DURHAM, England — Hearing voices may not be a sign of mental illness as much as it’s a clue that a person’s brain is simply well-tuned to many sounds. A new study finds that healthy people who hear voices have differently-wired brains that find speech patterns in other sounds.

Researchers from Durham University studied brain-response differences between two groups of people — those who have experienced hearing voices (auditory verbal hallucinations) and those who have never mistaken other sounds for speech. Participants in the study included 17 people with typical responses to sounds and 12 people who have experienced hearing voices, but do not have any mental health problems.

Participants underwent an MRI brain scan while listening to hidden speech sounds, known as sine-wave speech. Sine-wave speech to the untrained ear would sound something like birdsong or alien-type noises. Typically, people are able to make out these sounds only after they have been clued in to listen for them or taught to decode the hidden speech sounds. After people are trained, though, they can detect simple sentences within the sounds, such as “The clown had a funny face.”

Researchers found that less than half of those with typical listening skills noticed the hidden speech while 75 percent of the voice-hearers picked it up.

“It suggests that the brains of people who hear voices are particularly tuned to meaning in sounds,” says lead author Dr. Ben Alderson-Day in a university release.

Researchers were surprised that the voice-hearers had such strong neural responses to the sounds with hidden speech. Even before being told to listen for hidden speech, voice-hearers reported hearing the voices in the sounds. They found speech-like sounds faster and more easily than those who have never experienced the phenomenon 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. Nonetheless, these participants showed distinct neural responses to sounds containing disguised speech, as compared to sounds that were meaningless,” adds co-author Dr. Cesar Lima.

The authors believe this shows that the brains of voice-hearers are more perceptive to the hidden meanings in sounds. The areas of the brain that control attention were quickly activated in the brains of voice-hearers when they were exposed to hidden speech compared to when they were listening to vague sounds.

“These findings are a demonstration of what we can learn from people who hear voices that are not distressing or problematic,” says Alderson-Day.

Between 5 and 15 percent of the population has occasionally had the experience of hearing voices. Although not everyone who hears voices has a mental health problem, it is commonly associated with schizophrenia or bipolar disorder.

Researchers hope their findings could someday help scientists and clinicians find better ways to help those who are troubled by the voices they hear.

The study’s findings were published in the academic journal Brain.