title: Is motion perception deficit in schizophrenia a consequence of eye-tracking abnormality?
abstract: BACKGROUND
  Studies have shown that schizophrenia patients have motion perception deficit, which was thought to cause eye-tracking abnormality in schizophrenia. However, eye movement closely interacts with motion perception. The known eye-tracking difficulties in schizophrenia patients may interact with their motion perception.
  
  
  METHODS
  Two speed discrimination experiments were conducted in a within-subject design. In experiment 1, the stimulus duration was 150 msec to minimize the chance of eye-tracking occurrence. In experiment 2, the duration was increased to 300 msec, increasing the possibility of eye movement intrusion. Regular eye-tracking performance was evaluated in a third experiment.
  
  
  RESULTS
  At 150 msec, speed discrimination thresholds did not differ between schizophrenia patients (n = 38) and control subjects (n = 33). At 300 msec, patients had significantly higher thresholds than control subjects (p = .03). Furthermore, frequencies of eye tracking during the 300 msec stimulus were significantly correlated with speed discrimination in control subjects (p = .01) but not in patients, suggesting that eye-tracking initiation may benefit control subjects but not patients. The frequency of eye tracking during speed discrimination was not significantly related to regular eye-tracking performance.
  
  
  CONCLUSIONS
  Speed discrimination, per se, is not impaired in schizophrenia patients. The observed abnormality appears to be a consequence of impairment in generating or integrating the feedback information from eye movements. This study introduces a novel approach to motion perception studies and highlights the importance of concurrently measuring eye movements to understand interactions between these two systems; the results argue for a conceptual revision regarding motion perception abnormality in schizophrenia.
authors.affiliation: Department of Psychiatry, Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, Maryland 21228, USA. ehong@mprc.umaryland.edu
authors.forename: L Elliot
authors.initials: LE
authors.lastname: Hong
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Turano
authors.forename: Hugh B
authors.initials: HB
authors.lastname: O'Neill
authors.forename: Lei
authors.initials: L
authors.lastname: Hao
authors.forename: Ikwunga
authors.initials: I
authors.lastname: Wonodi
authors.forename: Robert P
authors.initials: RP
authors.lastname: McMahon
authors.forename: Gunvant K
authors.initials: GK
authors.lastname: Thaker
mesh_terms: D000293:Adolescent; D000328:Adult; D004192:Discrimination, Psychological / Q000502:physiology; D005260:Female; D005403:Fixation, Ocular; D006801:Humans; D008297:Male; D008875:Middle Aged; D009039:Motion Perception / Q000502:physiology*; D015835:Ocular Motility Disorders / Q000209:etiology* / Q000503:physiopathology*; D011597:Psychomotor Performance / Q000502:physiology*; D011698:Pursuit, Smooth; D012565:Schizophrenic Psychology; D013702:Temporal Lobe / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology; D055815:Young Adult