Limitations in ERP methodology with regard to the study of olfactory function have been discussed previously (Kayser et al., 2010). Briefly, most olfactory ERP studies have used peak and latency measurements of “prominent” deflections in individual ERP waveforms at midline or central scalp locations (i.e., Cz, Pz, C3/4) referenced to linked ears (cf. recommendations by Evans et al., 1993). However, the choice of the EEG recording reference for surface potentials is arbitrary, with linked ears, linked mastoids, nose, or common average reference schemes likely rendering a different ERP morphology (i.e., sequence and location of “prominent” deflections), and thereby potentially masking effects of interest (e.g., Kayser & Tenke, 2010). A related problem is the operational definition of an ERP component by means of identifying the “obvious” ERP waveform peaks (or approximations thereof by determining appropriate time integrals), and the selection of scalp regions or sites for statistical analysis, all of which is affected by the reference choice. However, these problems can be efficiently addressed by combining temporal principal components analysis (PCA) and current source density (CSD) methods (e.g., Kayser & Tenke, 2003, 2005, 2006a, 2006b).
