JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOUR 7, 864868 (1968) The Effects of Stimulus Uncertainty and S-R Transitional Probability on Paired-Associate Learning1

The Associative Probability Theory asserts that the greater the number of associates elicited by a stimulus, the greater the probability that one of these will be an appropriate mediator for new learning. The present study tested the adequacy of this theory in describing the effect of natural-language-sequential habits on PA learning. The transitional probability between pairs of words and the uncertainty of the probability distribution of words following a given word were computed from 985 student essays. On the basis of these norms, 3 PA lists were constructed with the stimulus terms either high or low in uncertainty and with either high or low transitional probabilities between stimulus and response terms. In all three lists fewer errors were made in learning pairs of high transitional probability but, contrary to expectations from the extension of Associative Probability Theory, stimuli of high uncertainty resulted in more errors. It is widely accepted that associations to a presented stimulus can serve to mediate and thus facilitate S-R learning. Underwood and Schulz (1960) describe an “Associative Prob-ability Theory ” (APT) to explain how such learning varies as a function of the number of associations. The idea of associative probability is simple: the greater the number of associates elicited by a stimulus, the greater is the probability that one of these will link up with another item. Thus an already established association, albeit weak, perhaps, can be used as the basic association for new learnin