title: The neural correlates of impaired collision avoidance in hemianopic patients.
abstract: OBJECTIVE
  The aim of this study was to assess the brain regions associated with impaired performance in a virtual, dynamic collision avoidance task, in a group of patients with homonymous visual field defects (HVFDs) because of unilateral vascular brain lesions.
  
  
  METHODS
  Overall task performance was quantitatively assessed as the number of collisions while crossing an intersection at two levels of traffic density. Twenty-six patients were divided into two subgroups using the median split method: patients with 'performance above average' (HVFD(A), i.e. lower number of collisions) and patients with 'performance below average' (HVFD(B), i.e. higher number of collisions). In order to identify the anatomical structures that might be specifically affected in HVFD(B) patients but spared in HVFD(A) patients, overlap, subtraction and voxel-based lesion-symptom mapping analyses were performed using the MRIcron software.
  
  
  RESULTS
  No significant difference in collision avoidance between patients with left- and right-hemispheric lesions was revealed. Separate lesion analysis in 12 patients with right- and 14 patients with left-hemispheric lesions showed that the cortical structures associated with impaired collision avoidance were the parieto-occipital region and posterior cingulate gyrus in the right hemisphere and the inferior occipital cortex and parts of the fusiform (occipito-temporal) gyrus in the left hemisphere.
  
  
  CONCLUSIONS
  In the present collision avoidance paradigm, impaired performance of patients with right-hemispheric lesions is associated with damage in the dorsal processing stream and potential impact on the visual spatial working memory (WM), while impaired performance of patients with left-hemispheric lesions is associated with damage in the ventral stream and potential impact on the visual object WM.
authors.affiliation: Centre for Ophthalmology, Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany. e_papage@yahoo.com
authors.forename: Eleni
authors.initials: E
authors.lastname: Papageorgiou
authors.forename: Gregor
authors.initials: G
authors.lastname: Hardiess
authors.forename: Horst
authors.initials: H
authors.lastname: Wiethölter
authors.forename: Hermann
authors.initials: H
authors.lastname: Ackermann
authors.forename: Klaus
authors.initials: K
authors.lastname: Dietz
authors.forename: Hanspeter A
authors.initials: HA
authors.lastname: Mallot
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schiefer
mesh_terms: D000063:Accidents, Traffic; D000328:Adult; D001334:Automobile Driving; D001362:Avoidance Learning / Q000502:physiology*; D001927:Brain Diseases / Q000503:physiopathology*; D003198:Computer Simulation; D004215:Distance Perception / Q000502:physiology; D006423:Hemianopsia / Q000503:physiopathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009039:Motion Perception / Q000502:physiology; D011597:Psychomotor Performance; D013028:Space Perception / Q000502:physiology; D014794:Visual Fields / Q000502:physiology*