Cochlear Implantation In Both Ears May Improve Speech Perception

Newswise — A new study suggests that sequential bilateral cochlear implantation, or the placement of cochlear implants in both of a child's ears through separate surgeries, has the potential to improve speech perception abilities in quiet and in noise. Cochlear implants are electronic devices that have the potential to restore partial hearing to the deaf.

Background: Binaural or two ear hearing enables optimal performance of the human auditory system. In normal hearing subjects binaural hearing is directly associated with improved speech understanding in quiet and in noise, as well as improved sound localization ability, when compared to listening with a single ear. Unilateral (hearing in one ear) and/or bilateral hearing loss may deprive individuals of these binaural mechanisms. Because of its widely recognized advantages, hearing professionals have for many years endeavored to provide effective binaural hearing to individuals with hearing impairment whenever technology has allowed.

Candidates for cochlear implantation must present with a bilateral severe-to-profound sensorineural hearing loss; however, despite loss of hearing in both ears, they receive only one cochlear implant. Until recent years, little attention was given to the deficits unilateral cochlear implant recipients might still experience by nature of being monaural listeners. In the past decade there have been numerous studies demonstrating that the majority of adult patients who receive bilateral cochlear implants are able to realize significant benefits on measures of speech perception and sound localization. Initial reports also suggest that benefits from bilateral implants may be realized by deafened children without language skills. These reports have led to increasing interest in bilateral implantation on the part of patients, parents, and hearing professionals.

A new study sets out to determine the extent to which bilateral implantation offers benefits on a number of measures. The study is particularly focused on measuring the effects of age at implantation and experience after activation of the second implant on speech perception performance. The authors of the study "Importance of Age and Post-Implantation Experience on Speech Performance in Children with Sequential Bilateral Cochlear Implants" are Brian R Peters, MD, and Jennifer Lake, both from the Dallas Otolaryngology Cochlear Implant Program, Ruth Litovsky, PhD from the University of Wisconsin " Madison, and Aaron Parkinson, PhD of Cochlear Americas. Their findings are being presented at the Annual Meeting of the American Otological Society, being held May 20-21, 2006, at the Hyatt-Regency Hotel, Chicago, IL.

Methodology: Thirty children, ages three to 13 years, were recipients of two cochlear implants, received in sequential surgeries, a minimum of six months apart. Age appropriate speech perception testing in quiet and in noise was performed preoperatively and again postactivation at three, six, and 12 months in both the unilateral and bilateral conditions in a repeated measures study design. Some older subjects were also tested at 24 months. Two-Way Repeated Measures Analysis of Variance (ANOVA) was used to determine statistical significance among device configurations and performance over time.

Results: Results for speech perception in quiet show that children implanted sequentially acquire open-set speech perception in the second ear relatively quickly (within six months). However, children under the age of eight years do so more rapidly and to an ultimately higher level of speech understanding ability than older children, consistent with the notion of a more "plastic" auditory system. Speech intelligibility for spondees in noise was significantly better under bilateral conditions than with either ear alone, and the bilateral benefit increased with time after activation of the second implant.

Conclusions: Bilateral sequentially implanted children who are successful users of their first device are able to obtain open set speech discrimination in their second ear, even when receiving their second implant as late as 13 years of age. Speech perception scores in the second ear improve with experience during the first six months of implant use. Scores continue to improve for up to 12 months in younger children. Further experience past six months may not add any additional improvement in older children. Speech perception scores in the second ear improve at a rate and achieve a final level at 12 months that is inversely related to the subject's age at the time they received their second implant. The younger the child the better the final second ear performance. Sequentially implanted children of all age groups in this study have better mean speech perception scores in background noise in the bilateral condition than with either implant alone. The performance in quiet may also be greater for the bilateral condition, but it did not reach statistical significance in this study.