Theory of mind and its relation to schizotypy

Frith (1992) suggested that many psychotic symptoms are associated with impaired theory of mind (ToM), the ability to represent the mental states of others. Langdon and Coltheart (1999) found an association in a nonclinical adult population between schizotypal traits and poorer ToM on a picture-sequencing task. The present study attempted to replicate and extend this finding using a ToM story task.

A total of 62 nonclinical individuals completed a schizotypy questionnaire (the Oxford-Liverpool Inventory of Feelings and Experiences; O-LIFE) and a set of ToM stories. Matched "physical" control stories were administered to control for general reasoning ability. Executive function and current verbal IQ were assessed using the Cognitive Estimates Test and the Quick Test, respectively.

Schizotypal traits analogous to positive symptoms of schizophrenia (UE scale of the O-LIFE) predicted poorer scores on the ToM task, but were unrelated to scores on physical stories. Individuals with high scores for total schizotypy on the O-LIFE did not differ in ToM from those with low total scores. There was no association between poorer ToM and schizotypal traits analogous to the "behavioural signs" of schizophrenia. Executive function and verbal IQ did not significantly predict story scores.

Positive schizotypal traits in the normal population are associated with subtle impairments in ToM, independent of reasoning ability, executive function, or verbal IQ. A strong association between poor ToM and "behavioural signs" may only appear in studies of schizophrenic patients, and not in studies of nonclinical individuals. The findings are discussed in relation to Frith's (1992) cognitive neuropsychological model of schizophrenia.