Fig. 3.

The data features extracted from primary visual cortex beamformer (panel c) virtual electrodes in Experiment 1, the cohort study. Plot (a) shows the whitened spectral amplitude for each of the 97 participants. The response is localised to posterior medial visual cortex (c). For spectra extracted from these peak locations, clear alpha, beta and gamma peaks are present for most participants and are more clearly revealed after the pre-whitening procedure. In the inset (b) the average spectra across all participants is plotted, with dotted lines indicating the standard error on the mean. Note how individual variability in the peak frequency of alpha and beta leads to a merging of these responses in the mean-average spectrum. Finally, in (d) the distribution of peak alpha, beta and gamma frequencies are plotted as separate histograms. Note that the alpha peak is calculated from the DCM fitting procedure in which alpha is explicitly modelled as a Gaussian (see methods), whereas the beta and gamma peaks are extracted from the search for the peak spectral amplitude in their respective ranges.