Abstract On the grounds that extraverts have a strong tendency to organize responses rather than analyze stimulus information (Brebner and Cooper, 1978) it was predicted that extraverts would respond more rapidly to the first of two rapidly successive stimuli than introverts. It was also hypothesized that the delay in responding to the second stimulus, which is termed the ‘psychological refractory period’, would be shorter for extraverts, and that using longer stimulus durations would lengthen reaction times but that extraverts would again be less affected than introverts. The results support the predictions and point to the importance of including individual differences in studies of the speed of performance.