As noted earlier, the EEG signal reflects the electrical potential between two electrodes, one of which is considered the “active” electrode site (i.e., the site of interest) and the other the reference. Choice of appropriate reference electrode location has been the source of much disagreement in the psychophysiology literature in recent years. Researchers have demonstrated that various reference electrode locations (Cz and linked ears, for example) produce different EEG results. The pros and cons of various reference electrode locations are discussed by others (Davidson et al., 2000; Hagemann, Naumann, & Thayer, 2001; Stroganova & Orekhova, 2007). In our work, we record EEG using Cz as the reference electrode and then re-reference the data via software to an average reference configuration (Lehmann, 1987). This re-referencing eliminates concerns that power values at each active site reflect interelectrode distance as much as they reflect electrical potential. At this point, there is debate about how many electrodes are adequate for average referencing.
