Visual system

The human eye
The image projected onto the retina is inverted due to the optics of the eye.

The visual system includes the eyes, the connecting pathways through to the visual cortex and other parts of the brain. The illustration shows the mammalian system.

The visual system is the part of the nervous system which allows organisms to see. It interprets the information from visible light to build a representation of the world surrounding the body. The visual system has the complex task of (re)constructing a three dimensional world from a two dimensional projection of that world. The psychological manifestation of visual information is known as visual perception.

Introduction

This article mostly describes the visual system of mammals, although other "higher" animals have similar visual systems. In this case, the visual system consists of:

• The eye, especially the retina
• The optic nerve
• The optic chiasma
• The optic tract
• The lateral geniculate nucleus
• The optic tectum (superior colliculus)
• The optic radiation
• The visual cortex
• The visual association cortex

Different species are able to see different parts of the light spectrum; for example, bees can see into the ultraviolet, while pit vipers can accurately target prey with their infrared imaging sensors.

Visual System Media

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  This diagram linearly (unless otherwise mentioned) tracks the projections of all known structures that allow for vision to their relevant endpoints in the human brain. Click to enlarge the image.

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  Representation of optic pathways from each of the 4 quadrants of view for both eyes simultaneously

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  S. Ramón y Cajal, Structure of the Mammalian Retina, 1900

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  Information flow from the eyes (top), crossing at the optic chiasma, joining left and right eye information in the optic tract, and layering left and right visual stimuli in the lateral geniculate nucleus. V1 in red at bottom of image.*(1543 image from Andreas Vesalius' Fabrica)

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  Six layers in the LGN

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  Scheme of the optic tract with image being decomposed on the way, up to simple cortical cells (simplified)

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  Visual cortex: V1; V2; V3; V4; V5 (also called MT)

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  Visual cortex is active even during resting state fMRI.

References

• David H. Hubel 1989. Eye, Brain and Vision. New York: Scientific American Library.
• David Marr 1982. Vision: A Computational Investigation into the Human Representation and Processing of Visual Information. San Francisco: Freeman.
• R.W. Rodiek 1988. The Primate Retina. In Comparative Primate Biology. vol 4 of Neurosciences. eds H.D. Steklis and J. Erwin. pp. 203–278. New York: A.R. Liss.
• Matthew Schmolesky, The Primary Visual Cortex Archived 2004-12-29 at the Wayback Machine
• Martin J. Tovée 1996. An introduction to the visual system. Cambridge University Press. ISBN 0-521-48339-5
• Andreas Vesalius 1543. De Humani Corporis Fabrica (On the Workings of the Human Body)
• Torsten Wiesel and David H. Hubel 1963. The effects of visual deprivation on the morphology and physiology of cell's lateral geniculate body. Journal of Neurophysiology 26, 978-993.

Other websites

• "Webvision: The Organization of the Retina and Visual System" - John Moran Eye Center at University of Utah
• VisionScience.com - An online resource for researchers in vision science.
• Journal of Vision - An online, open access journal of vision science.