03 October 2017
Hearing loss is diverse and the technologies available to help support people with hearing loss, equally so.
Everyone knows about hearing aids, and cochlear implants are certainly becoming better understood in the general community, but BAHA’s and other technologies are much less known. Also, which hearing technology will, and should, your child get?
There are many variables, so today we’ll try and give an overview of the different types of hearing technologies and when they might be used.
Obviously, every case is unique and parental choice is a huge part of the hearing technology choice for a child.
Before we can look at the hearing technologies you need to understand the different types of hearing loss.
Hearing loss can be segmented based on two main criteria – level of loss and type of loss.
Level of hearing loss
There are 4 major types of hearing loss; mild, moderate, severe and profound. The classification is based on the lowest decibel level a person can hear 50% of the time. In people with full hearing this is 0-20dB.
You can read a more detailed explanation of level so hearing loss and how they are measured in our blog post on audiograms.
The levels of hearing loss and their associated decibel level are shown below:
- Mild Loss - 20-40 dB: Cannot hear soft sounds. Can hear normal conversation in a quiet room, but not in a noisy environment
- Moderate Loss - 40-70 dB: Has difficulty hearing normal conversation.
- Severe Loss - 70-90 dB: Can only hear very loud speech next to the ear.
- Profound - 90+ dB: Can hear very little, if at all. Even the sound of a motorcycle would not be able to be heard.
Types of hearing loss
In addition to the level of hearing loss there are 3 main types of hearing loss; sensorineural, conductive and mixed.
- Sensorineural hearing loss: Those with sensorineural hearing loss have problems with the inner ear, this could be problems with the tiny hair cells in the ear or auditory nerve damage. Sensorineural hearing loss can either be congenital (i.e. the child is born with it) or acquired (through exposure to loud noises, infection, certain drugs etc). Sensorineural hearing loss varies from mild to profound.
- Conductive hearing loss: We discussed conductive hearing loss in our last blog post on microtia and atresia, but put simply those with conductive hearing loss have a fully functioning inner ear, but their ability to have sound reach that inner is reduced or completely blocked.
- Mixed hearing loss: As the name suggest mixed hearing loss is a combination of conductive and sensorineural hearing loss.
The type of technology used for different types and levels of hearing loss is shown below. Also, someone with a bilateral hearing loss may have different technologies in each ear, depending on the hearing loss in the individual ears.
Types of Hearing Technologies
As you can see there are a variety of different types of hearing technologies available, depending upon the type and severity of the hearing loss.
Some are more common than others, but we will try and give you an overview of each technology.
Auditory Brainstem Implants
Auditory brainstem implants are not a very common technology as they are only used for those with severe auditory nerve damage. This means that sound gets into the ear, it passes along the ear canal and even reached the cochlea without incident. However, once the cochlea has converted the sound to an electrical impulse to pass it up the auditory nerve and into the brain, the system breaks down. The auditory nerve is unable to pass the information to the brain due to the nerve damage.
An auditory brainstem implant replaces the damaged nerve by passing electrical impulses straight into the brainstem.
The implant is similar in function to a cochlear implant. They have a receiver and an electrode surgically implanted, with the electrode placed on the brainstem. On the outside of the head the person wears a sound processor, which takes in the sound and passes it to the receiver and electrode.
Unlike a cochlear implant an auditory brainstem implant cannot help someone distinguish between different sounds, therefore for people with this kind of hearing loss oral communication options may be a little more limited.
Bone Anchored Hearing Aids
Bone anchored hearing aids (BAHA) are used by people with a conductive or mixed hearing loss. At the Centre the majority of the children with a BAHA have microtia or atresia (which we spoke about in our blog last week.
Due to the problems with the formation of the ear or ear canal sound is unable to get to the cochlea in people with conductive hearing loss. Therefore they need a hearing aid that by passes those structures and provides sound directly to the cochlea.
A BAHA does this by taking in sound through a receiver and passing it to the skull through vibrations. These vibrations are then send to the cochlea.
In children the BAHA is worn on a soft band, but as children get older (from a minimum of 5 years) the part of the device can be implanted into the skull to allow a stronger vibration to reach the cochlea.
This video shows, in simple diagrams how a BAHA works.
For children, and adults, with a significant hearing loss cochlear implants are often the chosen form of hearing technology.
In essence the cochlear implant replaces the role of the cochlea in the ear. A sound processor is worn behind the ear, and that processor receives sounds from the outside world. These are then converted to an electrical impulse which is passed to a receiver, which has been surgically implanted under the skin. This receiver then passes the information to an electrode array in the cochlea. This electrode array than passes the sound information to the auditory nerve.
Due to the electrode array being placed in the cochlea any residual natural hearing the cochlea has, will be removed.
This video from Advanced Bionics shows really clearly how a cochlear implant works.
A CROS (or Contralateral Routing of Signals) hearing aid is only used in cases of severe to profound unilateral hearing loss, that is hearing loss on one side.
A CROS aid has a receiver on the side with hearing loss, which transmits the sound to a device on the hearing side. This means that the person has access to sounds from both sides, but cannot localise the sounds as they are both being heard on one side.
Hearing aids are probably the hearing technology most people are familiar with. The theory behind hearing aids is simple. They take in sound and alter and amplify it to the best level for an individual to hear.
The traditional view of hearing aids is that they sit behind the ear, with a mould inside the ear. However, as technology has progressed there are many different types, ranging from the visible behind the ear styles to those that sit completely inside the ear canal and are invisible.
Hybrid cochlear implants
For those people that have a severe high frequency loss, but can still hear low frequency sounds the hybrid cochlear implant is an option. This is very often the case for people who have lost part of their hearing due to aging.
Like the name suggest hybrid cochlear implants combine the functions of a cochlear implant and those of a hearing aid. So for the higher frequency sounds the hybrid cochlear implant acts like a traditional cochlear implant, and for the low frequency sound, it acts more like a traditional hearing aid.
Middle Ear Implants
Middle ear implants are for those who cannot benefit from traditional hearing aids. A microphone is worn on a processor, which site behind the ear. The sounds it detects are amplified and transmitted to a device surgically attached to the staples (a middle ear bone), which is located next to the cochlea. The implant translates the electronic sound to vibrations, which are passed to the cochlea.
It is worth bearing in mind that receiving hearing technology is only the beginning of hearing loss management. An overall therapy program, like that provided by the Cora Barclay Centre, means that children can learn to use their hearing technology to benefit them and to learn to listen and speak.
If you have a child with hearing technology and would like to learn more about how they can use it to learn to listen and speak, please get in touch.