THE MEASUREMENT OF STEADY-STATE VISUAL-EVOKED CORTICAL POTENTIALS USING AN ADAPTIVE NOISE CANCELER

A new software method for measuring steady-state visual evoked cortica l potentials (VECPs) has been developed using the principle of adaptiv e noise cancelling. The steady-state VECP is composed of narrow-band f requency components at harmonics of the stimulus frequency. In clinica l recordings, these signal components are masked by wide-band noise, p redominantly electroencephalographic activity and muscle noise. The st imulus frequency is exactly known and by using a reference sinusoid at the stimulus frequency (or its harmonics) the adaptive noise cancelle r (ANC) is able to cancel uncorrelated noise components from the recor ding. In effect, the ANC functions as an adaptive narrow-band-pass fil ter at the reference frequency. The performance of the ANC has been ev aluated using both simulated and physiological signals. The output of the ANC provides temporal information on the signal amplitude and phas e, and can be used to calculate the reliability of signal detection. F or this application, the ANC has a number of advantages over the fast Fourier transform: it is a more sensitive detector, it requires fewer calculations, it is less computationally intensive, it requires less m emory and it can be implemented in real time.