1 in 1000 children is born deaf. Depending on the type of hearing loss, cochlear implants can help deaf babies acquire speech almost as well as normally hearing babies.

Not too long ago, when a person was deaf they had to rely on sign language to communicate. Thanks to small implantable devices, known as cochlear implants, this has changed over the course of the past decades. About 1 in a 1000 children are born deaf, and 4 in 1000 adults in the US are profoundly deaf. To date, about 150,000 of these people have been implanted. For most of them, these neural prostheses are a lifeline that restores basic auditory function. Cochlear implants are perhaps the most successful neural prosthesis to date.

Cochlear implants work on a technical principle whose basic origins date back to the late 18th century, to Wolfgang von Kempelen. In 1769, von Kempelen, ingeniously invented the world’s first speaking machine that synthesized speech with a two part system – a circuit consisting of an acoustic source and a bank of acoustic filters. His work has inspired a long line of research and was further developed by famous engineers, such as Sir Charles Wheatstone, Alexander Graham Bell and Homer Dudley.

Today, cochlear implants use a related principle when they transmit sound electrically to the auditory nerve. The user wears a little device with an external microphone and sound processor that looks a lot like a hearing aid. An electrode array is surgically implanted into the cochlea (the little snail-shaped structure inside your ear). The sound processor sends signals to this electrode array as follows. It continuously breaks the sound from the microphone into several frequency bands (the bank of acoustic filters), ranging from low to high. In each frequency band, the cochlear implant processor extracts slow fluctuations in the signal. These slow fluctuations carry important speech information. Depending on how loud these slow fluctuations are in the acoustic sound, the implanted electrodes then shapes electric pulses (the source signal) and sends these pulses to the electrode array which stimulates the auditory nerve. When the auditory nerve is electrically activated, this generates a sense of hearing.

Typical components of a cochlear implant system.

Cochlear implants can be of great importance to the individual user who can go from hearing nothing to hearing again in a rather short time period of several months. It is difficult to overstate the impact this can have on the individual’s life quality – allowing them such basic cues as to hear that a bus is approaching from behind, or that someone entered the room, to helping them with more central functions such as being able to understand speech again or perhaps even appreciate music and dance. Not all cochlear implant users are equally successful at regaining these important functions. The reasons underlying these individual differences are a question for active research.

Visual Art credits:

http://www.hearingpocket.com/images/baby2.jpg

http://www.abc.net.au/rn/boyerlectures/images/2007/image.htm