An investigation into the vowel space area and vowel intelligibility among English-speaking children with cochlear implant in India

Background: Literature does show that studies of the vowel space area (VSA) can be helpful to know speech production skills in children with hearing impairment (HI) cochlear implant (CI). The need for the present study was to investigate speech production skills among children with CI, who receive Aural Rehab in nonnative language, i.e., English. The VSA offers an easy quick way to compare speech production accuracy among them to typically developing chidlren (TDC) peer group. Aim of the Study: The study aimed at investigating the VSA in F2 versus F1 space formed by vowels /a/, /i/, and /u/ in two groups of children (typically developing [TD] and children with CIs) and the intelligibility of the vowels spoken in the consonant-vowel-consonant (CVC) contexts. Methods: Two groups of subjects participated in the study, 100 children with CIs and 200 age-matched typically developing children. Recordings of vowels /a/, /i/, and /u/ in CVC were used for formant frequency extraction using Praat software, and the VSA was calculated. The recorded utterances were presented to three judges, for the estimation of the percentage of correct responses for identifying the vowel. The VSA for the vowels and the intelligibility scoring in percentage were valuated. Results: The results showed that the VSA among children with CI was significantly less compared to TDC. The reduced VSA represents limited articulatory movement in children with CI compared to children with TD for primary vowels embedded in CVC syllables. The vowel intelligibility for the three vowels in the CVC context was reduced for children with CI (70%) compared to that of children with TDC (95%). Discussion: Both first- and second-formant frequencies show distinct differences between both groups and consequently in the VSA. F1 is lower for /a/ for the CI group, while it is higher for vowel /i/ and /u/ for the CI group compared to the TDC group, while F2, the values were lower for /i/ but elevated significantly for both /a/ and /u/ compared to children in TDC. The intelligibility of their utterances (CVC) of children with CI was lower than that of TDC. Since the children were age- and gender-matched and were nonnative speakers of English, linguistic influences on measured values were minimum. Reasons for changed formant frequencies have to be explored further in terms of the influence of rehabilitation methods, visibility of articulatory movements required, and formant information coded by speech coding strategies. Correlation studies of the VSA and the speech intelligibility measures may assist in therapy outcomes and improve speech intelligibility in children with HI and modifications to mapping strategies employed. Conclusion: The F1 is lower for /a/ for the CI group, while it is higher for vowel /i/ and /u/ for the CI group compared to the TDC group, while F2, the values were lower for /i/ but elevated significantly for both /a/ and /u/ compared to children in TDC. The vowel triangle area was reduced in the speech of CI group subjects compared to that of the group of TDC.