April 29, 2004
Merging hearing technologies sounds good to researcher
WEST LAFAYETTE, Ind. A Purdue University researcher is combining two technologies hearing aids and cochlear implants to help improve speech understanding and sound quality for cochlear implant users.
Research by King Chung, an assistant professor in audiology, and colleagues shows that by applying advanced hearing aid technologies, such as preprocessors, to cochlear implants, background noise can be reduced, speech understanding enhanced and sound quality improved for cochlear implant users. Chung collaborated with Fan-Gang Zeng, a professor at the University of California, and Susan Waltzman, a professor at New York University School of Medicine.
"The common goals of hearing aids and cochlear implants are to enhance users' speech understanding and listening comfort, as well as improve the convenience of device use," says Chung, who studies issues related to hearing amplification and communication. "To achieve these goals, hearing aid and cochlear implant manufacturers have gone through different research and development paths."
Hearing aid technologies, many of which are not available in cochlear implants, are more advanced in reducing different types of background noises and increasing the convenience of hearing aid use, Chung says. Cochlear implant technologies have advanced in coding strategies, miniaturization of the speech processor and electrode mechanics.
"Our study shows that by combining these two technologies, cochlear implant users can understand speech better and be more comfortable when they listen in background noise," she says. "Cochlear implant users also prefer the conditions in which advanced hearing aid technologies were applied as a preprocessor to their cochlear implants."
The research is published in the current issue of Acoustic Research Letters Online. Chung and her co-authors will present their findings in May at the European Symposium in Pediatric Cochlear Implants in Geneva, Switzerland, and at the International Cochlear Implant Conference in Indianapolis.
Approximately 10 percent of the country's population suffers from hearing impairment, and the number is expected to grow as the population ages. Hearing aids are the most common remedy for people with hearing impairments, Chung says. Hearing aids have microphones to pick up sounds, then processors send the signals to the ear canal and through the auditory nerve to the brain for interpretation.
People with severe hearing loss may choose to use cochlear implants. There are more than 60,000 people worldwide with these implants, which work by providing direct electrical simulation to the auditory nerve. The microphone, speech processor and transmitter are placed on the outside of the ear similar to a hearing aid. The microphone picks up sounds from the environment so the speech processor can process and encode the incoming signal. Then, the transmitter sends the signal to a receiver implanted under the skin of the skull and to electrodes implanted in the inner ear. The electrodes directly stimulate the auditory nerve and the signal is sent to the brain for interpretation.
The two devices' main differences lie in how they send sound through our auditory system, Chung says. Hearing aids output acoustic signals to the ear canal. Cochlear implants, on the other hand, convert those acoustic signals into electronic impulses and directly stimulate the auditory nerve.
"There are many advanced hearing aid technologies that may help cochlear implant users," Chung says. "For example, hearing aids have adaptive directional microphones that can automatically track the direction of the background noise and maximally reduce the noise interference even if the noise is moving in the environment. Most cochlear implants do not use these advanced directional microphone technologies and, if they do, it is usually in a less sophisticated form.
"In addition, hearing aids have switchless telephone coils, so when a person talks on the phone, the hearing aid detects the magnetic field of the telephone headset and automatically switches to telecoil input, which does not pick up the background noise. Some children and older people with weak hands may not be able to manually switch back and forth from microphone to telecoil inputs with their cochlear implants. If advanced hearing aid technologies are used as preprocessors to cochlear implant speech processors, cochlear implant users may be able to take advantage of all these features."
Chung and her colleagues evaluated if hearing-aid technologies could help people with cochlear implants improve their speech understanding, especially in noisy environments.
Twelve subjects four with normal hearing, four with hearing aids and four with cochlear implants listened to prerecorded material that had been processed by hearing aids. The first prerecorded sounds were processed through a hearing aid with an omni-directional microphone, which picks up sounds from all directions. The second sets of recordings came from the same hearing aids programmed to directional microphones, which are more sensitive to sounds in front of the hearing aid user. The third sets of recordings combined directional microphones with noise-reduction algorithms. The noise-reduction algorithms are intended to reduce noise interference.
Participants were asked to repeat the processed words and to rank the ease of listening for each of the experimental conditions.
The average improvement on speech understanding for cochlear implant users, hearing aid users and people with normal hearing using the directional microphones were 11.7 percent, 21.5 percent and 23.7 percent, respectively. There were no differences in speech understanding between the directional microphone condition and the directional microphone plus noise-reduction algorithm condition. All subjects ranked omni-directional as the most difficult, and all but two participants with normal hearing identified the directional microphone plus noise-reduction algorithms as the easiest to listen to.
"This research is still in the preliminary stage, and we will continue to investigate the effects of applying different types of hearing aid technologies to cochlear implant users," Chung says. "We also will explore different methods to integrate these technologies. The advantage of this marriage of hearing aid and cochlear implant technologies may ensure timely delivery of advanced hearing aid technologies to cochlear implant users. In addition, the two industries may be able to combine resources to develop the next generation of signal processing technologies that can benefit both hearing aid and cochlear implants users."
Chung is now working on a similar study with a larger sample size and a new study with adaptive directional microphones. The latter is supported by a New Investigators Grant from the American Academy of Audiology.
Purdue's Department of Audiology and Speech Sciences is ranked among the top 10 in the nation by U.S.News & World Report. The master's and doctoral degree program in speech-language pathology and audiology are ranked third and eighth, respectively,
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Using hearing aid directional microphones
Hearing aids and cochlear implants are two major hearing enhancement technologies but yet share little in research and development. The purpose of this study was to determine whether hearing aid directional microphones and noise-reduction technologies could enhance cochlear implant users' speech understanding and ease of listening. Digital hearing aids serving as preprocessors were programmed to omni-directional microphone, directional microphone, and directional microphone plus noise reduction conditions. Three groups of subjects were tested with the hearing aid processed speech stimuli. Results indicated that hearing aids with directional microphones and noise reduction algorithms significantly enhanced speech understanding and listening comfort.