Amplitude Probability Distribution of Noise for Flash-Evoked Potentials and Robust Response Estimates

The distributional properties of brain activity accompanying evoked potentials ("noise") are investigated, and related robust estimates are evaluated. Much work in this area relies, implicitly or explicitly, on the assumption of normally distributed noise. This is a reasonable approximation, as our results for visual evoked potentials indicate: the distribution of the noise is in fact rather symmetric but mildly longer-tailed than to be expected for the normal distribution. Robust averages (trimmed means, redescending M-estimates), designed for handling such situations, offer only modest advantages compared to the ordinary average, as judged from an evaluation of the methods based on real data. In comparison, kernel smoothing of the average evoked potential offers a more substantial improvement.