14.6: The Science of Multilingualism Development

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Todd LaMarr

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Language Discrimination

One potential challenge for infants growing up with regular exposure to multiple languages is in discriminating between languages. Being able to separate the languages from very early on seems crucial given that the child has to establish different linguistic systems for the languages. ^{^[1]}

Early research on monolingual infants has demonstrated that newborns are able to discriminate between different languages but only if the languages belong to different rhythmic classes. For example, French newborns could discriminate English from Japanese, Spanish and Italian but not from Dutch (Nazzi, Bertoncini & Mehler, 1998; Ramus et al., 2000). The only study on multilingual exposure effects with newborns tested infants from multilingual English–Tagalog mothers who regularly used both languages during pregnancy (Byers-Heinlein, Burns & Werker, 2010). The experiment tested discrimination using a habituation paradigm in which infants were first exposed to either English or Tagalog sentences until their sucking rates to a special pacifier decreased below a predefined criterion (habitituation) and then were presented with sentences from the other language. Results revealed that both monolingual and multilingual infants showed an increase in their sucking after the language change, demonstrating that multilingual newborns were able to discriminate between both languages, just like monolinguals. ^{^[1]}

At the age of 4 months, monolingual infants begin to discriminate languages of the same rhythmical class from their native language (Bosch & Sebastián-Gallés, 2001; Chong, Vicenik & Sundara, 2018; Molnar, Gervain & Carreiras, 2014; Nazzi, Jusczyk & Johnson, 2000) suggesting that they have acquired some inventory of cues that help them separate their native language from other languages. Similar to monolinguals, multilinguals are able to discriminate between languages at the same age as monolinguals (Bosch & Sebastián-Gallés, 2001; Garcia, Guerrero-Mosquera, Colomer & Sebastian-Galles, 2018). For example, monolingual Basque and multilingual Spanish/Basque infants were first habituated with stimuli from one language, and then tested with stimuli from both languages. Results showed that both groups were able to discriminate between the two languages (Molnar, Gervain & Carreiras, 2014). This suggests that by the age of 4 months multilingual infants have detected some properties that separate their two languages and that they can assign these properties specifically to one of their languages. ^{^[1]}

Smiling caregiver holding infant with wide smile — Figure \(\PageIndex{1}\): Caregiver holding infant in arms. (^{^[2]})

Growth of Word Learning

Word learning starts in the second half of the first year of life, with some evidence for knowledge of a limited number of words as early as 6 months (Bergelson & Swingley, 2012; Tincoff & Jusczyk, 1999, 2012). Word learning then increases, often with a sharp acceleration, in the second year of life (Fenson, Dale, Reznick, Bates, Thal & Pethick, 1994). This early development is characterized by extensive individual variability in the sizes of both receptive and productive vocabularies. ^{^[1]}

Since multilingual infants' input is distributed over more than one language, they are likely to receive less input in each of their languages than monolinguals, which can have an impact on early lexical development. Moreover, since multilingual infants will vary in terms of the relative amount of input they receive in their languages, the languages might not develop at the same speed. Recent studies support these points. When multilinguals are evaluated on each of their languages separately, studies report that they lag behind monolinguals starting in the second year of life (Core, Hoff, Rumiche & Señor, 2013) and the relative amount of exposure for each language is related to the growth of that specific language (Grüter, Hurtado, Marchman & Fernald, 2014). ^{^[1]}

One crucial aspect when comparing monolingual and multilingual infants' trajectories of word learning is in how vocabulary is counted. One is conceptual vocabulary: counting every referent for which a child has a word for in either language (a French–German child would get a 1 for knowing either chien, hund, or both); another approach is total vocabulary, counting every word known across both languages (the same child would get a 2 for knowing both chien and hund). Considering how to measure multilingual vocabulary growth, especially when comparing to monolinguals, is critical as the results can vary greatly (Hoff et al., 2012). For example, a study comparing English–German and English monolingual 24 to 27 month old toddlers found that the multilinguals' total vocabularies were significantly larger than both their conceptual vocabularies and the English vocabularies of English-learning children (Junker & Stockman, 2002). Evidence also suggests that vocabulary growth is influenced by language dominance, with higher vocabulary scores in the dominant as compared to the non-dominant language (Hoff et al., 2012). What is clear is that when multilinguals' vocabulary levels are evaluated using measures that take into account both of their languages, they fall within a similar range as monolingual infants. When assessing the language development of multilinguals, the development of all of their languages should always be considered (Nayeb et al., 2021). ^{^[1]}

Toddler (1.5 years old) of Chinese decent — Figure \(\PageIndex{2}\): Toddler (1.5 years old) growing up in China. (^{^[3]})

Besides charting the growth trajectory of word learning through vocabulary knowledge, some studies have explored word learning by investigating the speed at which multilingual infants recognize words in each of their languages. Previous research with monolinguals has revealed that speed of language processing is related to later cognitive and language outcomes (Fernald, Perfors & Marchman, 2006; Hurtado, Marchman & Fernald, 2007; Marchman & Fernald, 2008). In a study with Spanish/English 30 month old multilinguals, results revealed that processing speed in each of the children’s languages was related to their vocabulary in that specific language (Marchman, Fernald & Hurtado, 2010). Similar findings were also shown in another study with 16 to 22 month old Spanish/English multilinguals (DeAnda, Hendrickson, Zesiger, Poulin-Dubois & Friend, 2018). This research suggests that language processing speed and vocabulary acquisition are linked in multilinguals, as had been found in monolinguals, but that this link is language specific. ^{^[1]}

^{^[1]} Höhle et al., (2020). Variability and stability in early language acquisition: Comparing monolingual and bilingual infants' speech perception and word recognition. Bilingualism: Language and Cognition, 23(1), 56-71. CC by 4.0

^{^[2]} Image by Jonathan Borba on Unsplash

^{^[3]} Image by chen lei on Unsplash