Abstract
Achromatic and chromatic thresholds for a 535-nm stimulus were determined during dark adaptation and against background luminances varying over a range of 2 × 107. In contrast to light thresholds, which decrease from photopic to scotopic values, curves for color thresholds first fall, then rise until they reach a steady level. The change of trend occurs before or at the transition from cone to rod function. The resulting increase of the photochromatic interval with dark adaptation and decreasing background luminance is described by a sigmoid function. The increment of color thresholds after the initial decline is tentatively attributed to chromatic desaturation caused by rod intrusion.
© 1972 Optical Society of America
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