ERP waveforms were extracted by synchronously averaging all trials having the correct behavioral responses for the target condition, producing one ERP waveform per electrode site per subject. For each subject, the peaks of the major ERP components, these being the N100, P200, N200, P300 (i.e. P3b) and N300, were extracted independently for each of the midline electrode sites of interest (MESOIs)6, these being Fz, FCz, Cz, CPz and Pz, using a semi-automated peak detection algorithm. Peak locations were adjusted manually where necessary, and if no discernable peak was present or the locations were ambiguous, the ERP component for that subject was omitted from further analysis. Grand average ERP waveforms and topographical maps for each of the ERP components were computed across groups.
