3–1.5). Fig. 2A shows RT-sorted violation minus control difference ERPimages of all participants’ single trial EEG at PZ, aligned both to the onset of words inducing a morphosyntactic violation, and to RT, and the corresponding ERP. Onset-aligned ERPimages (150-epoch Gaussian smoothing) revealed an onset-aligned P600 with a broad, flat morphology, whereas in RT-aligned ERPs, the component peaked sharply, corresponding to a focused positive component in the RT-locked ERPimage. Semantic violation difference ERPimages (see Fig. 2B) reveal a similar RT-aligned
late positivity and a stimulus-aligned N400. To quantify onset and reaction time locking, we employed three measures: RT bin peak latencies, Woody filter estimates of component latency, and response- versus phase-locked ITC. For the syntactic violation condition, bin latency strictly increased with bin RT and RT bins were unlikely
RG7204 mw to reflect activity with identical latency (corrected F(3, 76) = 28; p < 0.0001). Bin latency monotonically rose with bin RT (mean 33% fractional area latency and mean bin RT for fastest to slowest bin: 770/606, 854/760, 926/920 and 1037/1190 ms; Spearman’s rho = 1). RT quartile-binned ERP latencies also correlated with mean bin RT for semantic violation trials (rho = 1). Woody filter-estimated single-trial latencies of the late positivity following syntactic violations correlated strongly with single-trial RT (95% CI: .5, .73), but the N400 following semantic violations did not (95% CI: −.1, .22). During the P600 peak window, phase locking of low-frequency activity (as measured by ITC) was greater for RT-aligned than for onset-aligned trials AZD1208 molecular weight (95%
CI: 5.4–11% greater ITC for RT-aligned trials). Parameter estimates for the Woody filter and ITC analyses are summarised in Table 1. Arachidonate 15-lipoxygenase The present study used single-trial EEG analyses to distinguish response – from stimulus-aligned effects in a linguistic deviancy detection task including button presses directly following critical parts of the sentence. The late positive EEG deflection following linguistically deviant material was strictly RT aligned, with no distinct, second positive peak aligned to stimulus onset. The N400 following semantic deviations behaved like an exogenous component in that it was stimulus – rather than response-aligned (compatible with Cummings et al., 2006). These results confirm an important prediction of the P600-as-LC/NE-P3 perspective. A dissociation between RT and P600 would have falsified this theory; the positive finding allows for a neurophysiological grounding of the P600 by association with the LC/NE system (Nieuwenhuis et al., 2005). It could be argued that the repetitive nature of our stimuli and our explicit task caused the sentences to be perceived in a more task-heavy processing mode, causing the appearance of a P3-like component instead of the components expected for more naturalistic stimuli.