How a cochlear implant works
A cochlear implant bypasses the parts of the ear that no longer work properly by sending signals directly to the hearing nerve.
|1. A Microphone on the speech processor (worn on the outside) picks up sound and then converts it into a digital signal.|
|2. The signal is then transferred via an FM signal from the coil (attached to the head via a magnet) to the implant just under the skin.|
|3. The implant then sends the signals through the electrodes which have been inserted into the cochlea.|
|4. The electrodes pass the signal to the hearing nerve fibres in the cochlea and then the signal is passed up to the brain, giving the sensation of sound.|
A cochlear implant has to transfer a very complex set of information. It needs to provide the wearer with knowledge of:
- the frequencies of sound present (pitch) measured in Hertz (Hz)
- the levels of sound present (loudness) measured in Decibels (dB)
- the timing of the different sounds (temporal information).
There is a huge range of sounds in our environment, ranging from quiet, high pitched sounds like bird song or rustling leaves, to louder and broader sounds like music and traffic noise. The human ear can hear pitches of sound ranging from 20 – to 20,000Hz. It can hear a range of loudness from 0 to 120dB. It does this using around 15,000 cochlear hair cells and functioning nerve fibres.
Cochlear implants have between 12 and 22 electrodes to convey sound and so they are providing a significantly reduced amount of information compared to normal hearing. A visual interpretation of this could be a very blurred picture compared to a picture presented in high definition.
It is amazing how anyone can hear with such reduced information. The brain does an amazing job at interpreting this crude signal and, with time to adapt, patients can often hear very well with a cochlear implant.
For more information read ‘What Cochlear Implants Can Do‘
- What is a cochlear implant?
- How does it work?
- Who should have a cochlear implant?
- What does a cochlear implant sound like?
- Who manufactures cochlear implants?