Complexity of STG signals and linguistic rhythm: a methodological study for EEG data.

The superior temporal and the Heschl's gyri of the human brain play a fundamental role in speech processing. Neurons synchronize their activity to the amplitude envelope of the speech signal to extract acoustic and linguistic features, a process known as neural tracking/entrainment. Electroencephalography has been extensively used in language-related research due to its high temporal resolution and reduced cost, but it does not allow for a precise source localization. Motivated by the lack of a unified methodology for the interpretation of source reconstructed signals, we propose a method based on modularity and signal complexity. The procedure was tested on data from an experiment in which we investigated the impact of native language on tracking to linguistic rhythms in two groups: English natives and Spanish natives. In the experiment, we found no effect of native language but an effect of language rhythm. Here, we compare source projected signals in the auditory areas of both hemispheres for the different conditions using nonparametric permutation tests, modularity, and a dynamical complexity measure. We found increasing values of complexity for decreased regularity in the stimuli, giving us the possibility to conclude that languages with less complex rhythms are easier to track by the auditory cortex.

Infants' representation of asymmetric social influence.

In social groups, some individuals have more influence than others, for example, because they are learned from or because they coordinate collective actions. Identifying these influential individuals is crucial to learn about one's social environment. Here, we tested whether infants represent asymmetric social influence among individuals from observing the imitation of movements in the absence of any observable coercion or order. We defined social influence in terms of Granger causality; that is, if A influences B, then past behaviors of A contain information that predicts the behaviors and mental states of B above and beyond the information contained in the past behaviors and mental states of B alone. Infants (12-, 15-, and 18-month-olds) were familiarized with agents (imitators) influenced by the actions of another one (target). During the test, the infants observed either an imitator who was no longer influenced by the target (incongruent test) or the target who was not influenced by an imitator (neutral test). The participants looked significantly longer at the incongruent test than at the neutral test. This result shows that infants represent and generalize individuals' potential to influence others' actions and that they are sensitive to the asymmetric nature of social influence; upon learning that A influences B, they expect that the influence of A over B will remain stronger than the influence of B over A in a novel context. Because of the pervasiveness of social influence in many social interactions and relationships, its representation during infancy is fundamental to understand and predict others' behaviors.

Exposure to road traffic noise and cognitive development in schoolchildren in Barcelona, Spain: A population-based cohort study.

BACKGROUND: Road traffic noise is a prevalent and known health hazard. However, little is known yet about its effect on children's cognition. We aimed to study the association between exposure to road traffic noise and the development of working memory and attention in primary school children, considering school-outdoor and school-indoor annual average noise levels and noise fluctuation characteristics, as well as home-outdoor noise exposure. METHODS AND FINDINGS: We followed up a population-based sample of 2,680 children aged 7 to 10 years from 38 schools in Barcelona (Catalonia, Spain) between January 2012 to March 2013. Children underwent computerised cognitive tests 4 times (n = 10,112), for working memory (2-back task, detectability), complex working memory (3-back task, detectability), and inattentiveness (Attention Network Task, hit reaction time standard error, in milliseconds). Road traffic noise was measured indoors and outdoors at schools, at the start of the school year, using standard protocols to obtain A-weighted equivalent sound pressure levels, i.e., annual average levels scaled to human hearing, for the daytime (daytime LAeq, in dB). We also derived fluctuation indicators out of the measurements (noise intermittency ratio, %; and number of noise events) and obtained individual estimated indoor noise levels (LAeq) correcting for classroom orientation and classroom change between years. Home-outdoor noise exposure at home (Lden, i.e., EU indicator for the 24-hour annual average levels) was estimated using Barcelona's noise map for year 2012, according to the European Noise Directive (2002). We used linear mixed models to evaluate the association between exposure to noise and cognitive development adjusting for age, sex, maternal education, socioeconomical vulnerability index at home, indoor or outdoor traffic-related air pollution (TRAP) for corresponding school models or outdoor nitrogen dioxide (NO2) for home models. Child and school were included as nested random effects. The median age (percentile 25, percentile 75) of children in visit 1 was 8.5 (7.8; 9.3) years, 49.9% were girls, and 50% of the schools were public. School-outdoor exposure to road traffic noise was associated with a slower development in working memory (2-back and 3-back) and greater inattentiveness over 1 year in children, both for the average noise level (e.g., ‒4.83 points [95% CI: ‒7.21, ‒2.45], p-value < 0.001, in 2-back detectability per 5 dB in street levels) and noise fluctuation (e.g., ‒4.38 [‒7.08, ‒1.67], p-value = 0.002, per 50 noise events at street level). Individual exposure to the road traffic average noise level in classrooms was only associated with inattentiveness (2.49 ms [0, 4.81], p-value = 0.050, per 5 dB), whereas indoor noise fluctuation was consistently associated with all outcomes. Home-outdoor noise exposure was not associated with the outcomes. Study limitations include a potential lack of generalizability (58% of mothers with university degree in our study versus 50% in the region) and the lack of past noise exposure assessment. CONCLUSIONS: We observed that exposure to road traffic noise at school, but not at home, was associated with slower development of working memory, complex working memory, and attention in schoolchildren over 1 year. Associations with noise fluctuation indicators were more evident than with average noise levels in classrooms.

Before perceptual narrowing: The emergence of the native sounds of language.

The present study investigates the precursors of representations of phonemes in 4.5-month-olds. The emergence of phonemes has been mainly studied within the framework of perceptual narrowing, that is, infants tuning to their native language and losing sensitivity to non-native speech. One of the mechanisms behind this phenomenon is distributional learning. In this article, we tested the preference of 4.5-month-old infants using lists of pseudowords that resemble the vowel distribution of the native or a non-native language. We found that infants prefer listening to the lists mirroring the native language. The results suggest that infants can extract vowel information from novel stimuli, and they can map it on pre-existing knowledge on vowels that leads to a preference for the native lists.

Experience with research paradigms relates to infants' direction of preference.

Interpreting and predicting direction of preference in infant research has been a thorny issue for decades. Several factors have been proposed to account for familiarity versus novelty preferences, including age, length of exposure, and task complexity. The current study explores an additional dimension: experience with the experimental paradigm. We reanalyzed the data from 4 experiments on artificial grammar learning in 12-month-old infants run using the head-turn preference procedure (HPP). Participants in these studies varied substantially in their number of laboratory visits. Results show that the number of HPP studies is related to direction of preference: Infants with limited experience with the HPP setting were more likely to show familiarity preferences than infants who had amassed more experience with this paradigm. This evidence has important implications for the interpretation of experimental results: Experience with a given method or, more broadly, with the laboratory environment may affect infants' patterns of preferences.

The development of gaze following in monolingual and bilingual infants: A multi-laboratory study.

Determining the meanings of words requires language learners to attend to what other people say. However, it behooves a young language learner to simultaneously encode relevant non-verbal cues, for example, by following the direction of their eye gaze. Sensitivity to cues such as eye gaze might be particularly important for bilingual infants, as they encounter less consistency between words and objects than monolingual infants, and do not always have access to the same word-learning heuristics (e.g., mutual exclusivity). In a preregistered study, we tested the hypothesis that bilingual experience would lead to a more pronounced ability to follow another's gaze. We used a gaze-following paradigm developed by Senju and Csibra (Current Biology, 18, 2008, 668) to test a total of 93 6- to 9-month-old and 229 12- to 15-month-old monolingual and bilingual infants, in 11 laboratories located in 8 countries. Monolingual and bilingual infants showed similar gaze-following abilities, and both groups showed age-related improvements in speed, accuracy, frequency, and duration of fixations to congruent objects. Unexpectedly, bilinguals tended to make more frequent fixations to on-screen objects, whether or not they were cued by the actor. These results suggest that gaze sensitivity is a fundamental aspect of development that is robust to variation in language exposure.

Efficiency as a principle for social preferences in infancy.

Two separate research lines have shown that (1) infants expect agents to move efficiently toward goal states and that (2) infants navigate the social world selectively, preferring some individuals to others and attributing social preferences to others' agents. Here, we studied how the expectation of efficient actions influences infants' looking preferences and their inferences about others' preferences. We presented 15-month-olds with a set of videos containing three geometric figures depicting social agents. One of them (observer) watched how the other two agents acted to obtain a reward. Critically, the efficiency of their actions was manipulated. One agent reached the reward taking a direct efficient path (efficient agent), whereas the other agent took a curvilinear inefficient path (inefficient agent). At test, the observer approached each of them in two separate trials. Infants looked longer at the screen when the observer approached the inefficient agent rather than the efficient agent. In addition, infants showed a bias to track the actions of the efficient agent when efficient and inefficient agents acted simultaneously. In a second experiment, we rejected the possibility that infants' expectations in Experiment 1 resulted from differences in the movement repertoire of the agents. The results suggest that the principle of efficiency tunes infants' attention towards agents who previously acted efficiently rather than inefficiently and it guides infants' expectations in third-party scenarios-infants are surprised when a third agent approaches an agent who in the past acted inefficiently.

How does the bilingual experience sculpt the brain?

The ability to speak two languages often marvels monolinguals, although bilinguals report no difficulties in achieving this feat. Here, we examine how learning and using two languages affect language acquisition and processing as well as various aspects of cognition. We do so by addressing three main questions. First, how do infants who are exposed to two languages acquire them without apparent difficulty? Second, how does language processing differ between monolingual and bilingual adults? Last, what are the collateral effects of bilingualism on the executive control system across the lifespan? Research in all three areas has not only provided some fascinating insights into bilingualism but also revealed new issues related to brain plasticity and language learning.

The influence of bilingualism on the preference for the mouth region of dynamic faces.

Bilingual infants show an extended period of looking at the mouth of talking faces, which provides them with additional articulatory cues that can be used to boost the challenging situation of learning two languages (Pons, Bosch & Lewkowicz, 2015). However, the eye region also provides fundamental cues for emotion perception and recognition, as well as communication. Here, we explored whether the adaptations resulting from learning two languages are specific to linguistic content or if they also influence the focus of attention when looking at dynamic faces. We recorded the eye gaze of bilingual and monolingual infants (8- and 12-month-olds) while watching videos of infants and adults portraying different emotional states (neutral, crying, and laughing). When looking at infant faces, bilinguals looked longer at the mouth region as compared to monolinguals regardless of age. However, when presented with adult faces, 8-month-old bilingual infants looked longer at the mouth region and less at the eye region compared to 8-month-old monolingual infants, but no effect of language exposure was found at 12 months of age. These findings suggest that the bias to the mouth region in bilingual infants at 8 months of age can be generalized to other audiovisual dynamic faces that do not contain linguistic information. We discuss the potential implications of such bias in early social and communicative development.

Neuroanatomical Markers of Social Hierarchy Recognition in Humans: A Combined ERP/MRI Study.

Social hierarchy is an ubiquitous principle of social organization across animal species. Although some progress has been made in our understanding of how humans infer hierarchical identity, the neuroanatomical basis for perceiving key social dimensions of others remains unexplored. Here, we combined event-related potentials and structural MRI to reveal the neuroanatomical substrates of early status recognition. We designed a covertly simulated hierarchical setting in which participants performed a task either with a superior or with an inferior player. Participants showed higher amplitude in the N170 component when presented with a picture of a superior player compared with an inferior player. Crucially, the magnitude of this effect correlated with brain morphology of the posterior cingulate cortex, superior temporal gyrus, insula, fusiform gyrus, and caudate nucleus. We conclude that early recognition of social hierarchies relies on the structural properties of a network involved in the automatic recognition of social identity. SIGNIFICANCE STATEMENT: Humans can perceive social hierarchies very rapidly, an ability that is key for social interactions. However, some individuals are more sensitive to hierarchical information than others. Currently, it is unknown how brain structure supports such fast-paced processes of social hierarchy perception and their individual differences. Here, we addressed this issue for the first time by combining the high temporal resolution of event-related potentials (ERPs) and the high spatial resolution of structural MRI. This methodological approach allowed us to unveil a novel association between ERP neuromarkers of social hierarchy perception and the morphology of several cortical and subcortical brain regions typically assumed to play a role in automatic processes of social cognition. Our results are a step forward in our understanding of the human social brain.

Bilingualism at the core of the brain. Structural differences between bilinguals and monolinguals revealed by subcortical shape analysis.

Naturally acquiring a language shapes the human brain through a long-lasting learning and practice process. This is supported by previous studies showing that managing more than one language from early childhood has an impact on brain structure and function. However, to what extent bilingual individuals present neuroanatomical peculiarities at the subcortical level with respect to monolinguals is yet not well understood, despite the key role of subcortical gray matter for a number of language functions, including monitoring of speech production and language control - two processes especially solicited by bilinguals. Here we addressed this issue by performing a subcortical surface-based analysis in a sample of monolinguals and simultaneous bilinguals (N=88) that only differed in their language experience from birth. This analysis allowed us to study with great anatomical precision the potential differences in morphology of key subcortical structures, namely, the caudate, accumbens, putamen, globus pallidus and thalamus. Vertexwise analyses revealed significantly expanded subcortical structures for bilinguals compared to monolinguals, localized in bilateral putamen and thalamus, as well as in the left globus pallidus and right caudate nucleus. A topographical interpretation of our results suggests that a more complex phonological system in bilinguals may lead to a greater development of a subcortical brain network involved in monitoring articulatory processes.

Association between traffic-related air pollution in schools and cognitive development in primary school children: a prospective cohort study.

BACKGROUND: Air pollution is a suspected developmental neurotoxicant. Many schools are located in close proximity to busy roads, and traffic air pollution peaks when children are at school. We aimed to assess whether exposure of children in primary school to traffic-related air pollutants is associated with impaired cognitive development. METHODS AND FINDINGS: We conducted a prospective study of children (n = 2,715, aged 7 to 10 y) from 39 schools in Barcelona (Catalonia, Spain) exposed to high and low traffic-related air pollution, paired by school socioeconomic index; children were tested four times (i.e., to assess the 12-mo developmental trajectories) via computerized tests (n = 10,112). Chronic traffic air pollution (elemental carbon [EC], nitrogen dioxide [NO2], and ultrafine particle number [UFP; 10-700 nm]) was measured twice during 1-wk campaigns both in the courtyard (outdoor) and inside the classroom (indoor) simultaneously in each school pair. Cognitive development was assessed with the n-back and the attentional network tests, in particular, working memory (two-back detectability), superior working memory (three-back detectability), and inattentiveness (hit reaction time standard error). Linear mixed effects models were adjusted for age, sex, maternal education, socioeconomic status, and air pollution exposure at home. Children from highly polluted schools had a smaller growth in cognitive development than children from the paired lowly polluted schools, both in crude and adjusted models (e.g., 7.4% [95% CI 5.6%-8.8%] versus 11.5% [95% CI 8.9%-12.5%] improvement in working memory, p = 0.0024). Cogently, children attending schools with higher levels of EC, NO2, and UFP both indoors and outdoors experienced substantially smaller growth in all the cognitive measurements; for example, a change from the first to the fourth quartile in indoor EC reduced the gain in working memory by 13.0% (95% CI 4.2%-23.1%). Residual confounding for social class could not be discarded completely; however, the associations remained in stratified analyses (e.g., for type of school or high-/low-polluted area) and after additional adjustments (e.g., for commuting, educational quality, or smoking at home), contradicting a potential residual confounding explanation. CONCLUSIONS: Children attending schools with higher traffic-related air pollution had a smaller improvement in cognitive development.

Infants Prefer Tunes Previously Introduced by Speakers of Their Native Language.

Infants show attentional biases for certain individuals over others based on various cues. However, the role of these biases in shaping infants' preferences and learning is not clear. This study asked whether infants' preference for native speakers (Kinzler, Dupoux, & Spelke, 2007) would modulate their preferences for tunes. After getting equal exposure to two different tunes introduced by two speakers, 7-month-olds (N = 32) listened longer to the tune that was introduced by a native speaker compared to the tune that was introduced by a foreign speaker. This suggests that the social-emotional context in which exposure to stimuli occurs influences auditory preferences, and that the early emerging attentional biases might have important ramifications regarding social learning in early infancy.

Spontaneous brain activity predicts learning ability of foreign sounds.

Can learning capacity of the human brain be predicted from initial spontaneous functional connectivity (FC) between brain areas involved in a task? We combined task-related functional magnetic resonance imaging (fMRI) and resting-state fMRI (rs-fMRI) before and after training with a Hindi dental-retroflex nonnative contrast. Previous fMRI results were replicated, demonstrating that this learning recruited the left insula/frontal operculum and the left superior parietal lobe, among other areas of the brain. Crucially, resting-state FC (rs-FC) between these two areas at pretraining predicted individual differences in learning outcomes after distributed (Experiment 1) and intensive training (Experiment 2). Furthermore, this rs-FC was reduced at posttraining, a change that may also account for learning. Finally, resting-state network analyses showed that the mechanism underlying this reduction of rs-FC was mainly a transfer in intrinsic activity of the left frontal operculum/anterior insula from the left frontoparietal network to the salience network. Thus, rs-FC may contribute to predict learning ability and to understand how learning modifies the functioning of the brain. The discovery of this correspondence between initial spontaneous brain activity in task-related areas and posttraining performance opens new avenues to find predictors of learning capacities in the brain using task-related fMRI and rs-fMRI combined.

Learning phonetic categories in infancy: The role of word-context information.

Identifying the type of mechanisms at the core of phonetic categorization remains a central subject of research in infant language learning. Amongst different theories, one is that infants compute distributional information of phonemes based on their surrounding sounds (i.e., word context) such that phonemes that appear in different word contexts are more likely to be discriminated and categorized separately than phonemes that appear in similar word contexts. Following the procedure of Feldman et al. (2013a), we investigated the role of contextual information in the acquisition of phonetic categories in 8-month-old infants, using a non-native vowel contrast (English /ɒ/-/ʌ/). In Experiment 1, we established lack of discrimination of the non-native contrast without prior exposure to it. In Experiment 2, we manipulated the type of exposure prior to testing: half of the infants were exposed to minimal pair carriers (words that differ by one phoneme only; e.g., lituh and litoh), and the other half of the infants were exposed to non-minimal pair carriers (words formed by different phonemes; e.g., lituh and nutoh). All infants were tested for discrimination of the contrast (tuh vs. toh) presented as alternating (e.g., tuh-toh-tuh-toh) and non-alternating trials (e.g., tuh-tuh-tuh), as in Experiment 1. Infants in both conditions looked on average longer at alternating rather than non-alternating trials, suggesting that they discriminated the /ɒ/-/ʌ/ contrast after a brief exposure to the vowels embedded into words. Crucially, discrimination occurred regardless of whether words were minimal pair carriers or non-minimal pair carriers. A cross-experiment comparison revealed that infants showed different patterns of looking times based on whether they were exposed to the contrast before testing (Experiment 2) or not (Experiment 1). Our study shows that any type of word context helps infants to re-establish discrimination of non-native contrasts once sensitivity has been lost. These findings aid to better understand how the speech input modulates learning mechanisms during the establishment of phonetic categories in the first year of postnatal life.

Abstract processing of syllabic structures in early infancy.

Syllables are one of the fundamental building blocks of early language acquisition. From birth onwards, infants preferentially segment, process and represent the speech into syllable-sized units, raising the question of what type of computations infants are able to perform on these perceptual units. Syllables are abstract units structured in a way that allows grouping phonemes into sequences. The goal of this research was to investigate 4-to-5-month-old infants' ability to encode the internal structure of syllables, at a target age when the language system is not yet specialized on the sounds and the phonotactics of native languages. We conducted two experiments in which infants were first familiarized to lists of syllables implementing either CVC (consonant-vowel-consonant) or CCV (consonant-consonant-vowel) structures, then presented with new syllables implementing both structures at test. Experiments differ in the degree of phonological similarity between the materials used at familiarization and test. Results show that infants were able to differentiate syllabic structures at test, even when test syllables were implemented by combinations of phonemes that infants did not hear before. Only infants familiarized with CVC syllables discriminated the structures at test, pointing to a processing advantage for CVC over CCV structures. This research shows that, in addition to preferentially processing the speech into syllable-sized units, during the first months of life, infants are also capable of performing fine-grained computations within such units.

Monolingual and bilingual infants' attention to talking faces: evidence from eye-tracking and Bayesian modeling.

Introduction: A substantial amount of research from the last two decades suggests that infants' attention to the eyes and mouth regions of talking faces could be a supporting mechanism by which they acquire their native(s) language(s). Importantly, attentional strategies seem to be sensitive to three types of constraints: the properties of the stimulus, the infants' attentional control skills (which improve with age and brain maturation) and their previous linguistic and non-linguistic knowledge. The goal of the present paper is to present a probabilistic model to simulate infants' visual attention control to talking faces as a function of their language learning environment (monolingual vs. bilingual), attention maturation (i.e., age) and their increasing knowledge concerning the task at stake (detecting and learning to anticipate information displayed in the eyes or the mouth region of the speaker). Methods: To test the model, we first considered experimental eye-tracking data from monolingual and bilingual infants (aged between 12 and 18 months; in part already published) exploring a face speaking in their native language. In each of these conditions, we compared the proportion of total looking time on each of the two areas of interest (eyes vs. mouth of the speaker). Results: In line with previous studies, our experimental results show a strong bias for the mouth (over the eyes) region of the speaker, regardless of age. Furthermore, monolingual and bilingual infants appear to have different developmental trajectories, which is consistent with and extends previous results observed in the first year. Comparison of model simulations with experimental data shows that the model successfully captures patterns of visuo-attentional orientation through the three parameters that effectively modulate the simulated visuo-attentional behavior. Discussion: We interpret parameter values, and find that they adequately reflect evolution of strength and speed of anticipatory learning; we further discuss their descriptive and explanatory power.

An effect of bilingualism on the auditory cortex.

Two studies (Golestani et al., 2007; Wong et al., 2008) have reported a positive correlation between the ability to perceive foreign speech sounds and the volume of Heschl's gyrus (HG), the structure that houses the auditory cortex. More precisely, participants with larger left Heschl's gyri learned consonantal or tonal contrasts faster than those with smaller HG. These studies leave open the question of the impact of experience on HG volumes. In the current research, we investigated the effect of early language exposure on Heschl's gyrus by comparing Spanish-Catalan bilinguals who have been exposed to two languages since childhood, to a group of Spanish monolinguals matched in education, socio-economic status, and musical experience. Manual volumetric measurements of HG revealed that bilinguals have, on average, larger Heschl's gyri than monolinguals. This was corroborated, for the left Heschl's gyrus, by a voxel-based morphometry analysis showing larger gray matter volumes in bilinguals than in monolinguals. Since the bilinguals in this study were not a self-selected group, this observation provides a clear demonstration that learning a second language is a causal factor in the increased size of the auditory cortex.

EsPal: one-stop shopping for Spanish word properties.

This article introduces EsPal: a Web-accessible repository containing a comprehensive set of properties of Spanish words. EsPal is based on an extensible set of data sources, beginning with a 300 million token written database and a 460 million token subtitle database. Properties available include word frequency, orthographic structure and neighborhoods, phonological structure and neighborhoods, and subjective ratings such as imageability. Subword structure properties are also available in terms of bigrams and trigrams, biphones, and bisyllables. Lemma and part-of-speech information and their corresponding frequencies are also indexed. The website enables users either to upload a set of words to receive their properties or to receive a set of words matching constraints on the properties. The properties themselves are easily extensible and will be added over time as they become available. It is freely available from the following website: http://www.bcbl.eu/databases/espal/ .

Sensitivity to the sonority sequencing principle in rats (Rattus norvegicus).

Albeit diverse, human languages exhibit universal structures. A salient example is the syllable, an important structure of language acquisition. The structure of syllables is determined by the Sonority Sequencing Principle (SSP), a linguistic constraint according to which phoneme intensity must increase at onset, reaching a peak at nucleus (vowel), and decline at offset. Such structure generates an intensity pattern with an arch shape. In humans, sensitivity to restrictions imposed by the SSP on syllables appears at birth, raising questions about its emergence. We investigated the biological mechanisms at the foundations of the SSP, testing a nonhuman, non-vocal-learner species with the same language materials used with humans. Rats discriminated well-structured syllables (e.g., pras) from ill-structured ones (e.g., lbug) after being familiarized with syllabic structures conforming to the SSP. In contrast, we did not observe evidence that rats familiarized with syllables that violate such constraint discriminated at test. This research provides the first evidence of sensitivity to the SSP in a nonhuman species, which likely stems from evolutionary-ancient cross-species biological predispositions for natural acoustic patterns. Humans' early sensitivity to the SSP possibly emerges from general auditory processing that favors sounds depicting an arch-shaped envelope, common amongst animal vocalizations. Ancient sensory mechanisms, responsible for processing vocalizations in the wild, would constitute an entry-gate for human language acquisition.