In a visual RT experiment, 5 male Ss were each confronted with 2 lights and instructed to respond to 1 light but not respond when both lights occurred. The onset of the 2 lights was made asynchronous by 0, 12, 33, or 63 msec. Probability of inhibiting the response declined markedly for each delay and increased with RT. It was concluded that choice RT is correlated with the extent of the stimulus information processing and the duration of effective stimulation which has preceded initiation of the motor event. (PsycINFO Database Record (c) 2006 APA, all rights reserved)