Can dancers suppress the haptically mediated interpersonal entrainment during rhythmic sway?

Interpersonal entrainment emerges spontaneously when partners performing rhythmic movements together exchange sensory feedback about the other's movements. In this study, we asked whether couples of expert dancers, non-dancers and mixed couples can suppress the spontaneous haptically mediated inter-personal entrainment when their rhythmic sway is paced by differing metronome tempos. Fifty-four young participants formed three types of couples: nine dancer couples, consisting of individuals with at least eight years systematic practice in traditional Greek dance; nine non-dancer couples, consisting of individuals with no prior experience in dance and nine mixed couples, consisting of one dancer and one novice partner. Partners swayed rhythmically for 60 s, at different pacing frequencies (one at 0.25 Hz and the other at 0.35 Hz) under three haptic contact conditions: no contact between them; light fingertip touch established in the 2nd trial segment (30 s); and light fingertip touch released in the 2nd trial segment (30 s). Spectral analysis of the antero-posterior center of pressure displacement revealed that light touch increased the deviation of the dominant from the target (pacing) sway frequency, decreased the proportion of the signal's power at the target frequency and increased the coherence between the partners' sway signals (inter-personal coherence). These effects were specific to the mixed group whereas touch interference was weaker in non-dancers and absent in dancers. In addition, the coherence between the trial segments (intra-personal coherence) significantly decreased with touch only for the non-dancer while it remained unchanged for the dancer partner of the mixed group suggesting that the dancer was leading the non-dancer partner. It is concluded that systematic practice with traditional dance can modulate the spontaneous tendency towards haptically mediated interpersonal entrainment.     

Multi-person and multisensory synchronization during group dancing

Synchronized group dancing is one of the hallmarks of both coordination and cooperation in the humans species. While a large amount of research has focused on joint action in dyads, the mechanisms of coordination in larger groups are not well understood. In the present study, we explored the coordination dynamics of a group of folk dancers by examining the influence of three sensory-coupling channels on the stability of group coordination. Using 3D motion capture, we recorded a group of 13 expert folk dancers performing to the beat of music (auditory coupling) while holding hands in a circle (haptic coupling) and seeing their fellow dancers (visual coupling). Analyses of group synchrony using cluster phase analysis demonstrated that selective elimination of any one of the three types of sensory coupling significantly reduced group synchrony, where haptic coupling had the strongest effect on movements in the horizontal plane, but also impacted the vertical axis. This study provides some of the first evidence of how sensory couplings support multi-person coordination in a large group, and in particular the effect of body contact on this coordination.     

Effects of passive interpersonal light touch during walking on postural control responses: An exploratory study

The effects of passive interpersonal light touch (PILT) on postural stability can be observed through improved postural coordination through haptic feedback from the contact provider to the contact receiver while walking. It is unclear, however, whether PILT affects the contact receiver's detailed physical responses, such as muscle activity, body sway, and joint movements. In this study, surface electromyography and an inertial measurement unit were used simultaneously to explore changes in walking speed and control responses induced by PILT. We evaluated fourteen healthy participants for their walking speed and physical responses under two walking conditions: no-touch (NT) and PILT. As a physical response during walking, we measured muscle activity (rectus femoris, semitendinosus, tibialis anterior, and soleus muscles), body sway (pelvis and neck), and joint angles (direction of hip, knee, and ankle joint movements). In PILT condition, fingertip contact force was measured while the contact provider touched the third level of the recipient's lumbar spine. In comparison with the NT condition, PILT condition increased walking speed and decreased body sway on neck position. There were significant correlations between walking speed and neck sway regarding NT and PILT change values. Passive haptic information to the contact receiver may assist in the smooth shift of the center of gravity position during gait through interpersonal postural coordination. These findings suggest that PILT may provide an efficient and stable gait.     

Haptic cues for orientation and postural control

Haptic cues from fingertip contact with a stable surface attenuate body sway in subjects even when the contact forces are too small to provide physical support of the body. We investigated how haptic cues derived from contact of a cane with a stationary surface at low force levels aids postural control in sighted and congenitally blind individuals. Five sighted (eyes closed) and five congenitally blind subjects maintained a tandem Romberg stance in five conditions: (1) no cane; (2, 3) touch contact (<2 N of applied force) while holding the cane in a vertical or slanted orientation; and (4, 5) force contact (as much force as desired) in the vertical and slanted orientations. Touch contact of a cane at force levels below those necessary to provide significant physical stabilization was as effective as force contact in reducing postural sway in all subjects, compared to the no-cane condition. A slanted cane was far more effective in reducing postural sway than was a perpendicular cane. Cane use also decreased head displacement of sighted subjects far more than that of blind subjects. These results suggest that head movement control is linked to postural control through gaze stabilization reflexes in sighted subjects; such reflexes are absent in congenitally blind individuals and may account for their higher levels of head displacement.     

Rapid motor adaptations to subliminal frequency shifts during syncopated rhythmic sensorimotor synchronization

The synchronization of rhythmic arm movements to a syncopated metronome cue was studied in a step-change design whereby small tempo shifts were inserted at fixed time points into the metronome frequency. The cueing sequence involved three stimulus types: (1) target contact in synchrony with the metronome beats, (2) syncopated target contact midway in time between audible beats, and (3) syncopated target contact following either a +2% or -2% change in stimulus frequency. Analysis of normalized and aggregated data revealed that (1) during the syncopation condition the response period showed a rapid adaptation to the frequency-incremented stimulus period, (2) response period was less variable during syncopated movement, (3) mean synchronization error and variability, calculated during syncopation relative to the mathematical midpoint of the stimulus cycle, were reduced during syncopated movements, and (4) synchronization error following the frequency increment showed trends to return linearly to pre-increment values which was fully achieved in the -2% change condition only. The results suggest that frequency entrainment to stimulus period was possible during syncopated movement with the response and stimulus onsets 180 degrees out of phase. Most remarkably, 70-80% of the adaptation of the response period to the new stimulus period was immediately attained during the second half cycle of the syncopated movement. Finally, a mathematical model, based on recursion, was introduced that accurately modeled actual data as a function of the previous stimulus and response intervals and a weighted response of period error and synchronization error, which showed dominance of frequency entrainment over phase entrainment during rhythmic synchronization.     

Stabilization and destabilization of perception--action patterns influence the self-organized recruitment of degrees of freedom

The recruitment of an additional biomechanical degree of freedom in a unimanual rhythmic task was explored. Subjects were asked to synchronize adduction or abduction of their right index finger with a metronome, the frequency of which was increased systematically. In addition, haptic contact on or off the metronome beat was provided. Results showed that the pattern exhibiting the highest intrinsic stability recruited the vertical plane more than did the less stable one. Moreover, presence and location of haptic contact modulated coordination stability and therefore induced changes in the recruitment of the vertical plane. Thus, a trade-off was shown between coordination stability on the horizontal plane and recruitment of the vertical one. These findings suggest that recruitment of degrees of freedom is governed by general principles of coordination dynamics.     

The effects of viscous loading of the human forearm flexors on the stability of coordination

This experiment investigated whether the stability of rhythmic unimanual movements is primarily a function of perceptual/spatial orientation or neuro-mechanical in nature. Eight participants performed rhythmic flexion and extension movements of the left wrist for 30s at a frequency of 2.25 Hz paced by an auditory metronome. Each participant performed 8 flex-on-the-beat trials and 8 extend-on-the-beat trials in one of two load conditions, loaded and unload. In the loaded condition, a servo-controlled torque motor was used to apply a small viscous load that resisted the flexion phase of the movement only. Both the amplitude and frequency of the movement generated in the loaded and unloaded conditions were statistically equivalent. However, in the loaded condition movements in which participants were required to flex-on-the-beat became less stable (more variable) while extend-on-the-beat movements remained unchanged compared with the unload condition. The small alteration in required muscle force was sufficient to result in reliable changes in movement stability even a situation where the movement kinematics were identical. These findings support the notion that muscular constraints, independent of spatial dependencies, can be sufficiently strong to reliably influence coordination in a simple unimanual task.     

Simultaneous Event-Based and Emergent Timing: Synchronization,Continuation, and Phase Correction

It has been claimed that rhythmic tapping and circle drawing represent fundamentally different timing processes (event-based and emergent, respectively) and also that circle drawing is difficult to synchronize with a metronome and exhibits little phase correction. In the present study, musically trained participants tapped with their left hands, drew circles with their right (dominant) hands, and also performed both tasks simultaneously. In Experiment 1, they synchronized with a metronome and then continued on their own, whereas in Experiment 2, they synchronized with a metronome containing phase perturbations. Circle drawing generally exhibited reliable synchronization, although with greater variability than tapping, and also showed a clear phase-correction response that evolved gradually during the cycle immediately following a perturbation. When carried out simultaneously in synchrony, with or without a metronome, the two tasks affected each other in some ways but retained their distinctive timing characteristics. This shows that event-based and emergent timing can coexist in a dual-task situation. Furthermore, the authors argue that the two timing modes usually coexist in each individual task, although one mode is often dominant.     

Sensorimotor synchronization: A review of recent research (2006–2012)

Sensorimotor synchronization (SMS) is the coordination of rhythmic movement with an external rhythm, ranging from finger tapping in time with a metronome to musical ensemble performance. An earlier review (Repp, 2005) covered tapping studies; two additional reviews (Repp, 2006a, b) focused on music performance and on rate limits of SMS, respectively. The present article supplements and extends these earlier reviews by surveying more recent research in what appears to be a burgeoning field. The article comprises four parts, dealing with (1) conventional tapping studies, (2) other forms of moving in synchrony with external rhythms (including dance and nonhuman animals’ synchronization abilities), (3) interpersonal synchronization (including musical ensemble performance), and (4) the neuroscience of SMS. It is evident that much new knowledge about SMS has been acquired in the last 7 years.     

Experts see it all: configural effects in action observation

Biological motion perception is influenced by observers’ familiarity with the observed action. Here, we used classical dance as a means to investigate how visual and motor experience modulates perceptual mechanism for configural processing of actions. Although some ballet moves are performed by only one gender, male and female dancers train together and acquire visual knowledge of all ballet moves. Twenty-four expert ballet dancers (12 female) and matched non-expert participants viewed pairs of upright and inverted point light female and common dance movements. Visual discrimination between different exemplars of the same movement presented upright was significantly better in experts than controls, whilst no differences were found when the same stimuli were presented upside down. These results suggest expertise influences configural action processing. Within the expert group, effects were stronger for female participants than for males, whilst no differences were found between movement types. This observer gender effect could suggest an additional role for motor familiarity in action perception, over and above the visual experience. Our results are consistent with a specific motor contribution to configural processing of action.     

Synchrony Preference: Why Some People Go With the Flow and Some Don't

As work in organizations becomes more fluid and fast paced the effective execution of tasks often requires people to be temporally adaptable in working with others. This paper brings to light the importance of understanding how people relate to time in the context of social interactions. By integrating the research on time and social motives, we develop a relational perspective about time. We introduce the construct of synchrony preference, an individual difference that describes a willingness to adapt one's pace and rhythm within social interactions for the purpose of creating synchrony with others. We develop a measure of synchrony preference that we validate using multiple methods across 4 studies and 7 samples, which include over 1,400 individuals. In particular, we establish a nomological network and show that synchrony preference predicts flexible pacing behaviors, interpersonal facilitation, contribution to team synchrony, contribution to team performance, and job dedication. Our results reveal that both scholars and practitioners can benefit from considering people's preference for synchrony when working with others.     

Influence of Visual and Haptic Cues on Podokinetic After-Rotation

ABSTRACT

Active countercircling on a rotating platform for 15 min causes individuals to involuntarily circle in the same direction when they step in place on firm ground. This is referred to as podokinetic after-rotation (PKAR). It is unclear how interjecting brief periods of visual or haptic inputs for a stable orientation reference affects PKAR. The authors studied this issue in 16 healthy individuals who participated in three sessions each. Following active countercircling, participants attempted to step in place for 30 min on firm ground. In two of three sessions, participants received full visual input or made fingertip contact with a stationary object for 30 s during 30 min of ongoing PKAR. All participants slowed or stopped rotating during the presence of visual or haptic inputs and resumed PKAR after removal of these inputs. Exponential functions fitted to angular trunk velocity versus time plots revealed no significant differences across conditions (p > .05). The preservation of PKAR after brief exposure to a visual or haptic reference is consistent with a slowly decaying velocity storage that is not reset or dumped after exposure to conflicting visual or haptic cues.     

Inter- and intra-lower limb joint coordination of non-expert classical ballet dancers during tiptoe standing

The main objective of this study was to compare ballet dancers’ and non-dancers’ joint coordination during tiptoe standing. Nine female non-expert ballet dancers and nine female non-dancers were asked to perform heel-toe and tiptoe standing for approximately 30 s, during which the center of pressure (COP) and kinematic data from the metatarsophalangeal, ankle, knee, and hip joints were measured. Principal component analysis was performed on the angular displacements to determine joint coordination. The weighting vectors suggested that dancers’ ankle and knee joints fluctuated in-phase in the anteroposterior direction, whereas all combinations of adjacent joints had anti-phase coordination for non-dancers. In addition, there was a significant difference in the intra-joint coordination pattern between groups. In particular, dancers’ metatarsophalangeal (MP) and ankle joints tended to sway to the left-front or right-rear. However, there were no differences between the groups in the path length or rectangular COP. These results suggest that dancers maintained quiet postures via a decrease in the mechanical degree of freedom and that postural expertise may not be determined from a traditional COP analysis, even during unstable tiptoe standing. This in-phase coordination, which has an arch-like configuration, could be characteristic of dancers’ lithe legs.     

Coordination tending towards an anti-phase relationship determines greater sway reduction during entrainment with a simulated partner

The increased risk of falls in the older aged population demands the development of assistive robotic devices capable of effective balance support. For the development and increased user acceptance of such devices, which provide balance support in a human-like way, it is important to understand the simultaneous occurrence of entrainment and sway reduction in human-human interaction. However, sway reduction has not been observed yet during a human touching an external, continuously moving reference, which rather increased human body sway. Therefore, we investigated in 15 healthy young adults (27.20±3.55 years, 6 females) how different simulated sway-responsive interaction partners with different coupling modes affect sway entrainment, sway reduction and relative interpersonal coordination, as well as how these human behaviours differ depending on the individual body schema accuracy. For this, participants were lightly touching a haptic device that either played back an average pre-recorded sway trajectory (“Playback”) or moved based on the sway trajectory simulated by a single-inverted pendulum model with either a positive (Attractor) or negative (Repulsor) coupling to participant's body sway. We found that body sway reduced not only during the Repulsor-interaction, but also during the Playback-interaction. These interactions also showed a relative interpersonal coordination tending more towards an anti-phase relationship, especially the Repulsor. Moreover, the Repulsor led to the strongest sway entrainment. Finally, a better body schema contributed to a reduced body sway in both the “reliable” Repulsor and the “less reliable” Attractor mode. Consequently, a relative interpersonal coordination tending more towards an anti-phase relationship and an accurate body schema are important to facilitate sway reduction.     

人际同步对合作行为的促进机制及解释模型

同步作为集体仪式的核心要素, 对群体生存和发展具有重要意义。人际同步是一种特殊的协调行为, 具有锁时锁相的特征。近年来研究发现同步能够促进合作等亲社会行为, 具体的促进机制包括神经生理的激活、社会联结感的增强、认知灵敏度的提高和积极情绪的唤起, 学者们也从不同角度提出了三种不同的解释模型：自我-他人重叠模型、合作加强模型和集体沸腾模型。未来的研究需要进一步剖析同步行为的亲社会功能, 厘清同步效应的调节机制、特异性和普适性。     

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。     

Validating a visual version of the metronome response task

The metronome response task (MRT)—a sustained-attention task that requires participants to produce a response in synchrony with an audible metronome—was recently developed to index response variability in the context of studies on mind wandering. In the present studies, we report on the development and validation of a visual version of the MRT (the visual metronome response task; vMRT), which uses the rhythmic presentation of visual, rather than auditory, stimuli. Participants completed the vMRT (Studies 1 and 2) and the original (auditory-based) MRT (Study 2) while also responding to intermittent thought probes asking them to report the depth of their mind wandering. The results showed that (1) individual differences in response variability during the vMRT are highly reliable; (2) prior to thought probes, response variability increases with increasing depth of mind wandering; (3) response variability is highly consistent between the vMRT and the original MRT; and (4) both response variability and depth of mind wandering increase with increasing time on task. Our results indicate that the original MRT findings are consistent across the visual and auditory modalities, and that the response variability measured in both tasks indexes a non-modality-specific tendency toward behavioral variability. The vMRT will be useful in the place of the MRT in experimental contexts in which researchers’ designs require a visual-based primary task.     

Specificity of Postural Control: Comparing Expert and Intermediate Dancers

The expert–novice approach is inappropriate for studying postural control in sport and dance when novices are completely unable to perform relevant postural tasks and experts cannot demonstrate specific skills on everyday postural tasks. We tested expertise-specific differences on 6 static everyday and 5 dynamic dance-like postural tasks of varying difficulty in 13 professional and 12 intermediate nonprofessional dancers. Results showed a clear expert advantage on sway area for dance-like postural tasks, but not for static everyday tasks. This effect was also found for the control parameter of root mean square (RMS) velocity and partly for RMS amplitude of the difference signal between CoP and CoG line location. Results indicate that the expert advantage is task-specific and deliver new insights into the specificity of experts' postural performance.     

A study of EEG coherence in DCD children during motor synchronization task

This paper investigates the hypothesis that the coordination difficulties of DCD children are associated with an increased coherence in the cortical motor regions, which persists with age. Forty-eight children participated in the study (24 DCD and 24 Controls). Their ages ranged from 8 to 13 years, divided into three groups (8-9, 10-11, and 12-13 years old). Children were required to perform finger flexion or extension either in synchrony or in syncopation with a rhythmic metronome, while a 32-channel EEG was recorded. Along with stability measures of motor performance, we analyzed the spectral EEG coherence between intrahemispheric (left frontal/left central; left central/left parietal) and interhemispheric (left central/right central) sites. Spectral coherence assesses functional coupling between distant areas of the brain. Two frequency bands related to sensorimotor activation were chosen: alpha (8-12 Hz) and beta (12-30 Hz). The synchrony task was chosen as a rest condition against which the two syncopation conditions at 0.5 Hz and 1.3 Hz were contrasted. For intrahemispheric comparison, 8-9-year-old DCD children showed that coherence between fronto-central regions increased for both rhythms and conditions, as compared to controls. No difference was found for interhemispheric comparisons. As frontal sites are related to motor planning, our results suggest that youngest DCD children were forced to maintain a high level of pre-programming to compensate for the difficulties caused by the perceptual-motor requirements of the task in light of their coordination disorder.     

Articulatory constraints on interpersonal postural coordination

Cooperative conversation has been shown to foster interpersonal postural coordination. The authors investigated whether such coordination is mediated by the influence of articulation on postural sway. In Experiment 1, talkers produced words in synchrony or in alternation, as the authors varied speaking rate and word similarity. Greater shared postural activity was found for the faster speaking rate. In Experiment 2, the authors demonstrated that shared postural activity also increases when individuals speak the same words or speak words that have similar stress patterns. However, this increase in shared postural activity is present only when participants' data are compared with those of their partner, who was present during the task, but not when compared with the data of a member of a different pair speaking the same word sequences as those of the original partner. The authors' findings suggest that interpersonal postural coordination observed during conversation is mediated by convergent speaking patterns.