Everyday language input and production in 1,001 children from six continents.

Language is a universal human ability, acquired readily by young children, who otherwise struggle with many basics of survival. And yet, language ability is variable across individuals. Naturalistic and experimental observations suggest that children's linguistic skills vary with factors like socioeconomic status and children's gender. But which factors really influence children's day-to-day language use? Here, we leverage speech technology in a big-data approach to report on a unique cross-cultural and diverse data set: >2,500 d-long, child-centered audio-recordings of 1,001 2- to 48-mo-olds from 12 countries spanning six continents across urban, farmer-forager, and subsistence-farming contexts. As expected, age and language-relevant clinical risks and diagnoses predicted how much speech (and speech-like vocalization) children produced. Critically, so too did adult talk in children's environments: Children who heard more talk from adults produced more speech. In contrast to previous conclusions based on more limited sampling methods and a different set of language proxies, socioeconomic status (operationalized as maternal education) was not significantly associated with children's productions over the first 4 y of life, and neither were gender or multilingualism. These findings from large-scale naturalistic data advance our understanding of which factors are robust predictors of variability in the speech behaviors of young learners in a wide range of everyday contexts.

Characterization of children's verbal input in a forager-farmer population using long-form audio recordings and diverse input definitions.

There is little systematically collected quantitative empirical data on how much linguistic input children in small-scale societies encounter, with some estimates suggesting low levels of directed speech. We report on an ecologically-valid analysis of speech experienced over the course of a day by young children (N = 24, 6-58 months old, 33% female) in a forager-horticulturalist population of lowland Bolivia. A permissive definition of input (i.e., including overlapping, background, and non-linguistic vocalizations) leads to massive changes in terms of input quantity, including a quadrupling of the estimate for overall input compared to a restrictive definition (only near and clear speech), while who talked to and around a focal child is relatively stable across input definitions. We discuss implications of these results for theoretical and empirical research into language acquisition.

A systematic review suggests marked differences in the prevalence of infant-directed vocalization across groups of populations.

Anthropological reports have long suggested that speaking to young children is very infrequent in certain populations (notably farming ones), which is in line with scattered quantitative studies. A systematic review was undertaken to use available literature in order to estimate the extent of population variation. Database searches, expert lists, and citation searches led to the discovery of 29 reports on the frequency of vocalizations directed to infants aged 24 months or younger, based on systematic observations of spontaneous activity in the infant's natural environment lasting at least 30 min in length. Together, these studies provide evidence on 1314 infants growing up in a range of communities (urban, foraging, farming). For populations located outside of North America, the frequency with which vocalization was directed to urban infants was much higher than that for rural infants (including both foraging and farming, medians = 12.6 vs. 3.6% of observations contained infant-directed vocalization behaviors). We benchmarked this effect against socio-economic status (SES) variation in the United States, which was much smaller. Infants in high SES American homes were spoken to only slightly more frequently than those in low SES homes (medians = 16.4 vs. 15.1% of observations contained infant-directed vocalization behaviors). Although published research represents a biased sample of the world's populations, these results invite further cross-population research to understand the causes and effects of such considerable population group differences.

Vocal input and output among infants in a multilingual context: Evidence from long-form recordings in Vanuatu.

What are the vocal experiences of children growing up on Malakula island, Vanuatu, where multilingualism is the norm? Long-form audio-recordings captured spontaneous speech behavior by, and around, 38 children (5-33 months, 23 girls) from 11 villages. Automated analyses revealed most children's vocal input came from female adults and other children's voices, with small contributions from male adult voices. The greatest changes with age involved an increase in the input vocalizations from other children. Total input (collapsing across child-directed and overheard speech, and across languages) was ∼11 min per hour, which was at least 5 min (31%) lower than that found in other populations studied using comparable methods in previous literature, as well as in archival American data analyzed with the same algorithm. In contrast, children's own vocalization counts were two to four times higher than previous reports for North-American English-learning monolingual infants at matched ages, and comparable to estimates from archival American data, consistent with a resilient language-learning cognitive system for this aspect of vocal development. The strongest association between input and output was with vocalizations by other children, rather than those by adults, which is consistent with research in anthropology but less so with current theoretical trends in developmental psychology. These results invite further research in populations that are under-represented in developmental science. RESEARCH HIGHLIGHTS: Combining long-form recordings with automated analyses, we estimated infants potentially exposed to ∼2.6 languages heard ∼11 min of speech per hour. Infants' input was dominated by vocalizations from female adults and from other children, particularly for the oldest infants in our sample. The strongest association between children's own vocalization counts and input counts was with those of other children, and not those with adults. Results invite further research on individual, group, and population variability in input quantity and composition, and its potential effects on vocal development.

Infants' preference for speech is stable across the first year of life: Meta-analytic evidence.

Previous work suggested that humans' sophisticated speech perception abilities stem from an early capacity to pay attention to speech in the auditory environment. What are the roots of this early preference? We assess the extent to which it is due to it being a vocal sound, a natural sound, and a familiar sound through a meta-analytic approach, classifying experiments as a function of whether they used native or foreign speech and whether the competitor, against which preference is tested, was vocal or non-vocal, natural or artificial. We also tested for the effect of age. Synthesizing data from 791 infants across 39 experiments, we found a medium effect size, confirming at the scale of the literature that infants reliably prefer speech over other sounds. This preference was not significantly moderated by the language used, vocal quality, or naturalness of the competitor, nor by infant age. The current body of evidence appears most compatible with the hypothesis that speech is preferred consistently as such and not just due to its vocal, natural, or familiar nature. We discuss limitations of the extant body of work on speech preference, including evidence consistent with a publication bias and low representation of certain stimuli types and ages.

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.

Positive Valence Contributes to Hyperarticulation in Maternal Speech to Infants and Puppies.

Infant-directed speech often has hyperarticulated features, such as point vowels whose formants are further apart than in adult-directed speech. This increased "vowel space" may reflect the caretaker's effort to speak more clearly to infants, thus benefiting language processing. However, hyperarticulation may also result from more positive valence (e.g., speaking with positive vocal emotion) often found in mothers' speech to infants. This study was designed to replicate others who have found hyperarticulation in maternal speech to their 6-month-olds, but also to examine their speech to a non-human infant (i.e., a puppy). We rated both kinds of maternal speech for their emotional valence and recorded mothers' speech to a human adult. We found that mothers produced more positively valenced utterances and some hyperarticulation in both their infant- and puppy-directed speech, compared to their adult-directed speech. This finding promotes looking at maternal speech from a multi-faceted perspective that includes emotional state.

Combining observational and experimental approaches to the development of language and communication in rural samples: Opportunities and challenges.

Multiple approaches - including observational and experimental - are necessary to articulate powerful theories of learning. Our field's key questions, which rely on these varied methods, are still open. How do children perceive and produce language? What do they encounter in their linguistic input? What does the learner bring to the task of acquisition? Considerable progress has been made for the development of spoken English (especially by North American learners). Yet there is still a great deal to discover about how children in other populations proceed, especially populations in rural settings. To examine language learning in these populations, we need a multi-method approach. However, adapting and integrating methods, particularly experimental ones, to new settings can present immense challenges. In this paper, we discuss the opportunities and challenges facing researchers who aim to use a multimethodological approach in rural samples, and what the field of language acquisition can do to promote such work.

Factors structuring lexical development in toddlers: The effects of parental education, language exposure, and age.

A growing body of research suggests that individual variation in young children's word comprehension (indexed by response times and accuracy) is structured and meaningful. In this paper, we assess how children's word comprehension correlates with three factors: socio-economic status (indexed by maternal education), lingual status (based on language exposure), and age. We present results from 91 2- to 3-year-old children using a paired forced-choice task built on a child-friendly touch screen. Effects associated with maternal education and exposure to the tested language (French) were small, and they were greater for accuracy than response times. This pattern of results is compatible with an interpretation whereby the greatest effects of these two variables are on cumulative knowledge (vocabulary size) rather than on processing. Effects for age were larger and affected both accuracy and response times. Finally, response time variation did not mediate the effects of socio-economic status on accuracy or vice versa.

Socioeconomic status correlates with measures of Language Environment Analysis (LENA) system: a meta-analysis.

Using a meta-analytic approach, we evaluate the association between socioeconomic status (SES) and children's experiences measured with the Language Environment Analysis (LENA) system. Our final analysis included 22 independent samples, representing data from 1583 children. A model controlling for LENATM measures, age and publication type revealed an effect size of r z = .186, indicating a small effect of SES on children's language experiences. The type of LENA metric measured emerged as a significant moderator, indicating stronger effects for adult word counts than child vocalization counts. These results provide important evidence for the strength of association between SES and children's everyday language experiences as measured with an unobtrusive recording analyzed automatically in a standardized fashion.

Vocal development in a large-scale crosslinguistic corpus.

This study evaluates whether early vocalizations develop in similar ways in children across diverse cultural contexts. We analyze data from daylong audio recordings of 49 children (1-36 months) from five different language/cultural backgrounds. Citizen scientists annotated these recordings to determine if child vocalizations contained canonical transitions or not (e.g., "ba" vs. "ee"). Results revealed that the proportion of clips reported to contain canonical transitions increased with age. Furthermore, this proportion exceeded 0.15 by around 7 months, replicating and extending previous findings on canonical vocalization development but using data from the natural environments of a culturally and linguistically diverse sample. This work explores how crowdsourcing can be used to annotate corpora, helping establish developmental milestones relevant to multiple languages and cultures. Lower inter-annotator reliability on the crowdsourcing platform, relative to more traditional in-lab expert annotators, means that a larger number of unique annotators and/or annotations are required, and that crowdsourcing may not be a suitable method for more fine-grained annotation decisions. Audio clips used for this project are compiled into a large-scale infant vocalization corpus that is available for other researchers to use in future work.

Child-directed and overheard input from different speakers in two distinct cultures.

Despite the fact that in most communities interaction occurs between the child and multiple speakers, most previous research on input to children focused on input from mothers. We annotated recordings of Sesotho-learning toddlers living in non-industrial Lesotho in South Africa, and French-learning toddlers living in urban regions in France. We examined who produced the input (mothers, other children, adults), how much input was child directed, and whether and how it varied across speakers. As expected, mothers contributed most of the input in the French recordings. However, in the Sesotho recordings, input from other children was more common than input from mothers or other adults. Child-directed speech from all speakers in both cultural groups showed similar qualitative modifications. Our findings suggest that input from other children is prevalent and has similar features as child-directed from adults described in previous work, inviting cross-cultural research into the effects of input from other children.

ALICE: An open-source tool for automatic measurement of phoneme, syllable, and word counts from child-centered daylong recordings.

Recordings captured by wearable microphones are a standard method for investigating young children's language environments. A key measure to quantify from such data is the amount of speech present in children's home environments. To this end, the LENA recorder and software-a popular system for measuring linguistic input-estimates the number of adult words that children may hear over the course of a recording. However, word count estimation is challenging to do in a language- independent manner; the relationship between observable acoustic patterns and language-specific lexical entities is far from uniform across human languages. In this paper, we ask whether some alternative linguistic units, namely phone(me)s or syllables, could be measured instead of, or in parallel with, words in order to achieve improved cross-linguistic applicability and comparability of an automated system for measuring child language input. We discuss the advantages and disadvantages of measuring different units from theoretical and technical points of view. We also investigate the practical applicability of measuring such units using a novel system called Automatic LInguistic unit Count Estimator (ALICE) together with audio from seven child-centered daylong audio corpora from diverse cultural and linguistic environments. We show that language-independent measurement of phoneme counts is somewhat more accurate than syllables or words, but all three are highly correlated with human annotations on the same data. We share an open-source implementation of ALICE for use by the language research community, enabling automatic phoneme, syllable, and word count estimation from child-centered audio recordings.

A thorough evaluation of the Language Environment Analysis (LENA) system.

In the previous decade, dozens of studies involving thousands of children across several research disciplines have made use of a combined daylong audio-recorder and automated algorithmic analysis called the LENAⓇ system, which aims to assess children's language environment. While the system's prevalence in the language acquisition domain is steadily growing, there are only scattered validation efforts on only some of its key characteristics. Here, we assess the LENAⓇ system's accuracy across all of its key measures: speaker classification, Child Vocalization Counts (CVC), Conversational Turn Counts (CTC), and Adult Word Counts (AWC). Our assessment is based on manual annotation of clips that have been randomly or periodically sampled out of daylong recordings, collected from (a) populations similar to the system's original training data (North American English-learning children aged 3-36 months), (b) children learning another dialect of English (UK), and (c) slightly older children growing up in a different linguistic and socio-cultural setting (Tsimane' learners in rural Bolivia). We find reasonably high accuracy in some measures (AWC, CVC), with more problematic levels of performance in others (CTC, precision of male adults and other children). Statistical analyses do not support the view that performance is worse for children who are dissimilar from the LENAⓇ original training set. Whether LENAⓇ results are accurate enough for a given research, educational, or clinical application depends largely on the specifics at hand. We therefore conclude with a set of recommendations to help researchers make this determination for their goals.

Communicative cues in the absence of a human interaction partner enhance 12-month-old infants' word learning.

Is infants' word learning boosted by nonhuman social agents? An on-screen virtual agent taught infants word-object associations in a setup where the presence of contingent and referential cues could be manipulated using gaze contingency. In the study, 12-month-old Japanese-learning children (N = 36) looked significantly more to the correct object when it was labeled after exposure to a contingent and referential display versus a noncontingent and nonreferential display. These results show that communicative cues can augment learning even for a nonhuman agent, a finding highly relevant for our understanding of the mechanisms through which the social environment supports language acquisition and for research on the use of interactive screen media.

Longform recordings of everyday life: Ethics for best practices.

Recent advances in large-scale data storage and processing offer unprecedented opportunities for behavioral scientists to collect and analyze naturalistic data, including from underrepresented groups. Audio data, particularly real-world audio recordings, are of particular interest to behavioral scientists because they provide high-fidelity access to subtle aspects of daily life and social interactions. However, these methodological advances pose novel risks to research participants and communities. In this article, we outline the benefits and challenges associated with collecting, analyzing, and sharing multi-hour audio recording data. Guided by the principles of autonomy, privacy, beneficence, and justice, we propose a set of ethical guidelines for the use of longform audio recordings in behavioral research. This article is also accompanied by an Open Science Framework Ethics Repository that includes informed consent resources such as frequent participant concerns and sample consent forms.

WordSeg: Standardizing unsupervised word form segmentation from text.

A basic task in first language acquisition likely involves discovering the boundaries between words or morphemes in input where these basic units are not overtly segmented. A number of unsupervised learning algorithms have been proposed in the last 20 years for these purposes, some of which have been implemented computationally, but whose results remain difficult to compare across papers. We created a tool that is open source, enables reproducible results, and encourages cumulative science in this domain. WordSeg has a modular architecture: It combines a set of corpora description routines, multiple algorithms varying in complexity and cognitive assumptions (including several that were not publicly available, or insufficiently documented), and a rich evaluation package. In the paper, we illustrate the use of this package by analyzing a corpus of child-directed speech in various ways, which further allows us to make recommendations for experimental design of follow-up work. Supplementary materials allow readers to reproduce every result in this paper, and detailed online instructions further enable them to go beyond what we have done. Moreover, the system can be installed within container software that ensures a stable and reliable environment. Finally, by virtue of its modular architecture and transparency, WordSeg can work as an open-source platform, to which other researchers can add their own segmentation algorithms.

Child-Directed Speech Is Infrequent in a Forager-Farmer Population: A Time Allocation Study.

This article provides an estimation of how frequently, and from whom, children aged 0-11 years (Ns between 9 and 24) receive one-on-one verbal input among Tsimane forager-horticulturalists of lowland Bolivia. Analyses of systematic daytime behavioral observations reveal < 1 min per daylight hour is spent talking to children younger than 4 years of age, which is 4 times less than estimates for others present at the same time and place. Adults provide a majority of the input at 0-3 years of age but not afterward. When integrated with previous work, these results reveal large cross-cultural variation in the linguistic experiences provided to young children. Consideration of more diverse human populations is necessary to build generalizable theories of language acquisition.

Promoting Replicability in Developmental Research Through Meta-analyses: Insights From Language Acquisition Research.

Previous work suggests that key factors for replicability, a necessary feature for theory building, include statistical power and appropriate research planning. These factors are examined by analyzing a collection of 12 standardized meta-analyses on language development between birth and 5 years. With a median effect size of Cohen's d = .45 and typical sample size of 18 participants, most research is underpowered (range = 6%-99%; median = 44%); and calculating power based on seminal publications is not a suitable strategy. Method choice can be improved, as shown in analyses on exclusion rates and effect size as a function of method. The article ends with a discussion on how to increase replicability in both language acquisition studies specifically and developmental research more generally.

The more, the better? Behavioral and neural correlates of frequent and infrequent vowel exposure.

A central assumption in the perceptual attunement literature holds that exposure to a speech sound contrast leads to improvement in native speech sound processing. However, whether the amount of exposure matters for this process has not been put to a direct test. We elucidated indicators of frequency-dependent perceptual attunement by comparing 5-8-month-old Dutch infants' discrimination of tokens containing a highly frequent [hɪt-he:t] and a highly infrequent [hʏt-hø:t] native vowel contrast as well as a non-native [hɛt-haet] vowel contrast in a behavioral visual habituation paradigm (Experiment 1). Infants discriminated both native contrasts similarly well, but did not discriminate the non-native contrast. We sought further evidence for subtle differences in the processing of the two native contrasts using near-infrared spectroscopy and a within-participant design (Experiment 2). The neuroimaging data did not provide additional evidence that responses to native contrasts are modulated by frequency of exposure. These results suggest that even large differences in exposure to a native contrast may not directly translate to behavioral and neural indicators of perceptual attunement, raising the possibility that frequency of exposure does not influence improvements in discriminating native contrasts.