Psychology ETDs

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Many reaction time investigators have shown that as stimulus intensities increase response latencies decrease. In addition, Spiess (1971) demonstrated that the presentation of knowledge concerning the nature of the upcoming stimulus prior to its onset (preknowledge) could result in decreased reaction times. Spiess concluded that this preknowledge effect was interpretable within the framework of Grice's variable criterion model. Grice's model assumes that a response would occur when information concerning the onset of a stimulus reached a required level or criterion. The rate at which this information accumulates is determined by the intensity of the stimulus with stronger stimuli resulting in faster accumulation. According to Spiess, preknowledge resulted in a lower criterion, which was reflected by faster responses. The present experiment was designed to further investigate the feasibility of using the criterion model to explain the preknowledge effect. In the present study an attempt was made to manipulate stimulus expectancy by varying the probability that the stimulus would remain unchanged from one trial to the next. When the probability of change was low, the same stimulus that was presented on the previous trial should be expected on the subsequent trial, and when the probability of stimulus change was high, presentation of the same stimulus on the following trial would presumably be unexpected. Each subject received a series of stimuli with the probability of change being equal to .00, .10, .25, .50, .75, .90, or 1.00, resulting in seven groups of subjects, with each group receiving a sequence with one of these probabilities of stimulus change. The findings showed that stimuli following the predominant pattern (either having changed from the intensity presented on the previous trial or not depending on which sequence was being presented), were responded to more quickly than were stimuli that deviated from the overall pattern. These results were not easily interpretable using Grice's variable criterion model. The model could explain these findings, however, if two criteria were assumed to exist rather than the single criterion presently employed by the model, or if the rate of information accumulation was made to depend not only on stimulus intensity but also upon stimulus expectancy.

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First Committee Member (Chair)

G. Robert Grice

Second Committee Member

Carol Elizabeth Conrad

Third Committee Member

Henry Carleton Ellis

Fourth Committee Member

Thomas Patrick Friden



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Psychology Commons