The purpose of this work is to describe how the visual system groups surfaces of unequal lightness under complex patterns of illumination. We propose that the Gestalt principle of Grouping by Regularity explains this process better than the more often cited principle of Grouping by Similarity. In our first experiment we demonstrate that in a perceptual organization task, pitting proximity against illumination gradients, discounting the illuminant was contingent upon the periodicity of the illuminant. Traditional theories of lightness constancy and discounting the illuminant (Rock, Nijhawan, Palmer, & Tudor, 1992) cannot account for such effects. Three more experiments show that grouping is affected more by local luminance ratios than constant reflectance ratios. We conclude from these findings that Grouping by Regularity is a powerful grouping principle that operates pre-constancy.
Highlights
► Proposal of new Gestalt grouping principle that we call Grouping by Regularity. ► Grouping by Regularity may in some cases be stronger than Grouping by Similarity. ► Grouping by Regularity explains perceptual organization under complex illumination patterns. ► Grouping by Regularity may operate early, before lightness constancy.
