title: Behavioural and physiological limits to vision in mammals.
abstract: Human vision is exquisitely sensitive-a dark-adapted observer is capable of reliably detecting the absorption of a few quanta of light. Such sensitivity requires that the sensory receptors of the retina, rod photoreceptors, generate a reliable signal when single photons are absorbed. In addition, the retina must be able to extract this information and relay it to higher visual centres under conditions where very few rods signal single-photon responses while the majority generate only noise. Critical to signal transmission are mechanistic optimizations within rods and their dedicated retinal circuits that enhance the discriminability of single-photon responses by mitigating photoreceptor and synaptic noise. We describe behavioural experiments over the past century that have led to the appreciation of high sensitivity near absolute visual threshold. We further consider mechanisms within rod photoreceptors and dedicated rod circuits that act to extract single-photon responses from cellular noise. We highlight how these studies have shaped our understanding of brain function and point out several unresolved questions in the processing of light near the visual threshold.This article is part of the themed issue 'Vision in dim light'.
authors.affiliation: Department of Neurobiology, Duke University School of Medicine, Durham, NC 27710, USA field@neuro.duke.edu.
authors.forename: Greg D
authors.initials: GD
authors.lastname: Field
authors.affiliation: Stein Eye Institute, Department of Ophthalmology, UCLA, Los Angeles, CA 90095, USA asampath@jsei.ucla.edu.
authors.forename: Alapakkam P
authors.identifier: http://orcid.org/0000-0002-0785-9577
authors.initials: AP
authors.lastname: Sampath
mesh_terms: D000818:Animals; D008322:Mammals / Q000502:physiology*; D012684:Sensory Thresholds; D014785:Vision, Ocular; D014796:Visual Perception
keywords: photon detection; physical limits; rod photoreceptor; scotopic vision; signal processing; visual sensitivity