Influence of surround proximity on induction of brown and darkness.

Abstract

A bright white surround makes a yellow long-wavelength target look both browner and darker. We explored the parallel between these two types of induction by examining their dependence on the proximity of the bright surround to the target at two different time scales with 27ms and 1s stimulus durations. We assessed (a)brown induction by adjustment of target luminance to perceptual brown and yellow boundaries and (b)darkness induction by a successive matching procedure. We found that brown induction is a quick process that is robust even for 27ms stimuli. For darkness induction, there was a strong, spatially localized surround proximity effect for the 27ms stimuli and much weaker proximity effect for the 1s stimuli. For brown induction, proximity effects were generally weaker but still showed relatively stronger localized proximity effects for 27ms stimuli than for 1s stimuli. For these stimuli, darkness induction predicts the relative pattern but not the magnitudes of brown induction. Both brown and darkness inductions show the operation of quick, spatially localized processes that are apparently superseded by other processes for extended stimulus presentations.