What is hearing?
Hearing is the ability to perceive sound by detecting vibrations through the ear. Humans have a fairly narrow range of hearing compared to other species – frequencies that we are capable of hearing are between 20 Hz and 20,000 Hz, this is know as the audio, or sonic, range. Frequencies above that range are know as ultrasonic and those below are know as infrasonic. Dogs can hear ultrasound, that’s why they hear dog whistles and we don’t. Apparently snakes can sense infrasound though their bellies, and elephants, giraffes, dolphins and whales use it to communicate.
Listening and hearing are not the same thing and I think the distinction is important, especially when it comes to understanding a hearing loss and successfully using hearing aids. Listening is something you consciously do, it is the act of interpreting and understanding the sound that you heard.
Hearing loss and its causes
It’s estimated that 10% of the population have a hearing loss that is significant enough to impair communication. It is likely that far more than that 10% have a mild loss that is either not yet noticeable or not bad enough to cause them concern. Studies have shown that it takes an average of seven years from the first onset of hearing loss for someone to seek some kind of help or treatment. There are two types of hearing loss:
Sensorineural hearing loss
A sensorineural hearing loss is one that affects the nerves or hair-cells in the inner ear. Common causes include old age, noise exposure, ototoxic medications and Menieres disease. Sensorineural loss accounts for 90% of all hearing loss. Nerve and/or hair-cell damage does not only reduce the sounds that you can hear, it also affects your ability to understand sounds that you have heard – a very common problem is being able to hear someone talk but not being able to understand clearly what they are saying.
This type of hearing loss does not necessarily affect all of the sound you can hear equally. Imagine a piano, you can hear all of the notes from the full-range of keys being played, now if you remove or smash some of those keys and you can now only hear they remaining keys being played – a sensorineural loss is a bit like that, you can hear some frequencies perfectly and some not so well.
This type of hearing loss is permanent. There is no cure at the moment but there is strong hopes that stem-cell injections may offer a cure in the future.
Conductive hearing loss
A conductive hearing loss is one that affects the structures that transfer (conduct) the sound to the inner ear. Many cases are treatable. Wax and fluid build-up are easily removed, an infection can be treated with antibiotics, a ruptured eardrum can be patched and damaged middle ear bones can be replaced.
This type of hearing loss affects all sound equally, the opposite to sensorineural, if you have a conductive loss then all frequencies reduced by the same amount.
Hearing ringing or buzzing sounds that aren’t real
Tinnitus is the perception of sound within the ear in the absence of corresponding external sound. The sounds that people with tinnitus hear can vary from ticking, beeping, whooshing, buzzing or wind noise to musical tunes and songs. Some people experience a constant, steady sound and others have ever-changing sounds – some people have more than one sound at the same time.
Tinnitus can be caused by ear infections, wax build-up or stress but the most common reason is excessive exposure to loud noise. Sufferers are advised to try and stay stress-free, get enough sleep, avoid caffeine, use a hearing aid and to use low-level noise generators that help to mask the tinnitus sounds. Tinnitus tends to mostly occur in quiet situations, noise generators and hearing aids have proved to be very good at producing sounds to mask the tinnitus.