Changes of voice and articulation in children with cochlear implants

The different speech sounds are formed by the primary voice signal and by the shape of the articulation tract. With this mechanism, specific overtones, the formants, are generated for each vowel. The objective of this study was to investigate the fundamental frequency (F0) of the voice signal and the first three formants (F1-F3) as a parameter of the articulation in prelingually deafened children at different timepoints after cochlear implantation (CI) compared with children with normal speech development.

Using the Kay CSL 4300B, the fundamental frequency and the formants F1-F3 of the Swiss-German vowel /a/ were investigated at different timepoints after CI in 20 prelingually deafened children aged 3.8-10.2 years by means of spectrographic and linear predictive coding (LPC) analysis.

Children who had been operated before their fourth birthday showed no significant deviation in their fundamental frequency from age- and sex-matched peers, whereas a significant difference was documented in children who were older at the time of implantation. The first formant was very stable in every child and showed only discrete deviations from the normal range. The second and third formants, however, developed a broader scatter, but there was no systematic deviation of these formants to higher or lower values. The F1:F2 ratio was normal in children who were implanted at the age of up to 4 years and more centralized in children who were older at the time of implantation, as is known from the hearing impaired.

Our results indicate that prelingually deaf children who receive a cochlear implant before their fourth birthday attain a better acoustic control over their speech, normalizing their fundamental frequencies and improving their articulatory skills.