Late bloomer or language disorder? Differences in toddler vocabulary composition associated with long-term language outcomes.

Children with delays in expressive language (late talkers) have heterogeneous developmental trajectories. Some are late bloomers who eventually "catch-up," but others have persisting delays or are later diagnosed with developmental language disorder (DLD). Early in development it is unclear which children will belong to which group. We compare the toddler vocabulary composition of late talkers with different long-term outcomes. The literature suggests most children with typical development (TD) have vocabularies dominated by names for categories organized by similarity in shape (e.g., cup), which supports a bias to attend to shape when generalizing names of novel nouns-a bias associated with accelerated vocabulary development. Previous work has shown that as a group, late talkers tend to say fewer names for categories organized by shape and are less likely to show a "shape bias" than TD children. Here, in a retrospective analysis of 850 children, we compared the vocabulary composition of groups of toddlers who were late bloomers or persisting late talkers. At Time 1 (13-27 months), the persisting late talkers said a smaller proportion of shape-based nouns than both TD children and late bloomers who "caught up" to typically sized vocabularies months later (18-38-months). Additionally, children who received a DLD diagnosis between 4 and 7 years said a significantly smaller proportion of shape-based nouns in year two than TD children and children with other diagnoses (e.g., dyslexia). These findings bring new insight into sources of heterogeneity amongst late talkers and offer a new metric for assessing risk. RESEARCH HIGHLIGHTS: Toddler vocabulary composition, including the proportion of names for categories organized by shape, like spoon, was used to retrospectively compare outcomes of late talking children Persisting Late Talkers said a smaller proportion of shape-based nouns during toddlerhood relative to Late Bloomers (late talkers who later caught up to have typically-sized vocabularies) Children with later DLD diagnoses said a smaller proportion of shape-based nouns during toddlerhood relative to children without a DLD diagnosis The data illustrate the cascading effects of vocabulary composition on subsequent language development and suggest vocabulary composition may be one important marker of persisting delays.

Vocabulary and automatic attention: The relation between novel words and gaze dynamics in noun generalization.

Words direct visual attention in infants, children, and adults, presumably by activating representations of referents that then direct attention to matching stimuli in the visual scene. Novel, unknown, words have also been shown to direct attention, likely via the activation of more general representations of naming events. To examine the critical issue of how novel words and visual attention interact to support word learning we coded frame-by-frame the gaze of 17- to 31-month-old children (n = 66, 38 females) while generalizing novel nouns. We replicate prior findings of more attention to shape when generalizing novel nouns, and a relation to vocabulary development. However, we also find that following a naming event, children who produce fewer nouns take longer to look at the objects they eventually select and make more transitions between objects before making a generalization decision. Children who produce more nouns look to the objects they eventually select more quickly following the naming event and make fewer looking transitions. We discuss these findings in the context of prior proposals regarding children's few-shot category learning, and a developmental cascade of multiple perceptual, cognitive, and word-learning processes that may operate in cases of both typical development and language delay. RESEARCH HIGHLIGHTS: Examined how novel words guide visual attention by coding frame-by-frame where children look when asked to generalize novel names. Gaze patterns differed with vocabulary size: children with smaller vocabularies attended to generalization targets more slowly and did more comparison than those with larger vocabularies. Demonstrates a relationship between vocabulary size and attention to object properties during naming. This work has implications for looking-based tests of early cognition, and our understanding of children's few-shot category learning.

Formal theories clarify the complex: Generalizing a neural process account of the interaction of visual exploration and word learning in infancy.

The interaction of visual exploration and auditory processing is central to early cognitive development, supporting object discrimination, categorization, and word learning. Research has shown visual-auditory interactions to be complex, created from multiple processes and changing over multiple timescales. To better understand these interactions, we generalize a formal neural process model of early word learning to two studies examining how words impact 9- to 22-month-olds' attention to novelty. These simulations clarify the origin and nature of previously demonstrated effects of labels on visual exploration and the basis of mutual exclusivity effects in word learning. We use our findings to discuss key questions for this special section: what makes a good theory and how should formal theories interface with empirical paradigms and findings?

Sometimes it is better to know less: How known words influence referent selection and retention in 18- to 24-month-old children.

Young children are surprisingly good word learners. Despite their relative lack of world knowledge and limited vocabularies, they consistently map novel words to novel referents and, at later ages, show retention of these new word-referent pairs. Prior work has implicated the use of mutual exclusivity constraints and novelty biases, which require that children use knowledge of well-known words to disambiguate uncertain naming situations. The current study, however, presents evidence that weaker vocabulary knowledge during the initial exposure to a new word may be better for retention of new mappings. Children aged 18-24 months selected referents for novel words in the context of foil stimuli that varied in their lexical strength and novelty: well-known items (e.g., shoe), just-learned weakly known items (e.g., wif), and completely novel items. Referent selection performance was significantly reduced on trials with weakly known foil items. Surprisingly, however, children subsequently showed above-chance retention for novel words mapped in the context of weakly known competitors compared with those mapped with strongly known competitors or with completely novel competitors. We discuss implications for our understanding of word learning constraints and how children use known words and novelty during word learning.

Empirical Tests of a Brain-Based Model of Executive Function Development.

Executive function (EF) plays a foundational role in development. A brain-based model of EF development is probed for the experiences that strengthen EF in the dimensional change card sort task in which children sort cards by one rule and then are asked to switch to another. Three-year-olds perseverate on the first rule, failing the task, whereas 4-year-olds pass. Three predictions of the model are tested to help 3-year-olds (N = 54) pass. Experiment 1 shows that experience with shapes and the label "shape" helps children. Experiment 2 shows that experience with colors-without a label-helps children. Experiment 3 shows that experience with colors induces dimensional attention. The implications of this work for early intervention are discussed.

Enhancing the executive functions of 3-year-olds in the Dimensional Change Card Sort task.

Executive functions enable flexible thinking, something young children are notoriously bad at. For instance, in the dimensional change card sort (DCCS) task, 3-year-olds can sort cards by one dimension (shape), but continue to sort by this dimension when asked to switch (to color). This study tests a prediction of a dynamic neural field model that prior experience with the postswitch dimension can enhance 3-year-olds' performance in the DCCS. In Experiment 1A, a matching game was used to preexpose 3-year-olds (n = 36) to color. This facilitated switching from sorting by shape to color. In , 3-year-olds (n = 18) were preexposed to shape. This did not facilitate switching from sorting by color to shape. The model was used to explain this asymmetry.

Highchair philosophers: the impact of seating context-dependent exploration on children's naming biases.

We examine developmental interactions between context, exploration, and word learning. Infants show an understanding of how nonsolid substances are categorized that does not reliably transfer to learning how these categories are named in laboratory tasks. We argue that what infants learn about naming nonsolid substances is contextually bound - most nonsolids that toddlers are familiar with are foods and thus, typically experienced when sitting in a highchair. We asked whether 16-month-old children's naming of nonsolids would improve if they were tested in that typical context. Children tested in the highchair demonstrated better understanding of how nonsolids are named. Furthermore, context-based differences in exploration drove differences in the properties attended to in real-time. We discuss what implications this context-dependency has for understanding the development of an ontological distinction between solids and nonsolids. Together, these results demonstrate a developmental cascade between context, exploration, and word learning.

Word-Object Learning via Visual Exploration in Space (WOLVES): A neural process model of cross-situational word learning.

Infants, children, and adults have been shown to track co-occurrence across ambiguous naming situations to infer the referents of new words. The extensive literature on this cross-situational word learning (CSWL) ability has produced support for two theoretical accounts-associative learning (AL) and hypothesis testing (HT)-but no comprehensive model of the behavior. We propose Word-Object Learning via Visual Exploration in Space (WOLVES), an implementation-level account of CSWL grounded in real-time psychological processes of memory and attention that explicitly models the dynamics of looking at a moment-to-moment scale and learning across trials. We use WOLVES to capture data from 12 studies of CSWL with adults and children, thereby providing a comprehensive account of data purported to support both AL and HT accounts. Direct model comparison shows that WOLVES performs well relative to two competitor models. In particular, WOLVES captures more data than the competitor models (132 vs. 69 data values) and fits the data better than the competitor models (e.g., lower percent error scores for 12 of 17 conditions). Moreover, WOLVES generalizes more accurately to three "held-out" experiments, although a model by Kachergis et al. (2012) fares better on another metric of generalization (Akaike Information Criterion [AIC]/Bayesian Information Criterion [BIC]). Critically, we offer the first developmental account of CSWL, providing insights into how memory processes change from infancy through adulthood. WOLVES shows that visual exploration and selective attention in CSWL are both dependent on and indicative of learning within a task-specific context. Furthermore, learning is driven by real-time synchrony of words and gaze and constrained by memory processes over multiple timescales. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Learning words in space and time: probing the mechanisms behind the suspicious-coincidence effect.

A major debate in the study of word learning centers on the extension of categories to new items. The rational approach assumes that learners make structured inferences about category membership, whereas the mechanistic approach emphasizes the attentional and memory processes that form the basis of generalization behaviors. Recent support for the rational view comes from observations of the suspicious-coincidence effect: People generalize category membership narrowly when presented with three subordinate-level exemplars that share the same label and generalize category membership broadly when presented with one exemplar. Across three experiments, we examined the mechanistic basis of this effect. Results showed that the presentation of multiple subordinate-level exemplars led to narrow generalization only when the exemplars were presented simultaneously, even when the number of exemplars was increased from three to six. These data demonstrate that the suspicious-coincidence effect is firmly grounded in the general cognitive processes of attention, memory, and visual comparison.

Toward a Precision Science of Word Learning: Understanding Individual Vocabulary Pathways.

Toddlers vary widely in the rate at which they develop vocabulary. This variation predicts later language development and school success at the group level; however, we cannot determine which children with slower vocabulary development in the second year will continue to have difficulty. In this article, I argue that this is because we lack theoretical understanding of how multiple processes operate as a system to create individual children's pathways to word learning. I discuss the difficulties children face when learning even a single concrete noun, the multiple general cognitive processes that support word learning, and some evidence of rapid development in the second year. I present work toward a formal model of the word learning system and how this system changes over time. The long-term goal of this work is to understand how individual children's strengths and weaknesses create unique vocabulary pathways that enable us to predict outcomes and identify effective interventions.

Learning words in space and time: Contrasting models of the suspicious coincidence effect.

In their 2007b Psychological Review paper, Xu and Tenenbaum found that early word learning follows the classic logic of the "suspicious coincidence effect:" when presented with a novel name ('fep') and three identical exemplars (three Labradors), word learners generalized novel names more narrowly than when presented with a single exemplar (one Labrador). Xu and Tenenbaum predicted the suspicious coincidence effect based on a Bayesian model of word learning and demonstrated that no other theory captured this effect. Recent empirical studies have revealed, however, that the effect is influenced by factors seemingly outside the purview of the Bayesian account. A process-based perspective correctly predicted that when exemplars are shown sequentially, the effect is eliminated or reversed (Spencer, Perone, Smith, & Samuelson, 2011). Here, we present a new, formal account of the suspicious coincidence effect using a generalization of a Dynamic Neural Field (DNF) model of word learning. The DNF model captures both the original finding and its reversal with sequential presentation. We compare the DNF model's performance with that of a more flexible version of the Bayesian model that allows both strong and weak sampling assumptions. Model comparison results show that the dynamic field account provides a better fit to the empirical data. We discuss the implications of the DNF model with respect to broader contrasts between Bayesian and process-level models.

Learn locally, think globally. Exemplar variability supports higher-order generalization and word learning.

Research suggests that variability of exemplars supports successful object categorization; however, the scope of variability's support at the level of higher-order generalization remains unexplored. Using a longitudinal study, we examined the role of exemplar variability in first- and second-order generalization in the context of nominal-category learning at an early age. Sixteen 18-month-old children were taught 12 categories. Half of the children were taught with sets of highly similar exemplars; the other half were taught with sets of dissimilar, variable exemplars. Participants' learning and generalization of trained labels and their development of more general word-learning biases were tested. All children were found to have learned labels for trained exemplars, but children trained with variable exemplars generalized to novel exemplars of these categories, developed a discriminating word-learning bias generalizing labels of novel solid objects by shape and labels of nonsolid objects by material, and accelerated in vocabulary acquisition. These findings demonstrate that object variability leads to better abstraction of individual and global category organization, which increases learning outside the laboratory.

Corresponding delay-dependent biases in spatial language and spatial memory.

The present study addresses the relationship between linguistic and non-linguistic spatial representations. In three experiments we probe spatial language and spatial memory at the same time points in the task sequence. Experiments 1 and 2 show analogous delay-dependent biases in spatial language and spatial memory. Experiment 3 extends this correspondence, showing that additional perceptual structure along the vertical axis reduces delay-dependent effects in both tasks. These results indicate that linguistic and non-linguistic spatial systems depend on shared underlying representational processes. In addition, we also address how these delay-dependent biases can arise within a single theoretical framework without positing differing prototypes for linguistic and non-linguistic spatial systems.

Toddlers can adaptively change how they categorize: same objects, same session, two different categorical distinctions.

Two experiments demonstrate that 14- to 18-month-old toddlers can adaptively change how they categorize a set of objects within a single session, and that this ability is related to vocabulary size. In both experiments, toddlers were presented with a sequential touching task with objects that could be categorized either according to some perceptually salient dimension corresponding to a taxonomic distinction (e.g. animals vs. vehicles) or to some less obvious dimension (e.g. rigid vs. deformable). In each experiment, children with larger productive vocabularies responded to both dimensions, showing evidence of sensitivity to each way of categorizing the items. Children with smaller productive vocabularies attended only to the taxonomically related categorical grouping. These experiments confirm that toddlers can adaptively shift the basis of their categorization and highlight the dynamic interaction between the child and the current task in early categorization.

Aligning body and world: stable reference frames improve young children's search for hidden objects.

This study investigated how young children's increasingly flexible use of spatial reference frames enables accurate search for hidden objects by using a task that 3-year-olds have been shown to perform with great accuracy and 2-year-olds have been shown to perform inaccurately. Children watched as an object was rolled down a ramp, behind a panel of doors, and stopped at a barrier visible above the doors. In two experiments, we gave 2- and 2.5-year-olds a strong reference frame by increasing the relative salience and stability of the barrier. In Experiment 1, 2.5-year-olds performed at above-chance levels with the more salient barrier. In Experiment 2, we highlighted the stability of the barrier (or ramp) by maximizing the spatial extent of each reference frame across the first four training trials. Children who were given a stable barrier (and moving ramp) during these initial trials performed at above-chance levels and significantly better than children who were given a stable ramp (and moving barrier). This work highlights that factors central to spatial cognition and motor planning-aligning egocentric and object-centered reference frames-play a role in the ramp task during this transitional phase in development.

Reproducibility and a unifying explanation: Lessons from the shape bias.

The goal of science is to advance our understanding of particular phenomena. However, in the field of development, the phenomena of interest are complex, multifaceted, and change over time. Here, we use three decades of research on the shape bias to argue that while replication is clearly an important part of the scientific process, integration across the findings of many studies that include variations in procedure is also critical to create a coherent understanding of the thoughts and behaviors of young children. The "shape bias," or the tendency to generalize a novel label to novel objects of the same shape, is a reliable and robust behavioral finding and has been shown to predict future vocabulary growth and possible language disorders. Despite the robustness of the phenomenon, the way in which the shape bias is defined and tested has varied across studies and laboratories. The current review argues that differences in performance that come from even seemingly minor changes to the participants or task can offer critical insight to underlying mechanisms, and that working to incorporate data from multiple labs is an important way to reveal how task variation and a child's individual pathway creates behavior-a key issue for understanding developmental phenomena.

Confronting complexity: insights from the details of behavior over multiple timescales.

Young children tend to generalize novel names for novel solid objects by similarity in shape, a phenomenon dubbed 'the shape bias'. We believe that the critical insights needed to explain the shape bias in particular, and cognitive development more generally, come from Dynamic Systems Theory. We present two examples of recent work focusing on the real-time decision processes that underlie performance in the tasks used to measure the shape bias. We show how this work, and the dynamic systems perspective, sheds light on the controversy over the origins and development of the shape bias. In addition, we suggest that this dynamic systems perspective provides the right level for explanations of development because it requires a focus on the details of behavior over multiple timescales.

Fast Mapping but Poor Retention by 24-Month-Old Infants.

Four experiments explored the processes that bridge between referent selection and word learning. Twenty-four-month-old infants were presented with several novel names during a referent selection task that included both familiar and novel objects and tested for retention after a 5-min delay. The 5-min delay ensured that word learning was based on retrieval from long-term memory. Moreover, the relative familiarity of objects used during the retention test was explicitly controlled. Across experiments, infants were excellent at referent selection, but very poor at retention. Although the highly controlled retention test was clearly challenging, infants were able to demonstrate retention of the first 4 novel names presented in the session when referent selection was augmented with ostensive naming. These results suggest that fast mapping is robust for reference selection but might be more transient than previously reported for lexical retention. The relations between reference selection and retention are discussed in terms of competitive processes on 2 timescales: competition among objects on individual referent selection trials and competition among multiple novel name-object mappings made across an experimental session.

Too Much of a Good Thing: How Novelty Biases and Vocabulary Influence Known and Novel Referent Selection in 18-Month-Old Children and Associative Learning Models.

Identifying the referent of novel words is a complex process that young children do with relative ease. When given multiple objects along with a novel word, children select the most novel item, sometimes retaining the word-referent link. Prior work is inconsistent, however, on the role of object novelty. Two experiments examine 18-month-old children's performance on referent selection and retention with novel and known words. The results reveal a pervasive novelty bias on referent selection with both known and novel names and, across individual children, a negative correlation between attention to novelty and retention of new word-referent links. A computational model examines possible sources of the bias, suggesting novelty supports in-the-moment behavior but not retention. Together, results suggest that when lexical knowledge is weak, attention to novelty drives behavior, but alone does not sustain learning. Importantly, the results demonstrate that word learning may be driven, in part, by low-level perceptual processes.

What does it take to learn a word?

Vocabulary learning is deceptively hard, but toddlers often make it look easy. Prior theories proposed that children's rapid acquisition of words is based on language-specific knowledge and constraints. In contrast, more recent work converges on the view that word learning proceeds via domain-general processes that are tuned to richly structured-not impoverished-input. We argue that new theoretical insights, coupled with methodological tools, have pushed the field toward an appreciation of simple, content-free processes working together as a system to support the acquisition of words. We illustrate this by considering three central phenomena of early language development: referential ambiguity, fast-mapping, and the vocabulary spurt. WIREs Cogn Sci 2017, 8:e1421. doi: 10.1002/wcs.1421 For further resources related to this article, please visit the WIREs website.