Recovery of spatial vision during dark adaptation in normal subjects

We show, how sensitivity to sinusoidally-modulated gratings changes throughout the course of dark adaptation. The luminance required to resolve the bars of a variety of sinusoidal gratings of (0.6-14 c.p.d.) presented in the parafovea, was determined for 30 min following a full bleach. Data obtained for low and intermediate spatial frequencies (0.6 and 3.5 c.p.d.) was qualitatively similar to the classical dark adaptation function, showing discrete cone and rod phases. Threshold to a 14 c.p.d. grating fell initially, then after approximately 10 min, rose by between 0.40 and 1.17 log units. This effect was not apparent for the 8.3 c.p.d. grating, despite the fact that both spatial frequencies must have been detected by cones. The phenomenon has been attributed to rod-suppression of cone-mediated vision.