Hearing loss in old age might not mean a problem with the ears at all. Instead, our brains may just be getting worse at processing speech, especially in noisy places. Worse, if that background noise is also made up of speech that the listener can understand, they have even more trouble comprehending the person they're listening to.
The problem, says a new study published in the Journal of Neurophysiology, is deterioration in the midbrain and cortex, caused by aging. Normally a human can focus on a single speaker in a busy environment, picking out their speech even over the nattering of the surrounding crowd, but as we age, we get worse at distinguishing signal from noise.
To investigate the phenomenon, the researchers, from the University of Maryland, scanned the brains of young and old test subjects while they were listening to somebody speak. The tests were run a few ways, sometimes with no noise, sometimes with a second speaker using the same language as the first, and at other times with that second speaker using a language incomprehensible to the listener.
The result showed that, as we get older, we get worse at speech processing in general. "The older brain just drops part of the speech signal, even if the ears captured it all just fine," said co-author Jonathan Simon in a statement. "For older listeners, even when there isn't any noise, the brain is already having trouble processing the speech."
When the person we're trying to listen to is competing with other speakers, it gets worse. We have real problems separating out the speech from the noise. We compensate by concentrating harder, but even then, we miss a lot. "Older people need more time to figure out what a speaker is saying," Simon says. "They are dedicating more of their resources and exerting more effort than younger adults when they are listening to speech."
Some tricks work well, regardless of your age. If you can see the speaker's lips, that helps to better understand their speech. If you are talking to an older person, then, you should make sure they can see you and are paying attention to you, before speaking. Also, raising your voice won't help, because there's nothing wrong with their ears. It's the equivalent of shouting the same words over and over at a foreigner, hoping that they'll start understanding English if it's loud enough.
The cause of this deterioration is still unknown, but the researchers posit that it may be due to an "age-related imbalance between excitatory and inhibitory neural processes in the brain." This imbalance could lead to the overloading of the cortex when trying to comprehend speech.
The researchers are looking into the possibility that brain-training could help us retain our speech-processing abilities as we grow older, so now we just need to figure out why teenagers never listen, even though—according to this study—they can hear you perfectly well.