Central effects of residual hearing: implications for choice of ear for cochlear implantation

The study tested the hypothesis that among patients with similar levels of residual hearing in the nonimplanted ear, speech perception outcome is the same whether or not the implanted ear has profound or severe levels of hearing loss.

Retrospective.

Levels of hearing loss in postlingually deafened adults who had cochlear implantation at Johns Hopkins University (Baltimore, MD) between 1991 and 2002 were classified according to pure-tone averages as bilateral severe (n = 20), severe-profound (severe in one ear and profound in the other) (n = 23), and bilateral profound (n = 43). There was no significant difference in the age at onset and duration of deafness among the three patient groups. Individuals in the bilateral severe and severe-profound groups had comparable levels of severe hearing loss in their nonimplanted ears, whereas those in severe-profound and bilateral profound groups had comparable levels of profound hearing loss in their implanted ears. Speech perception performance was evaluated using words from the Consonant Nucleus Consonant word list, Hearing in Noise Test sentences in quiet, and Central Institute for the Deaf sentences through recorded presentation at 70 dB sound pressure level (SPL).

Despite the profound hearing loss of the implanted ear in the asymmetrical group, there was no significant difference in mean speech perception scores compared with the bilateral severe group within the first year after implant surgery. By comparison, the bilateral profound group had lower speech perception results compared with patients with residual hearing in one or both ears.

The study results suggest that implantation of the profoundly deafened ear does not diminish the functional advantage conferred by residual hearing in a patient with asymmetrical hearing loss. Therefore, the central auditory pathway may be the site at which persistent auditory function has its most beneficial effects.