Another important methodological difference between these studies is the choice of EEG recording reference. For instance, whereas Salisbury et al.14,27,28 employed a commonly-used linked-earlobes reference, Ford et al.20,26 recorded EEG with sternovertebral reference, and our lab10,33,34 and others8,11 have used nose-referenced recordings. The dependency of surface potentials on a recording reference (e.g., linked-mastoids, nose, average),38–40 and the way by which ERP components are quantified,41–44 crucially affect the identification and statistical analysis of N2 and P3. While the relative ERP topography is not affected by the reference choice (cf. discussion in Kayser et al.10), different references can substantially affect ERP amplitudes, peak latencies and their local maxima, depending on the direction of the underlying neuronal generator, which, of course, may differ between groups. For example, relatively preserved P3 amplitudes in schizophrenia may be a direct consequence of using a nose reference; at the same time, this recording reference is likely to amplify differences in N2 amplitude between schizophrenic patients and healthy controls.8,10,11,45 The critical point is that the choice of the recording reference may affect what aspect (e.g., time interval, scalp location) of the ERP signal is ultimately analyzed.
