title: Reduced crowding and poor contour detection in schizophrenia are consistent with weak surround inhibition.
abstract: BACKGROUND
  Detection of visual contours (strings of small oriented elements) is markedly poor in schizophrenia. This has previously been attributed to an inability to group local information across space into a global percept. Here, we show that this failure actually originates from a combination of poor encoding of local orientation and abnormal processing of visual context.
  
  
  METHODS
  We measured the ability of observers with schizophrenia to localise contours embedded in backgrounds of differently oriented elements (either randomly oriented, near-parallel or near-perpendicular to the contour). In addition, we measured patients' ability to process local orientation information (i.e., report the orientation of an individual element) for both isolated and crowded elements (i.e., presented with nearby distractors).
  
  
  RESULTS
  While patients are poor at detecting contours amongst randomly oriented elements, they are proportionally less disrupted (compared to unaffected controls) when contour and surrounding elements have similar orientations (near-parallel condition). In addition, patients are poor at reporting the orientation of an individual element but, again, are less prone to interference from nearby distractors, a phenomenon known as visual crowding.
  
  
  CONCLUSIONS
  We suggest that patients' poor performance at contour perception arises not as a consequence of an "integration deficit" but from a combination of reduced sensitivity to local orientation and abnormalities in contextual processing. We propose that this is a consequence of abnormal gain control, a phenomenon that has been implicated in orientation-selectivity as well as surround suppression.
authors.affiliation: Department of General Psychology, University of Padua, Padua, Italy. valentina.robol@gmail.com
authors.forename: Valentina
authors.initials: V
authors.lastname: Robol
authors.forename: Marc S
authors.initials: MS
authors.lastname: Tibber
authors.forename: Elaine J
authors.initials: EJ
authors.lastname: Anderson
authors.forename: Tracy
authors.initials: T
authors.lastname: Bobin
authors.forename: Patricia
authors.initials: P
authors.lastname: Carlin
authors.forename: Sukhwinder S
authors.initials: SS
authors.lastname: Shergill
authors.forename: Steven C
authors.initials: SC
authors.lastname: Dakin
mesh_terms: D000328:Adult; D005260:Female; D005556:Form Perception; D006801:Humans; D007266:Inhibition, Psychological; D008297:Male; D008875:Middle Aged; D009949:Orientation; D010364:Pattern Recognition, Visual; D010775:Photic Stimulation; D012559:Schizophrenia / Q000503:physiopathology*