Chapter

Introduction

Nigel Daw

in How Vision Works

Published in print January 2012 | ISBN: 9780199751617
Published online May 2012 | e-ISBN: 9780199932375 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780199751617.003.0001
Introduction

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The human visual system consists of a system for inspecting objects, starting with the fovea in the retina, and a system for noticing which objects should be inspected, and directing the eyes to look at them. In daylight, the cones are the photoreceptors used, with three types, leading to trichromatic color vision. At night, the rods are active. As the eyes move, the world appears to be stationary, which is accomplished by noticing and carrying forward a limited number of objects from one snapshot to the next. Most aspects of vision are relative—the brightness, color, motion, and depth of an object are all seen relative to the background. Finally, absence of activity in the neurons of the visual system is interpreted as continuity with the rest of the scene, so that lesions in the brain may simply not be noticed.

Keywords: visual system; fovea; rods; cones; vision is relative; lesions; noticing objects; inspecting objects

Chapter.  2008 words.  Illustrated.

Subjects: Neuropsychology

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