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The Listening Center is actively involved in both basic and clinical research programs that aim to maximize the benefits available from cochlear implants. Research in animal models of deafness at birth provide insights into a broad spectrum of circumstances that affect brain structure and function, particularly as related to a child's ability to learn through developmental stages.
We have examined the role that deafness plays in changing the connections within the hearing pathway. We have examined the notion of a "critical period" during which the brain can use restored hearing to open a window of opportunity for refined use of spoken language. Our results suggest that neural connections appear structurally normal very early in life, then begin deafness-induced changes in the pattern of contact between auditory cells in the brain. Research utilizing cochlear implants in animal models has demonstrated the ability to reverse deafness-induced changes in nerves that are critical to introducing activity into the hearing pathway.
The Listening Center tracks educational progress of implanted children using an educational resource matrix (ERM). The matrix was developed on the basis of observations that movement into a mainstream classroom setting is often accompanied by an initial increase in the need for support services, such as interpreters and speech-language therapists. Follow up of school-aged children with implants indicates that these children participate in mainstream education at a substantially higher rate and require diminishing levels of support services than children with similar hearing who use hearing aids. Long-term tracking of educational outcomes of implanted children continues as part of an ongoing assessment of cochlear implant rehabilitation.
Evaluation of the effectiveness of the cochlear implant in children has largely focused on the perception of speech and on language performance in standardized tests. Because the ultimate goal of cochlear implantation is to facilitate the use of spoken language, there is a clear need to evaluate the strategies adopted by implanted children in spontaneous communication. This information can also guide therapy to promote language learning.
To expand on our assessment of the implant experience in young children, The Listening Center has developed a video-analysis technique that assesses emerging language in even very young children for whom standardized tests are not useful. Results reveal significant gains in language acquisition in implanted children. Implanted children have nearly triple the rate of expressive vocabulary growth when compared with children using hearing aids.
The combination of earlier identification of hearing loss and access to early cochlear implantation has sparked an interest in results in terms of education, economics, emotional development, and cultural effects. The Listening Center is studying the emergence of one important aspect of educational success - reading. Our studies are investigating the methods by which newly restored access to all of the frequencies of speech sounds contained in words can be used to generate opportunities to acquire the skills needed to become effective readers.
The Listening Center leads a multicenter study of the impact of early cochlear implantation on childhood development. The Childhood Development after Cochlear Implantation (CDaCI) study is funded by the NIH. The goal of this longitudinal study is to determine the predictive value of variables as they relate to communication, behavior and educational outcomes of cochlear implantation in young children. The CDaCI study addresses the complexity of language development under conditions of restored hearing in the very young child when a variety of operational skills develop rapidly. The CDaCI study is also helping to determine the impact of medical and hearing assessment tools and parent-child interactions on levels of spoken language, speech recognition, selective attention, psychosocial developmental milestones, and quality of life attained with early cochlear implantation.
In addition to speech, the cochlear implant is capable of transmitting other complex sounds. The Listening Center is involved in collaborative research with the National Institutes of Health (NIH) in investigating how the cochlear implant conveys the complex information contained by music. By studying patterns of brain activity, it may be possible to design improved methods of encoding sound and training strategies to provide a fuller appreciation of the complex sounds contained in speech and music.
The sense of balance, like hearing, is based in the ear. Children and adults with severe hearing loss will occasionally experience dizziness (vertigo) and imbalance before and after cochlear implantation. Extended periods of vertigo and imbalance are rare but, when present, are treatable with exercise programs designed to elicit the brain's natural corrective mechanisms. Research by the Listening Center faculty has led to the development of diagnostic tests and treatment approaches that can limit the risk of balance disorders and help guide the choice for cochlear implantation.
Johns Hopkins' outcomes studies have assessed the impact on overall health and quality of life to determine the real-life benefit provided by cochlear implants. Implant users surveyed before and after their operation report dramatic results. These appraisals indicate that the cochlear implant ranks extremely high in the impact it has on quality of life and cost-effectiveness.