SYMPOSIA PAPER Published: 01 January 1973

Mechanism of Vision—A Review


The human retinal image is a pattern of light and dark that differs from a picture within the central nervous system. A remarkable characteristic is the “saccade,” a very fast flicking of the eyeballs such that a new focus of the image is formed on the cone cells of the central pit every few milliseconds. The saccade is especially important to reading when the day-vision cones function. The night-vision rods do not add much to day vision but are a fourth mechanism in respect to the three kinds of cones which enable the brain to distinguish contrasts between spectral hues. Despite the infinite variety of textures and settings with which colors are often perceived, there is a limited degree of color constancy of objects under varying conditions of brightness, size, and shape.

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Johnston, JW
, Chevy Chase, Md.
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Developed by Committee: E12
Pages: 3–17
DOI: 10.1520/STP34755S
ISBN-EB: 978-0-8031-4633-4
ISBN-13: 978-0-8031-0564-5