Welford (1952) initially proposed the single-channel theory to explain the Psychological Refractory Period (PRP) effect (Telford, 1931), that the reaction time (RT) to a second of two stimuli in close succession is lengthened and the delay increases as the time between the two stimuli (stimulus onset asynchrony, SOA) decreases. Recent literature (Pashler, 1994; Schubert, 1999) indicated that a bottleneck in information processing caused the PRP effect. However, different models were proposed and they disagree concerning the locus of the bottleneck and whether there exist multiple bottlenecks. PURPOSE: The purpose of this study was to identify possible neurological as well as the cognitive factors in a PRP model by using the reaction time fractionation technique with electromyography (EMG). This technique allows for the examination of both central and peripheral components in a PRP paradigm. METHODS: Twenty right-hand dominant college students (10 male, 26.0 ± 3.06 yrs; 10 female, 25.4 ± 2.27 yrs) were tested for their visual-manual reaction time for four consecutive days. A choice RT task followed by a simple RT task utilizing forearm pronation and supination movements as the PRP condition. Based on the EMG activity of the pronator teres and biceps brachii, RT and its fractionated components, premotor time and motor time, were measured for each movement. Participants were randomly assigned to two groups depends on their initial movement for the first response. A five-way ANOVA (Gender x Group x Movement x SOA x Response) was used for data analysis. RESULTS: Four-days of practice significantly reduced the PRP effect, and the practice reduced mainly PMT. Significant PRP effects were observed for RT, PMT as well as MT. The PRP effect was affected by the movement for the second response. Reaction Time for pronation was faster than supination in the second response and this difference was determined by MT but not PMT. Both PMT and MT contributed the PRP effect observed in RT. CONCLUSION: The significant PRP effect found for PMT and MT in the dual task situation support the conclusion that neurological as well as cognitive factors determine the extent of the delay of the second response in the PRP paradigm. The first motor response in a PRP paradigm inhibited the movement initiation for the second motor response.Keyword(s): assessment, measurement/evaluation, performance