Accuracy of /t/ Productions in Children with Cochlear Implants as Compared to Normal-Hearing, Articulation Age-Matched Peers

Children who receive cochlear implants (CIs) demonstrate considerable variability in speech sound production. Investigations focused on speech sound development in children with CIs have shown initial accelerated growth, followed by a plateau where consonant order of acquisition generally mirrors that of NH children, but is slower (Blamey, Barry, & Pascale, 2001; Serry & Blamey, 1999; Spencer & Guo, 2013). A notable exception to this pattern, /t/, has been shown to be acquired later-than normal in several investigations (Blamey et al., 2001; Chin, 2003; Ertmer, True Kloiber, Jongmin, Connell Kirleis, & Bradford, 2012). The primary purpose of this investigation was to 1) examine the accuracy of /t/ productions in children with CIs and 2) quantify subtle phonetic differences in correctly produced consonants and substituted consonants (or covert contrast). Two groups of children who had participated in a larger study that examined the influence of speech production abilities on speech perception scores of children with CI (Gonzalez, 2013) provided the speech stimuli for this investigation. The experimental group included nine congenitally deafened children with CI, ranging in age from 2;11 to 6;4 years (M=4;9), who were implanted by 3 years of age, had at least 12 months of device experience, and only used an oral mode of communication. These children were matched to typically developing children by articulation ability and gender. Recordings of the verbal responses on the OlimSpac were obtained from the Gonzalez (2013) study. Thirty-three graduate students in speech-language pathology rated the phonetic accuracy of /t/ and the phonemes that were found to be most often substituted for it, /d/ and /ʧ/ on a 7 point equal-appearing interval scale. A three-way ANOVA was performed to determine the differences in perceived consonant accuracy across: group, transcription category, and phoneme substitution. The significant interaction between group and transcription category was of particular interest. Results indicated that children with CIs did not show an unusually delayed development of /t/. When a confusion matrix was generated to depict overall OlimSpac performance, the NH group was noted to outperform the CI group across all phonemes. This would suggest that /t/ was not uniquely poorer in the CI group, but instead these children evidenced poorer phoneme accuracy in general. Finally, group differences also were apparent in substitutions of [t] for target /d/ and /ʧ/ productions (i.e., covert contrast). The clinical applications are described