The role of simultaneous contrast in brightness constancy.

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Abstract
Luminance matches were obtained between a 1 degree square test field viewed under variable illuminance and a photometric field of the same size. The function relating log matched luminance of the test field to the log of the ambient illuminance is linear over a range of more than 1 million to 1. When the background against which the test field is viewed is either "black" or a "gray" of the same reflectance as the test field, the matches do not differ greatly from predictions based on energy relationships. When the test field background is a "white" of higher reflectance that the test field, the slope of the function is less and the data are shifted to a lower position on the log matched luminance axis. The change in slope is a manifestation of the tendency towards brightness constancy. The shift in the ordinate position is a result of simultaneous contrast. It is concluded that one of the cues which tends to produce the tendency towards brightness constancy is a background of higher luminance than the test field.

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