How do we listen to sound? Sound travels into the ears as vibrations in the air. These vibrations then cause the eardrum to oscillate, and the vibrations are transmitted to the ossicles, a set of three tiny bones in the middle ear. Finally, the vibrations reach the cochlea, a spiral-shaped organ in the inner ear that resembles a snail’s shell. Hair cells in the cochlea convert the vibrations into electrical signals. When these signals reach the brain through the auditory nerve, we perceive the sound.
However, if the cochlea hair cells are damaged, their ability to convert the sound into electrical signals is impaired. It is not possible to improve this impairment with hearing aids or standard ear surgery.
The cochlear implant was developed to address this challenge. The sound picked up by a microphone is converted into electrical signals by a speech processor. These signals are transmitted to the implant, and then to electrodes inserted within the cochlea to directly stimulate the auditory nerve. Dr. William House, an American otologist, developed a single-channel cochlear implant in the 1950s. Although his invention enabled patients to perceive sound, it was unable to transmit the sound as clear words. Hence, the system functioned only as a support for patients to read speakers’ lips. Also, the number of people who received such implant surgery was limited.

The major breakthrough came in the 1970s with the development of a multichannel cochlear implant. Among the pioneers of multichannel cochlear implant technology were Dr. Ingeborg Hochmair, an electrical engineer at the Technical University of Vienna, and Professor Graeme Clark, an neuroscientist at the University of Melbourne. Working independently, both researchers developed multichannel cochlear implants that could deliver different sound frequencies to different regions of the cochlea. The first patient received Dr. Hochmair's multichannel cochlear implant in December 1977, and the first implantation of Professor Clark's device in August 1978. The basic design of their prototypes is still used in many cochlear implants today. Their work transformed the possibilities for people with profound hearing loss, enabling many to understand speech, communicate more effectively, and engage more fully with the world of sound.
Later, both researchers played important roles in bringing their innovations from the laboratory to clinical practice. Professor Clark worked closely with industry to advance the commercialization of his research with support from government partners in Australia, and his work evolved into the cochlear implant developed with Cochlear Limited which was established as a division of the Nucleus Group. Meanwhile, Dr. Ingeborg Hochmair and her husband, Professor Erwin Hochmair, founded MED-EL to continue advancing cochlear implant innovation. Their efforts helped shape the field and expand access to cochlear implants for people with hearing loss around the world.
Technological advancements have also extended beyond the implant itself. Continuous improvements in externally worn speech processors and audio processing software have enabled recipients to benefit from new features and enhanced hearing performance over time. In many cases, these upgrades can be provided without the need for additional surgery or replacement of the implanted device.

As sound transmission technology advances, the applicability of these devices has expanded. To date, more than a million people have been fitted with cochlear implants across the world, including 20,000 people in Japan. There, some 1,200 implant operations are carried out annually, including an increasing number of operations among children under seven and the elderly aged 60 and over.
For the elderly, preserving hearing ability is an important factor in maintaining their quality of life. Studies have shown an association between age-related hearing loss and cognitive decline in older adults. Cochlear implants are an effective option to support their verbal communications and social participation. Children with profound hearing loss can now often be identified through newborn hearing screening programs. With early cochlear implantation, appropriate device fitting, and language support, many children can develop spoken language from an early age.
Cochlear implants offer people with profound hearing loss new opportunities for auditory verbal communications, in addition to sign language and other various forms of languages and culture. These implant systems have grown into a technology that expands individuals’ life possibilities and can help fulfil their dreams and future plans. The multichannel cochlear implant, often termed “the most successful prosthesis,” will continue to support many people’s lives and futures through its evolution, representing a model case of biomedical engineering and human-machine interfacing.