Hidden Hearing Loss! A Newly Emerging Problem
Hidden Hearing Loss May Affect Up to 25% of The Population
We read a really interesting article a while ago that detailed the findings and ongoing research of David McAlpine, a professor of auditory neuroscience at the UCL Ear Institute in London. The article outlined the emerging understanding of a problem that has been named Hidden Hearing Loss. The name was first presented in 2011 and it pertains to a problem that according to some surveys up to 25% of us suffer with. Several surveys undertaken over the last few years suggest that more than a quarter of us have great difficulty understanding speech when there is competing noise, such as in a pub or restaurant. What is interesting though is that most said they had no problems with their hearing, from Professor McAlpines research it appears that this may be more common than we think and in fact may be directly related to what he calls hidden hearing loss.
Hidden Hearing Loss, what is it?
Hidden Hearing Loss is suspected when someone has problems with complex listening tasks, such as understanding speech in noisy environments, but doesn't seem to have impaired hearing by the usual measures. Professor McAlpine defines it as "People with this problem often have difficulty with complex listening tasks, such as deciphering speech among background noise. "This could be true of anyone with hearing loss. The difference with hidden hearing loss is that they don't necessarily have trouble hearing quiet sounds when there is no noise in the background, so the results of an audiometry test look fine. "
In other words, when a typical hearing test, a pure tone test of a person's hearing is undertaken, they will pass it with flying colours. Which indicates that there is no hearing loss present, however, they will still have real difficulties in social situations. Professor McAlpine thinks that this problem may well be on the rise, because he believes that the underlying cause of it is damage from noise exposure. Something that we increasingly face in an ever noisy world.
What causes Hidden Hearing Loss
Before we talk about hidden hearing, lets talk about general hearing loss. The type of hearing loss that is commonly called nerve deafness is caused by damage to tiny hair cell nerve endings in the inner ear. In essence they become worn and damaged and no longer react to sound stimulation. This breaks the chain of hearing at the frequencies that the damaged hair cells once reacted to. With Hidden Hearing loss the problem does not seem to be damage to these hair cells, it seems to be deeper in the synapses that connect the hair cells to the nerve of hearing. this means that there is still a break in the chain of hearing, but that break is more about quality of sound information passed rather than volumes. In essence, the input is still heard but the signal is corrupted.
It is believed that this damage is caused by exposure to noise,animal studies at Harvard found that sensitivity to quiet sounds in mice who were briefly exposed to loud noise, was reduced for a few days. This was in fact expected and the phonomenon is what is called a temporary threshold shift. However, what was not expected was the discovery that the mice had permanently lost half the connections between the hair cells and the auditory nerve fibres in a large region of their cochlea. This was quite a fascinating discovery and led to a better understanding of the difficulties that were being seen with people with so called hidden hearing loss.
At present, the damage is permenant, however, it is belived that we can possibly reverse the damage in the future by treating the surviving neurons with neurotrophins (promote healthy nerve growth), injected through the eardrum into the cochlea.
Currently, because of the nature of the problem, there is no easy test for Hidden Hearing Loss. The test used in the research is not available outside the confines of the laboratory. However, we can get indications of the problem when a full test hearing test battery is used. As we said, normal pure tone audiometry gives no indication of the problem. Thats why we also use a speech in noise test during our audiological testing process. This test shows up any anamolies in your understanding of speech in noise. Treating this problem at present is a non starter, hearing aids are probably a step too far for this issue although they may help in those noisy environments. We will monitor advancements in this particular area with interest.
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