Figure 3 shows the grand mean ERP waveforms (referenced to linked mastoids) for patients and controls for H2S stimuli (pooled across intensity) and blank air at all 49 recording sites. As in previous OERP studies using H2S stimuli (e.g., Kayser et al., 2010; Turetsky et al., 2003b, 2008), a prominent P2 at about 600 ms, which was broadly distributed over centroparietal sites, and an earlier N1, peaking at 350 ms at lateral-temporal sites, were present in both groups. In contrast, ERPs to blank air were virtually flat at all recording sites, indicating that any procedural requirements specific to H2S detection (e.g., those related to stimulus delivery, visual cuing, odor expectation, or foot pedal response) were not causing these OERP components. Similarly, although considerable eye movements, particularly blinks, were associated with H2S stimuli, eye artifacts, which occurred mostly beyond 600 ms, were effectively eliminated from the EEG traces.
