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Matched Filtering of Visual Evoked Potentials to Detect Acceleration (+Gz) Induced Blackout

Abstract : In air-combat maneuvering and on human centrifuges, moderate levels of positive acceleration ( + Gz), coupled with moderate rates of onset, produce visual symptoms which are ordinarily progressive: Decreasing visual sensitivity, dimming of the visual field, peripheral light-loss, and central light-loss (black-out). Since these symptoms provide warning of impending loss of consciousness, subjective visual symptoms are the most commonly used tolerance end point in acceleration research. In order to provide an Objective indication of the integrity of the visual system, we have developed (and continue to improve) a method for real-time monitoring of the steady-state visual evoked potential(VEP). Since significant degradation of visual functioning must be recognized in less than approximately four seconds, we required a previously unattained efficiency in producing and measuring the VEP. Using the Fast Fourier Transform (FFT), we developed a method for maximizing the signal-to-noise ratio: A digital, frequency domain, non-white-noise-matched filter, with evaluation only at the expected response peak. The coefficients of the matched filter are determined empirically by analysis of test data obtained in a static run, just prior to the dynamic ( + Gz) run. Experiments on the Navy's Human Centrifuge demonstrated that the response does progressively decrease, disappearing at black-out. Improved computer facilities have permitted evaluation of alternative methods of processing, and the effectiveness of such processing.