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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. 

Oxytocin is a neuropeptide positively associated with prosociality in adults. Here, we studied whether infants' salivary oxytocin can be reliably measured, is developmentally stable, and is linked to social behavior. We longitudinally collected saliva from 62 U.S. infants (44 % female, 56 % Hispanic/Latino, 24 % Black, 18 % non-Hispanic White, 11 % multiracial) at 4, 8, and 14 months of age and offline-video-coded the valence of their facial affect in response to a video of a smiling woman. We also captured infants' affective reactions in terms of excitement/joyfulness during a live, structured interaction with a singing woman in the Early Social Communication Scales at 14 months. We detected stable individual differences in infants' oxytocin levels over time (over minutes and months) and in infants' positive affect over months and across contexts (video-based and in live interactions). We detected no statistically significant changes in oxytocin levels between 4 and 8 months but found an increase from 8 to 14 months. Infants with higher oxytocin levels showed more positive facial affect to a smiling person video at 4 months; however, this association disappeared at 8 months, and reversed at 14 months (i.e., higher oxytocin was associated with less positive facial affect). Infant salivary oxytocin may be a reliable physiological measure of individual differences related to socio-emotional development. 

Objective. Maternal stress is a psychological response to the demands of motherhood. A high level of maternal stress is a risk factor for maternal mental health problems, including depression and anxiety, as well as adverse infant socioemotional and cognitive outcomes. Yet, levels of maternal stress (i.e., levels of stress related to parenting) among low-risk samples are rarely studied longitudinally, particularly in the first year after birth. Design. We measured maternal stress in an ethnically diverse sample of low-risk, healthy U.S. mothers of healthy infants (N = 143) living in South Florida across six time points between 2 weeks and 14 months postpartum using the Parenting Stress Index-Short Form, capturing stress related to the mother, mother-infant interactions, and the infant. Results. Maternal distress increased as infants aged for mothers with more than one child, but not for first-time mothers whose distress levels remained low and stable across this period. Stress related to mother-infant dysfunctional interactions lessened over the first 8 months. Mothers’ stress about their infants’ difficulties decreased from 2 weeks to 6 months, and subsequently increased from 6 to 14 months. Conclusions. Our findings suggest that maternal stress is dynamic across the first year after birth. The current study adds to our understanding of typical developmental patterns in early motherhood and identifies potential domains and time points as targets for future interventions. 

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. 

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.