Limiting the recruitment of degrees of freedom reduces the stability of perception-action patterns

The goal of the present study was to examine how recruiting/suppressing degrees of freedom affects the (differential) stability of two rhythmic perception-action patterns. In particular, participants synchronized either adduction-on-the-beat or abduction-on-the-beat movements of the right index finger with an auditory metronome. The stability of both patterns as performed in the horizontal plane was predicted to depend on the utilization, or recruitment, of the vertical plane of motion. Movements of the index finger were either free or physically restricted to the horizontal plane. The results showed that in the free condition, the vertical plane was recruited more in the more stable pattern (abduction-on-the-beat) than in the less stable pattern (adduction-on-the-beat). In the constrained condition, abduction-on-the-beat pattern was destabilized, whereas the stability of the adduction-on-the-beat pattern was preserved. These results suggest that the recruitment of the vertical plane of motion in the abduction-on-the-beat movements brought about an increase in the stability of this pattern. More generally, the trade-off between the stability of coordination patterns in the horizontal plane is based on a self-organizing process of recruitment in which neuromuscular factors are an intrinsic aspect.     

Torso movement constraint in stability of bimanual coordination

This study investigated the relation between postural movement and upper-limb coordination stability. Adults produced bimanual circles using in-phase and anti-phase coordination patterns in time to an increasing rate metronome (i.e., movement-time instruction) in the horizontal (e.g., tabletop) and vertical (e.g., "wall" perpendicular to body) planes. All participants produced the instructed in- and anti-phase patterns. Coordination stability (i.e., SD of relative phase) was larger for anti-phase than in-phase patterns in both planes; however, anti-phase coordination stability was lower in the vertical plane than in the horizontal plane. Torso movement was larger during anti-phase coordination patterns in the horizontal plane, whereas it was larger during in-phase coordination patterns in the vertical plane. These results indicate that different orientations of the same task can produce different results for stability of coordination. This information may be important for performing and learning complex motor-coordination movements (e.g., playing musical instruments).     

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.     

To Switch or Not to Switch: Recruitment of Degrees of Freedom Stabilizes Biological Coordination

Recruitment and suppression processes were studied in the swinging-pendulum paradigm (cf. P. N. Kugler & M. T. Turvey, 1987). The authors pursued the hypothesis that active recruitment of previously unmeasured degrees of freedom serves to stabilize an antiphase bimanual coordination pattern and thereby obviates the need for pattern switching from an antiphase to an in-phase coordination pattern, a key prediction of the H. Haken, J. A. S. Kelso, and H. Bunz (1985) model. In Experiment 1, 7 subjects swung single hand-held pendulums in time with an auditory metronome whose frequency increased. Pendulum motion changed from planar (2D) to elliptical (3D), and forearm motion (produced by elbow flexion-extension) was recruited with increasing movement rate for cycling frequencies typically above the pendulum's eigenfrequency. In Experiment 2, 7 subjects swung paired pendulums in either an in-phase or an antiphase coordinative mode as movement rate was increased. With the systematic increase in movement rate, the authors attempted to induce transitions from the antiphase to the in-phase coordinative pattern, with loss of stability the key mechanism of pattern change. Transitions from the antiphase to the in-phase coordinative mode were not observed. Pattern stability, as defined by the variability of the phase relation between the pendulums, was affected only a little by increasing movement rate. As in the single-pendulum case, pendulum motion changed from planar to elliptical, and forearm motion was recruited with increasing cycling frequency. Those results reveal a richer dynamics than previously observed in the pendulum paradigm and support the hypothesis that recruitment processes stabilize coordination in biomechanically redundant systems, thereby reducing the need for pattern switching.     

Anchoring in a novel bimanual coordination pattern

Anchoring in cyclical movements has been defined as regions of reduced spatial or temporal variability [Beek, P. J. (1989). Juggling dynamics. PhD thesis. Amsterdam: Free University Press] that are typically found at movement reversal points. For in-phase and anti-phase movements, synchronizing reversal points with a metronome pulse has resulted in decreased anchor point variability and increased pattern stability [Byblow, W. D., Carson, R. G., & Goodman, D. (1994). Expressions of asymmetries and anchoring in bimanual coordination. Human Movement Science, 13, 3-28; Fink, P. W., Foo, P., Jirsa, V. K., & Kelso, J. A. S. (2000). Local and global stabilization of coordination by sensory information. Experimental Brain Research, 134, 9-20]. The present experiment examined anchoring during acquisition, retention, and transfer of a 90 degrees phase-offset continuous bimanual coordination pattern (whereby the right limb lags the left limb by one quarter cycle), involving horizontal flexion about the elbow. Three metronome synchronization strategies were imposed: participants either synchronized maximal flexion of the right arm (i.e., single metronome), both flexion and extension of the right arm (i.e., double metronome within-limb), or flexion of each arm (i.e., double metronome between-limb) to an auditory metronome. In contrast to simpler in-phase and anti-phase movements, synchronization of additional reversal points to the metronome did not reduce reversal point variability or increase pattern stability. Furthermore, practicing under different metronome synchronization strategies did not appear to have a significant effect on the rate of acquisition of the pattern.     

Somatosensory driven interpersonal synchrony during rhythmic sway

Spontaneous synchrony emerges between individuals performing together rhythmic activities while communicating by means of sensory feedback. In this study, we examined the nature of interpersonal synchrony mediated by light fingertip contact when individuals sway rhythmically in the sagittal plane. The effect of traditional dance expertise on interpersonal synchrony was investigated. Sixty participants (30 dancers, 30 novices) formed three types of couples (10 expert couples, 10 novice couples, 10 mixed couples) and performed a rhythmical sway task (40s) that was either self or metronome paced (frequency: 0.25Hz). Cross spectral analysis of the center of pressure (CoP) displacement signals revealed that during self-paced sway fingertip contact evoked a decrease of the dominant sway frequency difference between partners, an increase in the coherence between the sway signals and a concentration of relative phase angles towards the in-phase (0°-20°) region. In metronome paced sway however, only expert dancers were able to benefit from haptic contact to further improve interpersonal synchrony. These findings suggest that haptic contact can stabilize the spontaneous coordination dynamics of two persons performing rhythmic sway together. The strength of the emerged synchrony depends on the individuals' expertise to integrate tactile and auditory information about sway.     

Temporal coordination and adaptation to rate change in music performance

People often coordinate their actions with sequences that exhibit temporal variability and unfold at multiple periodicities. We compared oscillator- and timekeeper-based accounts of temporal coordination by examining musicians' coordination of rhythmic musical sequences with a metronome that gradually changed rate at the end of a musical phrase (Experiment 1) or at the beginning of a phrase (Experiment 2). The rhythms contained events that occurred at the same periodic rate as the metronome and at half the period. Rate change consisted of a linear increase or decrease in intervals between metronome onsets. Musicians coordinated their performances better with a metronome that decreased than increased in tempo (as predicted by an oscillator model), at both beginnings and ends of musical phrases. Model performance was tested with an oscillator period or timekeeper interval set to the same period as the metronome (1:1 coordination) or half the metronome period (2:1 coordination). Only the oscillator model was able to predict musicians' coordination at both periods. These findings suggest that coordination is based on internal neural oscillations that entrain to external sequences.     

Temporal stability of rhythmic tapping “on” and “off the beat”: A developmental study

This study, following a dynamic pattern approach, examines age-related differences in the stability of unimanual rhythmic perception-action patterns. Thirty-six children, aged 7, 9, and 11 years, attempted to synchronize their finger tapping to the beats of an auditory metronome, either “on the beat” (i.e., in-phase coordination), or “off the beat” (i.e., antiphase coordination). The temporal stability of these perception- action patterns was measured by the variability of the relative phase between taps and auditory events and by the critical frequency, that is, the frequency at which a loss of stability was observed when the metronome frequency was increased. Age-related differences in stability were found for both relative phase variability and critical frequency. These findings suggest that the relative phase dynamics underlying perception-action coordination patterns change with age in the direction of an increased temporal stability. Received: 29 June 1998 / Accepted: 15 December 1998     

Phase Transitions and Critical Fluctuations in Rhythmic Coordination of Ipsilateral Hand and Foot

Four subjects performed rhythmic movements of the ankle and the wrist in time with an auditory metronome, in two modes of coordination, antiphase and in-phase. The forearm was placed in either a prone or a supine position. When movements were prepared in the antiphase mode, spontaneous transitions to the in-phase mode, or to phase wandering were observed as metronome frequency was increased. When prepared in the in-phase mode, transitions between in-phase modes or to phase wandering were occasionally observed. Predicted signature features of nonequilbrium phase transitions were noted, including loss of stability and critical fluctuations. The stability of the movement patterns was determined by spatial (dependent upon the direction of movement) rather than anatomical (dependent on the coupling of specific muscle groups) constraints. The position of the forearm had no consistent bearing upon the variability of the phase relations between the limbs, the frequency of phase transitions, or the time of onset of transitions. These results are discussed with reference to the coordination dynamics (e.g., multistability, loss of stability) of multijoint movements.     

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.     

The temporal representation of in-phase and anti-phase movements

We have proposed that the stability of bimanual coordination is influenced by the complexity of the representation of the task goals. Here, we present two experiments to explore this hypothesis. First, we examined whether a temporal event structure is present in continuous movements by having participants vocalize while producing bimanual circling movements. Participants tended to vocalize once per movement cycle when moving in-phase. In contrast, vocalizations were not synchronized with anti-phase movements. While the in-phase result is unexpected, the latter would suggest anti-phase continuous movements lack an event structure. Second, we examined the event structure of movements marked by salient turn-around points. Participants made bimanual wrist flexion movements and were instructed to move 'in synchrony' with a metronome, without specifying how they should couple the movements to the metronome. During in-phase movements, participants synchronized one hand cycle with every metronome beat; during anti-phase movements, participants synchronized flexion of one hand with one metronome beat and extension of the other hand with the next beat. The results are consistent with the hypothesis that the instability of anti-phase movements is related to their more complex (or absent) event representation relative to that associated with in-phase movements.     

Sensorimotor coordination generates extended agency

When we synchronize finger tapping with a visual metronome, we experience a strikingly robust phenomenon of extended agency known as Spizzo’s effect. This effect is the compelling sense that we are controlling the metronome. The effect arises even though the agent knows that the metronome operates autonomously. We propose that the extended agency here established over metronome pulses results from sensorimotor coordination. To test this hypothesis, we operationalize sensorimotor coordination in terms of the correlation structures in series of asynchronies or reaction times from two finger-tapping tasks. Analyses reveal that, whereas correlation structures vary across individuals and show a systematic drift towards nonstationarity with increasing metronome frequency conditions, the presence of correlation structure is co-extensive with Spizzo’s effect. We interpret this result as supporting the view that extended agency relies on sensorimotor coordination. Sensorimotor coordination, we suggest, may induce the effect by integrating the perception of visual pulses and the agency over tapping into a synesthetic experience.     

The timing effects of accent production in synchronization and continuation tasks performed by musicians and nonmusicians

Two groups of subjects differing in their musical expertise produced periodic finger-tapping sequences involving a pattern of accentuation. In some situations, the taps were synchronized with the clicks of a metronome. We recorded the trajectory of the subjects' finger displacement in the vertical plane, and the force and the moment of occurrence of the taps on the response key. Musicians tended to equalize the durations of the downstrokes at all positions in the sequence. Nonmusicians moved their finger quickly to produce the accent, and more slowly to produce the subsequent tap. These variations in the movement-execution time were partly compensated by opposite variations in the onsets of the movements, e.g., the short-duration movements were delayed. Despite these differences in their movement strategies, musicians and nonmusicians generated very similar tap-timing profiles. The intertap interval after the accent was lengthened regardless of the subjects' musical expertise and the metronome conditions (metronome present or absent). The lengthening did not depend on whether the interval before the accent was shortened (without the metronome) or not (with the metronome). It is suggested that an internal timekeeper may generate temporal goal points at which the keytaps should occur. The lengthening of the interval after the accent is attributed to transient changes in the working of the internal clock.     

Recruitment of degrees of freedom stabilizes coordination

By showing that transitions may be obviated by recruiting degrees of freedom in the coupled pendulum paradigm, the authors reveal a novel mechanism for coordinative flexibility. In Experiment 1, participants swung pairs of unconstrained pendulums in 2 planes of motion (sagittal and frontal) at 8 movement frequencies starting from either an in-phase or antiphase mode. Few transitions were observed. Measures of spatial trajectory showed recruitment effects tied to the stability of the initial coordinative pattern. When the motion of the pendulums was physically restricted to a single plane in Experiment 2, transitions were more common, indicating that recruitment delays--or even eliminates--transitions. Such recruitment complements transitions as a source of coordinative flexibility and is incorporated in a simple extension of the Haken-Kelso-Bunz (1985) model.     

Environmental coupling modulates the attractors of rhythmic coordination

A simple instance of coupling behavior to the environment is oscillating the hands in pace with metronome beats. This environmental coupling can be weaker (1 beat per cycle) or stronger (2 beats per cycle). The authors examined whether strength of environmental coupling enhanced the stability of in-phase bimanual coordination. Detuning by manipulanda that produced different left and right eigenfrequencies shifted the relative phase angle from 0 degrees, with the size of the shift larger for higher movement frequencies. Stronger environmental coupling was found to decrease this relative-phase shift, with accompanying increase and reduction, respectively, in recurrence quantification measures related to coordination stability and coordination noise. Stronger environmental coupling also increased oscillation amplitude. Results are considered from the perspective of parametric stabilization.     

The Dynamics of Bimanual Circle Drawing

A bimanual circle drawing task was employed to elucidate the dynamics of intralimb and interlimb coordination. Right-handed subjects were required to produce circles with both hands in either a symmetrical (mirror) mode (i.e. one hand moving clockwise, the other counter-clockwise) or in an asymmetrical mode (i.e. both hands moving clockwise or counter-clockwise). The frequency of movement was scaled by an auditory metronome from 1.50 Hz to 3.25 Hz in8 (8-sec) steps.In the asymmetrical mode,distortions ofthe movement trajectories, transient departures from the target pattern of coordination, and phase wandering were evident as movement frequency was increased. These features suggested loss of stability. Deviations from circular trajectories were most prominent for movements of the left hand. Transient departures from the required mode of coordination were also largely precipitated by the left hand. The results are discussed with reference to manual asymmetries and mechanisms of interlimb and intersegmental coordination.     

Interlimb coordination following stroke

Studies investigating whether simultaneous bilateral movements can facilitate performance of the impaired limb(s) of stroke patients have returned mixed results. In the present study we compared unilateral limb performance (amplitude, cycle duration) with performance during an interlimb coordination task involving both homologous (both arms, both legs) and non-homologous (one arm, one leg) limbs in stroke participants (n=7) and healthy age-matched controls (n=7). In addition, the effect of on-line augmented visual feedback on interlimb coordination was investigated. Participants performed cyclical flexion-extension movements of the arms and legs in the sagittal plane paced by an auditory metronome (1 Hz). Movement amplitudes were larger and cycle durations shorter during homologous limb coordination than non-homologous coordination. Compared with unilateral movements both groups had reduced movement amplitudes and the stroke group increased cycle duration when interlimb coordination tasks were performed. These effects were most evident during non-homologous (arm and leg) coordination. No evidence of facilitation of the impaired limb(s) was found in any of the interlimb coordination conditions. Augmented visual feedback had minimal effect on the movements of control participants but lead to an increase of cycle duration for stroke participants.     

The acquisition of bimanual coordination is mediated by anisotropic coupling between the hands

The present study was designed to test two predictions from the coupled oscillator model of multifrequency coordination. First, it was predicted that multifrequency tasks that match the inherent manual asymmetry (i.e., the preferred hand assigned to the faster tempo) would be easier to learn than tasks that do not match the inherent dynamics (i.e., the non-preferred hand assigned to the faster tempo). Second, in the latter case acquisition of the multifrequency coordination would involve a reorganisation of the coupling dynamics such that the faster hand would exert a greater influence on the slower hand than vice versa. Sixteen right-handed volunteers received extensive training on a 2:1 coordination pattern involving a bimanual forearm pronation-supination task. Participants were randomly assigned to one of two groups: 1L:2R in which the preferred right hand performed the higher frequency, or 2L:1R in which the non-preferred left hand performed the higher frequency. The dynamic stability of the patterns was assessed by the ability of participants to maintain the coordination pattern as movement frequency was increased. Changes in the directional coupling between the hands was assessed by transition pathways and lead-lag relationship evident in a 1:1 anti-phase frequency-scaled coordination task performed prior to and following three practice sessions of the 2:1 task. The predicted differential stability between the multifrequency patterns was evident in the initial acquisition sessions but by the end of training the two patterns evidenced equivalent stability. Unexpectedly, for both groups the fast hand displayed greater variability in amplitude and movement frequency than the slow hand perhaps reflecting anchoring afforded to the slow hand by synchronising movement endpoints with the auditory pacing metronome. Analysis of pre- to post-training changes to the coupling dynamics in the 1:1 anti-phase task support the hypothesis that acquisition of the 2L:1R pattern involved reorganisation of the inherent dynamics.     

Changes in coordination and variability during running as a function of head stability demands

The purpose of this study was to identify changes in segment/joint coordination and coordination variability in running with increasing head stability requirements. Fifteen strides from twelve recreational runners while running on a treadmill at their preferred speed were collected. Head stability demands were manipulated through real-time visual feedback that required head-gaze orientation to be contained within boxes of different sizes, ranging from 21 to 3 degrees of visual angle in 3-degree decrements. Coordination patterns and coordination variability were assessed between head and trunk segments, hip and knee joints, and knee and ankle joints in the three cardinal planes, respectively. Mean coupling angles and the standard deviation of the coupling angles at each individual point of the stance phase were calculated using a modified vector coding technique and circular statistics. As head stability demands increased, transverse plane head-trunk coordination was more anti-phase and showed increased head‑leading and decreased trunk‑leading patterns; for the lower extremity, there was increased in-phase and decreased anti-phase sagittal plane coordination. Increased head stability demands also resulted in an increase in coordination variability for both upper body and lower extremity couplings during the second half of the stance phase. Overall, the results provide evidence that coordinative adaptations to increasing head stability demands occur throughout the entire body: 1) through more independent control of the head relative to the trunk; 2) by increasing in-phase coordination between lower extremity joints, and 3) through increased coordination variability in the second half of stance in both upper body segmental and lower extremity joint couplings. These adaptations likely contribute to the reduction of the range of motion of the trunk in vertical direction.     

The coupled oscillator model of between-hand coordination in alternate-hand tapping: a reappraisal

Single and alternating hand tapping were compared to test the hypothesis that coordination during rhythmic movements is mediated by the control of specific time intervals. In Experiment 1, an auditory metronome was used to indicate a set of timing patterns in which a 1-s interval was divided into 2 subintervals. Performance, measured in terms of the deviation from the target patterns and variability, was similar under conditions in which the finger taps were made with 1 hand or alternated between the 2 hands. In Experiment 2, the modality of the metronome (auditory or visual) was found to influence the manner in which the produced intervals deviated from the target patterns. These results challenge the notion that bimanual coordination emerges from coupling constraints intrinsic to the 2-hand system. They are in accord with a framework that emphasizes the control of specific time intervals to form a series of well-defined motor events.