title: Examining encoding imprecision in spatial working memory in schizophrenia.
abstract: BACKGROUND
  Visuospatial working memory is not a unitary sketch pad but comprises independent dimensions of target distance and direction and at least two levels of detail (fine-grained and category level). The aim of this study was to examine these multiple aspects of encoding in patients with schizophrenia using a modified delayed response task.
  
  
  METHODS
  42 patients with schizophrenia and 48 healthy controls pointed, as accurately as possible from a fixed starting position, to the visual location of target stimuli presented to a touch-sensitive screen. An adaptive staircase procedure was used to equate stimulus duration for each individual. Encoding accuracy and maintenance of distance (mm) and direction ( degrees ) information was examined following a 0-second (immediate) or 4-second (unfilled) delay. Analyses utilized both absolute (unsigned) and signed data.
  
  
  RESULTS
  The results showed that the average duration required to detect a target was significantly longer in patients than controls. When stimulus duration was equated, (a) the absolute accuracy of distance and direction responses was not significantly different between groups at 0-second delay but was significantly reduced at 4-second delay in patients with schizophrenia, and (b) signed direction errors at 4-second delay were significantly different between groups at stimulus angles greater than 90 degrees .
  
  
  CONCLUSIONS
  The findings challenge previous suggestions of deficits in fine-grained encoding of spatial information in schizophrenia but confirm a difficulty maintaining both direction and distance details in working memory. Imprecision in spatial memory in schizophrenia also introduced greater bias from category level (prior) representations, especially in left hemi-space.
authors.affiliation: Centre for Clinical Research in Neuropsychiatry/Graylands Hospital and School of Psychiatry and Clinical Neurosciences, University of Western Australia, John XXIII Avenue, Mt. Claremont, WA, 6010, Australia. jobad@cyllene.uwa.edu.au
authors.forename: Johanna C
authors.initials: JC
authors.lastname: Badcock
authors.forename: David R
authors.initials: DR
authors.lastname: Badcock
authors.forename: Christina
authors.initials: C
authors.lastname: Read
authors.forename: Assen
authors.initials: A
authors.lastname: Jablensky
mesh_terms: D000328:Adult; D003072:Cognition Disorders / Q000175:diagnosis* / Q000523:psychology; D035061:Control Groups; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008569:Memory Disorders / Q000175:diagnosis* / Q000523:psychology; D008570:Memory, Short-Term; D008875:Middle Aged; D009483:Neuropsychological Tests / Q000706:statistics & numerical data*; D010775:Photic Stimulation; D011930:Reaction Time; D015203:Reproducibility of Results; D012559:Schizophrenia / Q000175:diagnosis*; D012565:Schizophrenic Psychology; D013028:Space Perception