The person who likes to hear his own voice on a recording is rare. It sounds fake, somehow, like it belongs to someone else.
For neuroscientists, that quality of otherness is more than a curiosity. Many mysteries remain about the origins of hallucinations, but a hypothesis suggests that when people hear voices, they are hearing their own thoughts disguised as someone else’s by a quirk of the brain.
Scientists would like to understand which parts of the brain allow us to recognize ourselves by speaking, but studying this using recordings of people’s own voices has proven difficult. When we speak, we not only hear our voice with our ears, but on some level we feel it as sound vibrations travel through the bones of the skull.
TO study published Wednesday in the Royal Society Open Science journal attempted a solution. A team of researchers investigated whether people could recognize their voices more accurately if they wore bone conduction hearing aids, which transmit sound through vibration. They found that sending a recording through the facial bones made it easier for people to distinguish their voices from those of strangers, suggesting that this technology provides a better way to study how we can tell when we’re speaking. That’s a potentially important step in understanding the origins of the hallucinated voices.
Recordings of our voices tend to sound louder than we expect, said Pavo Orepic, a postdoctoral researcher at the Swiss Federal Institute of Technology who led the study. Skull vibration makes your voice sound deeper to you than it does to a listener. But even adjusting recordings to sound quieter 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 the volunteers saying the syllable “ah” and then mixed each recording with other voices to produce sounds that were made up of 15 percent of a given person’s voice, then 30 percent, and so on. They then had some subjects listen to a series of sounds with bone conduction headphones, while others wore regular headphones, and another group tried laptop speakers. The volunteers indicated whether they thought each sound was similar to their own voice.
People with bone conduction hearing aids were more likely to correctly identify their own voices, the team found. When the researchers tried the same experiment with the voices of the subjects’ friends (pairs of friends were recruited specifically for the study), they found that bone conduction headphones made no difference in helping people identify familiar voices. It was only recognizing their own voices that became easier, suggesting that the devices are recreating some of what we feel and hear as we speak.
That opens a door to understanding how one’s brain takes this sensory information and turns it into self-recognition. In a study published last yearthe 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 its self-concept from sound, suggests Dr. Orepic, then perhaps they can figure out what’s different about people who hear voices in their heads that aren’t their own. Perhaps one day listening to recordings of voices, including his own, with bone conduction devices could help doctors make diagnoses, if the tool’s performance could be linked to psychiatric disorders.
In fact, the team has already begun to study how people who have had parts of their brains removed, for example to treat drug-resistant epilepsy, perform the task. The more the brain’s self-recognition network is disrupted by surgery, the more difficult the self-recognition task becomes, Dr. Orepic said, referring to the findings in a study that has not yet been peer-reviewed.
For a patientwhose personality changed substantially after her surgery and who was ultimately diagnosed with borderline personality disorder, the test revealed a surprising pattern.
“Every time I heard his voice, I thought it was someone else,” Dr. Orepic said. “And when he hears someone else, he says, ‘It’s me.'”
