Bilingual children are a more heterogenous group than their monolingual counterparts with respect to the sources of variation in their language learning environments, as well as the wide individual variation in their language abilities. Such heterogeneity in both individual difference factors and language abilities argues for the importance of an individual differences approach in research on bilingual development. The main objective of this article is to provide a review and synthesis of research on the sources of individual differences in the second language (L2) and heritage language (HL) development of child bilinguals. Several child-internal and child-external individual difference factors are discussed with respect to their influence on children’s dual language abilities. In addition, the emergent research on individual differences in bilingual children with developmental language disorder is reviewed. Both the theoretical and applied relevance of individual difference approaches to bilingual development are discussed.

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

This paper investigates the comprehension of Relative Clauses (RCs) in 15 Mandarin children with suspected Specific Language Impairment (SLI) (aged between 4; 5 and 6; 0) and 29 typically developing (TD) controls. Results from a Character Picture Matching Task indicate that (i) the subject RC was better understood than the object RC in children with SLI, but there was no asymmetry in the comprehension of the two RCs in TD children; (ii) the performance of children with SLI was significantly worse than that of their TD peers; (iii) children with SLI were prone to committing thematic role reversal errors and middle errors. In order to overcome the shortcomings of previous accounts, we therefore put forward the Edge Feature Underspecification Hypothesis, which can not only explain the asymmetry of comprehension seen in children with SLI but also shed light on the nature of errors committed by them in the task.

Words have meanings vastly undetermined by the contexts in which they occur. Their acquisition therefore presents formidable problems of induction. Lila Gleitman and colleagues have advocated for one part of a solution: indirect evidence for a word’s meaning may come from its syntactic distribution, via syntactic bootstrapping. But while formal theories argue for principled links between meaning and syntax, actual syntactic evidence about meaning is noisy and highly abstract. This paper examines the role that syntactic bootstrapping can play in learning modal and attitude verb meanings, for which the physical context is especially uninformative. I argue that abstract syntactic classifications are useful to the child, but that something further is both necessary and available. I examine how pragmatic and syntactic cues can combine in mutually constraining ways to help learners infer attitude meanings, but need to be supplemented by semantic information from the lexical context in the case of modals.

One approach to studying how children acquire language is to simulate language acquisition through computational modelling. Computational models implement theories of language acquisition and simulation outcomes can then be tested against existing real-world data or in new empirical research. It is more than ten years ago that Journal of Child Language published a special issue on the topic, edited and introduced by Brian MacWhinney (MacWhinney, 2010). Now is thus a good time to take stock of recent developments by bringing together a collection of articles that explore recent research and insights from computational modelling of child language acquisition.

The current study evaluated the separate and combined effects of bilingualism and Autism Spectrum Disorder (ASD) on informativeness and definiteness marking of referential expressions. Hebrew-speaking monolingual children (21 with ASD and 28 with typical language development) and Russian–Hebrew-speaking bilingual children (13 with ASD and 30 with typical language development) aged 4–9 years participated. Informativeness, indexed by referential contrasts, was affected by ASD, but not by bilingualism. Definiteness use was non-target-like in children with ASD and in bilingual children, and it was mainly predicted by children’s morpho-syntactic abilities in Hebrew. Language-universal and language-specific properties of referential use are discussed.

Learning new words and, subsequently, a lexicon, is a time-extended process requiring encoding of word-referent pairs, retention of that information, and generalization to other exemplars of the category. Some children, however, fail in one or more of these processes resulting in language delays. The present study examines the abilities of children who vary in vocabulary size (including both children with normal language (NL) and late talking (LT) children) across multiple timescales/processes – known and novel word mapping, novel word retention, and novel noun generalization. Results indicate that children with lower language skills suffer from deficits in quick in-the-moment mapping of known words compared to their NL peers, but age and vocabulary size rather than normative vocabulary ranking or NL/LT status better predicts performance on retention and generalization processes. Implications for understanding language development as a holistic process with multiple interacting variables are discussed.

There has recently been an increased interest in studying the language development of non-western languages. This is not new - it began in 1960’s and continued into the 1980’s and 1990’s. The current renewed interest is much welcomed, and will benefit from many of the experimental methods and theoretical insights developed over the past decades.

This study investigates how children aged two to eight years (N = 129) and adults (N = 29) use auditory and visual speech for word recognition. The goal was to bridge the gap between apparent successes of visual speech processing in young children in visual-looking tasks, with apparent difficulties of speech processing in older children from explicit behavioural measures. Participants were presented with familiar words in audio-visual (AV), audio-only (A-only) or visual-only (V-only) speech modalities, then presented with target and distractor images, and looking to targets was measured. Adults showed high accuracy, with slightly less target-image looking in the V-only modality. Developmentally, looking was above chance for both AV and A-only modalities, but not in the V-only modality until 6 years of age (earlier on /k/-initial words). Flexible use of visual cues for lexical access develops throughout childhood.

There is a current ‘theory crisis’ in language acquisition research, resulting from fragmentation both at the level of the approaches and the linguistic level studied. We identify a need for integrative approaches that go beyond these limitations, and propose to analyse the strengths and weaknesses of current theoretical approaches of language acquisition. In particular, we advocate that language learning simulations, if they integrate realistic input and multiple levels of language, have the potential to contribute significantly to our understanding of language acquisition. We then review recent results obtained through such language learning simulations. Finally, we propose some guidelines for the community to build better simulations.

This commentary makes the argument that the child-internal and child-external sources of individual differences in bilingual development are much the same as the sources of individual differences in monolingual development. It makes the further argument that the operation of the child-external influences results in differences between monolingual and bilingual development in the rate and sometimes in the outcome of language acquisition. An argument is made for the scientific and practical value of understanding the differences between monolingual and bilingual development, and future directions for research are suggested.

Syntactic bootstrapping is based on the premise that there are probabilistic correspondences between the syntactic structure in which a word occurs and the word’s meaning, and that such links hold, with some degree of generality, cross-linguistically. The procedure has been extensively discussed with respect to verbs, where it has been proposed as a mechanism for constraining the massive ambiguity that arises when inferring the meaning of a verb that is used to describe an event (Fisher, Hall, Rakowitz & Gleitman, 1994; Gleitman, 1990; Gleitman, Cassidy, Nappa, Papafragou & Trueswell, 2005). In her keynote paper (Hacquard, 2022), Hacquard focuses on classes of verbs for which inferences about meaning are arguably even harder, because they involve concepts that have no observable counterparts: these are attitude verbs such as think and want, and modals such as must and can. She walks us through, in meticulous detail, the limits of a purely syntactic bootstrapping mechanism, and she describes how augmenting syntactic information with pragmatic information, via pragmatic syntactic bootstrapping (Hacquard, 2022; Hacquard & Lidz, 2019), might address these limitations. The proposal is exciting, and the detail with which Hacquard works through these examples is impressive; she supports her arguments with behavioral experiments, corpus analyses, and two very targeted computational analyses. In this commentary I suggest that Hacquard’s proposal is laid out in sufficient detail such that a comprehensive computational modeling effort would be fruitful for evaluating and further developing her account.

Over recent decades much research has analyzed the relevance of 9- to 20- month-old infants’ early imitation skills (object- and language-based imitation) for language development. Yet there have been few systematic comparisons of the joint relevance of these imitative behaviors later on in development. This correlational study investigated whether multimodal imitation (gestural, prosodic, and lexical components) and object-based imitation are related to narratives and sociopragmatics in preschoolers. Thirty-one typically developing 3- to 4-year-old children performed four tasks to assess multimodal imitation, object-based imitation, narrative abilities, and sociopragmatic abilities. Results revealed that both narrative and sociopragmatic skills were significantly related to multimodal imitation, but not to object-based imitation, indicating that preschoolers’ ability to imitate socially relevant multimodal cues is strongly related to language and sociocommunicative skills. Therefore, this evidence supports a broader conceptualization of imitation behaviors in the field of language development that systematically integrates prosodic, gestural, and verbal linguistic patterns.

In the target article, Cristia, Foushee, Aravena-Bravo, Cychosz, Scaff, and Casillas (2023) convincingly show the need to broaden the current language acquisition research base, not only in linguistic diversity, but also in terms of regions and cultural groups studied. In conducting acquisition research in understudied populations, such as in rural settings, the authors highlight the importance of using a multi-method approach. They present the challenges in adapting these methods to new settings and offer possible ways to promote this type of research. In this commentary, we extend the discussion to understudied urban communities, as we encounter several of the concerns raised in Cristia et al. when collecting observational and experimental language acquisition data from Metro Manila, Philippines. We first describe the community we study, the challenges and modifications needed for conducting research in this setting, and end with a discussion of possible strategies to promote research in communities with understudied populations.

Paradis’ (2023) keynote article is a timely documentation of the ongoing shift in focus within childhood bilingualism research from investigating the factors that modulate majority or second language (ML/L2) attainment (Chondrogianni & Marinis, 2011) to understanding the sources of variation that lead to minority heritage language (HL) maintenance. This shift of focus into individual differences (IDs) in bilingual performance across both languages reflects converging research carried out in the past twenty years reporting that, when learning barriers are not at stake, bilingual children can reach ML outcomes. It also aligns with research findings suggesting that ML educational or linguistic outcomes are directly related to the successful attainment of HL educational and linguistic milestones, which, in turn, reinforce the need for the HL to be supported.

Instances of person-reference, in the form of personal pronouns, names, or terms of endearment, are frequently used in child-directed speech. Examining this aspect of parental input is especially relevant to children with autism, who experience difficulties with person-reference. In this study, we compared the person-reference during parent-child interactions of Bulgarian (N=37) and English-speaking (N=37) parents of children with autism, who were matched on the language ability of their child. English-speaking parents used significantly more personal pronouns to refer to their children, while Bulgarian-speaking parents used the child’s name more along with kinship terms. Furthermore, Bulgarian-speaking parents used significantly more different ways to refer to their child. These group differences were interpreted in the context of structural differences in the pronominal systems of Bulgarian and English, and in terms of culturally different discourse practices.

Like verbs, adjectives pose a challenge to the young word learner in that some – like red, round, rough, or rectangular – map onto properties that are detectable through the senses, while others – like ready, reasonable, or required – express abstract properties that have no reliable, physical correlate. Even for those adjectives whose properties are observable, how does a child know that one particular property is being highlighted above all others? The physical environment alone will not suffice. Just as with verbs, the child learning adjectives is faced with an inherent indeterminacy of meaning, which can only be resolved through the incorporation of cues originating from multiple sources.

This review describes a computational approach for modeling the development of speech motor control in infants. We address the development of two levels of control: articulation of individual speech sounds (defined here as phonemes, syllables, or words for which there is an optimized motor program) and production of sound sequences such as phrases or sentences. We describe the DIVA model of speech motor control and its application to the problem of learning individual sounds in the infant’s native language. Then we describe the GODIVA model, an extension of DIVA, and how chunking of frequently produced phoneme sequences is implemented within it.

Our knowledge and theories about language acquisition are skewed towards urban languages, and primarily English (Kidd & Garcia, 2022). Cristia and colleagues convincingly show that studies on the acquisition of rural languages are scarce. The authors suggest that in rural settings, combining experimental and observational approaches is critical to testing and sharpening our theories about language acquisition. Nevertheless, they also acknowledge the numerous challenges that make it difficult to conduct, analyse and publish this type of work.

Large individual differences in language skills are well documented in monolingual children (e.g., Kidd, Donnelly & Christiansen, 2018). In bilinguals, the broad variation is even more pronounced. Interestingly, some bilingual children might be weak in their Heritage Language (HL, also labeled as Minority Language, Home Language, Community Language), to which they have naturalistic exposure from birth. Others might be weak in their Societal Language (SL), the language of the surrounding and educational environment. Large individual differences are observed in neurotypical bilingually exposed children as well as in their bilingually raised peers with developmental language disorder, autism spectrum disorder, and hearing impairment (see also Armon-Lotem & Meir, 2016; Meir & Novogrodsky, 2020). Figure 1 visualizes individual differences in morphosyntactic skills of monolingual and bilingual children with typical language development aged 5;5–6;8 as indexed by the LITMUS Sentence Repetition tasks (the data are drawn from Armon-Lotem & Meir, 2016; Meir, 2018). While monolingual preschool children (MonoRU and MonoHE) show little variation, bilinguals with different levels of dominance (balanced bilinguals: BB; HL dominant: HL-D; SL dominant: SL-D) as determined by standardized tests exhibit large individual differences within each language and across their two languages.