Abstract
The perceptual constancies, of brightness, shape, color, and size, are thought to be critical for object recognition; objects should in some sense ‘look the same’, even when the conditions of lighting and viewing are altered. Yet the constancies are imperfect, their extent differing over individuals, tasks, and situations from around 5% to around 80% of ideal. Is this variation just random, or is there a principled reason? Based on the underlying physics, Reeves (Color Research & Application, 8, 1–3, 2018) argued that as the color of a sample becomes purer, color constancy should decline, whereas brightness constancy should improve. Extensive raw data exists for the 20 observers of Foster, Amano & Nascimento (Vision Research, 41, 285–293, 2001), who made both simultaneous and successive matches of central squares presented in simulated Mondrian displays illuminated at 20,000K and 6,500K. Regressions of constancy indexes against sample saturation support the color constancy prediction for 16 observers and the brightness constancy prediction for 19 observers. Accounts of constancy should also consider saturation.