Abstract
Critical flicker frequency and apparent brightness of a foveal test field were determined as functions of the luminance of an adjacent inducing field. Apparent brightness measurements were obtained by a binocular comparison method. Inducing luminance was varied through a range of 4.4 log units at each of three test-luminance levels: 0.55, 1.57 and 2.47 log ft-L. The apparent brightness of the intermittent test field, determined at the flicker-fusion threshold, continuously decreased as inducing luminance was raised. CFF, on the other hand, varied in a complex manner: increasing initially, reaching a maximum, and then declining. Over a wide range of inducing luminance, the enhancement of CFF was accompanied by a decrease in apparent brightness. This induced divergence is radically different from the parallel changes in CFF and apparent brightness that occur when test luminance is varied. It was hypothesized that entoptic stray light played a minor role, but that spatial inhibition in the retina could account for both the rise and the fall in CFF as well as the concomitant decrease in apparent brightness.
© 1961 Optical Society of America
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