title: Compromised late-stage motion processing in schizophrenia.
abstract: BACKGROUND
  Visual motion processing is compromised in schizophrenia, as shown in deficient velocity discrimination. Processing of motion signals comprises progressive stages along the geniculate-striate-extrastriate-cortex pathway. Based on neurophysiologic and brain lesion studies, a velocity discrimination deficit can implicate early-stage motion processing if it is contrast-dependent or late-stage motion processing if it is contrast-independent.
  
  
  METHODS
  To determine which stage underlies the deficient velocity discrimination in schizophrenia, we examined the effects of visual contrast on velocity discrimination. We measured velocity discrimination thresholds in schizophrenia patients (n = 34) and normal control subjects (n = 17) at both low and high contrasts, using each subject's contrast detection threshold to equate contrast levels.
  
  
  RESULTS
  Schizophrenia patients showed poor velocity discrimination that improved little with high contrast, whereas normal control subjects showed enhanced velocity discrimination with increased contrast.
  
  
  CONCLUSIONS
  The finding that the velocity discrimination deficit in schizophrenia is independent of contrast modulation implicates the later, rather than the earlier, stages of motion processing, which is mediated in the extrastriate cortex.
authors.affiliation: Department of Psychiatry, Harvard Medical School and McLean Hospital, Mailman Research Center, 115 Mill Street, Belmont, MA 02478, USA.
authors.forename: Yue
authors.initials: Y
authors.lastname: Chen
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Levy
authors.forename: Summer
authors.initials: S
authors.lastname: Sheremata
authors.forename: Philip S
authors.initials: PS
authors.lastname: Holzman
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016022:Case-Control Studies; D015350:Contrast Sensitivity / Q000502:physiology*; D004056:Differential Threshold / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009039:Motion Perception / Q000502:physiology*; D009483:Neuropsychological Tests; D010468:Perceptual Disorders / Q000209:etiology*; D010775:Photic Stimulation / Q000379:methods; D012559:Schizophrenia / Q000150:complications*; D012684:Sensory Thresholds / Q000502:physiology; D013223:Statistics as Topic; D013997:Time Factors