title: Elementary sensory deficits in schizophrenia indexed by impaired visual mismatch negativity.
abstract: BACKGROUND
  Mismatch negativity (MMN) is an automatic brain response to unexpected events. It represents a prediction error (PE) response, reflecting the difference between the sensory input and predictions. While deficits in auditory MMN are well known in schizophrenia, only few studies investigated impairments in predictive visual processing in schizophrenia. These studies used complex stimuli such as motion direction and emotional facial expressions. Here we studied whether automatic predictive processing of elementary features such as orientation is also impaired in schizophrenia.
  
  
  METHODS
  Altogether 28 patients with schizophrenia and 27 healthy controls matched in age, gender, and education participated in the study. EEG was recorded using 128 channels in the two experimental blocks. Using an oddball paradigm, horizontal stripes of Gabor patches were presented as frequent standards and vertical stripes as rare deviants in one block. Stimulus probabilities were swapped in the other block. Mismatch responses were obtained by subtracting responses to standard from those to deviant stimuli.
  
  
  RESULTS
  We found significant mismatch responses in healthy controls but not in patients in the prefrontal and occipital-parietal regions in the 90-200ms interval. Furthermore patients showed significantly decreased deviant minus standard difference waveforms relative to controls in the same regions with moderate to large effect sizes.
  
  
  CONCLUSIONS
  Our findings demonstrate that predictive processing of unattended low-level visual features such as orientation is impaired in schizophrenia. Our results complement reports of sensory deficits found in tasks requiring attentive processing and suggest that deficits are present in automatic visual sensory processes putatively mediated by glutamatergic functioning.
authors.affiliation: Department of Psychiatry and Psychotherapy, Semmelweis University, Balassa 6, H-1083 Budapest, Hungary. Electronic address: farkas.kinga@med.semmmelweis-univ.hu.
authors.forename: Kinga
authors.initials: K
authors.lastname: Farkas
authors.affiliation: Translational Neuromodeling Unit (TNU), Institute for Biomedical Engineering, University of Zurich & ETH Zurich, ETZ F 95, Gloriastrasse 35, CH-8092 Zurich, Switzerland; Laboratory for Social and Neural Systems Research, Department of Economics, University of Zurich, Rämistrasse 100, CH-8091 Zurich, Switzerland.
authors.forename: Gábor
authors.initials: G
authors.lastname: Stefanics
authors.affiliation: Department of Psychiatry and Psychotherapy, Semmelweis University, Balassa 6, H-1083 Budapest, Hungary.
authors.forename: Csilla
authors.initials: C
authors.lastname: Marosi
authors.affiliation: Department of Psychiatry and Psychotherapy, Semmelweis University, Balassa 6, H-1083 Budapest, Hungary.
authors.forename: Gábor
authors.initials: G
authors.lastname: Csukly
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology*; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D010775:Photic Stimulation; D012559:Schizophrenia / Q000503:physiopathology*; D012565:Schizophrenic Psychology; D014796:Visual Perception / Q000502:physiology*
keywords: EEG; ERP; MMN; Perceptual prediction error; Predictive coding; Schizophrenia; Visual mismatch negativity