Figure 7 gives the reference-free CSD transformations of the response-locked auditory and visual ERP waveforms at a representative subset of recording sites for both groups and conditions. Across modality, a mid-frontal response-related negativity (FRN), peaking at approximately 50 ms after response onset, was prominent for controls (Figure 7AB) but markedly reduced in patients (Figure 7CD). The FRN was preceded in both groups by distinct old/new effects overlapping the P3 source at medial-parietal (auditory) and mid-parietal (visual) sites, which were larger over the left than right hemisphere, particularly for auditory stimuli (cf. sites P3 and P4 in Figure 7AC). The P3 source was evidently terminated by the response, giving rise to a late negativity (LN) sink over posterior sites, which appeared to be more robust for old than new words.
