Noise and the absolute thresholds of cone and rod vision

Abstract

Literature data on light detection by cone and rod vision at absolute threshold are analysed in order (1) to decide whether the threshold performance of dark-adapted cone vision can, like that of rod vision, be consistently explained as limited by noise from a "dark light"; (2) to obtain comparable estimates of the dark noise and dark light of (foveal) cones and (peripheral) rods. The dark noise was estimated by a maximum-likelihood procedure from frequency-of-seeing data and compared with the dark light derived from increment-threshold functions. In both cone and rod vision, the estimated dark noise coincides with Poisson fluctuations of the estimated dark light if 17% (best estimate) of lambda max-quanta incident at the cornea produce excitations. At that fraction of quanta exciting, dark lights are equivalent to 112 isomerisations per sec in each foveal cone and 0.011 isomerisations per sec in each rod. It is concluded that (1) the threshold performance of dark-adapted cone as well as rod vision can be consistently described as noise-limited, but not by postulating a multi-quantum coincidence requirement for single receptors; (2) the underlying intrinsic activity in both the cone and the rod system is light-like as regards correspondence between noise effect and background adaptation effect. One possibility is that this activity is largely composed of events identical to the single-photon response, originating in the visual pigment, in cones as well as in rods.

Controlling the Gain of Rod-Mediated Signals in the Mammalian Retina

“…This work follows a long history of physiological studies of how weak backgrounds affect sensitivity of retinal signals (for review, see Shapley and Enroth-Cugell, 1984;Donner, 1992). Our conclusions are in general agreement with past work, with some notable differences.…”

“…A long history of behavioral work characterizes how weak background lights change the threshold of rod vision (for review, see Barlow, 1957;Donner, 1992). The physiological basis of these changes in behavioral threshold is unclear; although the effect of weak backgrounds on the electroretinogram (ERG) has been measured in primates (Frishman and Sieving, 1995), we know little about how weak backgrounds alter signal and noise in individual cells in primate retina.…”

Phototransduction in mouse rods and cones

“…The spontaneous activation of visual pigment molecules sets an ultimate limit on visual sensitivity [30][31][32][33]. In a toad rod, the rate of thermal activation of rhodopsin was measured to be 0.031 s −1 at 22°C, corresponding to an average wait of 2,000 years for the spontaneous activation of a given rhodopsin molecule to occur, based on a total of 2×10 9 rhodopsin molecules per cell [34].…”

Detection Sensitivity and Temporal Resolution of Visual Signals near Absolute Threshold in the Salamander Retina

“…Finally, the sensitivity of human observers (Hecht et al, 1942;Sakitt, 1972) is limited by neural noise whose magnitude is approximately comparable with the measured rate of spontaneous activation of rhodopsin in rods. However, behavioral studies involved significant experimental uncertainty about the number of photons reaching the retina and do not provide a unique estimate of the intrinsic neural noise (Barlow, 1977;Teich et al, 1982;Donner, 1992). Furthermore, physiological estimates of the rate of rhodopsin activation in mammalian rods are themselves subject to considerable uncertainty (Baylor et al, 1984).…”