The Anchoring Problem

Abstract

This chapter deals with the essential but only recently recognized problem of anchoring in lightness perception. Previously, lightness theories had no anchoring rules and thus could predict only relative lightness values, not specific values. An anchoring rule or set of rules is the final component required for a complete theory of veridical perception. Although it has not been widely recognized, most theories of lightness perception, including decomposition theories, can, at most, assign only relative lightness values to the surfaces in a scene. They may predict, for example, that a particular surface is five times lighter, or three times darker than a neighboring surface. To produce absolute lightness values requires an anchoring rule. This is a rule that identifies a specific value of lightness (like white or middle gray) with some property of the retinal image (like highest luminance, average luminance, or largest area).