Stimulus display and illustrations of spectral and spatial patterns of SSVEP amplitudes. Stimulus display and illustrations of spectral and spatial patterns of SSVEP amplitudes. (A) Screenshot of stimulus display and flicker frequencies. A total of 125 red and 125 blue dots were spatially intermingled and in continuous random motion. Red dots flickered at 11.98 Hz and blue dots at 16.77 Hz. A color change of the central fixation cross indicated the color of the to-be-attended dots. (B) The grand-average amplitude spectrum obtained by Fourier analysis of SSVEP waveforms elicited under the two attentional conditions averaged across a cluster of three occipital electrodes. Peak amplitudes are located at the two stimulation frequencies. (C) Spline-interpolated isocontour maps of the grand-average SSVEP amplitudes of the mean of both attentional conditions for red (Left) and blue (Right) dots. Black circles around electrode location Oz indicate the cluster of three posterior electrodes used for statistical analysis. (D) Statistical parametric maps of the estimated cortical current-density distributions that give rise to the SSVEP-amplitude difference between attended and unattended dots for both RDKs. Scale represents t2 values, and the P < 0.001 threshold for the attended versus unattended comparison corresponds to 8.34. Thresholds were corrected for multiple comparisons. Note that different scales were used. S. K. Andersen, and M. M. Müller PNAS 2010;107:31:13878-13882 ©2010 by National Academy of Sciences