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ABSTRACT Given the foundational nature of infant visual attention and potential cascading effects on later development, studies of individual variability in developmental trajectories in a normative sample are needed. We longitudinally tested newborns (N= 77) at 1–2 and 3–4 weeks, then again at 2, 4, 6, 8 and 14 months of age, assessing individual differences in their attention. Newborns viewed live stimuli (facial gesturing, rotating disk), one at a time, for 3 min each. Older infants viewed a 10‐s side‐by‐side social–nonsocial video (people talking, rotating disk). We found short‐term developmental stability of interindividual differences in infants’ overall, social, and nonsocial attention, within the newborn period (1–4 weeks), and within the later infancy period (2–14 months). Additionally, we found that overall attention, but not social and nonsocial attention, was developmentally stable long term (newborn through 14 months). This novel finding that newborn overall attention predicts later overall attention through the first year suggests a robust individual difference. This study is a first step toward developing individual difference measures of social and nonsocial attention. Future studies need to understand why newborns vary in their attention and to identify the potential impact of this variability on later social and cognitive development. 

ABSTRACT Infants’ nonverbal expressions—a broad smile or a sharp cry—are powerful at eliciting reactions. Although parents’ reactions to their own infants’ expressions are relatively well understood, here we studied whether adults more generally exhibit behavioral and physiological reactions tounfamiliarinfants producing various expressions. We recruited U.S. emerging adults (N = 84) prior to parenthood, 18–25 years old, 68% women, ethnically (20% Hispanic/Latino) and racially (7% Asian, 13% Black, 1% Middle Eastern, 70% White, 8% multiracial) diverse. They observed four 80‐s audio–video clips of unfamiliar 2‐ to 6‐month‐olds crying, smiling, yawning, and sitting calmly (emotionally neutral control). Each compilation video depicted 9 different infants (36 clips total). We found adults mirrored behaviorally and physiologically: more positive facial expressions to infants smiling, and more negative facial expressions and pupil dilation—indicating increases in arousal—to infants crying. Adults also yawned more and had more pupil dilation when observing infants yawning. Together, these findings suggest that even nonparent emerging adults are highly sensitive to unfamiliar infants’ expressions, which they naturally “catch” (i.e., behaviorally and physiologically mirror), even without instructions. Such sensitivity may have—over the course of humans’ evolutionary history—been selected for, to facilitate adults’ processing of preverbal infants’ expressions to meet their needs. 

Abstract This study examined the development of children's avoidance and recognition of sickness using face photos from people with natural, acute, contagious illness. In a U.S. sample of fifty‐seven 4‐ to 5‐year‐olds (46% male, 70% White), fifty‐two 8‐ to 9‐year‐olds (26% male, 62% White), and 51 adults (59% male, 61% White), children and adults avoided and recognized sick faces (ds ranged from 0.38 to 2.26). Both avoidance and recognition improved with age. Interestingly, 4‐ to 5‐year‐olds' avoidance of sick faces positively correlated with their recognition, suggesting stable individual differences in these emerging skills. Together, these findings are consistent with a hypothesized immature but functioning and flexible behavioral immune system emerging early in development. Characterizing children's sickness perception may help design interventions to improve health. 

Abstract Neurodevelopmental disorders are on the rise worldwide, with diagnoses that detect derailment from typical milestones by 3 to 4.5 years of age. By then, the circuitry in the brain has already reached some level of maturation that inevitably takes neurodevelopment through a different course. There is a critical need then to develop analytical methods that detect problems much earlier and identify targets for treatment. We integrate data from multiple sources, including neonatal auditory brainstem responses (ABR), clinical criteria detecting autism years later in those neonates, and similar ABR information for young infants and children who also received a diagnosis of autism spectrum disorders, to produce the earliest known digital screening biomarker to flag neurodevelopmental derailment in neonates. This work also defines concrete targets for treatment and offers a new statistical approach to aid in guiding a personalized course of maturation in line with the highly nonlinear, accelerated neurodevelopmental rates of change in early infancy. 

Abstract Infants vary in their ability to follow others’ gazes, but it is unclear how these individual differences emerge. We tested whether social motivation levels in early infancy predict later gaze following skills. We longitudinally tracked infants’ (N = 82) gazes and pupil dilation while they observed videos of a woman looking into the camera simulating eye contact (i.e., mutual gaze) and then gazing toward one of two objects, at 2, 4, 6, 8, and 14 months of age. To improve measurement validity, we used confirmatory factor analysis to combine multiple observed measures to index the underlying constructs of social motivation and gaze following. Infants’ social motivation—indexed by their speed of social orienting, duration of mutual gaze, and degree of pupil dilation during mutual gaze—was developmentally stable and positively predicted the development of gaze following—indexed by their proportion of time looking to the target object, first object look difference scores, and first face‐to‐object saccade difference scores—from 6 to 14 months of age. These findings suggest that infants’ social motivation likely plays a role in the development of gaze following and highlight the use of a multi‐measure approach to improve measurement sensitivity and validity in infancy research. 

Abstract In childhood, higher levels of temperamental fear—an early‐emerging proclivity to distress in the face of novelty—are associated with lower social responsivity and greater social anxiety. While the early emergence of temperamental fear in infancy is poorly understood, it is theorized to be driven by individual differences in reactivity and self‐regulation to novel stimuli. The current study used eye tracking to capture infants’ (N = 124) reactions to a video of a smiling stranger—a common social encounter—including infant gaze aversions from the stranger's face (indexing arousal regulation) and pupil dilation (indexing physiological reactivity), longitudinally at 2, 4, 6, and 8 months of age. Multilevel mixed‐effects models indicated that more fearful infants took more time to look away from a smiling stranger's face than less fearful infants, suggesting that high‐fear infants may have slower arousal regulation. At 2 and 4 months, more fearful infants also exhibited greater and faster pupil dilation before gaze aversions, consistent with greater physiological reactivity. Together, these findings suggest that individual differences in infants’ gaze aversions and pupil dilation can index the development of fearful temperament in early infancy, facilitating the identification of, and interventions for, risk factors to social disruptions. 

Abstract The present study explored behavioral norms for infant social attention in typically developing human and nonhuman primate infants. We examined the normative development of attention to dynamic social and nonsocial stimuli longitudinally in macaques (Macaca mulatta) at 1, 3, and 5 months of age (N = 75) and humans at 2, 4, 6, 8, and 13 months of age (N = 69) using eye tracking. All infants viewed concurrently played silent videos—one social video and one nonsocial video. Both macaque and human infants were faster to look to the social than the nonsocial stimulus, and both species grew faster to orient to the social stimulus with age. Further, macaque infants’ social attention increased linearly from 1 to 5 months. In contrast, human infants displayed a nonlinear pattern of social interest, with initially greater attention to the social stimulus, followed by a period of greater interest in the nonsocial stimulus, and then a rise in social interest from 6 to 13 months. Overall, human infants looked longer than macaque infants, suggesting humans have more sustained attention in the first year of life. These findings highlight potential species similarities and differences, and reflect a first step in establishing baseline patterns of early social attention development. 

Automated behavioral measurement using machine learning is gaining ground in psychological research. Automated approaches have the potential to reduce the labor and time associated with manual behavioral coding, and to enhance measurement objectivity; yet their application in young infants remains limited. We asked whether automated measurement can accurately identify newborn mouth opening—a facial gesture involved in infants’ communication and expression—in videos of 29 newborns (age range 9-29 days, 55.2% female, 58.6% White, 51.7% Hispanic/Latino) during neonatal imitation testing. We employed a 3-dimensional cascade regression computer vision algorithm to automatically track and register newborn faces. The facial landmark coordinates of each frame were input into a Support Vector Machine (SVM) classifier, trained to recognize the presence and absence of mouth opening at the frame-level as identified by expert human coders. The SVM classifier was trained using leave-one-infant-out cross validation (training: N = 22 newborns, 95 videos, 354,468 frames), and the best classifier showed an average validation accuracy of 75%. The final SVM classifier was tested on different newborns from the training set (testing: N = 7 newborns, 29 videos, 118,615 frames) and demonstrated 76% overall accuracy in identifying mouth opening. An intraclass correlation coefficient of .81 among the SVM classifier and human experts indicated that the SVM classifier was, on a practical level, reliable with experts in quantifying newborns’ total rates of mouth opening across videos. Results highlight the potential of automated measurement approaches for objectively identifying the presence and absence of mouth opening in newborn infants. 

Growing empirical evidence from the past quarter century reveals surprising sociality in newborns—infants in the first 28 postnatal days—including their ability to elicit and sustain contingent interactions with mutual gaze, social smiling, and sensitively timed, speech-like vocalizations. Newborns seem to have communicative expectations and behave as if they predict others’ goal-directed actions. Despite these discoveries, I review key barriers to progress in newborn developmental science. First, newborn social behavior research has almost exclusively focused on “average” development—based primarily on White, wealthy, English-speaking, Western, populations—treating interindividual differences as noise rather than meaningful, variability. Focusing almost exclusively on averages, especially with small sample sizes, ignores interindividual differences and hinders discoveries. Second, there are few studies of newborn sociality beyond the first postnatal week. In part, this gap in our understanding may be due to, and a consequence of, the mischaracterizations of newborns’ behaviors as passive, limited, disorganized, and low-level reflexes that are subcortically driven. Finally, researchers often assume that newborns’ behaviors are largely independent of experience. To the contrary, newborns’ need for nearly continuous social contact provides them with rich social learning opportunities, which have been shown to have lasting impacts on their development. Given the uniqueness and plasticity of this period, and their high vulnerability, developmental scientists are doing newborns a disservice by neglecting to characterize their social repertoires within and across diverse populations. Awareness of newborns’ social capacities will facilitate a more objective, accurate view of their social potential. 

Abstract Humans detect faces efficiently from a young age. Face detection is critical for infants to identify and learn from relevant social stimuli in their environments. Faces with eye contact are an especially salient stimulus, and attention to the eyes in infancy is linked to the emergence of later sociality. Despite the importance of both of these early social skills—attending to faces and attending to the eyes—surprisingly little is known about how they interact. We used eye tracking to explore whether eye contact influences infants' face detection. Longitudinally, we examined 2‐, 4‐, and 6‐month‐olds' (N = 65) visual scanning of complex image arrays with human and animal faces varying in eye contact and head orientation. Across all ages, infants displayed superior detection of faces with eye contact; however, this effect varied as a function of species and head orientation. Infants were more attentive to human than animal faces and were more sensitive to eye and head orientation for human faces compared to animal faces. Unexpectedly, human faces with both averted heads and eyes received the most attention. This pattern may reflect the early emergence of gaze following—the ability to look where another individual looks—which begins to develop around this age. Infants may be especially interested in averted gaze faces, providing early scaffolding for joint attention. This study represents the first investigation to document infants' attention patterns to faces systematically varying in their attentional states. Together, these findings suggest that infants develop early, specialized functional conspecific face detection.