Social Perception in the Infant Brain and Its Link to Social Behavior

The current longitudinal study (n = 98) utilized a developmental cognitive neuroscience approach to examine whether and how variability in social perception is linked to social behavior in early human development. Cortical responses to processing dynamic faces were investigated using functional near-infrared spectroscopy at 7 months. Individual differences in sociability were measured using the Early Childhood Behavior Questionnaire at 18 months. Confirming previous work with infants and adults, functional near-infrared spectroscopy results show that viewing changing faces recruited superior temporal cortices in 7-month-old infants, adding to the view that this brain system is specialized in social perception from early in ontogeny. Our longitudinal results show that greater engagement of the right superior temporal cortex at 7 months predicts higher levels of sociability at 18 months. This suggests that early variability in social perception is linked to later differences in overtly displayed social behavior, providing novel longitudinal evidence for a social brain-behavior association.

Love on the developing brain: Maternal sensitivity and infants' neural responses to emotion in the dorsolateral prefrontal cortex

Infancy is a sensitive period of development, during which experiences of parental care are particularly important for shaping the developing brain. In a longitudinal study of N = 95 mothers and infants, we examined links between caregiving behavior (maternal sensitivity observed during a mother-infant free-play) and infants' neural response to emotion (happy, angry, and fearful faces) at 5 and 7 months of age. Neural activity was assessed using functional Near-Infrared Spectroscopy (fNIRS) in the dorsolateral prefrontal cortex (dlPFC), a region involved in cognitive control and emotion regulation. Maternal sensitivity was positively correlated with infants' neural responses to happy faces in the bilateral dlPFC and was associated with relative increases in such responses from 5 to 7 months. Multilevel analyses revealed caregiving-related individual differences in infants' neural responses to happy compared to fearful faces in the bilateral dlPFC, as well as other brain regions. We suggest that variability in dlPFC responses to emotion in the developing brain may be one correlate of early experiences of caregiving, with implications for social-emotional functioning and self-regulation.

Genetic variability in the oxytocin system is linked to individual differences in cuddliness among human infants

Pleasant touch facilitates social interactions, affiliative behavior and emotional bonding, contributing to positive infant and child development. Oxytocin is presumed to play an important role in mediating these effects of pleasant touch on brain, body and behavior. However, little is known about the role the oxytocin system plays in pleasant touch during infancy. This study examined the hypothesis that genetic variability in the oxytocin system is linked to individual differences in infants' cuddliness operationalized as parent-reported behaviors indexing an infant's motivation to seek out and enjoy caregiver touch. Our results (N = 82) show that a polymorphism in CD38 (rs3796863), previously linked with increased release of oxytocin in adults, was associated with higher reported rates of cuddliness. In contrast, infants with CD38 genotype previously linked to autism spectrum disorder (ASD) and reduced release of oxytocin in adults, was associated with lower rates of cuddliness. These findings support the hypothesis that, from early in human ontogeny, genetic variation in the oxytocin system is systematically linked to individual differences in the reported motivation to seek out, and the enjoyment of receiving, pleasant caregiver touch. This provides novel insights into the neurohormonal processes involved in pleasant touch.

Variability in the expression and perception of positive affect in human infancy

Positive emotions play a critical role in guiding human behavior and social interactions. This study examined whether and how genetic variability in the oxytocin system is linked to individual differences in expressing positive affect in human infants. Our results show that genetic variation in CD38 (rs3796863), previously linked to increased release of oxytocin, was associated with higher rates of positive affective displays among a sample of 7-month-old infants, using established parent-report measures. Moreover, infants displaying increased levels of positive affect (smiling and laughter) also showed enhanced brain responses in the right inferior frontal cortex, a brain region previously linked to perception-action coupling, when viewing others smile at them. These findings suggest that, from early in development, genetic variation in the oxytocin system is associated with individual differences in expressed positive affect, which in turn are linked to differences in perceiving positive affect. This helps uncover the neurobiological processes accounting for variability in the expression and perception of positive affect in infancy.

Extending and refining the fearful ape hypothesis

The fearful ape hypothesis (FAH) presents an evolutionary-developmental framework stipulating that in the context of cooperative caregiving, unique to human great ape group life, heightened fearfulness was adaptive. This is because from early in human ontogeny fearfulness expressed and perceived enhanced care-based responding and cooperation with mothers and others. This response extends and refines the FAH by incorporating the commentaries' suggestions and additional lines of empirical work, providing a more comprehensive and nuanced version of the FAH. Specifically, it encourages and hopes to inspire cross-species and cross-cultural, longitudinal work elucidating evolutionary and developmental functions of fear in context. Beyond fear, it can be seen as a call for an evolutionary-developmental approach to affective science.

Infant and maternal responses to emotional facial expressions: A longitudinal study

The current longitudinal study (N = 107) examined mothers' facial emotion recognition using reaction time and their infants' affect-based attention at 5, 7, and 14 months of age using eyetracking. Our results, examining maternal and infant responses to angry, fearful and happy facial expressions, show that only maternal responses to angry facial expressions were robustly and positively linked across time points, indexing a consistent trait-like response to social threat among mothers. However, neither maternal responses to happy or fearful facial expressions nor infant responses to all three facial emotions show such consistency, pointing to the changeable nature of facial emotion processing, especially among infants. In general, infants' attention toward negative emotions (i.e., angry and fear) at earlier timepoints was linked to their affect-biased attention for these emotions at 14 months but showed greater dynamic change across time. Moreover, our results provide limited evidence for developmental continuity in processing negative emotions and for the bidirectional interplay of infant affect-biased attention and maternal facial emotion recognition. This pattern of findings suggests that infants' affect-biased attention to facial expressions of emotion are characterized by dynamic changes.

Maternal recognition of positive emotion predicts sensitive parenting in infancy

Research on parent-child relationships demonstrates the importance of maternal sensitivity for the development of children's emotion regulation, social competence, and health; thus, it is important to understand the emotional-cognitive capacities underlying maternal sensitivity. We followed 120 mothers and their full-term infants from the newborn period to 5 months postpartum. Mothers' emotion recognition during the newborn period was measured using a validated facial emotion recognition task assessing discrimination (d') of six facial expressions of emotion: happiness, fear, anger, sadness, disgust, and neutrality. Maternal behavior at 5 months postpartum was coded from a mother-infant free-play session using Ainsworth's Sensitivity Scales. Preregistered analyses revealed that mothers' ability to detect happiness specifically (but not other emotions such as fear or sadness) in the neonatal period predicted greater observed sensitivity 4 months later, β = .30, p = .002, ΔR² = .08. Results suggest that maternal recognition of positive emotion may be uniquely predictive of sensitive behavior in low-stress parent-infant interaction contexts. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Examining the Role of Socioeconomic Status and Maternal Sensitivity in Predicting Functional Brain Network Connectivity in 5-Month-Old Infants

Infancy is a sensitive period of human brain development that is plastically shaped by environmental factors. Both proximal factors, such as sensitive parenting, and distal factors, such as socioeconomic status (SES), are known predictors of individual differences in structural and functional brain systems across the lifespan, yet it is unclear how these familial and contextual factors work together to shape functional brain development during infancy, particularly during the first months of life. In the current study, we examined pre-registered hypotheses regarding the interplay between these factors to assess how maternal sensitivity, within the broader context of socioeconomic variation, relates to the development of functional connectivity in long-range cortical brain networks. Specifically, we measured resting-state functional connectivity in three cortical brain networks (fronto-parietal network, default mode network, homologous-interhemispheric connectivity) using functional near-infrared spectroscopy (fNIRS), and examined the associations between maternal sensitivity, SES, and functional connectivity in a sample of 5-month-old infants and their mothers (N = 50 dyads). Results showed that all three networks were detectable during a passive viewing task, and that maternal sensitivity was positively associated with functional connectivity in the default mode network, such that infants with more sensitive mothers exhibited enhanced functional connectivity in this network. Contrary to hypotheses, we did not observe any associations of SES with functional connectivity in the brain networks assessed in this study. This suggests that at 5 months of age, maternal sensitivity is an important proximal environmental factor associated with individual differences in functional connectivity in a long-range cortical brain network implicated in a host of emotional and social-cognitive brain processes.

The human fear paradox: Affective origins of cooperative care

Already as infants humans are more fearful than our closest living primate relatives, the chimpanzees. Yet heightened fearfulness is mostly considered maladaptive, as it is thought to increase the risk of developing anxiety and depression. How can this human fear paradox be explained? The fearful ape hypothesis presented herein stipulates that, in the context of cooperative caregiving and provisioning unique to human great ape group life, heightened fearfulness was adaptive. This is because from early in ontogeny fearfulness expressed and perceived enhanced care-based responding and provisioning from, while concurrently increasing cooperation with, mothers and others. This explanation is based on a synthesis of existing research with human infants and children, demonstrating a link between fearfulness, greater sensitivity to and accuracy in detecting fear in others, and enhanced levels of cooperative behaviors. These insights critically advance current evolutionary theories of human cooperation by adding an early-developing affective component to the human cooperative makeup. Moreover, the current proposal has important cultural, societal, and health implications, as it challenges the predominant view in Western, educated, industrialized, rich, and democratic (WEIRD) societies that commonly construe fearfulness as a maladaptive trait, potentially ignoring its evolutionary adaptive functions.

Fairness takes time: Development of cooperative decision making in fairness context

The current study examined the development of fairness behavior and tested whether children's fair choices are fast and intuitive or slow and deliberate. Reaction times were measured while 4- to 9-year-olds (N = 94, 49 girls, 84.6% White) completed a novel social decision-making task contrasting fair choices with selfish choices. Fairness behavior increased during childhood, shifting from predominantly selfish choices among young children to fair choices by 7 years of age. Moreover, young children's fair choices were slow and deliberate, whereas reaction times did not predict older children's choices. These findings contrast with adults' intuitive cooperation and point to protracted development and learning of cooperative decision making in fairness contexts.

Mother's engagement with infant linked to infant's responding to threat

The early development of threat perception in infancy might be dependent on caregiver context, but this link has not yet been studied in human infants. This study examined the emergence of the young infant's response to threat in the context of variations in caregiving behavior. Eighty infant-caregiver dyads (39 female infants, all of western European descent) visited the laboratory when the infant was 5 months old. Each dyad completed a free-play task, from which we coded for the mother's level of engagement: the amount of talking, close proximity, positive affect, and attention directed toward the infant. When the infant was 7 months old, they came back to the laboratory and we used functional near infrared spectroscopy and eye tracking to measure infants' neural and attentional responses to threatening angry faces. In response to threat, infants of more-engaged mothers showed increased brain responses in the left dorsolateral prefrontal cortex-a brain region associated with emotion regulation and cognitive control among adults-and reduced attentional avoidance. These results point to a role for caregiver behavioral context in the early development of brain systems involved in human threat responding.

Insights into the uniquely human origins of understanding other minds

We summarize research and theory to show that, from early in human ontogeny, much information about other minds can be gleaned from reading the eyes. This analysis suggests that eyes serve as uniquely human windows into other minds, which critically extends the target article by drawing attention to what might be considered the neurodevelopmental origins of knowledge attribution in humans.

Genetic variation in the oxytocin system and its link to social motivation in human infants

Frontal brain asymmetry has been linked to motivational processes in infants and adults, with left lateralization reflecting motivation to approach and right lateralization reflecting motivation to withdraw. We examined the hypothesis that variability in infants' social motivation may be linked to genetic variation in the oxytocin system. Eleven-month-old infants' brain responses and looking preferences to smiling and frowning individuals were assessed in conjunction with a polymorphism in CD38 (rs3796863) linked to autism spectrum disorder (ASD) and reduced oxytocin. Frontal brain asymmetry and looking preferences differed as a function of CD38 genotype. While non-risk A-allele carriers displayed left lateralization to smiling faces (approach) and a heightened looking preference for the individual who smiled, infants with the CC (ASD risk) genotype displayed withdrawal from smiling faces and a preference for the individual who frowned. Findings demonstrate that the oxytocin system is linked to brain and behavioral markers of social motivation in infancy.

Becoming uniquely human? Comparing chimpanzee to human infancy

Does comparing behavioral development between chimpanzees and humans during infancy hold the key to understanding what is uniquely human? Recent work shows that while many behaviors emerge at similar ages in chimpanzees, human infants develop behavioral traits underpinning our prosocial and ultra-cooperative nature at a much accelerated rate.

Variability in Infants' Functional Brain Network Connectivity Is Associated With Differences in Affect and Behavior

Variability in functional brain network connectivity has been linked to individual differences in cognitive, affective, and behavioral traits in adults. However, little is known about the developmental origins of such brain-behavior correlations. The current study examined functional brain network connectivity and its link to behavioral temperament in typically developing newborn and 1-month-old infants (M [age] = 25 days; N = 75) using functional near-infrared spectroscopy (fNIRS). Specifically, we measured long-range connectivity between cortical regions approximating fronto-parietal, default mode, and homologous-interhemispheric networks. Our results show that connectivity in these functional brain networks varies across infants and maps onto individual differences in behavioral temperament. Specifically, connectivity in the fronto-parietal network was positively associated with regulation and orienting behaviors, whereas connectivity in the default mode network showed the opposite effect on these behaviors. Our analysis also revealed a significant positive association between the homologous-interhemispheric network and infants' negative affect. The current results suggest that variability in long-range intra-hemispheric and cross-hemispheric functional connectivity between frontal, parietal, and temporal cortex is associated with individual differences in affect and behavior. These findings shed new light on the brain origins of individual differences in early-emerging behavioral traits and thus represent a viable novel approach for investigating developmental trajectories in typical and atypical neurodevelopment.

Probing infants' sensitivity to pupil size when viewing eyes

Sensitive responding to eye cues plays a key role in human social interactions. Pupil size provides subtle cues regarding a social interaction partner's arousal states. The current study assessed infants' sensitivity to and preference for differences in pupil size. Specifically, we examined White 14-month-old infants' pupillary responses when viewing own-race and other-race (Asian) eyes with dilating, constricting, and static medium-sized pupils. Our results show that, independent of race, infants' pupils dilated more when viewing eyes with dynamically changing (dilating and constricting) pupils than when viewing eyes with non-changing, static, and medium-sized pupils. We also measured infants' looking preferences, showing that, independent of race, infants preferentially attended to eyes with dilated pupils. Moreover, our results show that infants orient more quickly to pupillary changes in own-race eyes than in other-race eyes. These findings demonstrate that infants detect, but do not mimic, changes in pupil size in others and show a preference for eyes with dilated pupils.

Impression Formation in the Human Infant Brain

Forming an impression of another person is an essential aspect of human social cognition linked to medial prefrontal cortex (mPFC) function in adults. The current study examined the neurodevelopmental origins of impression formation by testing the hypothesis that infants rely on processes localized in mPFC when forming impressions about individuals who appear friendly or threatening. Infants’ brain responses were measured using functional near-infrared spectroscopy while watching 4 different face identities displaying either smiles or frowns directed toward or away from them (N = 77). This was followed by a looking preference test for these face identities (now displaying a neutral expression) using eyetracking. Our results show that infants’ mPFC responses distinguish between smiling and frowning faces when directed at them and that these responses predicted their subsequent person preferences. This suggests that the mPFC is involved in impression formation in human infants, attesting to the early ontogenetic emergence of brain systems supporting person perception and adaptive behavior.

Correction to: Epigenetic tuning of brain signal entropy in emergent human social behavior

An amendment to this paper has been published and can be accessed via the original article.

Epigenetic tuning of brain signal entropy in emergent human social behavior

BACKGROUND

How the brain develops accurate models of the external world and generates appropriate behavioral responses is a vital question of widespread multidisciplinary interest. It is increasingly understood that brain signal variability-posited to enhance perception, facilitate flexible cognitive representations, and improve behavioral outcomes-plays an important role in neural and cognitive development. The ability to perceive, interpret, and respond to complex and dynamic social information is particularly critical for the development of adaptive learning and behavior. Social perception relies on oxytocin-regulated neural networks that emerge early in development.

METHODS

We tested the hypothesis that individual differences in the endogenous oxytocinergic system early in life may influence social behavioral outcomes by regulating variability in brain signaling during social perception. In study 1, 55 infants provided a saliva sample at 5 months of age for analysis of individual differences in the oxytocinergic system and underwent electroencephalography (EEG) while listening to human vocalizations at 8 months of age for the assessment of brain signal variability. Infant behavior was assessed via parental report. In study 2, 60 infants provided a saliva sample and underwent EEG while viewing faces and objects and listening to human speech and water sounds at 4 months of age. Infant behavior was assessed via parental report and eye tracking.

RESULTS

We show in two independent infant samples that increased brain signal entropy during social perception is in part explained by an epigenetic modification to the oxytocin receptor gene (OXTR) and accounts for significant individual differences in social behavior in the first year of life. These results are measure-, context-, and modality-specific: entropy, not standard deviation, links OXTR methylation and infant behavior; entropy evoked during social perception specifically explains social behavior only; and only entropy evoked during social auditory perception predicts infant vocalization behavior.

CONCLUSIONS

Demonstrating these associations in infancy is critical for elucidating the neurobiological mechanisms accounting for individual differences in cognition and behavior relevant to neurodevelopmental disorders. Our results suggest that an epigenetic modification to the oxytocin receptor gene and brain signal entropy are useful indicators of social development and may hold potential diagnostic, therapeutic, and prognostic value.

The developmental origins of subliminal face processing

Sensitive responding to facial information is of key importance during human social interactions. Research shows that adults glean much information from another person's face without conscious perception, attesting to the robustness of face processing in the service of adaptive social functioning. Until recently, it was unclear whether such subliminal face processing is an outcome of extensive learning, resulting in adult face processing skills, or an early defining feature of human face processing. Here, we review recent research examining the early ontogeny and brain correlates of subliminal face processing, demonstrating that subliminal face processing: (1) emerges during the first year of life; (2) is multifaceted in response to transient (gaze, emotion) and stable (trustworthiness) facial cues; (3) systematically elicits frontal brain responses linked to attention allocation. The synthesized research suggests that subliminal face processing emerges early in human development and thus may play a foundational role during human social interactions. This offers a fresh look at the ontogenetic origins of unconscious face processing and informs theoretical accounts of human sociality.

Children's emotion perception in context: The role of caregiver touch and relationship quality

From early in development, attention to emotional facial expressions is biased toward threat. We examined whether caregiver availability affects children's emotion perception and possibly reduces threat bias. In 3 experiments, 4- and 5-year-old children were asked to detect threatening (angry) and nonthreatening (happy) facial expressions on a touch screen. Children completed the emotion detection task either with or without their caregiver sitting next to them on a bench, first using a between-subjects design where each child completed the task once (Experiment 1; N = 40) and then using a within-subjects design where each child completed the task twice (Experiment 2; N = 20). In Experiments 1 and 2, mere caregiver presence had no effect on children's emotion detection or threat bias. In Experiment 3, we increased the salience of caregiver presence by having children complete the task while holding hands with their caregiver (Experiment 3; N = 45). In dyads reporting high quality child-caregiver relationships, handholding facilitated detection of happy faces and significantly reduced children's threat bias. These findings suggest that caregiver touch impacts emotion perception in children as a function of relationship quality and that caregiver context plays a role in shaping children's responses to their social environment. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Epigenetic dynamics in infancy and the impact of maternal engagement

The contribution of nature versus nurture to the development of human behavior has been debated for centuries. Here, we offer a piece to this complex puzzle by identifying the human endogenous oxytocin system-known for its critical role in mammalian sociality-as a system sensitive to its early environment and subject to epigenetic change. Recent animal work suggests that early parental care is associated with changes in DNA methylation of conserved regulatory sites within the oxytocin receptor gene (OXTRm). Through dyadic modeling of behavior and OXTRm status across the first year and a half of life, we translated these findings to 101 human mother-infant dyads. We show that OXTRm is dynamic in infancy and its change is predicted by maternal engagement and reflective of behavioral temperament. We provide evidence for an early window of environmental epigenetic regulation of the oxytocin system, facilitating the emergence of individual differences in human behavior.

Neural evidence for the impact of facial trustworthiness on object processing in a gaze-cueing task in 7-month-old infants

Humans automatically judge a person's trustworthiness solely based on facial features and use these judgments to inform subsequent behavior. While recent studies demonstrate that already infants are sensitive to variance in facial trustworthiness, it remains unclear whether this variance also influences subsequent socio-cognitive processes. We investigated event-related brain responses (ERPs) to faces varying in trustworthiness in a gaze-cueing paradigm in 7-month-old infants. Our analysis focused on the ERP responses to cued or un-cued objects shown in isolation after the gaze-cue was presented. We observed an enhanced occipital positive slow wave (PSW) to un-cued compared to cued objects, suggesting a gaze-cueing effect irrespective of facial trustworthiness. Furthermore, objects in the un-cued condition elicited a larger fronto-central Nc when the gaze cue was provided by trustworthy compared to untrustworthy faces. This pattern suggests that while gaze cueing occurs irrespective of facial trustworthiness, allocation of attention, as indexed by modulation of the Nc amplitude, varies as a function of trustworthiness. Taken together, our results show that facial trustworthiness impacts object processing in the context of a gaze cueing paradigm, adding to the notion that it serves as an important social cue from early in ontogeny.

Psychological effects of breastfeeding on children and mothers

While the nutritional and physical health benefits of breastfeeding are well established, accumulating research demonstrates the far-reaching psychological effects of breastfeeding on children and their mothers. Here, we provide a non-exhaustive review of the empirical evidence, showing that breastfeeding impacts children's brain, cognitive, and socio-emotional development. In mothers, research is presented indicating that breastfeeding influences mood, affect, stress, and maternal care. The current review aims to provide a broad overview of existing findings on the psychological effects of breastfeeding, highlighting the important role that breastfeeding plays across several dimensions of psychological functioning. We also discuss the potential mechanisms that may underpin the observed effects, provide a constructive commentary on the limitations of the existing work, and put forth some considerations when evaluating this line of research.

Epigenetic modification of the oxytocin receptor gene is associated with emotion processing in the infant brain

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First developmental neuroimaging epigenetics study with human infants.

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Oxytocin receptor gene methylation (OXTRm) assessed in a large sample of infants.

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OXTRm predicts inferior frontal brain responses to emotional faces using fNIRS.

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Higher OXTRm linked to enhanced brain responses to angry and fearful faces.

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OXTRm contributes to variability in social brain function early in ontogeny.

The neural capacity to discriminate between emotions emerges early in development, though little is known about specific factors that contribute to variability in this vital skill during infancy. In adults, DNA methylation of the oxytocin receptor gene (OXTRm) is an epigenetic modification that is variable, predictive of gene expression, and has been linked to autism spectrum disorder and the neural response to social cues. It is unknown whether OXTRm is variable in infants, and whether it is predictive of early social function. Implementing a developmental neuroimaging epigenetics approach in a large sample of infants (N = 98), we examined whether OXTRm is associated with neural responses to emotional expressions. OXTRm was assessed at 5 months of age. At 7 months of age, infants viewed happy, angry, and fearful faces while functional near-infrared spectroscopy was recorded. We observed that OXTRm shows considerable variability among infants. Critically, infants with higher OXTRm show enhanced responses to anger and fear and attenuated responses to happiness in right inferior frontal cortex, a region implicated in emotion processing through action-perception coupling. Findings support models emphasizing oxytocin’s role in modulating neural response to emotion and identify OXTRm as an epigenetic mark contributing to early brain function.

The neurodevelopmental precursors of altruistic behavior in infancy

Altruistic behavior is considered a key feature of the human cooperative makeup, with deep ontogenetic roots. The tendency to engage in altruistic behavior varies between individuals and has been linked to differences in responding to fearful faces. The current study tests the hypothesis that this link exists from early in human ontogeny. Using eye tracking, we examined whether attentional responses to fear in others at 7 months of age predict altruistic behavior at 14 months of age. Our analysis revealed that altruistic behavior in toddlerhood was predicted by infants' attention to fearful faces but not happy or angry faces. Specifically, infants who showed heightened initial attention to (i.e., prolonged first look) followed by greater disengagement (i.e., reduced attentional bias over 15 seconds) from fearful faces at 7 months displayed greater prosocial behavior at 14 months of age. Our data further show that infants' attentional bias to fearful faces and their altruistic behavior was predicted by brain responses in the dorsolateral prefrontal cortex (dlPFC), measured through functional near-infrared spectroscopy (fNIRS). This suggests that, from early in ontogeny, variability in altruistic helping behavior is linked to our responsiveness to seeing others in distress and brain processes implicated in attentional control. These findings critically advance our understanding of the emergence of altruism in humans by identifying responsiveness to fear in others as an early precursor contributing to variability in prosocial behavior.

Early Reputation Management: Three-Year-Old Children Are More Generous Following Exposure to Eyes

To enhance their reputations, adults and even 5-year-old children behave more prosocially when being observed by others. However, it remains unknown whether children younger than five also manage their reputations. One established paradigm for assessing reputation management is the 'watching eyes paradigm,' in which adults have been found to be more prosocial in the presence of eyes versus control images. However, the robustness of this effect in adults has recently been called into question, and it has never been demonstrated in children. In Study 1, we used a method similar to that used in prior work: 3- and 5-year-old children took part in a prosocial task while in the presence of an image of eyes or flowers but without explicit mention or reference to the image. With this method, children did not show the watching eyes effect. In Study 2, 3-year-old children were tested with a modified watching eyes paradigm, wherein they first explicitly interacted either with images of eyes or with cloth flowers, and they then engaged in a prosocial task. With this modified watching eyes paradigm, 3-year-olds showed the predicted effect: They were more prosocial following exposure to eyes than flowers. These results offer potential insight into the mixed findings across the adult literature, such that the manner of exposure, and specifically how explicit the exposure is, may influence the watching eyes effect. Finally, no study to date has examined whether cues of human presence other than the eyes also influence prosociality. We found that children in the Mouth condition were prosocial at an intermediate level between the Eyes and Flowers conditions. Overall, the findings point to the remarkably early emergence of reputation management in human ontogeny.

The Eyes as Windows Into Other Minds

Eyes have been shown to play a key role during human social interactions. However, to date, no comprehensive cross-discipline model has provided a framework that can account for uniquely human responses to eye cues. In this review, I present a framework that brings together work on the phylogenetic, ontogenetic, and neural bases of perceiving and responding to eyes. Specifically, I argue for a two-process model: a first process that ensures privileged attention to information encoded in the eyes and is important for the detection of other minds and a second process that permits the decoding of information contained in the eyes concerning another person's emotional and mental states. To some degree, these processes are unique to humans, emerge during different times in infant development, can be mapped onto distinct but interconnected brain regions, and likely serve critical functions in facilitating cooperative interactions in humans. I also present evidence to show that oxytocin is a key modulator of sensitive responding to eye cues. Viewing eyes as windows into other minds can therefore be considered a hallmark feature of human social functioning deeply rooted in our biology.

Exploring the Role of Spatial Frequency Information during Neural Emotion Processing in Human Infants

Enhanced attention to fear expressions in adults is primarily driven by information from low as opposed to high spatial frequencies contained in faces. However, little is known about the role of spatial frequency information in emotion processing during infancy. In the present study, we examined the role of low compared to high spatial frequencies in the processing of happy and fearful facial expressions by using filtered face stimuli and measuring event-related brain potentials (ERPs) in 7-month-old infants (N = 26). Our results revealed that infants’ brains discriminated between emotional facial expressions containing high but not between expressions containing low spatial frequencies. Specifically, happy faces containing high spatial frequencies elicited a smaller Nc amplitude than fearful faces containing high spatial frequencies and happy and fearful faces containing low spatial frequencies. Our results demonstrate that already in infancy spatial frequency content influences the processing of facial emotions. Furthermore, we observed that fearful facial expressions elicited a comparable Nc response for high and low spatial frequencies, suggesting a robust detection of fearful faces irrespective of spatial frequency content, whereas the detection of happy facial expressions was contingent upon frequency content. In summary, these data provide new insights into the neural processing of facial emotions in early development by highlighting the differential role played by spatial frequencies in the detection of fear and happiness.

Neural evidence for the subliminal processing of facial trustworthiness in infancy

Face evaluation is thought to play a vital role in human social interactions. One prominent aspect is the evaluation of facial signs of trustworthiness, which has been shown to occur reliably, rapidly, and without conscious awareness in adults. Recent developmental work indicates that the sensitivity to facial trustworthiness has early ontogenetic origins as it can already be observed in infancy. However, it is unclear whether infants' sensitivity to facial signs of trustworthiness relies upon conscious processing of a face or, similar to adults, occurs also in response to subliminal faces. To investigate this question, we conducted an event-related brain potential (ERP) study, in which we presented 7-month-old infants with faces varying in trustworthiness. Facial stimuli were presented subliminally (below infants' face visibility threshold) for only 50ms and then masked by presenting a scrambled face image. Our data revealed that infants' ERP responses to subliminally presented faces differed as a function of trustworthiness. Specifically, untrustworthy faces elicited an enhanced negative slow wave (800-1000ms) at frontal and central electrodes. The current findings critically extend prior work by showing that, similar to adults, infants' neural detection of facial signs of trustworthiness occurs also in response to subliminal face. This supports the view that detecting facial trustworthiness is an early developing and automatic process in humans.

Audiovisual speech perception in infancy: The influence of vowel identity and infants' productive abilities on sensitivity to (mis)matches between auditory and visual speech cues

Recent studies suggest that infants' audiovisual speech perception is influenced by articulatory experience (Mugitani et al., 2008; Yeung & Werker, 2013). The current study extends these findings by testing if infants' emerging ability to produce native sounds in babbling impacts their audiovisual speech perception. We tested 44 6-month-olds on their ability to detect mismatches between concurrently presented auditory and visual vowels and related their performance to their productive abilities and later vocabulary size. Results show that infants' ability to detect mismatches between auditory and visually presented vowels differs depending on the vowels involved. Furthermore, infants' sensitivity to mismatches is modulated by their current articulatory knowledge and correlates with their vocabulary size at 12 months of age. This suggests that-aside from infants' ability to match nonnative audiovisual cues (Pons et al., 2009)-their ability to match native auditory and visual cues continues to develop during the first year of life. Our findings point to a potential role of salient vowel cues and productive abilities in the development of audiovisual speech perception, and further indicate a relation between infants' early sensitivity to audiovisual speech cues and their later language development.

Neural and Behavioral Evidence for Infants' Sensitivity to the Trustworthiness of Faces

Face evaluation is a key aspect of face processing in humans, serving important functions in regulating social interactions. Adults and preschool children readily evaluate faces with respect to a person's trustworthiness and dominance. However, it is unclear whether face evaluation is mainly a product of extensive learning or a foundational building block of face perception already during infancy. We examined infants' sensitivity to facial signs of trustworthiness (Experiment 1) and dominance (Experiment 2) by measuring ERPs and looking behavior in response to faces that varied with respect to the two facial attributes. Results revealed that 7-month-old infants are sensitive to facial signs of trustworthiness but not dominance. This sensitivity was reflected in infants' behavioral preference and in the modulation of brain responses previously linked to emotion detection from faces. These findings provide first evidence that processing faces with respect to trustworthiness has its origins in infancy and shed light on the behavioral and neural correlates of this early emerging sensitivity.

Children's altruistic behavior in context: The role of emotional responsiveness and culture

Altruistic behavior in humans is thought to have deep biological roots. Nonetheless, there is also evidence for considerable variation in altruistic behaviors among individuals and across cultures. Variability in altruistic behavior in adults has recently been related to individual differences in emotional responsiveness to fear in others. The current study examined the relation between emotional responsiveness (using eye-tracking) and altruistic behavior (using the Dictator Game) in 4 to 5-year-old children (N = 96) across cultures (India and Germany). The results revealed that increased altruistic behavior was associated with a greater responsiveness to fear faces (faster fixation), but not happy faces, in both cultures. This suggests that altruistic behavior is linked to our responsiveness to others in distress across cultures. Additionally, only among Indian children greater altruistic behavior was associated with greater sensitivity to context when responding to fearful faces. These findings further our understanding of the origins of altruism in humans by highlighting the importance of emotional processes and cultural context in the development of altruism.

Pupillary responses reveal infants' discrimination of facial emotions independent of conscious perception

Sensitive responding to others' emotions is essential during social interactions among humans. There is evidence for the existence of subcortically mediated emotion discrimination processes that occur independent of conscious perception in adults. However, only recently work has begun to examine the development of automatic emotion processing systems during infancy. In particular, it is unclear whether emotional expressions impact infants' autonomic nervous system regardless of conscious perception. We examined this question by measuring pupillary responses while subliminally and supraliminally presenting 7-month-old infants with happy and fearful faces. Our results show greater pupil dilation, indexing enhanced autonomic arousal, in response to happy compared to fearful faces regardless of conscious perception. Our findings suggest that, early in ontogeny, emotion discrimination occurs independent of conscious perception and is associated with differential autonomic responses. This provides evidence for the view that automatic emotion processing systems are an early-developing building block of human social functioning.

The developmental emergence of unconscious fear processing from eyes during infancy

From early in life, emotion detection plays an important role during social interactions. Recently, 7-month-old infants have been shown to process facial signs of fear in others without conscious perception and solely on the basis of their eyes. However, it is not known whether unconscious fear processing from eyes is present before 7months of age or only emerges at around 7months. To investigate this question, we measured 5-month-old infants' event-related potentials (ERPs) in response to subliminally presented fearful and non-fearful eyes and compared these with 7-month-old infants' ERP responses from a previous study. Our ERP results revealed that only 7-month-olds, but not 5-month-olds, distinguished between fearful and non-fearful eyes. Specifically, 7-month-olds' processing of fearful eyes was reflected in early visual processes over occipital cortex and later attentional processes over frontal cortex. This suggests that, in line with prior work on the conscious detection of fearful faces, the brain processes associated with the unconscious processing of fearful eyes develop between 5 and 7months of age. More generally, these findings support the notion that emotion perception and the underlying brain processes undergo critical change during the first year of life. Therefore, the current data provide further evidence for viewing infancy as a formative period in human socioemotional functioning.

Person-centred positive emotions, object-centred negative emotions: 2-year-olds generalize negative but not positive emotions across individuals

Prior work suggests that young children do not generalize others' preferences to new individuals. We hypothesized (following Vaish et al., 2008, Psychol. Bull., 134, 383-403) that this may only hold for positive emotions, which inform the child about the person's attitude towards the object but not about the positivity of the object itself. It may not hold for negative emotions, which additionally inform the child about the negativity of the object itself. Two-year-old children saw one individual (the emoter) emoting positively or negatively towards one and neutrally towards a second novel object. When a second individual then requested an object, children generalized the emoter's negative but not her positive emotion to the second individual. Children thus draw different inferences from others' positive versus negative emotions: Whereas they view others' positive emotions as person centred, they may view others' negative emotions as object centred and thus generalizable across people. The results are discussed with relation to the functions and implications of the negativity bias.

Duration of exclusive breastfeeding is associated with differences in infants' brain responses to emotional body expressions

Much research has recognized the general importance of maternal behavior in the early development and programing of the mammalian offspring's brain. Exclusive breastfeeding (EBF) duration, the amount of time in which breastfed meals are the only source of sustenance, plays a prominent role in promoting healthy brain and cognitive development in human children. However, surprisingly little is known about the influence of breastfeeding on social and emotional development in infancy. In the current study, we examined whether and how the duration of EBF impacts the neural processing of emotional signals by measuring electro-cortical responses to body expressions in 8-month-old infants. Our analyses revealed that infants with high EBF experience show a significantly greater neural sensitivity to happy body expressions than those with low EBF experience. Moreover, regression analyses revealed that the neural bias toward happiness or fearfulness differs as a function of the duration of EBF. Specifically, longer breastfeeding duration is associated with a happy bias, whereas shorter breastfeeding duration is associated with a fear bias. These findings suggest that breastfeeding experience can shape the way in which infants respond to emotional signals.