Theories of the psychological refractory period

Influence of stimulus discriminability on psychological refractory period effect

10 undergraduate students were tested in a psychological refractory period paradigm. Stimulus 1 was a visual discrimination task (same-different) and S2 was a 1,000-Hz tone. Discriminability of S1 and ISI were varied. Ss always had to respond to S2, but to S1 only when it was “same.” Discriminability of S1 was found to affect R2, irrespective of whether or not S1 was followed by an overt response. Such a result poses difficulties to expectancy and response-conflict theory.

Response time to a first signal as a function of time relationship to a second signal and mode of presentation

Using a random presentation of inter-stimulus intervals between stimulus 1 and stimulus 2 in a psychological refractory period paradigm, this experiment permitted comparison of data obtained earlier using a block presentation. With 10 male Ss per study, response time to stimulus 1 increased at higher inter-stimulus intervals under block presentations but not under random presentations. The results are interpreted to support time-sharing between the processing mechanisms of the two stimuli rather than a single channel theory.

Refractoriness in information processing

Two experiments on refractoriness were carried out in which the warning, first and second signals, S0, S1 and S2 respectively, were all single-valued, and the distributions of random intervals between S0 and S1, and S1 and S 2 were the same. In the first experiment the intervals in a trial were statistically independent: the null hypothesis, that the latencies of the two responses would be similar, was rejected, but the results were also found to agree with no existing alternative hypothesis. In the second experiment the intervals in a trial were conditionally related and the second response was found to be faster than in the first experiment. This is discussed in the context of the issue of serial or parallel processing of information.

The psychological refractory period as a function of performance of a first response

Proponents of a “single channel” theory of the psychological refractory period have not specified whether the single channel occupies only the decision component of the response selection, only the motor or response component, or both. In this experiment, the delay in the RT to the second of two successively presented stimuli was examined as a function of whether or not an overt motor response was made to the first stimulus, keeping the decision component constant. It was found that in both conditions RT2 was delayed, suggesting that the decision component was a part of the single channel. However, RT2 was delayed by a significantly greater amount if a motor response was required, indicating that the motor component is part of the single channel as well. Implications of the results for an expectancy theory of the psychological refractory period are discussed.