title: Enabling global processing in simultanagnosia by psychophysical biasing of visual pathways.
abstract: A fundamental aspect of visual cognition is our disposition to see the 'forest before the trees'. However, damage to the posterior parietal cortex, a critical brain region along the dorsal visual pathway, can produce a neurological disorder called simultanagnosia, characterized by a debilitating inability to perceive the 'forest' but not the 'trees' (i.e. impaired global processing despite intact local processing). This impairment in perceiving the global shape persists even though the ventral visual pathway, the primary recognition pathway, is intact in these patients. Here, we enabled global processing in patients with simultanagnosia using a psychophysical technique, which allowed us to bias stimuli such that they are processed predominantly by the intact ventral visual pathway. Our findings reveal that the impairment in global processing that characterizes simultanagnosia stems from a disruption in the processing of low-spatial frequencies through the dorsal pathway. These findings advance our understanding of the relationship between visuospatial attention and perception and reveal the neural mechanism mediating the disposition to see the 'forest before the trees'.
authors.affiliation: National Institutes of Health, 10 Center Drive, Bethesda, MD 20892-1365, USA. cibu.thomas@nih.gov
authors.forename: Cibu
authors.initials: C
authors.lastname: Thomas
authors.forename: Kestutis
authors.initials: K
authors.lastname: Kveraga
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Huberle
authors.forename: Hans-Otto
authors.initials: HO
authors.lastname: Karnath
authors.forename: Moshe
authors.initials: M
authors.lastname: Bar
mesh_terms: D000328:Adult; D000368:Aged; D000377:Agnosia / Q000150:complications* / Q000209:etiology; D015982:Bias; D001930:Brain Injuries / Q000150:complications / Q000473:pathology; D001931:Brain Mapping; D015350:Contrast Sensitivity; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D010296:Parietal Lobe / Q000000981:diagnostic imaging / Q000473:pathology; D010775:Photic Stimulation; D049268:Positron-Emission Tomography; D011601:Psychophysics; D011602:Psychophysiologic Disorders / Q000209:etiology*; D014795:Visual Pathways; D055815:Young Adult
chemical_list: D019788:Fluorodeoxyglucose F18