A new way of processing signals in cochlear implants lets users hear differences among musical instruments—a significant improvement over what standard implants offer, researchers say.
For those who use cochlear implants—technology that allows deaf and hard of hearing people to comprehend speech—hearing music has remained extremely challenging.
“Right now, cochlear-implant subjects do well when it’s quiet and there is a single person talking, but with music, noisy rooms, or multiple people talking, it’s difficult to hear,” says Les Atlas, professor of electrical engineering at the University of Washington.
“We are on the way to solving the issue with music.” Atlas believes that hearing music has possible links to hearing speech better in noisy settings, another goal of this research.
Atlas and collaborator Jay Rubinstein, a professor of otolaryngology and of bioengineering, recently published their initial findings in the journal IEEE Transactions on Neural Systems and Rehabilitation Engineering.
They hope to fine-tune the signal processing to make it compatible with cochlear implants already on the market so users can improve their music perception right away. They also are working on algorithms to better support device users’ perception of pitch and melody. “This is the critical first-step that opened the door,” Atlas says.
A cochlear implant is a small, electronic device that lets a person who is profoundly deaf or hard of hearing perceive sound. One piece is placed on the skin behind a person’s ear, while another portion is surgically inserted under the skin.
The implant works by directly stimulating the auditory nerve, bypassing damaged portions of the ear. The implant’s signals are sent to the brain, which recognizes the signals as sounds.
Cochlear implants are different from hearing aids, which amplify sounds so they can be detected by damaged ears.
Pitch and timbre
Scientists developed a new way to process the sounds of musical melodies and notes, which tend to be more complex than speech. Specifically, they tried to improve the ability of cochlear-implant users to detect pitch and timbre in songs.
Pitch is associated with the melody of a song and intonation when speaking. Timbre, while hard to define, relates most closely to the varying sounds that different instruments make when playing the same note. For example, a bass will sound much different from a flute when they both strike a middle C.
People who use cochlear implants usually perceive words by their syllables and rhythms, not through tone or inflection.
The researchers tested their new processing technique on cochlear-implant users by playing common melodies such as “Twinkle, Twinkle, Little Star” with the rhythms removed. They found that timbre recognition—the ability to distinguish between instruments—increased significantly, but the ability to perceive a melody was still difficult for most people.
“This is the first time anyone has demonstrated increased timbre perception using a different signal-processing system,” says Rubinstein. “With cochlear implants, we’ve always been oriented more toward speech sounds. This strategy represents a different way of thinking about signal processing for music.”
Co-authors are Xing Li, who recently completed her doctorate in electrical engineering; Kaibao Nie, an otolaryngology lecturer and adjunct lecturer in electrical engineering; and Nikita Imennov, who recently completed his doctorate in bioengineering.
The National Institutes of Health, the National Science Foundation, the US Army Research Office, the Institute of Translational Health Sciences at University of Washington, and a Virginia Merrill Bloedel Scholar Award supported the research.
Source: University of Washington