For group comparisons (N = 17), we have shown that a 31-channel EEG montage is entirely appropriate for the analysis of typical auditory ERP components (e.g., N1, N2, P3), revealing effectively the same waveforms and topographies at these sites compared to the original 129-channel ERPs (Kayser and Tenke, 2006b). Moreover, spherical spline interpolations of the data at sites missing in the low-density montage revealed reasonable approximations of the high-density data. The reason for this convergence between low- and high-density CSDs can be attributed to the spatial low-pass filter imposed on the data by averaging ERPs across many individuals, which will remove spatial and temporal noise that is unrelated to the grand mean ERPs.
