Implications of developmental plasticity for the language acquisition of deaf children with cochlear implants.

The study of language acquisition in profoundly deaf children with cochlear implants informs us about the developmental plasticity of the auditory system. Sensory activity leads to neural development, and the sustained effects of sensory inactivity can lead to a loss of responsiveness. These effects may be reversed by the subsequent provision of sensory stimulation, such as that delivered by cochlear implants. Behavioral and electrophysiological research on the effects of speech deprivation on language acquisition shows that the age and modality of language acquisition is an important determinant of adult linguistic performance. Studies on profoundly deaf children deprived of speech stimulation, and then provided with a cochlear implant giving them access to the speech frequencies, shows that congenitally deaf children implanted under the age of around 5 years are likely to perform better on speech perception and speech production tasks than children implanted at an older age. Further investigation is required to understand why these large individual differences exist. In addition, other key issues for research are the effects of compensatory visual and somatosensory development prior to implantation, whether there is a maturational delay that approximates to the period of speech deprivation prior to implantation, and whether there are a number of sensitive periods that together describe the cascade of processes that underlies language acquisition.