Written by Jane Campbell, Audiologist.
Normally we hear sounds when a sound wave travels through the ear canal, hitting the ear drum which wobbles when struck by a sound wave.
This movement in turn causes the middle ear bones, called the ossicles, to vibrate. The last of these ossicles is attached to your cochlea which is full of fluid and tiny little hair cells. As the last ossicle vibrates against the cochlea it causes a wave in the fluid, and the hair cells that sit on the bottom of the cochlea – like seaweed on the bottom of the ocean – move in a wave-like motion. It is this movement that is picked up by your nerves and brain and heard as a sound.
Bone conduction, however, is the method of hearing by transferring sound through the skull to your cochlea. We assess bone conduction thresholds when we do a standard hearing test. People who have chronic ear infections, disruption of the ossicular chain or malformations of the outer ear and ear canal may be able to hear better using bone conduction compared to when hearing sounds normally through their ears. For these people, using a bone conduction hearing aid or implant may enable them to have better hearing compared to using a standard hearing aid.
Even people without hearing loss can benefit from bone conduction hearing, with many bone conduction headphones coming on the market.
Both bone conduction hearing aids and bone conduction headphones sit on the mastoid bone of your skull, behind your ear, rather than in your ear, and transfer sounds via vibrations to your cochlea.
The benefit of a bone conduction hearing device is that it keeps your ears free, this can be beneficial to cyclists or runners who can use bone conduction headphones to listen to their music, while still being aware of the traffic around them. Similarly, a bone conduction hearing aid sits on the mastoid bone and not on the ear, helping to keep ears well aerated and free of infections.
Humans aren’t the only species that can use bone conduction to hear, too. Animals such as dolphins use bone conduction through their jaw bones to hear!