Stimulus complexities and response alternatives in the psychological refractory paradigm: Their effects on premotor and motor time

The problem. Stimulus complexity and response alternatives have been shown to independently affect the time required to react to paired stimuli. Few have used fractionation procedures to divide the reaction times (RTs) into central (PMT) and peripheral (MT) components. Therefore, it was the purpose of this study to determine these effects on the fractionated RT components.;Methods. Twenty-four subjects each responded to 48 dual and 24 single stimulus RT trials for four testing days. The task involved turning a handle with each hand in response to light stimuli. Group A involved a one-choice decision for each stimulus (S1 and S2). Groups B and C involved a two-choice S1 and a one-choice S2. Group B responded with supination or pronation whereas Group C responded or did not respond to S1. Group D involved a two-choice S1 and S2. Electromyography was used to fractionate the RTs. A 4 (GROUP) ;Findings. Increasing the complexity of the stimuli significantly increased the PMT component of the affected response, but did not effect the IRI of PMT or S1 errors. There were no response-alternative or task effects. Responding to S1 resulted in faster central processing of the second response with 50 ms between stimuli. The IRI of PMT increased with ISI (for ISIs greater than 100 ms). The supination-pronation S1 choice resulted in more S1 errors than the response-no response choice.;Conclusions. A parallel processing model with some response delay in the stimulus identification stage and in the response selection or response initiation stage was supported. Responding to the first stimulus does not have any neuromuscular effect on the second response. Fractionation of reaction times allows for a better understanding of the PRP phenomenon.