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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. 

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.