Evoked potential processing system with spectral averaging, adaptive

Abstract

The evoked potential processing system includes, in one embodiment, a spectral averaging method. Time based, digital pre-stimulus and post-stimulus electroencephalographic (EEG) signal streams are obtained and are converted into frequency spectrum signals. A differential spectrum is obtained. The differential spectrums from a plurality of sweeps are summed. The summed differential spectrum is then converted into a time based signal stream which contains the evoked potential (EP) signal therein. The EP signal can also be obtained utilizing a two-dimensional filter. Pre- and post-stimulus EEG signal streams for a sub-group of stimuli, wherein each stimulus in a group has the same intensity or frequency, are filtered by conventional averaging or spectral differential averaging. The time based, filtered, post-stimulus EEG signal streams are placed in an array and the array is then filtered by a two-dimensional Fast Fourier Transform (FFT) filter. The array is then filtered by a mask and the masked array is then transformed into a time based format by an inverse FFT. The adaptive averaging technique utilizes a computational formula which computes an estimated running signal to noise ratio. When the difference between the pre-stimulus running SNR and the post-stimulus running SNR is less than a predetermined threshold, further stimulation and acquisition of EEG signals stops. Hence, the post-acquisition processing of the EEG signals is limited to that number of EEG sweeps. The electrode wire configuration uses a cross wiring scheme wherein the shield of a particular wire is connected to the other electrode wire to eliminate artifacts in the respective electrode wire.