The ideal of scientific progress is that we accumulate measurements and integrate these into theory, but recent discussion of replicability issues has cast doubt on whether psychological research conforms to this model. Developmental research—especially with infant participants—also has discipline‐specific replicability challenges, including small samples and limited measurement methods. Inspired by collaborative replication efforts in cognitive and social psychology, we describe a proposal for assessing and promoting replicability in infancy research: large‐scale, multi‐laboratory replication efforts aiming for a more precise understanding of key developmental phenomena. The ManyBabies project, our instantiation of this proposal, will not only help us estimate how robust and replicable these phenomena are, but also gain new theoretical insights into how they vary across ages, linguistic communities, and measurement methods. This project has the potential for a variety of positive outcomes, including less‐biased estimates of theoretically important effects, estimates of variability that can be used for later study planning, and a series of best‐practices blueprints for future infancy research.

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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This study investigates infants' discrimination abilities for familiar and unfamiliar regional English accents. Using a variation of the head-turn preference procedure, 5-month-old infants demonstrated that they were able to distinguish between their own South-West English accent and an unfamiliar Welsh English accent. However, this distinction was not seen when two unfamiliar accents (Welsh English and Scottish English) were presented to the infants, indicating they had not acquired the general ability to distinguish between regional varieties, but only the distinction between their home accent and unfamiliar regional variations. This ability was also confirmed with 7-montholds, challenging recent claims that infants lose their sensitivity to dialects at around that age. Taken together, our results argue in favor of an early sensitivity to the intonation system of languages, and to the early learning of accentspecific intonation and potentially segmental patterns. Implications for the development of accent normalization abilities are discussed.Studies on language discrimination highlight young infants' sensitivity to linguistic rhythm through their ability to distinguish pairs of languages belonging to distinct rhythmic categories (e.g., English [stress-based] versus Japanese [mora-based],

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