Why Can’t I Hear in a Crowd?

Sometimes when an individual has a difficult time hearing, someone close to them insultingly suggests they have "selective hearing". When your mother used to accuse you of having "selective hearing," she meant that you listened to the part about going to the fair and (maybe intentionally) ignored the bit about cleaning your room.

But in reality it takes an amazing act of cooperation between your brain and your ears to have selective hearing.

Hearing in a Crowd

This scenario potentially feels familiar: you're feeling tired from a long day at work but your friends all really want to go out for dinner and drinks. And naturally, they want to go to the loudest restaurant (because it's trendy and the deep-fried cauliflower is the best in town). And you strain and struggle to follow the conversation for the entire evening.

But it's challenging, and it's taxing. This indicates that you could have hearing loss.

Maybe, you rationalize, the restaurant was simply too noisy. But no one else seemed to be struggling. The only person who appeared to be having trouble was you. Which makes you think: what is it about the crowded room, the cacophony of voices all trying to be heard, that throws hearing-impaired ears for a loop? Why is it that being able to hear in a crowd is so quick to go? The answer, according to scientists, is selective hearing.

How Does Selective Hearing Work?

The scientific name for what we're broadly calling selective hearing is "hierarchical encoding," and it doesn't happen in your ears at all. The majority of this process happens in the brain. At least, that's according to a new study performed by a team from Columbia University.

Scientists have recognized for quite some time that human ears basically work as a funnel: they compile all the impulses and then deliver the raw information to your brain. That's where the heavy lifting takes place, particularly the auditory cortex. That's the part of your gray matter that handles all those impulses, translating sensations of moving air into identifiable sounds.

Just what these processes look like had remained a mystery in spite of the existing knowledge of the role played by the auditory cortex in the process of hearing. Scientists were able, by making use of novel research techniques on people with epilepsy, to get a better picture of how the auditory cortex discerns voices in a crowd.

The Hearing Hierarchy

And here's what these intrepid scientists learned: there are two parts of the auditory cortex that manage most of the work in allowing you to identify individual voices. And in noisy settings, they enable you to isolate and amplify specific voices.

• Superior temporal gyrus (STG): Sooner or later your brain needs to make some value based decisions and this occurs in the STG after it receives the voices that were previously differentiated by the HG. The superior temporal gyrus figures out which voices you want to focus on and which can be confidently moved to the background.
• Heschl's gyrus (HG): This is the region of the auditory cortex that manages the first phase of the sorting process. Researchers found that the Heschl's gyrus (we're just going to call it HG from here on out) was processing each unique voice, separating them via individual identities.

When you have hearing loss, your ears are missing particular wavelengths so it's more difficult for your brain to differentiate voices (depending on your hearing loss it might be high or low frequencies). Your brain can't assign separate identities to each voice because it doesn't have enough information. As a result, it all blends together (which makes conversations hard to follow).

New Science = New Algorithm

Hearing aids currently have functions that make it less difficult to hear in noisy circumstances. But hearing aid makers can now include more of those natural functions into their algorithms because they have a better idea of what the process looks like. For instance, you will have a better capacity to hear and comprehend what your coworkers are talking about with hearing aids that assist the Heshl's gyrus and do a little more to separate voices.

The more we understand about how the brain works, especially in connection with the ears, the better new technology will be able to mimic what takes place in nature. And better hearing outcomes will be the result. Then you can focus a little more on enjoying yourself and a little less on straining to hear.