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.

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.

Seeing a Talking Face Matters: Gaze Behavior and the Auditory-Visual Speech Benefit in Adults' Cortical Tracking of Infant-directed Speech.

In face-to-face conversations, listeners gather visual speech information from a speaker's talking face that enhances their perception of the incoming auditory speech signal. This auditory-visual (AV) speech benefit is evident even in quiet environments but is stronger in situations that require greater listening effort such as when the speech signal itself deviates from listeners' expectations. One example is infant-directed speech (IDS) presented to adults. IDS has exaggerated acoustic properties that are easily discriminable from adult-directed speech (ADS). Although IDS is a speech register that adults typically use with infants, no previous neurophysiological study has directly examined whether adult listeners process IDS differently from ADS. To address this, the current study simultaneously recorded EEG and eye-tracking data from adult participants as they were presented with auditory-only (AO), visual-only, and AV recordings of IDS and ADS. Eye-tracking data were recorded because looking behavior to the speaker's eyes and mouth modulates the extent of AV speech benefit experienced. Analyses of cortical tracking accuracy revealed that cortical tracking of the speech envelope was significant in AO and AV modalities for IDS and ADS. However, the AV speech benefit [i.e., AV > (A + V)] was only present for IDS trials. Gaze behavior analyses indicated differences in looking behavior during IDS and ADS trials. Surprisingly, looking behavior to the speaker's eyes and mouth was not correlated with cortical tracking accuracy. Additional exploratory analyses indicated that attention to the whole display was negatively correlated with cortical tracking accuracy of AO and visual-only trials in IDS. Our results underscore the nuances involved in the relationship between neurophysiological AV speech benefit and looking behavior.

Seeing a talking face matters: Infants' segmentation of continuous auditory-visual speech.

Visual speech cues from a speaker's talking face aid speech segmentation in adults, but despite the importance of speech segmentation in language acquisition, little is known about the possible influence of visual speech on infants' speech segmentation. Here, to investigate whether there is facilitation of speech segmentation by visual information, two groups of English-learning 7-month-old infants were presented with continuous speech passages, one group with auditory-only (AO) speech and the other with auditory-visual (AV) speech. Additionally, the possible relation between infants' relative attention to the speaker's mouth versus eye regions and their segmentation performance was examined. Both the AO and the AV groups of infants successfully segmented words from the continuous speech stream, but segmentation performance persisted for longer for infants in the AV group. Interestingly, while AV group infants showed no significant relation between the relative amount of time spent fixating the speaker's mouth versus eyes and word segmentation, their attention to the mouth was greater than that of AO group infants, especially early in test trials. The results are discussed in relation to the possible pathways through which visual speech cues aid speech perception.

Seeing a talking face matters: The relationship between cortical tracking of continuous auditory-visual speech and gaze behaviour in infants, children and adults.

An auditory-visual speech benefit, the benefit that visual speech cues bring to auditory speech perception, is experienced from early on in infancy and continues to be experienced to an increasing degree with age. While there is both behavioural and neurophysiological evidence for children and adults, only behavioural evidence exists for infants - as no neurophysiological study has provided a comprehensive examination of the auditory-visual speech benefit in infants. It is also surprising that most studies on auditory-visual speech benefit do not concurrently report looking behaviour especially since the auditory-visual speech benefit rests on the assumption that listeners attend to a speaker's talking face and that there are meaningful individual differences in looking behaviour. To address these gaps, we simultaneously recorded electroencephalographic (EEG) and eye-tracking data of 5-month-olds, 4-year-olds and adults as they were presented with a speaker in auditory-only (AO), visual-only (VO), and auditory-visual (AV) modes. Cortical tracking analyses that involved forward encoding models of the speech envelope revealed that there was an auditory-visual speech benefit [i.e., AV > (A + V)], evident in 5-month-olds and adults but not 4-year-olds. Examination of cortical tracking accuracy in relation to looking behaviour, showed that infants' relative attention to the speaker's mouth (vs. eyes) was positively correlated with cortical tracking accuracy of VO speech, whereas adults' attention to the display overall was negatively correlated with cortical tracking accuracy of VO speech. This study provides the first neurophysiological evidence of auditory-visual speech benefit in infants and our results suggest ways in which current models of speech processing can be fine-tuned.

Input quality and speech perception development in bilingual infants' first year of life.

Individual differences in infants' native phonological development have been linked to the quantity and quality of infant-directed speech (IDS). The effects of parental and infant bilingualism on this relation in 131 five- and nine-month-old monolingual and bilingual Spanish and Basque infants (72 male; 59 female; from white middle-class background) were investigated. Bilingualism did not affect the developmental trajectory of infants' native and non-native speech perception and the quality of maternal speech. In both language groups, vowel exaggeration in IDS was significantly related to speech perception skills for 9-month-olds (r = -.30), but not for 5-month-olds. This demonstrates that bilingual and monolingual caregivers provide their infants with speech input that assists their task of learning the phonological inventory of one or two languages.

The effects of bilingualism on attentional processes in the first year of life.

Bilingualism is a powerful experiential factor, and its effects have been proposed to extend beyond the linguistic domain by boosting the development of executive functioning skills. Crucially, recent findings suggest that this effect can be detected in bilingual infants before their first birthday indicating that it emerges as a result of early bilingual exposure and the experience of negotiating two linguistic systems in infants' environment. However, these conclusions are based on only two research studies from the last decade (Comishen, Bialystok, & Adler, 2019; Kovács & Mehler, 2009), so to date, there is a lack of evidence regarding their replicability and generalizability. In addition, previous research does not shed light on the precise aspects of bilingual experience and the extent of bilingual exposure underlying the emergence of this early bilingual advantage. The present study addressed these two questions by assessing attentional control abilities in 7-month-old bilingual infants in comparison to same-age monolinguals and in relation to their individual bilingual exposure patterns. Findings did not reveal significant differences between monolingual and bilingual infants in the measure of attentional control and no relation between individual performance and degree of bilingual exposure. Bilinguals showed different patterns of allocating attention to the visual rewards in this task compared to monolinguals. Thus, this study indicates that bilingualism modulates attentional processes early on, possibly as a result of bilinguals' experience of encoding dual-language information from a complex linguistic input, but it does not lead to significant advantages in attentional control in the first year of life.

Lexical and Prosodic Pitch Modifications in Cantonese Infant-directed Speech.

The functions of acoustic-phonetic modifications in infant-directed speech (IDS) remain a question: do they specifically serve to facilitate language learning via enhanced phonemic contrasts (the hyperarticulation hypothesis) or primarily to improve communication via prosodic exaggeration (the prosodic hypothesis)? The study of lexical tones provides a unique opportunity to shed light on this, as lexical tones are phonemically contrastive, yet their primary cue, pitch, is also a prosodic cue. This study investigated Cantonese IDS and found increased intra-talker variation of lexical tones, which more likely posed a challenge to rather than facilitated phonetic learning. Although tonal space was expanded which could facilitate phonetic learning, its expansion was a function of overall intonational modifications. Similar findings were observed in speech to pets who should not benefit from larger phonemic distinction. We conclude that lexical-tone adjustments in IDS mainly serve to broadly enhance communication rather than specifically increase phonemic contrast for learners.

Depression and Anxiety in the Postnatal Period: An Examination of Infants' Home Language Environment, Vocalizations, and Expressive Language Abilities.

This longitudinal study investigated the effects of maternal emotional health concerns, on infants' home language environment, vocalization quantity, and expressive language skills. Mothers and their infants (at 6 and 12 months; 21 mothers with depression and or anxiety and 21 controls) provided day-long home-language recordings. Compared with controls, risk group recordings contained fewer mother-infant conversational turns and infant vocalizations, but daily number of adult word counts showed no group difference. Furthermore, conversational turns and infant vocalizations were stronger predictors of infants' 18-month vocabulary size than depression and anxiety measures. However, anxiety levels moderated the effect of conversational turns on vocabulary size. These results suggest that variability in mothers' emotional health influences infants' language environment and later language ability.

Prosodic cues in infant-directed speech facilitate young children's conversational turn predictions.

Experienced language users are able to predict when conversational turns approach completion, which allows them to attend to and comprehend their interlocutor's speech while planning and accurately timing their response. Adults primarily rely on lexico-syntactic cues to make such predictions, but it remains unknown what cues support these predictions in young children whose lexico-syntactic competence is still developing. This study assessed children's reliance on prosodic cues, specifically when predicting conversational turn transitions in infant-directed speech (IDS), the speech register that they encounter in day-to-day interactions that is characterized by exaggerated prosody compared with adult-directed speech (ADS). Young children (1- and 3-year-olds) completed an anticipatory looking paradigm in which their gaze patterns were recorded while they observed conversations that were produced in IDS or ADS and that contained prosodically complete utterances (lexico-syntactic and prosodic cues) and prosodically incomplete utterances (only lexico-syntactic cues). The 1-year-olds anticipated more turns that were signaled by prosodic cues (i.e., prosodically complete utterances) only in IDS, whereas the 3-year-olds did so in both IDS and ADS. These findings indicate that children anticipate the completion of conversational turns by relying on prosodic information in speech and that the prosodic exaggeration of IDS supports this ability while children's linguistic and conversational skills are still developing.

Infants use phonetic detail in speech perception and word learning when detail is easy to perceive.

Infants successfully discriminate speech sound contrasts that belong to their native language's phonemic inventory in auditory-only paradigms, but they encounter difficulties in distinguishing the same contrasts in the context of word learning. These difficulties are usually attributed to the fact that infants' attention to the phonetic detail in novel words is attenuated when they must allocate additional cognitive resources demanded by word-learning tasks. The current study investigated 15-month-old infants' ability to distinguish novel words that differ by a single vowel in an auditory discrimination paradigm (Experiment 1) and a word-learning paradigm (Experiment 2). These experiments aimed to tease apart whether infants' performance is dependent solely on the specific acoustic properties of the target vowels or on the context of the task. Experiment 1 showed that infants were able to discriminate only a contrast marked by a large difference along a static dimension (the vowels' second formant), whereas they were not able to discriminate a contrast with a small phonetic distance between its vowels, due to the dynamic nature of the vowels. In Experiment 2, infants did not succeed at learning words containing the same contrast they were able to discriminate in Experiment 1. The current findings demonstrate that both the specific acoustic properties of vowels in infants' native language and the task presented continue to play a significant role in early speech perception well into the second year of life.

Novel word learning deficits in infants at family risk for dyslexia.

Children of reading age diagnosed with dyslexia show deficits in reading and spelling skills, but early markers of later dyslexia are already present in infancy in auditory processing and phonological domains. Deficits in lexical development are not typically associated with dyslexia. Nevertheless, it is possible that early auditory/phonological deficits would have detrimental effects on the encoding and storage of novel lexical items. Word-learning difficulties have been demonstrated in school-aged dyslexic children using paired associate learning tasks, but earlier manifestations in infants who are at family risk for dyslexia have not been investigated. This study assessed novel word learning in 19-month-old infants at risk for dyslexia (by virtue of having one dyslexic parent) and infants not at risk for any developmental disorder. Infants completed a word-learning task that required them to map two novel words to their corresponding novel referents. Not at-risk infants showed increased looking time to the novel referents at test compared with at-risk infants. These findings demonstrate, for the first time, that at-risk infants show differences in novel word-learning (fast-mapping) tasks compared with not at-risk infants. Our findings have implications for the development and consolidation of early lexical and phonological skills in infants at family risk of later dyslexia.

Acoustic features of infant-directed speech to infants with hearing loss.

This study investigated the effects of hearing loss and hearing experience on the acoustic features of infant-directed speech (IDS) to infants with hearing loss (HL) compared to controls with normal hearing (NH) matched by either chronological or hearing age (experiment 1) and across development in infants with hearing loss as well as the relation between IDS features and infants' developing lexical abilities (experiment 2). Both experiments included detailed acoustic analyses of mothers' productions of the three corner vowels /a, i, u/ and utterance-level pitch in IDS and in adult-directed speech. Experiment 1 demonstrated that IDS to infants with HL was acoustically more variable than IDS to hearing-age matched infants with NH. Experiment 2 yielded no changes in IDS features over development; however, the results did show a positive relationship between formant distances in mothers' speech and infants' concurrent receptive vocabulary size, as well as between vowel hyperarticulation and infants' expressive vocabulary. These findings suggest that despite infants' HL and thus diminished access to speech input, infants with HL are exposed to IDS with generally similar acoustic qualities as are infants with NH. However, some differences persist, indicating that infants with HL might receive less intelligible speech.

Sensitivity to amplitude envelope rise time in infancy and vocabulary development at 3 years: A significant relationship.

Here we report, for the first time, a relationship between sensitivity to amplitude envelope rise time in infants and their later vocabulary development. Recent research in auditory neuroscience has revealed that amplitude envelope rise time plays a mechanistic role in speech encoding. Accordingly, individual differences in infant discrimination of amplitude envelope rise times could be expected to relate to individual differences in language acquisition. A group of 50 infants taking part in a longitudinal study contributed rise time discrimination thresholds when aged 7 and 10 months, and their vocabulary development was measured at 3 years. Experimental measures of phonological sensitivity were also administered at 3 years. Linear mixed effect models taking rise time sensitivity as the dependent variable, and controlling for non-verbal IQ, showed significant predictive effects for vocabulary at 3 years, but not for the phonological sensitivity measures. The significant longitudinal relationship between amplitude envelope rise time discrimination and vocabulary development suggests that early rise time discrimination abilities have an impact on speech processing by infants.

Atypical cortical entrainment to speech in the right hemisphere underpins phonemic deficits in dyslexia.

Developmental dyslexia is a multifaceted disorder of learning primarily manifested by difficulties in reading, spelling, and phonological processing. Neural studies suggest that phonological difficulties may reflect impairments in fundamental cortical oscillatory mechanisms. Here we examine cortical mechanisms in children (6-12 years of age) with or without dyslexia (utilising both age- and reading-level-matched controls) using electroencephalography (EEG). EEG data were recorded as participants listened to an audio-story. Novel electrophysiological measures of phonemic processing were derived by quantifying how well the EEG responses tracked phonetic features of speech. Our results provide, for the first time, evidence for impaired low-frequency cortical tracking to phonetic features during natural speech perception in dyslexia. Atypical phonological tracking was focused on the right hemisphere, and correlated with traditional psychometric measures of phonological skills used in diagnostic dyslexia assessments. Accordingly, the novel indices developed here may provide objective metrics to investigate language development and language impairment across languages.

Mothers speak differently to infants at-risk for dyslexia.

Dyslexia is a neurodevelopmental disorder manifested in deficits in reading and spelling skills that is consistently associated with difficulties in phonological processing. Dyslexia is genetically transmitted, but its manifestation in a particular individual is thought to depend on the interaction of epigenetic and environmental factors. We adopt a novel interactional perspective on early linguistic environment and dyslexia by simultaneously studying two pre-existing factors, one maternal and one infant, that may contribute to these interactions; and two behaviours, one maternal and one infant, to index the effect of these factors. The maternal factor is whether mothers are themselves dyslexic or not (with/without dyslexia) and the infant factor is whether infants are at-/not-at family risk for dyslexia (due to their mother or father being dyslexic). The maternal behaviour is mothers' infant-directed speech (IDS), which typically involves vowel hyperarticulation, thought to benefit speech perception and language acquisition. The infant behaviour is auditory perception measured by infant sensitivity to amplitude envelope rise time, which has been found to be reduced in dyslexic children. Here, at-risk infants showed significantly poorer acoustic sensitivity than not-at-risk infants and mothers only hyperarticulated vowels to infants who were not at-risk for dyslexia. Mothers' own dyslexia status had no effect on IDS quality. Parental speech input is thus affected by infant risk status, with likely consequences for later linguistic development.

The development of fast-mapping and novel word retention strategies in monolingual and bilingual infants.

The mutual exclusivity (ME) assumption is proposed to facilitate early word learning by guiding infants to map novel words to novel referents. This study assessed the emergence and use of ME to both disambiguate and retain the meanings of novel words across development in 18-month-old monolingual and bilingual children (Experiment 1; N = 58), and in a sub-group of these children again at 24 months of age (Experiment 2: N = 32). Both monolinguals and bilinguals employed ME to select the referent of a novel label to a similar extent at 18 and 24 months. At 18 months, there were also no differences in novel word retention between the two language-background groups. However, at 24 months, only monolinguals showed the ability to retain these label-object mappings. These findings indicate that the development of the ME assumption as a reliable word-learning strategy is shaped by children's individual language exposure and experience with language use.

Vocabulary matters! The relationship between verbal fluency and measures of inhibitory control in monolingual and bilingual children.

The role of early bilingual experience in the development of skills in the general cognitive and linguistic domains remains poorly understood. This study investigated the link between these two domains by assessing inhibitory control processes in school-aged monolingual and bilingual children with similar English receptive vocabulary size. The participants, 8-year-old monolinguals and bilinguals, completed two Verbal Fluency Tasks (VFTs), letter and category, and two measures of inhibitory control. Results showed that bilinguals outperformed monolinguals on the VFTs, but performance was similar on the inhibitory control measures approaching ceiling for both monolingual and bilingual children. Importantly, it was shown that both vocabulary proficiency and general inhibitory control skills underlie monolingual and bilingual children's performance on VFTs. These results demonstrate that vocabulary proficiency plays a fundamental role in comparing monolingual and bilingual VFT performance. The bilingual advantage found in this study seems to have escaped previous studies that did not account for vocabulary size in populations of bilingual and monolingual school-aged children.

Infant-directed speech from seven to nineteen months has similar acoustic properties but different functions.

This longitudinal study assessed three acoustic components of maternal infant-directed speech (IDS) - pitch, affect, and vowel hyperarticulation - in relation to infants' age and their expressive vocabulary size. These three individual components were measured in IDS addressed to infants at 7, 9, 11, 15, and 19 months (N = 18). All three components were exaggerated at all ages in mothers' IDS compared to their adult-directed speech. Importantly, the only significant predictor of infants' expressive vocabulary size at 15 and 19 months was vowel hyperarticulation, but only at 9 months and beyond, not at 7 months, and not pitch or affect at any age. These results set apart vowel hyperarticulation in IDS to infants as the critical IDS component for vocabulary development. Thus IDS, specifically the degree of vowel hyperarticulation therein, is a vehicle by which parents can provide the most optimal speech quality for their infants' linguistic and communicative development.

Novel Word Learning, Reading Difficulties, and Phonological Processing Skills.

Visual-verbal paired associate learning (PAL) refers to the ability to establish an arbitrary association between a visual referent and an unfamiliar label. It is now established that this ability is impaired in children with dyslexia, but the source of this deficit is yet to be specified. This study assesses PAL performance in children with reading difficulties using a modified version of the PAL paradigm, comprising a comprehension and a production phase, to determine whether the PAL deficit lies in children's ability to establish and retain novel object-novel word associations or their ability to retrieve the learned novel labels for production. Results showed that while children with reading difficulties required significantly more trials to learn the object-word associations, when they were required to use these associations in a comprehension-referent selection task, their accuracy and speed did not differ from controls. Nevertheless, children with reading difficulties were significantly less successful when they were required to produce the learned novel labels in response to the visual stimuli. Thus, these results indicate that while children with reading difficulties are successful at establishing visual-verbal associations, they have a deficit in the verbal production component of PAL tasks, which may relate to a more general underlying impairment in auditory or phonological processing. Copyright © 2016 John Wiley & Sons, Ltd.