Infants' perception of emotion from body movements

No influence of emotional expression on size underestimation of upright faces

Faces are a primary means of conveying social information between humans. One important factor modulating the perception of human faces is emotional expression. Face inversion also affects perception, including judgments of emotional expression, possibly through the disruption of configural processing. One intriguing inversion effect is an illusion whereby faces appear to be physically smaller when upright than when inverted. This illusion appears to be highly selective for faces. In this study, we investigated whether the emotional expression of a face (neutral, happy, afraid, and angry) modulates the magnitude of this size illusion. Results showed that for all four expressions, there was a clear bias for inverted stimuli to be judged as larger than upright ones. This demonstrates that there is no influence of emotional expression on the size underestimation of upright faces, a surprising result given that recognition of different emotional expressions is known to be affected unevenly by inversion. Results are discussed considering recent neuroimaging research which used population receptive field (pRF) mapping to investigate the neural mechanisms underlying face perception features and which may provide an explanation for how an upright face appears smaller than an inverted one. Elucidation of this effect would lead to a greater understanding of how humans communicate.

Conception and Development of the Warmth/Affection Coding System (WACS): A Novel Hybrid Behavioral Observational Tool for Assessing Parent-to-Child Warmth

A vast body of research and theory underscores the importance of parental warmth/affection (hereby 'warmth' and 'warmth/affection' are used interchangeably) as a distinct relational process that is fundamental to core developmental processes including parent-child attachment, socialization, emotion recognition and responsivity, and empathic development. The increasing focus on parental warmth as a viable transdiagnostic and specific treatment target for Callous-Unemotional (CU) traits highlights the critical need for a reliable and valid tool for measuring this construct within clinical contexts. However, existing assessment methods have limitations in their ecological validity, clinical utility, and the comprehensiveness of their coverage of core warmth subcomponents. In response to this clinical and research need, the observational Warmth/Affection Coding System (WACS) was developed to comprehensively measure parent-to-child warmth/affection. This paper chronicles the conception and development of the WACS, which adopts a hybrid approach of utilizing both microsocial and macro-observational coding methods to capture key verbal and non-verbal subcomponents of warmth that are currently underrepresented or poorly captured by existing assessment tools. Recommendations for implementation and future directions are also discussed.

Recognition of emotional body language from dyadic and monadic point-light displays in 5-year-old children and adults

Most child studies on emotion perception used faces and speech as emotion stimuli, but little is known about children's perception of emotions conveyed by body movements, that is, emotional body language (EBL). This study aimed to investigate whether processing advantages for positive emotions in children and negative emotions in adults found in studies on emotional face and term perception also occur in EBL perception. We also aimed to uncover which specific movement features of EBL contribute to emotion perception from interactive dyads compared with noninteractive monads in children and adults. We asked 5-year-old children and adults to categorize happy and angry point-light displays (PLDs), presented as pairs (dyads) and single actors (monads), in a button-press task. By applying representational similarity analyses, we determined intra- and interpersonal movement features of the PLDs and their relation to the participants' emotional categorizations. Results showed significantly higher recognition of happy PLDs in 5-year-olds and of angry PLDs in adults in monads but not in dyads. In both age groups, emotion recognition depended significantly on kinematic and postural movement features such as limb contraction and vertical movement in monads and dyads, whereas in dyads recognition also relied on interpersonal proximity measures such as interpersonal distance. Thus, EBL processing in monads seems to undergo a similar developmental shift from a positivity bias to a negativity bias, as was previously found for emotional faces and terms. Despite these age-specific processing biases, children and adults seem to use similar movement features in EBL processing.

Seven-months-old infants show increased arousal to static emotion body expressions: Evidence from pupil dilation

Human body postures provide perceptual cues that can be used to discriminate and recognize emotions. It was previously found that 7-months-olds' fixation patterns discriminated fear from other emotion body expressions but it is not clear whether they also process the emotional content of those expressions. The emotional content of visual stimuli can increase arousal level resulting in pupil dilations. To provide evidence that infants also process the emotional content of expressions, we analyzed variations in pupil in response to emotion stimuli. Forty-eight 7-months-old infants viewed adult body postures expressing anger, fear, happiness and neutral expressions, while their pupil size was measured. There was a significant emotion effect between 1040 and 1640 ms after image onset, when fear elicited larger pupil dilations than neutral expressions. A similar trend was found for anger expressions. Our results suggest that infants have increased arousal to negative-valence body expressions. Thus, in combination with previous fixation results, the pupil data show that infants as young as 7-months can perceptually discriminate static body expressions and process the emotional content of those expressions. The results extend information about infant processing of emotion expressions conveyed through other means (e.g., faces).

Emotion is perceived accurately from isolated body parts, especially hands

Body posture and configuration provide important visual cues about the emotion states of other people. We know that bodily form is processed holistically, however, emotion recognition may depend on different mechanisms; certain body parts, such as the hands, may be especially important for perceiving emotion. This study therefore compared participants' emotion recognition performance when shown images of full bodies, or of isolated hands, arms, heads and torsos. Across three experiments, emotion recognition accuracy was above chance for all body parts. While emotions were recognized most accurately from full bodies, recognition performance from the hands was more accurate than for other body parts. Representational similarity analysis further showed that the pattern of errors for the hands was related to that for full bodies. Performance was reduced when stimuli were inverted, showing a clear body inversion effect. The high performance for hands was not due only to the fact that there are two hands, as performance remained well above chance even when just one hand was shown. These results demonstrate that emotions can be decoded from body parts. Furthermore, certain features, such as the hands, are more important to emotion perception than others. STATEMENT OF RELEVANCE: Successful social interaction relies on accurately perceiving emotional information from others. Bodies provide an abundance of emotion cues; however, the way in which emotional bodies and body parts are perceived is unclear. We investigated this perceptual process by comparing emotion recognition for body parts with that for full bodies. Crucially, we found that while emotions were most accurately recognized from full bodies, emotions were also classified accurately when images of isolated hands, arms, heads and torsos were seen. Of the body parts shown, emotion recognition from the hands was most accurate. Furthermore, shared patterns of emotion classification for hands and full bodies suggested that emotion recognition mechanisms are shared for full bodies and body parts. That the hands are key to emotion perception is important evidence in its own right. It could also be applied to interventions for individuals who find it difficult to read emotions from faces and bodies.

Three- and six-year-old children are sensitive to natural body expressions of emotion: An event-related potential emotional priming study

Body movements provide a rich source of emotional information during social interactions. Although the ability to perceive biological motion cues related to those movements begins to develop during infancy, processing those cues to identify emotions likely continues to develop into childhood. Previous studies used posed or exaggerated body movements, which might not reflect the kind of body expressions children experience. The current study used an event-related potential (ERP) priming paradigm to investigate the development of emotion recognition from more naturalistic body movements. Point-light displays (PLDs) of male adult bodies expressing happy or angry emotional movements while narrating a story were used as prime stimuli, whereas audio recordings of the words "happy" and "angry" spoken with an emotionally neutral prosody were used as targets. We recorded the ERPs time-locked to the onset of the auditory target from 3- and 6-year-old children, and we compared amplitude and latency of the N300 and N400 responses between the two age groups in the different prime-target conditions. There was an overall effect of prime for the N300 amplitude, with more negative-going responses for happy PLDs compared with angry PLDs. There was also an interaction between prime and target for the N300 latency, suggesting that all children were sensitive to the emotional congruency between body movements and words. For the N400 component, there was only an interaction among age, prime, and target for latency, suggesting an age-dependent modulation of this component when prime and target did not match in emotional information. Overall, our results suggest that the emergence of more complex emotion processing of body expressions occurs around 6 years of age, but it is not fully developed at this point in ontogeny.

Age-of-actor effects in body expression recognition of children

Investigations of developmental trajectories for emotion recognition suggest that both face- and body expression recognition increases rapidly in early childhood and reaches adult levels of performance near the age of ten. So far, little is known about whether children's ability to recognise body expressions is influenced by the age of the person they are observing. This question is investigated here by presenting 119 children and 42 young adults with videos of children, young adults and older adults expressing emotions with their whole body. The results revealed an own-age advantage for children, reflected in adult-level accuracy for videos of children for most expressions but reduced accuracy for videos of older adults. Children's recognition of older adults' expressions was not correlated with children's estimated amount of contact with older adults. Support for potential influences of social biases on performance measures was minimal. The own-age advantage was explained in terms of children's reduced familiarity with body expressions of older adults due to aging related changes in the kinematics characteristics of movements and potentially due to stronger embodiment of other children's bodily movements.

Eleven-Month-Olds Link Sound Properties With Animal Categories

We examined 11-month-olds' tendency to generalize properties to category members, an ability that may contribute to the inductive reasoning abilities observed in later developmental periods. Across three experiments, we tested 11-month-olds' (N = 113) generalization of properties within the cat and dog categories. In each experiment, infants were familiarized to animal-sound pairings (i.e., dog barking; cat meowing) and tested on this association and the generalization of the sound property to new members of the familiarized categories. After familiarization with a single exemplar, 11-month-olds generalized the sound to new category members that were both highly similar and less similar to the familiarized animal (Experiment 1). When familiarized with mismatched animal-sound pairings (Experiment 2; i.e., dog meowing; cat barking), 11-month-olds did not learn or generalize the sound properties, suggesting that infants have pre-existing expectations about the links between the characteristic sound properties and the animal categories. When familiarized with unfamiliar sound-animal pairings (Experiment 3; i.e., dog-unfamiliar sound), 11-month-olds linked the animals with the novel sounds but did not generalize to new category members. Taken together, these findings highlight the conditions under which young infants generalize properties from one exemplar to other category members.

Look up to the body: An eye-tracking investigation of 7-months-old infants' visual exploration of emotional body expressions

The human body is an important source of information to infer a person's emotional state. Research with adult observers indicate that the posture of the torso, arms and hands provide important perceptual cues for recognising anger, fear and happy expressions. Much less is known about whether infants process body regions differently for different body expressions. To address this issue, we used eye tracking to investigate whether infants' visual exploration patterns differed when viewing body expressions. Forty-eight 7-months-old infants were randomly presented with static images of adult female bodies expressing anger, fear and happiness, as well as an emotionally-neutral posture. Facial cues to emotional state were removed by masking the faces. We measured the proportion of looking time, proportion and number of fixations, and duration of fixations on the head, upper body and lower body regions for the different expressions. We showed that infants explored the upper body more than the lower body. Importantly, infants at this age fixated differently on different body regions depending on the expression of the body posture. In particular, infants spent a larger proportion of their looking times and had longer fixation durations on the upper body for fear relative to the other expressions. These results extend and replicate the information about infant processing of emotional expressions displayed by human bodies, and they support the hypothesis that infants' visual exploration of human bodies is driven by the upper body.

Waist-to-Hip Ratio Sensitivity in Early Infancy

The waist-to-hip ratio (WHR) is correlated with health and associated with sex, attractiveness, and age judgments by adults. We examined the development of sensitivity to the WHR by testing 3.5-month-old infants' (N = 71) preference between images depicting different WHRs. Female 3.5-month-olds exhibited a preference for the WHR associated with attractiveness and mate value by adults (0.7) over a larger WHR (0.9). This preference was exhibited when infants were tested on upright stimuli but not when they were tested on inverted stimuli, indicating that low-level differences (e.g., curviness) were not driving performance. This sensitivity to WHR may lay the foundation for more explicit preferences and categorical associations later in life. In contrast to females, male infants failed to exhibit a significant preference for the 0.7 WHR in either orientation, replicating previous findings of female infants' superior processing of social stimuli. Implications for theories of the development of body knowledge and sex differences in social information processing are discussed.

Expanding Simulation Models of Emotional Understanding: The Case for Different Modalities, Body-State Simulation Prominence, and Developmental Trajectories

Recent models of emotion recognition suggest that when people perceive an emotional expression, they partially activate the respective emotion in themselves, providing a basis for the recognition of that emotion. Much of the focus of these models and of their evidential basis has been on sensorimotor simulation as a basis for facial expression recognition - the idea, in short, that coming to know what another feels involves simulating in your brain the motor plans and associated sensory representations engaged by the other person's brain in producing the facial expression that you see. In this review article, we argue that simulation accounts of emotion recognition would benefit from three key extensions. First, that fuller consideration be given to simulation of bodily and vocal expressions, given that the body and voice are also important expressive channels for providing cues to another's emotional state. Second, that simulation of other aspects of the perceived emotional state, such as changes in the autonomic nervous system and viscera, might have a more prominent role in underpinning emotion recognition than is typically proposed. Sensorimotor simulation models tend to relegate such body-state simulation to a subsidiary role, despite the plausibility of body-state simulation being able to underpin emotion recognition in the absence of typical sensorimotor simulation. Third, that simulation models of emotion recognition be extended to address how embodied processes and emotion recognition abilities develop through the lifespan. It is not currently clear how this system of sensorimotor and body-state simulation develops and in particular how this affects the development of emotion recognition ability. We review recent findings from the emotional body recognition literature and integrate recent evidence regarding the development of mimicry and interoception to significantly expand simulation models of emotion recognition.

Motion or emotion: Infants discriminate emotional biological motion based on low-level visual information

Infants' ability to discriminate emotional facial expressions and tones of voice is well-established, yet little is known about infant discrimination of emotional body movements. Here, we asked if 10-20-month-old infants rely on high-level emotional cues or low-level motion related cues when discriminating between emotional point-light displays (PLDs). In Study 1, infants viewed 18 pairs of angry, happy, sad, or neutral PLDs. Infants looked more at angry vs. neutral, happy vs. neutral, and neutral vs. sad. Motion analyses revealed that infants preferred the PLD with more total body movement in each pairing. Study 2, in which infants viewed inverted versions of the same pairings, yielded similar findings except for sad-neutral. Study 3 directly paired all three emotional stimuli in both orientations. The angry and happy stimuli did not significantly differ in terms of total motion, but both had more motion than the sad stimuli. Infants looked more at angry vs. sad, more at happy vs. sad, and about equally to angry vs. happy in both orientations. Again, therefore, infants preferred PLDs with more total body movement. Overall, the results indicate that a low-level motion preference may drive infants' discrimination of emotional human walking motions.

The Sensitivity to Threat and Affiliative Reward (STAR) model and the development of callous-unemotional traits

Research implicates callous-unemotional (CU) traits (i.e., lack of empathy, prosociality, and guilt, and reduced sensitivity to others' emotions) in the development of severe and persistent antisocial behavior. To improve etiological models of antisocial behavior and develop more effective treatments, we need a better understanding of the origins of CU traits. In this review, we discuss the role of two psychobiological and mechanistic precursors to CU traits: low affiliative reward (i.e., deficits in seeking out or getting pleasure from social bonding and closeness with others) and low threat sensitivity (i.e., fearlessness to social and non-social threat). We outline the Sensitivity to Threat and Affiliative Reward (STAR) model and review studies that have examined the development of affiliative reward and threat sensitivity across animal, neuroimaging, genetic, and behavioral perspectives. We next evaluate evidence for the STAR model, specifically the claim that CU traits result from deficits in both affiliative reward and threat sensitivity. We end with constructive suggestions for future research to test the hypotheses generated by the STAR model.

Infants use knowledge of emotions to augment face perception: Evidence of top-down modulation of perception early in life

While top-down modulation is believed to be central to adult perception, the developmental origins of this ability are unclear. Here, we present a direct, behavioral investigation of top-down modulation of perception in infancy using emotional face perception as a test case. We investigated whether 9-month-olds can modulate their face perception based on predictive, auditory emotional cues without any training or familiarization procedure. Infants first heard a 3-second emotional vocal sound (happy/angry) while their gaze was held in the center of the screen. Then, they were presented with a pair of emotional and neutral faces images without any audio sound. The faces were small (4.70° × 5.80°) and presented in randomized locations outside their focus of attention. We measured the initial latency to shift gaze to look at a congruent emotional face as an index of infants' pre-attentive perception of these faces. We found that infants' face perception was augmented by preceding emotional cues: They were faster to look at the emotional face after hearing an emotionally congruent sound than an incongruent one. Moreover, the emotional sounds boosted perception of congruent faces 200 ms after the onset of the faces. These top-down effects were robust for both happy and angry emotions, indicating a flexible and active control of perception based on different top-down cues. A control study further supported the view that the Congruency effect is due to a top-down influence on face perception rather than a rapid matching of cross-modal emotional signals. Together, these findings demonstrate that top-down modulation of perception is already quite sophisticated early in development. Raw data is available on Github (https://github.com/naiqixiao/CuedEmotion.git).

'Something in the way you move': Infants are sensitive to emotions conveyed in action kinematics

Body movements, as well as faces, communicate emotions. Research in adults has shown that the perception of action kinematics has a crucial role in understanding others' emotional experiences. Still, little is known about infants' sensitivity to body emotional expressions, since most of the research in infancy focused on faces. While there is some first evidence that infants can recognize emotions conveyed in whole-body postures, it is still an open question whether they can extract emotional information from action kinematics. We measured electromyographic (EMG) activity over the muscles involved in happy (zygomaticus major, ZM), angry (corrugator supercilii, CS) and fearful (frontalis, F) facial expressions, while 11-month-old infants observed the same action performed with either happy or angry kinematics. Results demonstrate that infants responded to angry and happy kinematics with matching facial reactions. In particular, ZM activity increased while CS activity decreased in response to happy kinematics and vice versa for angry kinematics. Our results show for the first time that infants can rely on kinematic information to pick up on the emotional content of an action. Thus, from very early in life, action kinematics represent a fundamental and powerful source of information in revealing others' emotional state.

Sex-specific scanning in infancy: Developmental changes in the use of face/head and body information

The current investigation sought to differentiate between contrasting perspectives of body knowledge development by determining whether infants' adult-like scanning of male and female bodies is dependent on relevant information from the face/head alone, the body alone, or a combination of both sources. Scanning patterns of 3.5-, 6.5-, and 9-month-olds (N = 80) in response to images that contained information relevant to sex classification in either the face/head or the body were examined. The results indicate that sex-specific scanning in the presence of only one source of relevant information (i.e., face/head or body) is present only at 9 months. Thus, although sex-specific scanning of bodies emerges as early as 3.5 months, information from both faces/heads and bodies is required until sometime between 6.5 and 9 months of age. These findings constrain theories of the development of social perception by documenting the complex interplay between body and face/head processing early in life.

Infant perception of sex differences in biological motion displays

We examined mechanisms underlying infants' ability to categorize human biological motion stimuli from sex-typed walk motions, focusing on how visual attention to dynamic information in point-light displays (PLDs) contributes to infants' social category formation. We tested for categorization of PLDs produced by women and men by habituating infants to a series of female or male walk motions and then recording posthabituation preferences for new PLDs from the familiar or novel category (Experiment 1). We also tested for intrinsic preferences for female or male walk motions (Experiment 2). We found that infant boys were better able to categorize PLDs than were girls and that male PLDs were preferred overall. Neither of these effects was found to change with development across the observed age range (∼4-18 months). We conclude that infants' categorization of walk motions in PLDs is constrained by intrinsic preferences for higher motion speeds and higher spans of motion and, relatedly, by differences in walk motions produced by men and women.

Family expressiveness relates to happy emotion matching among 9-month-old infants

Perceiving and understanding the emotions of those around us is an imperative skill to develop early in life. An infant's family environment provides most of their emotional exemplars in early development. However, the relation between the early development of emotion perception and family expressiveness remains understudied. To investigate this potential link to early emotion perception development, we examined 38 infants at 9 months of age. We assessed infants' ability to match emotions across facial and vocal modalities using an intermodal matching paradigm for angry-neutral, happy-neutral, and sad-neutral pairings. We also attained family expressiveness information via parent report. Our results indicate a significant positive relation between emotion matching and family expressiveness specific to the happy-neutral condition. However, we found no evidence for emotion matching for the infants as a group in any of the three conditions. These results suggest that family expressiveness does relate to emotion matching for the earliest developing emotional category among 9-month-old infants and that emotion matching with multiple emotions at this age is a challenging task.

Bodily Communication of Emotion: Evidence for Extrafacial Behavioral Expressions and Available Coding Systems

Although scientists dating back to Darwin have noted the importance of the body in communicating emotion, current research on emotion communication tends to emphasize the face. In this article we review the evidence for bodily expressions of emotions—that is, the handful of emotions that are displayed and recognized from certain bodily behaviors (i.e., pride, joy, sadness, shame, embarrassment, anger, fear, and disgust). We also review the previously developed coding systems available for identifying emotions from bodily behaviors. Although no extant coding system provides an exhaustive list of bodily behaviors known to communicate a panoply of emotions, our review provides the foundation for developing such a system.

Can Tai Chi and Qigong Postures Shape Our Mood? Toward an Embodied Cognition Framework for Mind-Body Research

Dynamic and static body postures are a defining characteristic of mind-body practices such as Tai Chi and Qigong (TCQ). A growing body of evidence supports the hypothesis that TCQ may be beneficial for psychological health, including management and prevention of depression and anxiety. Although a variety of causal factors have been identified as potential mediators of such health benefits, physical posture, despite its visible prominence, has been largely overlooked. We hypothesize that body posture while standing and/or moving may be a key therapeutic element mediating the influence of TCQ on psychological health. In the present paper, we summarize existing experimental and observational evidence that suggests a bi-directional relationship between body posture and mental states. Drawing from embodied cognitive science, we provide a theoretical framework for further investigation into this interrelationship. We discuss the challenges involved in such an investigation and propose suggestions for future studies. Despite theoretical and practical challenges, we propose that the role of posture in mind-body exercises such as TCQ should be considered in future research.

Visual scanning of male and female bodies in infancy

This study addressed the development of attention to information that is socially relevant to adults by examining infants' (N=64) scanning patterns of male and female bodies. Infants exhibited systematic attention to regions associated with sex-related scanning by adults, with 3.5- and 6.5-month-olds looking longer at the torsos of females than of males and looking longer at the legs of males than of females. However, this pattern of looking was not found when infants were tested on headless bodies in Experiment 2, suggesting that infants' differential gaze pattern in Experiment 1 was not due to low-level stimulus features, such as clothing, and also indicating that facial/head information is necessary for infants to exhibit sex-specific scanning. We discuss implications for models of face and body knowledge development.

Development of body emotion perception in infancy: From discrimination to recognition

Research suggests that infants progress from discrimination to recognition of emotions in faces during the first half year of life. It is unknown whether the perception of emotions from bodies develops in a similar manner. In the current study, when presented with happy and angry body videos and voices, 5-month-olds looked longer at the matching video when they were presented upright but not when they were inverted. In contrast, 3.5-month-olds failed to match even with upright videos. Thus, 5-month-olds but not 3.5-month-olds exhibited evidence of recognition of emotions from bodies by demonstrating intermodal matching. In a subsequent experiment, younger infants did discriminate between body emotion videos but failed to exhibit an inversion effect, suggesting that discrimination may be based on low-level stimulus features. These results document a developmental change from discrimination based on non-emotional information at 3.5 months to recognition of body emotions at 5 months. This pattern of development is similar to face emotion knowledge development and suggests that both the face and body emotion perception systems develop rapidly during the first half year of life.

Age-Dependent Changes of Thinking about Verbs

We investigated the knowledge of emotional and motor verbs in children and adolescents from three age ranges (8–11, 12–15, 16–19 years). Participants estimated the verbs familiarity, age of acquisition, valence, arousal, imageability, and motor- and emotion-relatedness. Participants were familiar with the verbs in our dataset. The younger (8–11) attributed an emotional character to the verbs less frequently than the middle (12–15) and the older (16–19) groups. In the 8–11 group males rated the verbs as emotion-related less frequently than females. Results indicate that processing verbal concepts as emotion-related develops gradually, and after 12–15 is rather stable. The age of acquisition (AoA) develops late: the older (16–19) had a higher awareness in reporting that they learnt the verbs earlier as compared to the estimations made by the younger (8–11 and 12–15). AoA positively correlated with attribution of emotion relatedness meaning that emotion-related verbs were learned later. Arousal was comparable across ages. Also it increased when attributing motor relatedness to verbs and decreased when attributing emotion relatedness. Reporting the verbs' affective valence (happy vs. unhappy) changes with age: younger (8–11) judged the verbs generally more “happy” than both the older groups. Instead the middle and the older group did not show differences. Happiness increased when processing the verbs as motor related and decreased when processing the verbs as emotion related. Age affected imageability: the younger (8–11) considered the verbs easier to be imagined than the two older groups, suggesting that at this age vividness estimation is still rough, while after 12–15 is stable as the 12–15 and 15–19 group did not differ. Imageability predicted arousal, AoA, emotion- and motor-relatedness indicating that this index influences the way verbs are processed. Imageability was positively correlated to emotion relatedness, indicating that such verbs were harder to be imagined, and negatively to motor relatedness. Imageablity positively correlated with valence meaning that verbs receiving positive valence were also those that were hard to be imagined, and negatively correlated with arousal, meaning that verbs that were harder to be imagined elicited low physiological activation. Our results give an insight in the development of emotional and motor-related verbs representations.

Integrated Emotion Processing in Infancy: Matching of Faces and Bodies

Accurate assessment of emotion requires the coordination of information from different sources such as faces, bodies, and voices. Adults readily integrate facial and bodily emotions. However, not much is known about the developmental origin of this capacity. Using a familiarization paired-comparison procedure, 6.5-month-olds in the current experiments were familiarized to happy, angry, or sad emotions in faces or bodies and tested with the opposite image type portraying the familiar emotion paired with a novel emotion. Infants looked longer at the familiar emotion across faces and bodies (except when familiarized to angry images and tested on the happy/angry contrast). This matching occurred not only for emotions from different affective categories (happy, angry) but also within the negative affective category (angry, sad). Thus, 6.5-month-olds, like adults, integrate emotions from bodies and faces in a fairly sophisticated manner, suggesting rapid development of emotion processing early in life.

Do infants discriminate non-linguistic vocal expressions of positive emotions?

Adults are highly proficient in understanding emotional signals from both facial and vocal cues, including when communicating across cultural boundaries. However, the developmental origin of this ability is poorly understood, and in particular, little is known about the ontogeny of differentiation of signals with the same valence. The studies reported here employed a habituation paradigm to test whether preverbal infants discriminate between non-linguistic vocal expressions of relief and triumph. Infants as young as 6 months who had habituated to relief or triumph showed significant discrimination of relief and triumph tokens at test (i.e. greater recovery to the unhabituated stimulus type), when exposed to tokens from a single individual (Study 1). Infants habituated to expressions from multiple individuals showed less consistent discrimination in that consistent discrimination was only found when infants were habituated to relief tokens (Study 2). Further, infants tested with tokens from individuals from different cultures showed dishabituation only when habituated to relief tokens and only at 10-12 months (Study 3). These findings suggest that discrimination between positive emotional expressions develops early and is modulated by learning. Further, infants' categorical representations of emotional expressions, like those of speech sounds, are influenced by speaker-specific information.

Age-congruency and contact effects in body expression recognition from point-light displays (PLD)

Recognition of older people’s body expressions is a crucial social skill. We here investigate how age, not just of the observer, but also of the observed individual, affects this skill. Age may influence the ability to recognize other people’s body expressions by changes in one’s own ability to perform certain action over the life-span (i.e., an own-age bias may occur, with best recognition for one’s own age). Whole body point light displays of children, young adults and older adults (>70 years) expressing six different emotions were presented to observers of the same three age-groups. Across two variations of the paradigm, no evidence for the predicted own-age bias (a cross-over interaction between one’s own age and the observed person’s age) was found. Instead, experience effects were found with children better recognizing older actors’ expressions of ‘active emotions,’ such as anger and happiness with greater exposure in daily life. Together, the findings suggest that age-related changes in one own’s mobility only influences body expression categorization in young children who interact frequently with older adults.

Further evidence of early development of attention to dynamic facial emotions: Reply to Grossmann and Jessen

Adults exhibit enhanced attention to negative emotions like fear, which is thought to be an adaptive reaction to emotional information. Previous research, mostly conducted with static faces, suggests that infants exhibit an attentional bias toward fearful faces only at around 7months of age. In a recent study (Journal of Experimental Child Psychology, 2016, Vol. 147, pp. 100-110), we found that 5-month-olds also exhibit heightened attention to fear when tested with dynamic face videos. This indication of an earlier development of an attention bias to fear raises questions about developmental mechanisms that have been proposed to underlie this function. However, Grossmann and Jessen (Journal of Experimental Child Psychology, 2016, Vol. 153, pp. 149-154) argued that this result may have been due to differences in the amount of movement in the videos rather than a response to emotional information. To examine this possibility, we tested a new sample of 5-month-olds exactly as in the original study (Heck, Hock, White, Jubran, & Bhatt, 2016) but with inverted faces. We found that the fear bias seen in our study was no longer apparent with inverted faces. Therefore, it is likely that infants' enhanced attention to fear in our study was indeed a response to emotions rather than a reaction to arbitrary low-level stimulus features. This finding indicates enhanced attention to fear at 5months and underscores the need to find mechanisms that engender the development of emotion knowledge early in life.

The association of temperament and maternal empathy with individual differences in infants' neural responses to emotional body expressions

We examined the role of infant temperament and maternal dispositional empathy in the neural processing of happy and fearful emotional body expressions in 8-month-old infants by measuring event-related brain potentials. Our results revealed that infants' tendency to approach novel objects and people was positively correlated with the neural sensitivity (attention allocation) to fearful expressions, while infant fearfulness was negatively correlated to the neural sensitivity to fearful expressions. Maternal empathic concern was associated with infants' neural discrimination between happy and fearful expression, with infants of more empathetically concerned mothers showing greater neural sensitivity (attention allocation) to fearful compared to happy expressions. It is critical that our results also revealed that individual differences in the sensitivity to emotional information are explained by an interaction between infant temperament and maternal empathic concern. Specifically, maternal empathy appears to impact infants' neural responses to emotional body expressions, depending on infant fearfulness. These findings support the notion that the way in which infants respond to emotional signals in the environment is fundamentally linked to their temperament and maternal empathic traits. This adds an early developmental neuroscience dimension to existing accounts of social-emotional functioning, suggesting a complex and integrative picture of why and how infants' emotional sensitivity varies.

The Development of Body Structure Knowledge in Infancy

Although we know much about the development of face processing, we know considerably less about the development of body knowledge-despite bodies also being significant sources of social information. One set of studies indicated that body structure knowledge is poor during the 1st year of life and spawned a model that posits that, unlike the development of face knowledge, which benefits from innate propensities and dedicated learning mechanisms, the development of body knowledge relies on general learning mechanisms and develops slowly. In this article, we review studies on infants' knowledge about the structure of bodies and their processing of gender and emotion that paint a different picture. Although questions remain, a general social cognition system likely engenders similar trajectories of development of knowledge about faces and bodies, and may equip developing infants with the capacity to obtain socially critical information from many sources.

Processing emotional body expressions: state-of-the-art

Processing emotional body expressions has become recently an important topic in affective and social neuroscience along with the investigation of facial expressions. The objective of the study is to review the literature on emotional body expressions in order to discuss the current state of knowledge on this topic and identify directions for future research. The following electronic databases were searched: PsychINFO, Ebsco, ERIC, ProQuest, Sagepub, and SCOPUS using terms such as "body," "bodily expression," "body perception," "emotions," "posture," "body recognition" and combinations of them. The synthesis revealed several research questions that were addressed in neuroimaging, electrophysiological and behavioral studies. Among them, one important question targeted the neural mechanisms of emotional processing of body expressions to specific subsections regarding the time course for the integration of emotional signals from face and body, as well as the role of context in the perception of emotional signals. Processing bodily expression of emotion is similar to processing facial expressions, and the holistic processing is extended to the whole person. The current state-of-the-art in processing emotional body expressions may lead to a better understanding of the underlying neural mechanisms of social behavior. At the end of the review, suggestions for future research directions are presented.

Attention to Faces Expressing Negative Emotion at 7 Months Predicts Attachment Security at 14 Months

To investigate potential infant-related antecedents characterizing later attachment security, this study tested whether attention to facial expressions, assessed with an eye-tracking paradigm at 7 months of age (N = 73), predicted infant-mother attachment in the Strange Situation Procedure at 14 months. Attention to fearful faces at 7 months predicted attachment security, with a smaller attentional bias to fearful expressions associated with insecure attachment. Attachment disorganization in particular was linked to an absence of the age-typical attentional bias to fear. These data provide the first evidence linking infants' attentional bias to negative facial expressions with attachment formation and suggest reduced sensitivity to facial expressions of negative emotion as a testable trait that could link attachment disorganization with later behavioral outcomes.

The development of sex category representation in infancy: matching of faces and bodies

Sex is a significant social category, and adults derive information about it from both faces and bodies. Research indicates that young infants process sex category information in faces. However, no prior study has examined whether infants derive sex categories from bodies and match faces and bodies in terms of sex. In the current study, 5-month-olds exhibited a preference between sex congruent (face and body of the same sex) versus sex-incongruent (face and body belonging to different genders) images. In contrast, 3.5-month-olds failed to exhibit a preference. Thus, 5-month-olds process sex information from bodies and match it to facial information. However, younger infants' failure to match suggests that there is a developmental change between 3.5 and 5 months of age in the processing of sex categories. These results indicate that rapid developmental changes lead to fairly sophisticated social information processing quite early in life.

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.

Discrimination of fearful and happy body postures in 8-month-old infants: an event-related potential study

Responding to others' emotional body expressions is an essential social skill in humans. Adults readily detect emotions from body postures, but it is unclear whether infants are sensitive to emotional body postures. We examined 8-month-old infants' brain responses to emotional body postures by measuring event-related potentials (ERPs) to happy and fearful bodies. Our results revealed two emotion-sensitive ERP components: body postures evoked an early N290 at occipital electrodes and a later Nc at fronto-central electrodes that were enhanced in response to fearful (relative to happy) expressions. These findings demonstrate that: (a) 8-month-old infants discriminate between static emotional body postures; and (b) similar to infant emotional face perception, the sensitivity to emotional body postures is reflected in early perceptual (N290) and later attentional (Nc) neural processes. This provides evidence for an early developmental emergence of the neural processes involved in the discrimination of emotional body postures.

Playful expressions of one-year-old chimpanzee infants in social and solitary play contexts

Knowledge of the context and development of playful expressions in chimpanzees is limited because research has tended to focus on social play, on older subjects, and on the communicative signaling function of expressions. Here we explore the rate of playful facial and body expressions in solitary and social play, changes from 12- to 15-months of age, and the extent to which social partners match expressions, which may illuminate a route through which context influences expression. Naturalistic observations of seven chimpanzee infants (Pan troglodytes) were conducted at Chester Zoo, UK (n = 4), and Primate Research Institute, Japan (n = 3), and at two ages, 12 months and 15 months. No group or age differences were found in the rate of infant playful expressions. However, modalities of playful expression varied with type of play: in social play, the rate of play faces was high, whereas in solitary play, the rate of body expressions was high. Among the most frequent types of play, mild contact social play had the highest rates of play faces and multi-modal expressions (often play faces with hitting). Social partners matched both infant play faces and infant body expressions, but play faces were matched at a significantly higher rate that increased with age. Matched expression rates were highest when playing with peers despite infant expressiveness being highest when playing with older chimpanzees. Given that playful expressions emerge early in life and continue to occur in solitary contexts through the second year of life, we suggest that the play face and certain body behaviors are emotional expressions of joy, and that such expressions develop additional social functions through interactions with peers and older social partners.

Tuning the developing brain to emotional body expressions

Reading others' emotional body expressions is an essential social skill. Adults readily recognize emotions from body movements. However, it is unclear when in development infants become sensitive to bodily expressed emotions. We examined event-related brain potentials (ERPs) in 4- and 8-month-old infants in response to point-light displays (PLDs) of happy and fearful body expressions presented in two orientations (upright and inverted). The ERP results revealed that 8-month-olds but not 4-month-olds respond sensitively to the orientation and the emotion of the dynamic expressions. Specifically, 8-month-olds showed (i) an early (200-400 ms) orientation-sensitive positivity over frontal and central electrodes, and (ii) a late (700-1100 ms) emotion-sensitive positivity over temporal and parietal electrodes in the right hemisphere. These findings suggest that orientation-sensitive and emotion-sensitive brain processes, distinct in timing and topography, develop between 4 and 8 months of age.

Current Understanding of What Infants See

The current understanding of what infants see varies greatly among healthcare and education specialists. Even among ophthalmologists and pediatric neurologists in charge of clinical examinations of infants, opinions vary on what infants perceive, recognize, and use for communication and learning. It is, therefore, of interest to review publications from several specialties to learn whether new information is available on the development of visual functions and use of vision. Ten percent of total publications on this subject are reviewed here based on the usefulness of their content for improving early diagnosis and intervention of vision disorders in infants.