Using a continuous recognition memory paradigm with unfamiliar faces, Guillem et al. (2001) recorded 13-channel ERPs referenced to the right ear lobe from 15 schizophrenia patients and 15 healthy controls. During implicit task instructions (indicate the gender), patients showed reduced early old/new effects at medial parietal sites overlapping a relative negative ERP deflection (N300), but no group differences of the old/new effect were observed during a late positive complex (P500). In contrast, during explicit task instructions (indicate item previously presented), patients showed reduced old/new effects over posterior sites during an extended late positive complex at about 500 ms, but an enhanced old/new effect over frontal sites at 700 ms. This complex and unexpected pattern of old/new effects is rather difficult to interpret, despite the excellent task manipulation.
