Examining encoding imprecision in spatial working memory in schizophrenia
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.
aCentre 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
bSchool of Psychology, University of Western Australia, School of Psychology, University of Western Australia, 35 Stirling Hwy, Crawley, WA, 6009, Australia
Corresponding 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.
ABSTRACT