Non-adjacent dependency learning: development, domain differences, and memory

Children learn their first language simply by listening to the linguistic utterances provided by their caregivers and other speakers around them. In order to extract meaning and grammatical rules from these utterances, children must track regularities in the input, which are omnipresent in language. The ability to discover and adapt to these statistical regularities in the input is termed statistical learning and has been suggested to be one of the key mechanisms underlying language acquisition. In this thesis, I investigated a special case of statistical learning, non-adjacent dependency (NAD) learning. NADs are grammatical dependencies between distant elements in an utterance, such as is and -ing in the sentence Mary is walking. I examined which factors play a role in the development of NAD learning by illuminating this process from different stand points: the first study compares NAD learning in the linguistic and the non-linguistic domain during the earliest stages of development, at 4 months of age. This study suggests that at this age, NAD learning seems to be domain-specific to language. The second study puts a spotlight on the development of NAD learning in the linguistic domain and proposes that there may be a sensitive period for linguistic NAD learning during early childhood. Finally, the third study shows that children can not only recall newly learned NADs in a test immediately following familiarization, but also recall them after a retention period, which is critical to show more long-term learning. Overall, the findings in this thesis further illuminate how NADs, as a spotlight into language acquisition, are learned, stored in memory, and recalled

Editors' Review and Introduction: Learning Grammatical Structures: Developmental, Cross‐Species, and Computational Approaches

Human languages all have a grammar, that is, rules that determine how symbols in a language can be combined to create complex meaningful expressions. Despite decades of research, the evolutionary, developmental, cognitive, and computational bases of grammatical abilities are still not fully understood. “Artificial Grammar Learning” (AGL) studies provide important insights into how rules and structured sequences are learned, the relevance of these processes to language in humans, and whether the cognitive systems involved are shared with other animals. AGL tasks can be used to study how human adults, infants, animals, or machines learn artificial grammars of various sorts, consisting of rules defined typically over syllables, sounds, or visual items. In this introduction, we distill some lessons from the nine other papers in this special issue, which review the advances made from this growing body of literature. We provide a critical synthesis, identify the questions that remain open, and recognize the challenges that lie ahead. A key observation across the disciplines is that the limits of human, animal, and machine capabilities have yet to be found. Thus, this interdisciplinary area of research firmly rooted in the cognitive sciences has unearthed exciting new questions and venues for research, along the way fostering impactful collaborations between traditionally disconnected disciplines that are breaking scientific ground

Statistically based chunking of nonadjacent dependencies.

How individuals learn complex regularities in the environment and generalize them to new instances is a key question in cognitive science. Although previous investigations have advocated the idea that learning and generalizing depend upon separate processes, the same basic learning mechanisms may account for both. In language learning experiments, these mechanisms have typically been studied in isolation of broader cognitive phenomena such as memory, perception, and attention. Here, we show how learning and generalization in language is embedded in these broader theories by testing learners on their ability to chunk nonadjacent dependencies—a key structure in language but a challenge to theories that posit learning through the memorization of structure. In two studies, adult participants were trained and tested on an artificial language containing nonadjacent syllable dependencies, using a novel chunking-based serial recall task involving verbal repetition of target sequences (formed from learned strings) and scrambled foils. Participants recalled significantly more syllables, bigrams, trigrams, and nonadjacent dependencies from sequences conforming to the language’s statistics (both learned and generalized sequences). They also encoded and generalized specific nonadjacent chunk information. These results suggest that participants chunk remote dependencies and rapidly generalize this information to novel structures. The results thus provide further support for learning-based approaches to language acquisition, and link statistical learning to broader cognitive mechanisms of memory

Structured sequence learning: animal abilities, cognitive operations, and language evolution

Human language is a salient example of a neurocognitive system that is specialized to process complex dependencies between sensory events distributed in time, yet how this system evolved and specialized remains unclear. Artificial Grammar Learning (AGL) studies have generated a wealth of insights into how human adults and infants process different types of sequencing dependencies of varying complexity. The AGL paradigm has also been adopted to examine the sequence processing abilities of nonhuman animals. We critically evaluate this growing literature in species ranging from mammals (primates and rats) to birds (pigeons, songbirds, and parrots) considering also cross‐species comparisons. The findings are contrasted with seminal studies in human infants that motivated the work in nonhuman animals. This synopsis identifies advances in knowledge and where uncertainty remains regarding the various strategies that nonhuman animals can adopt for processing sequencing dependencies. The paucity of evidence in the few species studied to date and the need for follow‐up experiments indicate that we do not yet understand the limits of animal sequence processing capacities and thereby the evolutionary pattern. This vibrant, yet still budding, field of research carries substantial promise for advancing knowledge on animal abilities, cognitive substrates, and language evolution.Animal science

Auditory statistical learning in children: Novel insights from an online measure

Nonadjacent dependency learning is thought to be a fundamental skill for syntax acquisition and often assessed via an offline grammaticality judgment measure. Asking judgments of children is problematic, and an offline task is suboptimal as it reflects only the outcome of the learning process, disregarding information on the learning trajectory. Therefore, and following up on recent methodological advancements in the online measurement of nonadjacent dependency learning in adults, the current study investigates if the recording of response times can be used to establish nonadjacent dependency learning in children. Forty-six children (mean age: 7.3 years) participated in a child-friendly adaptation of a nonadjacent dependency learning experiment (López-Barroso, Cucurell, Rodríguez-Fornells, & de Diego-Balaguer, 2016). They were exposed to an artificial language containing items with and without nonadjacent dependencies while their response times (online measure) were measured. After exposure, grammaticality judgments (offline measure) were collected. The results show that children are sensitive to nonadjacent dependencies, when using the online measure (the results of our offline measure did not provide evidence of learning). We therefore conclude that future studies can use online response time measures (perhaps in addition to the offline grammaticality judgments) to further investigate nonadjacent dependency learning in children

From sequences to cognitive structures : neurocomputational mechanisms

Ph. D. Thesis.Understanding how the brain forms representations of structured information distributed in time is a challenging neuroscientific endeavour, necessitating computationally and neurobiologically informed study. Human neuroimaging evidence demonstrates engagement of a fronto-temporal network, including ventrolateral prefrontal cortex (vlPFC), during language comprehension. Corresponding regions are engaged when processing dependencies between word-like items in Artificial Grammar (AG) paradigms. However, the neurocomputations supporting dependency processing and sequential structure-building are poorly understood. This work aimed to clarify these processes in humans, integrating behavioural, electrophysiological and computational evidence. I devised a novel auditory AG task to assess simultaneous learning of dependencies between adjacent and non-adjacent items, incorporating learning aids including prosody, feedback, delineated sequence boundaries, staged pre-exposure, and variable intervening items. Behavioural data obtained in 50 healthy adults revealed strongly bimodal performance despite these cues. Notably, however, reaction times revealed sensitivity to the grammar even in low performers. Behavioural and intracranial electrode data was subsequently obtained in 12 neurosurgical patients performing this task. Despite chance behavioural performance, time- and time-frequency domain electrophysiological analysis revealed selective responsiveness to sequence grammaticality in regions including vlPFC. I developed a novel neurocomputational model (VS-BIND: “Vector-symbolic Sequencing of Binding INstantiating Dependencies”), triangulating evidence to clarify putative mechanisms in the fronto-temporal language network. I then undertook multivariate analyses on the AG task neural data, revealing responses compatible with the presence of ordinal codes in vlPFC, consistent with VS-BIND. I also developed a novel method of causal analysis on multivariate patterns, representational Granger causality, capable of detecting flow of distinct representations within the brain. This alluded to top-down transmission of syntactic predictions during the AG task, from vlPFC to auditory cortex, largely in the opposite direction to stimulus encodings, consistent with predictive coding accounts. It finally suggested roles for the temporoparietal junction and frontal operculum during grammaticality processing, congruent with prior literature. This work provides novel insights into the neurocomputational basis of cognitive structure-building, generating hypotheses for future study, and potentially contributing to AI and translational efforts.Wellcome Trust, European Research Counci

Concurrent Learning of Adjacent and Nonadjacent Dependencies in Visuo-Spatial and Visuo-Verbal Sequences

Both adjacent and non-adjacent dependencies (AD and NAD) are present in natural language and other domains, yet the learning of non-adjacent sequential dependencies generally only occurs under favorable circumstances. It is currently unknown to what extent adults can learn AD and NAD, presented concurrently in spatial and verbal sequences during a single session, and whether a second session improves performance. In addition, the relationship between AD and NAD learning and other theoretically related cognitive and language processes has not yet been fully established. In this study, participants reproduced two types of sequences generated from an artificial grammar: visuo-spatial sequences with stimuli presented in four spatial locations, and visuo-verbal sequences with printed syllables. Participants were tested for incidental learning by reproducing novel sequences, half consistent with the grammar and half containing violations of either AD or NAD. The procedure was repeated on a second day. Results showed that both AD and NAD were learned in both visuo-spatial and visuo-verbal tasks, although AD learning was better than NAD and learning of NAD decreased over time. Furthermore, NAD learning for both spatial and verbal tasks was positively correlated with a language measure, whereas AD learning for both spatial and verbal tasks was negatively associated with working memory measures in the opposite domain. These results demonstrate that adults can learn both AD and NAD within a single session, but NAD learning is more easily disrupted than AD and both types of learning are sub-served by partially distinct cognitive processes. These findings increase our understanding of the processes governing the learning of AD and NAD in verbal and spatial domains

Processamento e aprendizagem de dependências não adjacentes por adultos falantes do português brasileiro

This thesis aims to investigate the learning and processing of non-adjacent dependencies (hereinafter, NADs) by adults from a psycholinguistic perspective. In this regard, we seek to assess the extent to which adults are able to learn NADs in a new language and for how long this learning is maintained, in addition to exploring the different configurations of NADs in a natural language, as well as the existence of multiple NADs that would influence the processing of these structures. With regard to processing, research using artificial languages points to ordering restrictions in NAD processing by adults (DE VRIES et al., 2012). So, our study explores the difference in the processing of multiple non-adjacent dependencies as a function of the configuration in which the dependencies are organized in a L1. We adopted the hypothesis that the existence of multiple DNAs, common in natural languages, and the configuration in which they are organized are factors that generate memory overload, being relevant for language processing. To investigate the question experimentally, two online tests were performed using the maze task with adult BP speakers. The results suggest that, although NADs in a nested configuration are possible constructions in BP, their processing is comparatively more demanding. With regard to learning, previous research suggests that NAD learning occurs early in language development (SANTELMANN & JUSCZYK, 1998; VAN HEUGTEN & SHI, 2010, among others). However, the ability of adults to learn NADs unconsciously and after a short training phase and the permanence of this learning remains uncertain. Thus, our objective was to analyze to what extent learning mechanisms that allow identification, abstraction and generalization of NADs remain in adults after consolidated the acquisition of a natural language and what would be the effects of time in maintaining this longterm learning. To investigate the question experimentally, three experimental activities using artificial language were conducted. In the first activity, participants in the experimental group listened to invented determiners and words that combined in a D+N structure for 3 minutes (step 1) and then had to choose which invented word best matched the determinant that appeared on the screen (step 2). Control group participants only performed the choice task. Participants in the experimental group had more correct and faster responses compared to the control group. In the second activity, participants were exposed to both stages for 7 consecutive days. The results showed learning of NAD patterns after the third day. The third experimental activity was performed 40 days after the second experiment, with the same participants, who were asked to repeat an experimental session. The results suggest that after 40 days, the participants still had some knowledge about NAD combinations. Taken together, our results suggest that NAD processing is essential for human cognition and that factors such as the configuration in which these dependencies are organized in a natural language can influence their processing. Furthermore, the results suggest that adult speakers with their L1 already consolidated are able to abstract new NAD patterns in an unknown language and apply them to new stimuli as efficiently as babies do, suggesting the existence of an important mechanism for the identification of morphophonological relationships of agreement, essential for human processing and cognition. In this way, the research carried out within the scope of this thesis intends to contribute to the discussion of important aspects involved in adult NAD learning and processing, both in a L1 and in a L2, focusing on the learning of non-adjacent dependencies and the processing of multiple NADs.Esta tese tem como objetivo investigar a aprendizagem e o processamento de dependências não adjacentes (doravante, DNAs) por adultos em uma perspectiva psicolinguística. Nesse sentido, buscamos avaliar em que medida adultos são capazes de aprender DNAs em uma nova língua e por quanto tempo essa aprendizagem se mantém, além de explorar as diversas configurações de DNAs em uma língua natural, assim como a existência de múltiplas DNAs que influenciariam no processamento dessas estruturas. No que diz respeito ao processamento, pesquisas usando línguas artificiais apontam para restrições de ordenamento no processamento de DNAs por adultos (De VRIES et al., 2012). Assim, nosso estudo explora diferença no processamento de múltiplas dependências não adjacentes em função da configuração em que as dependências se organizam em uma L1. Adotamos a hipótese de trabalho de que a existência de múltiplas DNAs, comuns nas línguas naturais, e a configuração em que se organizam são fatores que geram sobrecarga na memória, sendo relevante para o processamento da linguagem. Para investigar a questão experimentalmente, foram realizados dois testes online usando a tarefa de labirinto (maze task) com falantes adultos do PB. Os resultados sugerem que, apesar de DNAs em uma configuração aninhada serem construções possíveis no PB, seu processamento é comparativamente mais custoso. No que tange à aprendizagem, pesquisas anteriores sugerem que a aprendizagem de DNAs ocorre no início do desenvolvimento linguístico (SANTELMANN & JUSCZYK, 1998; VAN HEUGTEN & SHI, 2010, entre outros). Entretanto, a capacidade dos adultos de aprender DNAs implicitamente e após uma curta fase de treinamento e a permanência dessa aprendizagem permanece incerta. Assim, nosso objetivo foi analisar em que medida mecanismos de aprendizagem que permitem identificação, abstração e generalização de DNAs permanecem em adultos após consolidada a aquisição de uma língua natural e quais seriam os efeitos do tempo na manutenção dessa aprendizagem a longo prazo. Para investigar a questão experimentalmente, foram conduzidas três atividades usando língua artificial. Na primeira, participantes do grupo experimental ouviram determinantes e palavras inventados que se combinavam em uma estrutura D+N por 3 minutos (etapa 1) e, em seguida, deveriam escolher qual palavra inventada combinava melhor com o determinante que aparecia na tela (etapa 2). Participantes do grupo controle fizeram apenas a tarefa de escolha. Os participantes do grupo experimental tiveram mais respostas corretas e mais rápidas em comparação com o grupo controle. Na segunda atividade, os participantes foram expostos às duas etapas durante 7 dias consecutivos. Os resultados apontaram aprendizagem dos padrões de DNA após o terceiro dia. A terceira atividade experimental foi realizada 40 dias depois do segundo experimento, com os mesmos participantes, que foram solicitados a repetir uma sessão experimental. Os resultados sugerem que após 40 dias, os participantes ainda possuíam algum conhecimento a respeito das combinações de DNAs. Em conjunto, nossos resultados sugerem que o processamento de DNAs é essencial para a cognição humana e que fatores como a configuração em que essas dependências se organizam em uma língua natural podem influenciar no seu processamento. Além disso, os resultados sugerem que falantes adultos com sua L1 já consolidada são capazes de abstrair novos padrões de DNAs em uma língua desconhecida e aplicá-los a novos estímulos de maneira tão eficiente quanto bebês o fazem, sugerindo a existência de um mecanismo importante para a identificação das relações morfofonológicas de concordância, essenciais para o processamento e cognição humana. Dessa forma, a pesquisa desenvolvida no âmbito desta tese pretende contribuir para a discussão de aspectos importantes envolvidos na aprendizagem e processamento adulto de DNAs, tanto em uma L1 quanto em L2 focalizando a aprendizagem de dependências não adjacentes e o processamento de múltiplas DNAs.CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Characterisation of dynamics associated with skeletal muscle contraction initiated by Acetylcholine injection Ghabiba Modak.

Includes abstract.Includes bibliographical references.Lower motor neuron damage often results in flaccid paralysis in which the affected muscles are unable to be stimulated artificially via the supplying nerve. Such damage is common in patients who suffer from spinal cord injury and Multiple Sclerosis. Current practice for artificial recovery of muscle function involves stimulating the muscles directly by means of Functional Electrical Stimulation (FES), which requires 100-1000 times more current than that required for nerve stimulation, thus presenting the risk of pain receptor activation. A potential alternative exists in chemical stimulation by means of administration of the neurotransmitter, Acetylcholine (ACh). This study investigates the potential of this possibility by examining the response of two muscle types to extracellular administration of ACh