The role of dyadic combinations of infants' behaviors and caregivers' verbal and multimodal responses in predicting vocabulary outcomes.

There is robust evidence that infants' gestures and vocalisations and caregivers' contingent responses predict later child vocabulary. Recent studies suggest that dyadic combinations of infants' behaviors and caregivers' responses are more robust predictors of children's vocabularies than these behaviors separately. Previous studies have not yet systematically compared different types of dyadic combinations. This study aimed to compare the predictive value of (a) frequencies of infants' behaviors (vocalisations, points, and shows + gives) regardless of caregivers' responses, (b) frequencies of infants' behaviors that elicited verbal responses, (c) frequencies of infants' behaviors that elicited multimodal responses, and (d) frequencies of infants' behaviors that did not elicit any responses from caregivers. We examined 114 caregiver-infant dyads at 9-11 months and children's concurrent and longitudinal vocabulary outcomes at 2-4 years. We found that infants' points elicited a large proportion of verbal responses from caregivers which were related to children's later receptive vocabularies. We also found that only shows + gives that elicited caregivers' responses related to infants' concurrent gesture repertoires. In contrast, infants' behaviors that did not elicit responses negatively related to child vocabulary. The results highlight the importance of examining dyadic combinations of infants' behaviors and caregivers' responses during interactions when examining relations to children's vocabulary development.

Examining Dutch children's vocabularies across infancy and toddlerhood: Demographic effects are age-specific and task-specific.

Limited studies have examined demographic differences in children's vocabulary in longitudinal samples, while there are questions regarding the duration, direction, and magnitude of these effects across development. In this longitudinal study, we included over 400 Dutch children. Caregivers filled out N-CDIs when children were 9-11 months (measuring word comprehension, word production, and gestures) and around 2-5 years of age (measuring word production). At 2-5 years, we also administered a receptive vocabulary task in the lab. We examined demographic effects on vocabulary size across infancy and toddlerhood. We found a disadvantage for males in infants' gestures and toddlers' vocabulary production. We found a negative effect of maternal education on infants' caregiver-reported vocabulary, but a positive effect on toddlers' lab-administered receptive vocabulary. Lastly, we found a negative effect of multilingualism - but only for the lab-administered task. Examining predictors in large, longitudinal samples ensures their robustness and generalisability across development.

Effects of consonantal context on the learnability of vowel categories from infant-directed speech.

Recent studies have shown that vowels in infant-directed speech (IDS) are characterized by highly variable formant distributions. The current study investigates whether vowel variability is partially due to consonantal context, and explores whether consonantal context could support the learning of vowel categories from IDS. A computational model is presented which selects contexts based on frequency in the input and generalizes across contextual categories. Improved categorization performance was found on a vowel contrast in American-English IDS. The findings support a view in which the infant's learning mechanism is anchored in context, in order to cope with acoustic variability in the input.

Prosodic exaggeration within infant-directed speech: Consequences for vowel learnability.

Perceptual experiments with infants show that they adapt their perception of speech sounds toward the categories of the native language. How do infants learn these categories? For the most part, acoustic analyses of natural infant-directed speech have suggested that phonetic categories are not presented to learners as separable clusters of sounds in acoustic space. As a step toward explaining how infants begin to solve this problem, the current study proposes that the exaggerated prosody characteristic of infant-directed speech may highlight for infants certain speech-sound tokens that collectively form more readily identifiable categories. A database is presented, containing vowel measurements in a large sample of natural American English infant-directed speech. Analyses of the vowel space show that prosodic exaggeration in infant-directed speech has the potential to support distributional vowel learning by providing the learner with a subset of "high-quality" tokens that infants might attend to preferentially. Categorization models trained on prosodically exaggerated tokens outperformed models that were trained on tokens that were not exaggerated. Though focusing on more prominent, exaggerated tokens does not provide a solution to the categorization problem, it would make it easier to solve.

Infants' behaviours elicit different verbal, nonverbal, and multimodal responses from caregivers during early play.

Caregivers use a range of verbal and nonverbal behaviours when responding to their infants. Previous studies have typically focused on the role of the caregiver in providing verbal responses, while communication is inherently multimodal (involving audio and visual information) and bidirectional (exchange of information between infant and caregiver). In this paper, we present a comprehensive study of caregivers' verbal, nonverbal, and multimodal responses to 10-month-old infants' vocalisations and gestures during free play. A new coding scheme was used to annotate 2036 infant vocalisations and gestures of which 87.1 % received a caregiver response. Most caregiver responses were verbal, but 39.7 % of all responses were multimodal. We also examined whether different infant behaviours elicited different responses from caregivers. Infant bimodal (i.e., vocal-gestural combination) behaviours elicited high rates of verbal responses and high rates of multimodal responses, while infant gestures elicited high rates of nonverbal responses. We also found that the types of verbal and nonverbal responses differed as a function of infant behaviour. The results indicate that infants influence the rates and types of responses they receive from caregivers. When examining caregiver-child interactions, analysing caregivers' verbal responses alone undermines the multimodal richness and bidirectionality of early communication.

Linguistic Constraints on Statistical Word Segmentation: The Role of Consonants in Arabic and English.

Statistical learning is often taken to lie at the heart of many cognitive tasks, including the acquisition of language. One particular task in which probabilistic models have achieved considerable success is the segmentation of speech into words. However, these models have mostly been tested against English data, and as a result little is known about how a statistical learning mechanism copes with input regularities that arise from the structural properties of different languages. This study focuses on statistical word segmentation in Arabic, a Semitic language in which words are built around consonantal roots. We hypothesize that segmentation in such languages is facilitated by tracking consonant distributions independently from intervening vowels. Previous studies have shown that human learners can track consonant probabilities across intervening vowels in artificial languages, but it is unknown to what extent this ability would be beneficial in the segmentation of natural language. We assessed the performance of a Bayesian segmentation model on English and Arabic, comparing consonant-only representations with full representations. In addition, we examined to what extent structurally different proto-lexicons reflect adult language. The results suggest that for a child learning a Semitic language, separating consonants from vowels is beneficial for segmentation. These findings indicate that probabilistic models require appropriate linguistic representations in order to effectively meet the challenges of language acquisition.