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Mark McCourt, Barbara Blakeslee; Coming to terms with lightness and brightness: effects of stimulus configuration and instructions on brightness and lightness judgments. Journal of Vision 2008;8(6):291. doi: https://doi.org/10.1167/8.6.291.
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Depending on the experimental conditions, lightness (perceived reflectance) may refer to judgments that are identical to brightness judgments (perceived luminance), to local brightness-contrast judgments (the brightness difference between a target and its background), or that represent an independent dimension of achromatic experience (Arend & Spehar, 1993 a; b). This third dimension exists only when the illumination across regions of the display is visibly non-uniform and has been called “inferred-lightness” because it requires that the observer take account of the illuminant to make an inferential judgment of target reflectance (Blakeslee & McCourt, 2003). Because lightness judgments are based on different information under different conditions, lightness data generated in one condition may not be comparable to lightness data measured in another condition. We investigate this problem with regard to a history of data on simultaneous brightness/lightness contrast, by measuring brightness, brightness contrast and lightness in stimuli similar to those used in Gilchirst's early edge-substitution studies (Gilchrist, 1979; 1988; Gilchrist, Delman & Jacobsen, 1983). Our results clarify discrepancies in this literature which appear to stem from comparing different types of lightness judgments and from inadvertently using brightness as an index of lightness under conditions where inferred-lightness judgments are possible (Gilchrist, 1999; Gilchrist, 2006).
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