Have you ever been out with family or friends someplace where a lot of people were talking around you? Maybe at a restaurant, ball game, or your kids school events? Were you able to clearly hear what your small group was talking about or did you have trouble because their words were overshadowed by the chatter from others nearby?
The definition for “hidden” hearing loss is hearing loss that isn’t able to be detected by standard hearing tests. Many describe it as the inability to hear in a noisy environment. This type of hearing loss isn’t detectable through normal auditory testing. For those who have hidden hearing loss, their test results appear just like those with normal hearing.
Long-term or sudden extreme exposure to loud noises has the ability to cause damage to the delicate hair cells located within the inner ear. In healthy ears, we’re able to pick up sound waves which are then transmitted to the inner ear where vibrations occur. These vibrations act within the fluid-filled cochlea, a small cavity shaped much like a snail. The cochlea is divided into two sections that are separated by the basilar membrane. This membrane serves as the floor that the main hearing structure sits on.
When the vibration from sound waves develop, this causes the fluid that’s inside the cochlea to send ripples along the basilar membrane. The hair cells are able to collect this sound wave and transmit it into an electric signal. That signal is carried to the brain by the auditory nerve which allows us to “hear” the noise. Most learn in childhood to interpret this as a sound that we recognize based on repetition.
For someone with hidden hearing loss, these nerve cells in the ear, as well as the connection to the hair cells, have been damaged. This can make it harder to hear definite sounds in a noisy environment. Areas, where people congregate such as churches, boardrooms, or event centers, can wreak havoc on someone’s ability to follow a conversation.
It’s usually easier to hear quiet sounds when they aren’t being trampled by background noise. The risk of hidden hearing loss is higher in people who regularly use earbuds or headphones and love loud music, as well as people who work in loud environments.
According to Daniel B. Polley, PhD, Director of the Lauer Tinnitus Research Center at Mass. Eye and Ear, Associate Professor of Otolaryngology Head-Neck Surgery at Harvard Medical School and senior study author, “Between the increased use of personal listening devices or the simple fact that the world is a much noisier place than it used to be, patients are reporting as early as middle age that they are struggling to follow conversations in the workplace and in social settings, where other people are also speaking in the background. Current clinical testing can’t pick up what’s going wrong with this very common problem.”
Thanks to a study performed by Polley and his colleagues there may be a way to determine who is dealing with hidden hearing loss. Leaning towards the possibility that this condition stems from “abnormal connectivity and communication of nerve cells in the brain and ear”, the group reviewed over 100,000 patient records from the Massachusetts Eye and Ear. They narrowed it down to 23 test subjects ranging in age from young adult to middle-aged who presented with clinically normal hearing.
The first test that was administered to develop these biomarkers was designed to detect how effectively the beginning stages of sound processing functioned within the brain. By measuring the electrical EEG signals that occur at the surface of the ear, they were able to determine how well the subject detected slight yet rapid variations in the sound waves.
The second test utilized specialty glasses that were designed to measure the changes in a subject’s pupil diameter while they concentrated on a single speaker yet were exposed to other conversations in the background. This test was inspired by research done previously that successfully demonstrated how changes in pupil size could indicate how much cognitive effort one was using on a given task.
True to their expectations, there was a wide variation in the participants’ abilities to track a conversation even though their previous tests had deemed their hearing in the normal range. Based on this form of testing researchers were able to combine the changes in a person’s pupil diameter with measurements from their ear canal EEG.
They were then able to recognize which participants would do well and which ones would struggle to track speech in a noisy environment. These results are encouraging, though more research needs to be done in this area.
“Our study was driven by a desire to develop new types of tests. Our work shows that measuring cognitive effort in addition to the initial stages of neural processing in the brain may explain how patients are able to separate one speaker from a crowd,” shared lead study author Aravindakshan Parthasarathy, PhD, an investigator in the Eaton-Peabody Laboratories at Mass. Eye and Ear.
“Speech is one of the most complex sounds that we need to make sense of,” Dr. Polley said. “If our ability to converse in social settings is part of our hearing health, then the tests that are used have to go beyond the very first stages of hearing and more directly measure auditory processing in the brain.”
If you or a loved one are having trouble hearing where background noise is present, you may have hidden hearing loss. Be sure to mention this when you schedule an appointment with your hearing health professional.