Abstract
The accurate perception of object attributes such as surface lightness is vital for the successful interaction with the environment. However, it is unknown how the visual system assigns lightness values to surfaces based on the intensity distribution in the retinal image. It has been shown that the perceived lightness of an image region is influenced by its context but whether that influence involves so-called low-, mid- or high-level mechanisms is disputed. To probe the level of lightness perception psychophysically we manipulated the surface character of a target region and measured its influence on perceived lightness. We show that only when the target region was consistent with the perceptual interpretation of a surface it was subject to a subjective brightening (assimilation) effect. When the target region was consistent with a spotlight, and hence inconsistent with surface perception, there was no concomitant increase in perceived lightness. These results suggest that the effect of context on the lightness of an image region is not deterministic, but can instead be modulated by other attributes of the image region that imply a mid-level scene interpretation.