Sometimes larger, sometimes smaller: Measuring vocabulary in monolingual and bilingual infants and toddlers

Abstract

Vocabulary size is one of the most important early metrics of language development. Assessing vocabulary in bilingual children is complex because bilinguals learn words in two languages, which include translation equivalents (cross-language synonyms). We collected expressive vocabulary data from English and French monolinguals (n = 220), and English–French bilinguals (n = 184) aged 18–33 months, via parent report using the MacArthur-Bates Communicative Development Inventories, and quantified bilinguals’ vocabulary size using different approaches to counting translation equivalents. Our results showed that traditional approaches yield larger (word vocabulary) or smaller (concept vocabulary) quantification of bilinguals’ vocabulary knowledge relative to monolinguals. We propose a new metric, the bilingual adjusted vocabulary, that yields similar vocabulary sizes for monolinguals and bilinguals across different ages. Uniquely, this approach counts translation equivalents differently depending on the child’s age. This developmentally-informed bilingual vocabulary measure reveals differences in word learning abilities across ages, and provides a new approach to measure vocabulary in bilingual toddlers.

The more they hear the more they learn? Using data from bilinguals to test models of early lexical development

“…To put this in context, if a child was perfectly balanced in their language experience (e.g., 50% exposure to each language) their performance in each language would be equivalent to that of a monolingual 8 months younger, replicating previous results showing that monolinguals outperform same-age bilinguals in a looking-while-listening task (Wewalaarachchi et al, 2017). Our task measured bilinguals in a single language at a time, and this result parallels the robust finding that bilinguals have smaller vocabularies than their monolingual peers, but only when a single language is considered (Core et al, 2013;Ehl et al, 2020;Gonzalez-Barrero et al, 2020).…”

“…This overall monolingual-bilingual difference is observed in other tasks as well; for example, monolinguals show larger vocabularies than bilinguals when compared on a single language in parent reports like the CDI (Fenson et al, 2007). Nevertheless, when using instruments like parent reports it is possible to evaluate bilinguals in both their languages and combine their results into a single score that can then be compared to the monolingual score (Gonzalez-Barrero, et al, 2020). There is no straightforward way to create a combined score for bilinguals in the looking-while-listening tasks, and therefore any comparisons between monolingual and bilingual groups should be interpreted with care, even when bilinguals are tested in their dominant (most-heard) language.…”

“…Bilingual children learn words in both of their languages from early in development (De Houwer et al, 2006), and they develop vocabulary at a rate that is on par with their monolingual counterparts when words in both languages are taken into account (see Core et al, 2013;Ehl et al, 2020;Gonzalez-Barrero et al, 2020;Pearson et. al, 1993).…”

Multilingual toddlers’ vocabulary development in two languages: Comparing bilinguals and trilinguals

“…Although research on trilinguals' vocabulary development is quite limited (e.g., Albin & Gershkoff-Stowe, 2016;Arnaus Gil, Müller, Sette & Hüppop, 2020;Chevalier;2015;De Houwer, 2004;Montanari, 2010;Quay, 2011), extant studies indicate that the more trilingual children are exposed to one language, the more their vocabulary develops in that language compared to the other two (Montanari, 2010;Oller, 2010;Potgieter, 2016). There is little evidence that multilingualism reduces children's overall rate of word learning, given that monolinguals and bilinguals have similar vocabulary sizes when words from both languages are considered (Core, Hoff, Rumiche & Señor, 2013;De Houwer et al, 2014;Gonzalez-Barrero, Schott & Byers-Heinlein, 2020;Pearson et al, 1993).…”

Is there a bilingual disadvantage for word segmentation? A computational modeling approach

“…If the discovery of distributional regularities depends on frequency, bilingual environments should be more challenging; and, if word segmentation is indeed challenging for bilinguals, we should expect, for instance, a delay in vocabulary learning. However, when properly matched, bilinguals and monolinguals know similar numbers of words in their vocabularies (see Gonzalez-Barrero, Schott & Byers-Heinlein, 2020 for a recent article showing how different approaches quantifying vocabulary size in bilinguals can lead to different results). Another variable to take into account is that depending on the languages that children are exposed to, the overlap in the lexicon and phonology across the two languages may vary.…”