Principles of reverse-correlation analysis.

<p>Perceptual echoes in both sensory modalities are computed by means of reverse correlation. IRF is computed by averaging the cross-correlations from each stimulus-EEG pair (black line in middle plot). Average cross-correlations of randomly shifted stimulus-EEG pairs are used as statistical surrogates (red line in middle plot). Analysis 1 (bottom-left) represents the amplitude spectrum of the IRF over time lags between 250 and 1250 ms. The two different shades of red correspond to 2 and 3 standard errors across subjects. Analysis 2 (bottom-right) represents a time-frequency transform of the IRF; the color map corresponds to the effect size in z-score, with respect to the surrogate distribution.