Sustained pacifier use is associated with smaller vocabulary sizes at 1 and 2 years of age: A cross-sectional study.

Pacifier use during childhood has been hypothesized to interfere with language processing, but, to date, there is limited evidence revealing detrimental effects of prolonged pacifier use on infant vocabulary learning. In the present study, parents of 12- and 24-month-old infants were recruited in Oslo (Norway). The sample included 1187 monolingual full-term born (without visual, auditory, or cognitive impairments) infants: 452 (230 girls; 222 boys) 12-month-olds and 735 (345 girls; 390 boys) 24-month-olds. Parents filled out an online Norwegian Communicative Development Inventory (CDI), which assesses the vocabulary in comprehension and production for 12-month-old infants and in production only for 24-month-old infants. CDI scores were transformed into age- and sex-adjusted percentiles using Norwegian norms. Additionally, parents retrospectively reported their child's daytime pacifier use, in hours, at 2-month intervals, from birth to the assessment date. Maternal education was used to control, in the analyses, for the socio-economic status. We found that greater pacifier use in an infant's lifespan was associated with lower vocabulary size. Pacifier use later in life was more negatively associated with vocabulary size than precocious use, and increased the odds of being a low language scorer. In sum, our study moves beyond the findings of momentary effects of experimentally induced "impairment" in articulators' movement on speech perception and suggests that, from 12 months of age, constraints on the infant's speech articulators (pacifier use) may be negatively associated with word comprehension and production. RESEARCH HIGHLIGHT: We examined the relationship between pacifier use and vocabulary sizes in production at 24 months of age and comprehension and production at 12 months of age. Lifespan Pacifier Use (LPU) was negatively correlated with vocabulary sizes in comprehension and production among 12-month-old infants and negatively correlated with production for 24-month-olds. Later pacifier use was found to be more negatively correlated with vocabulary size in infants, as compared to more precocious use. The amount of pacifier use in the 2 months prior to a child's second birthday was predictive of a higher prevalence of low vocabulary scores in 24-month-olds.

Limited evidence of test-retest reliability in infant-directed speech preference in a large preregistered infant experiment.

Test-retest reliability-establishing that measurements remain consistent across multiple testing sessions-is critical to measuring, understanding, and predicting individual differences in infant language development. However, previous attempts to establish measurement reliability in infant speech perception tasks are limited, and reliability of frequently used infant measures is largely unknown. The current study investigated the test-retest reliability of infants' preference for infant-directed speech over adult-directed speech in a large sample (N = 158) in the context of the ManyBabies1 collaborative research project. Labs were asked to bring in participating infants for a second appointment retesting infants on their preference for infant-directed speech. This approach allowed us to estimate test-retest reliability across three different methods used to investigate preferential listening in infancy: the head-turn preference procedure, central fixation, and eye-tracking. Overall, we found no consistent evidence of test-retest reliability in measures of infants' speech preference (overall r = 0.09, 95% CI [-0.06,0.25]). While increasing the number of trials that infants needed to contribute for inclusion in the analysis revealed a numeric growth in test-retest reliability, it also considerably reduced the study's effective sample size. Therefore, future research on infant development should take into account that not all experimental measures may be appropriate for assessing individual differences between infants. RESEARCH HIGHLIGHTS: We assessed test-retest reliability of infants' preference for infant-directed over adult-directed speech in a large pre-registered sample (N = 158). There was no consistent evidence of test-retest reliability in measures of infants' speech preference. Applying stricter criteria for the inclusion of participants may lead to higher test-retest reliability, but at the cost of substantial decreases in sample size. Developmental research relying on stable individual differences should consider the underlying reliability of its measures.

Validation of an open source, remote web-based eye-tracking method (WebGazer) for research in early childhood.

Measuring eye movements remotely via the participant's webcam promises to be an attractive methodological addition to in-person eye-tracking in the lab. However, there is a lack of systematic research comparing remote web-based eye-tracking with in-lab eye-tracking in young children. We report a multi-lab study that compared these two measures in an anticipatory looking task with toddlers using WebGazer.js and jsPsych. Results of our remotely tested sample of 18-27-month-old toddlers (N = 125) revealed that web-based eye-tracking successfully captured goal-based action predictions, although the proportion of the goal-directed anticipatory looking was lower compared to the in-lab sample (N = 70). As expected, attrition rate was substantially higher in the web-based (42%) than the in-lab sample (10%). Excluding trials based on visual inspection of the match of time-locked gaze coordinates and the participant's webcam video overlayed on the stimuli was an important preprocessing step to reduce noise in the data. We discuss the use of this remote web-based method in comparison with other current methodological innovations. Our study demonstrates that remote web-based eye-tracking can be a useful tool for testing toddlers, facilitating recruitment of larger and more diverse samples; a caveat to consider is the larger drop-out rate.

Same name, different representational levels? Misalignment of indirect parent-reported and direct alternative forced choice measures of emotion word comprehension in preschool children.

This study assessed the relationship between preschoolers' directly and indirectly assessed emotion word comprehension. Forty-nine two-to-five-year-old Norwegian children were assessed in a tablet-based 4-alternative forced choice (AFC) task on their comprehension of six basic and six complex emotions using facial expression photographs. Parents reported emotion word comprehension and production of the same words. Parent-reported emotion word production interacted with age to predict preschoolers' performance, with a parent-child alignment only observed for older children. Parent-reported word comprehension did not significantly predict accuracy. The results suggest that, in preschoolers, direct and indirect assessments might address distinct representational levels of emotion word comprehension.

Coping with dialects from birth: Role of variability on infants' early language development. Insights from Norwegian dialects.

Previous research suggests that exposure to accent variability can affect toddlers' familiar word recognition and word comprehension. The current preregistered study addressed the gap in knowledge on early language development in infants exposed to two dialects from birth and assessed the role of dialect similarity in infants' word recognition and comprehension. A 12-month-old Norwegian-learning infants, exposed to native Norwegian parents speaking the same or two Norwegian dialects, took part in two eye-tracking tasks, assessing familiar word form recognition and word comprehension. Their parents' speech was assessed for similarity by native Norwegian speakers. First, in contrast to previous research, our results revealed no listening preference for words over nonwords in both monodialectal and bidialectal infants, suggesting potential language-specific differences in the onset of word recognition. Second, the results showed evidence for word comprehension in monodialectal infants, but not in bidialectal infants, suggesting that exposure to dialectal variability impacts early word acquisition. Third, perceptual similarity between parental dialects tendentially facilitated bidialectal infants' word recognition and comprehension. Forth, the results revealed a strong correlation between the raters and parents' assessment of similarity between dialects, indicating that parental estimations can be reliably used to assess infants' speech variability at home. Finally, our results revealed a strong relationship between word recognition and comprehension in monodialectal infants and the absence of such a relationship in bidialectal infants, suggesting that either these two skills do not necessarily align in infants exposed to more variable input, or that the alignment might occur at a later stage.

Mothers' and fathers' infant-directed speech have similar acoustic properties, but these are not associated with direct or indirect measures of word comprehension in 8-month-old infants.

Previous research on infant-directed speech (IDS) and its role in infants' language development has largely focused on mothers, with fathers being investigated scarcely. Here we examine the acoustics of IDS as compared to adult-directed speech (ADS) in Norwegian mothers and fathers to 8-month-old infants, and whether these relate to direct (eye-tracking) and indirect (parental report) measures of infants' word comprehension. Forty-five parent-infant dyads participated in the study. Parents (24 mothers, 21 fathers) were recorded reading a picture book to their infant (IDS), and to an experimenter (ADS), ensuring identical linguistic context across speakers and registers. Results showed that both mothers' and fathers' IDS had exaggerated prosody, expanded vowel spaces, as well as more variable and less distinct vowels. We found no evidence that acoustic features of parents' speech were associated with infants' word comprehension. Potential reasons for the lack of such a relationship are discussed.

e-Babylab: An open-source browser-based tool for unmoderated online developmental studies.

The COVID-19 pandemic massively changed the context and feasibility of developmental research. This new reality, as well as considerations about sample diversity and naturalistic settings for developmental research, highlights the need for solutions for online studies. In this article, we present e-Babylab, an open-source browser-based tool for unmoderated online studies targeted for young children and babies. e-Babylab offers an intuitive graphical user interface for study creation and management of studies, users, participant data, and stimulus material, with no programming skills required. Various kinds of audiovisual media can be presented as stimuli, and possible measures include webcam recordings, audio recordings, key presses, mouse-click/touch coordinates, and reaction times. An additional feature of e-Babylab is the possibility to administer short adaptive versions of MacArthur-Bates Communicative Development Inventories (Chai et al. Journal of Speech, Language, and Hearing Research, 63, 3488-3500, 2020). Information pages, consent forms, and participant forms are customizable. e-Babylab has been used with a variety of measures and paradigms in over 12 studies with children aged 12 months to 8 years (n = 1516). We briefly summarize some results of these studies to demonstrate that data quality, participant engagement, and overall results are comparable between laboratory and online settings. Finally, we discuss helpful tips for using e-Babylab and present plans for upgrades.

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.

Syntactic Cues Help Disambiguate Objects Referred to With Count Nouns: Illustration With Malay Children.

Children employ multiple cues to identify the referent of a novel word. Novel words are often embedded in sentences and children have been shown to use syntactic cues to differentiate between types of words (adjective vs. nouns) and between types of nouns (count vs. mass nouns). In this study, we show that children learning Malay (N = 67), a numeral classifier language, can use syntactic cues to perform even finer-grained disambiguation-between count nouns. The manipulation of congruence between lexical and syntactic cues reveals a clear developmental trajectory: while 5-year-olds use predominantly lexical cues, older children increasingly rely on syntactic cues, such that by 7 years of age, they disambiguate between objects referred to with count nouns using syntactic rather than lexical cues.

Tablet assessment of word comprehension reveals coarse word representations in 18-⁠20-month-old toddlers.

The present study explores the viability of using tablets in assessing early word comprehension by means of a two-alternative forced-choice task. Forty-nine 18-20-month-old Norwegian toddlers performed a touch-based word recognition task, in which they were prompted to identify the labeled target out of two displayed items on a touchscreen tablet. In each trial, the distractor item was either semantically related (e.g., dog-cat) or unrelated (e.g., dog-airplane) to the target. Our results show that toddlers as young as 18 months can engage meaningfully with a tablet-based assessment, with minimal verbal instruction and child-administrator interaction. Toddlers performed better in the semantically unrelated condition than in the related condition, suggesting that their word representations are still semantically coarse at this age. Furthermore, parental reports of comprehension, using the Norwegian version of the MacArthur-Bates Communicative Development Inventories, predicted toddlers' performance, with parent-child agreement stronger in the semantically unrelated condition, indicating that parents declare a word to be known by their child if it is understood at a coarse representational level. This study provides among the earliest evidence that remote data collection in 18-20 month-old toddlers is viable, as comparable results were observed from both in-laboratory and online administration of the touchscreen recognition task.

Improvements of Statistical Learning Skills Allow Older Children to Go Beyond Single-Hypothesis Testing When Learning Words.

Children learn words in ambiguous situations, where multiple objects can potentially be referents for a new word. Yet, researchers debate whether children maintain a single word-object hypothesis - and revise it if falsified by later information - or whether children establish a network of word-object associations whose relative strengths are modulated with experience. To address this issue, we presented 4- to 12-year-old children with sets of mutual exclusivity (fast-mapping) trials: offering them with obvious initial hypotheses (that the novel object is the referent for the novel word). We observe that children aged six years and above, despite showing a novelty bias and retaining this novel word - novel object association, also formed an association between the novel word and the name-known object, thereby suggesting that older children attend to more than one word-object association, in a manner similar to associative learning. We discuss our findings in the context of competing theoretical accounts related to word learning.

Toddlers raised in multi-dialectal families learn words better in accented speech than those raised in monodialectal families.

Multi-accent environments offer rich but inconsistent language input, as words are produced differently across accents. The current study examined, in two experiments, whether multi-accent variability affects infants' ability to learn words and whether toddlers' prior experience with accents modulates learning. In Experiment 1, two-and-a-half-year-old Norwegian toddlers were exposed, in their kindergarten, twice per day for one week, to a child-friendly audiovisual tablet-based e-book containing four novel pseudowords. Half of the toddlers heard the story in three Norwegian accents, whereas the other half heard it in one Norwegian accent. The results revealed no differences between conditions, suggesting that multi-accent variability did not hinder toddlers' word learning. In experiment 2, two-and-a-half-year-old Norwegian toddlers were exposed, in their homes, for one week, to the e-book featuring three Norwegian accents. The results revealed overall better learning in toddlers raised in bi-dialectal households, as compared to mono-dialectal peers - suggesting that accent exposure benefits learning in multi-accent environments.

A short version of the MacArthur-Bates Communicative Development Inventories with high validity.

The MacArthur-Bates Communicative Development Inventories (CDIs) are among the most widely used evaluation tools for early language development. CDIs are filled in by the parents or caregivers of young children by indicating which of a prespecified list of words and/or sentences their child understands and/or produces. Despite the success of these instruments, their administration is time-consuming and can be of limited use in clinical settings, multilingual environments, or when parents possess low literacy skills. We present a new method through which an estimation of the full-CDI score can be obtained, by combining parental responses on a limited set of words sampled randomly from the full CDI with vocabulary information extracted from the WordBank database, sampled from age-, gender-, and language-matched participants. Real-data simulations using versions of the CDI-WS for American English, German, and Norwegian as examples revealed the high validity and reliability of the instrument, even for tests having just 25 words, effectively cutting administration time to a couple of minutes. Empirical validations with new German-speaking participants confirmed the robustness of the test.

Children's Faithfulness in Imitating Language Use Varies Cross-Culturally, Contingent on Prior Experience.

Despite its recognized importance for cultural transmission, little is known about the role imitation plays in language learning. Three experiments examine how rates of imitation vary as a function of qualitative differences in the way language is used in a small indigenous community in Oaxaca, Mexico and three Western comparison groups. Data from one hundred thirty-eight 3- to 10-year-olds suggests that children selectively imitate when they understand the function of a given linguistic element because their culture makes frequent use of that function. When function is opaque, however, children imitate faithfully. This has implications for how children manage the imitation-innovation trade-off, and offers insight into why children imitate in language learning across development.

Shared understanding and idiosyncratic expression in early vocabularies.

To what extent do toddlers have shared vocabularies? We examined CDI data collected from 14,607 infants and toddlers in five countries and measured the amount of variability between individual lexicons during development for both comprehension and production. Early lexicons are highly overlapping. However, beyond 100 words, toddlers share more words with other toddlers in comprehension than in production, even when matched for lexicon sizes. This finding points to a structural difference in early comprehension and production: Toddlers are generalists in comprehension but develop a unique, expressive voice. Variability in production decreases after two years of age, suggesting convergence to a common expressive core vocabulary. We discuss potential exogenous and endogenous contributions to the inverted U-shaped development observed in young children's expressive lexical variability.

Evidence for Infant-directed Speech Preference Is Consistent Across Large-scale, Multi-site Replication and Meta-analysis.

There is substantial evidence that infants prefer infant-directed speech (IDS) to adult-directed speech (ADS). The strongest evidence for this claim has come from two large-scale investigations: i) a community-augmented meta-analysis of published behavioral studies and ii) a large-scale multi-lab replication study. In this paper, we aim to improve our understanding of the IDS preference and its boundary conditions by combining and comparing these two data sources across key population and design characteristics of the underlying studies. Our analyses reveal that both the meta-analysis and multi-lab replication show moderate effect sizes (d ≈ 0.35 for each estimate) and that both of these effects persist when relevant study-level moderators are added to the models (i.e., experimental methods, infant ages, and native languages). However, while the overall effect size estimates were similar, the two sources diverged in the effects of key moderators: both infant age and experimental method predicted IDS preference in the multi-lab replication study, but showed no effect in the meta-analysis. These results demonstrate that the IDS preference generalizes across a variety of experimental conditions and sampling characteristics, while simultaneously identifying key differences in the empirical picture offered by each source individually and pinpointing areas where substantial uncertainty remains about the influence of theoretically central moderators on IDS preference. Overall, our results show how meta-analyses and multi-lab replications can be used in tandem to understand the robustness and generalizability of developmental phenomena.

Young children's screen time during the first COVID-19 lockdown in 12 countries.

Older children with online schooling requirements, unsurprisingly, were reported to have increased screen time during the first COVID-19 lockdown in many countries. Here, we ask whether younger children with no similar online schooling requirements also had increased screen time during lockdown. We examined children's screen time during the first COVID-19 lockdown in a large cohort (n = 2209) of 8-to-36-month-olds sampled from 15 labs across 12 countries. Caregivers reported that toddlers with no online schooling requirements were exposed to more screen time during lockdown than before lockdown. While this was exacerbated for countries with longer lockdowns, there was no evidence that the increase in screen time during lockdown was associated with socio-demographic variables, such as child age and socio-economic status (SES). However, screen time during lockdown was negatively associated with SES and positively associated with child age, caregiver screen time, and attitudes towards children's screen time. The results highlight the impact of the COVID-19 lockdown on young children's screen time.

A statistical estimate of infant and toddler vocabulary size from CDI analysis.

For the last 20 years, developmental psychologists have measured the variability in lexical development of infants and toddlers using the MacArthur-Bates Communicative Development Inventories (CDIs) - the most widely used parental report forms for assessing language and communication skills in infants and toddlers. We show that CDI reports can serve as a basis for estimating infants' and toddlers'total vocabulary sizes, beyond serving as a tool for assessing their language development relative to other infants and toddlers. We investigate the link between estimated total vocabulary size and raw CDI scores from a mathematical perspective, using both single developmental trajectories and population data. The method capitalizes on robust regularities, such as the overlap of individual vocabularies observed across infants and toddlers, and takes into account both shared knowledge and idiosyncratic knowledge. This statistical approach enables researchers to approximate the total vocabulary size of an infant or a toddler, based on her raw MacArthur-Bates CDI score. Using the model, we propose new normative data for productive and receptive vocabulary in early childhood, as well as a tabulation that relates individual CDI measures to realistic lexical estimates. The correction required to estimate total vocabulary is non-linear, with a far greater impact at older ages and higher CDI scores. Therefore, we suggest that correlations of developmental indices to language skills should be made to vocabulary size as estimated by the model rather than to raw CDI scores.

A Bayesian-Inspired Item Response Theory-Based Framework to Produce Very Short Versions of MacArthur-Bates Communicative Development Inventories.

Purpose This study introduces a framework to produce very short versions of the MacArthur-Bates Communicative Development Inventories (CDIs) by combining the Bayesian-inspired approach introduced by Mayor and Mani (2019) with an item response theory-based computerized adaptive testing that adapts to the ability of each child, in line with Makransky et al. (2016). Method We evaluated the performance of our approach-dynamically selecting maximally informative words from the CDI and combining parental response with prior vocabulary data-by conducting real-data simulations using four CDI versions having varying sample sizes on Wordbank-the online repository of digitalized CDIs: American English (a very large data set), Danish (a large data set), Beijing Mandarin (a medium-sized data set), and Italian (a small data set). Results Real-data simulations revealed that correlations exceeding .95 with full CDI administrations were reached with as few as 15 test items, with high levels of reliability, even when languages (e.g., Italian) possessed few digitalized administrations on Wordbank. Conclusions The current approach establishes a generic framework that produces very short (less than 20 items) adaptive early vocabulary assessments-hence considerably reducing their administration time. This approach appears to be robust even when CDIs have smaller samples in online repositories, for example, with around 50 samples per month-age.

Infant categorization as a dynamic process linked to memory.

Recency effects are well documented in the adult and infant literature: recognition and recall memory are better for recently occurring events. We explore recency effects in infant categorization, which does not merely involve memory for individual items, but the formation of abstract category representations. We present a computational model of infant categorization that simulates category learning in 10-month-olds. The model predicts that recency effects outweigh previously reported order effects for the same stimuli. According to the model, infant behaviour at test should depend mainly on the identity of the most recent training item. We evaluate these predictions in a series of experiments with 10-month-old infants. Our results show that infant behaviour confirms the model's prediction. In particular, at test infants exhibited a preference for a category outlier over the category average only if the final training item had been close to the average, rather than distant from it. Our results are consistent with a view of categorization as a highly dynamic process where the end result of category learning is not the overall average of all stimuli encountered, but rather a fluid representation that moves depending on moment-to-moment novelty. We argue that this is a desirable property of a flexible cognitive system that adapts rapidly to different contexts.