Date of Award


Document Type


Degree Name

Master of Arts




Although Pavlov (1927) and Skinner (1938) had published articles dealing with the effects of less than 100% reinforcement upon acquisition and extinction, it was not until the Humphrey's investigation (1939) that partial reinforcement became an enigma for leaning theorists. Hull's theory came under the sharpest criticism because with a decrease in the number of reinforcement in acquisition there was not a corresponding decrease in habit strength as measured by resistance to extinction. Despite much criticism, Hull did not deet it necessary to consider the problem of partial reinforcement in his Principles of Behavior (1943). Humphreys, on the other hand, proposed an expectancy principle as an alternative theory, In his theory, conditioned responses are the consequences of the Ss expectation that reinforcement will appear. After reinforcement on every trail during acquisition, the extinction responses dissipate because the sudden shift from uniform reinforcement to uniform nonreinforcement makes it easy to change an expectation of uniform nonreinforcement. In extinction after partial reinforcement, however, the S continues to expect that reinforcement will be periodic as it was during acquisition, thus extinction is prolonged by his expectation that reinforcement will be re-introduced.

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