Wavelet domain nonlinear filtering for evoked potential signal enhancement

A wavelet domain nonlinear filtering method for improving the signal-to-noi se ratio (SNR) of the evoked potentials (EP) is proposed. The method modifi es the selective filtering technique proposed for edge detection in images by Xu et al. for the case of signals which require a smooth transition at t he edge points. It identifies the significant features of a noisy signal ba sed on the correlation between the scales of its nonorthogonal subband deco mpositions. The signal transition information from interscale correlation c oupled with the change in variance around the identified transition region is used to differentiate between noise and the signal. A nonlinear Function such as a Gaussian smoothing function applied around the identified edge i n the wavelet domain leads to smoothing in the signal space also. Numerical results obtained by applying the proposed nonlinear filtering method on mi ddle latency responses of auditory evoked potentials show that the method i s well suited for signal enhancement applications. (C) 2000 Academic Press.