Conversational conduct and the symptoms of schizophrenia.

In an attempt to refine further the argument that certain patients with schizophrenia have problems understanding the mental states of other people, appreciation of the Gricean maxims of quantity, quality, and relation, and the more contextually specific need to be polite was examined amongst patients differing in their current symptom profiles. Five sets of five stories were given to the subjects who had to choose the likely final piece of speech of one of the characters. Subjects chose from two alternatives, one adhered to the rule under question whereas the other flouted that rule. Patients with negative symptoms were inclined to flout all maxims with the exception of the maxim of relation which was adhered to by all groups. It is argued that these patients have a severe ''theory of mind'' deficit that encompasses knowledge of conversational rules. The performance of patients with paranoid delusions was more selective in that they often failed to respond in a polite fashion when this was indicated by the context but performed at a level with controls on the stories involving the original Gricean maxims. These effects were largely independent of current intellectual level. The results suggest that although patients with negative behavioural signs suffer a ''theory of mind'' deficit similar to that seen in autism, those with paranoid symptoms have a more specific ''online'' mentalising deficit which becomes evident only when the skill is challenged by situations where context-dependent behaviour is determined by an appreciation of another's mental state.