Vowel Production in Prelingually Deafened Mandarin-Speaking Children With Cochlear Implants

Purpose The purpose of this study was to characterize the acoustic profile and to evaluate the intelligibility of vowel productions in prelingually deafened, Mandarin-speaking children with cochlear implants (CIs). Method Twenty-five children with CIs and 20 age-matched children with normal hearing (NH) were recorded producing a list of Mandarin disyllabic and trisyllabic words containing 20 Mandarin vowels [a, i, u, y, ɤ, ɿ, ʅ, ai, ei, ia, ie, ye, ua, uo, au, ou, iau, iou, uai, uei] located in the first consonant–vowel syllable. The children with CIs were all prelingually deafened and received unilateral implantation before 7 years of age with an average length of CI use of 4.54 years. In the acoustic analysis, the first two formants (F1 and F2) were extracted at seven equidistant time locations for the tested vowels. The durational and spectral features were compared between the CI and NH groups. In the vowel intelligibility task, the extracted vowel portions in both NH and CI children were presented to six Mandarin-speaking, NH adult listeners for identification. Results The acoustic analysis revealed that the children with CIs deviated from the NH controls in the acoustic features for both single vowels and compound vowels. The acoustic deviations were reflected in longer duration, more scattered vowel categories, smaller vowel space area, and distinct formant trajectories in the children with CIs in comparison to NH controls. The vowel intelligibility results showed that the recognition accuracy of the vowels produced by the children with CIs was significantly lower than that of the NH children. The confusion pattern of vowel recognition in the children with CIs generally followed that in the NH children. Conclusion Our data suggested that the prelingually deafened children with CIs, with a relatively long duration of CI experience, still showed measurable acoustic deviations and lower intelligibility in vowel productions in comparison to the NH children.

The Effects of Intrinsic Acoustic Cues on Categorical Perception in Children with Cochlear Implants

Many previous studies researched the influence of external cues on speech perception, yet little is known pertaining to the role of intrinsic cues in categorical perception of Mandarin vowels and tones by children with cochlear implants (CI). This study investigated the effects of intrinsic acoustic cues on categorical perception in children with CIs, compared to normal-hearing (NH) children. Categorical perception experiment paradigm was applied to evaluate their identification and discrimination abilities in perceiving /i/-/u/ with static intrinsic formants and Tone 1 (T1)-Tone 2 (T2) with dynamic intrinsic fundamental frequency (F0) contours. Results for the NH group showed that vowel continuum of /i/-/u/ was less categorically perceived than T1-T2 continuum with significantly wider boundary width and less alignment between the discrimination peak and the boundary position. However, a different categorical perception pattern was depicted for the CI group. Specifically, the CI group exhibited less categoricalness in both /i/-/u/ and T1-T2. It suggested that the effects of intrinsic acoustic cues on categorical perception was proved for the normal-hearing children, while not for the hearing-impaired children with cochlear implants. In conclusion, acoustically dynamic cues can facilitate categorical perception of speech in NH children, whereas this effect will be inhibited by difficulties in processing spectral F0 information as in the CI users.

Acoustic development of vowel production in native Mandarin-speaking children

The present study aims to document the developmental profile of static and dynamic acoustic features of vowel productions in monolingual Mandarin-speaking children aged between three and six years in comparison to adults. Twenty-nine monolingual Mandarin children and 12 native Mandarin adults were recorded producing ten Mandarin disyllabic words containing five monophthongal vowel phonemes /a i u yɤ/. F1 and F2 values were measured at five equidistant temporal locations (the 20–35–50–65–80% points of the vowel's duration) and normalized. Scatter plots showed clear separations between vowel categories although the size of individual vowel categories exhibited a decreasing trend as the age increased. This indicates that speakers as young as three years old could separate these five Mandarin vowels in the acoustic space but they were still refining the acoustic properties of their vowel production as they matured. Although the tested vowels were monophthongs, they were still characterized by distinctive formant movement patterns. Mandarin children generally demonstrated formant movement patterns comparable to those of adult speakers. However, children still showed positional variation and differed from adults in the magnitudes of spectral change for certain vowels. This indicates that vowel development is a long-term process which extends beyond three years of age.

Second Language Perception of Mandarin Vowels and Tones

This study examines the discrimination of Mandarin vowels and tones by native English speakers with varying amounts of Mandarin experience, aiming to investigate the relative difficulty of these two types of sounds for English speakers at different learning stages, and the source of their difficulty. Seventeen advanced learners of Mandarin (Ex group), eighteen beginning learners (InEx group), and eighteen English speakers naïve to Mandarin (Naïve group) participated in an AXB discrimination task. The stimuli were two Mandarin vowel contrasts, /li–ly/ and /lu–ly/, and two tonal contrasts, T1–T4 and T2–T3. The predicted difficulty for each contrast was hypothesized based on the assimilation of these sounds to English reported in previous work. The results showed that the Naïve group was more accurate with vowel contrasts than with tones, suggesting that non-tonal language speakers without any Mandarin training are less sensitive to tonal distinction than to vowels. The two learner groups, on the other hand, were highly accurate with all contrasts except for the T2–T3 pair, and achieved significantly higher accuracy than the Naïve group on /li–ly/ and T1–T4. This lends support to the view that experience in Mandarin improves English speakers’ sensitivity to tonal distinction, helping them discriminate some tones as accurately as vowels. However, all three groups achieved low accuracy in discriminating T2 and T3, suggesting that this contrast may be inherently difficult and resistant to improvement. This study shows that various factors in addition to the native language experience may affect the perception of non-native vowels and tones.