Evidence for an intensity-coding oscillatory potential in the human electroretinogram

Electroretinograms (ERGs) were obtained from normal subjects to various combinations of stimulus and background intensities to examine if, as shown in rabbits, one of the oscillatory potentials (OP2) could be identified as reflecting the absolute intensity of the stimulus (i.e. the intensity irrespective of the state of retinal adaptation). The results presented clearly demonstrate that the peak time and the amplitude of OP2 are highly correlated with the absolute intensity of the stimulus. Linear regression analysis (for light- and dark-adapted data combined) yields a correlation coefficient of r = 0.98 for the peak time of OP2 and r = 0.88 for the amplitude of OP2. The latter equations were obtained from ERGs where the brightest flashes were delivered in light-adaptation and the dimmest in dark-adaptation. This is the first demonstration of a high correlation between the intensity of the stimulus and the amplitude and peak time of a human ERG component which is shown to be linear irrespective of the state of retinal adaptation.