Hess and Pretori revisited: resolution of some old contradictions.

Abstract

An early experiment by Hess and Pretori (1894) was replicated and modified in an attempt to determine why they failed to find the ratio principle later discovered by Wallach (1948). Separating the two surround-infield patterns by darkness made very little difference. However, allowing the observer to adjust the infield luminance (as in Wallach) rather than the surround luminance (as in Hess & Pretori) revealed some startling effects. At surround:infield luminance ratios greater than approximately 100∶1, there is no ratio effect; all infields appear equal and totally dark. Converging evidence is presented that Hess and Pretori’s data in this region actually represent surround-matching by the observers. Nor are ratio effects found with increments (infield brighter than surround). When free to match either infield luminances or ratios (by controlling infield luminance), observers match luminances. For decrements with ratios between 1∶1 and approximately 100∶1, lightness constancy and the ratio principle hold.