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 p erceived total luminance of a composite image? We investigate this question using a paradigm in which the observer attempts to judge, with feedback, w hich of two texture patches has higher total luminance. All patches are com posed of nine luminances, ranging linearly from 0 (black) to a maximum lumi nance (white: 160 cd/m(2) in one condition; 20.2 cd/m(2) in another conditi on). Luminance histograms of the patches being compared are experimentally varied to derive, for each luminance nu, the impact exerted by texture elem ents (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. perceive d texture luminance) that is proportional to its (the texel's) luminance. T he only exception occurs for texels of maximal luminance, which surprisingl y exert an impact that is slightly, but significantly, less than that exert ed by texels of the next lower luminance. We conclude that visual intensity coding for purposes of assessing overall luminance of inhomogeneous patche s is approximately veridical. In particular, texture luminance judgments ar e not mediated by a significant, compressive nonlinearity. (C) 2000 Elsevie r Science Ltd. All rights reserved.