Texture luminance judgments are approximately veridical

This paper investigates intensity coding in human vision. Specifically, we address the following question: how do different luminances influence the perceived total luminance of a composite image? We investigate this question using a paradigm in which the observer attempts to judge, with feedback, which of two texture patches has higher total luminance. All patches are composed of nine luminances, ranging linearly from 0 (black) to a maximum luminance (white: 160 cd/m(2) in one condition; 20.2 cd/m(2) in another condition). Luminance histograms of the patches being compared are experimentally varied to derive, for each luminance nu, the impact exerted by texture elements (texels) of luminance nu on texture luminance judgments. We find that impact is approximately proportional to texel luminance; That is, a texture element exerts, on average, an impact on texture brightness (i.e. perceived texture luminance) that is proportional to its (the texel's) luminance. The only exception occurs for texels of maximal luminance, which surprisingly exert an impact that is slightly, but significantly, less than that exerted by texels of the next lower luminance. We conclude that visual intensity coding for purposes of assessing overall luminance of inhomogeneous patches is approximately veridical. In particular, texture luminance judgments are not mediated by a significant, compressive nonlinearity.