To understand the difference between hearing aids and cochlear implants you’ve first got to understand how the ear works.
 
First, sound is caught by the outer ear, or pinna. This is the part of the body your child points to when you ask, Where’s your ear? The shape of the pinna helps us focus on where a sound is coming from. 

The first hearing aids created in the 1500s were shaped like the pinna of animals known to have good hearing. 

The sound then travels through the ear canal to the middle ear. The sound vibrations cause the eardrum, or tympanic membrane, to vibrate. The vibration is powerful enough to move the ossicles, three teeny tiny bones on the other side of the eardrum; first the malleus, or hammer, then the incus, or anvil, and finally the stapes, or stirrup. 
The stapes is the smallest bone in the human body. 

This is vitally important knowledge for games of Trivial Pursuit or Quiz Nights down at the pub. 

The stapes is attached to the oval window of the cochlea, a snail shaped structure in the inner ear. The cochlea is filled with fluid similar to spinal fluid and it is lined with hair cells. The vibrations caused by the ossicles create movement in the fluid which stimulates the hair cells. This is the point where the sound signal goes from being mechanical (vibrations) to neural (electric). The hair cells are arranged tonotopically with the high frequency sound found closest to the oval window and the low frequency sounds curving around the inside of the snail shape
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There are thousands of hair cells in the cochlea. The now neural signal is sent to the auditory nerve which carries it to the auditory cortex in the brain. This is the point we get all that sound and language processing stuff I talked about in last month’s newsletter.
So, let’s consider hearing loss. A conductive hearing loss means there is a problem with the outer or middle ear. This could range from a physical abnormality with the ossicles or pinna to glue ear which temporarily prevents proper movement in the middle ear. A sensorineural loss means that the hair cells within the cochlea are not working. However, often some of the hair cells continue to function. This is how we get different levels of hearing loss. Luckily we are able to benefit from numerous recent developments in hearing technology.

Hearing aids amplify sound. They require that the child has some functioning hair cells. A microphone, worn at ear level picks up sound, an amplifier increases the volume, and a speaker delivers the sound to the ear canal. The increased volume creates a more powerful mechanical signal vibrating the ossicles more, allowing a stronger fluid wave to stimulate more hair cells and hopefully accessing those that are still functioning.

A cochlear implant, on the other hand, directly stimulates the auditory nerve. Twentyfour electrodes are placed inside the cochlea tonotopically just as the hair cells are arranged and a receiver stimulator is embedded in the skull just over the ear. The exterior portion of the cochlear implant includes a microphone worn at ear level which picks up sound just like the hearing aid. 

The sound is then sent to the speech processor which is worn on a belt or, with the new Cochlear Freedom processor, at ear level. 
The processor is programmed specifically for the wearer. It selects characteristics of the sound and codes them. The code is then sent through a cable to the coil. The coil connects to the head via a magnet in the receiver stimulator under the skin. The coil transmits the code through the skin by radio frequencies. There, the code is converted into an electrical signal. The signal is sent to the electrodes inside the cochlea where they stimulate the auditory nerve just like the hair cells do.

If all of that was too long winded and boring for you, just remember, hearing aids amplify sounds, and cochlear implants stimulate the auditory nerve and that is the biggest difference between the two.

Ears with normal hearing have the ability to filter out most unwanted background noise. Unfortunately, hearing aids amplify all the sounds around them. Have you ever made an audio recording of someone talking? When the tape played back there was probably a lot of sounds that you hadn’t noticed when listening live that interfered with the speech signal. Listening though hearing aids can be similar.

One solution for a poor signal-to-noise ratio (S/N) is a personal FM system. 

The speaker wears a microphone and the speech signal is sent through the air via FM radio waves to a receiver worn by the child. The most popular FM system today is the MicroLink. In this system, the receiver is a small “boot” that hooks to the bottom of the hearing aid. The MicroLink allows children to benefit from a clear speech signal without wearing extra wires. 

FM systems can be used two ways. First, the hearing aid microphone can be left on so that, in the classroom, for instance, the child can hear his classmates but the teacher’s voice is louder (assuming she’s wearing the microphone of course). It is optimal for the speech signal to be 15-20dB louder than background noise.

The FM system can also be used with the hearing aid microphone off. This set up permits the child to hear only the teacher wearing the microphone with absolutely no competing noise.

Currently, Australian Hearing provides FM systems to children kindy age and above. However, you are quite entitled to request one for your younger child. 

School-aged children benefit from FM systems in the classroom because they significantly reduce the signal to noise ratio, allowing the child to hear the teacher without interference. FM systems are also useful at home when reading books or riding in the car so you don’t have to continually turn around to talk to the backseat.
 
It’s important to remember to only use the FM system at times when you are in the room and interacting with the child. If you wander to the next room and have a conversation with someone else, the child will hear the whole thing and will, most likely, be very
confused. This is good information to pass on to the teacher as well. 

The FM system should be used during group activities when the teacher is speaking to the whole class or a small group including the child with hearing impairment. Most importantly, remember to turn it off before heading to the toilet or discussing a child’s behaviour with another teacher!

While FMs are highly recommended for school-age children, infants and toddlers can also benefit from them. The American Speech-Language Hearing Association (ASHA) recommends all infant with hearing impairment are fitted with FMs to provide optimal S/N ratios so that the child can benefit from incidental speech without a degraded signal caused by background noise, distance, or reverberation.

As toddlers become mobile, FM systems allow parents to provide speech input at levels similar to those that occur at 6-8 inches from the ear. Language input is vital in the first few years of life. An FM system provides the best signal with which to provide it. 

If you haven’t already, talk with your audiologist about getting an FM system. Providing your child with the best listening environment possible allows her to learn speech and language with minimal interference.