Large depth effects on lightness in the absence of a large luminance range.

To investigate the role of luminance range for lightness computations in complex 3-dimensional scenes we measured the change in lightness of a surface embedded within a relatively low-luminance-range context, as its perceived spatial position shifted from one plane to another. Our experiment tested conflicting claims between the coplanar ratio principle, according to which large depth effects require a high overall luminance range, and the anchoring theory, which predicts that depth effects can occur with a low overall range, given a sufficiently large difference between the highest luminance values in the 2 planes. Our results show decisive support for the anchoring theory but also hint at a large expansion of the perceived range of reflectances (gray shades) relative to the actual range within each plane. This expansion is qualitatively consistent with anchoring theory's scale normalization principle, but it is surprising in magnitude. Together with our earlier findings showing a massive compression of the perceived reflectance range in unsegmented high-dynamic-range Mondrians, our results underline the urgency of the scaling problem in lightness theory (how luminance range is mapped onto lightness range), a companion of the anchoring problem (which point on the lightness scale is anchored to which point on the luminance scale). (PsycInfo Database Record (c) 2020 APA, all rights reserved).