It’s the rare person who likes to hear their own voice on a recording. It looks 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 one hypothesis suggests that when people hear voices, they hear their own thoughts disguised as another person’s mind.
Scientists want to understand which parts of the brain allow us to recognize ourselves speaking, but studying this using recordings of people’s own voices has proved difficult. When we talk, we not only hear our voice with our ears, but on some level we feel it as the sound vibrations travel through the bones of the skull.
A study published Wednesday in the journal Royal Society Open Science attempted a solution. A team of researchers investigated whether people could more accurately identify their own voice if they wore bone-conduction headphones, which transmit sound through vibrations. They found that sending a recording through the bones of the face made it easier for people to tell their own voices apart from those of strangers, suggesting that this technique provides a better way to study when we are speaking. This is a potentially important step in understanding the origin of hallucinatory voices.
Recordings of our voices sound louder than we expected, said Paavo Orepik, a postdoctoral researcher at the Swiss Federal Institute of Technology who led the study. The vibration of the skull makes your voice sound deeper to you than to the listener. But even adjusting recordings so they 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 in front of the ears.
The team recorded volunteers saying the syllable “ah” and then combined each recording with other sounds to create sounds that were made up of 15 percent of a given person’s voice, then 30 percent, and so on. Then, they asked some subjects to listen to a series of sounds with bone-conduction headphones, while others used normal headphones and another group tried laptop computer speakers. Volunteers indicated whether they thought each sound was similar to their own voice.
The team found that people with bone-conduction headphones were more likely to correctly identify their own voice. When the researchers tried the same experiment using the voices of the subjects’ friends – pairs of friends specially recruited for the study – they found that bone-conduction headphones made no difference to how well people identified familiar voices. Had to It only became easier to recognize their own voices, suggesting that the instruments are recreating what we feel and hear.
This opens a door to understanding how one’s brain takes this sensory information and transforms it into one’s identity. 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 activate as people work to identify themselves.
If scientists can understand how the brain constructs a concept of self from sound, Dr. Orepik suggests, then perhaps what they can do is differentiate between people who hear voices in their head that are not themselves. Perhaps someday listening to recordings of voices with bone conduction devices could help doctors diagnose if the device’s performance can be linked to psychiatric disorders.
In fact, the team has already begun to study how people who had part of their brains removed – for example to treat drug-resistant epilepsy – perform on the task. The more the brain’s self-recognition network is disturbed by surgery, the more difficult the task of self-recognition becomes, Dr. Orepik said, referring to findings in a study that has not yet been peer reviewed.
For one patient whose personality changed substantially after her surgery and who was eventually diagnosed with borderline personality disorder, testing revealed a surprising pattern.
“Every time he heard his voice, he thought it was someone else,” Dr. Orepik said. “And when she hears someone else, she says ‘It’s me.'”