Abstract:
Following the link first suggested by Frith (1992), interest in the relationship between theory of mind ability and schizophrenia has grown considerably. At the same time, evidence has been mounting for more general deficits and biases in social cognition among individuals experiencing either psychosis or sub-clinical schizotypal symptoms. The broad aim of the present thesis was to investigate the relationships between theory of mind, folk psychological explanations of intentional interpersonal actions and paranoid ideation in both clinical and non-clinical samples. Two theories formed the basis of this investigation - Frith's (1992) theory of mind account of schizophrenia (and persecutory delusions), and Bentall et al.'s (1994) theory that persecutory beliefs reflect a selfdefensive explanatory bias. Specific goals included examining folk explanations of behaviour in order to ideation idiosyncratic features of the folk psychology associated with paranoia. A second goal was to determine whether these features could be explained by performance on theory of mind tasks or by general delusional ideation. Third, drawing on continuity models of psychosis, this thesis also sought to ascertain whether the relationships between sub-clinical paranoid ideation, theory of mind performance, and folk psychological explanations, were comparable to those found with full-blown persecutory delusions.
Five studies were conducted in order to achieve these goals - the first three with student samples, the second with a sample from the general population, and the final study with individuals with schizophrenia. There was support for the presence of theory of mind deficits among both clinical and non-clinical samples experiencing psychotic and psychotic-like phenomena respectively. These deficits were associated with general delusional ideation in the non-clinical sample but were specifically linked to persecutory delusions in the clinical sample. There was also evidence that paranoia and theory of mind deficits were associated with generating more explanations for intentional interpersonal actions. This effect varied according to the perspective of the explainer. The self-defence account of paranoid beliefs received some support in the student studies, but there was no support for defensive explanatory biases among the clinical sample with persecutory delusions. These results are discussed in relation to the two theoretical models that underpin this research.
