Separate OERPs for strong, medium and weak odor intensity and blank air were averaged from artifact-free trials using the entire 2-s epoch. To obtain more stable waveforms, ERPs were pooled across nostrils because of their blocked presentation order (cf. Kayser et al., 2010) and because the side of odor stimulation is ranked as less important when measuring OERPs (e.g., Olofsson et al., 2006; Stuck et al., 2006). The means for the number of trials (±SD) used to compute these OERP averages were 27.8 ±5.0, 28.9 ±5.5, 30.1 ±4.1, and 32.8 ±5.5 (strong, medium, weak intensity and blank air, respectively) for CHR patients, and 31.0 ±4.2, 30.7 ±4.1, 32.1 ±5.8, and 33.5 ±4.5 for healthy controls (no fewer than 16 trials per OERP average), and there were no significant differences between patients and controls, F(1, 37) = 1.32, p = .26. ERP waveforms were screened for electrolyte bridges (Tenke & Kayser, 2001), low-pass filtered at 12.5 Hz (−12 dB/octave), and baseline-corrected using the 100 ms preceding stimulus onset.
