The multichannel cochlear implant

A cochlear implant does not amplify sound as a hearing aid does. A microphone and speech processor turn sound into electrical signals, and an array of electrodes inside the cochlea passes them to different regions of the auditory nerve, bypassing the damaged ear. French doctors tried a single electrode in the late 1950s; it worked poorly and failed quickly. In 1961 William House implanted a single-channel device in two people. They could perceive environmental sounds, and later single-channel devices helped people lipread, but speech came through badly distorted.

Graeme Clark, whose father had struggled with deafness, took the first chair of otolaryngology in Australasia at the University of Melbourne in October 1969. His department built a device that could stimulate several sites along the cochlea separately, the idea being that each site would carry a different band of frequencies. Three television telethons between 1974 and 1976 helped pay for it. A multichannel design by Ingeborg Hochmair and colleagues was first implanted in a patient in December 1977.

On 1 August 1978 Clark implanted the Melbourne prototype in Rod Saunders, a totally deaf man, at the Royal Victorian Eye and Ear Hospital. When different sites were stimulated, Saunders heard different vowels, matching the frequency bands that distinguish vowels in speech. The team went on to build a speech processor that patients could wear. By 1981 two deaf adults using the implant scored 34 and 36 percent on live open-set sentence tests without lipreading, and 68 and 98 percent with it.

The Melbourne results led to the company Cochlear Limited. In 1985 its implant became the first multichannel device approved by the US Food and Drug Administration for adults, and in 1990 the first cochlear implant of any type approved for deaf children over two. In 1991 Blake Wilson, at the Research Triangle Institute in North Carolina, reported continuous interleaved sampling, a processing strategy that let many users understand words and sentences with no visual cues. By December 2019 about 736,900 devices had been implanted worldwide, including about 65,000 in children in the United States.