title: Reduced contextual effects on visual contrast perception in schizophrenia and bipolar affective disorder.
abstract: BACKGROUND
  The salience of a visual stimulus is often reduced by nearby stimuli, an effect known as surround suppression of perceived contrast, which may help in locating the borders of an object. Weaker surround suppression has been observed in schizophrenia but it is unclear whether this abnormality is present in other mental disorders with similar symptomatology, or is evident in people with genetic liability for schizophrenia.
  
  
  METHODS
  By examining surround suppression among subjects with schizophrenia or bipolar affective disorder, their unaffected biological relatives and healthy controls we sought to determine whether diminished surround suppression was specific to schizophrenia, and if subjects with a genetic risk for either disorder would show similar deficits. Measuring perceived contrast in different surround conditions also allowed us to investigate how this suppression depends on the similarity of target and surrounding stimuli.
  
  
  RESULTS
  Surround suppression was weaker among schizophrenia patients regardless of surround configuration. Subjects with bipolar affective disorder showed an intermediate deficit, with stronger suppression than in schizophrenia but weaker than control subjects. Surround suppression was normal in relatives of both patient groups. Findings support a deficit in broadly tuned (rather than sharply orientation- or direction-selective) suppression mechanisms.
  
  
  CONCLUSIONS
  Weak broadly tuned suppression during visual perception is evident in schizophrenia and bipolar affective disorder, consistent with impaired gain control related to the clinical expression of these conditions.
authors: Graduate Program in Neuroscience,University of Minnesota,Minneapolis, MN,USA.
authors: M-P
authors: MP
authors: Schallmo
authors: Veterans Affairs Medical Center,Minneapolis, MN,USA.
authors: S R
authors: SR
authors: Sponheim
authors: Department of Psychology,University of Minnesota,Minneapolis, MN,USA.
authors: C A
authors: CA
authors: Olman
mesh_terms: D000328:Adult; D001714:Bipolar Disorder / Q000235:genetics*; D016022:Case-Control Studies; D015350:Contrast Sensitivity / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009949:Orientation; D010775:Photic Stimulation; D012559:Schizophrenia / Q000235:genetics*; D014793:Visual Cortex / Q000503:physiopathology*
keywords: Contextual modulation; gain control; genetic liability; surround suppression; unaffected relatives