Hidden hearing loss is a type of hearing difficulty people experience, even though their hearing tests show normal results. This condition is believed to be caused by damage to the connections between the inner ear’s hair cells and the nerves that send sound signals to the brain, known as cochlear synaptopathy. These connections, called synapses, are particularly sensitive to damage from loud noise or aging. When these synapses are damaged, the brain doesn’t get all the sound information it needs, making it harder to process and understand sounds clearly1. The condition is referred to as hidden hearing loss because it can be hard to diagnose, since it isn’t as easily detected during standard hearing tests.
In hidden hearing loss, hearing thresholds may be normal, but sound perception is impaired. Signs of hidden hearing loss include difficulty understanding speech in noisy environments, such as restaurants or crowded spaces, even though sounds can still be heard. Many people describe it as “I can hear, but I can’t understand,” highlighting the struggle to make sense of conversations1.
Other hidden hearing loss symptoms include needing to put in extra effort toward listening, which can lead to fatigue, sensitivity to loud sounds and trouble pinpointing where sounds are coming from. These symptoms often go unnoticed without advanced diagnostic tools, making it important to recognize the subtle challenges associated with hidden hearing loss.
Cochlear synaptopathy, the loss of synapses between inner hair cells and auditory nerve fibers, can lead to hidden hearing loss. The causes of this condition include:
Currently, there is no established hidden hearing loss treatment, but research is exploring ways to repair or regenerate the connections between inner hair cells and auditory nerve fibers. Hearing aids have proven effective for conditions like sensorineural hearing loss and tinnitus, and researchers are investigating their potential benefits for individuals with hidden hearing loss, particularly those who struggle to hear in noisy environments.
For hearing aids to be effective in hidden hearing loss cases, precise fitting is crucial, and Real-Ear Measurement (REM) plays a key role. REM objectively measures how well a hearing aid amplifies sound in the ear using a probe microphone, ensuring accurate adjustments and optimal performance2.
Diagnosing hidden hearing loss can be difficult, as it isn’t readily detected using common hearing tests, yet there are several behavioral and objective methods that can be employed.
Individuals with cochlear nerve damage often exhibit lower-than-expected word-recognition scores during a hearing test because the brain cannot properly process sounds. This can occur even when no hearing loss is detected during a standard hearing test. Examining word recognition scores from hearing tests can help identify this discrepancy3.
Another way to perform a hidden hearing loss test is through objective methods that test auditory function, including auditory brainstem response (ABR), frequency-following responses (FFR) and electrocochleography (ECoG). ABR measures how well the auditory nerve and brainstem respond to sound. Using electrodes placed on the scalp, it records electrical activity in response to sound stimuli4. FFR focuses on how the brain processes sound frequencies, while ECoG examines the electrical responses of the cochlea and auditory nerve to sound.
These tests provide information about different parts of the auditory system, and can help uncover the neural deficits underlying hidden hearing loss.
Hidden hearing loss and auditory processing disorder both affect the ability to hear and understand sounds but differ in their causes. Hidden hearing loss is caused by damage to the connections between inner hair cells in the cochlea and the auditory nerve, often due to noise exposure or aging. It results in difficulty hearing in noisy environments despite normal results on standard hearing tests.
In contrast, auditory processing disorder is a brain-based condition where the auditory system processes sounds incorrectly, even though the ears and auditory nerve function normally. This condition often leads to trouble understanding speech, following directions or distinguishing sounds.
1 Science Direct. “Hidden hearing loss: Fifteen years at a glance.” Science Direct, www.sciencedirect.com/science/article/pii/S0378595524000200.
2 NIH. “Hidden Hearing Loss: A Disorder with Multiple Etiologies and Mechanisms." NIH, pmc.ncbi.nlm.nih.gov/articles/PMC6612463.
3 NIH. "Diagnosing hidden hearing loss." NIH, www.nih.gov/news-events/nih-research-matters/diagnosing-hidden-hearing-loss.
4 NIH. "Toward a Diagnostic Test for Hidden Hearing Loss." NIH, pmc.ncbi.nlm.nih.gov/articles/PMC5017571.
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