Chapter 6 Clark Leonard Hull

Modified: 2025-01-23 8:17 PM CST

Clark Hull set out to construct a solid, scientific theory that would explain all of the features of learning. He was inspired by Newton and Euclid and created a complex mathematically based theory. Using the hypothetico-Deductive system, he tested his ideas, retaining those that passed experimental muster and discarding those that did not. As others found fault in his ideas, he attempted to correct his theory. He first proposed the theory in his 1943 book, revised it in this 1952 book, but passed away before writing the third book he had planned. At one point, his theory was nearly omnipresent in the psychology of learning. Today, however, it is mostly and example of a grand failure.

• Clark Hull
  • Sickly child (polio, typhoid fever) but gifted with mechanical ability
  • Early on studied aptitude testing, hypnosis, suggestibility, and verbal learning
  • Later, at Yale he was inspired by Newton and Euclid to create hypothetico-deductive theory for psychology

Hypothetico-Deductive system: a system using logic derived from a small set of given truths used to deduce new, derived, and logically consistent statements. After, those deductions are tested experimentally. Statements experimentally confirmed are kept and the others are discarded.

Operationism: The idea that science is best understood as a public, operationally defined enterprise in which phenomena may only be analyzed by methods that yield concrete results.

Hull was inspired by the success of modern physics:

• The many discoveries in modern physics leading up to the development of the atomic bomb also required the use of operationism.
• For instance, the many subatomic particles created by bombarding the nuclei of atoms were first described as intervening variables.
• Many experiments were run to determine if those unseen particles actually existed.
• Those particles that followed the paths predicted by atomic theory were deemed to exist despite never actually being observed themselves.
• The rise of modern physics occurred at around the same time as the emergence of Neobehaviorism and influenced it markedly.
• In psychology, the intervening variables that predicted particular behaviors were also viewed as real despite being unobservable.
• Percy Bridgman, a physicist and the author of an influential book, The Logic of Modern Physics (1928), was partly responsible for leading psychologists to imitate physicists.
• During the 20th century, physics was the quintessential model for how any science should operate and most psychologists aspired to make their science resemble it.
• Hull (1943) and Hull (1952) were his two main versions of his theory
• Hull's System
  • Stimulus variables
    • N = number of reinforced trials-->_SH_R
    • C_D = deprivation level-->D
    • S = stimulus intensity-->V
    • W = size of the reinforcer-->K
  • Intervening variables
    • 1. _SH_R--Habit strength (explains effects of practice)
      
    • 2. D--Drive (provides mechanism for reinforcement)
      
    • 3. V--Stimulus Intensity Dynamism (explains differences in environment)
      
    • 4. K--Incentive (added in 1952, explains differences due to size of reinforcement)
      
    • 5. _SE_R --Reaction Potential (the left hand side of equation = behavior)
      
    • 6. I_R<--Reactive Inhibition (explains extinction)
    • 7. _SI_R--Conditioned Inhibition (explains spontaneous recovery)
      
    • 7. _SL_R--Threshold (provides definition of acquisition)
      
    • 8. _SO_R--Oscillation (explains individual differences)
  • He wanted to make psychology as "scientific" as physics
    • He wrote (1935):

    "Scientific theory in its best sense consists of the strict logical deduction from definite postulates of what should be observed under specified conditions. If the deductions are lacking or are logically invalid, there is no theory; if the deductions involve conditions of observation which are impossible of attainment, the theory is metaphysical rather than scientific; and if the deduced phenomenon is not observed when the conditions are fulfilled, the theory is false."
    
    

  • His system was complex
    • Three types of variables: stimulus; organismic or intervening; and response
      • The four stimulus variables: number of reinforced trials, stimulus deprivation level, stimulus intensity, and size of the reinforcement (that last one added in the 1952 version) were measurable
      • The stimulus variables were linked respectively to: habit strength (H), drive (D), stimulus intensity dynamism (V), and incentive (K)
      • The response variables, the ones actually measured were: response latency (t). amplitude (A), number of responses until extinction (n), and response probability (p)
      • Hull's System (graphic)



The graphic above shows the relationships between Stimulus Variables, Intervening Variables, and Response Variables (from Marx & Hillix, 1963)

 

• Why did his system change?
• Crespi (1942) discovered that rats would run a maze faster after the experimenter made the food reward larger and they would run slower after the food reinforcer was made smaller
• Hull's (1943) version could not explain these data, so he added K, incentive to make his system work again
• Graphic Summary of Hull's System
  • 1943 Version (simplified)
    • _SE_R = _SH_R x D x V
      
  • 1952 Version (simplified)
  • _SE_R = _SH_R x D x V x K
• What about extinction and spontaneous recovery?
  • _SE_R = _SH_R x D x V x K - I_R - _SI_R - _SL_R
  • Reactive inhibition, I_R, builds up quickly, but goes away quickly (spontaneous recovery)
  • Conditioned inhibition, _SI_R, builds up slowly, but is permanent ( leads to extinction)
  • Threshold, _SL_R, accounted for the variability of learning acquisition

Learning Objective: Demonstrate what happens in Hull’s equation when H, D, V, or K have a zero value.

• Hull was an S-R theorist and used drive reduction as explanation for reinforcement
• His system largely abandoned following his death
• Kenneth Spence (Yale - Iowa Axis) was his most famous student
  • The "Yale (Hull) --Iowa (Spence) Axis was the imaginary line between those two universities
    • For a period, many psychologists waggishly proclaimed that the discipline revolved around that axis.
    • After Hull's death psychology moved on and Hullian psychology became passé

Kardas on Hull (full text)

Back to Learning Theory Main Page