Effects of environmental diversity on exploration and learning: The case of bilingualism.

Bilingual environments provide a commonplace example of increased complexity and uncertainty. Learning multiple languages entails mastery of a larger and more variable range of sounds, words, syntactic structures, pragmatic conventions, and more complex mapping of linguistic information to objects in the world. Recent research suggests that bilingual learners demonstrate fundamental variation in how they explore and learn from their environment, which may derive from this increased complexity. In particular, the increased complexity and variability of bilingual environments may broaden the focus of learners' attention, laying a different attentional foundation for learning. In this review, we introduce a novel framework, with accompanying empirical evidence, for understanding how early learners may adapt to a more complex environment, drawing on bilingualism as an example. Three adaptations, each relevant to the demands of abstracting structure from a complex environment, are introduced. Each adaptation is discussed in the context of empirical evidence attesting to shifts in basic psychological processes in bilingual learners. This evidence converges on the notion that bilingual learners may explore their environment more broadly. Downstream consequences of broader sampling for perception and learning are discussed. Finally, recommendations for future research to expand the scientific narrative on the impact of diverse environments on learning are provided. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Bilingual adaptations in early development.

Infants raised in bilingual homes redirect attention faster than infants raised in monolingual homes. How can mere exposure to a bilingual environment affect an infant's cognitive development? The more complex language environment may drive infants to explore (gather more information from) their visual environment to facilitate learning.

Early bilingual experience is associated with change detection ability in adults.

To adapt to their more varied and unpredictable (language) environments, infants from bilingual homes may gather more information (sample more of their environment) by shifting their visual attention more frequently. However, it is not known whether this early adaptation is age-specific or lasts into adulthood. If the latter, we would expect to observe it in adults who acquired their second language early, not late, in life. Here we show that early bilingual adults are faster at disengaging attention to shift attention, and at noticing changes between visual stimuli, than late bilingual adults. In one experiment, participants were presented with the same two visual stimuli; one changed (almost imperceptibly), the other remained the same. Initially, participants looked at both stimuli equally; eventually, they fixated more on the changing stimulus. This shift in looking occurred in the early but not late bilinguals. It suggests that cognitive processes adapt to early bilingual experiences.

Is mere exposure enough? The effects of bilingual environments on infant cognitive development.

Bilinguals purportedly outperform monolinguals in non-verbal tasks of cognitive control (the 'bilingual advantage'). The most common explanation is that managing two languages during language production constantly draws upon, and thus strengthens, domain-general inhibitory mechanisms (Green 1998 Biling. Lang. Cogn. 1, 67-81. (doi:10.1017/S1366728998000133)). However, this theory cannot explain why a bilingual advantage has been found in preverbal infants (Kovacs & Mehler 2009 Proc. Natl Acad. Sci. USA 106, 6556-6560. (doi:10.1073/pnas.0811323106)). An alternative explanation is needed. We propose that exposure to more varied, less predictable (language) environments drive infants to sample more by placing less weight on consolidating familiar information in order to orient sooner to (and explore) new stimuli. To confirm the bilingual advantage in infants and test our proposal, we administered four gaze-contingent eye-tracking tasks to seven- to nine-month-old infants who were being raised in either bilingual (n = 51) or monolingual (n = 51) homes. We could not replicate the finding by Kovacs and Mehler that bilingual but not monolingual infants inhibit learned behaviour (experiment 1). However, we found that infants exposed to bilingual environments do indeed explore more than those exposed to monolingual environments, by potentially disengaging attention faster from one stimulus in order to shift attention to another (experiment 3) and by switching attention more frequently between stimuli (experiment 4). These data suggest that experience-driven adaptations may indeed result in infants exposed to bilingual environments switching attention more frequently than infants exposed to a monolingual environment.

Attentional abilities constrain language development: A cross-syndrome infant/toddler study.

Typically developing (TD) infants adapt to the social world in part by shifting the focus of their processing resources to the relevant aspects of a visual scene. Any impairment in visual orienting may therefore constrain learning and development in domains such as language. However, although something is known about visual orienting in infants at risk of autism, very little is known about it in infants/toddlers with other neurodevelopmental disorders. This is partly because previous studies focused on older children and rarely compared the children to both chronological age (CA)- and mental age (MA)-matched TD controls. Yet, if visual orienting is important for learning and development, then it is imperative to investigate it early in development and ascertain whether it relates to higher level cognitive functions such as language. We used eye-tracking technology to directly compare visual orienting in infants/toddlers with one of three neurodevelopmental disorders-Down syndrome (DS), fragile X syndrome (FXS) and Williams syndrome (WS)-matched on CA or MA to TD controls (~15 months). We also measured language ability using the Mullen Scales of Early Learning (MSEL). We found that the ability to disengage attention from a visual stimulus in order to shift it to another visual stimulus is related to language ability in infants/toddlers irrespective of group affiliation. We also found that, contrary to the literature, infants and toddlers with DS (but not WS) are slow at disengaging attention. Our data suggest that orienting attention constrains language development and is impaired in DS.

Sleep is atypical across neurodevelopmental disorders in infants and toddlers: A cross-syndrome study.

This cross-syndrome study focuses on sleep and its relationship with language development. Children with neurodevelopmental disorders present with language delay. Typical language development is constrained by numerous factors including sleep. Sleep is often disrupted in adolescents/adults with neurodevelopmental disorders. We therefore hypothesised that sleep may be disrupted, and correlate with language development, in infants/toddlers with neurodevelopmental disorders. To test our hypothesis, we obtained sleep and vocabulary size data from 75 infants/toddlers with one of three neurodevelopmental disorders (Down syndrome [DS], fragile X syndrome [FXS], Williams syndrome [WS]). Sleep was indeed disrupted in these children. It was also positively associated with receptive vocabulary size in the infants/toddlers with DS and WS (we could not test the relationship between sleep and language in FXS due to lack of power). We argue that disrupted sleep may be a common occurrence in very young children with neurodevelopmental disorders, and it may relate to their ability to acquire their first language.

Precursors to language development in typically and atypically developing infants and toddlers: the importance of embracing complexity.

In order to understand how language abilities emerge in typically and atypically developing infants and toddlers, it is important to embrace complexity in development. In this paper, we describe evidence that early language development is an experience-dependent process, shaped by diverse, interconnected, interdependent developmental mechanisms, processes, and abilities (e.g. statistical learning, sampling, functional specialization, visual attention, social interaction, motor ability). We also present evidence from our studies on neurodevelopmental disorders (e.g. Down syndrome, fragile X syndrome, Williams syndrome) that variations in these factors significantly contribute to language delay. Finally, we discuss how embracing complexity, which involves integrating data from different domains and levels of description across developmental time, may lead to a better understanding of language development and, critically, lead to more effective interventions for cases when language develops atypically.

Why a developmental perspective is critical for understanding human cognition.

The evidence that Anderson (2014) marshals in support of his theory of neural reuse is persuasive. However, his theoretical framework currently lacks a developmental dimension. We argue that an account of the fundamental aspects of developmental change, as well as the temporal context within which change occurs, would greatly enhance Anderson's theory.

Audio-visual speech perception in infants and toddlers with Down syndrome, fragile X syndrome, and Williams syndrome.

Typically-developing (TD) infants can construct unified cross-modal percepts, such as a speaking face, by integrating auditory-visual (AV) information. This skill is a key building block upon which higher-level skills, such as word learning, are built. Because word learning is seriously delayed in most children with neurodevelopmental disorders, we assessed the hypothesis that this delay partly results from a deficit in integrating AV speech cues. AV speech integration has rarely been investigated in neurodevelopmental disorders, and never previously in infants. We probed for the McGurk effect, which occurs when the auditory component of one sound (/ba/) is paired with the visual component of another sound (/ga/), leading to the perception of an illusory third sound (/da/ or /tha/). We measured AV integration in 95 infants/toddlers with Down, fragile X, or Williams syndrome, whom we matched on Chronological and Mental Age to 25 TD infants. We also assessed a more basic AV perceptual ability: sensitivity to matching vs. mismatching AV speech stimuli. Infants with Williams syndrome failed to demonstrate a McGurk effect, indicating poor AV speech integration. Moreover, while the TD children discriminated between matching and mismatching AV stimuli, none of the other groups did, hinting at a basic deficit or delay in AV speech processing, which is likely to constrain subsequent language development.

Rethinking the concepts of 'local or global processors': evidence from Williams syndrome, Down syndrome, and Autism Spectrum Disorders.

Both Williams syndrome (WS) and Autism Spectrum Disorder (ASD) have been characterized as preferentially processing local information, whereas in Down syndrome (DS) the reported tendency is to process stimuli globally. We designed a cross-syndrome, cross-task comparison to reveal similarities and differences in local/global processing in these disorders. Our in-depth study compared local/global processing across modalities (auditory-verbal/visuo-spatial) and levels of processing (high/low) in the three syndromes. Despite claims in the literature, participants with ASD or WS failed to show a consistent local processing bias, while those with DS failed to show a reliable global processing bias. Depending on the nature of the stimuli and the task, both local and global processing biases were evident in all three neurodevelopmental disorders. These findings indicate that individuals with neurodevelopmental disorders cannot simply be characterized as local or global processors.

Concurrent Relations between Face Scanning and Language: A Cross-Syndrome Infant Study.

Typically developing (TD) infants enhance their learning of spoken language by observing speakers' mouth movements. Given the fact that word learning is seriously delayed in most children with neurodevelopmental disorders, we hypothesized that this delay partly results from differences in visual face scanning, e.g., focusing attention away from the mouth. To test this hypothesis, we used an eye tracker to measure visual attention in 95 infants and toddlers with Down syndrome (DS), fragile X syndrome (FXS), and Williams syndrome (WS), and compared their data to 25 chronological- and mental-age matched 16-month-old TD controls. We presented participants with two talking faces (one on each side of the screen) and a sound (/ga/). One face (the congruent face) mouthed the syllable that the participants could hear (i.e., /ga/), while the other face (the incongruent face) mouthed a different syllable (/ba/) from the one they could hear. As expected, we found that TD children with a relatively large vocabulary made more fixations to the mouth region of the incongruent face than elsewhere. However, toddlers with FXS or WS who had a relatively large receptive vocabulary made more fixations to the eyes (rather than the mouth) of the incongruent face. In DS, by contrast, fixations to the speaker's overall face (rather than to her eyes or mouth) predicted vocabulary size. These findings suggest that, at some point in development, different processes or strategies relating to visual attention are involved in language acquisition in DS, FXS, and WS. This knowledge may help further explain why language is delayed in children with neurodevelopmental disorders. It also raises the possibility that syndrome-specific interventions should include an early focus on efficient face-scanning behaviour.

Face processing in Williams syndrome is already atypical in infancy.

Face processing is a crucial socio-cognitive ability. Is it acquired progressively or does it constitute an innately-specified, face-processing module? The latter would be supported if some individuals with seriously impaired intelligence nonetheless showed intact face-processing abilities. Some theorists claim that Williams syndrome (WS) provides such evidence since, despite IQs in the 50s, adolescents/adults with WS score in the normal range on standardized face-processing tests. Others argue that atypical neural and cognitive processes underlie WS face-processing proficiencies. But what about infants with WS? Do they start with typical face-processing abilities, with atypicality developing later, or are atypicalities already evident in infancy? We used an infant familiarization/novelty design and compared infants with WS to typically developing controls as well as to a group of infants with Down syndrome matched on both mental and chronological age. Participants were familiarized with a schematic face, after which they saw a novel face in which either the features (eye shape) were changed or just the configuration of the original features. Configural changes were processed successfully by controls, but not by infants with WS who were only sensitive to featural changes and who showed syndrome-specific profiles different from infants with the other neurodevelopmental disorder. Our findings indicate that theorists can no longer use the case of WS to support claims that evolution has endowed the human brain with an independent face-processing module.

Genetic and environmental vulnerabilities in children with neurodevelopmental disorders.

One might expect that children with varying genetic mutations or children raised in low socioeconomic status environments would display different deficits. Although this expectation may hold for phenotypic outcomes in older children and adults, cross-syndrome comparisons in infancy reveal many common neural and sociocognitive deficits. The challenge is to track dynamic trajectories over developmental time rather than focus on end states like in adult neuropsychological studies. We contrast the developmental and adult approaches with examples from the cognitive and social domains, and we conclude that static models of adult brain lesions cannot be used to account for the dynamics of change in genetic and environmentally induced disorders in children.

Social cognition in williams syndrome: genotype/phenotype insights from partial deletion patients.

Identifying genotype/phenotype relations in human social cognition has been enhanced by the study of Williams syndrome (WS). Indeed, individuals with WS present with a particularly strong social drive, and researchers have sought to link deleted genes in the WS critical region (WSCR) of chromosome 7q11.23 to this unusual social profile. In this paper, we provide details of two case studies of children with partial genetic deletions in the WSCR: an 11-year-old female with a deletion of 24 of the 28 WS genes, and a 14-year-old male who presents with the opposite profile, i.e., the deletion of only four genes at the telomeric end of the WSCR. We tested these two children on a large battery of standardized and experimental social perception and social cognition tasks - both implicit and explicit - as well as standardized social questionnaires and general psychometric measures. Our findings reveal a partial WS socio-cognitive profile in the female, contrasted with a more autistic-like profile in the male. We discuss the implications of these findings for genotype/phenotype relations, as well as the advantages and limitations of animal models and of case study approaches.

When modularization fails to occur: a developmental perspective.

We argue that models of adult cognition defined in terms of independently functioning modules cannot be applied to development, whether typical or atypical. The infant brain starts out highly interconnected, and it is only over developmental time that neural networks become increasingly specialized-that is, relatively modularized. In the case of atypical development, even when behavioural scores fall within the normal range, they are frequently underpinned by different cognitive and neural processes. In other words, in neurodevelopmental disorders the gradual process of relative modularization may fail to occur.