Abstract

The rate of decrease of the logarithm of visual threshold at the fovea to a long-wavelength test after extinction of a 580-nm bleach is not described by an exponentially shaped function. Instead, there is a period of time during dark adaptation about midway between extinction of the bleach and complete recovery of sensitivity when threshold does not continue to decrease. The duration of this period can be up to ~1 a min depending on the illuminance of the bleach. The departure from an exponential time course of recovery is greater when the test stimulus is a disk which is defocused on the retina and sinusoidally modulated at 1 Hz than when the test stimulus is a disk which is focused on the retina and either flashed for 160 msec or sinusoidally modulated at 1 Hz. Losses of sensitivity with time are sometimes apparent about midway through recovery when the test is a defocused disk which is modulated sinusoidally at 1 Hz. When the test stimulus is a disk which is focused on the retina and flashed for 160 msec, sensitivity to test stimuli >580 nm may be described as changing successively from subtractive to additive to subtractive types of combination of L and M cone sensitivities.

© 1985 Optical Society of America