MMN amplitudes and latencies again varied between EEG references at different sites, showing the largest mid-frontocentral MMN for ERPs referenced to linked mastoids (peak latency 150 ms at Cz) and the smallest MMN for the average reference (160 ms; Fig. 12A). At the same time, MMN inversion at lateral-inferior temporoparietal sites (cf. TP9) was largest for the average reference and smallest for the linked-mastoids reference, as it should be because these ERP difference topographies are not affected by the EEG reference choice (i.e., for all between-topography correlations, r = 1.0). In contrast to the surface potential MMN topography, its CSD counterpart revealed off-midline (i.e., bihemispheric) frontocentral MMN maxima corresponding to temporoparietal MMN minima, similar to the auditory N1 CSD topography depicted in Figs. 8 and 9. Indeed, despite profound differences in amplitude and latency, the topographies of N1 (for LM at Cz: peak latency 125 ms, peak amplitude 3.1 µV) and MMN and were almost identical for this sample (N = 8; for ERP, r = 0.9854; for CSD, r = 0.9480), suggesting that the same neuronal tissue (i.e., primary auditory cortex) contributed to the generation of both N1 and MMN (cf. May and Tiitinen, 2010).
