Responses to lightness variations in early human visual cortex

Curr Biol. 2007 Jun 5;17(11):989-93. doi: 10.1016/j.cub.2007.05.005.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Brain Mapping
  • Contrast Sensitivity
  • Fixation, Ocular
  • Humans
  • Light*
  • Magnetic Resonance Imaging
  • Photic Stimulation
  • Visual Cortex / physiology
  • Visual Cortex / radiation effects*