Binaural (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.

However, unilateral (one ear) and/or bilateral hearing loss may deprive individuals of these binaural mechanisms. Because of its widely-recognized advantages, hearing professionals have endeavored to provide effective binaural hearing to individuals with hearing impairment  – whenever technology allows.

Further, 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.

Because of this, a new study set out to determine the extent of the benefits that bilateral implantation offers. The study was 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 Madison-based University of Wisconsin and Aaron Parkinson, PhD, of Cochlear Americas. Their findings were presented at the recent annual meeting of the American Otological Society.

Thirty children, ranging from ages three to 13, received two cochlear implants. The children obtained the implants in sequential surgeries, a minimum of six months apart.

Age-appropriate speech perception testing in both quiet and noise was performed preoperatively and after activation 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 for speech perception in quiet showed that children implanted sequentially acquire open-set speech perception in the second ear within six months.

However, children under the age of eight 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 respondees 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.

In conclusion, 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 age 13.

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.

Source: American Otological Society