Background: Cognitive models propose that auditory verbal hallucinations arise through defective self-monitoring and external attribution of inner speech. We used a paradigm that engages verbal self-monitoring to examine how deficits in this process are related to symptoms and diagnosis in patients with psychosis.
Method: We tested 45 patients with schizophrenia. Fifteen had current auditory hallucinations, 15 had a history of (but no current) auditory hallucinations, and 15 had delusions but neither current nor previous hallucinations. We also tested 10 patients with affective psychosis and current auditory hallucinations, and 20 healthy volunteers. Participants read single adjectives aloud while the source and the pitch of the on-line auditory verbal feedback was manipulated, then immediately identified the source of the speech they heard ('self'/'other'/'unsure').
Results: When reading aloud with distorted feedback of their own voice, patients with schizophrenia who had auditory hallucinations were more likely than controls to misidentify its source as 'other'. Patients with delusions but no current hallucinations displayed a similar deficit, although there was a trend for this to be less marked. Patients with a history of hallucinations did not differ from controls. Patients with hallucinations in the context of an affective disorder made more unsure responses rather than misattributions.
Conclusions: Difficulty with source monitoring was related to the acute psychotic state rather than a predisposition to hallucinations, and was evident in patients with affective psychosis as well as schizophrenia. External misattribution of source may reflect an impairment in verbal self-monitoring and/or the appraisal of ambiguous sensory material.