Evaluation of speech misattribution bias in schizophrenia

The attribution of self-generated speech to others could explain the experience of verbal hallucinations. To test this hypothesis, we developed a task to simultaneously evaluate (A) operations of self-other distinction and (B) operations that have the same cognitive demands as in A apart from self-other distinction. By adjusting A to B, operations of self-other distinction were specifically evaluated.

Thirty-nine schizophrenia patients and 26 matched healthy controls were required to distinguish between self-generated, other-generated and non-generated (self or other) sentences. The sentences were in the first, second or third person and were read in a male or female voice in equal proportions. Mixed multi-level logistic regression models were used to investigate the effect of group, sentence source, pronoun and gender of the heard sentences on response accuracy.

Patients differed from controls in the recognition of self-generated and other-generated sentences but not in general recognition ability. Pronoun was a significant predictor of response accuracy but without any significant interaction with group. Differences in the gender of heard sentences were not significant. Misattribution bias differentiated groups only in the self-other direction.

These data support the theory that misattribution of self-generated speech to others could result in verbal hallucinations. The syntactic (pronoun) factor could impact self-other distinction in subtypes of verbal hallucinations that are phenomenologically defined whereas the acoustic factor (gender of heard speech) is unlikely to affect self-other distinction.