External parts of the device includes a microphone, a speech processor (for converting sounds into electrical impulses), connecting cables, and a battery. Unlike a hearing aid, which just makes sounds louder, this invention selects information in the speech signal and then produces a pattern of electrical pulses in the patient's ear. It is impossible to make sounds completely natural, because a limited amount of electrodes are replacing the function of tens of thousands of hair cells in a normally hearing ear.
The implant has evolved over years and many different teams and individual researchers have contributed to its invention and improvement.
In 1957, Djourno and Eyries of France, William House of the House Ear Institute in Los Angeles, Blair Simmons of Stanford University, and Robin Michelson of the University of California, San Francisco, all created and implanted single-channel cochlear devices in human volunteers.
In the early 1970s, research teams led by William House of the House Ear Institute in Los Angeles; Graeme Clark of the University of Melbourne, Australia; Blair Simmons and Robert White of Stanford University; Donald Eddington of the University of Utah; and Michael Merzenich of the University of California, San Francisco, begin work on developing multi-electrode cochlear implants with 24 channels.
In 1977, Adam Kissiah a NASA engineer with no medical background designed a cochlear impant that is widely used today.
In 1991, Blake Wilson greatly improved the implants by sending signals to the electrodes sequentially instead of simultaneously - this increased clarity of sound.