Voices Only They Hear: Scientists May Finally Know the Source

The Core Problem of Auditory Hallucinations: A Biomarker for Schizophrenia Breakthrough

When you hear a voice in your head, you typically know who it belongs to. It’s usually just your own voice—a phenomenon we call inner speech.

“Inner speech is the voice in your head that silently describes your thoughts—what you’re doing, planning, or noticing,” explains Professor Thomas Whitford from the University of New South Wales in Sydney.

Most of us experience this daily, often without realizing it. However, for individuals suffering from schizophrenia, this process can unfold in a drastically different way. Professor Whitford’s team decided to examine this difference, publishing their findings in the prestigious journal Schizophrenia Bulletin.

The Science Behind Hearing Voices

One of the most common symptoms of schizophrenia is auditory hallucinations—patients hear voices that others cannot. These often take the form of comments, commands, or conversations, which can be terrifying for the patient.

Australian researchers decided to test whether these “voices in the head” could be a disrupted form of inner speech. This is a situation where the brain mistakenly interprets its own internally generated thoughts as sounds coming from an external source.

The Australian Study on Inner vs. Outer Speech

The experiment included 142 participants. Some suffered from schizophrenia and experienced auditory hallucinations. Others had the diagnosis but did not hear voices. The rest were entirely healthy.

The task prepared by the researchers seemed straightforward. Participants were asked to imagine silently pronouncing the syllable “bah” or “bih” precisely when one of these sounds was played through headphones. Crucially, they didn’t know if the sound they heard would match the sound they “spoke” in their mind.

Meanwhile, an electroencephalogram (EEG) recorded their brain activity with immense precision.

What the Results Revealed

The results showed that in healthy individuals, the brain successfully distinguishes an external sound from one resulting from inner speech. However, this was not the case for participants with schizophrenia—their brains failed to recognize the difference.

This is key: This failure to self-monitor explains why people with the disease hear voices—their brains incorrectly interpret their own thoughts as external sounds.

A Major Step Toward Objective Diagnosis

Until now, schizophrenia diagnosis relied mainly on behavioral observation and patient interviews. A robust, biological indicator (biomarker) that would allow objective identification of the disease was missing.

Professor Whitford’s team’s discovery could change that. The measurement of brain activity during the distinction between inner and outer speech revealed clear differences between healthy and affected individuals.

“This type of measurement has tremendous potential as a biomarker for schizophrenia development,” emphasizes Prof. Whitford.

Researchers now plan to test whether this method can predict the risk of psychosis before the first symptoms appear. If successful, psychiatrists will gain a powerful tool for the early schizophrenia diagnosis and more effective treatment.

What This Means for the Future of Psychiatry

This new discovery opens the door to a completely different perspective on schizophrenia. It shifts the view from a puzzle of the human psyche to a measurable disorder of brain function.

If further studies confirm these results, it is possible that within a few years, schizophrenia diagnosis will be based not only on patient interviews but also on objective neurological tests. This is a milestone toward better understanding, treating, and—potentially—preventing one of the most mysterious mental illnesses.

Read this article in Polish: Głosy, których nikt inny nie słyszy. Naukowcy już wiedzą skąd się biorą