A multi-lab study of bilingual infants: Exploring the preference for infant-directed speech

Abstract

From the earliest months of life, infants prefer listening to and learn better from infant-directed speech (IDS) than adult-directed speech (ADS). Yet, IDS differs within communities, across languages, and across cultures, both in form and in prevalence. This large-scale, multi-site study used the diversity of bilingual infant experiences to explore the impact of different types of linguistic experience on infants' IDS preference. As part of the multi-lab ManyBabies 1 project, we compared lab-matched samples of 333 bilingual and 385 monolingual infants' preference for North-American English IDS (cf. ManyBabies Consortium, 2020: ManyBabies 1), tested in 17 labs in 7 countries. Those infants were tested in two age groups: 6-9 months (the younger sample) and 12-15 months (the older sample). We found that bilingual and monolingual infants both preferred IDS to ADS, and did not differ in terms of the overall magnitude of this preference. However, amongst bilingual infants who were acquiring North-American English (NAE) as a native language, greater exposure to NAE was associated with a stronger IDS preference, extending the previous finding from ManyBabies 1 that monolinguals learning NAE as a native language showed a stronger preference than infants unexposed to NAE. Together, our findings indicate that IDS preference likely makes a similar contribution to monolingual and bilingual development, and that infants are exquisitely sensitive to the nature and frequency of different types of language input in their early environments.

Keywords: bilingualism; experimental methods; infant-directed speech; language acquisition; reproducibility; speech perception.

Figure 1.

Forest plot for the lab-matched dataset, separated by age group. Standardized effect sizes are shown for each lab, with error bars showing 95% confidence intervals. Each lab reported two effect sizes: one for the monolingual group (red triangles) and the other one for the bilingual group (blue circles). Within each age group, points are ordered by the difference between the monolingual and bilingual effect sizes, and this effect size difference is indicated by a black X. Points are scaled by inverse variance (i.e., more precise estimates are denoted by larger shapes). The points in the bottom panel show the global meta-analytic estimate.

Figure 2.

Linear trend between infants’ IDS preference and their percentage of time exposed to North American English (NAE). Blue line indicates a regression model between infants’ IDS preference and their NAE exposure (starting from zero). Red line indicates another regression model of the same relationship with a focus of NAE exposure between 25 to 75%. We note that the y-axis was truncated to highlight the trend such that some individual points are not plotted.