Referential delusions of communication and interpretations of gestures.

Gestures are an important aspect of non-verbal communication, but people with schizophrenia have poor comprehension of them. However, the tests of gesture comprehension that have been used present only scenes in which interpersonal meaning is communicated, though there is evidence that people with psychotic disorders tend to perceive communications where none were intended. Such mistakes about non-verbal behaviour are the hallmark of a subtype of delusions of reference identified as delusions of communication. Thus we hypothesised that patients with delusions of communication would tend to misinterpret incidental movements as gestures and, since delusions are often derogatory to the self, they would also tend to misinterpret gestures as insulting. Patients with acute psychotic symptoms (n=64) were recruited according to a 2 x 2 design (presence vs. absence of delusions of communication by presence vs. absence of auditory hallucinations). They, and 57 healthy controls, were presented with 20 brief video clips in which an actor either made a well-known gesture or an incidental movement. After each clip, they selected one of four interpretations: a correct interpretation if a gesture had been presented; the interpretation of a different gesture; an insulting interpretation; no gesture intended (correct for incidental movements). The patients made significantly more errors of all kinds than the controls, perceived significantly more of the incidental movements as gestures, and selected significantly more insulting interpretations of the clips. These differences between patients and controls were almost wholly due to patients with delusions of communication. These results suggest that the difficulties that people with delusions of communication experience in understanding gestures can be explained, at least in part, by the misattribution of self-generated internal events to external sources.