How Do We Hear?
Let’s start with your outer ear. There is actually a reason our ears are designed the way they are. They serve as a funnel to direct sound towards our inner ear. The contours of our ear canals are designed to actually boost certain frequencies that help us understand speech and our outer ears also help us locate where sound is coming from. The outer ear stops at the eardrum and then we enter the middle ear.
The middle ear is the mechanical part of the ear and consists of three little bones you learned about in school as the hammer, anvil, and stirrup or if you want to impress your friends you call them the malleus, incus, and stapes. The middle ear is also home to the Eustachian tube. You are probably more aware of the Eustachian tube than you are of any other part of your ear. The Eustachian tube’s function is to equalize the air pressure between your middle ear and outer ear. So when your ears “pop” driving up in the mountains or flying in an airplane that is your Eustachian tube at work. And often when your ears feel plugged and you can’t make them “pop” it is not working properly. When you hear something, sound waves are traveling down your ear canal, which causes your eardrum to vibrate setting off the mechanical function of the three bones, which boosts the signal and sends it to the inner ear.
That boosted signal that comes from the middle ear then causes ripples in the fluid of the cochlea. The cochlea is shaped like a snail and is filled with fluid. There is also a membrane, called the Basilar membrane that runs through the cochlea that has hair cells embedded in it. Different groups of hair cells are stimulated by different frequencies, or pitches. High pitched sounds, like a flute or piccolo, would stimulate hair cells near the base of the cochlea. Low pitched sounds, like a tuba, would stimulate the hair cells near the center of the cochlea. When the waves of the fluid move the hair cells they bump up against the Basilar membrane which causes a chemical reaction, turning the sound into an electrical signal that goes to the auditory nerve. The auditory nerve sends the signal to the brain, which then figures out what we heard.
The brain is where all the magic happens. If everything works properly in the ear, then the brain can work with it. But if the signal does not get through properly, then the brain is working with an incomplete signal. What happens next largely depends on our individual brains and the speed and strength of the interconnections across various parts of the brain. The brain takes in all that sound that surrounds us and maps it into different objects. This allows us to decide what we want focus on and what we want to ignore; what is important and what isn’t. And that can change from moment to moment, making it difficult to keep up. If you are watching something on TV that really interests you, then you may not “hear” a person in the same room say something (unless they get really annoyed and make you hear them). Have you ever been accused of having “selective hearing”? Now, you start to focus on them, rather than the TV. Or you may try to listen to both, which some people are better at than others (and that skill tends to weaken as we age). I used to be really good at being able to listen to two conversations at once, which came in handy on more than one occasion. But years before I developed a hearing loss I noticed that I could no longer do that as well as I once could.
Imagine that every word we hear is a jigsaw puzzle. Each word is made of different phonetic sounds that our brains piece together to turn into something that makes sense. As hearing loss begins, some of those puzzle pieces are being taken away. In the early stages of hearing loss, your brain may still be able to get the overall “puzzle” even with some missing pieces, though it does take more effort. This extra effort can create an additional strain on the brain. In fact, many new hearing device users have found that they have more energy at the end of the day because they’re no longer working so hard to decode every word they hear.
Memory and context both play an important role in our hearing. Those help you to fill in the gaps of a conversation that you are having in a really noisy restaurant. This can be a bit unreliable at times, especially if you have a hearing loss. I was having dinner with my daughter once in a noisy restaurant. We were talking along just fine and then she said something and I burst out laughing because what I “heard” (“monkey toes” in case you were wondering) made no sense at all, and was so far removed from the context of the conversation that I knew I had misheard her.
Do you remember the scene in the movie “My Cousin Vinny” where Joe Pesci is lying in bed in a ramshackle motel when a train roars by in the middle of the night? That first night it scared him to death but several nights later he slept right through it. Our brains adapt, and that sound had now become so normal that it no longer bothered him because he knew that it was supposed to be there. Let’s say you were alone in the house, asleep, and you heard a floorboard squeak. You would wake up right away with your heart pounding because that was a sound that shouldn’t be there in the middle of the night when you’re the only one home. So again, that’s context.
The ear is the mechanism that allows us to hear, but the brain is where it all comes together to make sense. If you are experiencing hearing loss then your brain cannot get all the information it needs access to and you are missing out.