Pickup, Graham; (2000) An investigation of schizotypy, 'theory of mind' and 'weak central coherence. Doctoral thesis (D.Clin.Psy), UCL (University College London).

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Abstract

This study investigated two psychological models of schizophrenia using the schizotypy paradigm, which assumes a continuum of psychosis-proneness in the normal population. Model 1 C. Friths (1992) cognitive neuropsychological model of schizophrenia arose from research in autism which showed that autistic people have impairments in theory of mind (ToM), the ability to represent the mental states of oneself and others. In extending this work into schizophrenia, C. Frith suggested that many psychotic symptoms are also associated with impaired ToM. On the basis of this model, it was predicted in the present study that high total scores on a standard measure of schizotypy within the normal population, would be associated with poor performance on tests of ToM. In line with C. Friths (1992) model, it was further expected that the poorest ToM would be associated with high scores for schizotypal traits analogous to behavioural signs of schizophrenia (such as social withdrawal, affective flattening or inappropriate speech and behaviour). Schizotypal traits analogous to the positive symptoms of schizophrenia (e.g. delusions and hallucinations) were expected to be more weakly associated with impaired ToM. Sixty-two normal volunteers completed a standard schizotypy questionnaire (the Oxford- Liverpool Inventory of Feelings and Experiences; O-LIFE), and a standard story test of ToM. A set of physical control stories was also administered to control for variation in participants ability to imagine abstract or hypothetical states of affairs, and to reason and make inferences. Subjects also completed the Cognitive Estimates Test to control for differences in executive function, and the Quick Test to control for verbal IQ. Only limited support was found for C. Friths (1992) model. Individuals scoring high on total schizotypy did not differ significantly in ToM ability from those whose total schizotypy was low. Contrary to C. Friths model, there was no association between poorer ToM and schizotypal traits analogous to the behavioural signs of schizophrenia. However, schizotypal traits analogous to positive symptoms were associated with poorer performance on the ToM task, as predicted by the model. There was no relation between schizotypy and scores on the physical stories, executive function, or verbal IQ tests, and it was concluded that positive schizotypal traits in the normal population are associated with difficulties representing mental states. Discussion focused on the differences between these results and the predictions from C. Friths model. The present data were also contrasted with those of Langdon and Coltheart (1999), whose findings did broadly support the theoretical predictions. It was concluded that differences between the present results and those of Langdon and Coltheart were largely a reflection of differences between the schizotypy questionnaires used in the two studies. It was also argued that a strong association between poor ToM and behavioural signs may only appear in studies of schizophrenic patients, and that the main effect in studies of schizotypy in normals is the association between poorer ToM and scores for positive schizotypal traits. Model 2 U. Frith (1989) suggested that autistic people have a cognitive style of weak central coherence (WCC), whereby they focus on detail at the expense of gestalt or overall meaning. By analogy with C. Friths (1992) extension of the ToM model from autism into schizophrenia, Pickup (1997) argued that psychotic symptoms may be associated with WCC, and found some empirical support for this in a study of schizophrenic patients. On the basis of Pickups hypothesis, it was predicted in the present study that high scores for total schizotypy in the normal population would be associated with WCC, as revealed by the ability to accurately and quickly find hidden objects in embedded figures stimuli. It was further expected that the best task performance would be associated with schizotypal traits analogous to autistic features, i.e. social withdrawal, affective flattening, or inappropriate speech and behaviour. Sixty four normal volunteers completed the O-LIFE schizotypy questionnaire and a new embedded figures test (EFT) designed for adults by Pickup (1997). Ravens Advanced Progressive Matrices were also administered to control for spatial IQ. The tests were given in the same session as the measures of theory of mind discussed above. No support was found for the theoretical predictions. There were no differences in performance on the EFT between participants divided into high and low total schizotypy groups, and none of the individual dimensions of schizotypy were significantly correlated with task performance. It was concluded that no support was found for Pickups (1997) suggestion that the WCC account of autism can be extended into schizophrenia. The implications of this finding and suggestions for future work were discussed.

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