Language in cochlear implant users

Abstract

The final goal of cochlear implant (CI) is to afford communication by auditory speech to a deaf patient. Satisfactory understanding of speech despite a fairly small amount of speech information via CI may indicate the significance of central processing in recognition of speech. Functional brain imaging revealed marked activity in the associated auditory area in the temporal lobe in postlingual deaf patients, while cortical activation was limited in the primary auditory area in prelingual deaf patients. Activation in the auditory cortex by visual language such as lip-reading also suggests "neural plasticity" in the brain. Accumulated observations of congenitally deaf children who received CI in their early years revealed that their ability in speech understanding reaches nearly the same level as normal hearing children. It was also demonstrated that expressive language in CI users correlates closely to perceptive language. Language development in congenitally deaf children was regarded to become nearly normal with a certain delay, if they were implanted at an early age before primary school. In respect to phonemes, not only vowels but also consonants were obtained progressively after implantation, and speech intelligibility was nearly equal to that of hearing aid users of "silver group". It was also found that language development does not reach a plateau even 5 years after implantation. Marked development in both expressive and cognitive language in CI users appears to indicate significance of plasticity in the brain especially during the period of language acquisition. Thus CI implantation at an early age would be highly recommended, if a system for objective evaluation of hearing for CI candidates and speech habilitation after implantation were established in CI centers in Japan.