Abstract
Brightness judgments are a key part of the primate brain's visual analysis of the environment. There is general consensus that the perceived brightness of an image region is based not only on its actual luminance, but also on the photometric structure of its neighborhood. However, it is unclear precisely how a region's context influences its perceived brightness. Recent research has suggested that brightness estimation may be based on a sophisticated analysis of scene layout in terms of inferred transparency, shadows and Gestalt grouping principles. The impressive explanatory power of such accounts calls into question the role of low-level mechanisms, such as lateral inhibition, as explanations for brightness phenomena. A key problem in resolving this issue has been that for the displays used so far, both explanations typically yield predictions in the same ‘direction’. For instance, in the well-known simultaneous contrast display, both accounts predict that the gray square on the black background will appear lighter than the one on the white background. To address this problem, we have devised three displays for which low-level and high-level analyses make qualitatively different predictions. In a series of experiments, we find that brightness percepts in these displays are governed by low-level stimulus properties, even when the percepts are inconsistent with higher-level interpretations of scene layout. These results point to the important role of low-level mechanisms in determining brightness percepts. Additionally, the results suggest that the brightness percepts we have observed in our experiments are engendered by mechanisms operating before the final perceptual output and remain, to a large extent, impervious to higher-level percepts.