Effects of task instructions and oscillation frequency on bimanual coordination

Increases in the oscillation frequency of bimanual movements produce a switch from an anti-phase (180° relative phase) to an in-phase (0° relative phase) coordination pattern. This finding is observed when subjects are instructed not to intervene when they feel themselves slipping out of the anti-phase pattern. The question addressed in this study concerned how performance would be affected if subjects were instructed to try to maintain the pattern at all times. This issue was addressed using two separate groups of subjects: one group was given the do not intervene instructions, the other group was told to try to stay with the pattern at all times. Forearm rotations were tested in 15 s trials, paced by an auditory metronome set at 1.0, 1.5, 2.0, 2.5, and 3.0 Hz. Frequency distributions of the point estimates of relative phase were analyzed. The Do not Intervene group replicated previous findings, as indicated by the development of a bimodal histogram of relative phase distributions with increases in oscillation frequency. However, a very different pattern of findings emerged with increases in oscillation frequency for the group told to stay with the anti-phase pattern. Rather than a bimodal distribution being developed, the data maintained 180° as its central tendency — no secondary distribution developed around 0° relative phase. These data suggest that volitional control can over-ride the inherent dynamical tendencies of the motor system.     

One-to-one and polyrhythmic temporal coordination in bimanual circle tracing

The authors manipulated movement amplitude in a bimanual circle-tracing task to alter the natural tracing frequency of the arms. Participants (N = 14) traced different-diameter circles simultaneously with the two arms in either in-phase (0 degrees) or antiphase (180 degrees) coordination, using the index fingers or plastic styli. Movement amplitude altered the natural tracing frequency of the arms, as demonstrated by the following 2 findings: (a) The larger the difference in circle diameter, the larger was the shift from the fixed-point values of 0 degrees and 180 degrees, and the shift increased as movement frequency increased. Those results are consistent with the manipulation of delta omega in the bimanual pendulum paradigm. (b) Increasing movement frequency induced transitions from 1:1 to non-1:1 coordination, contrary to findings in previous investigations of polyrhythmic coordination. Tactile feedback played a minimal role in stabilizing bimanual coordination in the current tasks.     

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).     

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.     

Interference effects in bimanual coordination are independent of movement type

Simultaneously executed limb movements interfere with each other. Whereas the interference between discrete movements is examined mostly from a cognitive perspective, that between rhythmic movements is studied mainly from a dynamical systems perspective. As the tools and concepts developed by both communities are limited in their applicability to the other domain, it remains unclear if a common cause underlies motor interference in both domains. We investigated the interference between simultaneously executed discrete and rhythmic wrist movements. The discrete movements' reaction time and movement time decreased with increasing rhythmic movement frequency. The discrete movements accelerated or decelerated the rhythmic movements in a manner that depended on movement frequency and the discrete movement's initiation phase. The acceleration/deceleration profile was bimodal at low frequencies and unimodal at high frequencies, mimicking the hallmark feature of rhythmic-rhythmic coordination, thus suggesting that interference between movements may be invariant across different movement types.     

Effects of visual and auditory guidance on bimanual coordination complexity

Perceptual guidance of movement with simple visual or temporal information can facilitate performance of difficult coordination patterns. Guidance may override coordination constraints that usually limit stability of bimanual coordination to only in-phase and anti-phase. Movement dynamics, however, might not have the same characteristics with and without perceptual guidance. Do visual and auditory guidance produce qualitatively different dynamical organization of movement? An anti-phase wrist flexion and extension coordination task was performed under no specific perceptual guidance, under temporal guidance with a metronome, and under visual guidance with a Lissajous plot. For the time series of amplitudes, periods and relative phases, temporal correlations were measured with Detrended Fluctuation Analysis and complexity levels were measured with multiscale entropy. Temporal correlations of amplitudes and relative phases deviated from the typical 1/f variation towards more random variation under visual guidance. The same was observed for the series of periods under temporal guidance. Complexity levels for all time series were lower in visual guidance, but higher for periods under temporal guidance. Perceptual simplification of the task’s goal may produce enhancement of performance, but it is accompanied by changes in the details of movement organization that may be relevant to explain dependence and poor retention after practice under guidance.     

Effects of S-R and R-R compatibility on bimanual movement time

Bimanual asymmetrical movements are generally found to be slower than symmetrical movements but asymmetrical movement normally involves visual separation of targets which might account for the effect. By using a system in which the subject controls two cursors on an oscilloscope screen by moving two levers the S-R relationship on either hand can be reversed, thus providing an asymmetrical movement task without visual separation of targets. Movement times for five right-handed subjects were recorded on four unimanual and six bimanual conditions varying with respect to both S-R and R-R compatibility. In the unimanual conditions, the left hand was found to be as fast as the right when the opposite S-R relationship was used. In the bimanual tasks visual separation of targets was a relatively minor factor movement time being strongly influenced by S-R compatibility and to a lesser degree by R-R compatibility. The results suggest that compatibility, rather than being a property of a single central channel, differs, as between the two cerebral hemispheres.     

Stability of inter-joint coordination during circle drawing: effects of shoulder-joint articular properties

The present study addressed the effect of articular conformity of the shoulder joint on the stability of inter-joint coordination during circular drawing movements. Twelve right-handed participants performed clockwise and counter-clockwise circular drawing movements at nine locations in the mid-sagittal plane. The task was paced acoustically at 1.0, 1.5 and 2.0 Hz and performed without visual control. Displacements of seven infrared light emitting diodes that were fixated at relevant joints were sampled at 100 Hz by means of a 3D-motion tracking system (Optotrak 3020). From these data, shoulder, elbow and wrist angular excursions were derived as well as the continuous relative phase of the proximal and distal joint pairs of the arm. The results confirmed earlier observations that the shoulder and elbow are more strongly coupled than the elbow and wrist in sagittal-plane movements. However, a typical characteristic of the architecture of the shoulder joint, that is, its built-in mechanical "joint play", was shown to induce a position-dependent variation in inter-joint coordination stability. We conclude that besides polyarticular-muscle induced synergies and inertial coupling, articular conformity of the shoulder joint constitutes an additional determinant of inter-joint coordination stability that, to date, has been neglected.     

The acquisition of movement skills: practice enhances the dynamic stability of bimanual coordination.

During bimanual movements, two relatively stable "inherent" patterns of coordination (in-phase and anti-phase) are displayed (e.g., Kelso, Am. J. Physiol. 246 (1984) R1000). Recent research has shown that new patterns of coordination can be learned. For example, following practice a 90 degrees out-of-phase pattern can emerge as an additional, relatively stable, state (e.g., Zanone & Kelso, J. Exp. Psychol.: Human Performance and Perception 18 (1992) 403). On this basis, it has been concluded that practice leads to the evolution and stabilisation of the newly learned pattern and that this process of learning changes the entire attractor layout of the dynamic system. A general feature of such research has been to observe the changes of the targeted pattern's stability characteristics during training at a single movement frequency. The present study was designed to examine how practice affects the maintenance of a coordinated pattern as the movement frequency is scaled. Eleven volunteers were asked to perform a bimanual forearm pronation-supination task. Time to transition onset was used as an index of the subjects' ability to maintain two symmetrically opposite coordinated patterns (target task - 90 degrees out-of-phase - transfer task - 270 degrees out-of-phase). Their ability to maintain the target task and the transfer task were examined again after five practice sessions each consisting of 15 trials of only the 90 degrees out-of-phase pattern. Concurrent performance feedback (a Lissajous figure) was available to the participants during each practice trial. A comparison of the time to transition onset showed that the target task was more stable after practice (p=0.025). These changes were still observed one week (p=0.05) and two months (p=0.075) after the practice period. Changes in the stability of the transfer task were not observed until two months after practice (p=0.025). Notably, following practice, transitions from the 90 degrees pattern were generally to the anti-phase (180 degrees ) pattern, whereas, transitions from the 270 degrees pattern were to the 90 degrees pattern. These results suggest that practice does improve the stability of a 90 degrees pattern, and that such improvements are transferable to the performance of the unpractised 270 degrees pattern. In addition, the anti-phase pattern remained more stable than the practised 90 degrees pattern throughout.     

Effects of attentional focus on movement coordination complexity

Attentional focus affects performance and learning of motor tasks. An external attentional focus (on the effects of movement) can lead to more efficient and effective movements compared to an internal focus (on body movement itself). According to the “constrained action hypothesis”, an external focus facilitates fast and reflexive movement control while an internal focus leads to disruption of automatic coordination processes. Such disruption should be apparent in the complexity of movement. In this study, multiscale entropy measures were used to investigate if the external focus is related to superior coordination complexity compared to internal focus. Twenty participants were divided in two groups that balanced over an unstable platform in fourteen trials over two days, either with internal or external focus of attention instructions, followed by seven retention trials on the third day. Multiscale entropy measures were used to quantify complexity of motions of the platform, the participant, and the composite of participant and platform motions. Results were contrary to expectations. For the external focus group, despite better overall performance, multiscale entropy values of participant and composite motions were lower in some scales compared to the internal focus group, especially in the first and last days. This may be consistent with previous findings that predictability increases during learning of a balance task. Results also indicate the need to identify the correct physiological interpretation of single or multiscale entropy measures. Further investigation is needed to establish if entropy differences are causally related to performance and learning advantages of the external focus.     

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.     

The interplay of attention and bimanual coordination dynamics

Despite their common origin, studies on motor coordination and on attentional load have developed into separate fields of investigation, bringing out findings, methods, and theories which are diverse if not mutually exclusive. Sitting at the intersection of these two fields, this article addresses the issue of behavioral flexibility by investigating how intention modifies the stability of existing patterns of coordination between moving limbs. It addresses the issue, largely ignored until now, of the attentional cost incurred by the central nervous system (CNS) in maintaining a coordination pattern at a given level of stability, in particular under different attentional priority requirements. The experimental paradigm adopted in these studies provides an original mix of a classical measure of attentional load, namely, reaction time, and of a dynamic approach to coordination, most suitable for characterizing the dynamic properties of coordinated behavior and behavioral change. Findings showed that central cost and pattern stability covary, suggesting that bimanual coordination and the attentional activity of the CNS involved in maintaining such a coordination bear on the same underlying dynamics. Such a conclusion provides a strong support to a unified approach to coordination encompassing a conceptualization in terms of information processing and another, more recent framework rooted in self-organization theories and dynamical systems models     

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.     

Cognitive activity shifts the attractors of bimanual rhythmic coordination

The attractors of bimanual rhythmic coordination are given as the solutions of a motion equation in relative phase. How are those attractors affected by cognitive activity? In 3 experiments, participants (N = 10 in Experiments 1 and 2; N = 5 in Experiment 3) were required to produce in-phase or antiphase coordination while they either did or did not perform an information-reduction task. The average absolute deviation from in-phase (0 degrees ) and antiphase (180 degrees ) satisfying a particular parameterization of the motion equation was amplified by cognitive activity. That amplification of absolute phase shift was the same for both in-phase and antiphase coordination. Furthermore, the amplification (in degrees) increased linearly with the magnitude of cognitive activity (in bits). Cognitive activity had limited influence on the variability of relative phase and did not affect its average signed deviation. Collectively, the results suggest that cognitive activity produces a shift in the attractors of bimanual coordination dynamics that is directionally nonspecific and is independent of movement speed, detuning, and the in-phase-antiphase distinction.     

Effects of learning and movement frequency on polyrhythmic tapping performance

This study examined the effect of learning a complex bimanual coordination task at different movement frequencies. 30 subjects performed 5:3 polyrhythmic tapping at either high, medium, or low movement frequency on a rhythmic synchronization task and then reproduced the polyrhythmic pattern repeatedly in the spontaneous task. Analysis showed that practice on the synchronization task qualitatively changed correct responses into anticipatory ones. The synchronization learning of the polyrhythm caused the anticipatory responses and so, may involve memorization of serial positions within the polyrhythm. Also, more anticipatory responses were indicated in performance at the medium and low frequencies than at the high frequency on the synchronization task. In addition, deviations of taps from expected tapping positions were observed in performance of the spontaneous task at the high frequency. These results suggest that the movement frequency qualitatively influenced the learning of this bimanual coordination. Especially at the high frequency, frequent shifts to other coordination patterns occurred on the spontaneous task. This means that the performance at higher frequency is more strongly affected by entrainment between the two hands.     

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.     

Attention as a mediating variable in the dynamics of bimanual coordination

The influence of focal attention on the coordination dynamics in a bimanual circle drawing task was investigated. Six right-handed and seven left-handed subjects performed bimanual circling movements, in two modes of coordination, symmetrical or asymmetrical. The frequency of movement was scaled by an auditory metronome from 1.50 Hz to 3.00 Hz in 7 steps. On each trial, subjects were required to attend either to the dominant hand, to a neutral position, or to the nondominant hand.The uniformity of the relative tangential angle was lower in asymmetrical than in symmetrical conditions, but was not influenced by the direction of attention. In the asymmetrical mode, shifts in RTA relations, suggestive of loss of stability, were evident as the movement frequency was increased. Typically, these shifts were mediated by distortions of the trajectory of the nondominant limb. When the nondominant hand was the focus of attention, movements of this hand were more circular, and temporal variability was reduced, at the cost of a greater deviation from the target frequency. Movements of the dominant hand were not affected by the direction of attention. The findings show that although directed attention acts to modify the coordination dynamics, it does so primarily at the level of the individual hands, rather then in terms of the relation between them.     

Performance asymmetries and coupling dynamics in the acquisition of multifrequency bimanual coordination

Sixteen right-handed participants without formal musical training performed a rhythmic multifrequency coordination task for several hours over a one-week period. Two groups were studied with respect to the assignment of hand to frequency: 1L:2R, in which the preferred right hand performed the higher frequency, and 2L:1R in which the non-preferred left hand performed the higher frequency. Performance asymmetries in terms of relative phase stability were initially expected and confirmed. The 1L:2R pattern was more stable than 2L:1R. It has been suggested that performance asymmetries result from asymmetrical coupling between the limbs as influenced by handedness. This study examined whether the acquisition of 2L:1R, the less stable of the two patterns, required the formation of asymmetrical coupling such that the faster hand would exert a greater forcing on the slower hand than vice versa, a supposition put forth in many studies of bimanual polyrhythmic tapping. The present data provide quantitative evidence that, in terms of stability (as quantified by relative phase uniformity, transition pathways, and lead-lag relations), handedness asymmetries, as well as acquired asymmetries, can be captured by low-dimensional dynamics consisting of symmetric and asymmetric coupling terms. Received: 18 November 1996 / Accepted: 6 May 1997