Genetic and environmental overlap between Chinese and English reading-related skills in Chinese children.

Phonological Skills in ESL Reading Development

Reading development in children, which involves phonological encoding by which print is mapped to sound, relies on a number of cognitive–linguistic skills. Many studies have confirmed that phonological awareness is a strong predictor of reading success (e.g., Melby-Lervåg, Lyster, & Hulme, 2012 ; Oakhill & Cain, 2012 ; Wagner, Torgesen, & Rashotte, 1994 ). It is further argued that accurate mental representation of speech sounds, as indicated by speech perception tasks, leads to the formation of distinct and accurate phonemic representations ( Boets, Wouters, van Wieringen, De Smedt, & Ghesquiere, 2008 ). A series of recent studies have examined the relations among speech perception, phonological awareness, and word reading abilities, both in L1 and in L2. For example, in a study of Korean-speaking ESL children, English speech perception and phonological awareness were important contributors to early English reading abilities, independent of English oral language skills ( Chiappe, Glaeser, & Ferko, 2007 ). As well as acquiring print-to-sound mapping, meanings of written words must be acquired. Therefore, oral vocabulary learning is a skill important to reading, as confirmed in previous studies (e.g., Bryant, MacLean, & Bradley, 1990 ). Moreover, vocabulary learning is supported by another important cognitive skill, namely phonological memory. Past studies have also shown a strong positive relation between phonological memory and vocabulary size ( Gathercole, Hitch, Service, & Martin, 1997 ). Because of the strong links between reading and the aforementioned skills, our investigation focused on the genetic and environment influences on these links.

Developmental and Cognitive Perspectives on Chinese–English Bilingual Reading Acquisition

A key question is whether proficiency in L1 helps or hinders development of L2. The two languages being examined in this study, namely Chinese and English, have enormous differences in both oral and written language systems. Broadly speaking, Chinese is logographic, while English is alphabetic. Because Chinese and English share few cognates (i.e., words that share a historical origin and have similar alphabets, spelling, and meaning across languages), Chinese ESL learners learn an independent set of English vocabulary and words in order to read English. Although there are shared consonants and vowels in the Chinese and English phonological systems, the presence of unique English phonemes usually causes perceptual difficulties in Chinese learners (e.g., A. Y. W. Chan, 2006 ). For example, Brown (2000) showed that Chinese learners of English were less able to discriminate /s-θ/ contrast in English (e.g., “sink” vs. “think”). A similar problem was observed in distinguishing the English front vowels /æ/and /e/ as appear in the word pair “bad–bed.” Such perceptual difficulties would hinder the formation of distinct representation of English phonemes as well as English reading. For all these reasons, one might anticipate that the better the knowledge of Chinese, the harder it might be to learn English.

However, the evidence points in the opposite direction: Research to date has shown significant positive associations between skills in the two languages. In Cheung et al.’s (2010) study, Chinese word reading, vocabulary, phonological awareness, and speech perception were significantly correlated with parallel English skills after the effects of age and nonverbal intelligence were controlled for ( r = .26 to .58). Similar results were obtained by McBride-Chang and Ho (2005) in their study of Chinese children aged between 4 and 5. This study showed significant associations between Chinese and English skills, including word reading, phonological awareness, and verbal memory ( r = .22 to .63). The significant relations between Chinese and English word reading were found to be stable across time ( McBride-Chang et al., 2008 ) and were observed in Chinese children living in English-speaking countries ( Bialystok, McBride-Chang, & Luk, 2005 ). To some extent, it could be that these correlations reflect some general task-taking ability. In general, these positive associations are important in showing that what develops is abstract knowledge, rather than just specific associations between letters or characters and sounds. Further, these findings support the idea that a portion of phonological skills is a general ability shared between the two languages, even when these languages have relatively distinct features. This fits with contemporary models of cross-linguistic transfer that maintain that transfer of skill from L1 to L2 operates at the functional level and involves a set of previously acquired meta-linguistic skills ( Genesee, Geva, Dressler, & Kamil, 2006 ). For instance, children who have an adequate level of phonological representations and phonological processing in their L1 would develop similar proficiency in discovering the sound-to-print correspondence in another language. Similarly, as Geva (1999) has argued, if positive and significant correlations are observed between parallel meta-linguistic skills in the two languages, it is very likely that there is a common underlying cognitive factor that controls the parallel skills in two languages (see also Gholamain & Geva, 1999 ). This account has important implications for teaching children in two languages, because it suggests that development of literacy will not be hampered by introducing a second language: On the contrary, it is possible that learning will be facilitated by making it easier to detect abstract similarities between the languages.

Genetic and Environmental Perspectives

The contrast between L1 and L2 is of particular interest for understanding the cognitive underpinnings of literacy development when a genetically informative twin paradigm is applied. We have noted how Chinese and English make an intriguing contrast in terms of linguistics differences. If individual differences in development depend on superficial features of the written or spoken language, we would expect very little overlap in skills in the two languages, or even some trade-offs between them. Yet evidence to date suggests the two languages support one another. An additional factor to be considered is the nature of exposure to the oral language of L1 and L2, which is the foundation for written language. Explicit training is generally thought to play little part in acquisition of the native language, and mastery of language structure proceeds on a similar trajectory without any need for formal instruction. However, English is taught to children in Hong Kong at kindergartens or schools from a very early age, and the environment for learning English is more diverse. We might therefore expect that individual differences in rate of development of L1 would reflect genetic factors, whereas for L2, environmental factors might be expected to predominate. We therefore can use the contrast between L1 and L2 to throw further light on the relative importance of genes and environment in the development of oral skills that underpin literacy.

It should be noted that the term environment is used in the field of behavior genetics to refer to any influence that is not genetic. Although it is possible to integrate measures of known environmental factors, such as school experiences, in a twin design, more usually, specific environmental factors are not directly assessed. Rather, the relative importance of genetic and environmental influences is estimated by comparing the degree of resemblance between monozygotic (MZ) and dizygotic (DZ) twins. Typically, twins grow up together in the same home and often attend the same school. Given the importance of environmental influences, we expect twins to resemble one another, regardless of zygosity. They differ, however, in their genetic similarity, with MZ twins being genetically identical, and DZ twins sharing, on average, 50% of their segregating genes. If MZ twins are more similar to one another than DZ twins, a genetic influence is suggested. Using this method, we can test whether there is a greater genetic influence on L1 versus L2 reading, and examine twin–cotwin similarities on a given task across languages to obtain evidence of shared genetic influence on skills in the two languages.

The Present Study

Using a twin study design, the present study aimed to disentangle genetic and environmental influences on children’s Chinese (L1) and English (L2) skills and their associations in 279 Chinese twin pairs. There were three research questions. First, what are the relative contributions of genes and environment to individual differences in Chinese and English reading and related cognitive–linguistic skills? Univariate twin analyses were conducted to indicate the relative contributions of genetic and environmental factors to these skills. Second, are parallel Chinese and English reading skills influenced by the same set of genes and/or environments? Bivariate twin analyses were conducted to examine the overlaps between genetic/environmental factors across L1 and L2. For instance, do the genetic factors contributing to Chinese word reading overlap with those contributing to English word reading? Last, to what extent do genes and environment contribute to the Chinese–English observed phenotypic correlation? The proportions of phenotypic correlations explained by genes and environment were computed.

Measures

All tasks described below had both English and Chinese versions. All measures were self-developed or adapted from standardized tests, and have been used and validated in previous studies ( Ho, Leung, & Cheung, 2011 ; McBride-Chang & Ho, 2005 ). We conducted a pilot test that measured the performance of 15 children at each grade level from kindergarten Grade 2 to primary school Grade 4 (aged from 4 to 10) in order to get information for arranging test items according to their difficulty level. Also, to ensure the test results were reliable, we included practice items in each task, and children were given feedback by the experimenters in these practice trials.

In both English and Chinese tests, children were instructed to read aloud a list of words one by one. The items had been selected to ensure an adequate range of difficulty to avoid floor and ceiling effects. The 85 words in the English test were adopted from a written word corpus that incorporated several authorized textbooks used in Hong Kong. These 85 words were arranged in ascending order of difficulty, and the first 49 items were divided into five sets of 8–11 words. Basal and ceiling rules were created according to the pilot test results so as to minimize administration time. The test began at an entry level corresponding to the child’s grade level. The testing proceeded if less than three errors were committed in a set. Otherwise, the tester moved to a set of lower difficulty or terminated testing when the child failed 15 consecutive items. We awarded one mark for each correct response. The Cronbach’s alpha was .99.

The Chinese test consisted of 198 items, with 150 two-character Chinese words adopted from the reading subtest of the Hong Kong Test of Specific Learning Difficulties in Reading and Writing (HKT–SpLD; Ho, Chan, Tsang, & Lee, 2000 ), a standardized test developed for Hong Kong primary school children. The other 48 items were a list of simple single Chinese characters that were more suitable for kindergarteners. The Cronbach’s alpha of the whole Chinese test was .99.

Receptive vocabulary

The two receptive vocabulary tests were selected based on their popularity and similarity in format—both tests used a target picture and three foils. The English vocabulary test was an adaptation of a standardized test, the Receptive One-Word Picture Vocabulary Tests (ROWPVT; Brownell, 2000 ). The Chinese receptive vocabulary test consisted of 80 items translated and adapted from the Peabody Picture Vocabulary Test (4th ed.; PPVT–IV; Dunn & Dunn, 2007 ). Different items were used for English and Chinese tests to avoid carryover effects. The correlation between the older version of the ROWPVT ( Gardner, 1985 ) and the PPVT-3 ( Dunn & Dunn, 1997 ) was reported as .79 ( Ukrainetz & Blomquist, 2002 ). On each trial, the child was asked to listen to a word presented orally by the experimenter and then point to the corresponding picture out of four options. The number of items of the English and Chinese test was 39 and 80, respectively, with good internal consistency (Cronbach’s alphas = .92 and .96, respectively). There were separate entry points tied to grade levels and a basal rule that required nine or all trials in the first 10 consecutive trials from the entry point.

Phonological awareness

The English and Chinese phonological tests measured children’s abilities in manipulating syllables and identifying subsyllabic phonological units. There were some differences in the two tasks’ formats, which were necessitated by differences between the languages in phonological structure in relation to literacy. The English test consisted of rime detection, syllable deletion, and initial phoneme deletion. The Cronbach’s alpha for the whole English phonological awareness test was .88. In the English rime-detection task, all items were modified items selected from the Alliteration and Rhyme subtest of the Phonological Assessment Battery ( Frederickson, Frith, & Reason, 1997 ). On each trial, we presented three English words to participants and instructed them to identify the two words having the same rime. For example, on the trial, “look/book/horse,” it was “look” and “book” that rhymed. The task started with two sample trials, which were followed by eight test trials. In the English syllable-deletion task, children were required to delete one syllable (at the initial, middle, or final position) from low-frequency three-syllable English words. For example, the experimenter asked the child to repeat orally the word jamboree and then mentally remove the middle syllable and say “jamree.” One mark was awarded for each correct response. On each trial of the initial phoneme deletion task, the experimenter read aloud an English word and asked the child to say the word with the initial phoneme taken away (e.g., say “fox” without the initial sound [answer “ox”]).

The Chinese phonological awareness task measured syllable and rhyme awareness. In the Chinese syllable deletion task, children were required to mentally delete one syllable (at the initial, middle, or final position) from a multisyllabic Chinese word orally presented by the experimenter and then say it aloud. There were 15 test items that were a mixture of real words, nonwords, or nonsense words. A real word was a word commonly used in daily life and carried lexical meaning (e.g., 望遠鏡 / mong6 jyun5 geng3 /[binoculars]). A nonword was a word created by combining random Cantonese syllables that did not carry a lexical meaning as a whole (e.g., 女任綠 / neoi5 jam6 luk6 /). A nonsense word was a word formed by combining nonsense Cantonese syllables that were phonologically legal but did not exist in written form (e.g., / fou2 moi1 peng5 /). In the Chinese rime detection task, the child was required to identify the syllable that rhymed with the target syllable among three options. On each trial, the experimenter first orally presented a target syllable (e.g., / jan4 /) and then read out three syllables (e.g., / ngaa4 /, / hau4 /, and / wan4 /; the correct response is /wan4/ ). The Cronbach’s alpha of the whole Chinese phonological awareness test was .88.

Phonological memory

The phonological memory span of the children was assessed by nonword repetition tasks. We assessed English phonological memory with the Children’s Test of Nonword Repetition ( Gathercole & Baddeley, 1996 ). Based on the pilot test’s data, we employed 16 test items of English pseudowords with a length of two to five syllables. On each trial, children were required to listen and repeat. The responses were marked by the experimenter on the site and recorded for later rating by a second rater. A similar test of phonological memory was constructed for measuring the skill in Chinese. There were 14 nonword strings constructed by combining two to seven Cantonese syllables that resulted in a meaningless chunk as a whole (e.g., / dim2 tou2 /). On each trial, the child was required to precisely repeat the nonword string presented aurally through headphones. When scoring a response, a point was awarded separately for each correct syllable and each correct order of two consecutive syllables. One point was deducted for each redundant syllable. For example, a correct response of a five-syllable nonword yielded a score of nine (5 points for correct pronunciation; 4 points for correct order). The inter-rater reliability indicated by the intraclass correlation coefficient was .82. The Cronbach’s alphas of the English and Chinese test were .87 and .90, respectively.