The brains of healthy people who hear voices may have an enhanced ability to detect meaningful speech patterns in ambiguous sounds, according to new research led by Durham University and University College London (UCL).
Many people who hear voices, also known as auditory verbal hallucinations, have a mental health condition such as schizophrenia or bipolar disorder. However, not all voice-hearers have mental illness. In fact, it is estimated that between five and 15 percent of the general population have had an occasional experience of hearing voices, with as many as one percent having more complex and regular voice-hearing experiences in the absence of any need for psychiatric care.
This study involved people who regularly hear voices, but do not have a mental health problem. The researchers say this insight into the brain mechanisms of healthy voice-hearers may ultimately help scientists find more effective ways to help people who find their voices disturbing.
The small-scale study involved 12 voice-hearers and 17 non voice-hearers. Participants listened to a set of disguised speech sounds known as sine-wave speech as they underwent an MRI brain scan. Usually these sounds can only be understood once people are either told to listen out for speech, or have been trained to decode the disguised sounds.
Sine-wave speech has been likened to the song of a bird or alien-like noises. However, after training, people are able to detect the simple sentences hidden underneath (such as “The boy ran down the path” or “The clown had a funny face”).
Nine out of the 12 (75 percent) voice-hearers reported hearing the hidden speech compared to eight out of the 17 (47 percent) non voice-hearers. In fact, during the experiment, many of the voice-hearers were able to detect the hidden speech before being told it was there, and were more likely to notice it earlier than other participants who had no history of hearing voices.
“We did not tell the participants that the ambiguous sounds could contain speech before they were scanned, or ask them to try to understand the sounds,” said co-author Dr. Cesar Lima from UCL’s Speech Communication Lab.
“Nonetheless, these participants showed distinct neural responses to sounds containing disguised speech, as compared to sounds that were meaningless. This was interesting to us because it suggests that their brains can automatically detect meaning in sounds that people typically struggle to understand unless they are trained.”
Specifically, the regions of the brain associated with attention and monitoring were found to automatically respond to sounds that contained hidden speech compared to sounds that were meaningless.
“These findings are a demonstration of what we can learn from people who hear voices that are not distressing or problematic,” said lead author Dr. Ben Alderson-Day, research fellow from Durham University’s Hearing the Voice project.
“It suggests that the brains of people who hear voices are particularly tuned to meaning in sounds, and shows how unusual experiences might be influenced by people’s individual perceptual and cognitive processes.”
In the long term, the researchers hope these findings will inform mental health policy and improve therapeutic practice in cases where people find their voices distressing and clinical help is sought.
The findings are published in the academic journal Brain.
Source: Durham University