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.     

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.     

The metabolic and cognitive energy costs of stabilising a high-energy interlimb coordination task

Kinematic (relative phase error), metabolic (oxygen consumption, heart rate) and attentional (baseline and cycling reaction times) variables were measured while participants practised a high energy-demanding, intrinsically unstable 90 degrees relative phase coordination pattern on independent bicycle ergometers. The variables were found to be strongly inter-correlated, suggesting a link between emerging performance stability with practice and minimal metabolic and attentional cost. The effects of practice of 90 degrees relative phase coordination on the performance of in-phase (0 degrees-phase) and antiphase (180 degrees-phase) coordination were investigated by measuring the relative phase attractor layouts and recording the metabolic and attentional cost of the three coordination patterns before and after practice. The attentional variables did not differ significantly between coordination patterns and did not change with practice. Before practice, the coordination performance was most accurate and stable for in-phase cycling, with antiphase next and 90 degrees-phase the poorest. However, metabolic cost was lower for antiphase than either in-phase or 90 degrees-phase cycling, and the pre-practice attractor layout deviated from that predicted on the basis of dynamic stability as an attractor state, revealing an attraction to antiphase cycling. After practice of 90 degrees-phase cycling, in-phase cycling remained the most accurate and stable, with 90 degrees-phase next and antiphase the poorest, but antiphase retained the lowest metabolic energy cost. The attractor layout had changed, with new attractors formed at the practised 90 degrees-phase pattern and its symmetrical partner of 270 degrees-phase. Considering both the pre- and post-practice results, attractors were formed at either a low metabolic energy cost but less stable (antiphase) pattern or at a more stable but higher metabolic energy cost (90 degrees-phase) pattern, but in neither case at the most stable and accurate (in-phase) pattern. The results suggest that energetic factors affect coordination dynamics and that coordination modes lower in metabolic energy expenditure may compete with dynamically stable modes.     

Age-related differences in the integration of sensory information during the execution of a bimanual coordination task

Young (n = 7) and elderly (n = 7) subjects performed bimanual coordination patterns in the transverse plane according to the in-phase or antiphase mode. Sensory information was manipulated through visual (with or without vision of the limbs) and proprioceptive input (with or without vibratory stimuli on one limb). Movement patterns with vibrations showed higher deviations from the intended relative phase than did those without vibrations. This finding suggests that the proprioceptive information induced by the vibrations and the movement interfered, leading to a disruption of the coordination patterns. In addition, as compared with the elderly, the young subjects performed more stable movements under normal circumstances but were more strongly affected by vibratory stimuli during the performance of in-phase movements. During antiphase movements, both age groups experienced a decrease of pattern stability. Furthermore, the absence or presence of visual feedback influenced the performance of the young subjects more than that of the elderly. The presence of vision led to stable in-phase movements, whereas a decrease of pattern stability was observed for antiphase movements. In general, these results demonstrate that manipulation of feedback sources affects young subjects more than elderly ones, and this can be related to a reduced sensory sensitivity as a function of aging.     

Bimanual finger tapping: effects of frequency and auditory information on timing consistency and coordination

The authors' goal in this study was to probe the basis for an earlier, unexpected finding that preferred-frequency finger tapping tends to have higher frequencies and to be less stable for in-phase than for antiphase tasks. In follow-up experiments, 3 protocols were employed: a preferred-frequency replication in both coordination modes, a metronome-driven matching of the preferred frequencies to each of the coordination modes, and a frequency scaling of both modes. The original findings were affirmed for preferred frequency. Tapping to a metronome had a differential effect on in-phase and antiphase: A more stable coupling across frequencies was exhibited during in-phase. Under frequency scaling, the antiphase pattern decomposed at lower frequencies than did in-phase, but no phase transitions were observed. The loss of stable coordination in both modes was attended by sudden increases in frequency differences between fingers and by phase wandering. The emergence of those effects is discussed in light of asymmetric modifications to the Haken-Kelso-Bunz model (H. Haken, J. A. S. Kelso, & H. Bunz, 1985) and the task constraints of tapping.     

Bimanual Finger Tapping: Effects of Frequency and Auditory Information on Timing Consistency and Coordination

The authors' goal in this study was to probe the basis for an earlier, unexpected finding that preferred-frequency finger tapping tends to have higher frequencies and to be less stable for in-phase than for antiphase tasks. In follow-up experiments, 3 protocols were employed: a preferred-frequency replication in both coordination modes, a metronome-driven matching of the preferred frequencies to each of the coordination modes, and a frequency scaling of both modes. The original findings were affirmed for preferred frequency. Tapping to a metronome had a differential effect on in-phase and antiphase: A more stable coupling across frequencies was exhibited during in-phase. Under frequency scaling, the antiphase pattern decomposed at lower frequencies than did in-phase, but no phase transitions were observed. The loss of stable coordination in both modes was attended by sudden increases in frequency differences between fingers and by phase wandering. The emergence of those effects is discussed in light of asymmetric modifications to the Haken-Kelso-Bunz model (H. Haken, J. A. S. Kelso, & H. Bunz, 1985) and the task constraints of tapping.     

Metabolic and attentional energy costs of interlimb coordination

The authors investigated metabolic and attentional energy costs as participants (N = 6) practiced in-phase, antiphase, and 90 degrees -phase cycling (order counterbalanced) on independent bicycle ergometers, with resistance (40 W/ergometer) and frequency (40 rpm) held constant. Coordination stabilized and became more accurate for all 3 cycling modes, as shown by measures of relative phase, but that collective variable could not account for other relevant attributes of the multifaceted motor behavior observed across the 3 coordination modes. In-phase and antiphase cycling were similar in stability and accuracy, but antiphase had the lowest metabolic and attentional energy costs. Because both homologous muscle action and perceptually symmetrical oscillations coincided in the in-phase mode, the absence of predominance of the inphase pattern showed that neither of those musculoskeletal and perceptual factors exclusively determined the strongest attractor of the coordination dynamics. Both metabolic and attentional costs declined with practice, consistent with the hypothesis that adaptive motor behavior is guided by sensory information concerning the energy demands of the task. Attentional cost was influenced not only by the information-processing demands of kinematic stability but also by the metabolic energy demands. Metabolic energy cost appeared to be the crucial determinant of the preferred solution for this coordination task.     

Intentional switching between patterns of bimanual coordination depends on the intrinsic dynamics of the patterns

Two predictions arising from previous theoretical and empirical work which demonstrated that spontaneous changes of bimanual coordination patterns result from a loss of pattern stability (i.e., a nonequilibrium phase transition) were tested: (a) that the time it takes to intentionally switch from one pattern to another depends on the differential stability of the patterns themselves; and (b) that an intention, defined as an intended behavioral pattern, can change the dynamical characteristics, e.g., the overall stability of the behavioral patterns. Subjects moved both index fingers rhythmically at one of six movement frequencies while performing either an in-phase or antiphase pattern of finger coordination. On cue from an auditory signal, subjects switched from the ongoing pattern to the other pattern. The relative phase of movement between the two fingers was used to characterize the ongoing coordinative pattern. The time taken to switch between patterns, or switching time, and relative phase fluctuations were used to evaluate the modified pattern dynamics resulting from a subject's intention to change patterns. Switching from the in-phase to the antiphase pattern was significantly slower than switching in the opposite direction for all subjects. Both the mean and distribution of switching times in each direction were found to be in agreement with model predictions. movement frequency had little effect on switching time, a finding that is also consistent with the model. Relative phase fluctuations were significantly larger when moving in the antiphase pattern at the highest movement frequencies studied. The results show that, although intentional influences act to modify a coordinative pattern's intrinsic dynamics, the influence of these dynamics on the resulting behavior is always present and is particularly strong at high movement frequencies.     

Pattern Stability and Error Correction During In-Phase and Antiphase Four-Ball Juggling

The authors studied pattern stability and error correction during in-phase and antiphase 4-ball fountain juggling. To obtain ball trajectories, they made and digitized high-speed film recordings of 4 highly skilled participants juggling at 3 different heights (and thus different frequencies). From those ball trajectories, the authors determined and analyzed critical events (i.e., toss, zenith, catch, and toss onset) in terms of variability of point estimates of relative phase and temporal correlations. Contrary to common findings on basic instances of rhythmic interlimb coordination, in-phase and antiphase patterns were equally variable (i.e., stable). Consistent with previous findings, however, pattern stability decreased with increasing frequency. In contrast to previous results for 3-ball cascade juggling, negative lag-one correlations for catch-catch intervals were absent, but the authors obtained evidence for error corrections between catches and toss onsets. That finding may have reflected participants' high skill level, which yielded smaller errors that allowed for corrections later in the hand cycle.     

Pattern stability and error correction during in-phase and antiphase four-ball juggling

The authors studied pattern stability and error correction during in-phase and antiphase 4-ball fountain juggling. To obtain ball trajectories, they made and digitized high-speed film recordings of 4 highly skilled participants juggling at 3 different heights (and thus different frequencies). From those ball trajectories, the authors determined and analyzed critical events (i.e., toss, zenith, catch, and toss onset) in terms of variability of point estimates of relative phase and temporal correlations. Contrary to common findings on basic instances of rhythmic interlimb coordination, in-phase and antiphase patterns were equally variable (i.e., stable). Consistent with previous findings, however, pattern stability decreased with increasing frequency. In contrast to previous results for 3-ball cascade juggling, negative lag-one correlations for catch-catch intervals were absent, but the authors obtained evidence for error corrections between catches and toss onsets. That finding may have reflected participants' high skill level, which yielded smaller errors that allowed for corrections later in the hand cycle.     

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.     

Intentional Switching Between Patterns of Bimanual Coordination Depends on the Intrinsic Dynamics of the Patterns

Two predictions arising from previous theoretical and empirical work which demonstrated that spontaneous changes of bimanual coordination patterns result from a loss of pattern stability (i.e., a nonequilibrium phase transition) were tested: (a) that the time it takes to intentionally switch from one pattern to another depends on the differential stability of the patterns themselves; and (b) that an intention, defined as an intended behavioral pattern, can change the dynamical characteristics, e.g., the overall stability of the behavioral patterns. Subjects moved both index fingers rhythmically at one of six movement frequencies while performing either an in-phase or antiphase pattern of finger coordination. On cue from an auditory signal, subjects switched from the ongoing pattern to the other pattern. The relative phase of movement between the two fingers was used to characterize the ongoing coordinative pattern. The time taken to switch between patterns, or switching time, and relative phase fluctuations were used to evaluate the modified pattern dynamics resulting from a subject's intention to change patterns. Switching from the in-phase to the antiphase pattern was significantly slower than switching in the opposite direction for all subjects. Both the mean and distribution of switching times in each direction were found to be in agreement with model predictions. Movement frequency had little effect on switching time, a finding that is also consistent with the model. Relative phase fluctuations were significantly larger when moving in the antiphase pattern at the highest movement frequencies studied. The results show that, although intentional influences act to modify a coordinative pattern's intrinsic dynamics, the influence of these dynamics on the resulting behavior is always present and is particularly strong at high movement frequencies.     

The effect of volition on the stability of bimanual coordination

The authors investigated how the intention to passively perform a behavior and the intention to persist with a behavior impact upon the spatial and temporal properties of bimanual coordination. Participants (N = 30) were asked to perform a bimanual coordination task that demanded the continuous rhythmic extension-flexion of the wrists. The frequency of movement was scaled by an auditory metronome beat from 1.5 Hz, increasing to 3.25 Hz in.25-Hz increments. The task was further defined by the requirement that the movements be performed initially in a prescribed pattern of coordination (in-phase or antiphase) while the participants assumed one of two different intentional states: stay with the prescribed pattern should it become unstable or do not intervene should the pattern begin to change. Transitions away from the initially prescribed pattern were observed only in trials conducted in the antiphase mode of coordination. The time at which the antiphase pattern of coordination became unstable was not found to be influenced by the intentional state. In addition, the do-not-intervene set led to a switch to an in-phase pattern of coordination whereas the stay set led to phase wandering. Those findings are discussed within the framework of a dynamic account of bimanual coordination.     

Anchoring strategies for learning a bimanual coordination pattern

Anchoring has been defined as synchronizing a point in a movement cycle with an external stimulus (W. D. Byblow, R. G. Carson, & D. Goodman, 1994). Previously, investigators have examined anchoring during in-phase and antiphase movements. The present authors examined anchoring during acquisition of a novel bimanual coordination pattern. Participants performed a 90 degrees pattern at 1 Hz, with a 2- or 4-Hz metronome. No group differences were found in pattern performance; however, the 4-Hz group developed more consistent anchoring relative to the metronome. Mechanical anchor-point variability differed by hand, position (midpoint vs. endpoint), and direction (flexion vs. extension) but not by metronome frequency. Those results support and extend previous findings but leave unanswered questions regarding the benefits and effectiveness of anchoring during a 90 degrees pattern.     

Coordination Dynamics of the Bipedal Galloping Pattern

A motion equation in relative phase was developed that incorporates the spatial-temporal pattern of the bipedal gallop along with the more commonplace patterns of the bipedal jump and walk-run. In 3 experiments, human participants (N = 6 per experiment) simulated the bipedal gait patterns through the rhythmic motions of hand-held pendulums. Predictions of the motion equation for coordination equilibria and their respective degrees of stability were confirmed. In particular, the gallop pattern was less stable than the fundamental in-phase and antiphase patterns but changed in qualitatively similar ways to those gaits as a function of limb asymmetry and movement frequency. The relation between the modeled coordination dynamics and the kinematic characteristics of real bipedal galloping is discussed     

Dual-Finger Preferred-Speed Tapping: Effects of Coordination Mode and Anatomical Finger and Limb Pairings

Interlimb and interfinger coordination were examined in a dual-finger tapping paradigm in which 16 subjects performed at preferred frequencies. Three bimanual finger combinations, in random order (2 index; 2 middle; and 1 index and 1 middle), were performed in in-phase and antiphase coordination modes, in addition to 1 unimanual combination (antiphase index-middle). Relative phase means were within 3&percent; accuracy for all conditions. A lower tapping frequency was found in all antiphase vs. in-phase conditions, accompanied by lower phasing variability and lower intrafinger consistency in the antiphase. When frequency was changed from the preferred rate, the 2 coordination modes became more alike in variability and, within the same frequency range, demonstrated no significant differences. The bimanual mixed-fingers tapping tended to have significantly lower phasing values (a small fixed point drift) and higher tapping frequencies than the symmetric conditions. The unimanual task was similar to all other antiphase conditions. Changes in preferred frequency with different coordination modes may be related to differing perceptual informational constraints. Current models addressing natural frequencies of coupled oscillators do not account for the present data.     

Coordination Dynamics of the Bipedal Galloping Pattern

A motion equation in relative phase was developed that incorporates the spatial-temporal pattern of the bipedal gallop along with the more commonplace patterns of the bipedal jump and walk-run. In 3 experiments, human participants (N = 6 per experiment) simulated the bipedal gait patterns through the rhythmic motions of hand-held pendulums. Predictions of the motion equation for coordination equilibria and their respective degrees of stability were confirmed. In particular, the gallop pattern was less stable than the fundamental in-phase and antiphase patterns but changed in qualitatively similar ways to those gaits as a function of limb asymmetry and movement frequency. The relation between the modeled coordination dynamics and the kinematic characteristics of real bipedal galloping is discussed.     

Diffusive,Synaptic, and Synergetic Coupling: An Evaluation Through In-Phase and Antiphase Rhythmic Movements

The in-phase and antiphase patterns of interlimb l:1 frequency locking were contrasted with respect to models of coordination dynamics in biological movement systems that are based on diffusive coupling, synaptic coupling, and synergetic principles. Predictions were made from each model concerning the stable relative phase phi between the rhythmic units, its standard deviation SDphi and the self-chosen coupled frequency omegasubc;. The experimental task involved human subjects oscillating two handheld pendulums either in-phase or antiphase. The eigenfrequencies of the two hand-pendulum systems were manipulated by varying the length and mass of each pendulum individually. Relative to an eigenfrequency difference of Delta equal to zero, |Deltaomega| > 0 displaced phi from phi = 0 and phi = pi, and amplified SDphi. omegasubc; decreased with |Deltaomega|. Both the displacement of phi and SDphi were greater in the antiphase mode. Additionally, the displacement of phi increased more sharply with |Delta| for antiphase than for in-phase coordination. In contrast, omegasubc; was identical for the two coordination modes. Of the models of interlimb coordination dynamics, the synergetic model was the most successful in addressing the pattern of dependencies of phi and SDphi. The specific forms of the functions relating omegasubc; and phi to Deltaomega pose challenges for all three models, however     

Intentional Switching Between Bimanual Coordination Patterns

Previous theoretical and empirical work indicates that intentional changes in a bimanual coordination pattern depends on the stability of the bimanual coordination pattern (Kelso, Schotz, & Schöner, 1988; Scholz & Kelso, 1990). The present experiments retest this notion when online Lissajous displays are provided. Switching to and from in-phase and antiphase and to and from 90° and 270° were tested in Experiment 1. Participants were able to very effectively produce the 180°, 90°, and 270° coordination patterns although performance of the in-phase coordination task was even more stable. The data indicated that switching to in-phase from antiphase was more rapid than vice versa and that switching times between 90° to 270° were similar. Experiment 2 investigated switching between 1:2 and 2:1 bimanual coordination patterns. The results indicated that switching time was similar between the 2:1 and 1:2 coordination tasks and that increases in stability over practice resulted in additional decreases in switching times. This provides additional evidence that the attractor landscape is fundamentally different dependent on the type of information provided the performer. What remains to be done is to reconcile these results with the various theories/perspectives currently used to describe and explain bimanual coordination.     

Effects of correct and transformed visual feedback on rhythmic visuo-motor tracking: tracking performance and visual search behavior

The effects of correct and transformed visual feedback on rhythmic unimanual visuo-motor tracking were examined, focusing on tracking performance (accuracy and stability) and visual search behavior. Twelve participants (reduced to 9 in the analyses) manually tracked an oscillating visual target signal in phase (by moving the hand in the same direction as the target signal) and in antiphase (by moving the hand in the opposite direction), while the frequency of the target signal was gradually increased to probe pattern stability. Besides a control condition without feedback, correct feedback (representing the actual hand movement) or mirrored feedback (representing the hand movement transformed by 180 degrees) were provided during tracking, resulting in either in-phase or antiphase visual motion of the target and feedback signal, depending on the tracking mode performed. The quality (accuracy and stability) of in-phase tracking was hardly affected by the two forms of feedback, whereas antiphase tracking clearly benefited from mirrored feedback but not from correct feedback. This finding extends previous results indicating that the performance of visuo-motor coordination tasks is aided by visual feedback manipulations resulting in coherently grouped (i.e., in-phase) visual motion structures. Further insights into visuo-motor tracking with and without feedback were garnered from the visual search patterns accompanying task performance. Smooth pursuit eye movements only occurred at lower oscillation frequencies and prevailed during in-phase tracking and when target and feedback signal moved in phase. At higher frequencies, point-of-gaze was fixated at a location that depended on the feedback provided and the resulting visual motion structures. During in-phase tracking the mirrored feedback was ignored, which explains why performance was not affected in this condition. Point-of-gaze fixations at one of the end-points were accompanied by reduced motor variability at this location, reflecting a form of visuo-motor anchoring that may support the pick up of discrete information as well as the control of hand movements to a desired location.