The electroretinogram (ERG) in the previously dark-adapted human eye evoked by double flashes of light of high intensity and short duration has shown after the first light stimulus a period of more than 500 msec of complete suppression of rod activity. During this period the second light flash evokes only cone components in the ERG. Regression lines calculated for the process of recovery of rod function from suppression indicate exponential recovery, the time constant of this process being 0.55 second. Time constant of the same order of magnitude was calculated both for the recovery of the a-wave and that of the total amplitude of the ERG response. However, the process of recovery of the a-wave begins and is completed some 200 msec earlier.
Elenius V. Cone and Rod Activity in the Electroretinogram Evoked by Double Flashes of Light. Arch Ophthalmol. 1969;81(5):618–621. doi:10.1001/archopht.1969.00990010620004