Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> By watching each other's lower oscillating leg, 2 seated Ss kept a common tempo and a particular phase relation of either 0 degrees (symmetric mode) or 180 degrees (alternate mode). This study investigated the differential stability of the 2 phase modes. In Experiment 1, in which Ss were instructed to remain in the initial phase mode, the alternate phase mode was found to be less stable as the frequency of oscillation increased. In addition, analysis of the nonsteady state cycles revealed evidence of a switching to the symmetric phase mode for the initial alternate phase mode trials. In Experiments 2 and 3, Ss were instructed to remain at a noninitial phase angle if it was found to be more comfortable. The transition observed between the 2 phase modes satisfies the criteria of a physical bifurcation--hysteresis, critical fluctuations, and divergence--and is consonant with previous findings on transitions in limb coordination within a person. Language: en <s> BIB001 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Between-person visual coordination of rhythmic limb movements was investigated under manipulation of both social and physical variables. Each member of a pair of participants oscillated a hand-held pendulum at the same tempo, with both visually coordinating their movements so as to maintain the alternate phase mode. Participants' social competence was assessed and they were paired to produce three types of combinations: high-high (HH), low-low (LL), and high-low (HL). The frequency of oscillation (set by a metronome) and the preferred frequency differ- ence of the pendulum combinations (set by changing the relative lengths of the pendulums to be coordinated) were manipulated. Mean relative phase angle 4 and its variability were measured as indices of coordination. Standard results from interlimb coordination were replicated in the manipulation of the physical vari- ables: (a) More breakdowns in phase locking (defined as mean 4s outside the stable 130 deg. to 230 deg. range) were observed for the higher fr... <s> BIB002 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Past research has shown that interpersonal interactions are characterized by a tacit coordination of motor movements of the participants and has suggested that the emergent synchrony might be explained by a coupled oscillator dynamic. This study investigates whether unintended between-person coordination can be demonstrated in a laboratory task that will allow an evaluation of whether such dynamical processes are involved. Ten pairs of participants performed a simple rhythmic task in which they had visual information about each other's movements but had no goal to coordinate. A cross-spectral analysis of the movements revealed higher coherence and a distribution of relative phase angles that was dominated by values near 0 deg. and 180 deg. These results support the hypothesis that dynamical organizing principles are involved in natural interpersonal synchrony. <s> BIB003 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Intraand interpersonal inter]imb coordination of pendulums swung from the wrist was investigated. For both kinds of coordination, the steady state and breakdown of bimanual rhythmic coordination as indexed by the time series of the relative phase angle it were studied under the manipulation of coordination mode, frequency of oscillation, and the difference in the eigenfrequencies (preferred tempos) of the individual oscillating limbs. The properties observed for both intraand interpersonal coordination were those predicted by a dynamical model of rhythmic coordination that considers the coordinated limbs coupled to be nonlinear oscillators. Using a regression method, the coupling strengths of the coupled system were recovered. As predicted by the dynamical model, the strength of the dynamic was generally greater for the in-phase than the anti-phase mode and decreased with increasing frequency. Further, the strength of the interpersonal interlimb coupling was weaker than that of intrapersonal interlimb coupling. <s> BIB004 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Cross-correlation and most other longitudinal analyses assume that the association between 2 variables is stationary. Thus, a sample of occasions of measurement is expected to be representative of the association between variables regardless of the time of onset or number of occasions in the sample. The authors propose a method to analyze the association between 2 variables when the assumption of stationarity may not be warranted. The method results in estimates of both the strength of peak association and the time lag when the peak association occurred for a range of starting values of elapsed time from the beginning of an experiment. <s> BIB005 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Mirror symmetry between individuals is a behavioral phenomenon that is commonly observed in conversation: individuals tend to mimic each other’s postures and gestures as a part of a shared dialog. The present work studies the process of symmetry building and symmetry breaking in the movements of pairs of individuals while imitating each others’ movements in dance. Spatial and temporal symmetries are found in the overall velocities from the results of full body motion tracking. This work was supported in part by NIA grant R29 AG14983-01 and a grant from the University of Notre Dame. We wish to thank Elizabeth Marsh who assisted in gathering these data. Corresponding author: Steven M. Boker, Department of Psychology, The University of Notre Dame, Notre Dame Indiana 46556, USA; sboker@nd.edu; http://www.nd.edu/ sboker. SYMMETRY IN SYNCHRONIZED MOVEMENT 2 <s> BIB006 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> The research was designed to evaluate interpersonal coordination during conversation with a new measurement tool. The experiment uses an analysis based on recurrence strategies, known as cross recurrence quantification, to evaluate the shared activity between 2 postural time series in reconstructed phase space. Pairs of participants were found to share more locations in phase space (greater recurrence) in conditions where they were conversing with one another to solve a puzzle task than in conditions in which they conversed with others. The trajectories of pairs of participants also showed less divergence when they conversed with each other than when they conversed with others as well. This is offered as objective evidence of interpersonal coordination of postural sway in the context of a cooperative verbal task. <s> BIB007 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> An order parameter equation for correlated limb movements was applied to rhythmic coordination between the limbs of two people. The interlimb coordination was established and maintained through vision. Manipulations of frequency competition, coupled frequency, and intended mode (in-phase or anti-phase) produced equilibria and fluctuations in relative phase predicted by the order parameter equation and confirmed originally in within-person coordination. It was concluded that there is an elementary coordination dynamics governing the rhythmic coordination between organisms as well as between components of a single organism. <s> BIB008 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Looking To Understand: The Coupling Between Speakers’ and Listeners’ Eye Movements and its Relationship to Discourse Comprehension Daniel C. Richardson (richardson@psych.stanford.edu) Department of Psychology, Stanford University Stanford, CA 94305, USA Rick Dale (rad28@cornell.edu) Department of Psychology, Cornell University Ithaca, NY 14853, USA Abstract discussing a diagram drawn on a whiteboard, figuring out together how to do something on a computer, or talking during a movie. Uniquely poised between perception and cognition, eye movements can reveal cognitive processes such as speech planning, language comprehension, memory, mental imagery and decision making. The current experiment investigates whether the eye movements of a speaker and a listener to a visual common ground can provide insight into a discourse. While their eye movements were being recorded, participants spoke extemporaneously about a TV show whose cast members they were viewing. Later, other participants listened to these speeches while their eyes were tracked. Within this naturalistic paradigm using spontaneous speech, a number of results linking eye movements to speech comprehension, speech production and memory were replicated. More importantly, a cross- recurrence analysis demonstrated that speaker and listener eye movements were coupled, and that the strength of this relationship positively correlated with listeners’ comprehension. Just as the mental state of a single person can be reflected in patterns of eye movements, the commonality of mental states that is brought about by successful communication is mirrored in a similarity between speaker and listener’s eye movements. Eye movement Research Introduction Imagine standing in front of a painting, discussing it with a friend. As you talk, your eyes will scan across the image, moving approximately three times a second. They will be drawn by characteristics of the image itself, areas of contrast or detail, as well as features of the objects or people portrayed. Eye movements are driven both by properties of the visual world and processes in a person’s mind. Your gaze might also be influenced by what your friend is saying, what you say in reply, what is thought but not said, and where you agree and disagree. If this is so, what is the relationship between your eye movements and those of your friend? How is that relationship related to the flow of conversation between you? Language use often occurs within rich visual contexts such as this, and the interplay between linguistic processes and visual perception is of increasing interest to psycholinguists and vision researchers (Henderson & Ferreira, 2004). As yet, however, such processes have been limited to experiments that examine the eye movements of the speaker or the listener in isolation. Language use, more often than not, occurs within a richer social context as well. Direct eye contact between conversants plays an interesting, crucial role in coordinating a conversation (Bavelas, Coates, & Johnson, 2002), and in conveying various attitudes or social roles (Argyle & Cook, 1976). The focus of the current experiment, however, is cases such as those introduced at the outset, where conversants are not looking at each other, but at some visual scene that is the topic of the conversation. More common examples might be Eye movements of a speaker If a speaker is asked to describe a simple scene, they will fixate the objects in the order in which they are mentioned, around 900ms before naming them (Griffin & Bock, 2000; Meyer, Sleiderink, & Levelt, 1998). Since such pictures can be identified rapidly, it is argued that during this time speakers are not just retrieving words but selecting and planning which to use. Eye movements of a listener Eye movement research has shown that there is a tight interdependence between speech recognition and visual perception. Eye movements to potential referents for a word can provide evidence for a lexical item being recognized before the word is finished being spoken. The link between visual and linguistic processing can also be seen in eye movements that disambiguate syntactic structures (Tanenhaus, Spivey Knowlton, Eberhard, & Sedivy, 1995) and anticipate the future agents of actions (Kamide, Altmann, & Haywood, 2003). Recent studies of the eye- movements of a participant engaged in a conversation with another naive participant reveal a remarkable sensitivity to the referential domains established by the task, the visual context and the preceding conversation (Brown-Schmidt, Campana, & Tanenhaus, 2004). Qualitatively, eye movement research reveals a very close, time-locked integration between visual and linguistic processing (Tanenhaus, Magnuson, Dahan, & Chambers, 2000). Although fixation times are heavily modulated by context, as a very rough quantitative guide, research suggests that listeners will fixate an object around 400-800ms after the name onset. <s> BIB009 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Previous research has demonstrated that people’s movements can become unintentionally coordinated during interpersonal interaction. The current study sought to uncover the degree to which visual and verbal (conversation) interaction constrains and organizes the rhythmic limb movements of coactors. Two experiments were conducted in which pairs of participants completed an interpersonal puzzle task while swinging handheld pendulums with instructions that minimized intentional coordination but facilitated either visual or verbal interaction. Cross-spectral analysis revealed a higher degree of coordination for conditions in which the pairs were visually coupled. In contrast, verbal interaction alone was not found to provide a sufficient medium for unintentional coordination to occur, nor did it enhance the unintentional coordination that emerged during visual interaction. The results raise questions concerning differences between visual and verbal informational linkages during interaction and how these differences may affect interpersonal movement production and its coordination. Interpersonal interaction often results in the movements of two interactants being coordinated. The dyadically defined goals that intentionally constrain interpersonal interaction are typically responsible for the emergence of this coordination. For instance, when two people are dancing, moving a table together, or walking step-by-step with one another, each individual’s behavior is coupled to their partner’s so a shared goal can be achieved in a fluid and unperturbed manner. However, although interpersonal coordination is typically understood as intentional, highly task constrained, and sometimes overtly controlled through physical contact, it is also the case that movement coordination can occur <s> BIB010 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Synchrony is a pervasive concept relevant to diverse domains in physics, biology, and the social sciences. This article reviews some of the evidence both from natural and human systems. Our main focus is on the role of synchrony in psychotherapy research. Its association with empathy, rapport and the therapeutic relationship has been pointed out repeatedly, yet close evaluation of empirical studies suggests that the evidence remains inconclusive. Particularly in naturalistic studies, research employing synchrony as a specific measure is still lacking. We suggest a new approach to studying synchrony in psychotherapies under field conditions: Image-differencing is a video-based algorithm quantifying the amount of movement in pre-selected regions. Our methodology can be compared to the approach from the seminal work of Condon & Ogston (1966). The statistical analysis we employ detects synchrony on a global level, irrespective of the specific body parts moving. Synchrony thus defined is considered a general measure of coordination of interacting individuals. Exemplary data show the feasibility of this approach and its potential contribution to psychotherapy research. <s> BIB011 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Conversational interactions are cooperatively constructed activities in which participants negotiate their entrances, turns and alignments with other speakers, oftentimes with an underlying long-term objective of obtaining some agreement. Obtaining a final and morally binding accord in a conversational interaction is of importance in a great variety of contexts, particularly in psychotherapeutic interactions, in contractual negotiations or in educational contexts. Various prosodic and gestural elements in a conversational interaction can be interpreted as signals of a speaker's agreement and they are probably of importance in the emergence of an accord in a conversational exchange. In this paper, we survey the social and psychological context of agreement seeking, as well as the existing literature on the visual and prosodic measurement of agreement in conversational settings. <s> BIB012 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Abstract Spontaneous social coordination has been extensively described in natural settings but so far no controlled methodological approaches have been employed that systematically advance investigations into the possible self-organized nature of bond formation and dissolution between humans. We hypothesized that, under certain contexts, spontaneous synchrony—a well-described phenomenon in biological and physical settings—could emerge spontaneously between humans as a result of information exchange. Here, a new way to quantify interpersonal interactions in real time is proposed. In a simple experimental paradigm, pairs of participants facing each other were required to actively produce actions, while provided (or not) with the vision of similar actions being performed by someone else. New indices of interpersonal coordination, inspired by the theoretical framework of coordination dynamics (based on relative phase and frequency overlap between movements of individuals forming a pair) were developed and us... <s> BIB013 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> This work aims at defining a computational model of human emotional entrainment. Music, as a non-verbal language to express emotions, is chosen as an ideal test bed for these aims. We start from multimodal gesture and motion signals, recorded in a real world collaborative condition in an ecological setting. Four violin players were asked to play, alone or in duo, a music fragment in two different perceptual feedback modalities and in four different emotional states. We focused our attention on phase synchronisation of the head motions of the players. From observation by subjects (musicians and observers), an evidence of entrainment emerges between players. The preliminary results, based on a reduced data set, however do not grasp fully this phenomenon. A more extended analysis is current subject of investigation. <s> BIB014 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Body movement synchrony (i.e. rhythmic synchronization between the body movements of interacting partners) has been described by subjective impressions of skilled counselors and has been considered to reflect the depth of the client-counselor relationship. This study analyzed temporal changes in body movement synchrony through a video analysis of client-counselor dialogues in counseling sessions. Four 50-minute psychotherapeutic counseling sessions were analyzed, including two negatively evaluated sessions (low evaluation groups) and two positively evaluated sessions (high evaluation groups). In addition, two 50-minute ordinary advice sessions between two high school teachers and the clients in the high rating group were analyzed. All sessions represent role-playing. The intensity of the participants' body movement was measured using a video-based system. Temporal change of body movement synchrony was analyzed using moving correlations of the intensity between the two time series. The results revealed (1) A consistent temporal pattern among the four counseling cases, though the moving correlation coefficients were higher for the high evaluation group than the low evaluation group and (2) Different temporal patterns for the counseling and advice sessions even when the clients were the same. These results were discussed from the perspective of the quality of client-counselor relationship. <s> BIB015 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> This study examined the influence of sex, social dominance, and context on motion-tracked head movements during dyadic conversations. Windowed cross-correlation analyses found high peak correlation between conversants' head movements over short (≈2-s) intervals and a high degree of nonstationarity. Nonstationarity in head movements was found to be positively related to the number of men in a conversation. Surrogate data analysis offsetting the conversants' time series by a large lag was unable to reject the null hypothesis that the observed high peak correlations were unrelated to short-term coordination between conversants. One way that high peak correlations could be observed when 2 time series are offset by a large time lag is for each time series to exhibit self-similarity over a range of scales. Multifractal analysis found small-scale fluctuations to be persistent, τ(q) 0.5. These results are consistent with a view that symmetry is formed between conversants over short intervals and that this symmetry is broken at longer, irregular intervals. <s> BIB016 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> This paper describes recent work on the automatic extraction of visual and audio parameters relating to the detection of synchrony in discourse, and to the modelling of active listening for advanced speech technology. It reports findings based on image processing that reliably identify the strong entrainment between members of a group conversation, and describes techniques for the extraction and analysis of such information. <s> BIB017 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> This research is concerned with synchronization (or entrainment), and in particular on emotional synchronization, which is likely to be an important driver of collaborative processes. We focus on ensemble musical performance, an ideal test-bed for the development of models and techniques for measuring creative social interaction in an ecologically valid framework. Ongoing work and early results on the automated analysis in real-time of non-verbal cues related to expressive gesture in social interaction is briefly presented. <s> BIB018 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> This paper presents a number of algorithms andrelated software modules for the automated analysisin real-time of non-verbal cues related to expressivegesture in social interaction. Analysis is based onPhase Synchronisation (PS) and RecurrenceQuantification Analysis. We start from the hypothesisthat PS is one of the low-level social signalsexplaining empathy and dominance in a small groupof users. Real- time implementation of the algorithmsis available in the EyesWeb XMI Social SignalProcessing Library. Applications of the approach isin user-centric media and in particular in activemusic listening (EU ICT FP7 Project SAME). <s> BIB019 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Nonverbal synchrony in face-to-face interaction has been studied in numerous empirical investigations focusing on various communication channels. Furthermore, the pervasiveness of synchrony in physics, chemistry and biology adds to its face-validity. This paper is focused on establishing criteria for a statistical evaluation of synchrony in human interaction. When assessing synchrony in any communication context, it is necessary to distinguish genuine synchrony from pseudosynchrony, which may arise due to random coincidence. By using a bootstrap approach, we demonstrate a way to quantify the amount of synchrony that goes beyond random coincidence, thus establishing an objective measure for the phenomenon. Applying this technique to psychotherapy data, we develop a hypothesis-driven empirical evaluation of nonverbal synchrony. The method of surrogate testing in order to control for chance is suitable to any corpus of empirical data and lends itself to better empirically informed inference. <s> BIB020 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> The decisive role of interpersonal coordination in social interactions is well established. As human beings, we are "experts" in decoding and producing social signals, learning since our birth. Though, equipping a machine with the same abilities represents a great challenge to design socially-accepted interfaces. Assessing automatically this coordination requires selecting the most relevant features. In this paper, various audio and visual features are investigated to characterize interactional synchrony in a cooperative task. A hierarchical representation of the similarity between extracted features is proposed. The properties of time-domain (correlation coefficients) and frequency-domain (coherence) synchrony measures are confronted. The presented results support the evidence that synchrony is a multimodal phenomenon. Moreover, it can be assessed both on local (short-length windows of interaction) or global scales (entire interaction). <s> BIB021 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> An experiment was conducted to investigate whether human observers use knowledge of the differences in focus of attention in multiparty interaction to identify the speaker amongst the meeting participants. A virtual environment was used to have good stimulus control. Head orientations were displayed as the only cue for focus attention. The orientations were derived from a corpus of tracked head movements. We present some properties of the relation between head orientations and speaker--listener status, as found in the corpus. With respect to the experiment, it appears that people use knowledge of the patterns in focus of attention to distinguish the speaker from the listeners. However, the human speaker identification results were rather low. Head orientations (or focus of attention) alone do not provide a sufficient cue for reliable identification of the speaker in a multiparty setting. <s> BIB022 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> This paper presents a multimodal system for real-time analysis of nonverbal affective social interaction in small groups of users. The focus is on two major aspects of affective social interaction: the synchronization of the affective behavior within a small group and the emergence of functional roles, such as leadership. A small group of users is modeled as a complex system consisting of single interacting components that can auto-organize and show global properties. Techniques are developed for computing quantitative measures of both synchronization and leadership. Music is selected as experimental test-bed since it is a clear example of interactive and social activity, where affective nonverbal communication plays a fundamental role. The system has been implemented as software modules for the EyesWeb XMI platform (http://www.eyesweb.org). It has been used in experimental frameworks (a violin duo and a string quartet) and in real-world applications (in user-centric applications for active music listening). Further application scenarios include entertainment, edutainment, therapy and rehabilitation, cultural heritage, and museum applications. Research has been carried out in the framework of the EU-ICT FP7 Project SAME (http://www.sameproject.eu). <s> BIB023 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Nonverbal synchrony is an important and natural element in human-human interaction. It can also play various roles in human-computer interaction. In particular this is the case in the interaction between humans and the virtual humans that inhabit our cyber worlds. Virtual humans need to adapt their behavior to the behavior of their human interaction partners in order to maintain a natural and continuous interaction synchronization. This paper surveys approaches to modeling synchronization and applications where this modeling is important. Apart from presenting this framework, we also present a quantitative method for measuring the level of nonverbal synchrony in an interaction and observations on future research that allows embedding such methods in models of interaction behavior of virtual humans. <s> BIB024 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> Objective: The authors quantified nonverbal synchrony—the coordination of patient's and therapist's movement—in a random sample of same-sex psychotherapy dyads. The authors contrasted nonverbal synchrony in these dyads with a control condition and assessed its association with session-level and overall psychotherapy outcome. Method: Using an automated objective video analysis algorithm (Motion Energy Analysis; MEA), the authors calculated nonverbal synchrony in (n = 104) videotaped psychotherapy sessions from 70 Caucasian patients (37 women, 33 men, mean age = 36.5 years, SD = 10.2) treated at an outpatient psychotherapy clinic. The sample was randomly drawn from an archive (N = 301) of routinely videotaped psychotherapies. Patients and their therapists assessed session impact with self-report postsession questionnaires. A battery of pre- and postsymptomatology questionnaires measured therapy effectiveness. Results: The authors found that nonverbal synchrony is higher in genuine interactions contrasted with pseudointeractions (a control condition generated by a specifically designed shuffling procedure). Furthermore, nonverbal synchrony is associated with session-level process as well as therapy outcome: It is increased in sessions rated by patients as manifesting high relationship quality and in patients experiencing high self-efficacy. Higher nonverbal synchrony characterized psychotherapies with higher symptom reduction. Conclusions: The results suggest that nonverbal synchrony embodies the patients' self-reported quality of the relationship and further variables of therapy process. This hitherto overlooked facet of therapeutic relationships might prove useful as an indicator of therapy progress and outcome. <s> BIB025 </s> Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines <s> Features <s> During face-to-face interpersonal interaction, people have a tendency to mimic each other. People not only mimic postures, mannerisms, moods or emotions, but they also mimic several speech-related behaviors. In this paper we describe how visual and vocal behavioral information expressed between two interlocutors can be used to detect and identify visual and vocal mimicry. We investigate expressions of mimicry and aim to learn more about in which situation and to what extent mimicry occurs. The observable effects of mimicry can be explored by representing and recognizing mimicry using visual and vocal features. In order to automatically analyze how to extract and integrate this behavioral information into a multimodal mimicry detection framework for improving affective computing, this paper addresses the main challenge: mimicry representation in terms of optimal behavioral feature extraction and automatic integration in both audio and video modalities. <s> BIB026
The first step in computing synchrony is to extract the relevant features of the dyad's motion. With the exception of Delaherche and Chetouani, who tried to model the coordination between movement features and prosodic features of speech (pitch, energy, pause, and vocalic energy) BIB021 , previous studies have focused on unimodal features. We can distinguish between studies focusing on the movement of a single body part and those capturing the overall movement of the dyad. Several acquisition techniques are prominent in the literature: motion-tracking devices, image-processing techniques (tracking algorithms, image differencing), and physiological sensors. Studies on a single body part usually use dedicated motion tracking devices (speaker tongue position  , finger motion BIB013 , eye movement BIB009 , hand motion  , leg motion BIB001 ). Several studies have focused on the coordination between the postural movements of the participants BIB007 ,  ,  , as postural movements can be mediated by a common tempo of verbal interaction. Numerous studies focus on head motion, which can convey emotion, acknowledgement, or active participation in an interaction. Head motion is captured using either a motion-tracking device BIB016 , BIB005 , BIB022 or a video-based tracking algorithm  ,  , BIB017 , BIB023 , BIB014 , BIB018 . Many studies capture the global movements of the participants BIB019 ,  , BIB006 , BIB021 , BIB011 , BIB012 , BIB024 , BIB020 , BIB025 , BIB015 ,  , BIB026 . Except for Boker and Rotondo BIB006 , who used a motiontracking device, these studies use a video-based algorithm to evaluate the dyad's motion. Other studies have also focused on the motion of an apparatus being actuated by the participants (swinging pendulum BIB008 , BIB004 , BIB002 , BIB003 , BIB010 or rocking chair  ).