Inner Speech Misattribution May Explain Auditory Hallucinations in Schizophrenia
Summary: New research from the University of New South Wales provides strong evidence that some auditory verbal hallucinations — hearing voices — arise when the brain fails to identify its own inner speech as self-generated. In healthy people, the brain predicts the sound of inner speech and dampens auditory responses; this predictive suppression appears to be disrupted in people who experience recent hallucinations.
Electroencephalography (EEG) recordings in the study showed that participants with recent auditory hallucinations had stronger, not weaker, auditory responses when their imagined speech matched an external sound. These findings support the long-standing theory that misattributed inner speech contributes to voice hearing and point toward a potential biological marker for identifying psychosis risk.
Key Facts:
- Prediction failure in the brain: The auditory cortex does not suppress responses to self-generated inner speech, which can cause internally produced voice-like experiences to be perceived as external.
- EEG evidence: People with recent auditory verbal hallucinations showed reversed brainwave suppression, with enhanced auditory responses when imagined and heard syllables matched.
- Clinical potential: The effect may serve as a neurophysiological biomarker to help identify people at higher risk of developing psychosis and guide early intervention strategies.
Source: University of New South Wales
Led by psychologists at UNSW Sydney, this study provides the clearest experimental support to date for the hypothesis that some hallucinated voices reflect a breakdown in corollary discharge — the brain mechanism that predicts and attenuates the sensory consequences of our own actions, including inner speech.
Inner speech and predictive suppression
Professor Thomas Whitford of the UNSW School of Psychology explains inner speech as the silent, verbal narration of thoughts — the voice inside your head that comments on what you’re doing, planning, or noticing. In typical brains, forming inner speech triggers a prediction of its auditory properties, and the auditory cortex reduces its response accordingly. This phenomenon is similar to the reduced auditory response we experience when we speak aloud because the brain expects the sound.
However, in individuals currently experiencing auditory verbal hallucinations (AVH), that predictive suppression appears to fail. Instead of reduced auditory activity when imagined and external sounds align, these individuals show an enhancement of auditory responses, making inner speech more likely to be perceived as coming from an external source.
How the study was conducted
The research recruited three groups: 55 people with schizophrenia-spectrum disorders who had AVH in the past week, 44 people with a schizophrenia-spectrum diagnosis but no recent or lifetime AVH, and 43 healthy control participants. During EEG recording sessions, participants listened through headphones to recordings of two simple syllables, “bah” or “bih.” At precise moments they were instructed to imagine saying one of those syllables. On some trials the imagined syllable matched the played sound; on others it did not. In passive trials participants did not imagine a syllable.
Healthy participants showed the expected suppression: when the heard syllable matched the imagined one, auditory cortex activity (measured by components such as the N1 response) was reduced compared with mismatch and passive conditions. This pattern indicates an intact predictive mechanism that attenuates responses to predicted, self-generated sounds.
In contrast, participants who had experienced recent AVH demonstrated the opposite pattern. Their N1 amplitude was enhanced when the imagined syllable matched the external sound, indicating a reversal of the normal suppression effect. The schizophrenia-spectrum group without recent AVH showed intermediate results, falling between healthy controls and those with active hallucinations.
Interpretation and clinical implications
These results strengthen the interpretation that some auditory hallucinations stem from a failure of the brain’s corollary discharge mechanism: inner speech is generated but not recognized as self-produced, so it is perceived as external. The study supplies one of the most direct empirical tests of this theory by using an electrophysiological marker of inner speech to compare neural responses across groups.
The authors note that this inner-speech-induced suppression effect could have translational value. If reliably measured, the reversal or loss of suppression might serve as a neurobiological indicator — a biomarker — of vulnerability to psychosis. Such a biomarker could help identify individuals at higher risk and enable earlier, targeted interventions that aim to prevent or mitigate full-blown psychotic episodes.
Professor Whitford emphasizes that understanding the biological mechanisms that underlie symptoms like hearing voices is an essential step toward developing more effective, mechanism-based treatments for schizophrenia-spectrum disorders.
Key Questions Answered:
A: The study indicates that hearing voices can occur when the brain misidentifies its own inner speech as external speech because predictive mechanisms that normally tag self-generated sounds fail.
A: Researchers used EEG to compare auditory-evoked potentials when participants imagined syllables while hearing matching or mismatching external sounds, revealing reversed suppression effects in those experiencing voices.
A: Demonstrating a measurable neural difference linked to hallucinations opens the possibility of objective biomarkers that could identify people at risk of psychosis earlier and inform targeted interventions.
About this research
Author: Lachlan Gilbert, University of New South Wales
Source: University of New South Wales
Contact: Lachlan Gilbert, University of New South Wales
Image credit: Neuroscience News
Original Research (open access): Corollary discharge dysfunction to inner speech and its relationship to auditory verbal hallucinations in patients with schizophrenia spectrum disorders — Thomas Whitford et al., Schizophrenia Bulletin.
Abstract (summary)
Background and hypothesis: Auditory-verbal hallucinations (AVH) are a core symptom of schizophrenia-spectrum disorders. A longstanding hypothesis proposes some AVH reflect misperceived inner speech due to corollary-discharge dysfunction. This study tested that idea using electrophysiological markers tied to inner speech.
Design: Participants produced an inner syllable at a specified time while an audible syllable was presented; the inner syllable either matched or mismatched the auditory stimulus. EEG measured auditory-evoked potential components (N1, P2, P3) across three groups: patients with current AVH (n=55), patients without current AVH (n=44), and healthy controls (n=43).
Results: Healthy controls displayed the expected reduction in N1 amplitude when imagined and heard syllables matched. The group with current AVH showed the opposite: an enhanced N1 amplitude in the match condition. The non-hallucinating patient group showed intermediate effects.
Conclusions: The findings support the theory that AVH are linked to abnormalities in the normal suppressive processes associated with inner speech. The inner speaking–induced suppression effect may have utility as a biomarker for schizophrenia-spectrum disorders and for indexing the tendency toward AVH at more severe levels of dysfunction.