3. Results

3.1 Developmental changes in vocabulary composition among Chinese infants (aged 1;0-1;4)

Bates et al. (1994) argued that it is important to examine the developmental changes in vocabulary composition by vocabulary level, rather than by chronological age (see also Pine & Lieven, 1990). Following their reasoning, we divided the infant participants into the following six groups based on their total production vocabulary: (1) 0 words (N = 30, 10.79% of the participant sample); (2) 1~5 words (N = 103, 37.05%); (3) 6~10 words (N = 58, 20.86%); (4) 11~20 words(N = 23, 8.27%); (5) 21~50 words (N = 44, 15.83%); (6) more than 50 words (N= 20, 7.19%). We also followed Bates et al. (1994) to define the various lexical categories: (1) Common nouns included items from the following 10 categories: animal names, body parts, clothing, food and drink, furniture, small household items, toys, vehicles, places to go except chengli, haibian (which are locative nouns), outside things except shangbian, tianshang, waimian (which are not common nouns). In total, there were 125 common nouns, making up 53.88% of the Infant Checklist; (2) Predicates included items from the verb category and the adjectives category. There were 65 predicates, making up 28.02% of the Infant Checklist; (3) Closed-class items included only 5 pronouns (5 items, 2.2% of the Infant Checklist); and (4) Social words included items referring to people and to routines, making up 14.66% of the Infant Checklist (34 items), which have been reported in the literature as the earliest acquired words by children in English and other languages (Bloom et al., 1993; Caselli et al., 1995; Caselli, Casadio & Bates, 1999; Kauschke & Hofmeister, 2002).

Figure 1(a) presents percent changes of the above four major categories as a function of the various vocabulary levels for Chinese infants. In order to clearly reveal the similarities and differences between Chinese-speaking children and English-speaking children, we present the data from Table 2 in Caselli et al. (1995) as Figure 1(b), which has comparable datapoints to Figure 1(a).

Figures 1(a) indicates that for young Chinese-speaking infants at the earliest stages of vocabulary development, social words accounted for 80% of their total production vocabulary, while common nouns represented only 10.56%. When the production vocabulary expanded to a mean of 7.33 words (i.e. between 6 to 10 words), social words still predominated but common nouns increased slightly from 10.56% to 16.24%. Common nouns increased dramatically when children acquire an average of 15 words (between 11 to 20), while the use of social words rapidly decreased. From there on, common nouns increased steadily to a peak of 48.52% when children acquired more than 50 words. A comparison of Figure 1(a) and Figure 1(b) shows that the complementary or contrasting developmental patterns for social words versus common nouns are strikingly similar for Chinese-speaking children and English-speaking children, in that increases in common nouns are accompanied by corresponding decreases in the proportion of social words.

It is clear from Figure 1 that common nouns and social words are the two largest categories, and there were very few closed-class items, for both Englishspeaking and Chinese-speaking children. However, while there was virtually no difference between predicates and closed-class items in terms of the number of words produced by English-speaking children, as reported by Bates et al. (1994) and Caselli et al. (1995), predicates appeared as early as common nouns did in Mandarin Chinese, even though the speed of increase did not match that of the common nouns within the first 50-word mark. This major difference between Chinese and English provides some support to the claim that verbs tend to appear earlier for Chinese-speaking children than for English-speaking children (Tardif et al., 1999; Tardif, 1996, 2006). Still, within the first 50 words, the percentage of common nouns exceeds that of the predicates in Chinese, and this was verified by paired-samples t-tests applied to the vocabulary levels between common nouns and predicates (all ps < .05).

3.2 Developmental changes in vocabulary composition among Chinese toddlers (aged 1;5-2;6)

In this section, we further focus on the developmental trajectory of common nouns, social words, predicates, and closed-class words for older Chinese-speaking toddlers (aged 1;5-2;6). Figure 2 presents the percentages of common nouns, social words, predicates, and closed-class words at each vocabulary level. Given that social words are not the core vocabulary for toddlers, and the proportion of social words decreases dramatically across vocabulary level, as shown in Figure 2, we will not further highlight the social words in this section.

Similar to the analyses of the infant data, the toddler participants were divided into the following eight groups based on their total production vocabulary:(1) 0~50 words (N = 70, 10.77% of the participant sample); (2) 51~100 words(N = 72, 11.08%); (3) 101~200 words (N = 103, 15.85%); (4) 201~300 words(N = 113, 17.38%); (5) 301~400 words (N = 80, 12.31%); (6) 401~500 words(N = 46, 7.08%); (7) 501~600 words (N = 69, 10.62%); (8) 601~710 words (N= 97, 14.92%). We used the same criteria in defining the lexical categories and in calculating the percentages of each category at each vocabulary level. Among the 710 words in the Toddler Checklist, there were 382 common nouns (53.8% of the checklist), 199 predicates (28%), 49 closed-class words (6.9%) from the five categories of connecting words, helping verbs, pronouns, quantifiers and articles, and question words, 62 social words (8.7%), and 18 others (2.5%).

Figure 2 shows that common nouns have complete dominance over other categories across all vocabulary levels beyond the 50-word mark. Within the first 50 words, the percentage of common nouns was similar to that of social words (37.11% and 32.43%, respectively), but it rapidly increased at the 51~100 word stage. Consistent with data from English, as reported in Bates et al. (1994), common nouns made up more than 50% of the total vocabulary for Chinesespeaking children with vocabularies between 101 and 200 words, and continued to increase slowly but then leveled off.

In contrast to common nouns, the proportion of predicates stayed roughly around 30% for the Chinese toddlers, without signif icant change across vocabulary levels. This percentage, however, is higher compared with children learning other languages at the same developmental vocabulary levels. For example, Caselli et al. (1999) observed a developmental pattern that the proportion of predicates increased from below 10% when vocabulary size was less than 50 to about 25% when vocabulary size reached 400~500 for both English and Italian children(aged from 1;6 to 2;6). Behrens (1998) used a longitudinal approach to study the production of verbs in ten children who acquired German, English and Dutch, and found that many verbs did not appear in the production vocabulary until the children entered their third and fourth year of life.

With respect to the percentage of closed-class words, Chinese toddlers did not show substantial increases during this period. This pattern indicates that closedclass words are difficult to learn. Bates et al. (1994) found that English-speaking children’s closed-class words do not show substantial development until they had acquired more than 400 words. In an input analysis, Goodman et al. (2008) also showed that the input frequency of closed-class words, though generally high, has the least influence on the order of acquisition in vocabulary development, as compared with the frequency effects of other categories such as nouns and verbs. One longitudinal study by Kong et al. (2004) also provided some evidence of the late acquisition of closed-class words by Chinese-speaking children. They found quantifiers and articles would develop rapidly only after four years of age, and pronouns except wo ‘I’ also appeared late.

3.3 First 50 words: a detailed analysis

According to Caselli et al. (1995), ‘first acquired’ is defined in terms of the percentage of children in the sample who are reported to produce the word. Table 2 presents the first 50 words in the production vocabulary of Mandarin-speaking infants by their decreasing order of appearance.

Table 2 shows that the first five words produced by Chinese-speaking children are all kinship terms. Consistent with the results of English-speaking and Italian-speaking children (Caselli et al., 1995; Gentner, 1982; Nelson, 1973), Chinese-speaking children’s two earliest acquired words were “daddy” (91.8%) and “mommy” (90.7%). The next two kinship terms were “grandma” (47.6%) and“grandpa” (35.2%). We attributed the results of these early kinship terms to the characteristics of the Chinese culture, where the immediate family members in the household often include both parents and grandparents. Before children can say anything, they are encouraged to address these members at homes, especially baba‘daddy’, mama ‘mommy’, yeye ‘grandpa’ and nainai ‘grandma’. The fifth earliest item was baobao ‘baby’, used to refer to the infant itself.

The semantic category of the next five words expanded from solely kinship terms to common nouns and words for routines. There were still two kinship terms among this set: ayi ‘auntie’, which can refer to mother’s sister and to any female similar to the child’s mother in age, and gege ‘elder brother’, for a male child older than the child. The two common nouns were words for animals, mao ‘cat’and gou ‘dog’ and one routine word is bu ‘no’.

These results are comparable to Italian-speaking children’s earliest vocabulary composition (Caselli et al., 1995) and to the findings of Tardif et al. (2008). While Italian-speaking children acquire an average of four kinship terms in their earliest ten words, Chinese-speaking children use 7 kinship items. As we discussed earlier, terms for people and routine were combined to form a large category-social words -and this is clearly reflected in the first ten words used by Chinese children. Kauschke and Hofmeister (2002) reported that personal-social words occupied 25.19% of German-speaking children’s earliest vocabulary. D’Odorico, Carubbi, Salerni and Calvo (2001) found that half of Italian-speaking children’s first 50 words are onomatopoeic words, routines or names of people (see also Caselli et al., 1995). These findings demonstrate the importance of social words, appearing as the first category in children’ expressive vocabulary regardless of the language the child is learning.

Consistent with the findings of Caselli et al. (1995) for English-speaking and Italian-speaking children, verbs did not appear in the first ten words produced by Chinese-speaking children. In Caselli et al. (1995), English-speaking children failed to produce any verb among the first 50 words, and then produced 4 verbs in the second 50 words; Italian-speaking children produced only one verb DARE‘to give’ among the first 50 words and added 4 more verbs when the vocabulary expanded to 100. In our study, Chinese-speaking children produced a total of 6 verbs among the first 50 words, bao ‘hug’, da ‘hit’, na ‘bring’ or ‘take’, yao‘want’, chi ‘eat’, and zou ‘walk’ or ‘go’. In the next 50 words, predicates (verbs and descriptive words) increased gradually: children produced 10 verbs and 10 adjectives among the second 50 words. In total, predicates constituted 29% of the first 100 words in child Mandarin, quite a large number compared to the percentages of predicates for English- and Italian-speaking children.

We now look at the 20 common nouns in the first 50 words. Among the first acquired common nouns, 6 were names of animals, such as mao ‘cat’, gou‘dog’, niao ‘bird’; 4 were words for food and drink, such as fan ‘food’ and rou‘meat’; 3 were words for outside things, such as hua ‘flower’ and shu ‘tree’; 2 were words for toy, 1 for body part, 1 for clothing, and 1 for household items. These words bear some common characteristics: (1) all of them are monosyllabic words, except wawa ‘doll’, with a syllabic reduplication; (2) most of them are for basic-level concepts, for example, yu ‘fish’; (3) most of them are related to early life experience of the child, about objects or items in the child’s immediate environment. These data are consistent with the findings of Gentner (1982) and Nelson (1973), in that the earliest common nouns are those for basic-level or socially relevant concepts.

Comparing the individual items first acquired by Chinese-speaking and English-speaking children, we can find both similarities and differences. As can be seen from Table 2, there are 19 items in total among the earliest acquired vocabulary by children from both languages: 7 items for people (grandma has two equivalents in Chinese, nainai and laolao, and grandpa also has two equivalents, yeye and laoye), 4 items for games and routines, 1 descriptive word, and the remaining items common nouns. However, in English-speaking children’s first 50 words, about 50% can be regarded as social words, and more than 40% are common nouns, whereas in Chinese-speaking children’s first 50 words, the percentages of social words and common nouns were similar (roughly around 40%), while the remaining 20% of words were mainly predicates (i.e. more predicates in child Mandrin than in child English).

3.4 The predictors of age of acquisition of early vocabulary

To understand the mechanisms underlying the similarities and differences between children learning Mandarin and other languages, we describe in this section our analyses of conceptual (imageability) and linguistic (frequency, length, and grammatical category) variables as predictors of the age of acquisition of early vocabulary. The imageability rating data from college students and other variables on common nouns and action verbs are presented in Table 3. On average, the rating results for nouns on imageability were higher than for verbs, F (1, 448) = 268.26, p < .001, which indicates that the referents to which the nouns correspond can readily generate a mental image. These rating results are consistent with the predictions of the SICI theory (Maguire et al., 2006). On the other hand, word frequency was higher for Chinese verbs than for Chinese nouns, F (1, 448) = 128.82, p < .001, which is consistent with some recent statistical analyses that show that Chinese-speaking children’s language input may contain more verbs of higher frequency (Sandhofer, Smith & Luo, 2000; Zhao & Li, 2008). In addition, these verbs were found to be significantly shorter in length than the nouns, F (1, 448) = 89.54, p < .001.

Pearson correlations between imageability, word frequency, word length, grammatical category membership, and the AoA of words are presented in Table 4. Both word frequency and word length were negatively correlated with the words’AoA (r = -0.451, p < .001, word frequency with AoA; and r = -0.428, p < .001, word length with AoA). This makes sense in that words that are shorter and higher in frequency tend to be acquired earlier. These two variables seem to have the most impact on the AoA of the child Mandrin lexicon (see regression analyses below). They also showed significant correlations with other variables (imageability and grammatical category) (all ps < .001). Imageability also significantly correlated with AoA (r = -0.099, p < .05). However, grammatical category membership did not correlate with AoA (r = 0.023, p > .1).

To explore the relative contributions of imageability, word frequency, word length (monosyllabic or multisyllabic words), and grammatical category (noun or verb) to the AoA of vocabulary, we ran multiple regression analyses with the AoA of words as the dependent variable and the four variables as predictors. The results of the final regression analysis are displayed in Table 5. Together, the four predicting variables accounted for 37.2% of the AoA variance, F (4, 445) = 67.38, p < .001. Their unique contributions were evaluated through the interpretations of squared semi-partial coefficients (sr2) (Cohen, Cohen, West & Aiken, 2003). Specifically, word frequency uniquely accounted for 14.1% of the AoA variance, word length 6.7%, imageability 5.2%, and grammatical category 1.3% (see Table 5). These data suggested that word frequency, word length, and imageability played predominant roles in predicting the AoA of words, with grammatical category playing a relatively smaller role.

Finally, based on the word length difference between nouns and verbs we observed, and on similar findings by Zhao and Li (2008), we further compared the percentages of monosyllabic and multisyllabic words in nouns and verbs at different vocabulary levels. The data are presented in Figure 3. Two observations should be noted here. First, the percentage of multisyllabic words increases rapidly as vocabulary grows. Second, different developmental patterns exist for nouns versus verbs with regard to this word length increase. While there were in general more monosyllabic than multisyllabic verbs, there were more multisyllabic nouns once children have reached the 100~200 vocabulary mark. The contrasting patterns of nouns and verbs indicate that syllable length may play differential roles on the development of different grammatical categories (see ‘General discussion’ below).