Next-Generation Clinical Testing For Hidden Hearing Loss

• Some people find it hard to follow a particular speech in noisy environments. 
• Existing auditory tests are not advanced enough to detect this type of hearing loss. 
• Researchers develop two sets of tests that can detect such ‘hidden’ hearing loss. 

According to the World Health Organization, about 466 million people in the world have disabling hearing loss. The number will likely increase in the coming years: by 2050, more than 900 million people will be affected by hearing loss.

It is caused by aging, exposure to excessive noise, chronic ear infections, certain infectious diseases, and genetic factors. Generally, hearing impairment starts from damage to the inner ear (cochlea) or the auditory nerve fibers.

At present, hearing loss is diagnosed via an audiogram that shows the faintest sounds a person can hear at different frequencies or pitches. It is categorized as mild (25 to 40 dB), moderate (41 to 70 dB), severe (71 to 90 dB), and profound (>90dB).

However, current clinical testing cannot detect all types of hearing loss. These days, more and more middle-aged people are reporting a specific problem: they struggle to follow conversations in places with a lot of background noise.

Because of the increased use of personal audio devices that are too loud, this type of hearing loss is becoming a common problem. Now researchers at Massachusetts Eye and Ear Infirmary and Harvard Medical School have developed a new type of tests that can detect such hearing loss.

How Does It Work?

To describe how people are able to separate a particular conversion from a noisy crowd, the research team measured cognitive effort as well as the initial stages of the neural processing in the brain.

They have shown that a pair of biomarkers of brain function could explain why a normal person sometimes struggles to follow a single sound in noisy surroundings. One of these biomarkers is responsible for listening effort, while the other one is responsible for measuring the ability to process quick alterations in frequencies.

Reference: eLife | DOI: 10.7554/eLife.51419 | The Harvard Gazette

Traditional audiograms cannot detect such hidden hearing loss, as they are not designed to capture neural changes that interfere with the sound processing ability.

In this study, researchers analyzed records of 100,000 patients who visited the audio clinic over a 16-year period. They found 10,000 patients with complaints of hearing difficulty, but their audiograms revealed nothing wrong.

To detect such ‘hidden’ hearing loss, the team developed two new tests:

1. Measure EEG signals form the ear canal’s surface
2. Measure changes in pupil diameter when the patient focuses on one speaker while others babbled in the background.

The first test captures how well rapid and subtle fluctuations in soundwaves are processed in the brain. The second test involves using specialized glasses to track pupil size, which shows how much cognitive effort has been expended on a task.

They performed these tests on 23 patients with clinically normal hearing (their ability to follow a particular sound in a noisy background varied significantly despite having a normal report of hearing conditions).

Read: 45 New Genes That Cause Blindness Or Cognitive Disorders

After merging their ear canal EEG signals and alterations in pupil diameter, researchers successfully identified which patients struggled to follow a particular sound in noisy environments — something that isn’t possible with conventional audiogram tests.