Dark adaptation and the rate of pigment regeneration

Abstract

The regeneration of visual pigments in vivo closely follows a monomolecular time course, consequently the regeneration rate is proportional to the quantity of bleached pigment at each moment. The psycho-physical dark adaptation curve follows this same time course, thus log threshold might be raised either by the quantity of pigment still bleached, or by the rate at which regeneration was proceeding. The regeneration after a 5-sec full bleach starts much faster than after a 2-min full bleach, thus the log threshold should be much higher if it is proportional to rate. The pigment regeneration was measured by densitometry and dark adaptation by psycho-physical thresholds after the same bleaches in the same conditions. The log threshold does not follow the rate of regeneration but rather closely the state of regeneration. However there is clearly a second threshold-raising factor which is discussed.