These basic principles equally apply to multichannel EEG montages, although their implications become more complicated with an increasing number of recording sites and simultaneously active dipoles, which change in time and space. The impact of choosing a different reference for ERP data obtained with an extended 10–20 system 67-channel EEG montage is illustrated in Figure 2, which directly compares three common reference schemes: a nose reference (NR), a linked-mastoids reference (LM; average of sites TP9 and TP10), and an average reference (mean ERP activity across all 67 sites; cf. Supplementary Fig. S1 for ERP waveforms plotted separately for each reference at 10–20 system sites, including their comparisons at midline sites). These ERPs were recorded from 44 healthy adults during a visual continuous recognition memory task employing foveal presentations of common English nouns or black-and-white photographs of unknown faces (for further details, see Kayser et al., 2010). Depending on the reference scheme, the resulting waveforms differ dramatically in their sequence of prominent deflections at any given scalp location, affecting their peak amplitude, peak latency and peak location. For words, for example,
