of spectra derived from wavelets or reduced interference distributions, in contrasts to the present FFT-based ERSPs derived from CSDs. By virtue of the reference-independent Laplacian transform (see Tenke & Kayser, 2012, for a review), both the temporal (tPCA) and the time-frequency CSD factors (tfPCA) are associated with factor scores that directly reflect neuronal generator patterns at scalp. In striking contrast to surface potentials, however, CSD-PCA factors do not suffer from the interpretational ambiguity (i.e., signal location, polarity, or phase) stemming from the choice of EEG reference (e.g., Kayser & Tenke, 2010), a problem that is compounded by spectral analysis (i.e., non-linear data transformations; cf. Tenke & Kayser, 2005) and, by extension, time-frequency analysis (e.g., cf. Fein et al., 1988; Guevara et al., 2005; Schiff, 2005).
