title: Perceptual grouping-dependent lightness processing in human early visual cortex.
abstract: Lightness, the perceived relative achromatic reflectance of a surface, depends strongly on the context within which the surface is viewed. Modest changes in the two-dimensional configuration or three-dimensional scene geometry may lead to profound variations in lightness even though the surface luminance remains constant. Despite recent progress, we are far from a complete understanding of how various aspects of spatial context affect lightness processing in the cortex. Here we use a novel stimulus to show that perceptual grouping through occluders can affect lightness. We first report behavioral results showing how lightness across occlusion depends on spatially distant image features, including luminance and contrast. Next using functional magnetic resonance imaging (fMRI) we show that human early visual cortex responds strongly to occlusion-dependent lightness variations with little or no attention. These results suggest that elements of three-dimensional scene interpretation play a role in early cortical processing of lightness.
authors.affiliation: Department of Psychology and National Research Center for Magnetic Resonance UMRAM, Bilkent University, Ankara, Turkey. hboyaci@bilkent.edu.tr
authors.forename: Huseyin
authors.initials: H
authors.lastname: Boyaci
authors.forename: Fang
authors.initials: F
authors.lastname: Fang
authors.forename: Scott O
authors.initials: SO
authors.lastname: Murray
authors.forename: Daniel
authors.initials: D
authors.lastname: Kersten
mesh_terms: D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D007088:Illusions / Q000502:physiology; D008029:Lighting; D008279:Magnetic Resonance Imaging; D010775:Photic Stimulation / Q000379:methods; D011594:Psychometrics; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*