title: Multiple components in photopic dark adaptation.
abstract: After extinction of a 580-nm bleach, the rate of decrease of the logarithm of visual threshold to a foveal long-wavelength test is not described by an exponentially shaped function. There is a period of time roughly midway between extinction of the bleach and complete recovery of sensitivity when the threshold does not continue to decrease. The duration of this period can be up to about a minute, depending on the illuminance of the bleach. The departure from an exponential time course of recovery during this period is more evident when the test stimulus is a disk that is defocused on the retina and sinusoidally modulated at 1 Hz than when the test stimulus is a sharp-edged disk that is either flashed for 160 msec or sinusoidally modulated at 1 Hz. Losses rather than plateaus of sensitivity with time are sometimes apparent--depending on the observer and stimulus parameters--roughly midway through recovery when the test is a defocused disk modulated sinusoidally at 1 Hz.
mesh_terms: D000221:Adaptation, Ocular; D003624:Darkness; D006801:Humans; D008027:Light; D011680:Pupil / Q000502:physiology; D012684:Sensory Thresholds; D014796:Visual Perception