The dependency of surface potentials on a recording reference (e.g., linked-mastoids, nose, average) and the approach used to measure ERP components are two issues that crucially affect their interpretation and statistical analysis (e.g., Kayser and Tenke, 2003, 2005; Nunez and Srinivasan, 2006). The first issue is that using a particular EEG reference scheme will determine the appearance of ERP waveforms (e.g., cf. Fig. 8 of Kayser et al., 2007), which can result in misidentification of prominent deflections as components, and subsequent bias in selecting electrodes for statistical analysis. Depending on the orientation of the equivalent current generators underlying a particular ERP deflection, the reference choice may also mask existing effects if the reference region is itself differentially affected (e.g., Nunez and Westdorp, 1994). Thus, different references may yield different experimental effects (groups or conditions), leading to an erroneous assumption that regional ERP effects reflect neuronal activity of underlying brain structures. The second issue concerns quantifying ERP effects in multichannel surface potentials, while avoiding experimenter bias when selecting time intervals and recording sites for statistical analysis, and ensuring statistical independency of the analyzed effects (cf. Kayser and Tenke, 2003, 2005).
