BRIGHTNESS CHANGES IN A COMPLEX FIELD WITH CHANGING ILLUMINATION

Abstract

A configuration of 5 Munsell neutral gray squares on a gray and white background and a modulus were haploscopically presented to 12 Ss. Each S made brightness estimates for the squares, their background, and the illumination of total field when illuminance was varied in 3 steps over 1.2 log units. Linear brightness functions were obtained on a log-log plot, where brightness estimates were plotted against illuminance. Mean slopes systematically decreased as the reflectance of test region became lower, but none were negative. The failure to find negative slopes would be a difficulty for Jameson and Hurvich's opponentprocess model. Some problematic issues concerning brightness constancy and contrast were discussed.