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Remote eye tracking with automated corneal reflection provides insights into the emergence and development of cognitive, social, and emotional functions in human infants and non-human primates. However, because most eye-tracking systems were designed for use in human adults, the accuracy of eye-tracking data collected in other populations is unclear, as are potential approaches to minimize measurement error. For instance, data quality may differ across species or ages, which are necessary considerations for comparative and developmental studies. Here we examined how the calibration method and adjustments to areas of interest (AOIs) of the Tobii TX300 changed the mapping of fixations to AOIs in a cross-species longitudinal study. We tested humans (N = 119) at 2, 4, 6, 8, and 14 months of age and macaques (Macaca mulatta; N = 21) at 2 weeks, 3 weeks, and 6 months of age. In all groups, we found improvement in the proportion of AOI hits detected as the number of successful calibration points increased, suggesting calibration approaches with more points may be advantageous. Spatially enlarging and temporally prolonging AOIs increased the number of fixation-AOI mappings, suggesting improvements in capturing infants’ gaze behaviors; however, these benefits varied across age groups and species, suggesting different parameters may be ideal, depending on the population studied. In sum, to maximize usable sessions and minimize measurement error, eye-tracking data collection and extraction approaches may need adjustments for the age groups and species studied. Doing so may make it easier to standardize and replicate eye-tracking research findings. 

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.

 

We (Meltzoff et al., 2018) described how Oostenbroek et al.’s (2016) design likely dampened infant imitation. In their commentary, Oostenbroek et al. (2018) argue that our points are post hoc. It is important for readers to know that they are not. Our paper restated “best practices” described in published papers. Based on the literature, the design used by Oostenbroek et al. (2016) would be predicted to dampen infant imitation. First, Oostenbroek et al.’s (2016) test periods were too brief. The stimulus presentation for each type of gesture was too short to ensure that neonates saw the display. The response measurement period did not allow neonates sufficient time to organize a motor response. Meltzoff and Moore (1983a, 1994) introduced experimental procedures specifically designed to address these issues (also, Simpson, Murray, Paukner, & Ferrari, 2014). Oostenbroek et al. did not capitalize on these procedural advances. Second, Oostenbroek et al. allowed uncontrolled experimenter–infant interactions during the test session itself. Previous papers on imitation provided analyses of how uncontrolled interactions with the experimenter can introduce “noise” in experiments of facial imitation (Meltzoff & Moore, 1983b, 1994). Third, Oostenbroek et al. used suboptimal eliciting conditions. Neonates cannot support their own heads; in Oostenbroek et al., infants’ heads were allowed to flop from side-to-side unsupported on the experimenter’s lap while the experimenter gestured with both hands. In addition, papers have listed techniques for maximizing visual attention (controlled lighting, homogeneous background) (Meltzoff & Moore, 1989, 1994). Oostenbroek et al. tested infants on a couch in the home. Despite a design that would blunt imitation, our reanalysis of Oostenbroek et al.’s data showed a response pattern that is consistent with the imitation of tongue protrusion (TP). In their commentary, Oostenbroek et al. (2018) now propose limiting analyses to a subset of their original controls. We reanalyzed their data accordingly. Again, the results support early imitation. Their cross-sectional data (Oostenbroek et al., 2016, Table S4) collapsed across age show significantly more infant TP in response to the TP demonstration than to the mean of the six dynamic face controls (mouth, happy, sad, mmm, ee, and click): t(104) = 4.62, p = 0.00001. The results are also significant using a narrower subset of stimuli (mouth, happy, and sad): t(104) = 3.20, p = 0.0018. These results rule out arousal, because the adult TP demonstration was significantly more effective in eliciting infant tongue protrusions than the category of dynamic face controls. Tongue protrusion matching is a robust phenomenon successfully elicited in more than two dozen studies (reviews: Meltzoff & Moore, 1997; Nagy, Pilling, Orvos, & Molnar, 2013; Simpson et al., 2014). There are more general lessons to be drawn. Psychology is experiencing what some call a “replication crisis.” Those who attempt to reproduce effects have scientific responsibilities, as do original authors. Both can help psychology become a more cumulative science. It is crucial for investigators to label whether or not a study is a direct replication attempt. If it is not a direct replication, procedural alterations and associated limitations should be discussed. It sows confusion to use procedures that are already predicted to dampen effects, without alerting readers. Psychology will be advanced by more stringent standards for reporting and evaluating studies aimed at reproducing published effects. Infant imitation is a fundamental skill prior to language and contributes to the development of social cognition. On this both Oostenbroek et al. and we agree. 

The meaning, mechanism, and function of imitation in early infancy have been actively discussed since Meltzoff and Moore’s (1977) report of facial and manual imitation by human neonates. Oostenbroek et al. (2016) claim to challenge the existence of early imitation and to counter all interpretations so far offered. Such claims, if true, would have implications for theories of social- cognitive development. Here we identify 11 flaws in Oostenbroek et al.’s experimental design that biased the results toward null effects. We requested and obtained the authors’ raw data. Contrary to the authors’ conclusions, new analyses reveal significant tongue- protrusion imitation at all four ages tested (1, 3, 6, and 9 weeks old). We explain how the authors missed this pattern and offer five recommendations for designing future experiments. Infant imitation raises fundamental issues about action representation, social learning, and brain–be-havior relations. The debate about the origins and development of imitation reflects its importance to theories of developmental science. 

In humans, socioeconomic status (SES) has profound outcomes on socio‐emotional development and health. However, while much is known about theconsequencesofSES, little research has examined thepredictorsofSESdue to the longitudinal nature of such studies. We sought to explore whether interindividual differences in neonatal sociality, temperament, and early social experiences predicted juvenile social status in rhesus monkeys (Macaca mulatta), as a proxy forSESin humans. We performed neonatal imitation tests in infants’ first week of life and emotional reactivity assessments at 2 and 4 weeks of age. We examined whether these traits, as well as the rearing environment in the first 8 months of life (with the mother or with same‐aged peers only) and maternal social status predicted juvenile (2–3 years old) social status following the formation of peer social groups at 8 months. We found that infants who exhibited higher rates of neonatal imitation and newborn emotional reactivity achieved higher social status as juveniles, as did infants who were reared with their mothers, compared to infants reared with peers. Maternal social status was only associated with juvenile status for infant dyads reared in the same maternal group, indicating that relative social relationships were transferred through social experience. These results suggest that neonatal imitation and emotional reactivity may reflect ingrained predispositions toward sociality that predict later outcomes, and that nonnormative social experiences can alter socio‐developmental trajectories. Our results indicate that neonatal characteristics and early social experiences predict later social outcomes in adolescence, including gradients of social stratification.