Input quantity and lexical acquisition

Investigating vocabulary acquisition in bilinguals is important for two reasons. Firstly, if MacLeod, Fabiano-Smith, Boegner-Page and Fontolliet (2012:133) are correct in regarding lexical acquisition as “a window on bilingual language development” in general, such

46 research can inform and perhaps correct general assumptions about the perceived disadvantage that bilingual learners are at compared to monolinguals in terms of language development. Bilinguals should not be judged on their abilities in only one of their languages, but rather in both if an accurate estimate of their linguistic abilities is to be obtained (MacLeod et al., 2012:133). Even so, a number of studies have indicated that, when assessed in the language to which she receives the most exposure, a bilingual is often capable of matching monolingual norms (cf., for example, Umbel, Pearson, Fernández, & Oller, 1992; Thordardottir, 2011). Additionally, research has shown that, whereas some bilinguals might have a smaller lexical vocabulary (i.e. a collection of terms denoting certain referents) than monolinguals in each of their languages, they do keep pace with monolinguals in terms of their conceptual vocabulary (i.e. their knowledge of referents, independent of language) (Pearson, Fernández, & Oller, 1993).

The second reason for investigating vocabulary acquisition in bilinguals is the ability of such studies to test hypotheses surrounding the role of input in language acquisition. Most children experience a period of rapid growth in their vocabulary between the point at which the first 25 to 50 words have been acquired and the onset of syntactic acquisition (Pearson et al., 1997:42). Whereas the child’s input remains relatively stable in this period, cognitive development may increase her ability to better “assimilate” the input – if so, this would suggest that there is no significant relation between amount of input and rate of early lexical acquisition (Pearson et al., 1997:42). This theory has been tested and consequently questioned by a number of studies since the early nineties. The first study offering direct evidence against this theory and, rather, in support of input quantity as determinant of vocabulary growth was that by Huttenlocher, Haight, Bryk, Seltzer and Lyons (1991). In this study, vocabulary size in 22 monolingual English children between 14 and 26 months was found to be related to how much their mothers spoke to them. The latter variable was measured by counting the number of words the mother directed at the child during the three hours of recorded mother-child interaction that had been obtained for all participants at the age of 16 months, i.e. at the first point when all the participants were observed interacting with their mothers during their daily activities (Huttenlocher et al., 1991:239). Similarly, a longitudinal study by Hart and Risley (1995) employing 42 monolingual English child participants found a strong, positive association between vocabulary size at certain points

47 over a two and a half year period and the number of words the participants’ caretakers spoke to them at those specific points in time.

Making use of the advantage that bilingual participants offer in terms of keeping child- internal factors constant, Pearson et al. (1997) used 25 English-Spanish bilinguals aged between eight and 30 months and residing in middle class homes in Miami, Florida, to test the relationship between input quantity and vocabulary size. The specific goals of the study were to establish the strength of the relationship between lexical learning in a given language and estimated exposure to that language, investigate the factors that affect this strength, and ascertain whether the relationship remains constant across all amounts of input or whether there is a certain exposure threshold below which lexical learning does not take place (Pearson et al., 1997:44).

Vocabulary observations were conducted approximately every two to four months, with the number of observations per participant varying between one and ten. At each observation point, parents were asked to complete, for each language, the MacArthur Communicative

Development Inventory (CDI), Toddler and Infant forms (1989) and its Spanish version, i.e.

the Toddler and Infant Inventario del Desarrollo de las Habilidades Comunicativas (Jackson-Maldonado & Bates, 1988). The CDI is a standardised instrument offering a measure of a child’s vocabulary based on parental reports – the parent is asked to indicate which of the words on a list the child comprehends and/or spontaneously produces at the time

of filling out the form.13 Whereas the CDI obviously cannot provide an exhaustive list of all

words that a child might know and so does not provide an exact indication of all words in a child’s vocabulary, it was highly suited to the study as it enabled a relative comparison of vocabulary size in a bilingual’s two languages, using the same instrument (Pearson et al., 1997:45-46).

At the first observation, parents were also asked to complete a language background questionnaire estimating the respective amounts of time a day or week that their child

13

Cf. the CDI website (http://mb-cdi.stanford.edu/cdiwelcome.htm) for information on the current editions of the various different language versions of this instrument.

48 interacts with monolingual and bilingual speakers of English and Spanish, and, in the case of bilingual interlocutors, what percentage of the interaction is devoted to each language (Pearson et al., 1997:46). Questionnaires were updated at each subsequent observation.

Results revealed a substantial relation between input quantity and vocabulary learning in a child’s second year of life in that the number of words in the participants’ vocabulary in a given language was found to be largely proportional to the amount of time they spent with speakers of that language (Pearson et al., 1997:51). The researchers admit that this correlation between input and vocabulary learning is “not perfect” as the strength of the relationship could potentially be influenced by a number of factors, starting with the possible inaccuracy of the parents’ estimation of input quantity in each language (Pearson et al., 1997:53). The OPOL strategy, which makes a quantification of input in each language easier, was not used in any of the participating households. Additionally, estimations of input might be skewed by the fact that bilinguals often are not conscious of the language that they are employing, and by the fact that there is inevitable uncertainty around which language a child chooses to focus on in a mixed-language environment (Pearson et al., 1997:53).

The possibility of an input threshold below which lexical learning does not take place was not supported by the data in this study ̶ in the case of participants whose exposure to a given language constitutes as little as 20% or less of their waking hours (within a relatively stable linguistic environment) the number of vocabulary items in that language was still proportional to the amount of input time in that language (Pearson et al., 1997:55). Such participants did not, however, eagerly or freely produce utterances in the language to which they received less than 20% exposure (Pearson et al., 1997:56). Whereas this study suggests that vocabulary learning will take place even at drastically reduced input levels, the researchers caution that this premise remains to be tested for the acquisition of grammar and phonology (Pearson et al., 1997:55).

Thordardottir (2011) investigated the relationship between quantity of exposure and receptive and expressive vocabulary scores among five-year-old French-English simultaneous bilinguals (i.e. bilinguals who are exposed to both languages from birth), using monolingual

49 controls. The study was conducted in Montreal, Canada, using 84 participants: 19 French monolinguals, 16 English monolinguals, 20 bilinguals dominant in French (in terms of quantity of exposure), 16 bilinguals dominant in English, and 13 bilinguals receiving relatively balanced exposure to both languages. Language exposure was measured by having parents complete a detailed language background questionnaire (developed by Thordardottir et al., 2006) which enquires as to the distribution of languages in the child’s life both at the time of testing and in the past, in the home, daycare and any other language environment that the child was regularly exposed to at some point in her life; and also as to the approximate amount of time she spent in each environment per week. In the case of both her languages, respectively, each participant’s pattern of exposure over time was subsequently calculated as a single number, i.e. the percentage of her lifetime that was spent receiving exposure to that language (Thordardottir, 2011:431).

Receptive vocabulary was measured using the Peabody Picture Vocabulary Test III (PPVT- III, Dunn & Dunn, 1997) and the Boehm Test of Basic Concepts–Preschool (Boehm, 2001) for English and the Canadian French adaptations of these instruments, i.e. the Épreuve de

vocabulaire en images Peabody (EVIP; Dunn, Thériault-Whalen, & Dunn, 1993) and the Test des concepts de base de Boehm, Version Préscolaire (Boehm, 1986) for French.

Expressive vocabulary was measured using the respective expressive vocabulary subtests of, for English, the Clinical Evaluation of Language Fundamentals–Preschool (Wiig, Secord, & Semel, 2004) and, for French, the Nouvelles épreuves pour l’examen du langage (Chevrie- Muller & Plaza, 2001).

Overall, results showed “a strong and systematic relationship” between amount of exposure to a language and performance in that language, but with differences between receptive and expressive vocabulary (Thordardottir, 2011:440). Whilst the relationship was more or less linear in the case of expressive vocabulary scores, it was less linear in the case of receptive vocabulary scores, where proficiency increased in line with increases in exposure only up to a certain point beyond which little further increase in proficiency was seen, despite further increases in exposure (Thordardottir, 2011:440). Additionally, it was found that the bilingual participants with unbalanced exposure fared significantly worse than monolinguals on both receptive and expressive vocabulary measures in the case of their non-dominant language. On

50 the other hand, those bilinguals who received relatively balanced exposure to both English and French (i.e. between 40% and 60% exposure to each) managed to keep up with monolinguals in terms of receptive vocabulary scores, but fared significantly worse on the expressive vocabulary measures – exposure of approximately 70% was found to be a necessary requirement for matching monolinguals on the latter measures (Thordardottir, 2011:441). These results indicate that in order for bilinguals to develop advanced, native-like skills in either one of their languages, more exposure is needed in the case of expressive vocabulary than in the case of receptive vocabulary (Thordardottir, 2011:441).

In a similar study by Thordardottir and Brandeker (2010, 2013) involving three-year-old French-English bilingual children, vocabulary scores also correlated significantly with quantity of previous exposure to the relevant language. In this study, those bilinguals with unbalanced exposure fared, in the case of their non-dominant language, significantly worse than monolingual controls, as did some of the bilinguals with relatively balanced exposure.

MacLeod et al. (2012) tested nine French-German simultaneous bilinguals (mean age = 52 months) in Québec, Canada, using the noun and verb subtests of the Patholinguistische

Diagnostik bei Sprachentwicklungsstörungen (Kauschke & Siegmüller, 2010) for German

receptive vocabulary, and the Évaluation du Vocabulaire en Images Peabody (Dunn & Thériault-Whalen, 1993) for French receptive vocabulary. Both tests require the participant to point to the one image, in a group of four images, that matches the word produced by the administrator. Parental interviews were conducted in order to gain an estimation of each child’s language exposure patterns. For this purpose, a language use questionnaire was devised, asking questions regarding the child’s age at first exposure to each language; the language(s) specific interlocutors use with the child; the language(s) the child uses with them in turn; the amount of time spent with each interlocutor in a typical week day or on the weekend; the language(s) used in the media that the child is exposed to; and the child’s productive and receptive abilities in each language (MacLeod et al., 2012:135). Language exposure was found to be unbalanced with all but one participant being exposed to French for at least 71% of a typical week (MacLeod et al., 2012:136).

51 Results revealed a statistically significant difference between participants’ scores on the German noun subtest and the French test, and between their scores on the German verb subtest and the French test, with scores for German being lower than those for French (MacLeod et al., 2012:138). Also, whereas the bilingual participants’ scores were comparable to those of monolinguals on the French test, their scores were lower than those of monolinguals on the German tests (MacLeod et al., 2012:140). A positive correlation was found between input and receptive vocabulary size in the case of the exposure dominant language, French, but no significant correlation was found in the case of German, the language of clearly reduced input (MacLeod et al., 2012:138). As no relationship was found between the participants’ German scores and the language of the media, the language use of family members, or the participants’ language preference, MacLeod et al. (2012:139-140) suggest that other factors, for example working memory, may perhaps be more determinant of lexical learning in the minority language than input.