title: Preserved local but disrupted contextual figure-ground influences in an individual with abnormal function of intermediate visual areas.
abstract: Visual perception depends not only on local stimulus features but also on their relationship to the surrounding stimulus context, as evident in both local and contextual influences on figure-ground segmentation. Intermediate visual areas may play a role in such contextual influences, as we tested here by examining LG, a rare case of developmental visual agnosia. LG has no evident abnormality of brain structure and functional neuroimaging showed relatively normal V1 function, but his intermediate visual areas (V2/V3) function abnormally. We found that contextual influences on figure-ground organization were selectively disrupted in LG, while local sources of figure-ground influences were preserved. Effects of object knowledge and familiarity on figure-ground organization were also significantly diminished. Our results suggest that the mechanisms mediating contextual and familiarity influences on figure-ground organization are dissociable from those mediating local influences on figure-ground assignment. The disruption of contextual processing in intermediate visual areas may play a role in the substantial object recognition difficulties experienced by LG.
authors.affiliation: UCL Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK. joseph.brooks@ucl.ac.uk
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Brooks
authors.forename: Sharon
authors.initials: S
authors.lastname: Gilaie-Dotan
authors.forename: Geraint
authors.initials: G
authors.lastname: Rees
authors.forename: Shlomo
authors.initials: S
authors.lastname: Bentin
authors.forename: Jon
authors.initials: J
authors.lastname: Driver
mesh_terms: D000377:Agnosia / Q000473:pathology* / Q000503:physiopathology*; D001244:Association; D001931:Brain Mapping; D005625:Frontal Lobe / Q000098:blood supply / Q000503:physiopathology*; D007839:Functional Laterality; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D010100:Oxygen; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011601:Psychophysics; D012660:Semantics; D055815:Young Adult
chemical_list: D010100:Oxygen