In contrast to a linked-mastoids and average reference, the nose reference represents a single reference location, resulting in an ERP waveform that is zero at all sample points (flat green lines at Nose insets in Fig. 2). This provides an excellent opportunity to visualize the impact of the reference for the ERP signal at all other sites, keeping in mind that the same principle applies to all references, not just the nose reference. Rereferencing the NR waveforms to the mean of TP9 and TP10 (LM) or of all recording sites (AR) means this new reference waveform is subtracted from all 67 recording sites. Thus, the inverted LM and AR reference waveforms are revealed at the Nose site (red and blue lines), indicating that substantial and complex ERP activity is removed from the nose-referenced ERPs, and that this removed ERP activity is highly specific to the particular reference scheme. Furthermore, by comparing these inverted reference waveforms for words and faces (Nose insets in Fig. 2A and B), it becomes obvious that NR and AR reference waveforms also depend uniquely on these two stimulus types (and by extension on task, paradigm, condition, modality, response requirements, etc.).
