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Hull, Clark Leonard

HULL, CLARK LEONARD

(b. Akron, New York, 24 May 1884; d. New Haven, Connecticut, 10 May 1952)

psychology, behavior theory, animal learning, aptitude testing, hypnotism, concept formation.

Hull was one of the most influential American psychologists during the period from 1930 to 1950. His main contribution is to be found in his neobehavioristic theory of behavior, which gave new impetus to animal learning research. In addition, he made important contributions to the fields of aptitude testing and hypnosis, and he is the author of a doctoral thesis on the development of concepts that was widely quoted in the psychological literature of the time.

Education . Hull was born in a log farmhouse near Akron, New York. He was the son of Leander Gilday Hull, an ill-tempered farmer who had little schooling because he was required to work as a boy, and Florence Trask, a gentle Connecticut woman who helped her husband to improve his reading after their marriage. When Hull was three or four years old, the family moved to Sickles, Michigan, and his formal education began in the one-room school of this tiny village. At seventeen, he passed a teacher’s examination and later taught at the same school for one year. He then attended West Saginaw High School for another year, where he experienced the conveniences of urban living for the first time in his life.

In 1903 Hull continued his studies in Michigan at the Academy of Alma College. There he became fascinated by geometrical reasoning and by the power of the deductive method to generate new knowledge. He wrote in his autobiography: “The study of geometry proved to be the most important event of my intellectual life; it opened to me an entirely new world—the fact that thought itself could generate and really prove new relationships from previously possessed elements” (1952a, p. 144).

At the end of his second year at the Academy, he suffered a severe bout of typhoid fever, which left him with a poor memory for names and delayed his entrance to college for a year. After his recovery, Hull enrolled in Alma College in 1906 as a freshman and took courses in mathematics, physics, and chemistry in order to prepare himself for a career as a mining engineer. Two years later, when working in the Oliver iron mines of Hibbing, Minnesota, he fell victim to an epidemic of poliomyelitis, which left him partially crippled and ended his early hopes for a career in engineering. Looking for a new occupation, he chose psychology; this new field of science was allied to philosophy in that it involved theory, and it would provide him an opportunity to design and work with technical laboratory equipment. As a preliminary survey for the subject, during his convalescence he studied the two volumes of William James’s Principles of Psychology, a book that made a deep and lasting impression on him. James’s functional psychology was one of the main influences on his psychological thought.

Once recovered from the polio attack, Hull entered the University of Michigan at Ann Arbor, where he received his BA degree in 1913. The head of the Department of Psychology, Walter B. Pillsbury, had just published his Psychology of Reasoning (1910), which probably reawakened Hull’s early interest in higher mental processes. More important, however, was the influence of John P. Shepard, a learning psychologist who introduced him to the rigorous methodology of experimental research and gave him a small Chinese-English dictionary containing the characters and common radicals that Hull would later use in his doctoral dissertation experiments.

In October 1914, after teaching for one year at a small normal school in Richmond, Kentucky, Hull began his graduate training at the University of Wisconsin in Madison. His hope was to contribute to a new experimental science of the higher mental processes. However, the practical atmosphere of the laboratory headed by Joseph Jastrow, a psychologist deeply committed to clinical psychology, led him into the field of applied psychology. During his second year, Hull began his practice in the technique of hypnosis as preparation for teaching an introductory course in medical psychology, which Jastrow had turned over to him. At about the same time, he was asked to teach a course in psychological tests and measurements, and he became involved in the field of psychometrics.

The Evolution of Concepts . In 1918 Hull obtained his PhD in psychology with a dissertation on the “Quantitative Aspects of the Evolution of Concepts” (1920), which was the first study on the subject made with a rigorous experimental methodology. Although the emphasis lay on the measurement of the efficacy of various methods of developing concepts, he included a final “qualitative experiment” designed to observe and determine the nature of the generalizing abstraction that mediates in concept formation.

Hull performed the quantitative experiments with a technique inspired by Hermann Ebbinghaus’s memory experiments. The material consisted of a series of Chinese characters with a common radical, which had to be discriminated and then associated to a nonsense syllable playing the role of the concept. The guiding principle for this experimental setting came from William James’s notion that the perception of similarity is the essence of reasoning. From the drawings of the common radical made by the subjects at different stages in the qualitative experiment, he reached the conclusion that concept formation was a trial-and-error learning process regulated by Edward L. Thorndike’s laws of effect and exercise.

Concept formation was only the first step for Hull on the way to a scientific explanation of reasoning and intelligence. On 5 March 1916 he wrote in his diary: “it seems almost certain now that I shall be a pure psychologist, and that my career will be in the free atmosphere of a great university.… I must set myself a limited task and try by everything in my power to become the supreme authority in that phase of the science.… The subject shall be the psychology of abstraction and concept formation, and perhaps, ultimately, of reasoning” (Hull, 1962, p. 814).

After getting his PhD degree, Hull became an assistant professor at the University of Wisconsin and began his work on aptitude testing. Concerned with the chaotic nature of the available material, he worked to improve the instruments and tried to build up a body of scientific knowledge with the help of statistics. For example, he conceived a “universal” assessment battery that might predict the probable vocational aptitude of a youth in each occupation. As this necessitated the computation of large numbers of correlations, he invented a correlation machine that performed nearly all of the arithmetical work automatically (Hull, 1925), which is now housed in the Smithsonian Institution in Washington, D.C. He also wrote Aptitude Testing (1928), a book that, according to his disciple Kenneth Spence, “did much to encourage the construction and validation of batteries of aptitude tests so as to yield a maximum of prediction in guidance” (Spence, 1952, p. 641).

In 1922 Hull was promoted to the rank of associate professor and was named director of the Laboratory of Psychology. He then began the research program that eventually led to the wealth of experiments reported in Hypnosis and Suggestibility: An Experimental Approach, published in 1933. Dissatisfied with the existing state of knowledge in a field so subjective and prone to deception, Hull planned a research program in which conditioned reflex techniques and physiological response records were used to get objective indexes of the hypnotic trance phenomena. He concluded from his data that hypnosis was a state of hypersuggestiblity or relatively heightened susceptibility to prestige suggestion, and that suggestion was a habit phenomenon. His explanation of suggestion was practically the same as that of Hyppolite Bernheim and other nineteenth-century psychologists, who considered it a kind of “ideomotor action,” or action produced by the thought processes. In the hypnotic trance, the subject reacts very easily to the ideas transmitted to him by the hypnotist. As Hull concluded, “a continuous stimulation by words associated with a particular act will bring the act, whether these words are those of the subject himself or of some other person.… The present hypothesis recognizes very fully the rôle played by ideomotor action in the field of hypnosis and suggestibility” (1933, p. 398).

From Reasoning to Learning . In February 1924, when the development of the correlation machine was well underway, Hull instituted a seminar on “reasoning” in order to isolate problems that could be made the object of experimental attack. A year later, in 1925, he studied John B. Watson’s behaviorism in another seminar for the purpose of determining “stimulus-response” definitions for the concepts of the “old” psychology of consciousness. By the end of the seminar, he had decided to attempt a neobehavioristic explanation of higher mental processes that would be more sophisticated than Watson's.

According to Hull’s own account (1952), it was the attack of Kurt Koffka, the Gestaltist, on the inadequacies of classical behaviorism that confirmed him in this decision. Having tried unsuccessfully to study in Germany with Koffka, he managed to bring him to Wisconsin. In January 1925, in a talk given at Madison, Koffka spent most of his time criticizing behaviorism; this critique left a poor impression on Hull. Instead of being converted to the Gestalt theory, he reached the conclusion “that Watson had not made out as clear a case for behaviorism as the facts warranted” (Hull, 1952, p. 154). Consequently, he decided to improve on Watson’s naive associationism with a theory of thinking that would be deductive and at the same time quite materialistic and totally reliant on the principles of mechanics.

Koffka’s objections were the catalysts that set in motion Hull’s approach to behavior theory, but probably more important was the impact of Wolfgang Köhler’s Mentality of Apes, a book that was translated into English in 1925. Köhler’s experiments on the use and making of instruments indicated that the chimpanzees did not learn punctual stimulus-response connections but rather the relationships between the different objects in their perceptual field. Their behaviors had a definite direction, coherence, and unity that was quite different from the blind trials and errors of the rats in the maze, and indicated some insight or understanding of the problem.

In the following years, Hull delineated the associative mechanisms of his new theory, such as the persisting stimulus of drive, the common response to different stimuli, the fractional anticipatory goal reaction, and the habit-family hierarchy, which later he would publish in separate articles. The persisting stimulus explained purpose because, since it is present in all the stimulus complexes of the habit sequence, it becomes conditioned to all the reactions taking place in it, and later is able to evoke the final act of the original series even in the absence of the external stimuli (Hull, 1930).

The common response to different stimuli mediated conceptual abstraction when there were no identical elements. Suppose, for instance, that R is a response conditioned to three stimuli— a, b, c—which are quite different from an objective point of view and have nothing in common. After the conditioning, they will be equivalent in eliciting R, and the kinesthetic stimulus produced by this response will be the element identical to all of them that explains the process of generalizing abstraction.

Hull drafted the mechanism of the fractional anticipatory goal reaction after observing the phenomenon of the antedating movements in the learning experiments. When a rat is approaching the food box in a maze, it tends to make mouth movements before reaching the food; these tiny fractions of the goal reaction guide the animal toward more specific goals than the drive stimulus, because the same drive can be satisfied with many goal reactions. They were the behaviorist equivalent to ideo-motor action, and their propioceptive stimulus played the role of guiding ideas.

The family-habit hierarchies were Hull’s answer to the Gestalt attacks on the atomistic theories of learning. In the natural environment there are typically multiple routes between a starting point and a goal, and therefore the organism learns alternative ways of moving from a common starting point to a common goal-position, where the reinforcing agent is placed. These alternatives constitute a “family” of equivalent responses because they are united by the fractional anticipatory goal response, which is the same in all of them. They also explain the detour experiments in which the straight line between the learner and the goal is blocked. In Köhler’s experiments, the monkey takes an alternate path, such as the stick, in order to grasp the banana that is beyond his reach, because this manipulative habit belongs to the same family as the habit of reaching food with the hands.

By the end of 1927, Hull decided to make these mechanisms known in a series of articles that he would later gather in a magnum opus whose possible titles were: “Psychology of the Thinking Processes, Mechanisms of Thought, Mechanisms of Mind, Mental Mechanisms …” (Hull, 1962, pp. 824–825). However, in January 1928, after reading Ivan P. Pavlov’s Conditioned Reflexes, he changed his plans and made the conditioned reflex the subject of his first theoretical article (1929). This marked the beginning of the process that eventually led him to the theory of learning.

In September 1929, Hull moved to Yale University as a research professor at the Institute of Human Relations, where he remained until his death. Although he was supposed to work on aptitude testing, his main goal was the construction of a system that integrated the learning theories of Thorndike and Pavlov. In 1935, when the director, Mark May, gave new impetus to the unification of social sciences, Hull played an increasingly prominent role at the institute. With May’s support, he organized a series of seminars and established contacts with the logical

positivists of the Vienna Circle. The alliance with this influential group gave prestige to his formal models and was instrumental in his rising to the forefront of American psychology. In this way, Hull’s projected magnum opus on thinking became a systematic theory of behavior.

In the summer of 1930, while teaching a summer course in the School of Education at Harvard University, Hull experienced considerable general opposition to his materialistic theory of knowledge. At the same time, however, discussions with the philosophers Clarence I. Lewis and Alfred N. Whitehead strengthened his interest in theory building. He read Isaac Newton’s Principia thoroughly, finding in this book a powerful scientific theory expressed in the mode of Euclidean geometry. From that point, Newton’s set of postulates and theorems would be the model that Hull would follow in his own theorizing.

Hull’s Behavior System . Hull developed his system in a piecemeal fashion. During the late 1930s he elaborated the key concepts in “miniature systems,” such as the Mathematico-Deductive Theory of Rote Learning(1940). A little later, in 1943, he offered the first complete set of sixteen postulates in the Principles of Behavior, his most widely known book. This volume was intended to present only the basic theoretical framework, which would eventually be used to explain more complicated behavioral phenomena. Explanation of such phenomena was then to be the subject of two further volumes focusing on individual and social behavior, respectively. However, as time passed, Hull became progressively more engrossed in the quantification of the system. A coronary attack in 1948 convinced him that he would not live long enough to complete this ambitious program. Nevertheless, he was able to publish a final revision in Essentials of Behavior(1951), and to finish the manuscript on the single organism’s behavior, which was published after his death under the title A Behavior System (1952).

Hull’s theory of behavior can be considered the best example of hypothetico-deductive system-making in psychology. Taking the biological adaptation of the organism to its environment as a frame of reference, it assumes that survival depends upon optimal conditions of food, water, and so on, as was demonstrated in Walter B. Cannon’s physiological research. When one of these conditions deviates from the optimum, the organism enters a state of need, which will be eliminated only through a particular sequence of movements called adaptive behavior.

It was the primary task of psychology to isolate the basic laws by which the stimulation arising from needs on the one hand, and from the external environment on the other, brings about such adaptive behavior. To fulfill this task, the use of unobservable logical constructs, or intervening variables, was permissible, provided that such constructs were functionally related to directly observable environmental events. The central postulates of Hull’s system were concerned with learning or “habit,” as he termed it. Being the highest and most significant phenomenon produced by the organic evolution, habit consisted in the strengthening of certain receptor-effector connections, or in the setting up of new connections, according to the principle of reinforcement.

In Principles of Behavior Hull put aside the associative mechanisms of his earlier theoretical articles and explained reinforcement in terms of drive reduction. For learning to take place, the contiguity of stimulus and response had to be closely associated with a diminution in the drive generated by a need, the Strength of Habit (S HR) depending on the number of times it was reinforced. The construct Drive (D) made reference to a general tendency to action generated by the state of need. For instance, in the need of food, the hunger drive will set organisms into a state of general restlessness.

The behavior’s concrete direction depended upon another hypothetical entity, the Drive Stimulus (SD), or stimuli produced by the drive, such as, for example, “hunger pangs,” the stomach contractions aroused by hunger. These persistent stimuli become conditioned to all the responses of the habit leading to the food, and in this way they play a leading role in behavior. Without their distinctiveness there could be no way for the animal to learn to go to one place for food when hungry and to another place for water when thirsty.

Drive (D) played a critical part not only in reinforcement, but also in Reaction Potential (S ER), the construct expressing the strength of the tendencies determining the vigor and persistency of the activity. The reaction potential equation is based on the assumption that Drive (D) interacts with Habit Strength (S HR) in a multiplicative fashion to yield a value for the Reaction Potential (S ER=S HR x D).

Hull’s Legacy . In the final revision of Essentials of Behavior (1951), Hull introduced substantial changes in the system to the point that, according to Sigmund Koch, it “defines a set of assumptions so radically different from those of Principles of Behavior as to constitute an essentially new theory” (1954, p.2).

The first change is in the conception of primary reinforcement. While in the 1943 postulates it depended upon physiological drive reduction, it came in 1951 to depend chiefly on the reduction of drive-produced stimuli (SD), or on the decrease of the goal stimulus produced by the fractional anticipatory goal response. This change, due in part to the fact that a nonnutritive substance such as saccharine acted as a powerful reinforcing agent, indicates that Hull was moving in the direction of a contiguity position, although he avoided any clear pronouncement on the critical factor of reinforcement and left the question open until new empirical evidence was available.

The second important change is that the quantitative aspects of reinforcement exert no influence upon habit strength; what counts is only the frequency with which reinforced trials have occurred. This was basically a contiguity theory of association formation, although he never renounced the reinforcement principle.

Hull’s last major work, A Behavior System (1952), is devoted to applying the principles to a variety of more complex behaviors, such as trial-and-error learning, discrimination learning, maze learning and problem solving. Hull returns to the old mechanism of the “fractional anticipatory goal response” to explain latent learning and Edward C. Tolman’s cognitive expectancies. In the chapter on problem solving, Hull considers insight basically in the same way as in his article on “The Mechanism of the Assembly of Behavior Segments in Novel Combinations Suitable for Problem Solution” (1935). Therefore, in a sense the book is the continuation of the projected magnum opus on thinking processes. But Hull limited himself to animal learning, leaving the treatment of abstract thinking to the third volume on social behavior, which he never completed. As a result of his premature death, caused by a heart disease, his system remained unfinished. He married to Bertha E. Iutzi; they had two children: Ruth T. and Richard T. Hull.

Hull’s behavior theory has been subject to scathing criticisms since the early 1950s. Some of his theoretical formulations were not as tight as advertised and depended upon very weak empirical evidence. Psychology since the 1950s has progressed in a direction at variance with the premises of Hullian behaviorism. The fall of logical positivism in the philosophy of science and the advent of modern cognitive psychology have put in evidence the weaknesses of the stimulus-response schema.

Hull’s influence, however, cannot be minimized. Judging by the number of experimental studies engendered by his theory, he was the most influential of the American neobehaviorists between 1930 and 1950. He also trained a raft of psychologists at Yale. A member of the National Academy of Sciences, he was honored by the presidency of the American Psychological Association in 1936, and in 1945 received the Warren Medal from the Society of Experimental Psychologists. He was a powerful leader in the discipline, and the precision of his theorizing made a deep impression on his disciples, including Kenneth W. Spence. Spence, working at the University of Iowa, developed Hull’s system into what came to be called the Hull-Spence theory and trained many who would become leading American experimental psychologists of the 1950s and 1960s.

BIBLIOGRAPHY

Mainly to compensate for his bad memory, Hull recorded in a notebook his ideas concerning all sorts of psychological subjects during the period from October 1902 to April 1952. The notebooks, which he called his “idea books,” are held in the archives of the University of Yale. Together with the mimeographed IHR seminar notes and “memoranda,” they offer a detailed record of the development of his theory. Extensive excerpts from the “idea books” were published by Robert B. Ammons in the 1962 monograph of Perceptual and Motor Skills mentioned below.

WORKS BY HULL

“Quantitative Aspects of the Evolution of Concepts.” Psychological Monographs 28 (1920): 1–123.

“An Automatic Correlation Calculating Machine.” Journal of the American Statistical Association 20 (1925): 522–531.

Aptitude Testing. Yonkers-on-Hudson, NY: World Book, 1928.

“A Functional Interpretation of the Conditioned Reflex.” Psychological Review 36 (1929): 498–511.

“Knowledge and Purpose as Habit Mechanisms.” Psychological Review 37 (1930): 511–525.

“Goal Attraction and Directing Ideas Conceived as Habit Phenomena.” Psychological Review 38 (1931): 487–506.

Hypnosis and Suggestibility: An Experimental Approach. New York: Appleton, 1933.

“The Concept of the Habit-Family Hierarchy and the Maze Learning.” Psychological Review 41 (1934): 33–52, 134–152.

“The Mechanism of the Assembly of Behavior Segments in Novel Combinations Suitable for Problem Solution.” Psychological Review 42 (1935): 219–245.

“Mind, Mechanism and Adaptive Behavior.” Psychological Review 44 (1937): 1–32. APA Presidential Address delivered in Hanover, New Hampshire, on 4 September 1937. Hull’s first miniature system on adaptive behavior.

With Carl I. Hovland, Robert T. Ross, et al. Mathematico-Deductive Theory of Rote Learning: A Study in Scientific Methodology. New Haven, CT: Yale University Press, 1940.

Principles of Behavior: An Introduction to Behavior Theory. New York: Appleton, 1943.

“Behavior Postulates and Corollaries: 1949.” Psychological Review 57 (1950): 173–180.

Essentials of Behavior. New Haven, CT: Yale University Press. 1951.

“Clark L. Hull.” In A History of Psychology in Autobiography. Vol. 4, edited by Edwin G. Boring et al., 143–162 Worcester, MA: Clark University, 1952a.

A Behavior System: An Introduction to Behavior Theory Concerning the Individual Organism. New Haven, CT: Yale University Press, 1952b.

“Psychology of the Scientist: IV. Passages from the ‘Idea Books’ of Clark L. Hull.” Perceptual and Motor Skills 15 (1962): 807–882.

Mechanisms of Adaptive Behavior: Clark L. Hull’s Theoretical Papers, with Commentary. Edited by Abram Amsel and Michael E. Rashotee. New York: Columbia University Press, 1984. A collection of the papers published in the Psychological Review from 1929 to 1950.

OTHER SOURCES

Beach, Frank. “Clark Leonard Hull.” In Biographical Memoirs. vol. 33, edited by the National Academy of Sciences, 125–141. New York: Columbia University, 1959. With a complete bibliography of Hull’s published writings.

Gondra, José M. “Clark Hull’s Cognitive Articles: A New Perspective on His Behavior System.” Revista de Historia de la Psicología 22 (2001): 113–134.

———. Mecanismos Asociativos del Pensamiento: La “Obra Magna” Inacabada de Clark L. Hull. Bilbao, Spain: Desclée de Brouwer, 2007.

Kimble, Gregory A. “Psychology from the Standpoint of a Mechanist: An Appreciation of Clark L. Hull.” In Portraits of Pioneers in Psychology. Vol. 1, edited by Gregory A. Kimble et al., 209–225. Washington, DC: American Psychological Association, 1991.

Koch, Sigmund. “Clark L. Hull.” In Modern Learning Theory, edited by William K. Estes et al., 1–176. New York: Appleton, 1954.

Logan, Frank A. “The Hull-Spence Approach.” In Psychology: A Study of a Science. Vol. 1, edited by Sigmund Koch, 293–358. New York: McGraw-Hill, 1959.

Smith, Lawrence D. Behaviorism and Logical Positivism. Stanford, CA: Stanford University Press, 1986.

Spence, Kenneth W. “Clark L. Hull: 1884–1952.” American Journal of Psychology 65 (1952): 639–646.

Triplet, Rodney G. “The Relationship of C. L. Hull’s Hypnosis Research to His Later Learning Theory.” Journal of the History of the Behavioral Sciences 18 (1982): 22–31.

José María Gondra

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Clark Leonard Hull

Clark Leonard Hull

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.

Further Reading

There is a short biography of Hull by Frank A. Beach in Biographical Memoirs of the National Academy of Sciences, vol. 33 (1959), and an autobiographical narrative in Edwin G. Boring and others, eds., A History of Psychology in Autobiography, vol. 4 (1952). An interesting exposition of Hull and of the various movements in psychology contemporary with and preceding neobehaviorism is in Melvin H. Marx and William A. Hillix, Systems and Theories in Psychology (1963). □

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Hull, Clark Leonard

Clark Leonard Hull

1884-1952
American psychologist who was a primary representative of the neobehaviorist school.

Clark L. Hull was born in a country farmhouse near Akron, New York, on May 24, 1884. He attended high school for a year in West Saginaw, Michigan, 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, Connecticut, on May 10, 1952.

Further Reading

Beach, Frank A. Biographical memoirs. The National Academy of Sciences, vol. 33. 1959

Boring, Edwin G., et al., eds. A history of psychology in autobiography. vol. 4, 1952.

Marx, Melvin H. and William A. Hillix. Systems and theories in psychology. 1963.

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