Schizophrenia’s auditory hallucinations may result from the brain‘s failure to recognize its own inner monologue, according to new research by Australian psychologists.
The study, conducted at UNSW Sydney and published in Schizophrenia Bulletin, marks a major step toward identifying physical indicators unique to schizophrenia. Currently, no existing medical test—such as a blood test or brain scan—can objectively isolate the disorder.
Auditory Hallucinations
“Inner speech is the voice in your head that silently narrates your thoughts – what you’re doing, planning, or noticing,” said lead author Professor Thomas Whitford. “Most people experience inner speech regularly, often without realising it, though there are some who don’t experience it at all.”
“Our research shows that when we speak – even just in our heads – the part of the brain that processes sounds from the outside world becomes less active,” Whitford continued. “This is because the brain predicts the sound of our own voice. But in people who hear voices, this prediction seems to go wrong, and the brain reacts as if the voice is coming from someone else.”
Whitford is not the first researcher to suspect that auditory hallucinations common to schizophrenia sufferers represent misattributed instances of one’s own internal monologue, but this work finally provides some confirmation for the theory.
“This idea’s been around for 50 years, but it’s been very difficult to test because inner speech is inherently private,” Whiteford explained.
Schizophrenia and the Brain
The study involved 142 participants, divided into three groups based on their schizophrenia symptoms. The first group included individuals who had experienced recent auditory hallucinations within the past week. The second group consisted of people living with schizophrenia who had no recent or historical hallucinations, and the third was a control group of healthy participants without schizophrenia.
Researchers used electroencephalography (EEG) to measure participants’ brainwave activity while they followed audio instructions through headphones. They were told to imagine saying “bah” or “bih” as those sounds played. The EEG data revealed stark differences across the three groups.
Schizophrenia Test Results
Participants with no history of auditory hallucinations showed suppressed activity in the auditory cortex during the matching sound task—mirroring the brain’s natural response when speaking aloud. By contrast, those who had recently experienced hallucinations exhibited heightened brain activity, indicating that their brains failed to predict their own inner speech.
“Their brains reacted more strongly to inner speech that matched the external sound, which was the exact opposite of what we found in the healthy participants,” Prof. Whitford explained. “This reversal of the normal suppression effect suggests that the brain’s prediction mechanism may be disrupted in people currently experiencing auditory hallucinations, which may cause their own inner voice to be misinterpreted as external speech.”
Participants with schizophrenia but no recent hallucinations showed responses between the other two groups, suggesting that even less severe cases may be detectable through this new method.
Working Toward Early Treatment
The team’s findings provide the most direct support yet for the theory that schizophrenia involves misattributed inner speech.
“It was always a plausible theory – that people were hearing their own thoughts spoken out loud – but this new approach has provided the strongest and most direct test of this theory to date,” Prof. Whitford said.
Moving forward, Whitford plans to investigate whether these measurements align with individuals transitioning into psychosis. By developing an objective physical to determine a patient’s psychosis risk, care providers could provide essential early treatment.
“This sort of measure has great potential to be a biomarker for the development of psychosis,” Prof. Whitford concluded. “Ultimately, I think that understanding the biological causes of the symptoms of schizophrenia is a necessary first step if we hope to develop new and effective treatments.”
The paper, “Corollary Discharge Dysfunction to Inner Speech and Its Relationship to Auditory Verbal Hallucinations in Patients with Schizophrenia Spectrum Disorders,” appeared in Schizophrenia Bulletin on October 21, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.