The current study characterized voice onset time (VOT) and vowel onset fundamental frequency (F0) in the production of three Vietnamese alveolar stops (i.e. /t̪ʰ/, /t/, and /d/) by monolingual Vietnamese children and adults. Eighty Vietnamese children aged 3–7 years and 16 adults aged 22–44 years participated in this study. Unlike speakers of other languages with a three-way voicing contrast, Vietnamese children were able to produce distinct categories for the three Vietnamese stop categories by 3 years of age. However, differences in vowel onset F0 among the three voicing categories were not significant in any age group. These findings enhance our understanding of how Vietnamese children acquire three-way voicing contrast in stop production and offer broader insights into stop consonant acquisition across languages.

The purpose of the current study was to revisit a controversial topic: whether frequencies of phonological consonant and vowel classes differ in speech directed to children and to adults. In addition, the current study investigated whether the frequency of phonological consonant and vowel classes changes with children’s increasing chronological and/or developmental age. This study analyzed speech input from 44 adults to four different age groups of listeners (i.e., three groups of children at 6, 18, and 36 months of age and one group of adult listeners) in terms of frequency of occurrence of consonant and vowel classes. Results revealed that consonant stop, nasal, fricative and glide manner classes as well as all four consonant place classes were significantly different in speech directed to the four different age groups. A perspective is discussed to better understand the nature of frequency input of phonological sound classes.

The present study examined the speech production of three-year-old Korean–English bilingual (KEB) children. English and Korean stops, as well as front vowels in both languages, were compared acoustically among the KEB children, then also measured against those of their age-equivalent monolingual counterparts. Evidence of distinctive phonetic categorization in bilingual children was more salient in vowels than in stops. Vowels and stops produced by the bilingual children were not significantly different from those of their monolingual counterparts. The findings suggest that, similar to other language domains, two linguistic systems are apparent in the phonetic production component of three-year-old KEB children, but that phonetic distinctiveness in production may not emerge holistically in an across-the-board fashion, appearing earlier in vowels than stops. Thus, the phonetic production systems of the two languages may develop with only limited interaction in simultaneous KEB children exposed to two languages at an early age.

The purpose of this study was to conduct an acoustic examination of the obstruent stops produced by Korean–English bilingual children in connection with the question of whether bilinguals establish distinct categories of speech sounds across languages. Stop productions were obtained from ninety children in two age ranges, five and ten years: thirty Korean–English bilinguals, thirty monolingual Koreans and thirty monolingual English speakers. Voice-Onset-Time (VOT) lag at word-initial stop and fundamental frequency (f0) in the following vowel (hereafter vowel-onset f0) were measured. The bilingual children showed different patterns of VOT in comparison to both English and Korean monolinguals, with longer VOT in their production of Korean stop consonants and shorter VOT for English. Moreover, the ten-year-old bilinguals distinguished all stop categories using both VOT and vowel-onset f0, whereas the five-year-olds tended to make stop distinctions based on VOT but not vowel-onset f0. The results of this study suggest that bilingual children at around five years of age do not yet have fully separate stop systems, and that the systems continue to evolve during the developmental period.

The phonetic characteristics of canonical babbling produced by Korean- and English-learning infants were compared with consonant and vowel frequencies observed in infant-directed speech produced by Korean- and English-speaking mothers. For infant output, babbling samples from six Korean-learning infants were compared with an existing English babbling database (Davis & MacNeilage, 1995). For ambient language comparisons, consonants and vowels in ten Korean and ten English infant-directed speech (IDS) samples were analyzed. The two infant groups demonstrated similar consonant patterns, but showed different vowel patterns from one another. For both languages, infant vowel patterns were related to those of ambient language IDS. Ambient language patterns were manifested in infant vowel output, perhaps because vowels are more perceptually and motorically available in the input and output capacities of babbling infants.

This study compared segmental distribution patterns for consonants and vowels in English infant-directed speech (IDS) and adult-directed speech (ADS). A previous study of Korean indicated that segmental patterns of IDS differed from ADS patterns (Lee, Davis & MacNeilage, 2008). The aim of the current study was to determine whether such differences in Korean are universal or language-specific. Results indicate that consonant distribution patterns of English IDS were significantly different from English ADS. Speakers who used IDS produced fewer fricatives, affricates, nasals and liquids, but more stops and glides, than speakers who used ADS. In terms of vowels, IDS speakers produced more high-back vowels /u Ʊ/ and /ɔI/ diphthongs than ADS speakers. These results indicate both general trends and language-specific segmental distribution patterns in IDS. When compared to previous findings on ADS and IDS in Korean, these results for English give support to a more general assertion that segmental distribution patterns in IDS seem to be mediated by linguistic and cultural factors across languages.