The ratio principle holds over a million-to-one range of illumination

Abstract

A pattern of five gray squares ranging from white to black was presented to observers at four levels of illumination, spanning a range of six log units. This replicated an earlier experiment by Jameson and Hurvich (1961) in which a 1.1-log-unit range was used. Three measures of perception were used: (1) a "lightness" measure consisting of a square of variable luminance surrounded by a bright white field (after Jameson & Hurvich), (2) a Munsell chart, and (3) a "brightness" measure consisting of a square of variable luminance surrounded by complete darkness (after Heinemann, 1955; Leibowitz, Mote, & Thurlow, 1953; and Leibowitz, Myers, & Chinetti, 1955). The first two measures yielded the same results-a very high degree of constancy over the entire range. No diverging or negative functions were found. The brightness measure yielded almost no constancy, but did yield approximate luminance matching. It is argued that these results, together with those of three other published studies, indicate that the concept of intensity dependence is not valid. It is also suggested that the term "brightness constancy" is a misnomer, since brightness varies with illumination. © 1988 Psychonomic Society, Inc.