Speech Perception and Sound Localization by Adults with Bilateral Cochlear Implants

Adult patients with bilateral cochlear implants report a significant gain in health-related quality of life relative to having a single cochlear implant. Gains are found in multiple domains—in this article, we focus on hearing and speech understanding. There are several factors that likely contribute to the hearing-related gain in quality of life. The provision of bilateral implants improves the probability that (1) if there are large between-ear differences in speech recognition, then the ear with the best recognition ability will be stimulated; (2) patients will benefit from the head shadow effect, which provides large gains in speech intelligibility; (3) patients will receive the relatively smaller benefits due to summation and squelch; and (4) patients will be able to better localize sound sources in the horizontal plane by using interaural-level difference cues. It is reasonable to suppose that these improvements in performance combine to reduce the stress that is associated with listening via electrical stimulation and thereby improve hearing-related quality of life.