Does the Complexity of S2 Have Any Effect Upon RT1? A Controversy in the PRP Literature

Abstract

The purpose of this experiment was to test several explanations that have been given to account for what has been termed the Psychological Refractory Period effect. Specifically the question addressed was what effect does varying the complexity and uncertainty of stimulus-response pairs have upon the subsequent reaction time. The experiment employed a within-subject Latin square design in which 12 undergraduates completed four test conditions on separate days. The task was to respond to a visual stimulus (maximum of 4 possible lights) by depressing a telegraph key with the index or middle fingers of either the right or left hands (maximum of 4 possible responses). It was possible to produce four conditions. Condition 1-1 (usual PRP paradigm), 1-2 (simple reaction time followed by a choice reaction time), 2-1 (choice RT followed by simple RT), and 2-2 (choice RT followed by choice RT). In addition, 36% of all trials were uninformed catch trials, i.e., either S1 and/or S2 did not occur when the subject was expecting it to occur. The subjects completed 50 single-choice control reaction-time trials before each condition. The interstimulus interval in all conditions for both experiments varied randomly among 100, 200, 300, and 400 msec. There was no statistical support for the claim that increasing the number of choices in S2-R2 will lengthen RT1. These results are discussed in terms of McLeod's (1977) parallel-processing model.