N1 amplitude effects are illustrated in F1. A four-way analysis of variance (ANOVA) of N1 amplitude assessed effects of group, condition, stimulus (/ba/, noise), and scalp site (Fz, Cza, Cz). N1 amplitudes in response to /ba/ were larger than those in response to noise (F=8.46, df=1, 28, p=0.007). The condition-by-group interaction indicated that the magnitude of the condition effect differed across groups (F=4.07, df=2, 56, p<0.03, with Greenhouse-Geisser correction), with condition being significant for both comparison subjects (F=33.44, df=2, 28, p<0.0001, with Greenhouse-Geisser correction) and patients (F=7.35, df=2, 28, p=0.004, with Greenhouse-Geisser correction). For comparison subjects, the N1 amplitude during the silent baseline condition was larger than during directed inner speech, which was larger than the amplitude during listening (F1). In patients, the baseline N1 amplitude was not significantly larger than the amplitude during directed inner speech but was larger than the amplitude during listening (F1). In addition, the baseline N1 amplitude was somewhat smaller in the patients than in the comparison subjects (F=3.62, df=1, 28, p=0.07), but the N1 amplitude for directed inner speech was equivalent in the two groups (F=0.10, df=1, 28, p=0.76), consistent with our hypothesis.
An ANOVA for N1 amplitude in response to the checkerboard did not approach significance for group, condition, or the interaction of group and condition.
None of the Spearman correlations between the N1 effect (i.e., N1 amplitude during the silent baseline condition minus the N1 amplitude during directed inner speech) and SAPS summary scores for hallucinations and delusions and BPRS scores for hallucinatory behavior and unusual thought content was significant.