Is auditory imagery defective in patients with auditory hallucinations?

Abstract

Background. A variant of the ‘inner speech’ theory of auditory verbal hallucinations in schizophrenia suggests that there is an abnormality of the relationship between the ‘inner voice’ and ‘inner ear’, such that hallucinators are unable to distinguish inner ‘imagined’ speech from real external speech, and so misrecognize inner speech as alien.

Methods. Five experiments were carried out comparing 12 schizophrenic patients who were highly prone to hallucinate, with seven patients who were not, on a series of auditory imagery tasks that are differentially dependent on inner voice/inner ear partnership for successful performance: parsing meaningful letter/number strings; the verbal transformation effect; phoneme judgements; pitch judgements, and homophony and rhyme judgements.

Results. Contrary to our hypothesis, there was no evidence that the group with the propensity to hallucinate were impaired on tasks requiring normal inner ear/inner voice partnership.

Conclusions. Together with previous work indicating no impairment of the phonological loop in patients who hallucinate, these results suggest that inner speech and auditory verbal hallucinations are not connected in a simplistic or direct way. Indeed, a reappraisal of psychological models of hallucinations in general may be warranted.