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Roger Knight, Eileen Knight; Surface color matching under uniform vs. non-uniform mesopic light levels. Journal of Vision 2009;9(14):61. doi: 10.1167/9.14.61.
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© ARVO (1962-2015); The Authors (2016-present)
There are light-level dependent changes in color vision that occur during mesopic vision that pose a challenge for the perception of constant surface color. Such challenges may occur when regions of a surface are differentially illuminated, as from shadowing. Color signals from each region may be processed differently (e.g., more or less rod, S-cone involvement) to produce different color percepts. Thus, perceiving constant surface color may be impaired when surfaces are seen under non-uniform, compared to uniform mesopic illumination. The present study used a visual search task to measure surface color matching across uniform and non-uniform mesopic light levels. Dark-adapted observers viewed a two-chambered light box with each chamber containing an array of spectrally calibrated colored paper samples (Color-aid, NY). Light level in each chamber was independently controlled. The observers‘ task was to view a color test sample (2o x 2o) under one level of illumination and locate its physical match from an array in the adjacent chamber that was illuminated by either the same (uniform) or different (non-uniform) light level. Under non-uniform illumination, light level differed by one log unit across the two chambers. The physical match to the test sample was present in the adjacent chamber's array on 80% of the trials. Twenty test samples, chosen to represent a large region of color space, and 20 arrays of 25 color samples each were used. Signal detection theory was used to characterize matching performance. Performance depended on light level and uniformity of illumination across the two chambers. Under uniform illumination, the general effect of decreasing light level between 20-2 Lux was an overall decrement in matching performance regardless of sample color and this decrement in performance was significantly increased under non-uniform illumination. This differential decline in performance under non-uniform illumination is not completely explained by either a light-level dependent change in color appearance or a reduction in color discrimination. Our finding that matching surface color is more impaired under non-uniform than uniform levels of illumination suggests that constant surface color perception is influenced by one or more light-level dependent processes associated with mesopic vision.
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