Wednesday, September 09, 2009

Pairing cochlear implant, hearing aid benefits adults with hearing loss

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Adults with severe hearing loss benefit from pairing a cochlear implant in one ear with a hearing aid in the other ear, even though the sound signals from each device are very different, according to a School of Medicine study published in the Journal of the American Academy of Audiology.

The patients were better able to hear spoken words and to locate the direction of a sound with both devices turned on compared with either device alone. Additionally, the patients liked the fuller, richer sound they heard when using both devices.

"It is increasingly common to place cochlear implants in both ears when patients have profound hearing loss on both sides, but the majority of these bilateral implants are done in children," said lead author Lisa Potts, Ph.D., research instructor in otolaryngology. "Many adults lose their hearing as they age, and it may not be financially or physically possible for them to undergo surgery for two cochlear implants. So it is important to know if there is a benefit to using a hearing aid plus a single cochlear implant."

Each of the 19 study participants received a cochlear implant in one ear and a hearing aid for the other ear from WUSTL surgeons at Barnes-Jewish Hospital. The participants were seen at the Adult Cochlear Implant and Aural Rehabilitation Division at the School of Medicine for cochlear implant programming and hearing aid fitting.

Because the participants were profoundly hearing impaired, the hearing aid restored only partial hearing in one ear, while the cochlear implant gave them a greater level of hearing in the other ear. In addition to the imbalance in sound levels, each device processes sound information in a unique way: A cochlear implant translates sounds into electrical impulses that directly stimulate the hearing nerves of the inner ear, while a hearing aid amplifies sounds so the ear can sense its acoustic vibrations. Specialists have questioned whether patients could adequately integrate the asymmetric signals from implants and hearing aids.

This study showed that when the participants used both a cochlear implant and a hearing aid, speech recognition improved by an average of 14 percent over when they used just an implant or just a hearing aid. When both devices were active, participants also made fewer mistakes in determining sound direction — they were better able to say which loudspeaker emitted sound in a semicircular array of 15 loudspeakers placed 10 degrees apart.

Interestingly, when the participants wore both devices, speech recognition and localization was equally good, no matter the direction of the sound source. That was surprising because of the lower sound correction in the hearing aid ear.

"That result really got our attention," Potts said. "It shows that even when patients have minimal hearing with a hearing aid, it still helps them get input and helps them catch important sound cues. The two inputs are complementing each other. Hearing aids are better at giving temporal speech cues, while implants supply a fuller spectrum of sound frequencies."

Potts said the brain learns to integrate these two separate signals. The sound signals meet in the brainstem and cross all along the auditory pathway up to the brain's hearing centers, which interpret the signals as one sound.

When asked about their subjective sense of how well they heard with the devices, most patients said they felt they heard sound better with both devices turned on.

When both devices were on, they described the sound as "louder, clearer and more natural," "more complete" and having "a little extra depth, richness and volume."

The participants — eight men and 11 women — ranged in age from 26 to 79, with an average age of 50. Almost half had some hearing impairment before age 6.

But nearly all were adults when diagnosed with severe to profound deafness. The patients' ages or hearing history had no statistically significant effect on the results of the hearing tests conducted in the study.