The Developmental Origins of Gaze‐Following in Human Infants

During the first year of life, infants develop the capacity to follow the gaze of others. This behavior allows sharing attention and facilitates language acquisition and cognitive development. This article reviews studies that investigated gaze‐following before 12 months of age in typically developing infants and discusses current theoretical perspectives on early GF. Recent research has revealed that early GF is highly dependent on situational constraints and individual characteristics, but theories that describe the underlying mechanisms have partly failed to consider this complexity. We propose a novel framework termed the perceptual narrowing account of GF that may have the potential to integrate existing theoretical accounts.     

Contingency Learning and Reactivity in Preterm and Full‐Term Infants at 3 Months

Learning difficulties in preterm infants are thought to reflect impairment in arousal regulation. We examined relationships among gestational age, learning speed, and behavioral and physiological reactivity in 55 preterm and 49 full‐term infants during baseline, contingency, and nonreinforcement phases of a conjugate mobile paradigm at 3 months corrected age. For all infants, negative affect, looking duration, and heart rate levels increased during contingency and nonreinforcement phases, whereas respiratory sinus arrhythmia (RSA, an index of parasympathetic activity) decreased and Cortisol did not change. Learners showed greater RSA suppression and less negative affect than nonleamers. This pattern was particularly evident in the preterm group. Overall, preterm infants showed less learning, spent less time looking at the mobile, and had lower Cortisol levels than full‐term infants. Preterm infants also showed greater heart rate responses to contingency and dampened heart rate responses to nonreinforcement compared to full‐term infants. Findings underscore differences in basal and reactivity measures in preterm compared to full‐term infants and suggest that the capacity to regulate parasympathetic activity during a challenge enhances learning in preterm infants.     

Within‐rhythm Class Native Language Discrimination Abilities of Basque‐Spanish Monolingual and Bilingual Infants at 3.5 Months of Age

Language rhythm determines young infants' language discrimination abilities. However, it is unclear whether young bilingual infants exposed to rhythmically similar languages develop sensitivities to cross‐linguistic rhythm cues to discriminate their dual language input. To address this question, 3.5‐month‐old monolingual Basque, monolingual Spanish and bilingual Basque‐Spanish infants' language discrimination abilities (across low‐pass filtered speech samples of Basque and Spanish) have been tested using the visual habituation procedure. Although falling within the same rhythmic class, Basque and Spanish exhibit significant differences in their distributions of vocalic intervals (within‐rhythmic class variation). All infant groups in our study successfully discriminated between the languages, although each group exhibited a different pattern. Monolingual Spanish infants succeeded only when they heard Basque during habituation, suggesting that they were influenced by native language recognition. The bilingual and the Basque monolingual infants showed no such asymmetries and succeeded irrespective of the language of habituation. Additionally, bilingual infants exhibited longer looking times in the test phase as compared with monolinguals, reflecting that bilingual infants attend to their native languages differently than monolinguals. Overall, results suggest that bilingual infants are sensitive to within‐rhythm acoustic regularities of their native language(s) facilitating language discrimination and hence supporting early bilingual acquisition.     

Eye‐Tracking as a Measure of Responsiveness to Joint Attention in Infants at Risk for Autism

Reduced responsiveness to joint attention (RJA), as assessed by the Early Social Communication Scales (ESCS), is predictive of both subsequent language difficulties and autism diagnosis. Eye‐tracking measurement of RJA is a promising prognostic tool because it is highly precise and standardized. However, the construct validity of eye‐tracking assessments of RJA has not been established. By comparing RJA an eye‐tracking paradigm to responsiveness to joint attention during the ESCS, the current study evaluated the construct validity of an eye‐tracking assessment of RJA for 18‐month‐old infant siblings of children with autism. Relations between measures of RJA and concurrent language skills and autistic symptomatology were assessed. Correlations between measures of ESCS RJA and eye‐tracking RJA were statistically significant, but few relations between either ESCS or eye‐tracking assessments of RJA and language or symptoms were observed. This study establishes the construct validity of eye‐tracking assessments of RJA.     

Increased Focus on the Mouth Among Infants in the First Year of Life: A Longitudinal Eye‐Tracking Study

This study examines face‐scanning behaviors of infants at 6, 9, and 12 months as they watched videos of a woman describing an object in front of her. The videos were created to vary information in the mouth (speaking vs. smiling) and the eyes (gazing into the camera vs. cueing the infant with head turn or gaze direction to an object being described). Infants tended to divide their attention between the eyes and the mouth, looking less at the eyes with age and more at the mouth than the eyes at 9 and 12 months. Attention to the mouth was greater on speaking trials than on smiling trials at all three ages, and this difference increased between 6 and 9 months. Despite consistent results within subjects, there was considerable variation between subjects. This raises the question of whether a developmental “norm” of face scanning in infancy ought to be pursued. Rather, these data add to emerging evidence suggesting that individual differences in face scanning might reliably predict aspects of later development.     

Development of Tactile Responses in Human Preterm and Full‐Term Infants From 30 to 40 Weeks Postconceptional Age

Maturation of tactile sensitivity prior to term was examined in 36 preterm and 13 full‐term infants using a fixed‐trial, habituation procedure. Each infant was presented with a series of 8 habituation (arm stroke), 2 novel (arm lift), and 2 recovery (arm stroke) stimulus trials while heart rate and body movements were recorded. Maturation was observed with a gradual increase in the magnitude of the stimulus‐elicited cardiac acceleration and cardiac‐movement coupling from 30 to 40 weeks postconceptional age. The majority of infants displayed habituation—an excitatory response (heart rate acceleration and body movement)—to the initial presentation of a tactile stimulus, response decline with repeated stimulations, and renewed response to a novel stimulus. A substantial number of infants (40%) failed to respond initially to the tactile stimulus, increased responding over several stimulus presentations, and failed to discriminate the presentation of a novel stimulus. We speculate that these differences in response patterns observed over all ages represent individual difference in the perception of stimulus intensity.     

Physiological Regulation at 9 Months of Age in Infants Prenatally Exposed to Cigarettes

The primary purpose of this study was to examine the association between prenatal cigarette exposure and physiological regulation at 9 months of age. Specifically, we explored the possibility that any association between prenatal cigarette exposure and infant physiological regulation was moderated by postnatal environmental tobacco smoke (ETS) exposure or infant gender. We evaluated whether male infants with prenatal cigarette exposure or infants who were also exposed to ETS after birth had the highest levels of physiological dysregulation. Respiratory sinus arrhythmia (RSA) was obtained from 206 (142 exposed and 64 nonexposed) infants during a baseline period and during procedures designed to elicit both positive and negative affect. There was a significant suppression of RSA during the negative affect task for nonexposed infants, but not for exposed infants. Postnatal ETS exposure did not moderate this association; however, gender did moderate this association such that boys with prenatal cigarette exposure had a significant increase in RSA rather than the suppression seen among both nonexposed boys and girls. These results provide additional support for the idea that boys are particularly vulnerable to the effects of prenatal cigarette exposure.     

Long‐Term Memory for an Emotional Interpersonal Interaction Occurring at 5 Months of Age

We examined infants' long‐term retention of a single unique emotional experience into early childhood. Twenty‐month‐olds who had participated in a still‐face procedure at 5 months (experience group) fixated the face of the person who had instigated the still face significantly less than the faces of 2 other novel persons. Control 20‐month‐olds (no‐experience group) looked longer overall and fixated the target person equally or more than the 2 novel persons. In short, children who interacted with a stranger in the laboratory under both natural and anomalous social conditions just once when they were infants apparently retained a specific memory of that person and the experience into toddlerhood.     

A Comparative Study of Arm‐Restraint Methodology: Differential Effects of Mother and Stranger Restrainers on Infants' Distress Reactivity at 6 and 9 Months of Age

This study examined both differential patterns and the stability of infants' (N = 70) distress reactivity across mother and stranger arm‐restraint conditions when infants were 6 and 9 months of age. Reactivity measures included observational variables for the rise, intensity, and duration of infant distress as well as motor activities associated with escape behaviors. Correlation analyses revealed that infant behaviors during arm restraint were modestly stable across conditions and over time; however, mean comparisons also showed that infants' distress responses appear to be sensitive to protocol parameters (whether restrainer is mother or stranger). At 6 months of age, infants cried more during maternal restraint than with strangers and exhibited escape behaviors more frequently with mothers. Findings further indicate that infants' distress reactivity undergoes developmental alterations from 6 to 9 months of age, with infants crying more quickly, reaching peak intensity of distress faster, and displaying more distress at 9 months compared to 6 months. These changes in infants' reactivity were particularly accentuated during maternal compared to stranger restraint conditions at 9 months of age.     

Infants' Evolving Representations of Object Motion During Occlusion: A Longitudinal Study of 6‐ to 12‐Month‐Old Infants

Infants' ability to track temporarily occluded objects that moved on circular trajectories was investigated in 20 infants using a longitudinal design. They were first seen at 6 months and then every 2nd month until the end of their 1st year. Infants were presented with occlusion events covering 20% of the target's trajectory (effective occlusion interval ranged from 500–4,000 msec). Gaze was measured using an ASL 504 infrared eye‐tracking system. Results effectively demonstrate that infants from 6 months of age can represent the spatiotemporal dynamics of occluded objects. Infants at all ages tested were able to predict, under certain conditions, when and where the object would reappear after occlusion. They moved gaze accurately to the position where the object was going to reappear and scaled their timing to the current occlusion duration. The average rate of predictive gaze crossings increased with occlusion duration. These results are discussed as a 2‐factor process. Successful predictions are dependent on strong representations, themselves dependent on the richness of information available during encoding and graded representations.     

Looking Behavior at Test and Relational Memory in 6‐Month‐Old Infants

Small‐scale eye‐tracking research lends support to behavioral studies of relational memory by 6 months of life. Here, in the largest eye‐tracking test of relational memory to date (n = 276), we replicate these findings and examine the impact of excluding data based on looking behavior characteristics at test. Past work examining infants' preferential looking toward arbitrary‐paired objects and scenes has excluded infants from analysis based upon “insufficient looking” at test. Yet, research suggests that variation in looking behavior may be associated with looking patterns during encoding, as well as trait‐like differences in visual and cognitive processing. Similar to past research, we observed evidence for relational memory among 6‐month‐olds. In keeping with past research, when infants were excluded based on “insufficient looking,” we observed evidence for relational memory only when infants were tested immediately. However, when exclusion criteria were relaxed, infants specifically demonstrated preferential looking during a presumably more difficult delay‐plus‐interference condition. Moreover, analyses revealed that looking behavior during encoding was associated with looking behavior at test. Together, results suggest that infants do possess rudimentary relational memory capabilities, but that experimenters' ability to detect these capabilities is influenced by both experimental conditions and individual differences in looking behavior.     

Consequences of Eye Color,Positioning, and Head Movement for Eye‐Tracking Data Quality in Infant Research

Eye tracking has become a valuable tool for investigating infant looking behavior over the last decades. However, where eye‐tracking methodology and achieving high data quality have received a much attention for adult participants, it is unclear how these results generalize to infant research. This is particularly important as infants behave different from adults in front of the eye tracker. In this study, we investigated whether eye physiology, positioning, and infant behavior affect measures of eye‐tracking data quality: accuracy, precision, and data loss. We report that accuracy and precision are lower, and more data loss occurs for infants with bluish eye color compared to infants with brownish eye color. Moreover, accuracy was lower for infants positioned in a high chair or in the parents' lap compared to infants positioned in a baby seat. Finally, precision decreased and data loss increased as a function of time. We highlight the importance of data quality when comparing multiple groups, as differences in data quality can affect eye‐tracking measures. In addition, we investigate how two different measures to quantify infant movement influence eye‐tracker data quality. These findings might help researchers with data collection and help manufacturers develop better eye‐tracking systems for infants.     

Stress Pattern Preference in Spanish‐Learning Infants: The Role of Syllable Weight

As a result of exposure, infants acquire biases that conform to the rhythmic properties of their native language. Previous lexical stress preference studies have shown that English‐ and German‐, but not French‐learning infants, show a bias toward trochaic words. The present study explores Spanish‐learning infants' lexical stress preferential patterns and the role of syllable weight at 9 months of age. Spanish is a syllable‐timed language with no vowel reduction and variable stress. Around 50% of the word types in Spanish are disyllabic, with a superior proportion of trochees than iambs (60% and 40%, respectively). Experiment 1 with CV.CV pseudo‐words failed to reveal a clear trochaic bias in 9‐month‐old Spanish‐learning infants. However, when preference was explored with items containing a heavy syllable (CVC.CV and CV.CVC, respectively), both a trochaic (Experiment 2) and an iambic preference (Experiment 3) could be elicited. These results suggest that knowledge about the close and highly regular link between heavy syllables and stress assignment in Spanish can be easily acquired and determines infants' preference at 9 months of age, while for CV.CV items, the trochaic bias appears to be weak. Our results broaden the current knowledge on the factors that determine the emergence of rhythmic biases.     

Distinguishing Mother–Infant Interaction From Stranger–Infant Interaction at 2, 4, and 6 Months of Age

Observers watched videotaped face‐to‐face mother–infant and stranger–infant interactions of 12 infants at 2, 4, or 6 months of age. Half of the observers saw each mother paired with her own infant and another infant of the same age (mother tapes) and half saw each infant paired with his or her mother and with a stranger (infant tapes). Observers were asked to judge which was the mother–infant dyad in each pair. Observers' accuracy improved as infants aged and was above chance for both mother and infant tapes when infants were 6 months. Differences between mother–infant and stranger–infant dyadic communication patterns also emerged as the infants aged. At 6 months, mother–infant dyads had more symmetrical communication and less asymmetrical communication than stranger–infant dyads.     

Maternal Into‐The‐Face Behavior,Shared Attention,and Infant Distress During Face‐to‐Face Play at 12 Months: Bi‐directional Contingencies

We describe a new maternal intrusion behavior, moving a toy or hand “into‐the‐face” of the infant, and we investigate its bi‐directional associations with infant‐initiated shared attention, infant distress, and infant gaze, during mother–infant face‐to‐face play at 12 months. The play was videotaped split‐screen, with infants seated in a high chair. Videotapes were coded on a 1‐sec time base for mother and infant gaze (at partner, toy, both, or gaze away); infant distress; and maternal intrusion behavior, “into‐the‐face.” We defined “infant‐initiated shared attention” as mother and infant looking in the same second at a toy that the infant‐initiated interest in. We documented that maternal into‐the‐face behavior decreased the likelihood of infant‐initiated shared attention, increased the likelihood of infant distress, and decreased the likelihood of infant gazing away. Reciprocally, infant distress and gazing away increased the likelihood of mother into‐the‐face. In moments when the dyad was engaged in infant‐initiated shared attention, mother into‐the‐face was less likely. This work documents bi‐directional contingencies in the regulation of maternal intrusion and infant behavior during face‐to‐face play at 12 months. We suggest that mother into‐the‐face behavior disturbs an aspect of the infant's experience of recognition.     

The Development of Rational Imitation in 9‐ and 12‐Month‐Old Infants

Studies on rational imitation have provided evidence for the fact that infants as young as 12 months of age engage in rational imitation. However, the developmental onset of this ability is unclear. In this study, we investigated whether 9‐ and 12‐month‐olds detect voluntary and implicit as well as nonvoluntary and explicit constraints in the head touch task. Three groups of infants watched video sequences, which displayed a person illuminating a lamp using the head. The hands of the model were either free, occupied by voluntarily holding a blanket, or nonvoluntarily restrained by being tied to the table. An additional control group of infants watched the model turning on the lamp by using the hand. Given that the majority of infants imitated the head touch when the model's hands were free, there was evidence for rational imitation in comparison to the condition in which the model's hands were tied to the table, but not in comparison to the condition in which the hands were occupied by holding a blanket. Nine‐month‐olds showed no differences in their behavior according to the condition. These findings clarify the onset of rational imitation by showing that 12‐month‐olds (but not 9‐month‐olds) take into account a situational constraint only when the constraint is nonvoluntary and explicit.     

Disappearing Décalage: Object Search in Light and Dark at 6 Months

Infants search for an object hidden by an occluder in the light months later than one hidden by darkness. One explanation attributes this décalage to easier action demands in darkness versus occlusion, whereas another attributes it to easier representation demands in darkness versus occlusion. However, search tasks typically confound these two types of demands. This article presents a search task that unconfounds them to better address these two explanations of the “dark advantage.” Objects were hidden by submersion in liquid instead of occlusion with a screen, allowing infants to search with equally simple actions in light versus dark. In Experiment 1, 6‐month‐olds unexpectedly showed a dark disadvantage by discriminating when an object was hidden in the light but not the dark. Experiment 2 addressed the possibility that representation demands were higher in the dark than the light and showed that infants’ search in the dark increased to match that in the light, but not exceed it. Six‐month‐olds can thus search for a hidden object both when action demands are simplified and when a noncohesive substance rather than a cohesive occluder hides the object, supporting aspects of both action‐demand and representation‐demand explanations of décalage in search behavior.     

Infant Sex Moderates the Effects of Maternal Pre‐ and Postnatal Stress on Executive Functioning at 8 Months of Age

Previous studies report that early life stress, including maternal pre‐ and postnatal stress, has adverse effects on cognitive development and that these associations might be sex‐specific. However, no studies exist on early life stress and infant executive functioning (EF). The aim of this study was to examine the relationship between maternal pre‐ and postnatal stress and infant EF, and whether these associations are moderated by infant sex. Maternal prenatal depressive, general anxiety, and pregnancy‐specific anxiety symptoms were measured three times, and postnatal depressive and general anxiety symptoms were measured 6 months postpartum. Infant EF was assessed with a modified A‐not‐B task 8 months postpartum (N = 214). Maternal postnatal general anxiety predicted poorer EF in girls in comparison with boys. Moreover, there was a trend toward an interaction between prenatal anxiety and infant sex such that prenatal anxiety predicted infant EF differently in girls and in boys. No association was found between depressive symptoms or pregnancy‐specific anxiety symptoms and infant EF. These findings suggest that maternal anxiety may have sex‐specific effects on early EF and that pre‐ and postnatal stress may differently affect infant EF/cognitive development. The implications of these findings and important future directions are discussed.     

Perception of Multisensory Gender Coherence in 6‐ and 9‐Month‐Old Infants

One of the most salient social categories conveyed by human faces and voices is gender. We investigated the developmental emergence of the ability to perceive the coherence of auditory and visual attributes of gender in 6‐ and 9‐month‐old infants. Infants viewed two side‐by‐side video clips of a man and a woman singing a nursery rhyme and heard a synchronous male or female sound track. Results showed that 6‐month‐old infants did not match the audible and visible attributes of gender, and 9‐month‐old infants matched only female faces and voices. These findings indicate that the ability to perceive the multisensory coherence of gender emerges relatively late in infancy and that it reflects the greater experience that most infants have with female faces and voices.     

Getting into the Groove: The Development of Tempo‐Flexibility Between 10 and 18 Months of Age

Despite good early rhythm processing abilities, and clear enjoyment of music, infants appear not to be able to spontaneously synchronize their movement to the beat of a song (Zentner and Eerola, Proceedings of the National Academy of Sciences, 107, 2010, 5768). We present a new social bell‐ringing task designed to facilitate synchronous movement to music in infants. Ten‐month‐olds, 18‐month‐olds, and adults were played musical tracks of various tempos and given handheld bells to ring, in the presence of either a live experimenter or an animated nonsocial stimulus. Surface electromyography (EMG) was used to measure the timing of arm movements during periods of bell ringing. Infants showed no evidence of synchronous bell ringing at any tempo. However, while the 10‐month‐olds did not modulate their ringing to the music tempo, the 18‐month‐olds showed tempo‐flexibility. Moreover, 18‐month‐olds displayed more associated behaviors such as bouncing and rocking in the absence (rather than presence) of a social partner, whereas the behavior of the 10‐month‐olds was not modulated by the presence or absence of a social partner. The results suggest a distinction between “moving together” and “moving to the beat,” which may have separate underlying mechanisms and developmental trajectories.