Prior bisensory studies in reaction time (RT) have not obtained a pure speed measure of response latency. Errors in tracking tasks and differential latencies to bisensory stimuli are confounded with pure response latency; such results cannot adequately explain the psychological refractory period (PRP). Using pairs of visual stimuli, event uncertainty was held at 0 while temporal uncertainty was manipulated. Results show: (1) a general rise in mean 1st RT as a function of ISI length, (2) the PRP seems inversely related to "practice" of Ss, (3) some evidence for extinction of competing responses accounting for the shapes of the RT curves. A competing response theory was offered to explain PRP, thought a special case of the "Temporary Inhibition of Response" phenomenon. (18 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)