first torn between two schools of psychological thought which prevailed at the time: early behaviorism and Gestalt psychology. He was not long in deciding in favor of the former.
After an experimental project on the influence of tobacco smoking on mental and motor efficiency, Hull was offered the opportunity to teach a course in psychological tests and measurements. Gladly accepting it, he changed the name to "aptitude testing" and worked hard at developing it as a sound basis for vocational guidance. The material which he collected in this course was gathered into a book, Aptitude Testing (1928). Next, with the help of a grant from the National Research Council, he built a machine that automatically prepared the correlations he needed in his test-construction work.
In 1929 Hull became a research professor of psychology at the Institute of Psychology at Yale University, later incorporated into the Institute of Human Relations. He came to certain definite conclusions about psychology, and in 1930 he stated that psychology is a true natural science, that its primary laws are expressible quantitatively by means of ordinary equations, and that quantitative laws even for the behavior of groups as a whole could be derived from the same primary equations.
The next 10 years were filled with projects dealing not only with aptitude testing but with learning experiments, behavior theory, and hypnosis. As a representative of behaviorism, Hull fell into that school's neobehaviorist period of the 1930s and early 1940s. His basic motivational concept was the "drive." His quantitative system, based on stimulus-response reinforcement theory and using the concepts "drive reduction" and "intervening variables," was highly esteemed by psychologists during the 1940s for its objectivity.
Hull was probably the first psychologist to approach hypnosis with the quantitative methodology customarily used in experimental psychology. This combination of experimental methods and the phenomena provided by hypnosis yielded many appropriate topics for experimental problems by his students. Hypnosis and Suggestibility, the first extensive systematic investigation of hypnosis with experimental methods, was published in 1933, incorporating the earlier, and better, part of the hypnosis program that Hull had carried out at the University of Wisconsin.
In 1940 Hull published, jointly with C. I. Hovland, R. T. Ross, M. Hall, D. T. Perkins, and F. B. Fitch, Mathematico-Deductive Theory of Rote Learning. Three years later his Principles of Behavior was published, followed by a revision of his theories in Essentials of Behavior (1951). Hull expressed learning theory in terms of quantification, by means of equations which he had derived from a method of scaling originally devised by L. L. Thurstone. In his last book, A Behavior System (1952), Hull applied his principles to the behavior of single organisms. His system stands as an important landmark in the history of theoretical psychology. He died in New Haven, Conn., on May 10, 1952.