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Causation is a core feature of human cognition and language. How children learn about intricate causal meanings is yet unresolved. Here, we focus on how children learn verbs that express causation. Such verbs, known as lexical causatives (e.g., break and raise), lack explicit morphosyntactic markers indicating causation, thus requiring that the child generalizes the causal meaning from the context. The language addressed to children presumably plays a crucial role in this learning process. Hence, we tested whether adults adapt their use of lexical causatives to children when talking to them in day-to-day interactions. We analyzed naturalistic longitudinal data from 12 children in the Manchester corpus (spanning from 20 to 36 months of age). To detect semantic generalization, we employed a network approach with semantics learned from cross-situational contexts. Our results show an increasing trend in the expansion of causative semantics, observable in both child speech and child-directed speech. Adults consistently maintain somewhat more intricate causative semantic networks compared to children. However, both groups display evolving patterns. Around 28-30 months of age, children undergo a reduction in the degree of causative generalization, followed by a slightly time-lagged adjustment by adults in their speech directed to children. These findings substantiate adults' adaptation in child-directed speech, extending to semantics. They highlight child-directed speech as a highly adaptive and subconscious teaching tool that facilitates the dynamic processes of language acquisition.

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We present an exploratory cross-linguistic analysis of the quantity of target-child-directed speech and adult-directed speech in North American English (US & Canadian), United Kingdom English, Argentinian Spanish, Tseltal (Tenejapa, Mayan), and Yélî Dnye (Rossel Island, Papuan), using annotations from 69 children aged 2-36 months. Using a novel methodological approach, our cross-linguistic and cross-cultural findings support prior work suggesting that target-child-directed speech quantities are stable across early development, while adult-directed speech decreases. A preponderance of speech from women was found to a similar degree across groups, with less target-child-directed speech from men and children in the North American samples than elsewhere. Consistently across groups, children also heard more adult-directed than target-child-directed speech. Finally, the numbers of talkers present in any given clip strongly impacted children's moment-to-moment input quantities. These findings illustrate how the structure of home life impacts patterns of early language exposure across diverse developmental contexts.

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There is substantial evidence that children's apparent omission of grammatical morphemes in utterances such as "She play tennis" and "Mummy eating" is in fact errors of commission in which contextually licensed unmarked forms encountered in the input are reproduced in a context-blind fashion. So how do children stop making such errors? In this study, we test the assumption that children's ability to recover from error is related to their developing sensitivity to longer-range dependencies. We use a pre-registered corpus analysis to explore the predictive value of different cues with regards to children's verb-marking errors and observe a developmental pattern consistent with this account. We look at context-independent cues (the identity of the specific verb being used) and at the relative value of context-dependent cues (the identity of the specific subject+verb sequence being used). We find that the only consistent effect across a group of 2- to 3-year-olds and a group of 3- to 4-year-olds is the relative frequency of unmarked forms of specific subject+verb sequences being used. The relative frequency of unmarked forms of the verb alone is predictive only in the younger age group. This is consistent with an account in which children recover from making errors by becoming progressively more sensitive to context, at first the immediately preceding lexical contexts (e.g., the subject that precedes the verb) and eventually more distant grammatical markers (e.g., the fronted auxiliary that precedes the subject in questions). RESEARCH HIGHLIGHTS: We provide a corpus analysis investigating input effects on young children's verb-marking errors (e.g., Mummy go) across development (between 2 and 4 years of age). We find evidence that these apparent errors of omission are in fact input-driven errors of commission that persist into the third year of life. We compare the relative effect on error rates of context-independent (e.g., verb) and context-dependent (e.g., subject+verb sequence) cues across developmental time. Our findings support the proposal that children recover from making verb-marking errors by becoming progressively more sensitive to preceding context.

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Exposure to talker variability shapes how learning unfolds in the lab, and occurs in the everyday speech infants hear in daily life. Here, we asked whether aspects of talker variability in speech input are also linked to the onset of word production. We further asked whether these effects were redundant with effects of speech register (i.e., whether speech input was adult- vs. child-directed). To do so, we first extracted a set of highly common nouns from a longitudinal corpus of home recordings from North-American English-learning infants. We then used the acoustic variability in how these tokens were said to predict when the children first produced these same nouns. We found that in addition to frequency, variability in how words sound in 6-17 month's input predicted when children first said these words. Furthermore, while the proportion of child-directed speech also predicted the month of first production, it did so alongside measurements of acoustic variability in children's real-world input. Together, these results add to a growing body of literature suggesting that variability in how words sound in the input is linked to learning both in the lab and in daily life. RESEARCH HIGHLIGHTS: Talker variability shapes learning in the lab and exists in everyday speech; we asked whether it predicts word learning in the real world. Acoustic measurements of early words in infants' input (and their frequency) predicted when infants first said those same words. Speech register also predicted when infants said words, alongside effects of talker variability. Our results provide a deeper understanding of how sources of variability inherent to children's input connect to their learning and development.

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BACKGROUND: Variability in the vocabulary outcomes of children with cochlear implants (CIs) is partially explained by child-directed speech (CDS) characteristics. Yet, relatively little is known about whether and how mothers adapt their lexical and prosodic characteristics to the child's hearing status (before and after implantation, and compared with groups with normal hearing (NH)) and how important they are in affecting vocabulary development in the first 12 months of hearing experience. AIMS: To investigate whether mothers of children with CIs produce CDS with similar lexical and prosodic characteristics compared with mothers of age-matched children with NH, and whether they modify these characteristics after implantation. In addition, to investigate whether mothers' CDS characteristics predict children's early vocabulary skills before and after implantation. METHODS & PROCEDURES: A total of 34 dyads (17 with NH, 17 with children with CIs; ages = 9-32 months), all acquiring Italian, were involved in the study. Mothers' and children's lexical quantity (tokens) and variety (types), mothers' prosodic characteristics (pitch range and variability), and children's vocabulary skills were assessed at two time points, corresponding to before and 1 year post-CI activation for children with CIs. Children's vocabulary skills were assessed using parent reports; lexical and prosodic characteristics were observed in semi-structured mother-child interactions. OUTCOMES & RESULTS: Results showed that mothers of children with CIs produced speech with similar lexical quantity but lower lexical variety, and with increased pitch range and variability, than mothers of children with NH. Mothers generally increased their lexical quantity and variety and their pitch range between sessions. Children with CIs showed reduced expressive vocabulary and lower lexical quantity and variety than their peers 12 months post-CI activation. Mothers' prosodic characteristics did not explain variance in children's vocabulary skills; their lexical characteristics predicted children's early vocabulary and lexical outcomes, especially in the NH group, but were not related to later language development. CONCLUSIONS & IMPLICATIONS: Our findings confirm previous studies on other languages and support the idea that the lexical characteristics of mothers' CDS have a positive effect on children's early measures of vocabulary development across hearing groups, whereas prosodic cues play a minor role. Greater input quantity and quality may assist children in the building of basic language model representations, whereas pitch cues may mainly serve attentional and emotional processes. Results emphasize the need for additional longitudinal studies investigating the input received from other figures surrounding the child and its role for children's language development. WHAT THIS PAPER ADDS: What is already known on the subject Mothers' CDS is thought to facilitate and support language acquisition in children with various language developmental trajectories, including children with CIs. Because children with CIs are at risk for language delays and have acoustic processing limitations, their mothers may have to produce a lexically simpler but prosodically richer input, compared to mothers of children with NH. Yet, the literature reports mixed findings and no study to our knowledge has concurrently addressed the role of mothers' lexical and prosodic characteristics for children's vocabulary development before implantation and in the first 12 months of hearing experience. What this study adds to the existing knowledge The study shows that mothers of children with CIs produce input of similar quantity but reduced variety, and with heightened pitch characteristics, compared to mothers of children with NH. There was also a general increase in mothers' lexical quantity and variety, and in their pitch range, between sessions. Only their lexical characteristics predicted children's early vocabulary skills. Their lexical variety predicted children's expressive vocabulary and lexical variety only in the NH group. What are the practical and clinical implications of this work? These findings expand our knowledge about the effects of maternal input and may contribute to the improvement of early family-centred intervention programmes for supporting language development in children with CIs.

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Brand and licensed characters frequently appear on children's breakfast cereal boxes and are known to affect children's product perceptions, selection, and consumption. However, less is known about their impact on parents' perceptions of foods they purchase for their child. The present study assessed the impact of brand and licensed characters featured on three children's breakfast cereal packages on parents' intentions and perceptions in an online experiment. Parents of children aged 2-12 years (n = 1013) were randomized into one of two conditions: breakfast cereals containing brand and licensed characters or breakfast cereals without any characters. Within each condition, participants viewed three breakfast cereal brands in random order per their assigned condition and reported their purchase intentions, healthfulness perceptions, and perceptions of appeal to children using 5-point Likert scales. No significant differences in purchase intentions (p = 0.91), perceived healthfulness (p = 0.52) or perceived child appeal (p = 0.59) were observed between the experimental and control groups. However, exploratory moderation analyses revealed that educational attainment moderated the impact of experimental condition on purchase intentions (p for interaction = 0.002) such that participants with a bachelor's degree in the character condition reported 0.36 points lower purchase intentions compared to the control with no difference between conditions for those with an associate's degree/trade school or high school degree or less. This study did not find an impact of brand and licensed characters on children's breakfast cereals, suggesting that their primary appeal is directly to children. Parents with higher educational attainment may be skeptical of characters on cereal brands. Additional research on the impact of brand and licensed characters on other products, in real-world settings, is needed.

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Theories of language development-informed largely by studies of Western, middleclass infants-have highlighted the language that caregivers direct to children as a key driver of language learning. However, some have argued that language development unfolds similarly across environmental contexts, including those in which childdirected language is scarce. This raises the possibility that children are able to learn from other sources of language in their environments, particularly the language directed to others in their environment. We explore this hypothesis with infants in an indigenous Tseltal-speaking community in Southern Mexico who are rarely spoken to, yet have the opportunity to overhear a great deal of other-directed language by virtue of being carried on their mothers' backs. Adapting a previously established gaze-tracking method for detecting early word knowledge to our field setting, we find that Tseltal infants exhibit implicit knowledge of common nouns (Exp. 1), analogous to their US peers who are frequently spoken to. Moreover, they exhibit comprehension of Tseltal honorific terms that are exclusively used to greet adults in the community (Exp. 2), representing language that could only have been learned through overhearing. In so doing, Tseltal infants demonstrate an ability to discriminate words with similar meanings and perceptually similar referents at an earlier age than has been shown among Western children. Together, these results suggest that for some infants, learning from overhearing may be an important path toward developing language.

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Child-directed print corpora enable systematic psycholinguistic investigations, but this research infrastructure is not available in many understudied languages. Moreover, researchers of understudied languages are dependent on manual tagging because precise automatized parsers are not yet available. One plausible way forward is to limit the intensive work to a small-sized corpus. However, with little systematic enquiry about approaches to corpus construction, it is unclear how robust a small corpus can be made. The current study examines the potential of a non-sequential sampling protocol for small corpus development (NSP-SCD) through a cross-corpora and within-corpus analysis. A corpus comprising 17,584 words was developed by applying the protocol to a larger corpus of 150,595 words from children's books for 3-to-10-year-olds. While the larger corpus will by definition have more instances of unique words and unique orthographic units, still, the selectively sampled small corpus approximated the larger corpus for lexical and orthographic diversity and was equivalent for orthographic representation and word length. Psycholinguistic complexity increased by book level and varied by parts of speech. Finally, in a robustness check of lexical diversity, the non-sequentially sampled small corpus was more efficient compared to a same-sized corpus constructed by simply using all sentences from a few books (402 books vs. seven books). If a small corpus must be used then non-sequential sampling from books stratified by book level makes the corpus statistics better approximate what is found in larger corpora. Overall, the protocol shows promise as a tool to advance the science of child language acquisition in understudied languages.

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Preterm birth is a risk factor for language difficulties. To better understand the language development of preterm-born infants, the current study investigated the concurrent associations between parent-infant conversations and the development of 22 preterm-born and 25 term-born infants at 2 years of age. Conversations occurring during mother/father-infant free-play interactions were analyzed to characterize features of parental speech (volubility, speech rate, lexical diversity, and morphosyntactic complexity) and parent-infant exchanges (parent responsiveness, turn-taking, and conversational balance). The infants' language development (receptive communication and expressive communication) and non-language development (cognitive, social-emotional, and executive function) was assessed using standardized measures. Parent-infant conversations were associated with both language and non-language development. This suggests that parent-infant conversations may support language development directly and/or through advancing non-language skills that could promote language learning. The associations between parent-infant conversations and development varied as a function of birth status (preterm or term). This finding may signal the operation of different developmental processes within preterm- and term-born groups. Finally, infant development was differentially associated with mother-infant and father-infant conversations. This may point to the distinct contributions made by mothers and fathers to the development of both preterm- and term-born infants. To optimize language outcomes, these findings indicate that families should be guided to tailor parent-infant conversations to the unique developmental needs and processes of preterm-born infants. Families should also be supported to leverage the distinct developmental contributions of mothers and fathers. Future recommendations are made regarding how to investigate the proposed preterm-term differences in language development processes and the differential developmental contribution of mothers and fathers.

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Speakers design their multimodal communication according to the needs and knowledge of their interlocutors, phenomenon known as audience design. We use more sophisticated language (e.g., longer sentences with complex grammatical forms) when communicating with adults compared with children. This study investigates how speech and co-speech gestures change in adult-directed speech (ADS) versus child-directed speech (CDS) for three different tasks. Overall, 66 adult participants (Mage = 21.05, 60 female) completed three different tasks (story-reading, storytelling and address description) and they were instructed to pretend to communicate with a child (CDS) or an adult (ADS). We hypothesised that participants would use more complex language, more beat gestures, and less iconic gestures in the ADS compared with the CDS. Results showed that, for CDS, participants used more iconic gestures in the story-reading task and storytelling task compared with ADS. However, participants used more beat gestures in the storytelling task for ADS than CDS. In addition, language complexity did not differ across conditions. Our findings indicate that how speakers employ different types of gestures (iconic vs beat) according to the addressee's needs and across different tasks. Speakers might prefer to use more iconic gestures with children than adults. Results are discussed according to audience design theory.

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OBJECTIVE: Sugar-sweetened beverages (SSB) are heavily advertised globally, and SSB consumption is linked to increased health risk. To reduce unhealthy food marketing, Chile implemented a regulation for products classified as high in energies, sugar, saturated fat or sodium, starting with a 2016 ban on child-targeted advertising of these products and adding a 06.00-22.00 daytime advertising ban in 2019. This study assesses changes in television advertising prevalence of ready-to-drink beverages, including and beyond SSB, to analyse how the beverage industry shifted its marketing strategies across Chile's implementation phases. DESIGN: Beverage advertisements were recorded during two randomly constructed weeks in April-May of 2016 (pre-implementation) through 2019 (daytime ban). Ad products were classified as 'high-in' or 'non-high-in' according to regulation nutrient thresholds. Ads were analysed for their programme placement and marketing content. SETTING: Chile. RESULTS: From pre-regulation to daytime ban, child-targeted, daytime and total ads decreased by 51·8 percentage points (p.p.), 51·5 p.p. and 61·8 p.p. for high-in products and increased by 62·9 p.p., 54·9 p.p. and 61·8 p.p. for non-high-in products (Ps < 0·001). Additionally, total ready-to-drink beverage ads increased by 5·4 p.p. and brand-only ads (no product shown) by 7 p.p. CONCLUSIONS: After the regulation implementation, 'high-in' ads fell significantly, but 'non-high-in' ads rose and continued using strategies targeting children and being aired during daytime. Given research showing that advertising one product can increase preferences for a different product from that same brand and product categories, broader food marketing regulation approaches may be needed to protect children from the harmful effects of food marketing.

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The purpose of the current study was to revisit a controversial topic: whether frequencies of phonological consonant and vowel classes differ in speech directed to children and to adults. In addition, the current study investigated whether the frequency of phonological consonant and vowel classes changes with children's increasing chronological and/or developmental age. This study analyzed speech input from 44 adults to four different age groups of listeners (i.e., three groups of children at 6, 18, and 36 months of age and one group of adult listeners) in terms of frequency of occurrence of consonant and vowel classes. Results revealed that consonant stop, nasal, fricative and glide manner classes as well as all four consonant place classes were significantly different in speech directed to the four different age groups. A perspective is discussed to better understand the nature of frequency input of phonological sound classes.

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What makes a word easy to learn? Early-learned words are frequent and tend to name concrete referents. But words typically do not occur in isolation. Some words are predictable from their contexts; others are less so. Here, we investigate whether predictability relates to when children start producing different words (age of acquisition; AoA). We operationalized predictability in terms of a word's surprisal in child-directed speech, computed using n-gram and long-short-term-memory (LSTM) language models. Predictability derived from LSTMs was generally a better predictor than predictability derived from n-gram models. Across five languages, average surprisal was positively correlated with the AoA of predicates and function words but not nouns. Controlling for concreteness and word frequency, more predictable predicates and function words were learned earlier. Differences in predictability between languages were associated with cross-linguistic differences in AoA: the same word (when it was a predicate) was produced earlier in languages where the word was more predictable.

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OBJECTIVE: Childhood obesity is on the rise in South Africa (SA), and child-directed marketing (CDM) is one of the contributing factors to children's unhealthy food choices. This study assessed CDM on packaged breakfast cereals available in SA supermarkets and their nutritional quality. DESIGN: Photographic images were examined in a descriptive quantitative study. A codebook of definitions of CDM was developed for this purpose. REDCap, an online research database, was used for data capturing, and SPSS was used for data analyses including cross-tabulations and one-way ANOVA. SETTING: The current study was set in the Western Cape province of SA. SUBJECTS: Photographic images of all packaged breakfast cereals sold in major retailers in the Western Cape province of SA in 2019 were studied. RESULTS: CDM strategies were classified as direct (to the child) or indirect (through the parent). A total of 222 breakfast cereals were studied, of which 96·9 % had a nutritional or health claim, 95·0 % had illustrations, 75·2 % had product and consumption appeals, 10·8 % had characters, 10·8 % consisted of different appeals, 8·6 % alluded to fantasy and 7·7 % had role models. In breakfast cereals with direct CDM, the protein and fibre content was significantly lower than in breakfast cereals without direct CDM. This study found a significantly higher total carbohydrate and total sugar content in breakfast cereals with direct CDM than those without direct CDM. CONCLUSION: CDM was highly prevalent in breakfast cereals sold in SA. Regulations to curb the marketing of packaged foods high in nutrients of concern is recommended.

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With the growing burden of non-communicable diseases (NCDs), countries across the globe are finding ways to reduce the consumption of ultra-processed food and drinks including sugar-sweetened beverages (SSBs). South Africa implemented a health promotion levy (HPL) in April 2018 as one strategy to reduce sugar intake. Such efforts are frequently countered or mitigated by industry action in various ways, including through marketing and advertising strategies. To better understand trends in the extent of advertising, this paper analyses advertising expenditures and exposure of children to SSB advertisements in South Africa. Using Nielsen's monthly data on advertising expenditure before and after the introduction of the HPL, for the period January 2013 to April 2019, the results show that manufacturers spent ZAR 3683 million to advertise their products. Advertising expenditure on carbonated drinks accounted for over 60% (ZAR 2220 million) of the total expenditure on SSBs. The results also show that companies spend less in advertising powdered SSBs (an average of ZAR 0.05 million per month). Based on expenditure patterns, television (TV) was the preferred medium of advertisements, with companies prioritizing what is often considered children's and family viewing time. Urgent mandatory regulations are needed to prevent child-directed marketing.

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BACKGROUND: Indirect speech and language therapy, such as parent-implemented intervention, has been shown to be an effective approach for young children with speech and language disorders. However, relatively few studies have compared outcomes of parent-directed therapy with child-directed intervention, that is, individual therapy of a child delivered by a speech and language therapist (SLT). Although speech and language therapists (SLTs) regard parental engagement as imperative for successful intervention, currently they predominantly use child-directed intervention. AIM: To evaluate the effect of parent- versus child-directed speech-language therapy embedded in usual care intervention for young children with developmental language disorder (DLD). METHODS & PROCEDURES: In a randomized trial, forty-six 3-year-old monolingual children with DLD were assigned to parent-directed intervention or child-directed intervention groups. In addition, all children received usual care in special-language daycare centres. Outcomes included children's language development and functional communication, parents' language output, parents' perceptions and their self-efficacy. These were assessed at three time intervals, that is, at baseline, immediately after 6 months of treatment, and 1 year after baseline. The parent-directed intervention consisted of twelve 50-min sessions every 2 weeks with parent and child, consisting of parental training with immediate feedback by (SLTs. Children in the child-directed intervention group received individual speech-language therapy in weekly 30-min sessions for 6 months. OUTCOMES & RESULTS: Intervention in both groups was equally effective. All children improved significantly in receptive and expressive language measures as well as in functional communication at all intervals. All parents used significantly more language support strategies and were less concerned about their child's participation in communication. Parents in the parent-directed intervention group reported increased self-efficacy in stimulating their child's language development. In contrast, parents in the child-directed intervention group reported a decrease in self-efficacy. Though modest, these group differences were significant in both the short and long terms. Both parents and SLTs were positive about the parent-directed intervention. CONCLUSIONS & IMPLICATIONS: The effects of parent- and child-directed intervention for young children with DLD are similar. The parent-directed intervention adds to treatment options for parents as well as for SLTs and creates choices for shared decision-making. WHAT THIS PAPER ADDS: What is already known on the subject Language therapy for young children with DLD comprises various delivery models. Two of these are child- and parent-directed therapy by SLTs. Compared with no treatment, both delivery models are effective, but it is unclear if one of these results in better language outcomes than the other. SLTs value child-directed intervention more highly than indirect approaches where treatment is delivered by others. This study aims to compare the relative effectiveness of parent-directed intervention with child-directed intervention, both parts of multi-component usual care intervention. What this paper adds to existing knowledge This randomized trial indicates that a parent-directed intervention model is as effective as child-directed intervention by SLTs for children's language development and functional communication. Parents' use of language support strategies was also similar in both intervention models, in the short and long terms. Like in child-directed therapy, parent-directed intervention reduces parents' concerns. Contrary to child-directed treatment, parent-directed intervention increases parents' self-efficacy, that is, supporting their child's language development. What are the potential or actual clinical implications of this work? Though SLTs predominantly choose a child-directed intervention model, the study results show that they can consider parent-directed approaches too. There are no significant differences in children's language outcomes as a function of parent- or child-directed intervention. Furthermore, parents and SLTs were positive about the parent-directed intervention program and the SLTs evaluated it as valuable and feasible.

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Across languages, word frequency and rank follow a power law relation, forming a distribution known as the Zipfian distribution. There is growing experimental evidence that this well-studied phenomenon may be beneficial for language learning. However, most investigations of word distributions in natural language have focused on adult-to-adult speech: Zipf's law has not been thoroughly evaluated in child-directed speech (CDS) across languages. If Zipfian distributions facilitate learning, they should also be found in CDS. At the same time, several unique properties of CDS may result in a less skewed distribution. Here, we examine the frequency distribution of words in CDS in three studies. We first show that CDS is Zipfian across 15 languages from seven language families. We then show that CDS is Zipfian from early on (six-months) and across development for five languages with sufficient longitudinal data. Finally, we show that the distribution holds across different parts of speech: Nouns, verbs, adjectives and prepositions follow a Zipfian distribution. Together, the results show that the input children hear is skewed in a particular way from early on, providing necessary (but not sufficient) support for the postulated learning advantage of such skew. They highlight the need to study skewed learning environments experimentally.

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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.

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Language in touchscreen apps could be useful as an additional source of children's language input, alongside child directed speech (CDS) and books. Here we performed the first analysis of language in apps, as compared with books and CDS. We analysed language in 18 of the most popular educational apps targeting pre-schoolers and compared their language content to children's books and CDS with respect to types of constructions and psycholinguistic features of words. We found that apps contained lower frequency words and had lower lexical diversity compared to CDS, and shorter utterances compared to books. Apps may thus provide an enriched supplementary form of input for young children, due to containing less frequent words. However, apps do not expose children to a high proportion of questions and complex sentences, both of which are crucial for supporting child's development of structurally rich constructions.

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What is the function of immature vocalizing in early learning environments? Previous work on infants in the United States indicates that prelinguistic vocalizations elicit caregiver speech which is simplified in its linguistic structure. However, there is substantial cross-cultural variation in the extent to which children's vocalizations elicit responses from caregivers. In the current study, we ask whether children's vocalizations elicit similar changes in their immediate caregivers' speech structure across two cultural sites with differing perspectives on how to interact with infants and young children. Here, we compare Tseltal Mayan and U.S. caregivers' verbal responses to their children's vocalizations. Similar to findings from U.S. dyads, we found that children from the Tseltal community regulate the statistical structure of caregivers' speech simply by vocalizing. Following the interaction burst hypothesis, where clusters of child-adult contingent response alternations facilitate learning from limited input, we reveal a stable source of information that may facilitate language learning within ongoing interaction.

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