Misattribution of self-generated speech in relation to hallucinatory proneness and delusional ideation in healthy volunteers.

When patients with hallucinations and delusions encounter their own distorted speech they tend to mistakenly attribute it to someone else. This external misattribution of self-generated material is thought to be associated with 'positive' psychotic symptoms. The aim of the present study was to examine this process in relation to the predisposition to hallucination-like experiences and unusual beliefs in a healthy population. Fifty-seven volunteers completed assessments of hallucination proneness and delusional ideation and performed a source-monitoring task. Participants listened to a series of pre-recorded words for which the source (self/non-self) and acoustic quality (undistorted/distorted) of the speech were varied across trials. Participants indicated whether the words were spoken in their own or another person's voice via a button press. Misattribution errors were greatest when participants made source judgements about their own distorted speech (p < 0.01) and were positively correlated with delusional ideation scores, particularly the level of conviction with which delusional ideas were held (p = 0.03), and there was a trend for a positive correlation with hallucination proneness scores. There was a negative correlation between unsure responses and delusional ideation when participants were processing their own distorted speech (p = -0.03). The misattribution of self-generated speech occurs in healthy individuals with high levels of psychotic-like experiences. This suggests that the same cognitive impairments may underlie psychotic phenomena in healthy individuals as in patients with psychotic disorders, consistent with a continuum model of psychosis.