Attentional load associated with performing and stabilizing a between-persons coordination of rhythmic limb movements

Dynamics in interbrain synchronization while playing a piano duet

Humans interact with each other through actions that are implemented by sensory and motor processes. To investigate the role of interbrain synchronization emerging during interpersonal action coordination, electroencephalography data from 13 pairs of pianists were recorded simultaneously while they performed a duet together. The study aimed to investigate whether interbrain phase couplings can be reduced to similar bottom-up driven processes during synchronous play, or rather represent cognitive top-down control required during periods of higher coordination demands. To induce such periods, one of the musicians acted as a confederate who deliberately desynchronized the play. As intended, on the behavioral level, the perturbation caused a breakdown in the synchronization of the musicians' play and in its stability across trials. On the brain level, interbrain synchrony, as measured by the interbrain phase coherence (IPC), increased in the delta and theta frequency bands during perturbation as compared to non-perturbed trials. Interestingly, this increase in IPC in the delta band was accompanied by the shift of the phase difference angle from in-phase toward anti-phase synchrony. In conclusion, the current study demonstrates that interbrain synchronization is based on the interpersonal temporal alignment of different brain mechanisms and is not simply reducible to similar sensory or motor responses.

Paradoxical decrease of imitation performance with age in children

Imitation development was studied in a cross-sectional design involving 174 primary-school children (aged 6-10), focusing on the effect of actions' complexity and error analysis to infer the underlying cognitive processes. Participants had to imitate the model's actions as if they were in front of a mirror ('specularly'). Complexity varied across three levels: movements of a single limb; arm and leg of the same body side; or arm and leg of opposite body sides. While the overall error rate decreased with age, this was not true of all error categories. The rate of 'side' errors (using a limb of the wrong body side) paradoxically increased with age (from 9 years). However, with increasing age, the error rate also became less sensitive to the complexity of the action. This pattern is consistent with the hypothesis that older children have the working memory (WM) resources and the body knowledge necessary to imitate 'anatomically', which leads to additional side errors. Younger children might be paradoxically free from such interference because their WM and/or body knowledge are insufficient for anatomical imitation. Yet, their limited WM resources would prevent them from successfully managing the conflict between spatial codes involved in complex actions (e.g. moving the left arm and the right leg). We also found evidence that action side and content might be stored in separate short-term memory (STM) systems: increasing the number of sides to be encoded only affected side retrieval, but not content retrieval; symmetrically, increasing the content (number of movements) of the action only affected content retrieval, but not side retrieval. In conclusion, results suggest that anatomical imitation might interfere with specular imitation at age 9 and that STM storages for side and content of actions are separate.

Interpersonal synchronization of spontaneously generated body movements

Interpersonal movement synchrony (IMS) is central to social behavior in several species. In humans, IMS is typically studied using structured tasks requiring participants to produce specific body movements. Instead, spontaneously generated (i.e., not instructed) movements have received less attention. To test whether spontaneous movements synchronize interpersonally, we recorded full-body kinematics from dyads of participants who were only asked to sit face-to-face and to look at each other. We manipulated interpersonal (i) visual contact and (ii) spatial proximity. We found that spontaneous movements synchronized across participants only when they could see each other and regardless of interpersonal spatial proximity. This synchronization emerged very rapidly and did not selectively entail homologous body parts (as in mimicry); rather, the synchrony generalized to nearly all possible combinations of body parts. Hence, spontaneous behavior alone can lead to IMS. More generally, our results highlight that IMS can be studied under natural and unconstrained conditions.

Endogenous sources of interbrain synchrony in duetting pianists

When people interact with each other, their brains synchronize. However, it remains unclear whether interbrain synchrony (IBS) is functionally relevant for social interaction or stems from exposure of individual brains to identical sensorimotor information. To disentangle these views, the current dual-EEG study investigated amplitude-based IBS in pianists jointly performing duets containing a silent pause followed by a tempo change. First, we manipulated the similarity of the anticipated tempo change and measured IBS during the pause, hence, capturing the alignment of purely endogenous, temporal plans without sound or movement. Notably, right posterior gamma IBS was higher when partners planned similar tempi, it predicted whether partners' tempi matched after the pause, and it was modulated only in real, not in surrogate pairs. Second, we manipulated the familiarity with the partner's actions and measured IBS during joint performance with sound. Although sensorimotor information was similar across conditions, gamma IBS was higher when partners were unfamiliar with each other's part and had to attend more closely to the sound of the performance. These combined findings demonstrate that IBS is not merely an epiphenomenon of shared sensorimotor information but can also hinge on endogenous, cognitive processes crucial for behavioral synchrony and successful social interaction.

Effects of rhythmic auditory stimulation on upper-limb movements in patients with Parkinson's disease

INTRODUCTION

Rhythmic auditory stimulation (RAS) is an effective technique extensively used to alleviate lower-limb bradykinesia in patients with Parkinson's disease (PD). However, RAS effects on upper-limb bradykinesia have not been well studied. This study investigated immediate effects of RAS on upper-limb movements in PD patients and healthy people.

METHODS

PD patients (n = 23) and age- and gender-matched healthy controls (n = 23) executed left-hand, right-hand, and both-hand movement tasks of the Purdue Pegboard Test when listening to the beats of RAS, including 100%, 110%, and 120% of the baseline tempo, which was fastest movement performance of each participant without the aid of RAS. Sequence of RAS and tasks was randomized for each participant.

RESULTS

PD patients had slower upper-limb movements than did health controls. An interaction was found between RAS and tasks. In both patients and controls and for all task conditions, 120%RAS induced higher scores than did 110% RAS, and the latter induced higher scores than did 100%RAS. In both patients and controls and for all RAS conditions, the right-hand condition induced higher scores than did the left-hand condition, and the latter induced higher scores than did the both-hand condition.

CONCLUSIONS

RAS was effective in regulating upper-limb movements in PD patients, which may be explained by rich neural connections between auditory and motor cortical areas in humans. Clinical practitioners should consider using RAS in clinical therapy. Future neuroimaging studies are needed to explore neural mechanisms of RAS in PD patients.

The Components of Interpersonal Synchrony in the Typical Population and in Autism: A Conceptual Analysis

Interpersonal synchrony – the tendency for social partners to temporally co-ordinate their behaviour when interacting – is a ubiquitous feature of social interactions. Synchronous interactions play a key role in development, and promote social bonding and a range of pro-social behavioural outcomes across the lifespan. The process of achieving and maintaining interpersonal synchrony is highly complex, with inputs required from across perceptual, temporal, motor, and socio-cognitive domains. In this conceptual analysis, we synthesise evidence from across these domains to establish the key components underpinning successful non-verbal interpersonal synchrony, how such processes interact, and factors that may moderate their operation. We also consider emerging evidence that interpersonal synchrony is reduced in autistic populations. We use our account of the components contributing to interpersonal synchrony in the typical population to identify potential points of divergence in interpersonal synchrony in autism. The relationship between interpersonal synchrony and broader aspects of social communication in autism are also considered, together with implications for future research.

Effects of unintentional coordination on attentional load

The goal of this study was to evaluate the impact of unintentional (spontaneous) coordination on high attentional visual load. More precisely, we wondered whether such coordination could free up some attentional resources and help improve performance in other more demanding attentional tasks. An experiment was performed in which participant attentional allocation was challenged by performing three tasks simultaneously while simultaneously being induced to unintentional entrain to an environmental rhythm. The first task was an interception task associated with a Stroop test to increase their attentional load. The second task was a reaction time test to alarms in different modalities (auditory, visual and bimodal) which was used to assess participant attentional load. The third task was a motor task in which participants were asked to swing their legs at a preferred frequency. The interface background brightness intensity was either synchronized in real time using a bidirectional coupling to participant leg movement or the background brightness was not changing at all. Our results on the reaction time task demonstrated that participants exhibited better reaction times for alarms in the bimodal condition than in the auditory condition and lastly for the visual condition. Also, participants exhibited a lower reaction time to alarms when the background brightness was synchronizing with their leg regardless the alarm modality. Overall, our study suggests a beneficial effect of unintentional environmental coordination on attentional resource allocation and highlights the importance of bidirectionality in interaction.

The effect of inherent and incidental constraints on bimanual and social coordination

The current investigation was designed to examine the influence of inherent and incidental constraints on the stability characteristics associated with bimanual and social coordination. Individual participants (N = 9) and pairs of participants (N = 18, 9 pairs) were required to rhythmically coordinate patterns of isometric forces in 1:1 in-phase and 1:2 multi-frequency patterns by exerting force with their right and left limbs. Lissajous information was provided to guide performance. Participants performed 13 practice trials and 1 test trial per pattern. On the test trial, muscle activity from the triceps brachii muscles of each arm was recorded. EMG-EMG coherence between the two EMG signals was calculated using wavelet coherence. The behavioral data indicated that individual participants performed the 1:1 in-phase pattern more accurately and with less variability than paired participants. The EMG coherence analysis indicated significantly higher coherence for individual participants than for the paired participants during the 1:1 in-phase pattern, whereas no differences were observed between groups for the 1:2 coordination pattern. The results of the current investigation support the notion that neural crosstalk can stabilize 1:1 in-phase coordination when contralateral and ipsilateral signals are integrated via the neuromuscular linkage between two effectors.

In and out of synchrony-Behavioral and physiological dynamics of dyadic interpersonal coordination

Interpersonal synchrony, the temporal coordination of actions, emotions, thoughts and physiological processes, is a widely studied ubiquitous phenomenon. Research has already established that more synchrony is not always more beneficial, especially in the fields of emotional and physiological synchrony. Despite this fact, the dominant tone in the literature is that behavioral interpersonal synchrony is a pro-social phenomenon, and hence, in social contexts, more behavioral synchrony is generally considered better. In accordance with that tone, the naturally occurring dynamics of moving in and out of synchrony have rarely been studied or considered as an adaptive state. In the present article, we aim to present a new model of interpersonal synchrony, based on the existing literature assessing synchrony as well as the ideas of complex dynamical systems. At the core of our model is the idea that two tendencies exist simultaneously, one to synchronize with others and another to move out of synchrony and act independently. We suggest that an adaptive interpersonal system is a flexible one, able to continuously adjust itself to the social context. We suggest that the concept of meta-stability might be a marker of such a flexible interpersonal system. Moreover, the model considers both behavioral and physiological aspects in order to provide a more extensive account. We present research implications of the model, as well as a demonstration of the model's applicability to data, and provide code researchers can use to analyze their own data in these methods. Finally, we discuss future directions in detail.

Sound matters: The impact of auditory deprivation on movement precision in rowing

Purpose of the study was to quantify the importance of auditory feedback for movement precision in elevated rowing task difficulty with elite athletes under normal and masked hearing conditions. It was hypothesized that rowing with masked hearing would reduce the precision of movement, particularly at the non-usual/less-preferred stroke frequencies (SF). Self-reported questionnaires helped to understand the difficulty of the task. Twenty rowers completed 2 × 1000 m-distance-blocks, each separated into 4 × 250 m, with increasing SF 18, 20, 22 24 strokes/minute once with normal and once with masked hearing. Precision was determined as the deviation between the SF target and the SF actually performed (DSF). Athletes' subjective perception was requested before and after the experiment. A 2 (hearing condition) × 4 (SF 18, 20, 22, 24) repeated measures ANOVA showed systematically larger DSF during masked hearing for all SFs compared to the DSF in the normal hearing condition (p < .01). Further, the highest DSFs were found for SF 18 and 24 in both hearing conditions (no interaction effect). The athletes' perception of the relevance of natural movement sounds for their rowing performance changed when evaluated before and after the experiment. Rowing without hearing was evaluated as mentally more demanding than physically. The results confirmed our initial assumptions and showed the relevance of natural auditory information for movement precision in rowing practice, even at a high level of expertise.

Influence of perceived emotion and gender on social motor coordination

Theorists have long postulated that facial properties such as emotion and sex are potent social stimuli that influence how individuals act. Yet extant scientific findings were mainly derived from investigations on the prompt motor response upon the presentation of affective stimuli, which were mostly delivered by means of pictures, videos, or text. A theoretical question remains unaddressed concerning how the perception of emotion and sex would modulate the dynamics of a continuous coordinated behaviour. Conceived in the framework of dynamical approach to interpersonal motor coordination, the present study aimed to address this question by adopting the coupled-oscillators paradigm. Twenty-one participants performed in-phase and anti-phase coordination with two avatars (male and female) displaying three emotional expressions (neutral, happy, and angry) at different frequencies (100% and 150% of the participant's preferred frequency) by executing horizontal rhythmic left-right oscillatory movements. Time to initiate movement (TIM), mean relative phase error (MnRP), and standard deviation of relative phase (SDRP) were calculated as indices of reaction time, deviation from the intended pattern of coordination, and coordination stability, respectively. Results showed that in anti-phase condition at 150% frequency, MnRP was lower with the angry and the female avatar. In addition, coordination was found to be more stable with the male avatar than the female one when both displaying neutral emotion. But the happy female avatar was found to elicit more stable coordination than the neutral female avatar. These results implied that individuals are more relaxed to coordinate with the female than the male, and the sensorimotor system becomes more flexible to coordinate with an angry person. It is also suggested social roles influence how people coordinate, and individuals attend more to interact with a happy female. In sum, the present study evidenced that social perception is embodied in the interactive behaviour during social interaction.

Does interpersonal movement synchronization differ from synchronization with a moving object?

We examined whether movement synchronization is different during coordination with another person than during coordination with a moving object. In addition, the influence of belief in the other person's agency was assessed. Participants synchronized their lower-arm movements with a computer-controlled rhythmic reference movement. The reference movements were pre-recorded, biological movements and were identical in all conditions. They were presented either by means of a confederate's arm in a motor-driven manipulandum or by means of movements of the manipulandum alone. To assess the influence of the belief in the confederate's agency, participants either were or were not informed that the confederate's movements were motor driven. The strength of coupling between the participant's movements and the reference movements was assessed in terms of the standard deviation of relative phase and the time needed to re-establish the coordination pattern after an unexpected perturbation of the reference signal. Mean relative phase indicated whether the participant was leading or lagging the reference movements. Coupling strength was not affected by the presence of another person in the coordination task, nor by the belief in this person's agency. However, participants had a stronger tendency to lead while synchronizing with the manipulandum, indicating that they responded differently to the observed kinematics of this moving object than to the kinematics of the confederate's arm movements, at least when the confederate's agency was assumed. Hence, although neither the involvement of another person nor the participant's belief in this person's agency affected coupling strength, the form of the coupling seemed to be influenced by the former factor, suggesting a different attunement to the reference movements during a joint-action situation. Future research is required to determine whether these interpretations extend to unintentional and bidirectional coordination, in which agency is not only assumed but actually effectuated.

Rowing Crew Coordination Dynamics at Increasing Stroke Rates

In rowing, perfect synchronisation is important for optimal performance of a crew. Remarkably, a recent study on ergometers demonstrated that antiphase crew coordination might be mechanically more efficient by reducing the power lost to within-cycle velocity fluctuations of the boat. However, coupled oscillator dynamics predict the stability of the coordination to decrease with increasing stroke rate, which in case of antiphase may eventually yield breakdowns to in-phase. Therefore, this study examined the effects of increasing stroke rate on in- and antiphase crew coordination in rowing dyads. Eleven experienced dyads rowed on two mechanically coupled ergometers on slides, which allowed the ergometer system to move back and forth as one ‘boat’. The dyads performed a ramp trial in both in- and antiphase pattern, in which stroke rates gradually increased from 30 strokes per minute (spm) to as fast as possible in steps of 2 spm. Kinematics of rowers, handles and ergometers were captured. Two dyads showed a breakdown of antiphase into in-phase coordination at the first stroke rate of the ramp trial. The other nine dyads reached between 34–42 spm in antiphase but achieved higher rates in in-phase. As expected, the coordinative accuracy in antiphase was worse than in in-phase crew coordination, while, somewhat surprisingly, the coordinative variability did not differ between the patterns. Whereas crew coordination did not substantially deteriorate with increasing stroke rate, stroke rate did affect the velocity fluctuations of the ergometers: fluctuations were clearly larger in the in-phase pattern than in the antiphase pattern, and this difference significantly increased with stroke rate. Together, these results suggest that although antiphase rowing is less stable (i.e., less resistant to perturbation), potential on-water benefits of antiphase over in-phase rowing may actually increase with stroke rate.

Embodiment of intersubjective time: relational dynamics as attractors in the temporal coordination of interpersonal behaviors and experiences

This paper addresses the issue of “being together,” and more specifically the issue of “being together in time.” We provide with an integrative framework that is inspired by phenomenology, the enactive approach and dynamical systems theories. To do so, we first define embodiment as a living and lived phenomenon that emerges from agent-world coupling. We then show that embodiment is essentially dynamical and therefore we describe experiential, behavioral and brain dynamics. Both lived temporality and the temporality of the living appear to be complex, multiscale phenomena. Next we discuss embodied dynamics in the context of interpersonal interactions, and briefly review the empirical literature on between-persons temporal coordination. Overall, we propose that being together in time emerges from the relational dynamics of embodied interactions and their flexible co-regulation.

Aging induced loss of complexity and dedifferentiation: consequences for coordination dynamics within and between brain, muscular and behavioral levels

Growing evidence demonstrates that aging not only leads to structural and functional alterations of individual components of the neuro-musculo-skeletal system (NMSS) but also results in a systemic re-organization of interactions within and between the different levels and functional domains. Understanding the principles that drive the dynamics of these re-organizations is an important challenge for aging research. The present Hypothesis and Theory paper is a contribution in this direction. We propose that age-related declines in brain and behavior that have been characterized in the literature as dedifferentiation and the loss of complexity (LOC) are: (i) synonymous; and (ii) integrated. We argue that a causal link between the aforementioned phenomena exists, evident in the dynamic changes occurring in the aging NMSS. Through models and methods provided by a dynamical systems approach to coordination processes in complex living systems, we: (i) formalize operational hypotheses about the general principles of changes in cross-level and cross-domain interactions during aging; and (ii) develop a theory of the aging NMSS based on the combination of the frameworks of coordination dynamics (CD), dedifferentiation, and LOC. Finally, we provide operational predictions in the study of aging at neural, muscular, and behavioral levels, which lead to testable hypotheses and an experimental agenda to explore the link between CD, LOC and dedifferentiation within and between these different levels.

Difficulty leading interpersonal coordination: towards an embodied signature of social anxiety disorder

Defined by a persistent fear of embarrassment or negative evaluation while engaged in social interaction or public performance, social anxiety disorder (SAD) is one of the most common psychiatric syndromes. Previous research has made a considerable effort to better understand and assess this mental disorder. However, little attention has been paid to social motor behavior of patients with SAD despite its crucial importance in daily social interactions. Previous research has shown that the coordination of arm, head or postural movements of interacting people can reflect their mental states or feelings such as social connectedness and social motives, suggesting that interpersonal movement coordination may be impaired in patients suffering from SAD. The current study was specifically aimed at determining whether SAD affects the dynamics of social motor coordination. We compared the unintentional and intentional rhythmic coordination of a SAD group (19 patients paired with control participants) with the rhythmic coordination of a control group (19 control pairs) in an interpersonal pendulum coordination task. The results demonstrated that unintentional social motor coordination was preserved with SAD while intentional coordination was impaired. More specifically, intentional coordination became impaired when patients with SAD had to lead the coordination as indicated by poorer (i.e., more variable) coordination. These differences between intentional and unintentional coordination as well as between follower and leader roles reveal an impaired coordination dynamics that is specific to SAD, and thus, opens promising research directions to better understand, assess and treat this mental disorder.

Factors that determine directional constraint in ipsilateral hand-foot coordinated movements

In performing simultaneous rhythmic movements of the ipsilateral hand and foot, there are differences in the level of stability between same directional (stable) and opposite directional (unstable) movements. This is the directional constraint. In this study, we investigated three factors ("interaction in efferent process," "interaction of afferent signals," and "error correction") proposed to underlie for the directional constraint. We compared the performance of three tasks: (1) coordination of actively moved ipsilateral hand and foot, (2) active hand movement in coordination with passively moved foot, (3) active hand movement not coordinated with a passively moved foot. In each task, both same and opposite directional movements were executed. There was no difference between performance estimated with success rate for the first and second task. The directional constraint appeared in both tasks. Thus, the interaction in efferent processes, which was shown to be responsible for the directional constraint in bimanual coordination, was not involved with the directional constraint of ipsilateral hand-foot coordination. The directional constraint did not appear in the third task, which suggested that "interaction of afferent signals" also had no contribution. These results indicated that "error correction" must be the most critical of these factors for mediating the directional constraint in ipsilateral hand-foot coordinated movements.

Patterns of horse-rider coordination during endurance race: a dynamical system approach

In riding, most biomechanical studies have focused on the description of the horse locomotion in unridden condition. In this study, we draw the prospect of how the basic principles established in inter-personal coordination by the theory of Coordination Dynamics may provide a conceptual and methodological framework for understanding the horse-rider coupling. The recent development of mobile technologies allows combined horse and rider recordings during long lasting natural events such as endurance races. Six international horse-rider dyads were thus recorded during a 120 km race by using two tri-axial accelerometers placed on the horses and riders, respectively. The analysis concentrated on their combined vertical displacements. The obtained shapes and angles of Lissajous plots together with values of relative phase between horse and rider displacements at lower reversal point allowed us to characterize four coordination patterns, reflecting the use of two riding techniques per horse's gait (trot and canter). The present study shows that the concepts, methods and tools of self-organizing dynamic system approach offer new directions for understanding horse-rider coordination. The identification of the horse-rider coupling patterns constitutes a firm basis to further study the coalition of multiple constraints that determine their emergence and their dynamics in endurance race.

Don't rock the boat: how antiphase crew coordination affects rowing

It is generally accepted that crew rowing requires perfect synchronization between the movements of the rowers. However, a long-standing and somewhat counterintuitive idea is that out-of-phase crew rowing might have benefits over in-phase (i.e., synchronous) rowing. In synchronous rowing, 5 to 6% of the power produced by the rower(s) is lost to velocity fluctuations of the shell within each rowing cycle. Theoretically, a possible way for crews to increase average boat velocity is to reduce these fluctuations by rowing in antiphase coordination, a strategy in which rowers perfectly alternate their movements. On the other hand, the framework of coordination dynamics explicates that antiphase coordination is less stable than in-phase coordination, which may impede performance gains. Therefore, we compared antiphase to in-phase crew rowing performance in an ergometer experiment. Nine pairs of rowers performed a two-minute maximum effort in-phase and antiphase trial at 36 strokes min⁻¹ on two coupled free-floating ergometers that allowed for power losses to velocity fluctuations. Rower and ergometer kinetics and kinematics were measured during the trials. All nine pairs easily acquired antiphase rowing during the warm-up, while one pair’s coordination briefly switched to in-phase during the maximum effort trial. Although antiphase interpersonal coordination was indeed less accurate and more variable, power production was not negatively affected. Importantly, in antiphase rowing the decreased power loss to velocity fluctuations resulted in more useful power being transferred to the ergometer flywheels. These results imply that antiphase rowing may indeed improve performance, even without any experience with antiphase technique. Furthermore, it demonstrates that although perfectly synchronous coordination may be the most stable, it is not necessarily equated with the most efficient or optimal performance.

Location but not amount of stimulus occlusion influences the stability of visuomotor coordination

The current study examined whether the amount and location of available movement information influenced the stability of visuomotor coordination. Participants coordinated a handheld pendulum with an oscillating visual stimulus in an inphase and antiphase manner. The effects of occluding different amounts of phase at different phase locations were examined. Occluding the 0°/180° phase locations (end-points) significantly increased the variability of the visuomotor coordination. The amount of occlusion had little or no affect on the stability of the coordination. We concluded that the end-points of a visual rhythm are privileged and provide access to movement information that ensures stable coordination. The results are discussed with respect to the proposal of Bingham (Ecol Psychol 16:45–43, 2004) and Wilson et al. (Exp Brain Res 165:351–361, 2005) that the relevant information for rhythmic visual coordination is relative direction information.

Coordination dynamics in a socially situated nervous system

Traditional theories of cognitive science have typically accounted for the organization of human behavior by detailing requisite computational/representational functions and identifying neurological mechanisms that might perform these functions. Put simply, such approaches hold that neural activity causes behavior. This same general framework has been extended to accounts of human social behavior via concepts such as “common-coding” and “co-representation” and much recent neurological research has been devoted to brain structures that might execute these social-cognitive functions. Although these neural processes are unquestionably involved in the organization and control of human social interactions, there is good reason to question whether they should be accorded explanatory primacy. Alternatively, we propose that a full appreciation of the role of neural processes in social interactions requires appropriately situating them in their context of embodied-embedded constraints. To this end, we introduce concepts from dynamical systems theory and review research demonstrating that the organization of human behavior, including social behavior, can be accounted for in terms of self-organizing processes and lawful dynamics of animal-environment systems. Ultimately, we hope that these alternative concepts can complement the recent advances in cognitive neuroscience and thereby provide opportunities to develop a complete and coherent account of human social interaction.

Impairments of social motor coordination in schizophrenia

It has been demonstrated that motor coordination of interacting people plays a crucial role in the success of social exchanges. Abnormal movements have been reported during interpersonal interactions of patients suffering from schizophrenia and a motor coordination breakdown could explain this social interaction deficit, which is one of the main and earliest features of the illness. Using the dynamical systems framework, the goal of the current study was (i) to investigate whether social motor coordination is impaired in schizophrenia and (ii) to determine the underlying perceptual or cognitive processes that may be affected. We examined intentional and unintentional social motor coordination in participants oscillating hand-held pendulums from the wrist. The control group consisted of twenty healthy participant pairs while the experimental group consisted of twenty participant pairs that included one participant suffering from schizophrenia. The results showed that unintentional social motor coordination was preserved while intentional social motor coordination was impaired. In intentional coordination, the schizophrenia group displayed coordination patterns that had lower stability and in which the patient never led the coordination. A coupled oscillator model suggests that the schizophrenia group coordination pattern was due to a decrease in the amount of available information together with a delay in information transmission. Our study thus identified relational motor signatures of schizophrenia and opens new perspectives for detecting the illness and improving social interactions of patients.

The stability of rhythmic movement coordination depends on relative speed: the Bingham model supported

Following many studies showing that the coupling in bimanual coordination can be perceptual, Bingham (Ecol Psychol in 16:45-53, 2001; 2004a, b) proposed a dynamical model of such movements. The model contains three key hypotheses: (1) Being able to produce stable coordinative movements is a function of the ability to perceive relative phase, (2) the information to perceive relative phase is relative direction of motion, and (3) the ability to resolve this information is conditioned by relative speed. The first two hypotheses have been well supported (Wilson and Bingham in Percept Psychophys 70:465-476, 2008; Wilson et al. in J Exp Psychol Hum 36:1508-1514, 2010a), but the third was not supported when tested by de Rugy et al. (Exp Brain Res 184:269-273, 2008) using a visual coordination task that required simultaneous control of both the amplitude and relative phase of movement. The purposes of the current study were to replicate this task with additional measures and to modify the original model to apply it to the new task. To do this, we conducted two experiments. First, we tested the ability to produce 180° visual coordination at different frequencies to determine frequencies suitable for testing in the de Rugy et al. task. Second, we tested the de Rugy et al. task but included additional measures that yielded results different from those reported by de Rugy et al. These results were used to elaborate the original model. First, one of the phase-driven oscillators was replaced with a harmonic oscillator, so the resulting coupling was unidirectional. This change resulted in the model producing less stable 180° coordination behavior beyond 1.5 Hz consistent with the results obtained in Experiment 1. Next, amplitude control and phase correction elements were added to the model. With these changes, the model reproduced behaviors observed in Experiment 2. The central finding was that the stability of rhythmic movement coordination does depend on relative speed and, thus, all three of the hypotheses contained in the original Bingham model are supported.

Factors influencing children's performances of a steady-state bimanual coordination task

Children ages 4, 6, and 8 years and adults performed self-selected, continuous, unimanual and bimanual coordination tasks for 30 s. The length of time performing the task was investigated as a potential control parameter As hypothesized, all groups spent less time in antiphase than in in-phase coordination as the trial continued. These results were interpreted as evidence that the length of time performing a task is a control parameter embedded in any task. The importance of studying control parameters in various developing systems is discussed.

Neuroimaging coordination dynamics in the sport sciences

Key methodological issues for designing, analyzing, and interpreting neuroimaging experiments are presented from the perspective of the framework of Coordination Dynamics. To this end, a brief overview of Coordination Dynamics is introduced, including the main concepts of control parameters and collective variables, theoretical modeling, novel experimental paradigms, and cardinal empirical findings. Basic conceptual and methodological issues for the design and implementation of coordination experiments in the context of neuroimaging are discussed. The paper concludes with a presentation of neuroimaging findings central to understanding the neural basis of coordination and addresses their relevance for the sport sciences. The latter include but are not restricted to learning and practice-related issues, the role of mental imagery, and the recovery of function following brain injury.

Multilevel coordination stability: integrated goal representations in simultaneous intra-personal and inter-agent coordination

The influence of integrated goal representations on multilevel coordination stability was investigated in a task that required finger tapping in antiphase with metronomic tone sequences (inter-agent coordination) while alternating between the two hands (intra-personal coordination). The maximum rate at which musicians could perform this task was measured when taps did or did not trigger feedback tones. Tones produced by the two hands (very low, low, medium, high, and very high) could be the same as, or different from, one another and the (medium-pitched) metronome tones. The benefits of feedback tones were greatest when they were close in pitch to the metronome and the left hand triggered low tones, while the right hand triggered high tones. Thus, multilevel coordination was facilitated by tones that were easy to integrate with, but perceptually distinct from, the metronome, and by compatibility of movement patterns and feedback pitches.

Rocking together: dynamics of intentional and unintentional interpersonal coordination

The current study investigated the interpersonal coordination that occurred between two people when sitting side-by-side in rocking chairs. In two experiments participant pairs rocked in chairs that had the same or different natural periods. By instructing pairs to coordinate their movements inphase or antiphase, Experiment 1 investigated whether the stable patterns of intentional interpersonal coordination were consistent with the dynamics of within person interlimb coordination. By instructing the participants to rock at their own preferred tempo, Experiment 2 investigated whether the rocking chair movements of visually coupled individuals would become unintentionally coordinated. The degree to which the participants fixated on the movements of their co-actor was also manipulated to examine whether visual focus modulates the strength of interpersonal coordination. As expected, the patterns of coordination observed in both experiments demonstrated that the intentional and unintentional interpersonal coordination of rocking chair movements is constrained by the self-organizing dynamics of a coupled oscillator system. The results of the visual focus manipulations indicate that the stability of a visual interpersonal coupling is mediated by attention and the degree to which an individual is able to detect information about a co-actor's movements.

Neuromuscular and spatial constraints on bimanual hand-held pendulum oscillations: dissociation or combination?

The present work investigated the effects of spatial and neuromuscular constraints on the mean states and variability of interlimb coordination patterns performed in the para-sagittal plane of motion in a hand-held pendulum oscillation task. Nine right-handed students had to oscillate two pendulums through wrist adduction-abduction movements. Relative movement direction was manipulated by asking participants to perform both isodirectional and non-isodirectional movements. Participants were required to grab the pendulums either with both forearms in the same neutral or supine posture or with one forearm in neutral while the other one was in prone-inversed position. When both forearms were in a similar posture, isodirectional movements were generated predominantly by simultaneous activation of homologous muscle groups whereas non-isodirectional movements mainly resulted from simultaneous activation of non-homologous muscle groups. When forearms were in dissimilar posture, isodirectional movements were generated predominantly by the simultaneous activation of non-homologous muscle groups whereas non-isodirectional movements mainly resulted from simultaneous activation of homologous muscle groups. Standard deviation of relative phase and absolute error of relative phase were analyzed for each forearm posture condition. We hypothesized that neuromuscular and spatial constraints would affect two different aspects of coordination performance, i.e., pattern stability and accuracy, respectively. Comparison of the results obtained for similar and dissimilar postures suggested that changes of pattern stability were mediated by changes in the nature of the muscle activation patterns that gave rise to wrist movement in each condition. On the other hand, the results also showed that movement direction exclusively affected phase shift. The findings are consistent with the conclusion of Park et al. [Park, H., Collins, D. R., & Turvey, M. T. (2001). Dissociation of muscular and spatial constraints on patterns of interlimb coordination. Journal of Experimental Psychology: Human Perception and Performance, 27, 32-47.] that neuromuscular constraints affect variability of relative phase (attractor strength) and spatial constraints affect the shift of relative phase (attractor location).

Developmental Differences in the Use of Visual Information During a Continuous Bimanual Coordination Task

The authors examined the influence of different amounts of visual information when children 4 (CH4), 6 (CH6), and 8 (CH8) years of age, and adults (n = 12 in each group) performed a steady-state bimanual circle-drawing coordination task at self-selected speeds. All participants maintained in-phase coordination, but different strategies for maintaining the pattern emerged. A predictable relationship between variability and age was not observed, in that the CH8 group was not necessarily more consistent than the CH6 and CH4 groups. The authors conclude that children are transitioning from dependence on kinesthetic feedback to reliance on visual feedback around age 8, as suggested by L. Hay, C. Bard, M. Fleury, and N. Teasdale (1991; L. Hay, M. Fleury, C. Bard, & N. Teasdale, 1994; L. Hay & C. Redon, 1997), and that future studies are needed to further explore visual and kinesthetic feedback as potential control parameters during coordination tasks in developing children.

Distinguishing the noise and attractor strength of coordinated limb movements using recurrence analysis

The variability of coupled rhythmic limb movements is assumed to be a consequence of the strength of a movement's attractor dynamic and a constant stochastic noise process that continuously perturbs the movement system away from this dynamic. Recently, it has been suggested that the nonlinear technique of recurrence analysis can be used to index the effects of noise and attractor strength on movement variability. To test this, three experiments were conducted in which the attractor strength of bimanual wrist-pendulum movements (using coordination mode, movement frequency and detuning), as well as the magnitude of stochastic perturbations affecting the variability of these movements (using a temporally fluctuating visual metronome) was manipulated. The results of these experiments demonstrate that recurrence analysis can index parametric changes in the attractor strength of coupled rhythmic limb movements and the magnitude of metronome induced stochastic perturbations independently. The results of Experiments 1 and 2 also support the claim that differences between the variability of inphase and antiphase coordination, and between slow and fast movement frequencies are due to differences in attractor strength. In contrast to the standard assumption that the noise that characterizes interlimb coordination remains constant for different magnitudes of detuning (Delta omega) the results of Experiment 3 suggest that the magnitude of noise increases with increases in |Delta omega|.

Plane of motion mediates the coalition of constraints in rhythmic bimanual coordination

The authors hypothesized that the modulation of coordinative stability and accuracy caused by the coalition of egocentric (neuromuscular) and allocentric (directional) constraints varies depending on the plane of motion in which coordination patterns are performed. Participants (N = 7) produced rhythmic bimanual movements of the hands in the sagittal plane (i.e., up-and-down oscillations resulting from flexion-extension of their wrists). The timing of activation of muscle groups, direction of movements, visual feedback, and across-trial movement frequency were manipulated. Results showed that both the egocentric and the allocentric constraints modulated pattern stability and accuracy. However, the allocentric constraint played a dominant role over the egocentric. The removal of vision only slightly destabilized movements, regardless of the effects of directional and (neuro)muscular constraints. The results of the present study hint at considering the plane in which coordination is performed as a mediator of the coalition of egocentric and allocentric constraints that modulates coordinative stability of rhythmic bimanual coordination.

A neuro-mechanical model for interpersonal coordination

The present study investigates the coordination between two people oscillating handheld pendulums, with a special emphasis on the influence of the mechanical properties of the effector systems involved. The first part of the study is an experiment in which eight pairs of participants are asked to coordinate the oscillation of their pendulum with the other participant's in an in-phase or antiphase fashion. Two types of pendulums, A and B, having different resonance frequencies (Freq A=0.98 Hz and Freq B=0.64 Hz), were used in different experimental combinations. Results confirm that the preferred frequencies produced by participants while manipulating each pendulum individually were close to the resonance frequencies of the pendulums. In their attempt to synchronize with one another, participants met at common frequencies that were influenced by the mechanical properties of the two pendulums involved. In agreement with previous studies, both the variability of the behavior and the shift in the intended relative phase were found to depend on the task-effector asymmetry, i.e., the difference between the mechanical properties of the effector systems involved. In the second part of the study, we propose a model to account for these results. The model consists of two cross-coupled neuro-mechanical units, each composed of a neural oscillator driving a wrist-pendulum system. Taken individually, each unit reproduced the natural tendency of the participants to freely oscillate a pendulum close to its resonance frequency. When cross-coupled through the vision of the pendulum of the other unit, the two units entrain each other and meet at a common frequency influenced by the mechanical properties of the two pendulums involved. The ability of the proposed model to address the other effects observed as a function of the different conditions of the pendulum and intended mode of coordination is discussed.

Timing and distance characteristics of interpersonal coordination during locomotion

Most studies about human locomotion only tend to consider single subjects walking alone in a stationary environment. Nevertheless, human subjects have often to plan and generate their locomotor trajectories according to one another's displacements. Therefore, in the present study we address the question of the interpersonal coordination when pairs of subjects walk simultaneously. Six pairs of subjects walking face to face, backwards and forwards on a 8 m x 2 m track were involved in our experiment. Within each pair, the leader (L) was required to break the initial interpersonal distance whereas the follower (F) had to maintain this distance constant (1, 2 or 3 m). We measured their position and analyzed their travelled distance, the time course of their linear displacement, and the kinematics parameters of their steps. Our results show that F travels smaller distances than L and that even if they are highly correlated, some temporal delays exist between displacements of L and F with greater values when the interpersonal distance increases (from 1 to 3 m). These results are discussed in terms of high level imitation, i.e. bidirectional interactions with mutual influences of each subject on one another.

The effect of visuo-motor transformations on hand-foot coordination: evidence in favor of the incongruency hypothesis

Understanding how multiple constraints contribute to the emergence of coordinated behavior has been the topic of considerable debate in cognitive sciences. The present experiment addressed the issue of the effects of visual motion structures (iso- and non-isodirectionality) on the stability of hand-foot coordination patterns. Visuo-motor transformations--decorrelating the perceived movement direction from the actually generated direction--were applied to both in-phase and anti-phase patterns. Two mutually exclusive hypotheses--the "visual grouping hypothesis" and the "incongruency hypothesis"--were tested. The results indicated that both conditions of transformed visual feedback destabilized the actual performed coordination patterns. Thus, despite the existence of common underlying principles that govern both the perceived motion pattern and the generation of hand-foot coordination patterns, it appeared that perceptual grouping principles were not exploited to monitor the production of coordination. These results strongly suggest that the congruency between the performed pattern and the perceived visual feedback is the primary factor determining the (in)stability of hand-foot coordination patterns.

Human movement coordination implicates relative direction as the information for relative phase

The current studies explore the informational basis of the coupling in human rhythmic movement coordination tasks. Movement stability in these tasks is an asymmetric U-shaped function of mean relative phase; 0 degrees is maximally stable, 90 degrees is maximally unstable and 180 degrees is intermediate. Bingham (2001, 2004a, 2004b) hypothesized that the information used to perform coordinated rhythmic movement is the relative direction of movement, the resolution of which is determined by relative speed. We used an experimental paradigm that entails using a circular movement to produce a linear motion of a dot on a screen, which must then be coordinated with a linearly moving computer controlled dot. This adds a component to the movement that is orthogonal to the display. Relative direction is not uniquely defined between orthogonal components of motion, but relative speed is; it was therefore predicted that the addition of the component would only introduce a symmetric noise component and not otherwise contribute to the U-shape structure of movement stability. Results for experiment 1 supported the hypothesis; movement that involved the additional component was overall less stable than movement that involved only the parallel component along which relative direction can be defined. Two additional studies ruled out alternative explanations for the pattern of data in experiment 1. Overall, the results strongly implicate relative direction as the information underlying performance in rhythmic movement coordination tasks.

Interaction of neuromuscular, spatial and visual constraints on hand-foot coordination dynamics

In the present study, we investigated the contributions of motor and perceptual processes to directional constraints as observed during hand-foot coordination. Participants performed cyclical flexion-extension movements of the right hand and foot under two coordination modes: in-phase (isodirectional) and antiphase (non-isodirectional). Those tasks were performed either with full vision or no vision of the limbs. Depending on the position of the forearm (prone or supine), the coordination patterns were performed with similar and dissimilar neuro-muscular coupling with respect to their phylogenetic origin as antigravity muscles. Results showed that the antiphase pattern was more difficult to maintain than the in-phase pattern and that neuro-muscular coupling significantly influenced the coordination dynamics. Moreover, the effect of vision differed as a function of both neuro-muscular coupling and coordination mode. Under dissimilar neuro-muscular coupling, the presence of visual feedback stabilized the in-phase pattern and destabilized the antiphase pattern. In contrast, visual feedback did not influence pattern stability during conditions of similar neuro-muscular coupling. These results shed light on the complex interactions between motor and perceptual (visual) constraints during the production of hand-foot coordination patterns.