When loud noise damages hair cells within the inner ear it's called noise induced hearing loss (NIHL). Many tests can detect this damage to hair cells from noise, but there's another, hidden way loud sounds can damage hearing. Before loud noises damage hair cells, they can already have damaged the extremely sensitive nerve fibers inside the ear. This hearing damage is prevalent in young people, but isn't so easy to detect and is rarely tested. That's why it is called hidden hearing loss.
In 2014, it was discovered that nerve fibers within the ears are more sensitive to sound damage than hair cells and may be damaged before hearing loss is detected. Still there are few tests used to detect this early type of hearing loss. In part, that's because, according to Charles Liberman, director of MEEI's Eaton Peabody Laboratory in this an article on ScienceDaily, "you can lose up to 90 percent of your cochlear nerve fibers without a change in the ability to detect a tone in quiet."
In other words, the hearing damage is there but can't be tested by a routine hearing test. Furthermore, this damage is hard to see with traditional methods. However, in the 2014 study researchers managed to devise tests to see and record this damage.
Building on that important 2014 research, a new study reported on in PLOS ONE done by the Massachusetts Eye and Ear has shown that this hidden hearing loss is prevalent in young people who are routinely overexposed to loud sounds.
In order to detect cochlear synaptopathy or what is known as hidden hearing loss, researchers from Massachusetts Eye and Ear compared how well college aged subjects could detect speech in noise--hear in a crowded, noisy place--to an "electrophysiological measure of the health of the auditory nerve." They discovered that college students routinely exposed to loud noise had a sluggish response from this auditory nerve and this sluggish response was accompanied by a decreased ability to understand people talking in a noisy environment.
People who had less exposure to loud noises or who routinely protected their hearing, had a more vigorous auditory response and could more easily understand speech in noise. As an aside, being unable to understand speech in background noise is an early warning sign of hearing loss and is typical of those in their fifties or sixties experiencing hearing loss. But this isn't the only test to show signs of premature hearing loss or hidden hearing loss in the younger generation.
Another study conducted on 170 children from the ages of 11 to 17 showed that younger people had an increase in tinnitus--another early marker for hearing loss. According to the study's author, Larry Roberts PhD, "even though they could still hear as well as their peers, those experiencing tinnitus were more likely to have a significantly reduced tolerance for loud noise, which is considered a sign of hidden damage to the nerves that are used in processing sound."
Hidden hearing loss indicates damage to hearing that may be permanent. Unfortunately routine testing for this hidden hearing loss is not widely available. The best way to make sure this damage doesn't occur is to protect ears from noise. Protection can come in the form of earplugs, avoiding loud noise situations entirely, and not allowing you or your children to listen to any continuous sound for too long without protection. Things like a hair dryer or a lawn mower can damage hearing because of the length of time exposed. Too loud, too long, too close are the three things to remember when it comes to protecting your or your child's hearing. If you'd like to learn more about how you can protect your hearing, please see your hearing health professional. If you need help finding a hearing health provider click HERE to be connected with the largest network of trusted hearing health professionals in the nation!