For H2S stimuli, this CSD-PCA strategy has supported the importance of N1 and P2 as two distinct ERP components reflecting distinct, sequential stages of odor processing (Lorig, 2000). Our previous study (Kayser et al., 2010) revealed prominent bilateral N1 sinks over lateral frontotemporal sites, along with a corresponding mid-frontopolar source, presumably reflecting an early (about 300 ms), modality-specific processing stage during odor perception, with putative generators within the medial temporal lobe and/or basal cortical regions (i.e., piriform cortex and orbital frontal cortex; cf. Martzke et al., 1997; Seubert et al., 2013). Importantly, this prominent negative deflection is substantially attenuated at lateral temporal recording sites in surface potentials when a linked-mastoid, linked-ears or nose reference is used because the generator underlying an olfactory N1 evidently creates an isopotential line involving these common reference locations and lateral-inferior sites (i.e., T7/8, FT9/10, P9/10). These common reference schemes yield a smaller, volume-conducted N1 at midline sites, which is nevertheless considered an integral part of the basic olfactory ERP morphology (e.g., Turetsky et al., 2003a). In contrast, the ensuing olfactory P2 is not compromised by
