The dark-adapted retina is presented with a cyclical stimulation of brief flashes of near threshold luminance. The plot of perception probability (recorded across each 30-sec exposure) versus time shows a damped oscillatory behavior. The time constant of the decay process is found to increase as eccentricity exceeds, say, 30°. This effect is discussed by taking into account some psychophysical data recorded by stimulating the two eyes, in succession, and after inspection to the time course of cortical evokedpotential under prolonged testing.