A new study may help to explain why people with normal hearing struggle to follow conversations in noisy environments. Researchers at Massachusetts Eye and Ear are determining that a pair of biomarkers of brain function may hold the answer. The two biomarkers, one for listening effort and the other which measures the ability to process rapid changes in frequencies, can explain why a person with normal hearing may have trouble following conversations in loud places. These conclusions might pave the way for the design of next-generation clinical testing for hidden hearing loss.
Noise, aging, and other factors cause hearing loss, which affects 48 million Americans. Hearing loss arises from damage to the sensory cells of the inner ear, the cochlea. The cochlea converts sounds into electrical signals for the brain. A diagnosis of hearing loss is by elevation in the faintest sound level required to hear a brief tone. The level appears on an audiogram, which is the gold standard of hearing testing.
Hidden Hearing Loss
Hidden hearing loss is a loss of hearing that standard hearing tests can’t calculate. Typically, the first step in measuring hearing loss is using an audiogram. Unfortunately, for people with hidden hearing loss, the audiogram reads just like someone with normal hearing. Hidden hearing loss arises from abnormal connectivity and communication of nerve cells in the brain and ear, not in the sensory cells that convert sound waves into electrochemical signals.
The study developed from a desire to create new methods of hearing testing. The world we live in is getting noisier all of the time, and people are reporting hearing problems earlier in life. People are having particular difficulty hearing conversations in the workplace and social settings. The current testing available can’t detect the problem. This lack of testing is driving the researchers to develop new ways of hearing testing.
To address hidden hearing loss, the researchers are developing objective biomarkers that may explain the hidden hearing loss complaints. The research team developed two sets of tests. One measured electrical EEG signals from the surface of the ear canal to detect how well the early stages of sound processing in the brain were encoding fluctuations in sound waves. The other used specialized glasses to measure changes in pupil diameter when test subjects focused their attention on one speaker.
Twenty-three subjects with clinically normal hearing underwent the tests, and their ability to follow conversations varied. By combining the measures, the investigators could identify which subjects struggled and which ones passed the test. Encouraged by the results, the researchers believe that testing must go beyond the first stages of hearing and directly measure auditory processing in the brain.
If you are having difficulty hearing conversations in noisy places, you might be experiencing the beginning stages of hearing loss. Plan a hearing evaluation with a hearing healthcare professional who can diagnose and treat your hearing loss in its early stages.