A link between hearing voices and hearing one’s own voice

He’s the rare person who likes to hear his own voice on a recording. It feels wrong, somehow – as if it belongs to someone else.

For neuroscientists, this quality of otherness is more than a curiosity. Many mysteries remain about the origins of hallucinations, but one hypothesis suggests that when people hear voices, they hear their own thoughts disguised as another person’s by a brain quirk.

Scientists would like to understand which parts of the brain allow us to recognize ourselves speaking, but studying this using recordings of people’s voices has proven tricky. When we speak, we not only hear our voice with our ears, but we feel it on some level as the sound vibrations pass through the bones of the skull.

A study published Wednesday in the journal Royal Society Open Science attempted a workaround. A team of researchers investigated whether people could recognize their voice more accurately if they wore bone conduction headphones, which transmit sound by vibration. They found that sending a recording through facial bones made it easier for people to distinguish their voice from that of strangers, suggesting the technology offers a better way to study how we can tell when we speak. This is a potentially important step in understanding the origins of hallucinated voices.

Recordings of our voices tend to sound higher than expected, said Pavo Orepic, a postdoctoral researcher at the Swiss Federal Institute of Technology who led the study. The skull vibration makes your voice sound deeper to yourself than to a listener. But even adjusting recordings to sound lower doesn’t recreate the experience of hearing your own voice. As an alternative, the team tried using bone conduction headphones, which are commercially available and often rest on the listener’s cheekbones just in front of the ear.

The team recorded volunteers saying the syllable “ah,” then mixed each recording with other voices to produce sounds that consisted of 15% of a given person’s voice, then 30%, and so on. . Next, some subjects listened to a series of sounds with bone conduction headphones, while others used normal headphones and another group tried laptop speakers. The volunteers indicated whether they thought each sound sounded like their own voice.

People wearing bone conduction headphones were more likely to correctly identify their own voice, the team found. When the researchers tried the same experiment using the voices of the subjects’ friends – pairs of friends were recruited specifically for the study – they found that the bone conduction headphones made no difference in helping people identify familiar voices. It’s only the recognition of their own voice that has become easier, suggesting that the devices recreate some of what we feel and hear when we speak.

This opens the door to understanding how the brain takes this sensory information and transforms it into self-recognition. In a study published last year, the group recorded the neural activity of people performing these listening tasks and reported the existence of a network of brain regions that are activated when people work to identify themselves.

If scientists can understand how the brain constructs self-concept from sound, suggests Dr Orepic, then they may be able to unpack what’s different about people who hear voices in their heads that aren’t their own. . Maybe one day listening to recordings of voices, including his own, with bone conduction devices could help doctors make diagnoses, if the device’s performance could be linked to psychiatric disorders.

In fact, the team has already started studying how people who have had parts of their brains removed — to treat drug-resistant epilepsy, for example — accomplish the task. The more the brain’s self-recognition network is disrupted by surgery, the more difficult the self-recognition task becomes, said Dr Orepic, referring to the results of a study that has not yet been evaluated by peers.

For a patient, whose personality changed dramatically after her surgery and who was eventually diagnosed with borderline personality disorder, the test revealed a startling pattern.

“Every time she heard his voice she thought it was someone else,” Dr Orepic said. “And when she hears someone else, she says ‘It’s me’.”