Hull used the word drive to describe the state of behavioral arousal resulting from a biological need. In Hull's system, drive was the energy that powered behavior. But drive was not pleasant. Drive was an uncomfortable state resulting from a biological need, so drive was something the animal tried to eliminate. The animal searched for food in order to reduce the hunger drive. Hull believed the animal would repeat any behavior that reduced a drive, if the same need occurred again. Therefore Hull's theory was called a drive-reduction theory of motivation.
Hull's theory inspired an enormous amount of research. No other psychological theory was so daringly precise. Hull used specific formulas to predict the likelihood of specific behaviors. He specified that the probability that a particular stimulus would lead to a particular response (the "excitation potential") using a formula. You do not have to memorize this; it is offered as an example of the precision to which Hull aspired:
Excitation potential = S H R [D x K x J x V]...where....
S H R was the number of reinforced training trials
D was the amount of biological deprivation or drive
K was the size or magnitude of the goal
J was the delay before the animal was allowed to pursue the goal
V was the intensity of the stimulus that set off the behavior
What happened to Hull's theory?
Each variable was given a precise operational definition, to aid research and replication. Hull hoped to make psychology as scientific and precise in its predictions as physics or chemistry. However, things did not work out that way. Many predictions based on Hull's equations did not come true. Researchers responded by altering the system, adding variables or subtracting others, adjusting parameters, trying to make it all work. Finally researchers began to realize it was never going to work. There could not be such a simple system for predicting animal behavior.
What happened to the study of learning, after Hull?
The abandonment of Hull's theory occurred about 30 years after he proposed it. An entire generation of researchers had followed a false lead! By the early 1970s journal articles contained bitter references to "30 years of fruitless Hullian research." The study of learning veered off into different directions. Bolles (1990) commented, "Hull would have been unable to read a present-day research paper; none of it would have made any sense!"
Hull's theory may have disappeared from present day motivational research, but not before it had a big impact on the field. Many motivational theories of the 1950s and 1960s were reactions to then-dominant Hullian theories. These included the proposals for cognitive motives as well as Maslow's motivational psychology, both discussed later in this chapter. All were conceived as alternatives to Hull's drive-reduction approach.