title: Visual masking as a probe for abnormal gamma range activity in schizophrenia.
abstract: BACKGROUND
  Visual masking procedures assess very early stages of visual perception. Patients with schizophrenia consistently show deficits on visual masking tasks, and these deficits likely reflect vulnerability to schizophrenia. We conducted two experiments to determine whether visual masking procedures can reveal underlying abnormalities in gamma range oscillations in schizophrenia.
  
  
  METHODS
  In the first experiment, we conducted nonlinear modeling of visual masking performance data from 89 male schizophrenic patients and 20 male comparison subjects. In the second experiment, electrophysiological recordings of event-related gamma activity were taken during a visual masking task in a subset of eight patients and seven control subjects.
  
  
  RESULTS
  In the first experiment, nonlinear modeling of the performance data revealed evidence of oscillations in the gamma range (30 and 35 Hz) for the comparison group but not patients. In the second experiment, the comparison group, but not the patients, showed a burst of gamma range activity 200-400 msec following target presentation. The difference between patients and comparison subjects in this time period was significant (p <.05).
  
  
  CONCLUSIONS
  Visual masking procedures can serve as a probe for underlying gamma range activity, which appears to be aberrant in schizophrenia. Perceptual problems in schizophrenia may, at least in part, be due to a failure to establish and/or maintain gamma range oscillations.
authors.affiliation: Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, Los Angeles, California 90024-1759, USA.
authors.forename: Michael Foster
authors.initials: MF
authors.lastname: Green
authors.forename: Jim
authors.initials: J
authors.lastname: Mintz
authors.forename: Dustin
authors.initials: D
authors.lastname: Salveson
authors.forename: Keith H
authors.initials: KH
authors.lastname: Nuechterlein
authors.forename: Bruno
authors.initials: B
authors.lastname: Breitmeyer
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Light
authors.forename: David L
authors.initials: DL
authors.lastname: Braff
mesh_terms: D016022:Case-Control Studies; D004594:Electrophysiology; D005074:Evoked Potentials, Visual; D006801:Humans; D008297:Male; D009778:Occipital Lobe / Q000503:physiopathology*; D010296:Parietal Lobe / Q000503:physiopathology*; D012559:Schizophrenia / Q000503:physiopathology*; D014796:Visual Perception