Schizophrenia Research
Volume 100, Issue 1 , Pages 144-152, March 2008

Examining encoding imprecision in spatial working memory in schizophrenia

  • Johanna C. Badcock

      Affiliations

    • 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
    • Corresponding Author InformationCorresponding author. Centre for Clinical Research in Neuropsychiatry/Graylands Hospital, Private Mail Bag No 1, Claremont WA 6910, Australia. Tel.: +61 8 9347 6429; fax: +61 8 9384 5128.
    • ,
  • David R. Badcock

      Affiliations

    • School of Psychology, University of Western Australia, School of Psychology, University of Western Australia, 35 Stirling Hwy, Crawley, WA, 6009, Australia
    • ,
  • Christina Read

      Affiliations

    • 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
    • ,
  • Assen Jablensky

      Affiliations

    • 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

Received 7 May 2007; received in revised form 2 August 2007; accepted 2 August 2007. published online 05 September 2007.

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.

Method

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 (°) 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°.

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.

Keywords: Schizophrenia, Working memory, Encoding, Maintenance, Delayed response, Cognition

 

PII: S0920-9964(07)00337-4

doi:10.1016/j.schres.2007.08.005

Schizophrenia Research
Volume 100, Issue 1 , Pages 144-152, March 2008

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