Development of multi-channel cochlear implants Clark hypothesized that hearing, particularly for speech, might be reproduced in people with
deafness if the damaged or underdeveloped ear were bypassed, and the auditory nerve electrically stimulated to reproduce the coding of sound. His initial doctoral research at
the University of Sydney investigated the effect of the rate of electrical stimulation on single cells and groups of cells in the auditory brain-stem response, the centre where frequency discrimination is first decoded. Clark's research demonstrated that an electrode bundle with 'graded stiffness' would pass without injury around the tightening spiral of the cochlea to the speech frequency region. Until this time he had difficulty identifying a way to place the electrode bundle in the cochlea without causing any damage. He achieved a breakthrough during a vacation at the beach; he conceptualized using a
seashell to replicate the human
cochlea, and grass blades (which were flexible at the tip and gradually increasing in stiffness) to represent the electrodes. Clark demonstrated that the electrode bundle needed to be free, with wires terminated in circumferential bands to reduce friction against the cochlear wall, facilitating insertion. The bands had to be wide enough to minimize charge density for safety yet narrow enough for precise nerve fiber stimulation to enable frequency place coding. To address safety concerns, Clark conducted experiments showing a minimal risk of meningitis from middle ear infections if a fibrous tissue sheath formed around the electrode bundle. This sheath was derived from a connective tissue graft taken from the patient and placed at the cochlear entry point. The first cochlear implant was invented and developed by Dr.
William F. House. House's device was a single electrode configuration, compared to the multiple electrode device developed by Clark. Clark's first multi-channel cochlear implant operation was done at the
Royal Victorian Eye and Ear Hospital in 1978 by Clark and Dr. Brian Pyman. The first person to receive the implant was Rod Saunders who had lost his hearing aged 46. Less than one year later, a second patient was implanted. George Watson, an Australian
World War II veteran, had lost his hearing after a bomb blast thirteen years earlier. An audiologist working on Clark's team at the time described the team's first two patients as, ''"guys who'd put up with anything and continue to keep coming in and support the work.".'' After successfully completing the surgery in 1978, with his post-doctoral colleague, Yit Chow Tong, Clark discovered how multi-channel
electrical stimulation of the brain could reproduce
frequency and
intensity as pitch and loudness in severely-to-profoundly deaf adults who originally had hearing before going deaf. Electrical stimulation at low rates (50 pulses/sec) was perceived as a pitch of the same frequency, but at rates above 200 pulses/sec, what was heard was poorly discriminated and a much higher pitch. This discovery established that the timing of electrical stimuli was important for low pitch when this had been difficult to determine with sound. But
discrimination of pitch up to 4000
Hz is required for speech understanding, so Clark emphasized early in the development of his cochlear implant that "place coding through multi-channel stimulation" would have to be used for the important mid-to-high speech frequencies. Clark and Tong next discovered that place of stimulation was experienced as timbre, but without a strong pitch sensation. The patient could identify separate sensations according to the site of stimulation in the
cochlea. At the end of 1978, Clark and Tong made the discovery that the speech processing strategy coded the second formant as place of stimulation along the cochlear array, the
amplitude of the second formant as current level, and the voicing frequency as pulse rate across the formant channels. in December 1978, Clark arranged that his
audiologist present open-set words to his first patient, who was able to identify several correctly. As a result, Clark went on to operate on a second patient who had been deaf for 17 years. He was able to show that the speech coding strategy was not unique to one person's brain response patterns, and that the memory for speech sounds could persist for many years after the person became deaf. In 1982, Clark supervised clinical studies required by the U.S.
Food and Drug Administration (FDA). In 1985, following a global trial, the FDA approved his multi-channel cochlear implant for adults aged 18 and over who had hearing before becoming deaf. It became the first multi-channel cochlear system approved as safe and effective for speech understanding through both electrical stimulation and lip reading. In 1990, the FDA extended approval for a 22-channel cochlear implant for children aged 2 to 17. From 1985 to 1990, Clark’s team at the Cochlear Implant Clinic in Melbourne, along with clinics worldwide, found that their speech coding strategies allowed up to 60% of children to understand words and sentences using electrical stimulation alone, without lip-reading. The addition of high-frequency bands led to further improvements in speech perception, production, and language scores.
The Bionic Ear Institute In 1970, Clark was appointed Foundation Professor of Otolaryngology at the University of Melbourne and became one of the first Laureate Professors in 2000, recognizing his international scientific achievements. He held this position until his retirement in 2004, leading cochlear implant research as Head of the Department of Otolaryngology. His research was funded initially by an appeal through a Telethon, and then a Public Interest Grant from the Australian government. His ongoing research to understand the functioning and improve the cochlear implant was through his grants from the National Health and Medical Research Council of Australia, the Australian Research Council, The US National Institutes of Health, and The Cooperative Research Center program. In 1983 the
Bionic Ear Institute was founded by Clark, as an independent, non-profit, medical research organization. The goal of the Bionic Ear Institute was, "to give deaf children and adults the opportunity to participate as fully as possible in the hearing world and to find new ways to restore brain function". The Bionic Ear Institute renamed itself the
Bionics Institute in 2011 due to an expansion of its aims to not just improve the bionic ear, but to develop a bionic eye and devices capable of deep brain stimulation. ==Charity foundations==