Signed <i>r</i>² values between auditory oddball amplitudes at all time points and channels with visual P300 BCI performance (defined as the number errors during the web browsing task) in red for positive correlations and in blue for negative correlations (A).

<p>Two elements were selected from the matrix (marked by green circles in A) for visualization using scatter plots (B) showing a correlation of <i>r</i> = 0.9 (<i>p</i> < 0.01) on electrode C3 and a correlation of <i>r</i> = −0.9 (<i>p</i> < 0.01) on electrode Oz. Finally, topographic distributions of the signed <i>r</i>² values are shown at the bottom (C). Note that due to the use of “number of errors” as performance measure positive correlations indicate a decrease in performance with increasing amplitude, whereas negative correlations indicate an increase of performance with decreasing amplitude.