ERGs and Noise: Detection Probability, Time and Amplitude Errors

Abstract

The effect of background noise on a waveform is to change it in a manner which to some extent depends upon statistical parameters of the signal and the noise. When the signal-to-noise ratio is low the signal may be masked by the noise so that it is not detected most of the time, that is the probability of detection is close to zero. As the signal-to-noise ratio increases, the probability of detecting the signal increases. This process can be described by a curve of probability of detection as a function of signal-to-noise ratio. Measurements of the amplitude and implicit time of the signal have ranges of errors associated with them which also depend upon the signal-to-noise ratio, tending to be large when the signal-to-noise ratio is low, and decreasing as the signal-to-noise ratio improves. These general concepts can be readily applied to electroretinography measurements, and some model ERG and noise waveforms are described and compared with live recordings. The model system is used to obtain measurements of the probability of detection and of the time and amplitude errors which occur at different signal-to-noise ratios. Some techniques are discussed for estimating these effects in practical cases.

From the Howe Laboratory of Ophthalmology, Harvard Medical School, Massachusetts Eye and Ear Infirmary. This study was supported in part by the United States Health Center Grant No. EY00292, the General Research Support Grant No. FR05485 from the National Institute of Health, and Research Grant No. EY00885–01 from the National Institute of Health, United States Public Health Service.