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.     

Interaction of directional,neuromuscular and egocentric constraints on the stability of preferred bimanual coordination patterns

We investigated how the relative direction of limb movements in external space (iso- and non-isodirectionality), muscular constraints (the relative timing of homologous muscle activation) and the egocentric frame of reference (moving simultaneously toward/away the longitudinal axis of the body) contribute to the stability of coordinated movements. In the first experiment, we attempted to determine the respective stability of isodirectional and non-isodirectional movements in between-persons coordination. In a second experiment, we determined the effect of the relative direction in external space, and of muscular constraints, on pattern stability during a within-person bimanual coordination task. In the third experiment we dissociated the effects on pattern stability of the muscular constraints, relative direction and egocentric frame of reference. The results showed that (1) simultaneous activation of homologous muscles resulted in more stable performance than simultaneous activation of non-homologous muscles during within-subject coordination, and that (2) isodirectional movements were more stable than non-isodirectional movements during between-persons coordination, confirming the role of the relative direction of the moving limbs in the stability of bimanual coordination. Moreover, the egocentric constraint was to some extent found distinguishable from the effect of the relative direction of the moving limbs in external space, and from the effect of the relative timing of muscle activation. In summary, the present study showed that relative direction of the moving limbs in external space and muscular constraints may interact either to stabilize or destabilize coordination patterns.     

Coordination of complex bimanual multijoint movements under increasing cycling frequencies: The prevalence of mirror-image and translational symmetry

The present study examined the principles underlying inter and intralimb coordination constraints during performance of bimanual elbow–wrist movements at different cycling frequencies (from 0.75 Hz to 2.50 Hz). Participants performed eight coordination tasks that consisted of a combination of in-phase (IN) and/or anti-phase (AN) coordination modes between both elbows and wrists (interlimb), with isodirectional (Iso) or non-isodirectional (NonI) coordination modes within each limb (intralimb). As expected, the principle of muscle homology (in-phase coordination), giving rise to mirror symmetrical movements with respect to the mid-sagittal plane, had a powerful influence on the quality of global coordinative behavior both between and within limbs. When this principle was violated (i.e., when the anti-phase mode was introduced in one or both joint pairs), the non-isodirectional intralimb mode exhibited a (de)stabilizing role in coordination, which became more pronounced at higher cycling frequencies. However, pattern loss with increasing cycling frequency resulted not only in convergence toward the more stable in-phase patterns with the elbows and wrists but also to the anti-phase patterns (which were associated with directional compatibility of within-limb motions). Moreover, participants generally preserved their initial mode of coordination (either in-phase or anti-phase) in the proximal joints (i.e., elbows) while shifting from anti-phase to in-phase (or vice versa) with their distal joint pair (i.e., wrists). Taken together, these findings reflect the impact of two immanent types of symmetry in bimanual coordination: mirror-image and translational symmetry.     

The control of amplitude and direction in a bimanual coordination task

Bimanual coordination requires task-specific control of the spatial and temporal characteristics of the movements of both hands. The present study focused on the spatial relationship between hand movements when their amplitude and direction were manipulated. In the experiment in question, participants were instructed to draw two lines simultaneously. These two lines were instructed to be drawn in mirror symmetric or perpendicular directions of each other while the length was instructed to be the same or different. The coordinative quality of amplitude control was compared when the task required symmetric and asymmetric bimanual spatial coordination patterns. Results showed that the amplitude accuracy decreased when different amplitudes and/or directions had to be generated simultaneously. The coordinative quality of direction was also compared when the task required symmetric and asymmetric bimanual spatial coordination patterns. Unlike amplitude, the direction accuracy was largely independent of coordination symmetry/asymmetry of direction or amplitude. The results suggest that the coordinative quality of amplitude control does not only interfere with amplitude asymmetry, but it also interferes with direction asymmetry. Moreover, in bimanual coordination amplitude control is more vulnerable to the influence of direction control demands than vice versa.     

Perception and action influences on discrete and reciprocal bimanual coordination

For nearly four decades bimanual coordination, “a prototype of complex motor skills” and apparent “window into the design of the brain,” has been intensively studied. Past research has focused on describing and modeling the constraints that allow the production of some coordination patterns while limiting effective performance of other bimanual coordination patterns. More recently researchers have identified a coalition of perception-action constraints that hinder the effective production of bimanual skills. The result has been that given specially designed contexts where one or more of these constraints are minimized, bimanual skills once thought difficult, if not impossible, to effectively produce without very extensive practice can be executed effectively with little or no practice. The challenge is to understand how these contextual constraints interact to allow or inhibit the production of complex bimanual coordination skills. In addition, the factors affecting the stability of bimanual coordination tasks needs to be re-conceptualized in terms of perception-related constraints arising from the environmental context in which performance is conducted and action constraints resident in the neuromotor system.     

Asymmetries in Coupling Dynamics of Perception and Action

The influence of information-based dynamics on coordination dynamics of rhythmic movement was examined with special reference to the expression of asymmetries. In Experiment 1, right-handed subjects performed unimanual, rhythmical movements in coordination with either a discrete or continuous visual display. The right hand-visual display system defined a more stable perception-action collective than the left, particularly when continuous visual information was available. In Experiment 2, the same subjects performed rhythmic bimanual movements in coordination with a continuous visual display. The action collective was inherently more stable than the perception-action collective, although similar patterns were observed at both levels. Importantly, the dynamics of the perception-action collective impinged upon the dynamics of the action collective in terms of stability. Asymmetries remained evident between limbs in the bimanual preparations, with the left hand exhibiting greater limit-cycle variability and also a tendency to more often effect transitions at the action couple. Features of dynamical models that capture characteristics of manual asymmetries are discussed.     

Egocentric reference frame bias in the palmar haptic perception of surface orientation

The effect of egocentric reference frames on palmar haptic perception of orientation was investigated in vertically separated locations in a sagittal plane. Reference stimuli to be haptically matched were presented either haptically (to the contralateral hand) or visually. As in prior investigations of haptic orientation perception, a strong egocentric bias was found, such that haptic orientation matches made in the lower part of personal space were much lower (i.e., were perceived as being higher) than those made at eye level. The same haptic bias was observed both when the reference surface to be matched was observed visually and when bimanual matching was used. These findings support the conclusion that, despite the presence of an unambiguous allocentric (gravitational) reference frame in vertical planes, haptic orientation perception in the sagittal plane reflects an egocentric bias.     

Coordination dynamics and attentional costs of continuous and discontinuous bimanual circle drawing movements

It has been suggested that the temporal control of rhythmic unimanual movements is different between tasks requiring continuous (e.g., circle drawing) and discontinuous movements (e.g., finger tapping). Specifically, for continuous movements temporal regularities are an emergent property, whereas for tasks that involve discontinuities timing is an explicit part of the action goal. The present experiment further investigated the control of continuous and discontinuous movements by comparing the coordination dynamics and attentional demands of bimanual continuous circle drawing with bimanual intermittent circle drawing. The intermittent task required participants to insert a 400ms pause between each cycle while circling. Using dual-task methodology, 15 right-handed participants performed the two circle drawing tasks, while vocally responding to randomly presented auditory probes. The circle drawing tasks were performed in symmetrical and asymmetrical coordination modes and at movement frequencies of 1Hz and 1.7Hz. Intermittent circle drawing exhibited superior spatial and temporal accuracy and stability than continuous circle drawing supporting the hypothesis that the two tasks have different underlying control processes. In terms of attentional cost, probe RT was significantly slower during the intermittent circle drawing task than the continuous circle drawing task across both coordination modes and movement frequencies. Of interest was the finding that in the intermittent circling task reaction time (RT) to probes presented during the pause between cycles did not differ from the RT to probes occurring during the circling movement. The differences in attentional demands between the intermittent and continuous circle drawing tasks may reflect the operation of explicit event timing and implicit emergent timing processes, respectively.     

The impact of perceptual, cognitive and motor factors on bimanual coordination

Bimanual coordination is governed by constraints that permit congruent movements to be performed more easily than incongruent movements. Theories concerning the origin of these constraints range from low level motor-muscle explanations to high level perceptual–cognitive ones. To elucidate the processes underlying coordinative constraints, we asked subjects to use a pair of left–right joysticks to acquire corresponding pairs of congruent and incongruent targets presented on a video monitor under task conditions designed to systematically modulate the impact of several perceptual–cognitive processes commonly required for bimanual task performance. These processes included decoding symbolic cues, detecting goal targets, conceptualizing movements in terms of goal target configuration, planning movement trajectories, producing saccades and perceiving visual feedback. Results demonstrate that constraints arise from target detection and trajectory planning processes that can occur prior to movement initiation as well as from inherent muscle properties that emerge during movement execution, and that the manifestation of these constraints can be significantly altered by the ability to visually monitor movement progress.     

Symmetry constraints mediate the learning and transfer of bimanual coordination patterns across planes of motion

The authors investigated whether neuromuscular and directional constraints are dissociable limitations that affect learning and transfer of a bimanual coordination pattern. Participants (N = 9) practiced a 45 degrees muscular relative phasing pattern in the transverse plane over 4 days. The corresponding to-be-learned spatial relative phasing was 225 degrees. Before, during, and following practice, the authors administered probe tests in the sagittal plane to assess transfer of learning. In the probe tests, participants performed various patterns characterized by different muscular and spatial relative phasing (45 degrees, 45 degrees, 45 degrees, 225 degrees, 225 degrees, 45 degrees, and 225 degrees, 225 degrees). The acquisition of the to-be-learned pattern in the transverse plane resulted in spontaneous positive transfer of learning only to coordination patterns having 45 degrees of spatial relative phase, irrespective of muscular phasing. Moreover, transfer occurred in the sagittal plane to coordination patterns that had symmetry properties similar to those of the to-be-learned pattern. The authors conclude that learning and transfer of spatial features of coordination patterns from the transverse to the sagittal plane of motion are mediated by mirror-symmetry constraints.     

Re-examining structural constraints on the initiation of bimanual movements: the role of starting locations, movement amplitudes, and target locations

Structural constraints affect the coordination of bimanual movements in ways that have been taken to suggest that the specification of different movement amplitudes is subject to strong intermanual interference effects. Most experiments taken to support this notion, however, confounded variations of movement amplitudes with symmetry in starting locations and variations in target location. The present experiment was designed to further investigate the relative influence of the parameters starting location, movement amplitude, and target location on bimanual movement coordination. Participants performed simultaneous reaching movements with the left and right hand from same and different starting locations to same and different target locations. On each trial, two movements could match on none, one, or all of the parameters. We assessed the influence of each parameter by comparing conditions in which only a single parameter matched between the two hands with conditions in which all parameters differed. The reaction-time data revealed some challenging results for previous studies: (1) same starting locations significantly delayed movement initiation; (2) specifying movement amplitudes had virtually no effect on movement initiation, whereas (3) selecting same target locations significantly benefited the bimanual responses. These findings cannot be taken to support the notion that amplitude specification affects the initiation of bimanual movements. Rather, they support the notion that the initial starting locations of the two hands and the selection of target locations decide about the ease with which we perform bimanual reaching movements.     

Bimanual training reduces spatial interference

The authors investigated whether training can reduce bimanual directional interference by using a star-line drawing paradigm. Participants (N = 30) were required to perform rhythmical arm movements with identical temporal but differing directional demands. Moreover, the effectiveness of part-task training in which each movement was practiced in isolation was compared with that of whole-task training in which only combined movements were performed. Findings revealed that bimanual training substantially reduced spatial interference, but unimanual training did not. The authors therefore concluded that the spatial coupling of the limbs is not implemented in a rigid way; instead, the underlying neural correlate can undergo plastic changes induced by training. Moreover, the practical implication that emerged from the present study is that athletic, musical, or ergonomic skills that require a high degree of interlimb coordination are best served by whole-task practice.     

Bimanual Training Reduces Spatial Interference

The authors investigated whether training can reduce bimanual directional interference by using a star-line drawing paradigm, Participants (N = 30) were required to perform rhythmical arm movements with identical temporal but differing directional demands. Moreover, the effectiveness of part-task training in which each movement was practiced in isolation was compared with that of whole-task training in which only combined movements were performed. Findings revealed that bimanual training substantially reduced spatial interference, but unimanual training did not. The authors therefore concluded that the spatial coupling of the limbs is not implemented in a rigid way; instead, the underlying neural correlate can undergo plastic changes induced by training. Moreover, the practical implication that emerged from the present study is that athletic, musical, or ergonomic skills that require a high degree of interlimb coordination are best served by whole-task practice.     

Distinct ways of timing movements in bimanual coordination tasks: contribution of serial correlation analysis and implications for modeling

Bimanual coordination dynamics have been conceived as the outcome of a global coordinative system, and coordination stability properties and theories of underlying processes have often been generalized over various bimanual tasks. In unimanual timing tasks it has been shown that different timing processes are involved according to tasks, yielding distinctive correlation properties in the within-hand temporal patterns. In this study we compare unimanual with bimanual, tapping with oscillation, and self-paced with externally paced tasks, and we analyze the correlation properties of temporal patterns at both the component level and the coordinative level. Results show that the distinctive signatures of event-based versus emergent, and self-paced versus synchronization timing control known from unimanual tasks persist in the corresponding bimanual coordination tasks. Accordingly, we argue that these different timing processes, and related temporal patterns at the component level, constitute a task-dependent background on which coordination builds. One direct implication of these results is that the bimanual coordination paradigm should be considered multifaceted and not governed by some unitary generic principle. We discuss the need to assess the relationship between temporal patterns at the component level and the collective level, and to integrate serial (long-range) correlation properties into bimanual coordination models. Finally, we test whether the architectures of current bimanual coordination models can account for the experimentally observed serial correlations.     

Haptic parallelity perception on the frontoparallel plane: the involvement of reference frames

It has been established that spatial representation in the haptic modality is subject to systematic distortions. In this study, the haptic perception of parallelity on the frontoparallel plane was investigated in a bimanual matching paradigm. Eight reference orientations and 23 combinations of stimulus locations were used. The current hypothesis from studies conducted on the horizontal and midsagittal planes presupposes that what is haptically perceived as parallel is a product of weighted contributions from both egocentric and allocentric reference frames. In our study, we assessed a correlation between deviations from the veridical and hand/arm postures and found support for the role of an intermediate frame of reference in modulating haptic parallelity on the frontoparallel plane as well. Moreover, a subject-dependent biasing influence of the egocentric reference frame determines both the reversal of the oblique effect and a scaling effect in deviations as a function of bar position.     

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.     

Local stability in coordinated rhythmic movements: fluctuations and relaxation times

An experiment was conducted to examine the stability of the anti-phase and in-phase modes of coordination by means of both fluctuations and relaxation times. Participants (n=6) performed a rhythmic bimanual forearm coordination task that required them to oscillate their forearms in-phase and anti-phase while grasping two manipulanda at fixed frequencies ranging from 0.6 to 1.8 Hz. Relaxation times were measured as the time taken to return to a stable mode following the application of a transient mechanical torque. It was found that relaxation times were not different statistically across participants, frequencies, and coordinative modes. However, fluctuations, as indicated by the mean S.D. of relative phase across individual frequency plateaus, were significantly greater in the anti-phase than in the in-phase mode of coordination, p<0.05. Whilst providing new empirical support for the notion that relaxation times should be of the same order of magnitude at frequencies outside transition regions, the findings suggest that the level of stochastic noise in the anti-phase mode is greater than that of the in-phase mode. Implications are made for the future assessment of local pattern stability.     

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).     

Perception-action coupling during bimanual coordination: the role of visual perception in the coalition of constraints that govern bimanual action

Constraints pertaining to interlimb coordination have been studied extensively in the past decades. In this debate, F. Mechsner (2004) has taken a provocative position by putting primary emphasis on perceptual principles that mediate coordinative stability. Whereas the present authors agree that the role of perceptual principles is of critical importance during coordination, they take issue with Mechsner's extreme position and with the evidence forwarded to support a purely perceptual-cognitive approach to bimanual coordination. More specifically, the authors emphasize that current knowledge about brain function argues against a dualism between perception and action, criticize the presented evidence that posture manipulations during coordination provide decisive evidence against motoric and muscular constraints, and report on potential pitfalls associated with the use of visual transformation procedures to support complex coordination patterns.     

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.