POSTPERCEPTUAL EFFECTS AND P300 LATENCY

P300 latency is commonly thought to provide a chronometric index of th e duration of perceptual processing. Because the evidence in favor of this assumption is controversial, we examined whether P300 latency is influenced by perceptual processes, response selection, and by motoric processes in two experiments using a two-choice spatial stimulus-resp onse compatibility (SRC) task. Both experiments revealed additive effe cts of perceptual difficulty with spatial SRC in reaction time and P30 0 latency. In addition, Experiment 2 showed that P300 latency measured in average waveforms is insensitive to motoric processes. The influen ce of spatial SRC on P300 latency disagrees with the view that P300 la tency is sensitive only to stimulus evaluation processes. However, P30 0 latency may be used to discriminate between influences on premotoric and motoric processing stages. A response conflict account for the SR C effect on P300 latency is suggested.