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=Clark L. Hull= Clark Leonard Hull (1884-1952) was an American psychologist who started off his academic career by learning in a one-room schoolhouse, and ending it as a research professor at Yale University. He was a researcher who emphasized controlled experiments in his studies. Hull’s primary area of interest was in learning theories. He is known for his drive-stimulus theory, which is also known as systematic behavior theory. He also conducted research on hypnosis, but his drive-stimulus theory was his main area of study. He was recognized by the academic community by many awards, honors, and titles. Hull was president of the American Psychological Association, he was elected into the American Academy of Arts and Sciences, and awarded the Warren Medal. Hull influenced many of his students, who went on to become well-known psychologists themselves.

Background
Clark Hull was born in a log house on a farm near Akron, New York in 1884. He was born to a powerful father who was known to have a violent temper. His mother, born in Connecticut, was a shy woman who got married at the age of fifteen. Clark’s father didn’t get a lot of schooling because his father worked a lot as a child, so he didn’t learn how to read and was eventually taught by his wife (Bingham et al., 1952). After the age of about three, his parents and younger brother moved to a farm in Michigan where he and his brother helped with chores around the house. At this time he attended a one-room country school where there were about twenty to thirty people. At this time, Clark found arithmetic easy but found grammar a bit difficult (Bingham et al., 1952). At seventeen he passed a teacher’s examinations test and taught at the country school. Wanting to know more about the world, he moved onto high school in West Saginaw and then Alma College. In college, he grew more fond of math, especially geometry. As he was about to graduate, he attended a banquet where the food was contaminated and got typhoid fever. Many died during that time and Clark himself almost died. He was left with permanent amnesia and a general bad memory for names which affected him throughout the rest of his life (Bingham et al., 1952). As Clark's health improved, he laid the groundwork to study mining engineering. As Clark was about to begin his job at the iron mines, he developed poliomyelitis which left him paralyzed with one leg. During his recovery period he discovered his love of philosophy and involving theory in the process. Studying psychology suited his desires nicely and he began his journey by reading William James’ book Principles of Psychology (Bingham et al., 1952). A little after he started reading, his eyes would become weak and his mother would read to him until his eyes became strong enough for him to read on his own. A year later, he decided to teach back home in the one room school, which had expanded to two-rooms. After his two years teaching, he married Bertha Lutzi with very little money (Bingham et al., 1952). Upon finishing his teaching career they both decided to enroll as students at the University of Michigan. After graduating, he was able to secure a teaching position in Kentucky while also working on experiments on the side. Clark sought a teaching assistant position and finally got one at the University of Wisconsin where his first two years he worked as a half-time assistant and his next two years as a full time instructor (Bingham et al., 1952).

In addition to his other teachings, he was able to teach a psychological test and measurement course. Because he loved the mathematical portion of the course, he changed the class to aptitude testing, which focused on scientific basis of vocational guidance (Bingham et al., 1952). On the side, Hull also conducted research to build a machine that could perform all the correlational work for him automatically. After teaching the aptitude testing class, Clark went on to teaching an introductory class for premedical students. While teaching this class he particularly took notice of suggestion and hypnosis. This was the starting point of his experimental testing in this field in which Clark focused on the quantitative methodology in experimental psychology. After ten years of in-depth research, he wrote the book Hypnosis and Suggestibility in 1933 (Bingham et al., 1952). After writing the book, he decided to continue in experimental field by teaching this course in addition to the premedical course. Clark had a great desire to teach this course and felt as though this specific type of science was the foundation of true psychology. In 1929 he was called to the Institute of Psychology at Yale University as a research professor of psychology where he worked on the problems concerning systematic behavior theory (Bingham et al., 1952). In 1930, he came to several conclusions about psychology: the first was that he believed that psychology is a true natural science. The second was that its primary laws are expressed quantitatively by moderate number equations and that all complex behavior or single individuals will be derived as second laws. The third was that the primary laws with the behavior (based on the condition) can also be derived as quantitative laws from the same primary equation (Bingham et al., 1952). As he and other psychologists (Neal E. Miller, John Dollard, and O.H Mower) looked into these ideas more, they sought to understand what underlined conditioned reflex and behavior while also seeking to understand Freud and others like him (Bingham et al., 1952). This eventually led to his work that he is primarily known for: Principles of Behavior.

Research and Work
Hull’s primary interest was in theories of learning and behaviors that lead to learning. This was the goal of most of his research; in the end Hull created his own learning theory sometimes referred to as drive theory or systematic behavior theory. He also showed interest in hypnosis, but this was not his top priority in his work and research life (Hovland, 1952). In both his drive theory and hypnosis research, Hull made sure that his experiments were under strict control. Also, in his work he emphasized quantitative data so everything could be analyzed more precisely, and less open to interpretation than previous studies on the topics (Hovland, 1952).

Drive Theory/Systematic Behavior Theory
Clark Hull found inspiration for his own theory of learning after learning about Ivan Pavlov’s idea of conditional reflexes, and Watson’s system of behaviorism (Hilgard & Bower, 1975). Hull’s theory would seem to fall into the category of being a behaviorist system, as it followed loosely in the footsteps of Watson. He also was impacted by Edward Thorndike, as he adapted his theory to include and agree with Thorndike’s law of effect (Hilgard & Bower, 1975).

After Hull discovered his interest in learning theories from Pavlov, Watson, and Thorndike, he dedicated much of his own laboratory work to perfecting his own theory. Also, many experiments concerning his learning theory came from Hull’s students, who carried out many different experiments in Hull’s lab after finding inspiration from seminars and lectures in classes that Hull taught (Hovland, 1952).

Hull’s theory of learning, known as systematic behavior theory or drive theory, is a type of reinforcement system, which means that in learning, habits are initially formed by reinforcing certain behaviors. Reinforcement of a response to a behavior supplies an effect that satisfies a need. In other words, this satisfaction of needs helps create habits out of behaviors. Specifically, Hull’s theory posits that behaviors that satisfy needs, later described by Hull as cravings rather than needs, reduce these cravings. He called this concept drive-reduction, or drive-stimulus reduction (Hilgard & Bower, 1975).

One of Hull’s earliest published books on the topic of drive reduction was called Principles of behavior (1943), but as soon as this was published, he started writing revisions to his own work. Hull wanted to be as thorough as possible in his system, so after revising it multiple times, he finally wrote his final explanation in A behavior system (1952). His final book, which was published after Hull died, dealt much more with questions of application of his theory than his first book did (Hilgard & Bower, 1975).

Hypnosis
Although hypnosis was not his main interest of study, it is a notable part of Hull’s research career. While previous studies on hypnosis seemed to lack quantitative information and strict control in experiments, Hull put forth his studies to fill this gap. His studies showed that behaviors and ideas that had been linked to hypnosis in the past were not exclusive to hypnotism. Some of these behaviors and ideas that he proved to be non-exclusive to hypnosis were catalepsy, sleepiness, and post-hypnotic suggestion (Krout, 1934).

Hull’s largest contribution to the world of hypnosis was his belief that hypnosis is not at all related to sleep. His research even goes as far as to say that hypnosis is the opposite of sleep, because he found that hypnosis gave responses linked to alertness rather than lethargy. In Hull’s research, some of his subjects even felt that hypnotism made their sensitivity and alertness better (Krout,1934). In fact, many of Hull’s subjects in hypnotic states did believe that their senses had increased (Young, 1934). They genuinely thought their senses were better, but this was never proven to be a significant result.

Hull’s research indicated that hypnotic states and waking states are the same, besides a few simple differences. One of these differences is that subjects in hypnotic states respond to suggestions more readily than those in a waking state. The only other notable difference is that Hull believed that those in hypnotic states were better able to remember events that had happened far in the subject’s past (Young, 1934). Other than those two differences, not much differentiated between waking and hypnotic states, according to Hull’s controlled studies. In addition, Hull dispelled the ideas linked to hypnotism such as above average memory, ability to learn better, and perception (Young, 1934). He narrowed down the field of hypnotism, and proved that some things were not true about previous beliefs and accepted knowledge of hypnotism.

Early Impact
In 1936 Hull worked with students and associates and together they started a series of evening seminars that became known as “Monday Night Meetings”. They would discuss topics such as conditioned reflexes, behavior laws, and Freud’s psychoanalysis. These meetings became popular with many kinds of people, such as psychologists, sociologists, and anthropologists and sometimes as many as seventy people would attend (Beach, 1959).

Later in life when Hull was in poor health, he had the help of his research assistants and volunteers to conduct his experiments. He also relied on people to keep him up to date on current discussions on current psychological experiments and theories that he was unable to attend and participate in. Some of these former students and associates were Kenneth Spence, Neal Miller, and John Dollard (Beach, 1959).

Awards and Recognition
Clark Hull has been honored by a number of scientific societies. Hull was president of the American Psychological Association from 1935-1936 (Beach, 1959). Hull was elected into the American Academy of Arts and Sciences in 1935 and also to the National Academy of Arts and Sciences in 1936. The Society of Experimental Psychologists awarded him the prized Warren Medal in 1945 (Hovland, 1952).

Hull was one of the most frequently cited psychologists during the 1940’s and 1950’s (Hovland, 1952). Aptitude Testing (1928) was a widely quoted textbook and his work Hypnosis and Suggestibility: An Experimental Approach (1933) was widely studied. Hull’s Principles of Behavior (1943) was one of the most widely cited books in psychology (Hovland, 1952). In an old Handbook of Experimental Psychology, his work was mentioned on over eighty pages, which was more than all other scientists at the time (Hovland, 1952). In previous issues of the Journal of Experimental Psychology and the Psychological Review over forty percent of the bibliographies included one or more of his writings (Hovland, 1952).

Important People Influenced by Hull
Hull advised and inspired a number of graduate students and psychologists that went on to revise his theories and make contributions to the field of psychology. Some of these important people influenced by Hull were Neal Miller, John Dollard, Kenneth Spence, and Janet Taylor Spence.

Neal Miller and John Dollard
Dollard taught anthropology, psychology and sociology at Yale and was interested in studying social class and specific learning experiences. Miller studied under Hull at Yale, which is where he earned his Ph.D. Miller also founded the Laboratory of Physiological Psychology at Rockefeller University in New York, which is where he conducted research on animal training and this work helped to develop biofeedback (Coons, 2002). Miller and Dollard collaborated and developed a social learning theory that was successfully applied to psychotherapy and understanding. Their book, Social Learning and Imitation, listed the four fundamentals necessary for instrumental learning. These were drive, cue, response and reward and were based off of Hull’s drive reduction theory of learning (Sahakian, 1976) . They used a similar construct to Hull’s theory, however, they proposed that any strong stimulus could have motivating or drive properties without essentially being tied to the need of that particular organism (Sonoma.edu).

Kenneth Spence
Kenneth Spence was one of the most well-known of Hull’s graduate students. He developed and extended Hull's neo-behaviorist theory into what came to be called the Hull-Spence theory of conditioning, learning, and motivation. This theory states that people learn stimulus-response associations when a stimulus and response occur together, and reinforcement motivates the person to engage in the behavior and increases the occurrence of the learned behavior (Bali, 2008). Spence contributed to the study of incentive motivation and developing mathematical formulation and equations to describe learning acquisition (Bali, 2008). Spence attributed improvement in performance to motivational factors rather than the habit factors of Hull’s theory. He believed that reinforcement was not always necessary for learning to occur and that people can learn through latent learning (Bali, 2008). He also developed a discrimination learning theory (Complete Dictionary of Scientific Biography, 2008). His discrimination theory suggests that there are gradients of excitatory and inhibitory potential that are generated around the values of the stimulus that are either reinforced or not (Bali, 2008).

Janet Taylor Spence
Janet Taylor Spence began her research while working as a graduate student with Kenneth Spence at the University of Iowa. Kenneth became her husband in 1960. Her research was on anxiety and was an extension of the Hull-Spence hypothesis. She studied anxiety as a dispositional trait, or “drive”, which is the component of Hull’s motivational theory (American Psychology, 2004). She predicted that people with higher anxiety levels would show higher levels of eyelid conditioning than those with lower levels of anxiety (American Psychology, 2004). Spence then developed her own instrument to measure her hypothesis, the Taylor Manifest Anxiety Scale (American Psychology, 2004). Her later research focused primarily on elaborating Hull’s drive theory (American Psychology, 2004).