Single Sideband Encoder (SSE) for Better Speech and Music Coding in Cochlear Implants

Principal Investigator: Kaibao Nie

Over 10 percent of the world population suffers from different degrees of hearing loss. People with mild-to moderate deafness can be helped with hearing aids which make sound louder. For severe-to-profound hearing loss, cochlear implantation is now the only acceptable clinical practice for restoring hearing. The number of people in the U.S. alone who could benefit from cochlear implants is estimated to be between 250,000 and 1,000,000 and the criteria for implantation have been expanding since the technology was first FDA-approved in 1985.

We developed an approach for addressing the poor temporal coding in cochlear implants. Inspired by the coherent demodulation theory developed in Prof. Les Atlas’s lab, we took a new approach to signal demodulation. Our proposed strategy is based on harmonic single sideband encoding (HSSE) to transform a high-frequency acoustic signal to a low-rate stimulation pulse train [13, 14]. In the HSSE coding strategy, both the smoothed envelope and temporal fine structure are faithfully coded in the pulse trains that can be potentially perceivable to implant patients. A sound is split into a number of subbands, each of which is tracking the harmonic in the original sound. Harmonics are rich in natural sound and crucial for speech and music perception. Next, all the harmonics are demodulated to the frequency location of the first harmonic or fundamental frequency (F0) using single sideband demodulation. The single-sideband demodulation is capable of unloading a lowfrequency signal from a high-frequency signal without loss of information, in particular the temporal fine structure. Pulse trains are generated by half-wave rectifying and then sampling each demodulated signal with interleaved pulse trains at high stimulation rates. Most importantly, when harmonics are present, cross-channel pulse trains all oscillate at the same rate (F0), producing a strong pitch percept.

Cochlear implantation is now the only available technology to treat profound hearing loss. Over 278 million people suffer from moderate to profound hearing loss globally. And, approximately one million people in the U.S. who are either deaf or unable to hear normal conversation at all, even when using a hearing aid. The minimum age of implantation has been reduced to 12 months old by the FDA. In addition, bilateral cochlear implantation and hybrid implants combining a cochlear implant with a hearing aid for people with residual hearing can further boost the potential market for cochlear implants. It is an objective of the US Health and Human Services’ Healthy People 2020 initiative to increase the proportion of people who are deaf or very hard of hearing and who have new cochlear implants. The number of people with hearing loss is growing as baby boomers experience age-related hearing loss, the third most prevalent health complaint in older adults following arthritis and stroke. In addition, hearing loss is the most common service-connected disability among veterans. More effective sound coding strategies are vital to the success of future cochlear implants and can substantially increase market share for a manufacturer. Despite the downturn in the world economy, Cochlear Ltd has reported that its revenues grew 15% to $694.7 million in 2009 [18].

For more info, contact: Laura Dorsey

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