SSVEP SNR. (a) Grand mean FFT ERP amplitude spectra across all participants plotted for harmonics 1–5. Warmer colours indicate higher SSVEP amplitudes. The colour map is scaled to highlight later harmonics; the slice through the first harmonic in fact extends to 2.10 μV (b) Differences in grand mean spectra for the high and low accuracy groups. (c) Grand mean SSVEP amplitude topographies at the first harmonic, averaged across all flicker frequencies, plotted separately for the high and low classification accuracy groups. (d) Scatter plot of the positive relationship between mean SSVEP SNR at the first harmonics and QWERTY classification accuracy. (e) Grand mean FFT amplitude spectra at the first harmonic for each cued frequency during template training.