The development of speech production following cochlear implantation

Conversational speech samples were analysed over a six-year period post-operatively for nine profoundly deaf children implanted with the Cochlear Limited 22-electrode cochlear implant between ages 2-5 years. Four years post-implant, at least 90% of all syllables produced by each child were intelligible, although only one of the children (who had suffered a progressive hearing loss) had over 10% intelligible syllables prior to implantation. Over the 6-year period, the mean number of intelligible words per utterance increased from 0.15 to 4.2 and the mean number of syllables (counting both intelligible and unintelligible syllables) increased from 1.7 to 5.2, indicating an increase in complexity as well as intelligibility. The speech samples were transcribed phonetically and percentage correct analyses were conducted on the transcripts. These analyses showed a steady improvement in the percentage of correctly produced monophthongs, diphthongs and consonants. There was a corresponding rise in the percentage of words that were produced without phonetic errors. Following six years of implantation, the speech acquisition process was incomplete, although there was no evidence to suggest at plateau in performance.