As seen in F1, schizophrenia patients and healthy comparison subjects clearly showed the N170 component over temporoparietal positions (electrodes P7 and P8). The statistical analysis for the N170 amplitudes revealed significant main effects for condition (F=127.7, df=1, 50, p<0.0001) and group (F=7.7, df=1, 50, p<0.01). Furthermore, significant condition-by-group (F=4.4, df=1, 50, p<0.05) and condition-by-side (F=4.1, df=1, 50, p<0.05) interaction effects occurred. To analyze these interactions in more detail, differences in amplitudes of the N170 to faces and buildings were calculated and further analyzed with a post hoc ANOVA with side (P7, P8) and group (comparison subjects, schizophrenia patients) as factors. The significant main effect of group (F=4.4, df=1, 50, p<0.05) indicated that schizophrenia patients had lower differences in event-related potential amplitudes for faces versus buildings than did the comparison subjects. The significant main effect of side (F=4.1, df=1, 50, p<0.05) indicated higher differences over the right compared with the left side. To analyze whether face processing was selectively impaired, we compared the N170 amplitudes between comparison subjects and patients separately for both conditions. Patients had significantly reduced N170 amplitudes for faces (P7: t=–2.8, df=50, p<0.01; P8: t=–2.7, df=50, p<0.01) but not, or only as a tendency, for buildings (P7: t=–1.6, df=50, n.s.; P8: t=–1.8, df=50, p<0.10).
For the healthy group, no sex differences occurred for the N170 amplitudes (condition by sex: F=0.22, df=1, 26, n.s.).
For the P1 amplitude, a significant main effect of condition occurred (F=24.3, df=1, 50, p<0.001), indicating higher amplitudes for faces (mean=5.9, SD=0.4) than for buildings (mean=5.2, SD=0.4). P2 amplitudes differed significantly between groups (main effect of group: F=4.7, df=1, 50, p<0.05), with higher amplitudes for patients (mean=6.8, SD=0.5) relative to comparison subjects (mean=5.3, SD=0.5). No significant condition-by-group interactions were found (P1: F=0.6, df=1, 50, n.s.; P2: F=0.5, df=1, 50, n.s.).
Neither N170 amplitudes nor the differences between faces and buildings correlated with medication in chlorpromazine equivalents or with Positive and Negative Syndrome Scale scores.