Greater attention to socioeconomic status in developmental research can improve the external validity, generalizability, and replicability of developmental science.

Psychological researchers have been criticized for making broad presumptions about human behavior based on limited sampling. In part, presumptive generalizability is reflected in the limited representation of sociodemographic variation in research reports. In this analysis, we examine time-trends in reporting of a key sociodemographic construct relevant to many aspects of child development-socioeconomic status (SES)-across six mainstream developmental journals (Infancy, Child Development, Developmental Science, Developmental Psychology, Infant and Child Development, and Infant Behavior & Development) between 2016 and 2022. Findings point to limited reporting of SES across developmental journals and across time. Reporting rates varied significantly by region and by topic of development. In terms of specific indicators of SES, there was consistent use of income and caregiver education as SES indicators. The epistemic costs of the lack of integration of socio-economic factors in developmental research are addressed. Pathways to greater integration of SES are proposed. RESEARCH HIGHLIGHTS: We analyzed reporting and representation of socioeconomic status in published studies on early child development. A large proportion of published studies did not report any socio-economic information. Suggestions for greater attention to socioeconomic status are proposed.

The development of tone discrimination in infancy: Evidence from a cross-linguistic, multi-lab report.

We report the findings of a multi-language and multi-lab investigation of young infants' ability to discriminate lexical tones as a function of their native language, age and language experience, as well as of tone properties. Given the high prevalence of lexical tones across human languages, understanding lexical tone acquisition is fundamental for comprehensive theories of language learning. While there are some similarities between the developmental course of lexical tone perception and that of vowels and consonants, findings for lexical tones tend to vary greatly across different laboratories. To reconcile these differences and to assess the developmental trajectory of native and non-native perception of tone contrasts, this study employed a single experimental paradigm with the same two pairs of Cantonese tone contrasts (perceptually similar vs. distinct) across 13 laboratories in Asia-Pacific, Europe and North-America testing 5-, 10- and 17-month-old monolingual (tone, pitch-accent, non-tone) and bilingual (tone/non-tone, non-tone/non-tone) infants. Across the age range and language backgrounds, infants who were not exposed to Cantonese showed robust discrimination of the two non-native lexical tone contrasts. Contrary to this overall finding, the statistical model assessing native discrimination by Cantonese-learning infants failed to yield significant effects. These findings indicate that lexical tone sensitivity is maintained from 5 to 17 months in infants acquiring tone and non-tone languages, challenging the generalisability of the existing theoretical accounts of perceptual narrowing in the first months of life. RESEARCH HIGHLIGHTS: This is a multi-language and multi-lab investigation of young infants' ability to discriminate lexical tones. This study included data from 13 laboratories testing 5-, 10-, and 17-month-old monolingual (tone, pitch-accent, non-tone) and bilingual (tone/non-tone, non-tone/non-tone) infants. Overall, infants discriminated a perceptually similar and a distinct non-native tone contrast, although there was no evidence of a native tone-language advantage in discrimination. These results demonstrate maintenance of tone discrimination throughout development.

Effects of socio-economic status on infant native and non-native phoneme discrimination.

Infants undergo fundamental shifts in perception that are reported to be critical for language acquisition. In particular, infants' perception of native and non-native sounds begins to align with the properties of their native sound system. Thus far, empirical evidence for this transition - perceptual narrowing - has drawn from socio-economically and linguistically narrow populations from limited world regions. In this study, infants were sampled across diverse socio-economic strata and linguistic development in Singapore. One hundred and 16 infants were tested on their ability to discriminate both a native phonetic contrast (/ba/ versus /da/) and a non-native Hindi contrast (/ta/ versus /ʈa). Infants ranged in age from 6 to 12 months. Associations between age and discrimination varied by contrast type. Results demonstrated that infants' native sensitivities were positively predicted by family SES, whereas non-native sensitivities were not. Maternal socio-economic factors uniquely predicted native language sensitivity. Findings suggest that infants' sensitivity to native sound contrasts is influenced by their family socio-economic status. RESEARCH HIGHLIGHTS: We investigated effects of socio-economic status on infant speech perception. Infants were tested on native and non-native speech discrimination. Socio-economic status predicted native speech discrimination. Maternal occupation was a key predictor of native speech discrimination.

The home literacy environment mediates effects of socio-economic status on infant vocabulary development.

It is well attested that high socio-economic status (SES) is associated with larger vocabulary size estimates in young children. This has led to growing interest in identifying associations and mechanisms that may contribute to this relationship. In this study, parent-child reading behaviors were investigated in relation to vocabulary size in a large-scale study of linguistically and socio-economically diverse families. This study sampled 902 infants in Singapore, a multilingual society. Both single-language (dominant and non-dominant) and dual-language vocabulary size estimates were obtained and related to family SES, demographic details, and home literacy activities. Results demonstrated that both single-language (dominant and non-dominant) and dual-language infant vocabulary size estimates were predicted by parental education levels. Further analyses revealed that parent-child book reading activities mediated the relationship between parental education and infant vocabulary size. Findings suggest that shared book reading may narrow effects of socio-economic disparities on early language development. RESEARCH HIGHLIGHTS: Socio-economic status (SES) was examined in relation to infant vocabulary size in a linguistically and socio-economically diverse setting. Mediating effects of the home literacy environment on infant vocabulary size were measured. Socio-economic factors, notably parental education, had both direct and indirect effects on vocabulary size. The home literacy environment mediated effects of SES on infant vocabulary size.

Sensitivity to visual cues within motion events in monolingual and bilingual infants.

It is well known that infants undergo developmental change in how they respond to language-relevant visual contrasts. For example, when viewing motion events, infants' sensitivities to background information ("ground-path cues," e.g., whether a background is flat and continuous or bounded) change with age. Prior studies with English and Japanese monolingual infants have demonstrated that 14-month-old infants discriminate between motion events that take place against different ground-paths (e.g., an unbounded field vs a bounded street). By 19 months of age, this sensitivity becomes more selective in monolingual infants; only learners of languages that lexically contrast these categories, such as Japanese, discriminate between such events. In this study, we investigated this progression in bilingual infants. We first replicated past reports of an age-related decline in ground-path sensitivity from 14 to 19 months in English monolingual infants living in a multilingual society. English-Mandarin bilingual infants living in that same society were then tested on discrimination of ground-path cues at 14, 19, and 24 months. Although neither the English nor Mandarin language differentiates motion events based on ground-path cues, bilingual infants demonstrated protracted sensitivity to these cues. Infants exhibited a lack of discrimination at 14 months, followed by discrimination at 19 months and a subsequent decline in discrimination at 24 months. In addition, bilingual infants demonstrated more fine-grained sensitivities to subtle ground cues not observed in monolingual infants.

Effects of face masks on language comprehension in bilingual children.

Due to the COVID-19 pandemic, many children receive language input through face coverings. The impact of face coverings for children's abilities to understand language remains unclear. Past research with monolingual children suggests that hearing words through surgical masks does not disrupt word recognition, but hearing words through transparent face shields proves more challenging. In this study, we investigated effects of different face coverings (surgical masks and transparent face shields) on language comprehension in bilingual children. Three-year-old English-Mandarin bilingual children (N = 28) heard familiar words in both English and Mandarin spoken through transparent face shields, surgical masks, and without masks. When tested in English, children recognized words presented without a mask and through a surgical mask, but did not recognize words presented with transparent face shields, replicating past findings with monolingual children. In contrast, when tested in Mandarin, children recognized words presented without a mask, through a surgical mask, and through a transparent face shield. Results are discussed in terms of specific properties of English and Mandarin that may elicit different effects for transparent face shields. Overall, the present findings suggest that face coverings, and in particular, surgical masks do not disrupt spoken word recognition in young bilingual children.

Diversity and representation in infant research: Barriers and bridges toward a globalized science of infant development.

Psychological researchers have become increasingly concerned with generalized accounts of human behavior based on narrow participant representation. This concern is particularly germane to infant research as findings from infant studies are often invoked to theorize broadly about the origins of human behavior. In this article, we examined participant diversity and representation in research published on infant development in four journals over the past decade. Sociodemographic data were coded for all articles reporting infant data published in Child Development, Developmental Science, Developmental Psychology, and Infancy between 2011 and 2022. Analyses of 1682 empirical articles, sampling approximately 1 million participants, revealed consistent under-reporting of sociodemographic information. For studies that reported sociodemographic characteristics, there was an unwavering skew toward White infants from North America/Western Europe. To address a lack of diversity in infant studies and its scientific impact, a set of principles and practices are proposed to advance toward a more globally representative science.

Language acquisition in a multilingual society: English vocabulary norms and predictors in Singaporean children.

In this study, infant vocabulary development was tracked in a multilingual society (Singapore) within a socioeconomically diverse sample. The sample comprised 1316 infants from 17.4 to 27.7 months (669 females, 647 males; 88% Chinese race, 4% Malay, 4% Indian, and 0.004% mixed-race [4% declined to provide race information]). Children varied in English language exposure and socioeconomic status. Analyses focused on identifying demographic predictors of English vocabulary size in multilingually exposed infants. Adaptations of the Macarthur-Bates Communicative Development Inventory for English, Mandarin, and Malay are provided as well as English vocabulary norms that account for variation in English exposure. This manuscript reports the first set of English language norms-calibrated to English exposure-for multilingual infants in a non-Western setting.

Effects of interracial experience on the race preferences of infants.

Over their first year of life, infants express visual preferences for own- versus other-race faces. This developmental transition has primarily been investigated in monoracial societies where infants have limited personal or societal contact with other races. We investigated whether previously reported visual preferences for race generalize to a multiracial society (i.e., Singapore). In addition, we investigated effects of caregiver race on visual preferences for race. In Experiment 1, race preferences were measured at 3, 6, and 9 months of age for own-race (Chinese) versus other-race (Indian) faces in infants with no regular interaction with Indian-race individuals. Singaporean infants displayed a significant visual preference for Indian-race faces at each age group. Furthermore, infants raised with other-race caregivers demonstrated an age-related increase in other-race visual preferences. The visual preferences of infants for other-race faces were predicted by the extent of other-race contact. In Experiment 2, we confirmed that an other-race visual preference was not exclusive to Indian faces in a sample of 6-month-old Singaporean Chinese infants who demonstrated a similar other-race visual preference for Caucasian faces over Chinese faces. Findings are discussed in terms of the influence of other-race contact on visual preferences for race in infants.

Improving the generalizability of infant psychological research: The ManyBabies model.

Yarkoni's analysis clearly articulates a number of concerns limiting the generalizability and explanatory power of psychological findings, many of which are compounded in infancy research. ManyBabies addresses these concerns via a radically collaborative, large-scale and open approach to research that is grounded in theory-building, committed to diversification, and focused on understanding sources of variation.

Infants recognize words spoken through opaque masks but not through clear masks.

COVID-19 has modified numerous aspects of children's social environments. Many children are now spoken to through a mask. There is little empirical evidence attesting to the effects of masked language input on language processing. In addition, not much is known about the effects of clear masks (i.e., transparent face shields) versus opaque masks on language comprehension in children. In the current study, 2-year-old infants were tested on their ability to recognize familiar spoken words in three conditions: words presented with no mask, words presented through a clear mask, and words presented through an opaque mask. Infants were able to recognize familiar words presented without a mask and when hearing words through opaque masks, but not when hearing words through clear masks. Findings suggest that the ability of infants to recover spoken language input through masks varies depending on the surface properties of the mask.

Cognitive flexibility and parental education differentially predict implicit and explicit racial biases in bilingual children.

Prior research has suggested that bilingual children demonstrate reduced social bias relative to their monolingual peers. In particular, they exhibit less implicit bias against racial outgroups. However, the cognitive determinants of racial bias in bilingual children remain unclear. In the current study, relationships between racial bias and three cognitive factors (inhibitory control, cognitive flexibility, and perspective-taking ability), along with language proficiency and parental education, were investigated in a sample of bilingual preschoolers (N = 55). Children were bilingual learners of English and Mandarin. Results demonstrated that implicit bias was predicted by cognitive flexibility, independent of variation in inhibitory control, second language vocabulary, perspective taking, and parental education. In contrast, explicit bias was predicted by parental education alone and not by cognitive or linguistic factors. Findings suggest that increased cognitive flexibility, often thought to be an outgrowth of bilingual experience, may also be associated with a reduction in implicit bias. Findings are discussed in terms of specific mechanisms that may link cognitive factors, bilingualism, and racial bias.

The development of gaze following in monolingual and bilingual infants: A multi-laboratory study.

Determining the meanings of words requires language learners to attend to what other people say. However, it behooves a young language learner to simultaneously encode relevant non-verbal cues, for example, by following the direction of their eye gaze. Sensitivity to cues such as eye gaze might be particularly important for bilingual infants, as they encounter less consistency between words and objects than monolingual infants, and do not always have access to the same word-learning heuristics (e.g., mutual exclusivity). In a preregistered study, we tested the hypothesis that bilingual experience would lead to a more pronounced ability to follow another's gaze. We used a gaze-following paradigm developed by Senju and Csibra (Current Biology, 18, 2008, 668) to test a total of 93 6- to 9-month-old and 229 12- to 15-month-old monolingual and bilingual infants, in 11 laboratories located in 8 countries. Monolingual and bilingual infants showed similar gaze-following abilities, and both groups showed age-related improvements in speed, accuracy, frequency, and duration of fixations to congruent objects. Unexpectedly, bilinguals tended to make more frequent fixations to on-screen objects, whether or not they were cued by the actor. These results suggest that gaze sensitivity is a fundamental aspect of development that is robust to variation in language exposure.

Vowel, consonant, and tone variation exert asymmetrical effects on spoken word recognition: Evidence from 6-year-old monolingual and bilingual learners of Mandarin.

Most children are raised in a bilingual environment. However, compared with monolingual language acquisition, relatively little is known about how bilingual children acquire native phonology. Moreover, much less is known about how children acquire knowledge of tone languages in comparison with consonant-vowel languages such as English. In this study, 6-year-old Mandarin monolingual and English-Mandarin bilingual learners were tested on their sensitivity to vowel, consonant, and lexical tone mispronunciations of known words in a preferential looking task (N = 48; Experiment 1) and in an explicit judgment task (N = 48; Experiment 2). Results demonstrated that in Experiment 1 both monolingual and bilingual participants were sensitive to vowel mispronunciations. Bilingual children were also sensitive to consonant and tone mispronunciations. When sensitivity to mispronunciations was compared with correct pronunciations, monolingual and bilingual participants were similarly sensitive to consonant mispronunciations and similarly insensitive to tones, but they demonstrated subtle variance in vowel sensitivity. In Experiment 2, both groups demonstrated reduced sensitivity to tone mispronunciations relative to vowel and consonant mispronunciations. Therefore, in both implicit and explicit tasks, participants demonstrated asymmetrical sensitivity to segments (vowels and consonants) and tones. Our findings are discussed in terms of influences of phonological variation and language background on children's word knowledge.

Sensitivity to race in language comprehension in monolingual and bilingual infants.

Past studies suggest that monolingual and bilingual infants respond differently to race information in face discrimination and social learning tasks. In particular, bilingual infants have been shown to respond more similarly to own- and other-race individuals, in contrast to monolingual infants, who respond preferentially to own-race individuals. In the current study, we investigated monolingual and bilingual sensitivity to speaker race in spoken word recognition. Two-year-old infants were presented with spoken words in association with visual targets. Words were presented in association with own- or other-race actors and were either correctly pronounced or mispronounced. Measuring speech-responsive eye movements to visual targets, we analyzed fixation to visual targets for correct and mispronounced words in relation to speaker race for each group. When presented with own-race speakers, both monolingual and bilingual infants associated correctly pronounced labels, but not mispronounced labels, with visual targets. When presented with other-race speakers, bilingual infants responded similarly. In contrast, monolingual infants did not fixate visual targets regardless of whether words were correctly pronounced or mispronounced by an other-race speaker. Results are discussed in terms of the sensitivities of bilingual and monolingual infants to novelty, learned associations between race and language, and prior social experiences.

Building a collaborative Psychological Science: Lessons learned from ManyBabies 1.

The field of infancy research faces a difficult challenge: some questions require samples that are simply too large for any one lab to recruit and test. ManyBabies aims to address this problem by forming large-scale collaborations on key theoretical questions in developmental science, while promoting the uptake of Open Science practices. Here, we look back on the first project completed under the ManyBabies umbrella - ManyBabies 1 - which tested the development of infant-directed speech preference. Our goal is to share the lessons learned over the course of the project and to articulate our vision for the role of large-scale collaborations in the field. First, we consider the decisions made in scaling up experimental research for a collaboration involving 100+ researchers and 70+ labs. Next, we discuss successes and challenges over the course of the project, including: protocol design and implementation, data analysis, organizational structures and collaborative workflows, securing funding, and encouraging broad participation in the project. Finally, we discuss the benefits we see both in ongoing ManyBabies projects and in future large-scale collaborations in general, with a particular eye towards developing best practices and increasing growth and diversity in infancy research and psychological science in general. Throughout the paper, we include first-hand narrative experiences, in order to illustrate the perspectives of researchers playing different roles within the project. While this project focused on the unique challenges of infant research, many of the insights we gained can be applied to large-scale collaborations across the broader field of psychology.

Monolingual but not bilingual infants demonstrate racial bias in social cue use.

Bilingualism exerts early and pervasive effects on cognition, observable in infancy. Thus far, investigations of infant bilingual cognition have focused on sensitivity to visual memory, executive function, and linguistic sensitivity. Much less research has focused on how bilingualism impacts processing of social cues. The present study sought to investigate whether bilingualism modulates the expression of one aspect of social processing: early racial bias. Using a gaze-following paradigm, we investigated whether 18- to 20-month-old monolingual and bilingual infants favored their own race. Results demonstrated that monolingual infants favored their own race in following a model whose direction of gaze signaled an event. In contrast, bilingual infants demonstrated race-neutral gaze-following patterns, relying more heavily on the reliability of the behavior of the model over race. Findings suggest that bilingualism may have protective effects against the early emergence of racial bias.

The impact of foreign language caregiving on native language acquisition.

There is increasing interest in the influence of language input during children's early years. Over the first 3 years of life, children are highly sensitive to the quantity and quality of language input they receive. The focus of this study was on whether learning a different language in the early years affects the acquisition of English over the longer term. In this study, we investigated effects of foreign language (Hokkien) caregiving on the eventual acquisition of English as well as on memory traces of Hokkien. We sampled individuals who received foreign language caregiving in Hokkien during their early years either predominantly or in addition to English. Our control group had lifetime primary exposure to English. We compared the Hokkien- and English-only reared groups on phonological, semantic, and grammatical knowledge in English. We also compared the groups on memories for Hokkien tonal phonology and vocabulary. Overall, there were no statistically significant differences in performance in English tasks between groups, yet the Hokkien-reared group demonstrated selective learning advantages in reacquiring Hokkien tonal contrasts. Findings are discussed with reference to the effects of timing and language input on later language proficiency.

Bilingual Infants Demonstrate Advantages in Learning Words in a Third Language.

Prior research suggests that bilingualism may endow infants with greater phonological flexibility. This study investigated whether this flexibility facilitates word learning in additional languages (n = 96). Experiment 1 compared 18- to 20-month-old monolingual (English) and bilingual (English/Mandarin) infants on their ability to learn words distinguished by click consonants from a Southern African language, Ndebele. English-Mandarin bilingual infants were sensitive to Ndebele click contrasts, but monolingual English infants were not. In Experiments 2a and 2b, we investigated whether enhanced bilingual sensitivity extended to analogous nonlinguistic labels: hand claps and finger snaps. Although discriminated by infants, neither group distinguished words labeled by hand claps and finger snaps. Results suggest that bilingual infants' sustained openness to non native contrast may facilitate the uptake of words in distant languages.

Novel Word Learning in Bilingual and Monolingual Infants: Evidence for a Bilingual Advantage.

Previous studies revealing that monolingual and bilingual infants learn similar sounding words with comparable success are largely based on prior investigations involving single-feature changes in the onset consonant of a word. There have been no investigations of bilingual infants' abilities to learn similar sounding words differentiated by vowels. In the current study, 18-month-old bilingual and monolingual infants (n = 90) were compared on their sensitivity to a vowel change when learning the meanings of words. Bilingual infants learned similar sounding words differing by a vowel contrast, whereas monolingual English- and Mandarin-learning infants did not. Findings are discussed in terms of early constraints on novel word learning in bilingual and monolingual infants.