Harvard Medical School scientists have discovered two biomarkers that explain why it can be difficult for a person without hearing problems to follow conversations in noisy environments.
According to the Hearing Health Foundation, one in five Americans age 12 and over has hearing issues and 50% of those over 75 years of age have hearing loss as the number of cases increases with age. Exposure to noise is one of the main causes of hearing loss. However, according to Daniel B. Polley of Harvard Medical School, between the increasing use of personal hearing aids and the simple fact that the world is a much noisier place than it used to be, patients at the age of 50, report that they find it difficult to follow conversations in the workplace and in social environments where other people also talk.
Undetectable hearing loss
He and his team have published a study on this hidden hearing loss in eLife magazine. The researchers identified two biomarkers of brain function: the first represents “auditory effort” and the second the ability to process rapid changes in frequency. The latter can explain this hearing loss and even help design new clinical tests. Those that exist today “cannot detect what is wrong with this very common problem,” says Professor Daniel B Polley. The former is the “listening effort” and the latter the ability to process rapid frequency changes.
Classical hearing loss is diagnosed by employing an audiogram. The sound level must be loud so that the patient can hear the ‘beep’. However, in the case of hidden hearing loss, the audiogram does not detect these hearing problems. These hearing problems are related to abnormal communication between the nerve cells in the brain and the ear. In the case of conventional hearing loss, the sensory cells that convert sound waves into electrochemical signals are damaged.
1 in 10 affected patients
To carry out their research, the researchers reviewed more than 100,000 patient records over a period of 16 years. One in ten patients was found to have complained about hearing problems when the audiogram was normal. Consequently, the scientific team developed two series of tests with 23 participants. The first one measured the early stages of sound processing in the brain. The second one used specialized glasses to measure changes in the diameter of the pupils of the patients, while they focused their attention on the speaker, while others talked near them.
Hearing Tests must evolve
As expected, the ability of participants to follow their conversations while other people were talking in the background was greatly affected despite their good hearing audiograms. By combining the results of both tests, the researchers were able to determine which people suffered from a hidden hearing loss. According to Dr. Polley, speech is one of the most complicated sounds to understand and if our ability to speak in social environments is part of our hearing health, then the tests used should go beyond the early stages of hearing and measure the auditory processing in the brain more directly.
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