On Measuring and Modeling Physiological Synchrony in Dyads

Physiological synchrony within a dyad, or the degree of temporal correspondence between two individuals' physiological systems, has become a focal area of psychological research. Multiple methods have been used for measuring and modeling physiological synchrony. Each method extracts and analyzes different types of physiological synchrony, where ‘type’ refers to a specific manner through which two different physiological signals may correlate. Yet, to our knowledge, there is no documentation of the different methods, how each method corresponds to a specific type of synchrony, and the statistical assumptions embedded within each method. Hence, this article outlines several approaches for measuring and modeling physiological synchrony, connects each type of synchrony to a specific method, and identifies the assumptions that need to be satisfied for each method to appropriately extract each type of synchrony. Furthermore, this article demonstrates how to test for between-dyad differences of synchrony via inclusion of dyad-level (i.e., time-invariant) covariates. Finally, we complement each method with an empirical demonstration, as well as online supplemental material that contains Mplus code.     

Assessing cross-partner associations in physiological responses via coupled oscillator models

A host of theoretical frameworks suggest associations of physiological signals between two individuals within a romantic relationship. However, few studies have provided empirical evidence of such associations using physiological reactivity from both partners in the dyad. In this study we use measures of respiration and heart rate from romantic partners recorded across three laboratory tasks. We examine the interrelations of each measure between both dyad members using coupled linear oscillators (Boker & Nesselroade, 2002). These models were used to capture oscillations in respiration and heart rate, and to examine interdependence in the physiological signals between both partners. Results show that associations were detectable within all three tasks, with different patterns of coupling within each task. Discussion centers on ways to investigate the synchrony of physiological responses across within relationships, including the promises of and obstacles for doing so.     

Increasing specificity in perceptual development: infants' detection of nested levels of multimodal stimulation

This research assessed the development of infants' sensitivity to two nested amodal temporal relations in audible and visible events. Their detection of global temporal synchrony between visible and audible impacts and internal temporal structure nested within each impact specifying object composition (single versus compound objects) was assessed. Infants of 4, 7, and 11 weeks of age were habituated to a single and a compound object striking a surface and then received test trials depicting a change in synchrony or object composition. Results indicated an interaction between age and condition where sensitivity to synchrony was present by 4 weeks and remained stable across age, whereas sensitivity to composition emerged later, by 7 weeks, and increased dramatically with age. These findings converge with other recent findings to illustrate a pattern of increasing specificity in the development of perception, where infants first detect global and later detect embedded relations. The early sensitivity to global relations may provide an organizational framework for development by focusing infant attention on unitary events, guiding and constraining further exploration, and buffering infants from learning incongruent relations.     

Infant–mother and infant–father synchrony: The coregulation of positive arousal

To examine the coregulation of positive affect during mother–infant and father–infant interactions, 100 couples and their first‐born child were videotaped in face‐to‐face interactions. Parents' and infant's affective states were coded in one‐second frames, and synchrony was measured with time‐series analysis. The orientation, intensity, and temporal pattern of infant positive arousal were assessed. Synchrony between same‐gender parent–infant dyads was more optimal in terms of stronger lagged associations between parent and infant affect, more frequent mutual synchrony, and shorter lags to responsiveness. Infants' arousal during mother–infant interaction cycled between medium and low levels, and high positive affect appeared gradually and was embedded within a social episode. During father–child play, positive arousal was high, sudden, and organized in multiple peaks that appeared more frequently as play progressed. Mother–infant synchrony was linked to the partners' social orientation and was inversely related to maternal depression and infant negative emotionality. Father–child synchrony was related to the intensity of positive arousal and to father attachment security. Results contribute to research on the regulation of positive emotions and describe the unique modes of affective sharing that infants coconstruct with mother and father. ©2003 Michigan Association for Infant Mental Health.     

Mother and infant coordinate heart rhythms through episodes of interaction synchrony

Animal studies demonstrated the powerful impact of maternal-infant social contact on the infant's physiological systems, yet the online effects of social interactions on the human infant's physiology remain poorly understood. Mothers and their 3-month old infants were observed during face-to-face interactions while cardiac output was collected from mother and child. Micro-analysis of the partners’ behavior marked episodes of gaze, affect, and vocal synchrony. Time-series analysis showed that mother and infant coordinate heart rhythms within lags of less than 1 s. Bootstrapping analysis indicated that the concordance between maternal and infant biological rhythms increased significantly during episodes of affect and vocal synchrony compared to non-synchronous moments. Humans, like other mammals, can impact the physiological processes of the attachment partner through the coordination of visuo-affective social signals.     

14 challenges and their solutions for conducting social neuroscience and longitudinal EEG research with infants

The use of electroencephalography (EEG) to study infant brain development is a growing trend. In addition to classical longitudinal designs that study the development of neural, cognitive and behavioural functions, new areas of EEG application are emerging, such as novel social neuroscience paradigms using dual infant-adult EEG recordings. However, most of the experimental designs, analysis methods, as well as EEG hardware were originally developed for single-person adult research. When applied to study infant development, adult-based solutions often pose unique problems that may go unrecognised. Here, we identify 14 challenges that infant EEG researchers may encounter when designing new experiments, collecting data, and conducting data analysis. Challenges related to the experimental design are: (1) small sample size and data attrition, and (2) varying arousal in younger infants. Challenges related to data acquisition are: (3) determining the optimal location for reference and ground electrodes, (4) control of impedance when testing with the high-density sponge electrode nets, (5) poor fit of standard EEG caps to the varying infant head shapes, and (6) ensuring a high degree of temporal synchronisation between amplifiers and recording devices during dual-EEG acquisition. Challenges related to the analysis of longitudinal and social neuroscience datasets are: (7) developmental changes in head anatomy, (8) prevalence and diversity of infant myogenic artefacts, (9) a lack of stereotypical topography of eye movements needed for the ICA-based data cleaning, (10) and relatively high inter-individual variability of EEG responses in younger cohorts. Additional challenges for the analysis of dual EEG data are: (11) developmental shifts in canonical EEG rhythms and difficulties in differentiating true inter-personal synchrony from spurious synchrony due to (12) common intrinsic properties of the signal and (13) shared external perturbation. Finally, (14) there is a lack of test-retest reliability studies of infant EEG. We describe each of these challenges and suggest possible solutions. While we focus specifically on the social neuroscience and longitudinal research, many of the issues we raise are relevant for all fields of infant EEG research.     

The coregulatory effects of emotionally focused therapy

This study examined the heart rate synchrony between a single couple in emotionally focused therapy (EFT) as a method of measuring coregulatory effects over the course of treatment. A clinician who is an EFT certified therapist, supervisor, and trainer administered all eight sessions in a private practice setting. Surrogate synchrony analysis assessed heart rate synchrony between partners, indicating that significant heart rate synchrony was more likely over time. Significant heart rate synchrony was more likely during sessions that focused on clients’ sharing attachment injuries, bonds, and longings with their partner compared to sessions more focused on cognitive processing of the relationship. Additionally, there were delays in heart rate synchrony that occurred between the couple, which may be indicative of the emotional processing speed of the empathic response of each partner. Understanding the physiological synchrony patterns between dyads in treatment could clarify the potential of coregulation in the therapeutic process.     

Functioning within a relationship: mother-infant synchrony and infant sleep

The aim of this study was to investigate the coupling of the biological system of infant sleep and the social system of mother-infant synchrony. Before birth and shortly after birth the systems appear to be connected, but it is unclear whether this remains the case over time. This study therefore examined whether infant sleep measured at 6 weeks and 5 months could predict mother-infant gaze synchrony after a social challenge at 5 months (N=84). Infant sleep was measured in terms of sleep bout duration, which normally increases during this period. Gaze was defined in terms of looking at each other's head simultaneously, known as gaze synchrony, or looking elsewhere. Results showed that infant sleep could predict the temporal dynamics of the mother-infant interaction in terms of flexibility of gaze pattern shifts. The larger the increase in sleep bout duration over age, the more flexible the interaction appeared to be. Maternal Age, type of feeding and change of feeding appeared to function as confounding variables in this relation. Infant sleep could not predict percentage of synchrony (central tendency measure) or the average sequence length of gaze patterns (temporal dynamic measure).     

Tonal synchrony in mother–infant interaction based on harmonic and pentatonic series

This study reports the occurrence of ‘tonal synchrony’ as a new dimension of early mother–infant interaction synchrony. The findings are based on a tonal and temporal analysis of vocal interactions between 15 mothers and their 3-month-old infants during 5 min of free-play in a laboratory setting. In total, 558 vocal exchanges were identified and analysed, of which 84% reflected harmonic or pentatonic series. Another 10% of the exchanges contained absolute and/or relative pitch and/or interval imitations. The total durations of dyads being in tonal synchrony were normally distributed (M = 3.71, SD = 2.44). Vocalisations based on harmonic series appeared organised around the major triad, containing significantly more simple frequency ratios (octave, fifth and third) than complex ones (non-major triad tones). Tonal synchrony and its characteristics are discussed in relation to infant-directed speech, communicative musicality, pre-reflective communication and its impact on the quality of early mother–infant interaction and child's development.     

Schizotypal traits are not related to multisensory integration or audiovisual speech perception

Multisensory integration, the binding of sensory information from different sensory modalities, may contribute to perceptual symptomatology in schizophrenia, including hallucinations and aberrant speech perception. Differences in multisensory integration and temporal processing, an important component of multisensory integration, are consistently found in schizophrenia. Evidence is emerging that these differences extend across the schizophrenia spectrum, including individuals in the general population with higher schizotypal traits. In the current study, we investigated the relationship between schizotypal traits and perceptual functioning, using audiovisual speech-in-noise, McGurk, and ternary synchrony judgment tasks. We measured schizotypal traits using the Schizotypal Personality Questionnaire (SPQ), hypothesizing that higher scores on Unusual Perceptual Experiences and Odd Speech subscales would be associated with decreased multisensory integration, increased susceptibility to distracting auditory speech, and less precise temporal processing. Surprisingly, these measures were not associated with the predicted subscales, suggesting that these perceptual differences may not be present across the schizophrenia spectrum.     

Psychophysiological Synchrony During Verbal Interaction in Romantic Relationships

Previous studies about romantic relationships have shown that the reciprocal influence between partners occurs not only at the behavioral and socio‐emotional levels, but also at the psychophysiological level. This reciprocal influence is expressed in a pattern of physiological synchrony between partners (i.e., coordinated dynamics of the physiological time series). The main aim of the present study was to explore the presence of a pattern of physiological synchrony in electrodermal activity (EDA) during a couple interaction task. A second objective was to compare the synchrony levels during a negative interaction condition versus a positive interaction condition. Finally, we analyzed the association between synchrony and self‐perception of empathy, dyadic empathy, and relationship satisfaction. Thirty‐two couples (64 individuals) participated in this study. Each couple performed a structured interaction task while the EDA of both partners was being registered. The quantification of synchrony was based on the cross‐correlation of both members' EDA time‐series. In order to control for coincidental synchrony, surrogate datasets were created by repeatedly shuffling the original data of spouses X and Y of a dyad and computing synchronies on the basis of the shuffled data (pseudosynchrony values). Our results confirmed the presence of significant EDA synchrony during the interaction. We also found that synchrony was higher during the negative interactions relative to the positive interactions. Additionally, physiological synchrony during positive interaction was higher for those couples in which males scored higher in dyadic empathy. The clinical implications of these findings are discussed.     

Developmental changes in associations between auditory-visual events

The goal of the present study was twofold: to examine the influence of two amodal properties, co-location and temporal synchrony, on infants' associating a sight with a sound, and to determine if the relative influence of these properties on crossmodal learning changes with age. During familiarization 2-, 4-, 6- and 8-month-olds were presented two toys and a sound, with sights and sounds varying with respect to co-location and temporal synchrony. Following each familiarization phase infants were given a paired preference test to assess their learning of sight-sound associations. Measures of preferential looking revealed age-related changes in the influence of co-location and temporal synchrony on infants' learning sight-sound associations. At all ages, infants could use temporal synchrony and co-location as a basis for associating an auditory with a visual event and, in the absence of temporal synchrony, co-location was sufficient to support crossmodal learning. However, when these cues conflicted there were developmental changes in the influence of these cues on infants' learning auditory-visual associations. At 2 and 4 months infants associated the sounds with the toy that moved in synchrony with the sound's rhythm despite extreme violation of co-location of this sight and sound. In contrast, 6- and 8-month-olds did not associate a specific toy with the sound when co-location and synchrony information conflicted. The findings highlight the unique and interactive effects of distinct amodal properties on infants' learning arbitrary crossmodal relations. Possible explanations for the age shift in performance are discussed.     

Maternal and infant touching behaviours during perturbed interactions: Associations with maternal depressive symptomatology and infant crying

Touch is an important means through which mothers and infants co-regulate during periods of stress or perturbation. The present study examined the synchrony of maternal and infant touching behaviours among 41 mother-infant dyads, some of whom were deemed at-risk due to maternal depressive symptomatology. Mothers and their 4-month-old infants participated in the Still-Face (maternal emotional unavailability; SF) and Separation (maternal physical unavailability; SP) procedures. Infant crying was examined across procedures and investigated as a brief period of perturbation. Results revealed that mothers and infants displayed a positive pattern of tactile synchrony (coordinated, analogous changes in touch) during infant crying episodes. However, dyads in the high depression group displayed significantly less affectionate touch during instances of infant crying. Furthermore, more depressive symptoms were associated with less maternal and infant touch and lower rates of infant crying. This group of dyads may be less expressive via touch, be less affected by disruptions in their interactions, have impaired regulatory abilities, or simply require minimal amounts of touch to mutually regulate following social stressors and during brief perturbation periods. These findings enrich our limited knowledge about the dynamic interplay of maternal and infant touch and inform preventative intervention programs for at-risk groups.     

Chronic stress in the mother-infant dyad: Maternal hair cortisol,infant salivary cortisol and interactional synchrony

Stress physiology is shaped by early experience, with enduring effects on health. The relation of chronic maternal physiological stress, as indexed by hair cortisol, to infants’ stress systems and to mother-infant interaction quality has not been established. We examined maternal hair and salivary cortisol, six-month-old infants’ salivary cortisol, and mother-infant interaction in 121 mother-infant dyads. High maternal hair cortisol was related to higher infant average salivary cortisol concentration. Maternal hair cortisol and bedtime salivary cortisol were both uniquely related to infant bedtime salivary cortisol. Mothers with higher hair cortisol were more intrusive and had lower positive engagement synchrony with their infants. Maternal intrusiveness moderated the association of maternal hair cortisol and infant salivary cortisol, such that maternal hair and infant average salivary cortisol were related only when mothers were more intrusive. Maternal chronic physiological stress may upregulate infants’ developing stress systems, particularly in the context of lower mother-infant interaction quality.     

人际同步性现象：探索心理咨询过程中同盟关系的新视角

人际同步性是指两个或两个以上的人的言语特点、行为表现、生理指标以及神经生理活动在时间上出现重合的现象, 得益于近10年内技术上的突破, 研究者开始对心理咨询领域的人际同步现象进行初步的探索, 试图从该视角揭示心理咨询过程中咨访双方的互动模式和同盟建立的内在机制。近期研究主要关注非言语同步、生理同步、人际脑同步与同盟及其影响因素之间的关系, 并针对它们各自对同盟的作用机制发展出了相应的理论。未来的研究者可以更多地关注同盟动态变化过程中的人际同步性, 发展整合理论来回应同盟建立的内在机制, 并在临床应用上促进具有人际同步性的心理咨询互动过程。     

Dyadic synchrony among young Latina mothers and their toddlers: The role of maternal and child behavior

Synchronous interactions are an important indicator of parent-child relationship quality with positive implications for child development. Latina adolescent mothers face several demographic challenges that place them at risk for less synchronous interactions. To identify factors that may facilitate more optimal parent-child relationships in this population, our study examined maternal sensitivity and children’s behavioral styles as joint predictors of dyadic synchrony among young Latina mothers and their toddlers. Mother-toddler dyads (N = 170) were observed interacting across different tasks, and toddlers’ behavior was observed during the administration of a developmental test. Results of multivariate regressions revealed additive effects of maternal sensitivity and child behavioral styles (i.e., dysregulation and positive attentional control). Maternal sensitivity related to higher dyadic synchrony for the entire sample. Positive attentional control was related to higher dyadic synchrony for mother-daughter dyads only. Although no gender differences in dyadic synchrony or the behavior style variables emerged, the relative contribution of maternal and child factors differed by child gender, suggesting that mothers may have responded differently to similar behavior and affect displayed by boys and girls. The findings provide insights regarding factors that contribute to dyadic synchrony in this understudied population and emphasize the need to consider child gender when studying parent-child interactions in young Latina families.     

Spouses' Cortisol Associations and Moderators: Testing Physiological Synchrony and Connectedness in Everyday Life

In this study, associations were examined between cortisol levels of wives and husbands in 47 heterosexual married couples. Both partners' salivary cortisol levels were measured at the same moments seven times a day on 2 typical weekdays. After accounting for the effects of the diurnal rhythm of cortisol and relevant control variables, dyadic hierarchical linear modeling indicated significant positive linkages between partners' cortisol levels, consistent with the hypothesized within‐couple physiological synchrony. Variables reflecting more (spousal presence) or less connectedness (loneliness, being alone) were also collected at the time of each cortisol sample. Results indicated that husbands' cortisol levels were higher at moments they reported feeling lonelier and lower at moments they were in the presence of their spouse. Wives' cortisol levels were higher at moments they were alone. In addition, wife–husband cortisol synchrony was stronger for husbands who spent relatively more time with their spouse across the study period—even after accounting for time spent with others in general. These findings suggest that marital partners evidence positive within‐couple cortisol associations, and that connectedness (particularly physical closeness) may underpin spouses' physiological synchrony.     

On the discrepant results in synchrony judgment and temporal-order judgment tasks: a quantitative model

Research on the perception of temporal order uses either temporal-order judgment (TOJ) tasks or synchrony judgment (SJ) tasks, in both of which two stimuli are presented with some temporal delay and observers must judge the order of presentation. Results generally differ across tasks, raising concerns about whether they measure the same processes. We present a model including sensory and decisional parameters that places these tasks in a common framework that allows studying their implications on observed performance. TOJ tasks imply specific decisional components that explain the discrepancy of results obtained with TOJ and SJ tasks. The model is also tested against published data on audiovisual temporal-order judgments, and the fit is satisfactory, although model parameters are more accurately estimated with SJ tasks. Measures of latent point of subjective simultaneity and latent sensitivity are defined that are invariant across tasks by isolating the sensory parameters governing observed performance, whereas decisional parameters vary across tasks and account for observed differences across them. Our analyses concur with other evidence advising against the use of TOJ tasks in research on perception of temporal order.     

When I move,you move: Associations between automatic and person-coded measures of infant-mother synchrony during free-play using virtual in-home data collection

The relationship between movement synchrony and global scores of behavioral synchrony were investigated during a naturalistic free-play between 33 infants (ages 12- to 24-months) and their mothers using a video-conferencing platform. We assessed movement synchrony by applying an automatic tool, motion-energy analysis (MEA), to the obtained video data. Dyadic movement synchrony was associated with higher levels of maternal sensitivity, infant involvement, dyadic reciprocity, and a child-led interaction pattern. This demonstrates the feasibility of using MEA as an automatic tool for assessing movement synchrony in mother-infant dyads and its application for investigating naturalistic at-home free play sessions in a remote setting.     

The Bursts and Lulls of Multimodal Interaction: Temporal Distributions of Behavior Reveal Differences Between Verbal and Non‐Verbal Communication

Recent studies of naturalistic face‐to‐face communication have demonstrated coordination patterns such as the temporal matching of verbal and non‐verbal behavior, which provides evidence for the proposal that verbal and non‐verbal communicative control derives from one system. In this study, we argue that the observed relationship between verbal and non‐verbal behaviors depends on the level of analysis. In a reanalysis of a corpus of naturalistic multimodal communication (Louwerse, Dale, Bard, & Jeuniaux, 2012 ), we focus on measuring the temporal patterns of specific communicative behaviors in terms of their burstiness. We examined burstiness estimates across different roles of the speaker and different communicative modalities. We observed more burstiness for verbal versus non‐verbal channels, and for more versus less informative language subchannels. Using this new method for analyzing temporal patterns in communicative behaviors, we show that there is a complex relationship between verbal and non‐verbal channels. We propose a “temporal heterogeneity” hypothesis to explain how the language system adapts to the demands of dialog.