Clark Hull

(1884 - 1952)

Compiled by Jana Schrock (May 1999)

Hull Biography
Time Line

Clark Hull grew up handicapped and contracted polio at the age of 24, yet he became one of the great contributors to psychology. His family was not well off so his education had to be stopped at times. Clark earned extra money through teaching. Originally Clark aspired to be a great engineer, but that was before he fell in love with the field of Psychology. By the age of 29 he graduated from Michigan University. When Clark was 34 when he received his Ph.D. in Psychology at the University of Wisconsin in 1918. Soon after graduation he became a member of the faculty at the University of Wisconsin, where he served for 10 years. Although one of his first experiments was an analytical study of the effects of tobacco on behavioral efficiency, his life long emphasis was on the development of objective methods for psychological studies designed to determine the inderlying principles of behavior.

Hull devoted the next 10 years to the study of hypnosis and suggestibility, and in 1933 he published Hypnosis and Suggestibility, while employed as a research professor at Yale University. This is where he developed his major contribution, an elaborate theory of behavior based on Pavlov's laws of conditioning. Pavlov provoked Hull to become greatly interested in the problem of conditioned reflexes and learning. In 1943 Hull published, Principles of Behavior, which presented a number of constructs in a detailed Theory of Behavior. He soon he became the most cited psychologist.

Hull believed that human behavior is a result of the constant interaction between the organism and its environment. The environment provides the stimuli and the organism responds, all of which is observable. Yet there is a component that is not observable, the change or adaptation that the organism needs to make in order to survive within it's environment. Hull explains, "when survival is in jeopardy, the organism is in a state of need (when the biological requirements for survival are not being met) so the organism behaves in a fashion to reduce that need" ( Schultz & Schultz, 1987, p 238). Simply, the organism behaves in such a way that reinforces the optimal biological conditions that are required for survival.

Hull was an objective behaviorist. He never considered the conscious, or any mentalistic notion. He tried to reduce every concept to physical terms. He viewed human behavior as mechanical, automatic and cyclical, which could be reduced to the terms of physics. Obviously, he thought in terms of mathematics, and felt that behavior should be expressed according to these terms. "Psychologist must not only develop a thorough understanding of mathematics, they must think in mathematics" (Schultz & Schultz, 1987, p 239). In Hull's time three specific methods were commonly used by researchers; observation, systematic controlled observation, and experimental testing of the hypothesis. Hull believed that an additional method was needed, - The Hypothetico Deductive method. This involves deriving postulates from which experimentally testable conclusions could be deduced. These conclusions would then be experimentally tested.

Hull viewed the drive as a stimulus, arising from a tissue need, which in turn stimulates behavior. The strength of the drive is determined upon the length of the deprivation, or the intensity / strength of the resulting behavior. He believed the drive to be non-specific, which means that the drive does not direct behavior rather it functions to energize it. In addition this drive reduction is the reinforcement. Hull recognized that organisms were motivated by other forces, secondary reinforcements. " This means that previously neutral stimuli may assume drive characteristics because they are capable of eliciting responses that are similar to those aroused by the original need state or primary drive" (Schultz & Schultz, 1987, p 240). So learning must be taking place within the organism.

Hull's learning theory focuses mainly on the principle of reinforcement; when a S-R relationship is followed by a reduction of the need, the probability increases that in future similar situations the same stimulus will create the same prior response. Reinforcement can be defined in terms of reduction of a primary need. Just as Hull believed that there were secondary drives, he also felt that there were secondary reinforcements - " If the intensity of the stimulus is reduced as the result of a secondary or learned drive, it will act as a secondary reinforcement" ( Schultz & Schultz, 1987, p 241). The way to strengthen the S-R response is to increase the number of reinforcements, habit strength.

Clark Hull's Mathematico Deductive Theory of Behavior relied on the belief that the link between the S-R relationship could be anything that might effect how an organism responds; learning, fatigue, disease, injury, motivation, etc. He labeled this relationship as "E", a reaction potential, or as sEr. Clark goal was to make a science out of all of these intervening factors. He classified his formula

sEr = (sHr x D x K x V) - (sIr + Ir) +/- sOr

as the Global Theory of Behavior. Habit strength, sHr, is determined by the number of reinforces. Drive strength, D, is measured by the hours of deprivation of a need. K, is the incentive value of a stimulus, and V is a measure of the connectiveness. Inhibitory strength, sIr, is the number of non reinforces. Reactive inhibition, Ir, is when the organism has to work hard for a reward and becomes fatigued. The last variable in his formula is sOr, which accounts for random error. Hull believed that this formula could account for all behavior, and that it would generate more accurate empirical data, which would eliminate all ineffective introspective methods within the laboratory (Thomson, 1968).

Although Hull was a great contributor to psychology, his theory was criticized for the lack of generalizability due to the way he defined his variables in such precise quantitative terms. "Thus, Hull's adherence to a mathematical and formal system of theory building is open to both praise and criticism" (Schultz & Schultz, 1987, p 242).

Time Line
1884 Hull was born
1918 Received Ph.D. from University of Wisconsin
19 publication of the literature on tests and measurements
19 Becomes research Professor at Yale
193 Hypnosis and Suggestibility , published
1940 Mathematico - Deductive Theory of Rote Learning: A study in Scientific Methodology was published.
19 Principles of Behavior was published
1951 The Essentials of Behavior was published
1952 A Behavior System was published
1952 Hull died

Hothersall, D. 1995. History of Psychology, 3rd ed., Mcgraw-Hill:NY
Schultz, D.P. & Schultz, S.E. (1987). A History of Modern Psychology. Harcourt Brace Jovanovich Publications.
Thomson, R. (1968). A Pelican History of Psychology. Penguin Books Publications. (pp 237-242)

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