Losses of foveal flicker sensitivity during dark adaptation following extended bleaches

Flicker sensitivity to a small foveal test stimulus can decrease appreciably during the period of dark adaptation that follows extinction of a bleach. For 20 min diameter, long wavelength tests that followed 70% L cone bleaches of various wavelengths, 18 Hz flicker sensitivity decreased precipitously (i.e. within about 45 sec) by about 1.5-2.0 log units beginning at about 100-200 sec following extinction of the bleach. For short wavelength tests that followed long wavelength bleaches, the corresponding precipitous losses of flicker sensitivity were relatively small and early; flicker sensitivity decreased by about 0.6-1.0 log units beginning no later than 60 sec following extinction of the bleach. Whenever flicker sensitivity decreased precipitously, the losses of flicker sensitivity were followed by plateaus of M cone dominated flicker sensitivity. For combinations of test and bleaching wavelengths that did not cause flicker sensitivity to decrease precipitously, flicker sensitivity instead decreased gradually over a prolonged period of time, and incorporated a substantial L cone contribution. The precipitous suppression of flicker sensitivity found for certain combinations of bleaching and test wavelengths appears to depend on the action of a broadly tuned, red-green spectrally opponent process.