I didn’t start covering hearing in my Intro Psych course until the earbud-style headphones became popular. When I heard music emanating from a student’s earbuds from the back of the room, I knew it was time for us to have a conversation.
In the cochlea, the stereocilia closest to the oval window are the ones responsible for hearing high-pitched sounds. Exposure to loud sounds causes a tsunami to rush over those stereocilia, causing them to bend over farther than they are supposed to resulting in permanent damage (Oghalai, 1997).
The Center for Hearing Loss Help has a nice image of a bundle of pristine stereocilia and a bundle of damaged cilia. In fact, this is an interesting article on diplacusis, where one ear hears a pitch that is just above or just below the pitch heard by the other ear (Center for Hearing Loss Help, 2015).
In class, after walking students through the structure and workings of the ear, I go to this webpage (Noise Addicts, n.d.) that has 3-second sound files of pitches ranging from 22 kHz down to 8 kHz. I start with the 22 kHz, which none of my students can hear, and then move to lower pitches one by one. I cannot hear them until I get down to about 14 kHz. Fifty years of being exposed to sound, with the last 16 years spent in a noisy urban environment – and more than one rock concert – has likely taken its toll. I have friends in their 70s who have spent their lives in a quiet town who have no problem hearing 17 kHz. Of course exposure to loud sounds is not the only factor that can affect hearing loss for high-pitched sounds, but it is a common factor.
Some time ago, I had a student who knew that he had some hearing loss, but he had no idea of the extent of it. When I played the sounds in class, he was stunned to see students reacting to the high-pitched sounds that he couldn’t hear. The first frequency he heard was a mere 8 kHz. He immediately made an appointment with an audiologist. He was (just barely) young enough that he qualified for a special program that got him hearing aids for free. The first time he was in class after getting them, he told me that he was floored by how much he could hear – and how much he hadn’t been hearing.
Another student who spent a couple years working as a bouncer at a (very loud) club was 23 years old, and the first frequency he heard was 12 kHz.
In Mary Roach’s book Grunt, she writes that the problem with most hearing protection is that not only does it protect against loud sounds, but it also makes it hard to hear softer sounds. This is especially problematic for combat soldiers. They need to protect their hearing in case of a sudden explosion or gunfire, but they need to be able to hear what their fellow soldiers are saying. There are now ear cuffs that protect against loud noises but also amplify quieter sounds. In this 3-minute YouTube video, Roach describes the hearing problem and how these new ear cuffs work. A student of mine, who is in the army, said he got to try out the ear cuffs – although not in combat, and he was very impressed with how well they worked.
Knowing how their ears work can help students make informed decisions about how they would like to treat their ears. With that knowledge, students may make better decisions that will affect them for their rest of their lives.
Center for Hearing Loss Help. (2015). Diplacusis -- the strange world of people with double hearing. Retrieved from http://hearinglosshelp.com/blog/diplacusisthe-strange-world-of-people-with-double-hearing/
Noise Addicts. (n.d.). Hearing test -- can you hear this? Retrieved from http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearing-test/
Oghalai, J. S. (1997). Hearing and hair cells. Retrieved November 4, 2017, from http://www.neurophys.wisc.edu/auditory/johc.html