There was variability across subjects in the location of the maximum of the spatial distribution of the P3a and P3b components across midline electrode sites. Table 3 shows a breakdown by midline electrode site of the location of the P3a and P3b maximal amplitude across subjects. As expected from the spatial distributions of the grand average topographical maps in Figure 1, most subjects had a spatial maximum of the P3b at the parietal electrode site (Pz), while for the P3a there was a more even distribution of subjects across Cz, CPz, Pz, and POz.
