Catherine Bow

The development of speech production following cochlear implantation

Conversational speech samples were analysed over a six-year period postoperatively 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 a plateau in performance.

A critical level of hearing for speech perception in children

Cochlear implants have raised questions about how children with profoundly impaired hearing can learn spoken language. This study addresses the question of whether there is a critical level of hearing for the development of adequate speech perception abilities. A comparison of the relationships between speech perception scores and spoken language scores shows that a group of profoundly deaf children using hearing aids process spoken language in a way that is fundamentally different from two groups of children with severe and moderate hearing losses. We infer that there is a critical level of hearing below which speech perception relies very heavily on linguistic processing to compensate for limited auditory information. We also show that a cochlear implant can promote profoundly deaf children from below to above the critical level of hearing.

Comparison of methods in speech acquisition research

The paper examines the effect of choices involved in speech acquisition research among children with impaired hearing. Choices involving transcription method, sampling procedures, subject selection and statistical approaches affect the outcome of any research. Two recent papers used different methodological approaches to examine the conversational speech samples of children with impaired hearing and arrived at differing conclusions about their rates of improvement. To compare these results, a further data set was examined using both methodologies. The analyses indicated a closer alignment of results than was immediately obvious from the two previous studies, suggesting that the different results were primarily due to differences in methodology.