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WE HAVE ALWAYS BEEN BIONIC

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Earlier methods to improve deficient hearing dealt only with the outer ear.The first approach was the hearing aid, which in early days took the form of an ear horn, a trumpet-shaped device held up to the ear. The ear horn worked like a megaphone or the large hornlike devices seen on Edisons early phonographs, but in reverse; the large cross-sectional area of the horn captured more sound energy than the ears small opening could and funneled that enhanced sound into the ear itself. With the advent of electricity, however, a hearing aid be- came something different. It changed sound into an electrical signal that was processed and amplified,and then changed back into a louder, clearer sound fed directly into the hearing-impaired ear through a speakerbut still not going directly into the auditory nerves.

Electrical hearing aids were in use by the late nineteenth century. An electrical unit called the Akoulathon, invented in 1898, was being sold commercially in 1901. Like early telephones, it used a carbon transmitteror microphone of the type invented in the 1870s.Then, as in the development of computers, advances in electronicsfirst the vacuum tube that amplified the signals going to the ear, followed by transistors and integrated circuitsled to todays extremely small and efficient hearing aids.

DIGITAL EARS

Todays hearing aids certainly help those with hearing loss but do not qualify as true bionic additions because they are not directly implanted into the body or connected to its neural system. But help for the hearing-impaired reached bionic status in the late 1950s,when several researchers explored the possibility of direct electrical stimulation of the cochlear nerves.The expectation was that if the nerves were in- tact, stimulating them directly might produce the sensation of sound in the brain. Considerable development led to the cochlear implant, todays most mature neural prosthesisthe only one that is commer- cially availableand the most widespread, with some 30,000 im- planted since 1999.

The cochleanamed after the Latin word for snail”—is a

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