In summary, we found bilateral reductions of N2 sink and P3 source amplitudes during tonal and phonetic oddball tasks in schizophrenic patients. The present study also found evidence that silently counting targets during these oddball tasks imposes a response requirement that differs substantially from a button press condition and is associated with a late, relative positivity over left temporal sites, which is reduced in patients. This positivity may influence the laterality of overlapping ERP components (e.g., P3) observed for different tasks (e.g., tonal vs. phonetic) or study groups (i.e., heathy controls vs. schizophrenic patients), particularly with conventional ERP measures that are influenced by the EEG recording reference. The employed CSD-PCA approach clearly separated this superimposed silent-counting effect from N2 sink and P3 source activity, that is, neuronal current generator patterns underlying these two prototypical ERP components. However, it is not likely that this methodological insight can easily account for reports of asymmetric P3 reductions in schizophrenia during typical oddball tasks. Rather, it seems more parsimonious to hypothesize that differences in neuroanatomy between patient samples involving asymmetric impairments of temporal lobe
