Slowed decay of the monkey's cone receptor potential by intense stimuli, and protection from this effect by light adaptation

Abstract

Decay of the late RP (receptor potential) becomes very slow when the stimulus intensity for saturating amplitude of the late RP is exceeded. In macaque monkey this was shown earlier for the rod late RP, and is now shown at higher stimulus intensities for the cone late RP. These slowly decaying responses to “overdriving” stimuli are referred to, respectively, as rod and cone aftereffects. Since these aftereffects greatly prolong the response to a given stimulus, they must degrade the ability of the visual system to resolve stimuli in the time domain. For the rod late RP our preceding paper shows that this problem is handled by suppression of the rod late RP at photopic intensities, apparently by a cone-initiated pathway acting through the horizontal cell as inhibitory interneuron. In this paper we show that the cone aftereffect, which occurs only at high photopic intensities, is quickly dissipated by light adaptation at those intensities. In other words, light adaptation is highly effective in protecting against the cone aftereffect. The cones are thus capable of resolving stimuli in the time domain at considerably higher stimulus intensities than would otherwise be possible. This provides a significant upward extension of the intensity range of useful vision.