14-month-old infants detect a semantic mismatch when occluded objects are mislabeled.

When infants start mastering their first language, they may start to notice when words are used incorrectly. Around 14-months of age, infants detect incorrect labeling when they are presented with an object which is labeled while still visible. However, things that are referred to are often out of sight when we communicate about them. The present study examined infants' detection of semantic mismatch when the object was occluded at the time of labeling. Specifically, we investigated whether mislabeling that referred to an occluded object could elicit a semantic mismatch. We showed 14-month-old Danish-speaking infants events where an onscreen agent showed an object and then hid it in a box. This was followed by another agent's hand pointing at the box, and a concurrent auditory category label played, which either matched or did not match the hidden object. Our results indicate that there is an effect of semantic mismatch with a larger negativity in incongruent trials. Thus, infants detected a mismatch, as indicated by a larger n400, when occluded objects were mislabeled. This finding suggests that infants can sustain an object representation in memory and compare it to a semantic representation of an auditory category label.

Adaptable and Robust EEG Bad Channel Detection Using Local Outlier Factor (LOF).

Electroencephalogram (EEG) data are typically affected by artifacts. The detection and removal of bad channels (i.e., with poor signal-to-noise ratio) is a crucial initial step. EEG data acquired from different populations require different cleaning strategies due to the inherent differences in the data quality, the artifacts' nature, and the employed experimental paradigm. To deal with such differences, we propose a robust EEG bad channel detection method based on the Local Outlier Factor (LOF) algorithm. Unlike most existing bad channel detection algorithms that look for the global distribution of channels, LOF identifies bad channels relative to the local cluster of channels, which makes it adaptable to any kind of EEG. To test the performance and versatility of the proposed algorithm, we validated it on EEG acquired from three populations (newborns, infants, and adults) and using two experimental paradigms (event-related and frequency-tagging). We found that LOF can be applied to all kinds of EEG data after calibrating its main hyperparameter: the LOF threshold. We benchmarked the performance of our approach with the existing state-of-the-art (SoA) bad channel detection methods. We found that LOF outperforms all of them by improving the F1 Score, our chosen performance metric, by about 40% for newborns and infants and 87.5% for adults.

Semantic systems are mentalistically activated for and by social partners.

A recently discovered electrophysiological response, the social N400, suggests that we use our language system to track how social partners comprehend language. Listeners show an increased N400 response, when themselves not, only a communicative partner experiences a semantic incongruity. Does the N400 reflect purely semantic or mentalistic computations as well? Do we attribute language comprehension to communicative partners using our semantic systems? In five electrophysiological experiments we identified two subcomponents of the social N400. First, we manipulated the presence-absence of an Observer during object naming: the semantic memory system was activated by the presence of a social partner in addition to semantic predictions for the self. Next, we induced a false belief-and a consequent miscomprehension-in the Observer. Participants showed the social N400, over and above the social presence effect, to labels that were incongruent for the Observer, even though they were congruent for them. This effect appeared only if participants received explicit instructions to track the comprehension of the Observer. These findings suggest that the semantic systems of the brain are not merely sensitive to social information and contribute to the attribution of comprehension, but they appear to be mentalistic in nature.

Mirroring Communicative Actions: Contextual Modulation of Mu Rhythm Desynchronization in Response to the 'Back-Of-Hand' Action in 9-Month-Old Infants.

This study measured mu rhythm desynchronization (MRD), while nine-month-old infants observed an agent extend her arm and hand, palm up ('back-of-hand action') either in social (object and recipient present), individual (object present, recipient absent), or social object-absent (recipient present, object absent) situations across two experiments. In addition, infants' MRD was measured as they reached for objects. Results revealed significant mu desynchronization in the right centro-parietal region selectively for the social group, indicating that infants processed the back-of-hand action as an object-directed request. Findings suggest to extend the action reconstruction account to object-directed communicative actions as well.

NEAR: An artifact removal pipeline for human newborn EEG data.

Electroencephalography (EEG) is arising as a valuable method to investigate neurocognitive functions shortly after birth. However, obtaining high-quality EEG data from human newborn recordings is challenging. Compared to adults and older infants, datasets are typically much shorter due to newborns' limited attentional span and much noisier due to non-stereotyped artifacts mainly caused by uncontrollable movements. We propose Newborn EEG Artifact Removal (NEAR), a pipeline for EEG artifact removal designed explicitly for human newborns. NEAR is based on two key steps: 1) A novel bad channel detection tool based on the Local Outlier Factor (LOF), a robust outlier detection algorithm; 2) A parameter calibration procedure for adapting to newborn EEG data the algorithm Artifacts Subspace Reconstruction (ASR), developed for artifact removal in mobile adult EEG. Tests on simulated data showed that NEAR outperforms existing methods in removing representative newborn non-stereotypical artifacts. NEAR was validated on two developmental populations (newborns and 9-month-old infants) recorded with two different experimental designs (frequency-tagging and ERP). Results show that NEAR artifact removal successfully reproduces established EEG responses from noisy datasets, with a higher statistical significance than the one obtained by existing artifact removal methods. The EEGLAB-based NEAR pipeline is freely available at https://github.com/vpKumaravel/NEAR.

The role of social signals in segmenting observed actions in 18-month-old children.

Learning about actions requires children to identify the boundaries of an action and its units. Whereas some action units are easily identified, parents can support children's action learning by adjusting the presentation and using social signals. However, currently, little is understood regarding how children use these signals to learn actions. In the current study, we investigate the possibility that communicative signals are a particularly suitable cue for segmenting events. We investigated this hypothesis by presenting 18-month-old children (N = 60) with short action sequences consisting of toy animals either hopping or sliding across a board into a house, but interrupting this two-step sequence either (a) using an ostensive signal as a segmentation cue, (b) using a non-ostensive segmentation cue and (c) without additional segmentation information between the actions. Marking the boundary using communicative signals increased children's imitation of the less salient sliding action. Imitation of the hopping action remained unaffected. Crucially, marking the boundary of both actions using a non-communicative control condition did not increase imitation of either action. Communicative signals might be particularly suitable in segmenting non-salient actions that would otherwise be perceived as part of another action or as non-intentional. These results provide evidence of the importance of ostensive signals at event boundaries in scaffolding children's learning.

Understanding the causes and consequences of variability in infant ERP editing practices.

The current study examined the effects of variability on infant event-related potential (ERP) data editing methods. A widespread approach for analyzing infant ERPs is through a trial-by-trial editing process. Researchers identify electroencephalogram (EEG) channels containing artifacts and reject trials that are judged to contain excessive noise. This process can be performed manually by experienced researchers, partially automated by specialized software, or completely automated using an artifact-detection algorithm. Here, we compared the editing process from four different editors-three human experts and an automated algorithm-on the final ERP from an existing infant EEG dataset. Findings reveal that agreement between editors was low, for both the numbers of included trials and of interpolated channels. Critically, variability resulted in differences in the final ERP morphology and in the statistical results of the target ERP that each editor obtained. We also analyzed sources of disagreement by estimating the EEG characteristics that each human editor considered for accepting an ERP trial. In sum, our study reveals significant variability in ERP data editing pipelines, which has important consequences for the final ERP results. These findings represent an important step toward developing best practices for ERP editing methods in infancy research.

Infants Learn to Follow Gaze in Stages: Evidence Confirming a Robotic Prediction.

Gaze following is an early-emerging skill in infancy argued to be fundamental to joint attention and later language development. However, how gaze following emerges is a topic of great debate. Representational theories assume that in order to follow adults' gaze, infants must have a rich sensitivity to adults' communicative intention from birth. In contrast, learning-based theories hold that infants may learn to gaze follow based on low-level social reinforcement, without the need to understand others' mental states. Nagai et al. (2006) successfully taught a robot to gaze follow through social reinforcement and found that the robot learned in stages: first in the horizontal plane, and later in the vertical plane-a prediction that does not follow from representational theories. In the current study, we tested this prediction in an eye-tracking paradigm. Six-month-olds did not follow gaze in either the horizontal or vertical plane, whereas 12-month-olds and 18-month-olds only followed gaze in the horizontal plane. These results confirm the core prediction of the robot model, suggesting that children may also learn to gaze follow through social reinforcement coupled with a structured learning environment.

Electrophysiological investigation of infants' understanding of understanding.

Social cognition might play a critical role in language acquisition and comprehension, as mindreading may be necessary to infer the intended meaning of linguistic expressions uttered by communicative partners. In three electrophysiological experiments, we explored the interplay between belief attribution and language comprehension of 14-month-old infants. First, we replicated our earlier finding: infants produced an N400 effect to correctly labelled objects when the labels did not match a communicative partner's beliefs about the referents. Second, we observed no N400 when we replaced the object with another category member. Third, when we named the objects incorrectly for infants, but congruently with the partner's false belief, we observed large N400 responses, suggesting that infants retained their own perspective in addition to that of the partner. We thus interpret the observed social N400 effect as a communicational expectancy indicator because it was contingent not on the attribution of false beliefs but on semantic expectations by both the self and the communicative partner. Additional exploratory analyses revealed an early, frontal, positive-going electrophysiological response in all three experiments, which was contingent on infants' computing the comprehension of the social partner based on attributed beliefs.

Infants' conceptual representations of meaningful verbal and nonverbal sounds.

In adults, words are more effective than sounds at activating conceptual representations. We aimed to replicate these findings and extend them to infants. In a series of experiments using an eye tracker object recognition task, suitable for both adults and infants, participants heard either a word (e.g. cow) or an associated sound (e.g. mooing) followed by an image illustrating a target (e.g. cow) and a distracter (e.g. telephone). The results showed that adults reacted faster when the visual object matched the auditory stimulus and even faster in the word relative to the associated sound condition. Infants, however, did not show a similar pattern of eye-movements: only eighteen-month-olds, but not 9- or 12-month-olds, were equally fast at recognizing the target object in both conditions. Looking times, however, were longer for associated sounds, suggesting that processing sounds elicits greater allocation of attention. Our findings suggest that the advantage of words over associated sounds in activating conceptual representations emerges at a later stage during language development.

Speech Intonation Induces Enhanced Face Perception in Infants.

Infants' preference for faces with direct compared to averted eye gaze, and for infant-directed over adult-directed speech, reflects early sensitivity to social communication. Here, we studied whether infant-directed speech (IDS), could affect the processing of a face with direct gaze in 4-month-olds. In a new ERP paradigm, the word 'hello' was uttered either in IDS or adult-direct speech (ADS) followed by an upright or inverted face. We show that the face-specific N290 ERP component was larger when faces were preceded by IDS relative to ADS. Crucially, this effect is specific to upright faces, whereas inverted faces preceded by IDS elicited larger attention-related P1 and Nc. These results suggest that IDS generates communicative expectations in infants. When such expectations are met by a following social stimulus - an upright face - infants are already prepared to process it. When the stimulus is a non-social one -inverted face - IDS merely increases general attention.

Two-year-old children preferentially transmit simple actions but not pedagogically demonstrated actions.

Children are sensitive to both social and non-social aspects of the learning environment. Among social cues, pedagogical communication has been shown to not only play a role in children's learning, but also in their own active transmission of knowledge. Vredenburgh, Kushnir and Casasola, Developmental Science, 2015, 18, 645 showed that 2-year-olds are more likely to demonstrate an action to a naive adult after learning it in a pedagogical than in a non-pedagogical context. This finding was interpreted as evidence that pedagogically transmitted information has a special status as culturally relevant. Here we test the limits of this claim by setting it in contrast with an explanation in which the relevance of information is the outcome of multiple interacting social (e.g., pedagogical demonstration) and non-social properties (e.g., action complexity). To test these competing hypotheses, we varied both pedagogical cues and action complexity in an information transmission paradigm with 2-year-old children. In Experiment 1, children preferentially transmitted simple non-pedagogically demonstrated actions over pedagogically demonstrated more complex actions. In Experiment 2, when both actions were matched for complexity, we found no evidence of preferential transmission of pedagogically demonstrated actions. We discuss possible reasons for the discrepancy between our results and previous literature showing an effect of pedagogical cues on cultural transmission, and conclude that our results are compatible with the view that pedagogical and other cues interact, but incompatible with the theory of a privileged role for pedagogical cues.

"I don't know but I know who to ask": 12-month-olds actively seek information from knowledgeable adults.

Active social communication is an effective way for infants to learn about the world. Do pre-verbal and pre-pointing infants seek epistemic information from their social partners when motivated to obtain information they cannot discover independently? The present study investigated whether 12-month-olds (N = 30) selectively seek information from knowledgeable adults in situations of referential uncertainty. In a live experiment, infants were introduced to two unfamiliar adults, an Informant (reliably labeling objects) and a Non-Informant (equally socially engaging, but ignorant about object labels). At test, infants were asked to make an impossible choice-locate a novel referent among two novel objects. When facing epistemic uncertainty-but not at other phases of the procedure-infants selectively referred to the Informant rather than the Non-Informant. These results show that pre-verbal infants use social referencing to actively and selectively seek information from social partners as part of their interrogative communicative toolkit. A video abstract of this article can be viewed at https://youtu.be/23dLPsa-fAY.

Probing communication-induced memory biases in preverbal infants: Two replication attempts of Yoon, Johnson and Csibra (2008).

In a seminal study, Yoon, Johnson and Csibra [PNAS, 105, 36 (2008)] showed that nine-month-old infants retained qualitatively different information about novel objects in communicative and non-communicative contexts. In a communicative context, the infants encoded the identity of novel objects at the expense of encoding their location, which was preferentially retained in non-communicative contexts. This result had not yet been replicated. Here we attempted two replications, while also including a measure of eye-tracking to obtain more detail of infants' attention allocation during stimulus presentation. Experiment 1 was designed following the methods described in the original paper. After discussion with one of the original authors, some key changes were made to the methodology in Experiment 2. Neither experiment replicated the results of the original study, with Bayes Factor Analysis suggesting moderate support for the null hypothesis. Both experiments found differential attention allocation in communicative and non-communicative contexts, with more looking to the face in communicative than non-communicative contexts, and more looking to the hand in non-communicative than communicative contexts. High and low level accounts of these attentional differences are discussed.

Neural signatures of recognition memory in 10- to 12-month-old infants.

Understanding memory mechanisms is crucial in the study of infant social and cognitive development. Here, we show that the Nc ERP component, known to reflect frequency-related attentional and/or memory processes, is a good candidate to investigate infant recognition memory. Previous paradigms have only investigated the effect of frequency during on-line stimulus presentation, but not during stimulus encoding. In this paper, we present a novel method for measuring the neural correlates of recognition memory and the 'degree' of familiarity in 10- to 12-month-old infants. During a familiarization phase, two images were presented frequently, while another two images were presented infrequently to the infants. In the test phase, the infrequent familiar, the frequent familiar, and the novel stimuli, were all presented with equal probability. We found larger Nc amplitudes following the familiar stimuli compared to the novel ones. The 'degree' of familiarity, on the other hand, did not modulate the Nc amplitude. These results can only be explained with memory-related processes, since in our paradigm the on-line presentation frequency did not vary. Furthermore, the lack of familiarization frequency effect suggests that the Nc might be a neural correlate of declarative memory.

Fourteen-month-old infants track the language comprehension of communicative partners.

Infants employ sophisticated mechanisms to acquire their first language, including some that rely on taking the perspective of adults as speakers or listeners. When do infants first show awareness of what other people understand? We tested 14-month-old infants in two experiments measuring event-related potentials. In Experiment 1, we established that infants produce the N400 effect, a brain signature of semantic violations, in a live object naming paradigm in the presence of an adult observer. In Experiment 2, we induced false beliefs about the labeled objects in the adult observer to test whether infants keep track of the other person's comprehension. The results revealed that infants reacted to the semantic incongruity heard by the other as if they encountered it themselves: they exhibited an N400-like response, even though labels were congruous from their perspective. This finding demonstrates that infants track the linguistic understanding of social partners.

Neural signatures for sustaining object representations attributed to others in preverbal human infants.

A major feat of social beings is to encode what their conspecifics see, know or believe. While various non-human animals show precursors of these abilities, humans perform uniquely sophisticated inferences about other people's mental states. However, it is still unclear how these possibly human-specific capacities develop and whether preverbal infants, similarly to adults, form representations of other agents' mental states, specifically metarepresentations. We explored the neurocognitive bases of eight-month-olds' ability to encode the world from another person's perspective, using gamma-band electroencephalographic activity over the temporal lobes, an established neural signature for sustained object representation after occlusion. We observed such gamma-band activity when an object was occluded from the infants' perspective, as well as when it was occluded only from the other person (study 1), and also when subsequently the object disappeared, but the person falsely believed the object to be present (study 2). These findings suggest that the cognitive systems involved in representing the world from infants' own perspective are also recruited for encoding others' beliefs. Such results point to an early-developing, powerful apparatus suitable to deal with multiple concurrent representations, and suggest that infants can have a metarepresentational understanding of other minds even before the onset of language.

The Fixation Distance to the Stimulus Influences ERP Quality: An EEG and Eye Tracking N400 Study.

In a typical visual Event Related Potential (ERP) study, the stimulus is presented centrally on the screen. Normally an ERP response will be measured provided that the participant directs their gaze towards the stimulus. The aim of this study was to assess how the N400 component of an ERP was affected when the stimulus was presented in the foveal, parafoveal or peripheral vision of the participant's visual field. Utilizing stimuli that have previously produced an N400 response to action incongruities, the same stimuli sequences were presented at 0°, 4°, 8° and 12° of visual angle from a fixation location. In addition to the EEG data, eye tracking data were recorded to act as a fixation control method and to allow for eye artifact detection. The results show a significant N400 effect in the right parieto-temporal electrodes within the 0° visual angle condition. For the other conditions, the N400 effect was reduced (4°) or not present (8° and 12°). Our results suggest that the disappearance of the N400 effect with eccentricity is due to the fixation distance to the stimulus. However, variables like attentional allocation could have also had an impact on the results. This study highlights the importance of presenting a stimulus within the foveal vision of the participant in order to maximize ERP effects related to higher order cognitive processes.