Clark Leonard Hull had a tough childhood. In his late teens, an outbreak of typhoid fever took the lives of several of his classmates. Then, at the age of 24, Hull contracted polio, which precipitated his change from mining engineer to psychologist.
Hull was skilled at inventing equipment his needed to perform an experiment. For a study on the effect of tobacco on performance, he designed a system for delivering heated air (tobacco and tobacco filled) to the subjects so they would not know which experimental treatment they were receiving. Similarly, Hull constructed a machine to calculate inter-item correlations for a series of studies he performed on aptitude testing.
Not surprisingly, Hull believed that people are basically machines. His complex theory of learning is a combination of Newton’s deductive method, Pavlov’s classical conditioning, and Euclidean geometry. For Hull, experimental observations were validity checks on the internal postulates he had previously deduced.
Hull’s Hypothetico-Deductive Theory includes habit strength (the tendency to respond), evenly spaced trials, and reinforcement. Using inferred state and intervening variables, Hull described learning as an interactive system of probabilities.
Too complex for many and too theoretical for others, Hull was a pioneer in using animal research to generalize to human behavior. Despite his poor eyesight and poor health, Hull set a standard of experimental excellent and theoretical integrity which still serves as a model today.