The stimuli for the Korean NRT are nonsense words that increase in length from 1 to 4 syllables and conform to Korean phonotactic constraints (see Table 2). Monosyllabic nonwords were composed of an onset consonant, a nuclear vowel, and a coda consonant (i.e., CVC form). Multisyllabic nonwords were in either CV or CVC forms. These stimuli were designed to include common phonological processes such as tensification (e.g., [sikt^*ɛban]), neutralization (e.g., [pat^hoŋdatʨ^*u]), palatalization (e.g., [ʃimwasoʨ^hʌn]), lateralization of nasal onset consonant ([tasɛʨ^hulɿok]), etc. Three Korean-speaking graduate students enrolled in doctoral program in Linguistics or Speech and Hearing Science examined the 16 stimuli. They confirmed that these words are not semantically related to real Korean words and do not violate Korean phonotactic constraints. The auditory stimuli given to the participants were produced by a Korean female speaker. She was asked to read the 16 nonwords written in Korean as naturally as possible, and her utterances were recorded in an acoustic booth. Each stimulus was presented to the participants once over headphones without visual stimuli such as written forms. The participant was asked to repeat each word, proceeding from 1- to 4-syllabic nonwords. The participants’ oral responses were recorded and digitized for subsequent phonetic transcription and evaluation.

The recorded responses were transcribed and evaluated to determine whether the target phonemes were correctly produced. Substituted and deleted phonemes were considered incorrect productions, whereas distortions, as marked by diacritics, were considered correct productions (e.g., nasalization of vowels such as in [nãnɨn]). The performance of each participant was converted to numerical values by computing the PPC, PCC, and PVC. To examine the reliability of the phonetic transcription, all recorded stimuli were evaluated by two other professors who are native speakers of Korean and professionally trained to evaluate articulatory accuracy of Korean phonemes. The average values of PPCs for all participants by the three evaluators were 93.63%, 91.23%, and 91.29%, respectively. A Cronbach’s alpha for the inter-rater’s reliability was .82, which is much greater than the significance level of .70. That is, consistency in evaluating articulatory accuracy is very high among the three evaluators. To compare performance of the three groups, a univariate analysis of variance (ANOVA) and a Scheffe post-hoc test were chosen to explore any significant group differences for PPC, PCC and PVC. Then, patterns of phonological processes found in KEB children were reviewed to determine which Korean consonants and vowels are most challenging. In addition, a two-way repeated measures ANOVA was conducted to see whether the syllable length has something to do with the performance of the Korean NRT. For this statistical analysis, the four syllable lengths (i.e., monosyllabic nonwords, disyllabic nonwords, 3-syllabic nonwords, and 4-syllabic nonwords) and the three groups were served as main effects. As a follow-up test for any significant interaction of the length and the group, several independent t-tests were conducted.

The means and standard deviations for PPC, PCC, and PVC were calculated and presented in Table 3 and Figure 1. Overall, KEB children produced Korean phonemes less correctly than KEB adults and KM children. A one-way ANOVA revealed significant group differences for PPC (F = 8.055, p = .022), PCC (F = 4.897, p = .014), and PVC (F = 5.123, p = .012). According to a follow-up Scheffe post-hoc test, KEB children produced phonemes less correctly than KEB adults (p = .007) and KM children (p = .003). Both PCC and PVC of the KEB child group were significantly lower than those of the KEB adult group (p = .037 and p = .041) and the KM child group (p = .026 and p = .019). In sum, articulatory accuracy for consonants and vowels in KEB children was lower than KEB adults and KM children. Speech errors by KEB children were most frequent in the consonant /ʨ^h /. A palato-alveolar affricate /ʨ^h / was realized as its lenis counterpart /ʨ/ in [tasɛʨ^hulɿok] or as an alveolar stop /t^h/ in [ʨ^hɨm] and [p^hɛʨ^ham]. The second most frequent speech errors were found in a liquid, where the coda /l/ is deleted in /tasɛʨ^hulɿok/ and /tuŋʨ^humolha/. The vowel /o/ was diphthongized as in English /oʊ/ in the context that the coda consonant is deleted in [tasɛʨ^hulɿok]. Interestingly, the bilabial nasal stop /m/ was substituted by /n/ in [pɛs^*om] and the glottal fricative /h/ was substituted by /r/ in [tuŋʨ^humolha].

The objective of the present study was to examine whether English as L2 negatively affects articulatory accuracy of Korean as L1 and whether the degree of L1 phonological attrition varies depending on the age of arrival to the U.S. For this purpose, the research question asked whether KEB children and adults under the influence of English produce Korean phonemes with lower accuracy than KM children and whether KEB children who were exposed to English early in life perform poorer than KEB adults who were exposed to English later in life. The results of the Korean NRT indicated that KEB children produced Korean phonemes, including consonants and vowels, significantly less correctly than KEB adults and KM children. With respect to syllable-length, KEB children performed poorer than KEB adults for monosyllabic and 4-syllabic nonwords and than KM children for disyllabic and 4-syllabic nonwords.

Some speech errors are explicable by the influence of English on Korean. The /l/-deletion in /tasɛʨ^hulɿok/ produced by KEB children implies the influence of English on Korean in the sense that English /l/ is generally realized as a dark ‘l’, i.e., [ɫ] in a coda position. Such an allophonic variation may have caused /l/-deletion in speech production of Korean nonwords. The diphthongization of the vowel /o/ at the word-finial position (e.g., [tasɛʨ^hulnoʊ]) supports L2 influence as well, because the English vowel /oʊ/ is always realized as a diphthong. In addition, the loss of aspiration and stopping of /ʨ^h/ can be explained by the interference of English. The Korean consonant /ʨ^h/ is similar but slightly different from the English consonant /ʧ/. As argued by Flege’s Speech Learning Model (or SLM), a similar but slightly different sound between the two languages is more challenging to produce correctly than a new or very different sound between the two (Flege, 1987; 1992). Therefore, SLM may account for inaccuracy of the consonant /ʨ^h/. Nonetheless, other phonological processes such as the substitution of /m/ with /n/ or the substitution of /h/ with /r/ are rather obscure to be explained by the influence of English. Rather, these two substitution processes are explicable in terms of assimilation processes of place of articulation, where the bilabial nasal coda consonant assimilates to the alveolar onset fricative (i.e., /m/ → /n/ / [+alveolar] V __#) and where the glottal fricative onset consonant assimilates to the preceding alveolar liquid consonant (i.e., /h/ → /ɿ/ / [+alveolar, +liquid] __ ).

Nonetheless, one should be cautious to conclude that early exposure to English as L2 hinders phonological development of Korean. Some parents are afraid of teaching young children two languages simultaneously as some researchers claim that second language acquisition (SLA) early in life hinders the mastery of one’s mother tongue and even causes delays in language and cognitive development (Lee, 2003; Seo, 2003 as mentioned in Shin, 2004). These studies, however, provided neither empirical evidences of the negative effect of SLA nor significant correlations between SLA and developmental disorders. In contrasts, other studies argued that being exposed to two languages enhances mental growth and flexibility (Ben-Zeev, 1984; Bialystok, 1999; Leopold, 1949; Vygotsky, 1986) and may even delay the onset of dementia (Bialystok, Craik, & Freedman, 2007). There is growing evidence that being bilingual does not cause language disorders or mental retardation in recent years (see also Bialystok, 2009).

Investigating Korean-English bilinguals is worthwhile. According to the U.S. census (2010), Korean is the 7^th most spoken language in the U.S. and 90% of Korean parents with children in first or second grade in Korea begin their child’s English education between the ages of 3 and 5 according to a study by the Korea Institute of Child Care and Education(2011). The pros and cons of early childhood education of English as L2 are still debated in Korea, thus the influence of L2 English on the speech production of L1 Korean would attract attention not only from language educators and speech therapists but also from the nonprofessional population. Understanding phonological development in Korean-English bilinguals may help educators and clinicians construct their developmental reference data, develop appropriate curricula, and support speech and language development in both languages. Also, it may help parents who are interested in bilingual education determine child-rearing or education for their child.

The findings of the Korean NRT suggest that acquisition of English as L2 early in life may negatively influence the articulatory accuracy of Korean phonemes; however, acquisition of English later in life may not. Previous studies of L1 attrition suggest that children or early bilinguals who were exposed to L2 but intercepted from L1 exposure before the age of 7 are more susceptible to L1 attrition than adult or late bilinguals (Birdsong, 1992; Caramazza, Yeni-Komshian, Zurif, & Carbone, 1973; Fillmore, 1991; Ventureyra et al., 2004). The results of the task in this study are congruent with results of literature on L1 attrition, where KEB adults who were exposed to English at the age of 11 or older produced consonants and vowels more correctly than KEB children did. However, it is noteworthy that four KEB child participants were intensively exposed to L2 but blocked off from L1 exposure before the age 6, at which most children master producing Korean consonants and vowels (Kim, 1996; Kim, Pae, & Park, 2007). Therefore, the lower accuracy of KEB children may be attributed to the premature development of Korean articulation and phonology rather than the negative effect of learning English early in life. It would be interesting to investigate whether these child participants would eventually be able to reach the level of articulatory accuracy of Korean monolingual speakers. Further, a future research may examine whether Flege’s SLM hold true for L1 attrition of articulation and phonology. For this purpose, a study should address similarities and dissimilarites between the two languages with respect to articulatory and phonological characteristics and develop appropriate experimental methodology.