April 01, 2008 –
The cochlear implant’s microphone/speech processor is worn externally; the receiver is embedded under the skin behind the ear.
Twenty-seven year old UC Irvine graduate student Tiffany Chua was born with Pendred’s Syndrome, a hereditary metabolic condition that causes severe hearing impairment. She is one of nearly 300 million people worldwide with moderate to profound hearing loss in both ears.
Had she been born today, Chua could have received cochlear implants, tiny electronic devices surgically placed into the inner ear to stimulate the auditory nerve. And should she have deaf children, the cochlear implants available to them will outperform by far the current technology, due in large part to the work of CALIT2-affiliated UCI researchers.
Encoding Auditory Information
The cochlear implant consists of two pieces. An external speech processor with a tiny microphone, which picks up, amplifies and digitizes sounds, is worn behind the ear. The resulting signals are sent electromagnetically to a receiver implanted under the skin, where the signals are converted to electrical impulses that stimulate the auditory nerve.
The first commercial cochlear implants approved by the FDA in the mid-1980s were rudimentary by today’s standards. “Basically, they just helped the recipients lip-read better,” says Fan-Gang Zeng, professor of otolaryngology who is researching ways to improve the devices.
Today, cochlear implants provide most of their 100,000 users with sound that is crisp enough to allow telephone conversations.
Researchers often refer to them as “bionic ears.” The devices use electrodes to do the work of missing hair cells that, in a hearing person, convert sound into electrical impulses. The average human ear contains 3,000 rows of these hair cells; the ultimate cochlear implant would contain one electrode for each of these missing cells.
But the cochlea is only the size of a fingertip, giving researchers little room to navigate.
Nanotechnology Boosts Output
The earliest devices contained only one electrode. Now, without increasing the size of the implant, scientists using microtechnology have designed devices containing 22 electrodes. Zeng believes within the next decade, nanotechnology will allow researchers to build 1,000-electrode devices, giving the brain a 50-fold boost in the number of electrical impulses it can receive.
In addition, Zeng says, a single device will one day combine cochlear implant and wireless technology. “Everything could be merged onto a single ear-piece device,” he says. “Not only could you get telephone signals, but it would have a directional microphone that could pick up one voice and block out all others in a noisy environment. That would be very helpful for normal-hearing people as well as the hearing-impaired.
“I think the technology is already available,” he adds. “The challenge is: how do we adapt the interface for medical applications?”
Chua (left) and Zeng focus on improving signal processing and speech recognition in the devices.
Seeking Solutions
One person searching for those answers is Chua, a doctoral candidate in biomedical engineering, who was also a 2006-07 CALIT2-Emulex graduate fellow. Her personal experience with hearing impairment led her to cochlear implant research, and as a member of Zeng’s research team, she focuses on signal processing to improve speech perception in users. “There is a lot to be done,” she says. “Good-performing patients can hear well in quiet, but listening in noisy situations is still a challenge.”
Investigators are looking for the answers in cell-phone technology. Patients with cochlear implants have a hard time identifying pitch, Zeng says, making it difficult for them to distinguish between men’s and women’s voices. “It turns out there is something that cell phones do pretty well that cochlear implants do not,” he says. “We’re trying to adapt that for the implants.”
UCI ear and skull-base surgeon Hamid Djalilian is working on a different idea: a probe-like device, surgically implanted directly into the auditory nerve, which bypasses the hair cells. “That could give us better ability to get higher fidelity sound,” he says.
These devices have another potential application: enhancing hearing for the non-deaf to a super-sharp level. Using ultrasonic sensors, scientists could decrease the frequency of very high-pitched sounds, converting them to those that humans could decipher. “This could help soldiers identify threats quicker than normal sounds,” says Zeng.
Djalilian believes the multidisciplinary research team is headed in the right direction. “We’re at the forefront,” he says. “I think the next big advance in hearing is going to come out of UCI.”
— Anna Lynn Spitzer
