Increased Reporting of Speech in Degraded Stimuli in Schizophrenia: A Case Control Study with Sine-Wave-Speech

People who hear voices may have strong prior expectations of speech, so that noisy auditory signals are resolved as speech. Data in non-clinical voice hearers suggest that voice hearing may involve sensitivity to speech in degraded stimuli. This has yet to be examined in people with schizophrenia (SZ).

In this case-control study, we presented sine-wave-speech (SWS; made by replacing the formants in speech with pure tone whistles) to people with SZ (n = 63) and healthy controls (HC; n = 27). SWS is typically unintelligible on first exposure. However, once the listener knows that it is potentially intelligible as speech (by exposure to the unaltered speech template, which thus serves as a prior expectation), relatively high levels of comprehension are achieved. Our participants first listened to intelligible and unintelligible SWS and reported whether they heard speech. They were then exposed to the speech templates, and then the first phase was repeated.

Compared to HC, people with SZ reported hearing more speech before template exposure. The Reveal increased both groups' false alarms and reporting of speech, but there was no interaction with group. Change in hit rates after the Reveal correlated with hallucinations, which is consistent with a greater influence of the priors enhancement in SZ patients who hear voices.

These findings suggest that people with SZ have stronger expectations of speech. This task has validity for hallucinatory voice hearing. It is also simple and convenient to administer, and may prove useful in detecting prodromal risk, as well as acute exacerbation in voice hearing.