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Sarah Elliott, Dingcai Cao; Hue perception under scotopic light levels. Journal of Vision 2011;11(11):361. doi: 10.1167/11.11.361.
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© ARVO (1962-2015); The Authors (2016-present)
The color appearance of an object under scotopic luminance conditions varies depending on the context in which the object is viewed, irrespective of the photopically assigned color. Specifically, an object will appear bluish-green when viewed in isolation, but may appear red or orange when accompanied by a separate object with a higher scotopic luminance (Pokorny et al., 2006). Previous studies on relational scotopic color used free viewing in space and time and very large samples. We investigated the spatial and temporal stimulus conditions required to illicit relational hue percepts under scotopic conditions. A 1 deg test ring was viewed at a 7 deg retinal eccentricity on a CRT covered by neutral density filters. The test luminance was approximately −4 log photopic cd/m2. The test ring was surrounded by either 2 (simple context) or 4 (complex context) 1 deg inducing rings, split evenly on each side of the test ring. For a total of 120 (×10 repeats) trials, the stimulus duration (5 temporal presentations), inducer spacing (3 conditions), and inducer contrast (4 conditions, from −80 to +80% contrast) were varied for both simple and complex context. A hue scaling technique was used to measure perceived hue and saturation. In the absence of inducers, observers did report hue percepts, although perceived saturation was low (5–15%). In the presence of inducers, the test appearance shifted between reddish-yellows to bluish-greens with a change in inducer(s) contrast polarity, and more reddish hues were perceived with a decrease in inducer spacing. Hue percepts were consistent across stimulus durations, and overall, less red content was reported with complex context. Spread light alone is not sufficient to account for hue shifts, suggesting higher-order color mechanisms play a role in hues percepts at scotopic light levels.
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