The prototypical word learning situation in western, middle-class cultures is dyadic: an adult addresses a child directly, ideally in a manner sensitive to their current focus of attention. But young children also seem to learn many of their words in polyadic situations through overhearing. Extending the previous work of Akhtar and colleagues, in the current two studies we gave 18-month-old infants opportunities to acquire novel words through overhearing in situations that were a bit more complex: they did not socially interact with the adult who used the new word before the word learning situation began, and the way the adult used the new word was less transparent in that it was neither a naming nor a directive speech act. In both studies, infants learned words equally well (and above chance) whether they were directly addressed or had to eavesdrop on two adults. Almost from the beginning, young children employ diverse learning strategies for acquiring new words.

Psychological scientists have become increasingly concerned with issues related to methodology and replicability, and infancy researchers in particular face specific challenges related to replicability: For example, high-powered studies are difficult to conduct, testing conditions vary across labs, and different labs have access to different infant populations. Addressing these concerns, we report on a large-scale, multisite study aimed at (a) assessing the overall replicability of a single theoretically important phenomenon and (b) examining methodological, cultural, and developmental moderators. We focus on infants’ preference for infant-directed speech (IDS) over adult-directed speech (ADS). Stimuli of mothers speaking to their infants and to an adult in North American English were created using seminaturalistic laboratory-based audio recordings. Infants’ relative preference for IDS and ADS was assessed across 67 laboratories in North America, Europe, Australia, and Asia using the three common methods for measuring infants’ discrimination (head-turn preference, central fixation, and eye tracking). The overall meta-analytic effect size (Cohen’s d) was 0.35, 95% confidence interval = [0.29, 0.42], which was reliably above zero but smaller than the meta-analytic mean computed from previous literature (0.67). The IDS preference was significantly stronger in older children, in those children for whom the stimuli matched their native language and dialect, and in data from labs using the head-turn preference procedure. Together, these findings replicate the IDS preference but suggest that its magnitude is modulated by development, native-language experience, and testing procedure.

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Children can represent events in our everyday life in both non‐linguistic and linguistic formats. We aimed to investigate whether non‐linguistic representations are changed once children acquire their linguistic counterparts. In the present study, we explored whether and how language changes the perception of simple means‐end actions using an eye‐tracking paradigm. Children between 12 and 24 months of age heard a sentence containing a verb and subsequently watched an action video. Results show an interfering influence of language on action perception at 12 months and a facilitating influence at 24 months. However, this was only the case for verbs that are already in the toddlers' productive vocabulary but not for those that are acquired later. Taken together, the results suggest that a communication between non‐linguistic and linguistic representations starts early and develops in the second year of life. The successful facilitatory influence depends on the productive repertoire of the language in question.

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 project, we compared lab-matched samples of 333 bilingual and 385 monolingual infants’ preference for North-American English IDS (cf. ManyBabies Consortium, in press (MB1)), 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 MB1 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.

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