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.

This study introduces a method ideally suited for investigating toddlers’ ability to detect mispronunciations in lexical representations: pupillometry. Previous research has established that the magnitude of pupil dilation reflects differing levels of cognitive effort. Building on those findings, we use pupil dilation to study the level of detail encoded in lexical representations with 30-month-old children whose lexicons allow for a featurally balanced stimulus set. In each trial, we present a picture followed by a corresponding auditory label. By systematically manipulating the number of feature changes in the onset of the label (e.g., baby ∼ daby ∼ faby ∼ shaby), we tested whether featural distance predicts the degree of pupil dilation. Our findings support the existence of a relationship between featural distance and pupil dilation. First, mispronounced words are associated with a larger degree of dilation than correct forms. Second, words that deviate more from the correct form are related to a larger dilation than words that deviate less. This pattern indicates that toddlers are sensitive to the degree of mispronunciation, and as such it corroborates previous work that found word recognition modulated by sub-segmental detail and by the degree of mismatch. Thus, we establish that pupillometry provides a viable alternative to paradigms that require overt behavioral response in increasing our understanding of the development of lexical representations.

In a seminal study, Stager and Werker (1997) reported findings showing that 14-month-old English-learning infants have the

Child characteristics, family factors, and preschool factors are all found to affect the rate of bilingual children's vocabulary development in heritage language (HL). However, what remains unknown is the relative importance of these three sets of factors in HL vocabulary growth. The current study explored the complex issue with 457 Singaporean preschool children who are speaking either Mandarin, Malay, or Tamil as their HL. A series of internal factors (e.g., non-verbal intelligence) and external factors (e.g., maternal educational level) were used to predict children's HL vocabulary growth over a year at preschool with linear mixed effects models.The results demonstrated that external factors (i.e., family and preschool factors) are relatively more important than child characteristics in enhancing bilingual children's HL vocabulary growth. Specifically, children's language input quantity (i.e., home language dominance), input quality (e.g., number of books in HL), and HL input quantity at school (i.e., the time between two waves of tests at preschool) predict the participants’ HL vocabulary growth, with initial vocabulary controlled. The relative importance of external factors in bilingual children's HL vocabulary development is attributed to the general bilingual setting in Singapore, where HL is taken as a subject to learn at preschool and children have fairly limited exposure to HL in general. The limited amount of input might not suffice to trigger the full expression of internal resources. Our findings suggest the crucial roles that caregivers and preschools play in early HL education, and the necessity of more parental involvement in early HL learning in particular.

Children’s interpretations of sentences containing focus particles do not seem adult-like until school age. This study investigates how German 4-year-old children comprehend sentences with the focus particle ‘nur’ (only) by using different tasks and controlling for the impact of general cognitive abilities on performance measures. Two sentence types with ‘only’ in either pre-subject or pre-object position were presented. Eye gaze data and verbal responses were collected via the visual world paradigm combined with a sentence-picture verification task. While the eye tracking data revealed an adult-like pattern of focus particle processing, the sentence-picture verification replicated previous findings of poor comprehension, especially for ‘only’ in pre-subject position. A second study focused on the impact of general cognitive abilities on the outcomes of the verification task. Working memory was related to children’s performance in both sentence types whereas inhibitory control was selectively related to the number of errors for sentences with ‘only’ in pre-subject position. These results suggest that children at the age of 4 years have the linguistic competence to correctly interpret sentences with focus particles, which–depending on specific task demands–may be masked by immature general cognitive abilities.