ERP waveforms were extracted by averaging all trials for each condition. Grand average ERP waveforms were produced by averaging the ERPs within a group by condition factor. Grand average topographical maps were also computed at each time point to display the ongoing spatial distribution of ERP amplitudes. Based on the grand average topographic maps, amplitudes and latencies of the ERP components at electrode Pz (P3b), Cz (P3a) and FCz (N2a and N2b) were extracted for each subject using a semi-automated peak detection algorithm. P3a and N2a were measured on each subject’s rare non-target grand average while P3b and N2b were measured on each subject’s target condition average. Peak locations were checked and adjusted manually where necessary and, if no discernable peak was present or the locations were ambiguous, that particular ERP component for that subject was coded as missing. Statistical analysis was then applied to the N2 and P3 amplitudes and latencies.
