Word recognition by children listening to speech processed into a small number of channels: Data from normal-hearing children and children with cochlear implants

Objective: The aims of this study were 1) to determine the number of channe ls of stimulation needed by normal-hearing adults and children to achieve a high level of word recognition and 2) to compare the performance of normal -hearing children and adults listening to speech processed into 6 to 20 cha nnels of stimulation with the performance of children who use the Nucleus 2 2 cochlear implant. Design: In Experiment 1, the words from the Multisyllabic Lexical Neighborh ood Test (MLNT) mere processed into 6 to 20 channels and output as the sum of sine waves at the center frequency of the analysis bands. The signals we re presented to normal-hearing adults and children for identification In Ex periment 2, the wideband recordings of the MLNT words were presented to ear ly-implanted and late-implanted children who used the Nucleus 22 cochlear i mplant. Results: Experiment 1: Normal-hearing children needed more channels of stim ulation than adults to recognize words. Ten channels allowed 99% correct wo rd recognition for adults; 12 channels allowed 92% correct word recognition for children. Experiment 2: The average level of intelligibility for both early-and late-implanted children was equivalent to that found for normal-h earing adults listening to four to six channels of stimulation. The best in telligibility for implanted children was equivalent to that found for norma l-hearing adults listening to six channels of stimulation. The distribution of scores for early- and late-implanted children differed. Nineteen percen t of the fate-implanted children achieved scores below that allowed by a 6- channel processor, None of the early-implanted children fell into this cate gory. Conclusions: The average implanted child must deal with a signal that is si gnificantly degraded. This is likely to prolong the period of language acqu isition. The period could be significantly shortened if implants were able to deliver at least eight functional channels of stimulation. Twelve functi onal channels of stimulation would provide signals near the intelligibility of wideband signals in quiet.