Despite its loadings peak frequency, the spectral composition of the alpha ERD factor revealed considerable contributions from lower frequencies (i.e., theta and delta; Fig. 7A), indicating that the event-related desychronization of alpha and theta oscillations around 400–800 ms covaried in this paradigm for this sample of young individuals. To corroborate the interpretation that this time-frequency component is nevertheless consistent with an alpha ERD conceptualization, an additional CSD-tfPCA solution was derived from ERSP data restricted to spectra between 8 and 30 Hz (i.e., excluding delta and theta frequencies). The resulting first five CSD-tfPCA factors were highly similar to the first five factors extracted from the original 1–30 Hz ERSP data, yielding highly correlated factor loadings (r > .983) and factor scores (r > .986) between corresponding alpha ERD and NVS ERS factors (see supplementary Fig. S4).
