You can buy a good pair of bone conduction headphones for under $150. Some of your students may have seen them or own a set. Here’s a little information to add to your next Intro Psych hearing lecture, or at least some information to hold onto in case a student asks. If you teach Biopsych, you can dig even deeper into this topic – or have your students do the digging.
Bone conduction headphones, such as Aftershokz Trekz Air, send vibrations through, well, bone. The headphones speakers are generally positioned against the cheek bone or upper jaw bone right in front of each ear. The cheek bones carry the vibrations through to the temporal bone – the bone that surrounds the cochlea. While the specifics are still under investigation, we know that these vibrations cause the cochlear fluid to move, triggering the cilia that send their messages to the auditory cortex where we hear sound. It could be that the bone vibrations cause the fluid in the cochlea to move due to a change in pressure, the vibrations in the bone put pressure on the walls of the cochlea causing them to compress, or the vibrations in the bone could cause waves in the cerebrospinal fluid in the skull thereby causing waves in the cochlea (Dauman, 2013). Or all three.
All of those routes explain how someone with middle ear damage can hear through bone conduction. The vibrations bypass the bones of the middle ear and affect the cochlea directly. Bone conduction hearing devices (previously called bone anchored hearing aids) are for people with issues with their outer or middle ears. These devices can either be surgically implanted with a speaker attached by magnet or just temporarily attached with adhesive (Hearing Link, 2017).
The vibrations produced by bone conduction headphones also cause vibrations in the skin and cartilage of the outer ear as well as vibrations in the temporal bone of the skull. Those vibrations cause air to move in the outer ear, triggering the bones of the middle ear to move, and so on, resulting in sound. This may not contribute much to what we hear through bone conduction, but it contributes more if we wear ear plugs with our bone conduction headphones. That brings us to the occlusion effect (Dauman, 2013).
While you may not be familiar with the occlusion effect (I wasn’t), everyone with some amount of hearing has experienced it. While talking, plug your ears with your fingers. Your voice will sound up to 20 decibels louder (Ross, 2004).
We hear our own voices through bone conduction. With our outer ears open, the vibrations that come through the bone can vibrate on out through the outer ear. With our outer ears plugged, the vibrations cannot escape and so reverberate back through the middle ear, amplifying our voices. This is one of the reasons some people don’t like (unvented) earmold hearing aids; they completely block the ear canal making our voice sound funny (Ross, 2004). Most earmold hearing aids now come with a vent – an opening that allows the vibrations caused by our voices to escape.
Why use bone conduction headphones?
There are several advantages to using bone conduction headphones (Banks, 2019).
If you are walking, running, or biking on the open road, bone conduction headphones allow you to listen to your tunes without blocking your ear canal. You’ll have a greater chance of hearing that car coming up behind you, but, of course, all of the research on attention tells us that you still may not attend to the sound of the car. Or you may not hear the car at all if the sound of it is masked by whatever you’re listening to through your headphones (May & Walker, 2017). In terms of this sort of safety, bone conduction headphones are likely not worse than any other kind of headphone or speaker (Granados, Hopper, & He, 2018).
If you use earmold hearing aids, you can use bone conduction headphones with them.
If you are a scuba diver, you can use a bone conduction microphone and headphones to both speak and listen underwater (see for example Logosease).
If you have tinnitus, bone conduction headphones can provide auditory stimulation to the cochlea that may reduce tinnitus while allowing you to still have a conversation in, say, a work environment (British Tinnitus Association, n.d.; Schweitzer, 2018), although the research here is scant (Manning, Mermagen, & Scharine, 2017).
Can bone conduction headphones produce hearing loss when listening at loud volumes just like regular headphones can?
After scouring journals and reading opinions from all corners of the internet, my conclusion, pending further evidence, is a tentative and cautious affirmative; bone conduction headphones can cause hearing loss. Anything that can produce loud sounds, including regular headphones cranked up to a high volume, causes hearing loss by producing tsunamis that damage the cilia in the cochlea. Since bone conduction headphones are also causing waves in the cochlea, it stands to reason that waves caused by bone conduction could also reach tsunami strength. But, then again, maybe bone conduction cannot produce those kind of waves. Some research here would be nice. If you know of any, please let me know!
Banks, L. (2019). Best bone conduction headphones of 2019: A complete guide. Retrieved February 11, 2019, from https://www.everydayhearing.com/hearing-technology/articles/bone-conduction-headphones/
British Tinnitus Association. (n.d.). Sound therapy (sound enrichment). Retrieved February 11, 2019, from https://www.tinnitus.org.uk/sound-therapy
Dauman, R. (2013). Bone conduction : An explanation for this phenomenon comprising complex mechanisms. European Annals of Otorhinolaryngology, Head and Neck Diseases, 130(4), 209–213. https://doi.org/10.1016/j.anorl.2012.11.002
Granados, J., Hopper, M., & He, J. (2018). A usability and safety study of bone-conduction headphones during driving while listening to audiobooks. Proceedings of the Human Factors and Ergonomics Society Annual Meeting, 62(1).
Hearing Link. (2017). Bone conduction hearing devices. Retrieved February 11, 2019, from https://www.hearinglink.org/your-hearing/implants/bone-conduction-hearing-devices/
Manning, C., Mermagen, T., & Scharine, A. (2017). The effect of sensorineural hearing loss and tinnitus on speech recognition over air and bone conduction military communications headsets. Hearing Research, 349, 67–75.
May, K., & Walker, B. N. (2017). The effects of distractor sounds presented through bone conduction headphones on the localization of critical environmental sounds. Applied Ergonomics, 61, 144–158.
Ross, M. (2004). Dr. Ross on hearing loss. Retrieved February 11, 2019, from http://www.hearingresearch.org/ross/hearing_loss/the_occlusion_effect.php
Schweitzer, G. (2018). Bone conduction headphones for hearing loss and tinnitus. Retrieved February 11, 2019, from https://rewiringtinnitus.com/trekz-titanium-bone-conduction-headphones/