Engineering Sound

Learn about IEEE Senior Member Hugh McDermott's work on acoustic hearing aids and cochlear implants

7 November 2008

profileWhen IEEE Senior Member Hugh McDermott was a child, he was passionate about everything to do with music; he loved listening to it, played instruments, and built makeshift radios and amplifiers. Now he’s taking his love of sound to another level to help those who can’t hear.

“When I finished my degree, I wanted to do research instead of working in industry,” says McDermott, 49. “I was interested in hearing because I’m really into music. I play the cello and was in amateur orchestras throughout high school.”

Today his research could affect the estimated half-billion hearing-impaired individuals worldwide. McDermott develops acoustic hearing aids and cochlear implants—electronic chips that drive electrodes placed in the auditory portion of the inner ear (the spiral-shaped cochlea) that process and transmit sound signals to the brain.

To recognize his research, which has become internationally renowned, the University of Texas in Dallas will in March award McDermott—a professor of auditory communication and signal processing at the University of Melbourne in Australia—its first Callier Prize (and with it US $10 000, which McDermott plans to use to advance his research) for advances in the diagnosis and treatment of communication disorders.

In his nearly three decades in the lab, McDermott has continuously improved upon previous generations of auditory electronics by heightening their sensitivity to speech frequencies, downplaying ambient sound, translating higher speech frequencies to lower and more easily heard registers, and streamlining the functioning of the devices.

McDermott says he owes his choice of a career to a newspaper ad that piqued his interest in the field, years ago. He had just earned a bachelor’s degree in applied science in 1981 from the University of Melbourne when he spotted an ad for Ph.D. candidates interested in cochlear implant research at the university’s department of otolaryngology, the medical branch specializing in the diagnosis and treatment of head and neck disorders, including hearing disorders. With the assistance of an Australian government scholarship, he applied and was accepted. (The program began as a master’s research course that McDermott was able to convert to a Ph.D. program after a year because of the quality of his work.)

YEARS OF IMPROVEMENTS The program involved upgrading existing hearing devices. Implants that electronically stimulated inner ear nerves, making it possible for deaf patients to hear, had been around since the 1950s. In the 1960s and ’70s, their performance improved dramatically; one of the first new-generation devices was implanted in a Melbourne patient in 1978 by the university’s otolaryngology researchers. The newer devices stimulated the cochlea through many separate electrodes as opposed to just one in earlier models, increasing the range of sound sensations that could be created in a deaf ear. Soon after, a company in Sydney now called Cochlear Ltd. produced the first commercial version of that device. The milestone turned Australia into a world leader in cochlear implants.

Hearing results from the movement of hair cells (acoustic sensor cells) inside the cochlea that convert vibrations into electrical impulses. These are then transmitted through neurons to the brain for interpretation. Electrically stimulating nerves in the inner ear induces hearing sensations that can be controlled so that people can understand speech and identify many other types of sound.

Today’s cochlear devices are significantly smaller than past models. A slim package containing a microphone, sound processor, and battery sitting behind the ear transmits digital signals through the skin to an electronic stimulator and an array of electrodes implanted in the inner ear. But when McDermott was doing his doctoral research, the devices were big—the external sound processor had to be carried in a pocket or on a belt—clumsy to use, and sucked battery power.

“The main part of my Ph.D. studies involved designing an implantable chip for a device that performed better than the commercial ones at the time,” he says. “While my design did not get manufactured, some of its novel ideas later found their way into commercial devices.”

McDermott earned his doctoral degree in otolaryngology in 1988—although his research was in electrical engineering—and then continued his research at the university, funded by grants, government contracts, private industry, and benefactors. During this time he joined IEEE, spending seven years as associate editor of its Transactions on Neural Systems and Rehabilitation Engineering.

THE BREAKTHROUGH His next hurdle was fine-tuning his device to highlight speech and downplay ambient sound. “The hearing implants were fine if there was no background noise, but they weren’t good in restaurants, so-so over the phone, and hopeless at parties,” he says.

The trick was, and continues to be, making the device capable of better conveying information about the particular sounds that users need to hear. The ear transmits all auditory information through several tens of thousands of hair cells and neurons. By comparison, hearing devices rely on 22 electrodes at most to transmit that same information, making it difficult to separate speech from background noise. McDermott and his team improved the way sounds are analyzed and represented electrically in the electrode array. This upgrade of the sound processor helped implant users to hear speech, even in background noise, more easily. That technology became commercially available in the mid-1990s.

Since then, McDermott has been improving acoustic hearing aids as well as continuing cochlear implant research at Melbourne University. For example, most people whose hearing impairment is not severe enough for an implant tend to have problems picking up higher frequencies, where most speech information resides. Background noise usually occurs at lower frequencies. One way to address that is to digitally transfer important speech sounds to lower frequencies, an old idea that needed better compression techniques and more powerful processors to carry off. Last year, the Swiss firm Phonak was the first to unveil such processing in its product line.

Ironically, developing a device to transmit music, the thing that propelled McDermott into this field, remains elusive. Twenty-two electrodes are insufficient to translate the complexity and detail of music. The solution may lie in combining the latest technologies of acoustic hearing aids and cochlear implants, which requires fitting hearing-impaired people with two different devices. But the next big leap in cochlear implant performance will require a radical increase in the number of electrodes.

“You might need hundreds of electrodes to start to hear a difference from current devices,” says McDermott. “It’s not a simple thing to increase. Ultimately the answer may lie in biotechnology—transforming stem cells into new cochlear hair cells and neurons—but that’s a long way off,” he adds. “The natural ear is a pretty hard act to follow.”

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