Responses to lightness variations in early human visual cortex.
Lightness is the apparent reflectance of a surface, and it depends not only on the actual luminance of the surface but also on the context in which the surface is viewed [1-10]. The cortical mechanisms of lightness processing are largely unknown, and the role of early cortical areas is still a matter of debate [11-17]. We studied the cortical responses to lightness variations in early stages of the human visual system with functional magnetic resonance imaging (fMRI) while observers were performing a demanding fixation task. The set of dynamically presented visual stimuli included the rectangular version of the classic Craik-O'Brien stimulus [3, 18, 19] and a variant that led to a weaker lightness effect, as well as a pattern with actual luminance variations. We found that the cortical activity in retinotopic areas, including the primary visual cortex (V1), is correlated with context-dependent lightness variations.
Boyaci
Huseyin
H
Department of Psychology, University of Minnesota, Minneapolis, Minnesota 55455, USA. boyac003@umn.edu <boyac003@umn.edu>
Fang
Fang
F
Murray
Scott O
SO
Kersten
Daniel
D
D001931:Brain Mapping; D015350:Contrast Sensitivity; D005403:Fixation, Ocular; D006801:Humans; D008027:Light; D008279:Magnetic Resonance Imaging; D010775:Photic Stimulation; D014793:Visual Cortex / Q000502:physiology / Q000528:radiation effects*