Analysis of retinal light adaptation with the flicker electroretinogram.

To study the retinal light adaptation we measured and analyzed the flicker electroretinogram response to stimuli that varied in temporal frequency, retinal illuminance, and modulation depth. The responses measured at 100% modulation showed the classic adaptation pattern, being independent of mean retinal illuminance at low temporal frequencies, consistent with Weber adaptation, and increasing in proportion to mean retinal illuminance at high temporal frequencies, consistent with linearity. At 25% modulation, however, high-frequency linearity was not found. The response amplitude consistently showed a minimum at 40-48 Hz. When modulation was systematically varied, response amplitudes measured at 16 and 22 Hz showed Weber adaptation at all modulations and response phase was relatively constant with modulation, whereas response amplitudes at 40 and 48 Hz showed adaptation at low modulations but linearity at high modulations and response phase varied with modulation. We conclude that retinal gain controls also operate at high temporal frequencies.