Both early and late old/new effects were accompanied by inverted old/new effects over lateral anterior-frontal and/or lateral inferior occipitoparietal or temporoparietal sites. While we reported similar inverted old/new effects occurring at various information processing stages in our prior studies using this advanced CSD-PCA approach (Kayser et al., 2007, 2009), these observations are genuinely new to the literature. The inverted old/new effects consisted of reasonable local topographies and were clearly not a by-product of computational indeterminacies along the edge of the EEG montage when using a spherical spline CSD algorithm. While there were no group differences in the early inverted old/new effects, the late inverted old/new effects at lateral inferior temporoparietal sites were greater in patients than controls. The meaning of this finding is not immediately clear, but it seems to supplement the observation that the patients’ late old/new source effects (i.e., old-greater-than-new) were restricted to the medial parietal region. It also adds further evidence to the notion that the neuronal generator patterns underlying the late left parietal old/new effects are different between schizophrenic patients and healthy adults, a difference that will crucially affect ERP measures based on reference-dependent surface potentials.
