Abstract

The effect of pre-exposures of brief duration and relatively low brightness on the contrast sensitivity of fovea was investigated. Monocular measurements on two observers were made with a centrally fixated one-degree square testpatch against a surround 27° in diameter. First the contrast threshold was measured after 10 minutes of adaptation to brightnesses of 0.010, 0.10, and 1.0 ft-L. Then the course of adaptation was measured by the contrast threshold after pre-exposures which immediately followed the aforementioned adaptation brightnesses. (Adaptation brightness served as the background brightness for the contrast threshold.) The pre-exposures were 0.10, 1.0, and 10 ft-L for 1, 10, and 100 sec. Not all combinations of adaptation brightness and pre-exposure were used. Contrast threshold increased as background brightness increased and the eye’s sensitivity to contrast decreased with increasing duration and brightness of pre-exposure above a critical value of 100 ft-L-sec.

© 1960 Optical Society of America

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