Abstract

Previous studies of lightness contrast and constancy have used matching procedures to assess perceptual effects. Many experiments indicate that constant luminance ratios give constant lightness matches, suggesting lightness contrast as an explanation of lightness constancy. Other studies fail to support this conclusion. We felt that the contradictory results might be due to the difficulty of making lightness matches in the face of large brightness differences. Thus we had observers make absolute lightness judgments of center-surround targets over a large range of contrast ratios and luminance. We first used brief (300-ms) flashes to keep the eye in a fixed state of light adaptation. The results surprised us. We found that lightness constancy failed for every subject: generally low and high luminances were judged to be blacker than middle luminances for a wide range of contrast ratios. When longer (7-s) flashes were used, however, we obtained good constancy. We then tried brief flashes following light-adapting fields to ascertain if the constancy found for longer flashes could be attributed to adaptation. The results were negative. Our tentative conclusion is that constancy fails for brief flashes due to their transient nature, not to the lack of adaptation. Apparently, sustained viewing is necessary for lightness constancy.

© 1988 Optical Society of America