. Hull perhaps added somewhat more to our knowledge of the behavior of the rat than Titchener did to our understanding Clark Hull 7 of human consciousness, but not much. His basic approach turned out to be, to use a precisely appropriate metaphor in his world of rats and mazes, a blind alley.

One of Hull's starting points was in noting that conditioning theory failed to deal convincingly with motivation. He was astute enough to recognize that motivation may be viewed as either a learned aspect of behavior (as Guthrie viewed it) or as a behavioral determinant independent of learning (as Tolman viewed it). Either way, it needed to be given greater importance. Hull drew on Freud's "instincts" as motivating forces, but changed the word to "drives" in his own formulations.

Late in his life and work, in 1952, even before the futility of his modeling endeavors became evident, Hull finally admitted that his system probably applied only to hungry rats.

INVESTIGATIVE STRATEGY

Clark Hull concluded that:

1. We should begin with specific testable postulates, even if based on minimal evidence. Then we derive concrete, empirically verifiable deductions from these and test them.

2. The task of a theorist is to formulate postulates so they will lead to unequivocal deductions.

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3. The worth of a theory resides in how much research it generates and how consistent with its thoretical deductions the findings are.

4. He was willing to put himself on the line with his predictions. His willingness to be wrong was a remarkable virtue. He was constantly revising his theories in light of empirical results.

These first four points represent Hull's most lasting contribution to experimental psychology. No one before Tolman and Hull was as careful, as sophisticated, or as precise in experimental design. Their research models of compared groups were later supplanted by other models, like Skinner's single-subject designs, but the sophistication in experimental design that grew out of their work outlived their research programs and is still a characteristic feature of American academic psychology.

Also part of Clark Hull's approach was:

5. In theorizing, a very heavy emphasis on intervening variables, cast in mathematical form.

6. Kenneth Spence was intimately associated with Hull throughout most of Hull's career. It was Spence who finally urged Hull to adopt Tolman's "intervening variable" concept and approach.

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DRIVE AND REINFORCEMENT

1. Drive is based on animal's need-state -- hunger, thirst, sexual arousal, pain, or whatever. Drive activates behavior -- any behavior.

2. Reinforcement occurs whenever the drive is reduced; leading to learning of whatever response solves the animal's problem. Thus the reduction in need serves as reinforcement and produces reinforcement of the response that leads to it.

3. Basic approach: need-related motivation, drive, and S-R learning are produced by (and only by) reinforcement. The S-R connection is called "Habit.":

4. Hull held that drives are substitutable in motivating behavior. If a hungry animal has learned a given response to get food, it should be easy to transfer the same response to get water. Early studies tended to confirm this motivation transfer, but more recent experiments have failed to find such motivation transfer when proper care is taken to use sources of drive that can be independently manipulated. It now appears that what happens with difference sources of drive is very unpredictable.

An alternative formulation was proposed by Miller & Dollard. Using a similar habit construct, they proposed that any strong stimulus can have motivating or drive properties without being tied to the needs of the organism.

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HABIT AND BEHAVIOR

1. Drive and habit act together to determine the strength of behavior. Thus the strength of behavior depends on both:

a. animal's motivation at time of testing b. amount of prior learning

Neither motivation nor prior learning alone will tell us what animal do.

2. Habit is built up as result of drive reduction

3. Habit strength depends on four different classes of independent variables:

a. Number of reinforced trials b. Magnitude of reward c. Immediacy or delay of reinforcement d. interval between CS onset and U.S..

4. Behavior can be characterized by both frequency and magnitude, and the two measures need not be correlated. There might be a very frequent response of low amplitude or a rare response of high amplitude.

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EVIDENCE REGARDING DRIVE...

Habit is indeed built up as result of drive reduction.
2. Experimental work has shown that there are other variables. For example, Neal Miller carried out a series of studies showing that placing food directly in the stomach is reinforcing but food in the mouth is much more reinforcing. 3. Sheffield proposed that it is not drive or need reduction that constitutes reinforcement; but simply the occurrence of a consumatory response. A rat learns a response when this response lets it eat, mate, explore, etc.

4. Ultimately, the pure drive-reduction view of reinforcement was abandoned.

PURPOSE AND INCENTIVE

1. Hull's first papers on learning theory in 1929 and 1930 were attempts to show that the purposiveness in behavior which Tolman had demonstrated could be explained with Pavlovian S-R associations. Hull sought to extend the S-R framework from Pavlov's original conditioning situation to the kind of situation in which behavior appears highly flexible, adaptive, and intelligent (like rats in T-mazes, we might say with tongue in cheek).

2. "Fractional anticipatory goal responses."

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This is the idea that we anticipate the reinforcing event at the end of the chain and it motivates the rat back at the beginning of the chain. We make fractional anticipatory goal responses" (rG --r for the anticipatory response and G. For the goal) that are themselves somewhat rewarding to us. For instance, someone's fantasies of sexual intercourse yet to come, and the movements and secretions associated with those fantasies, are themselves somewhat rewarding. This led to the very productive insight that it works best to work backward in teaching chains of behavior.

3. Hull recognized that variables can affect performance without materially affecting learning. Crespi (1942) ran a study in which different amounts of food did not affect learning but did affect performance. Hull concluded that a fractional anticipatory goal reaction becomes a conditioned reinforcing stimulus, with reinforcing consequences. His final explanation of Crespi's results was that animals getting more food have a more vigorous rG conditioned to the goal box.

4. Hull's explanation for the latent learning demonstrated by Tolman was that "habit strength" had built up on early trials but performance was poor because incentive motivation was low. When the rat found food, considerable incentive motivation was suddenly present.

HABIT FAMILY HIERARCHIES

1. This somewhat intimidating phrase refers to alternative behavior sequences that lead to the same goal. Component acts of these sequences become conditioned to the same fractional anticipatory goal reactions and in this sense constitute a "family."

2. The weaker responses in this hierarchy -- farther to reinforcement, or more difficult to make, etc., are less likely behavior sequences (the law of less work), and thus lower in the Clark Hull 13 habit-family hierarchy. That is, they are less likely to occur, even though they're there and available.

3. It appears to me (Victor) that this concept might be applied to complexes, with a variety of different defense mechanisms serving the repressive, discomfort-reducing function.

OSCILLATION AND THRESHOLDS

1. Following Guthrie's lead, Hull was one of the earlier psychologists to recognize that behavior is essentially probabilistic. There is considerable variability in what a rat or person does.

2. He proposed that in order for behavior to occur, the factors that produce it must create a tendency to respond that is greater than a given threshold. He also assumed that the threshold varies randomly in time according to an oscillating

Clark Hull 14 function. This is surely wrong; it is not too difficult to identify factors inside the person or environment that could affect this threshold. But with his rats, Hull was essentially saying that behavior can be predicted only on the average, over a period of time, or over a group of animals.

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Bibliography

Hull, C.L.. (1933) Hypnosis and Suggestibility: An Experimental Approach. Whales: Crown House Publishing.

Hull, C.L. (1943) Principals of Behavior: An Introduction to Behavior Theory. Appleton.

Schultz, D.P. & Schultz, S.E. (1987). A History of Modern Psychology. Harcourt Brace Jovanovich Publications.

Hothersall, D. 1995. History of Psychology, 3rd ed., Mcgraw-Hill:NY

Thomson, R. (1968). A Pelican History of Psychology. Penguin Books Publications. (pp 237-242)

Bruner, J.S. (2004) A Short History of Psychological Theories of Learning. Daedalus. Retrieved July 14, 2006 from www.questia.com.