Abstract

The electrical response of the human retina (the ERG) has strong nonlinear response components to flickering lights. We have used these nonlinear responses to probe the organization of the retina. By presenting the eye with stimuli composed of sums of sinusoids and measuring the difference frequency we investigated the early stages of temporal processing. We find that there is a fast (corner frequency at 50 Hz), low pass (down to 0.25 Hz), temporal stage to the visual system. By measuring the ERG response as a function of the mixture ratio and phase of combinations of red (633 nm) and green (543 nm) lights we find that there is a nonlinearity prior to combination of the LWS and MWS cone signals. In addition, we find that the phase relation of the lights required to produce the minimal response is frequency dependent (measurements were made at 3.4 log td). We have also collected psychophysical estimates of visual threshold under conditions similar to those for the ERG data. The uniform field threshold data show no evidence of these early retinal nonlinearities, even though the ERG data can be measured in conditions below psychophysical threshold. Alternative models that attempt to reconcile these results include nonlinear gain control mechanisms and separation of the visual response into on- and off-channels with a later recombination before detection.

© 1992 Optical Society of America