Prediction of BCI performance based on the alpha rhythm. (a) Spatial distribution of alpha during relaxation with eyes closed. Alpha amplitude is highest over the electrode subset that was used for classification (i.e., PO3,4,7-10, and Oz,1,2), with absolute peaks at electrodes PO7 and PO8. (b) Correlation between alpha power at electrode pair PO3-PO4 and peak classification accuracy (r = .66). The grey line gives a linear fit. (c) Mean impedances across participants show lower impedance for PO3-PO4 than for PO7-PO8. This possibly explains why the former pair is more predictive of BCI performance than the latter.