How Do Hearing Aids Work?
The most recent estimates suggest that as many as 800 million people around the world suffer from some sort of hearing loss; and that hearing loss can be caused by aging, infection, trauma, or environmental issues. Either way, for many who suffer from hearing loss it is enough of a nuisance as to interrupt daily life significantly. Fortunately, today's hearing aids are technologically advanced enough to restore at least some lost hearing. The question is; how do they work?
How hearing aids work really depends on the type of device we're talking about. But before getting to that we must discuss the different types of hearing loss. Hearing loss can be divided into two types: conductive and sensorineural. Conductive hearing loss is such that when sound waves enter the ear canal they are interrupted and prohibited from completing the chain of events that results in electrical impulses being sent from the nerves to the brain. This interruption can be caused by excessive ear wax, ear infections, damage to the eardrum, and so on.
On the other hand, sensorineural hearing loss doesn't prevent sound waves from completing their journey; it just lessens the effect of those sound waves as they pass through the ear. This is most commonly caused by the normal wear and tear of aging. But it can also be caused by the same types of factors that cause conductive hair loss. Just so you know sensorineural is the most common type of hearing loss around the world.
Amplifying Hearing Aids
Amplifying hearing aids are the ones used to treat most cases of sensorineural hearing loss. These devices consist of a battery, microphone, receiver, and amplifier. How they work is very similar to a typical PA system which might amplify the human voice or music. There are several styles of amplifying hearing aids that can be fitted inside or outside the ear but they all work on the same principle.
The microphone picks up sound waves from the local environment, sends those sound waves to the transmitter which in turn, sends them on to the amplifier. The biggest difference between these hearing aids and a PA system is that the hearing aid is much more sensitive to even the most subtle of noises. The biggest downside to these types of hearing aids is that they amplify all of the sound waves in a given spectrum, regardless of what they are.
Fortunately, as time has passed amplifying hearing aids have been transformed from analog to digital devices. New, digital hearing aids can be programmed for a variety of hearing environments depending on the needs of the user. This allows certain signals to be filtered out while others are being amplified, giving the user much more clarity. They are by no means perfect, but they are far better than the early hearing aids of 20 and 30 years ago.
Cochlear implants are not hearing aids in the same sense that amplification devices are. They are designed for people who are profoundly deaf because of a variety of conditions. They work by completely bypassing the mechanical parts of the ear and directly stimulating the auditory nerve. A cochlear is a two-part system consisting of a surgical implant and an external processing system. The external component consists of a microphone, sound processor, and the transmitter. The implant consists of a receiver and an electrical system.
With cochlear implants the prosthetic portion is attached to the skull, underneath the surface of the skin and just behind the ear. The electrical system is attached directly to the auditory nerve and, through time, fuses with the tissue to become incorporated with the body. The implant is generally fixed with a metal plate so that the external device can be attached using a magnet. The external device "hears" the sound, processes it, and then transmits it to the implanted receiver. The receiver then sends signals to the auditory nerve which are interpreted by the brain as sounds.
Bone-Anchored Hearing Aids
One of the newest types of hearing aids on the market is similar to cochlear implants. It's called the bone anchored hearing aid and it also bypasses the inner workings of the ear. It is a bit more invasive than cochlear implants and requires a prosthesis to be implanted within the skull. The prosthesis has a post which protrudes through the skin somewhere on the side of the head near the ear.
An external device, which performs the same function as the external device on the cochlear implant, attaches to the implant through a spring-loaded or coupling system designed to detach instantly on impact. When the external device transmits a signal to the receiver, the receiver translates those signals into electrical impulses which cause the implants to vibrate accordingly. In turn the skull bones vibrate and send those signals to the auditory nerve.
With both the bone-anchored hearing aid and cochlear implants natural hearing is not restored. Rather, a synthesized sort of hearing is what's made available. Although neither reproduces sounds completely accurately they provide a close enough simulation that most users can function at a fairly normal level. But just like amplifying hearing aids, they also need to be tested and programmed in order to achieve maximum benefit.