Schizophrenia Bulletin Advance Access published online on July 11, 2008
Schizophrenia Bulletin, doi:10.1093/schbul/sbn069
Reasoning Anomalies Associated With Delusions in Schizophrenia
2 Macquarie Centre for Cognitive Science, Macquarie University, NSW, Australia
3 Schizophrenia Research Unit, Sydney South West Area Health, NSW, Australia
4 Cognition and Connectivity panel, Schizophrenia Research Institute, NSW, Australia
5 School of Psychiatry, University of New South Wales, NSW, Australia
1 To whom correspondence should be addressed; tel: +61 2 9850 6733, fax: +61 2 9850 6059, e-mail: robyn{at}maccs.mq.edu.au.
Deluded people differ from nondeluded controls on attributional style questionnaires and probabilistic-reasoning and theory-of-mind (ToM) tasks. No study to date has examined the relations between these 3 reasoning anomalies in the same individuals so as to evaluate their functional independence and potentially inform theories of delusion formation. We did so in 35 schizophrenic patients with a history of delusions, 30 of whom were currently deluded, and 34 healthy controls. Compared with healthy controls, patients showed (a) a jumping-to-conclusions bias and a bias to overadjust when confronted with a change of evidence on probabilistic-reasoning tasks, (b) an excessive externalizing attributional bias, and (c) performance deficits on 3 ToM tasks. Probabilistic-reasoning and ToM measures correlated, while attributional-bias scores were independent of other task measures. A general proneness to delusional ideation correlated with probabilistic-reasoning and ToM measures, while externalizing bias was unrelated to the study measures of delusional ideation. Personalizing bias associated specifically with paranoia across the clinical and nonclinical participants. Findings are consistent with a common underlying mechanism in schizophrenia which contributes to the anomalies on probabilistic-reasoning and ToM tasks associated with delusions. We speculate that this mechanism is impairment of the normal capacity to inhibit "perceived reality" (the evidence of our senses), a capacity that evolved as part of the "social brain" to facilitate intersubjective communication within a shared reality.
Keywords: psychosis / reality distortion / social cognition / belief