Evaluation of the signal-to-noise ratio for average evoked potentials: determination of interstimulus interval and averaging number.
Repetitive stimuli have to be presented to improve the signal-to-noise ratio for the identification of evoked potential of the brain. The averaging method has been widely used for the response to repetitive stimuli. It should be noted that if the stimulus frequency is synchronized with the rhythm of the background noise of an electroencephalogram, the colored noise can only poorly be eliminated by the averaging method. This paper discusses the interstimulus interval of the stimuli and the requisite averaging number from the viewpoint of the S/N ratio of averaging evoked potentials. First, using the a priori information of the evoked potential and background noise, we determine the interstimulus interval of the stimuli. Next, under presentation of the stimulus with the interstimulus interval thus determined, the data of the electrical activity are recorded, and the requisite averaging number is obtained such that the S/N ratio of the average evoked potential becomes larger than the required S/N ratio. The results were applied to the data of the photic evoked potential in response to light-flashes in a healthy male.
Nakamura
M
M
Department of Electrical Engineering, Saga University, Japan.
Nishida
S
S
Shibasaki
H
H
D000328:Adult; D004569:Electroencephalography / Q000379:methods*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D012016:Reference Values