Achromatic constancy and adaptation level

Theories of lightness constancy are frequently based on luminance ratio or adaptation level explanations. In a previous study, we found lightness constancy as a function of invariant contrast relations under sustained viewing, but not for brief stimulus durations. We hypothesized that the observed constancy occurred either as a result of adaptation to the overall stimulus luminance and/or due to the constant luminance ratios. In this study, we measured achromatic constancy in varying adaptation conditions. Stimuli consisted of center test regions with contiguous surrounds presented in Maxwellian view. Ten center/surround ratios were used in each of three test luminance level conditions and in six adaptation conditions. Subjects judged either the lightness or brightness of the center test region. We found constant lightness judgments, with constant ratios, independent of adaptation level. However, brightness judgments varied when the center luminance was slightly below or above the surround luminance.