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Hull, Clark was a milestone in the evolution of scientific psy- chology. Immanuel Kant had argued that psychol- John F. Kihlstrom ogy could never be a science, because the mind, University of California, Berkeley, being immaterial, could not be observed and Berkeley, CA, USA measured. The nineteenth-century psychophysi- cists and physiological – Weber, Fechner, Helmholtz, and Donders – quickly pro- Clark L. Hull was born in Akron, New York, ved Kant wrong. Even so, Wilhelm Wundt argued on May 24, 1884, and died in New Haven, that scientific , as a natural science Connecticut, on May 10, 1952. After early expe- (Naturwissenschaft), was limited to the study of rience as a teacher in a one-room schoolhouse, immediate experience, that is, to sensation and and later as a school principal and apprentice perception. The so-called “higher” mental pro- mining engineer, he received his AB, with cesses, such as memory and thought, were too a major in psychology, from the University far away, as it were, from the instigating physical of Michigan in 1913. He then moved to the stimulus, and the underlying physiology was University of Wisconsin for graduate study, deemed too complex, so they were relegated to working with Joseph Jastrow (Blumenthal 1990; Geisteswissenschaft. By the end of the nineteenth Jastrow 1930) and others and taking his PhD in century, however, Hermann von Ebbinghaus 1918. He then joined the faculty at Wisconsin (1885/1964) and (1896) before moving to Yale in 1929 as a Research had proved Wundt wrong with respect to memory. Professor in the Institute of Psychology, which Hull, adapting Ebbinghaus’s methods with was later folded into the Institute of Human Chinese characters as the stimulus materials, did Relations (IHR), an interdisciplinary group the same for concept formation, a function central of social scientists and psychiatrists whose mem- to thinking. In the process, Hull invented the bers included John Dollard, Neal Miller, and memory drum, which was to serve as an essential O.H. Mowrer. At IHR, Monday-evening seminars instrument for the study of verbal learning up until drew dozens of participants. He later was the introduction of the computer. appointed Sterling Professor in the Department Hull’s involvement with the study of individ- of Psychology (Beach 1959; Hovland 1952; Hull ual differences had two quite different sources. At 1952b). Wisconsin, he had been assigned to teach a course Best known for his theory of learning, Hull’s on aptitude testing. This led him to publish an career actually went through a number of phases. early and influential textbook on the subject, His doctoral dissertation on concept formation advocating objective tests for use in vocational

# Springer Nature Switzerland AG 2019 V. Zeigler-Hill, T. K. Shackelford (eds.), Encyclopedia of Personality and Individual Differences, https://doi.org/10.1007/978-3-319-28099-8_1760-1 2 Hull, Clark counseling (Hull 1928). Aggravated by the tests of physiological functions, sensory motor, tedium of computing masses of interitem correla- and “higher” mental processes. The study yielded tions, he invented a “correlation machine” which few significant effects on psychological functions, took raw data on paper tape and generated squares but more important than the results obtained were and cross products. The device served psychome- the experimental controls employed. Long before tricians well into the 1950s, when high-speed Beecher (1955) introduced the concept of digital computers rendered it obsolete. A copy the placebo to medical research, Hull understood is now in the collection of the Smithsonian that the results of drug studies might be artifacts of Institution. suggestion and expectation on the part of both The second source was hypnosis. How Hull experimenters and subjects. In an attempt to con- became interested in hypnosis is not clear trol for such effects, Hull invented an “experimen- (Kihlstrom 2004), but one of his teaching assign- tal pipe” which used an electric element to allow ments at Wisconsin had been a course on psychol- subjects to inhale heated air instead of tobacco ogy for premedical students previously taught by smoke, through asbestos fibers (!) to simulate the Jastrow, who had an interest in the subject. In any effects of drawing on a pipe; the subjects were event, he and his students produced an extraordi- blindfolded while the experimenter smoked his nary corpus of experimental work on the subject, own pipe to simulate the odor of tobacco. The culminating in his monograph on Hypnosis and “bite” of tobacco smoke on the tongue was simu- Suggestibility (Hull 1933). Although there had lated by increasing the temperature of the inhaled been experimental work on hypnosis before, air. Subjects were literally blindfolded subjects, so mostly at Harvard, Hull’s programmatic efforts – they could not tell the difference between experi- including investigations of “waking” suggestibil- mental and control trials. All Hull neglected to do ity as well as phenomena such as amnesia, was to blind the experimenter as well. hypermnesia, and the transcendence of normal Hull’s larger reputation, of course, rests on his voluntary capacities – marked the first “golden contributions to stimulus-response learning the- age” of hypnosis research (the second began in ory (Hull 1943, 1952a; see also Hilgard 1948, the 1960s). 1987; Hilgard and Marquis 1940). Inspired by As its title suggests, Hull believed that hypno- Newton’s Principia and Whitehead and Russell’s sis was a special case of suggestibility, and Principia Mathematica, and employing the he invented a mechanical device to quantify hypothetical-deductive method to generate exper- responses to the postural sway test. Using this iments, he developed a comprehensive “behavior and similar devices, Hull explored the correlations system” consisting of definitions, postulates, cor- between various forms of suggestibility and ollaries, theorems, and proofs, all expressed in between suggestibility and intelligence and other mathematical form such as his famous equations, -aN personality characteristics. Hull was less inter- SER = SHR xDand SHR = 1–10 . In Hull’s ested in individual differences in suggestibility, theory, the excitatory potential of a response to a however, and more interested in hypnosis as a stimulus is a function of habit strength and drive habit phenomenon, acquired through learning, strength. Drive strength is a matter of deprivation, showing the typical negatively accelerated learn- habits are acquired through learning, learning ing curve. Nervous administrators at Yale brought occurs by repeatedly reinforcing responses to an end to Hull’s program of hypnosis research, stimuli, and reinforcement is a matter of drive although he did publish outlines of 40 experiments reduction. on suggestibility and 102 on hypnosis, many of Unfortunately, the precision of Hull’s theory which would be worth doing even today. was also its undoing. Examined closely, for exam- Also while at Wisconsin, Hull did pioneering ple, it appeared to predict that both acquisition and research on the effects of smoking on various extinction were impossible (Gleitman et al. 1954). aspects of human performance (Hull 1924). In addition, Tolman demonstrated “latent” learn- Smokers and nonsmokers completed a battery of ing, in the absence of reinforcement, undermining Hull, Clark 3 the role of drive reduction (Tolman and Honzik behavior in order to obtain the same rewards that 1930), while Skinner (1938) offered a competing they receive from their actions. Imitation is wide- system based on reinforcement that did not spread because the culture reinforces it strongly, involve hypothetical mediating variables such as as a means of maintaining social conformity and drive and drive reduction. Nevertheless, in its discipline. broad outlines, Hullian learning theory influenced Miller and Dollard distinguished between two both Eysenck’s(1952) early experimental inves- forms of imitation. In matched-dependent behav- tigations of personality and Wolpe’s(1958) tech- ior, only the model recognizes the cues that elicit nique of systematic desensitization. the behavior. A good example is crowd behavior, Although based mostly on animal research, where people engage in certain actions (like Hull’s theory was intended to encompass human applause or yelling) simply because other people behavior as well and the behavior of groups as are doing so, without knowing why. Copying is a well as individuals. A major project at IHR was much more deliberate act, in which one person the exploration of connections between his behav- consciously conforms his or her behavior to ior system and Freudian psychoanalytic theory. that of another person. This entails awareness of Psychoanalysis was, by any measure, the domi- the cues that elicit the behavior of the model. nant theory of personality and psychotherapy at Imitative behavior is central to social learning the time, and the two theories were obviously and thus to personality. It is readily observed in linked by their emphasis on drive reduction. even the youngest children and indeed whenever Aside from Hull himself, the leading figures in one person possesses more authority or knowl- this effort were John Dollard, a sociologist who edge than another. Imitation, especially matched- made major contributions to understanding race dependent behavior, is the chief means by which relations, but who had also trained as psychoana- patterns of behavior are passed from one person to lyst in Berlin, and Neal Miller, a another. whose dissertation had analyzed fear as a condi- Social learning theory subsequently shed its tioned drive and who had himself been analyzed Hullian origins and focused more on expectation in Vienna by Heinz Hartmann (he couldn’t afford and other cognitive processes and observational Freud’s fee). learning in the absence of reinforcement (Bandura Under Hull’s auspices, the IHR group 1977; Rotter 1954). The final product of Hull’s produced a huge amount of influential work, IHR group was Personality and Psychotherapy,a including a major treatise on Frustration and wholesale reformulation of psychoanalytic theory Aggression (Dollard et al. 1939), which argued in terms of Hullian learning theory, with analyses that aggression was a reflexive response to the of drive and its reduction, and the resolution of frustration of goal-directed behavior. The theory various forms of conflict – approach avoidance, has since undergone considerable revision and approach-approach, and avoidance-avoidance refinement (Berkowitz 1989); but the connection (Dollard and Miller 1950). of the original formulation to psychoanalysis is Hull served as president of the American obvious. Psychological Association in 1936. He received Another product of Hull’s IHR group, less many other honors in his lifetime, including elec- obviously tied to psychoanalysis, was the first tion to the National Academy of Sciences and the statement of social learning theory (Miller and American Academy of Arts and Sciences. In rec- Dollard 1941), with its emphasis on imitation as ognition of his work, in 1945 Hull received the a secondary drive acquired through reinforce- Warren Medal of the Society of Experimental ment. For Miller and Dollard, imitation was not Psychologists, honoring “his careful development just behavior: by virtue of reinforcement, it took of a systematic theory of behavior...in a precise on the properties of an acquired or secondary and quantitative form.... A truly unique achieve- drive. Thereafter, the individual is motivated to ment in the to date.” imitate the behavior of others – to copy their 4 Hull, Clark

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