P3b amplitude for each subject for the target and P3a amplitude for the rare non-target conditions (maximum positive peak in a time window from 300–500 ms) were measured at the midline electrode (Fz, FCz, Cz, CPz, Pz, POz, or Oz) at which the spatial distribution peak was maximal for the ERP and ERP difference waveforms for that subject. The amplitude and latency of the P3b and P3a were then extracted at the selected electrode site. BVA’s semi-automated peak detection algorithm was used to extract the P3b and P3a peaks, with manual adjustment of the peak location as necessary, based on temporal and spatial distribution of the ERP component. Where the P300 was absent or ambiguous for a subject, the component was scored as missing. Five subjects did not show clear P3b peaks and 10 subjects did not show clear P3a peaks, and so these participants were omitted from the relevant statistical analysis. Behavioral data for target (reaction time and accuracy) and rare non-target (accuracy) conditions were extracted over a period of 750 ms following stimulus presentation.
