Abstract
Higher-luminance surrounds turn yellow targets to brown, but we know little about what features of surrounds, especially complex ones, control the induction of brown. To assess the role of surround complexity, we compared homogeneous and complex surrounds consisting of irregularly placed, overlapping 2°-diameter achromatic disks whose luminance varied from minimum to maximum of the CRT monitor. Homogeneous and disk surrounds were presented at the same space-average mean luminance at three different luminance levels. Observers adjusted the luminance of a foveal 2°- diameter target to either the minimum luminance that made the test region appear pure yellow (yellow boundary) or the maximum luminance that made the test region appear pure brown (brown boundary). Between these boundaries, the target appeared butterscotch. Results showed that both brown and yellow boundaries shifted to higher luminance as surround luminance increased. For brown boundaries, there was little difference between homogeneous and disk surrounds. Results for yellow boundaries were more variable but most observers tested to date showed little difference between homogeneous and disk surrounds. Thus, the overall surround light level seems to be most important for determining the light levels producing brown and yellow. In contrast, surround complexity seems to be unimportant for determining these levels, at least for the present stimuli.