Cochlear Implants in Both Ears Help Deaf Localize Sound, Hear Speech in Noisy Backgrounds

Newswise — In the United States alone, about 13,000 adults and nearly 10,000 children have received a cochlear implant, an electronic device that stimulates the hearing nerve in people with severe to profound hearing loss who can derive little or no benefit from hearing aids.

Cochlear implants do not restore hearing; they allow deaf people to hear sounds, which the user must then interpret into speech. As with any electronic hearing device, a person with a cochlear implant faces distinctive communication challenges, particularly with localizing sound, i.e. identifying the location of sounds, and making sense of speech in a noisy environment.

Typically, cochlear implants are implanted in just one ear. Researchers Ruth Litovsky and Patti Johnstone of the Waisman Center, University of Wisconsin, and Jennifer Arcaroli and Aaron Parkinson of Clinical Studies, Cochlear Americas, and the clinical team from Dallas Cochlear (Dr. Bob Peters and Jennifer Lake) questioned if having an implant in both ears (bilateral implantation) would improve the ability to localize sound and understand speech. The results of their study, "Effect of Experience on Sound Localization and Speech Intelligibility in Noise in Adults and Children with Bilateral Cochlear Implants," will be presented at the Mid Winter Meeting of the Association for Research in Otolaryngology (http://www.aro.org) being held February 22-26, 2004 at the Adam's Mark Hotel, Daytona Beach, FL. Methodology: Two studies were completed; one on adults and another on children.

Adults: Seventeen post-lingually deaf (deaf after development of speech) adults who had been deaf for less than 15 years received simultaneous bilateral cochlear implants (Nucleusâ„¢). Ability to identify the location of sound was tested at three months post-surgery; ability to understand speech in noise was tested at three and six months post-surgery.

Children: The children who were enrolled in this study, aged eight to 12, received cochlear implants successively (second implant after first successful implant). Children were tested on sound localization, right to left discrimination, and understanding of speech in noise using computerized games. Three children were tested at three and nine months post-activation of the implant, and some children were only tested at nine months. Several children with a unilateral cochlear implant also participated. In order to assess the extent to which bilateral cochlear implants improve performance, testing was conducted with both cochlear implants activated, and with only one implant activated.

Results:

Adults: None of the adults had identical hearing in both ears post-surgically. Each demonstrated a "good" or "bad" ear, the determination of which was highly correlated with pre-surgery audiological assessment. Speech in quiet discrimination scores ranged from five to 25 percent. For the majority of adults, sound localization performance is significantly better under bilateral conditions compared with either ear in isolation. On the speech tests, performance is significantly better under a number of conditions with competing noise, and the bilateral benefit was especially evident at six months post-activation compared with three months.

Children: The largest benefit from bilateral cochlear implants was observed in speech understanding in the presence of interfering speech, as well as in quiet. Children also showed improvement with experience, as noted by better performance at nine months than three months after activation of the second cochlear implant. However, performance on sound localization and right/left discrimination was generally poor with little evidence for improved performance with bilateral cochlear implants.

Conclusion: This work suggests that bilateral cochlear implants can improve sound localization and the ability to understand speech in a noisy environment in adults. In children, the benefit was especially noted in the speech-in-noise tests. The ability to fully recognize the benefit of having two cochlear implants may require time after implantation during which the user learns to use both ears and to utilize binaural cues.