I Can't Hear You

Working in New York City, I see a lot of patients who think they have hearing loss. They can’t hear conversations at business dinners. They have to ask people to repeat themselves at parties. They struggle to hear phone calls when they are walking down the street. These aren’t necessarily older people, by the way. Most of them are young and healthy with no history of hearing loss.

Last week, one such patient came in at her husband’s request.

“He keeps complaining he has to yell from the other room to get my attention. Why can’t I hear him?” she asked.

“Because you don't want to hear what he's saying?” I joked.

She didn’t laugh.

“Let me take a look,” I said, proceeding to check for earwax. Much to my disappointment, there was no sticky glob to remove that would magically restore her hearing. So I looked for other possibilities, like fluid in her middle ear, an external ear infection, or exostoses, which are bony growths in the ear canal that happen from swimming in cold waters. I also made her try to pop her ear so I could check that her eardrum was moving. Everything looked good.

Next, I gave her a hearing test. It too was normal.

“So what’s going on?” she asked.

Here’s a lesson on how hearing works.

Sound travels through the air in waves. When soundwaves get to your eardrum, they make it vibrate at the same frequency as the sound wave. High-pitched sounds cause a fast vibration (think Mariah Carey’s whistle tones) and low-pitched sounds cause a slow vibration (think Barry White when he's in the groove).

On the other side of the eardrum, inside the middle ear, there are three tiny ear bones called ossicles. Their Latin names are malleus, incus, and stapes, but I prefer their common names–hammer, anvil, and stirrup–because they sound like something Thor would use. These ear bones make a “chain,” connecting the eardrum to the hearing organ, or cochlea. When the eardrum vibrates, the chain of tiny bones also vibrates, which then vibrates the part of the cochlea called the round window.

The cochlea Is not a simple organ, but here are the basics. The cochlea is spiral-shaped, like a snail, and filled with fluid. Along its inside edges, suspended in a bath of fluid, are tiny hair cells. These hair cells connect to the auditory or hearing nerve, which goes to your brain. On the wider end of the spiral, facing the middle ear, is a membrane that seals in the fluid. This wider end is called the round window.

When a sound wave is transmitted through the chain of tiny ear bones to the round window, it has kind of the same effect as a drum, causing the fluid in the cochlea to vibrate. This vibration makes the hair cells wiggle. Each hair cell wiggles for a specific frequency, like dancers in a 1970s variety show, based on its distance from the round window. Higher frequency sounds with shorter wavelengths wiggle the hair cells closest to the round window. Longer, lower frequency sound waves make the hair cells farther inside the cochlea wiggle. All that wiggling stimulates the auditory nerve, which then transmits those signals to the brain. Then our brain then has to make sense of all that noise.

Putting it all together

You’re excited about the 20th Anniversary of Wicked on Broadway, so you flip through Youtube and find this incredible video of Jessica Vosk singing Defying Gravity. The sound waves float into your ears and vibrate your eardrum. That, in turn, makes Thor’s tools vibrate, and, since they are connected to the round window, they send that vibration to the fluid inside the cochlea. The vibrating fluid wiggles your tiny hair cells, which activates the hearing nerve. The hearing nerve then sends a signal to your brain, which makes you swoon and maybe even listen to the whole video again, because, I mean, the pipes on this lady!

This is how normal hearing works. Sound goes in, ear transmits the sound to the brain, and the brain processes the sound. Anything that gets in the way of this circuit can make it harder for you to hear.

But hearing is not the same as listening.

It’s easy to assume that your brain notices everything you hear, but it’s not that simple. Your ears are constantly getting bombarded by sounds, from the low hum of traffic to the screeching of brakes on train tracks. Since your ears aren’t filtering the sounds (unless you are a smarty pants who wears noise-cancelling ear buds), your brain has to decide which sounds are important and which ones to ignore.

The part of your brain where this deciding happens is called the auditory cortex, or hearing central. Even though a particular sound comes in, you may or may not perceive it if your auditory cortex decides otherwise. In other words, even if a sound gets through your ears with normal hearing, you won’t “listen” unless your brain tells you to.

Back to Jessica.

Imagine you are sitting in a quiet room trying to write an article about how hearing works, when your teenager’s phone rings. Her ringtone is the chorus of Jessica singing Nobody’s Side from the musical Chess–your daughter is a huge Broadway fan. The loud sound makes you jump up and burst into song because, in a split second, it got from your ear to your brain and back to your body, startling you out of your writer’s block. You are clearly not going to be able to work from home today.

Annoyed with your teenager and her intrusive phone, you decide to do your writing in a busy midtown coffee shop. Outside, an ambulance siren wails by. Gridlocked cars honk through a green light. The person sitting next to you spills juicy details to his friend about his disastrous date the night before, but you barely notice. Then a patron walks by and her phone goes off with a ringtone of Jessica singing What Baking Can Do–Jessica is very popular. Even though you love that song, you are so focussed on explaining the cochlea, you hardly look up.

Your brain is getting bombarded by many different sounds, but your auditory cortex filters through them and decides which ones are important enough for you to listen to. In this case, you don’t listen to any of them, because you are almost done with your article.

Now, imagine there is noise everywhere you go. (If you live in New York, you don’t have to imagine it.) There is so much background noise, your brain often spends more time filtering than listening. To make things more complicated, most background noises are high frequency sounds. Consonants are also high frequency sounds. Since consonants are how we understand language in English, it’s easy to see why it’s harder to understand what someone is saying when they are in a noisy environment. No wonder you can’t hear your boss across the table at Avra. All those high-frequency sounds blend together.

Fast forward a few years. After spending so much time filtering, your brain has gone into survival mode. Even back in your quiet room, you don’t notice louder sounds, like when your husband calls you from the next room. He starts complaining that you never seem to “hear” him these days and suggests you get your hearing checked. So you go to your doctor and get a hearing test. It is normal.

Your ears can hear, but your brain isn’t listening. And now, you understand why.