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The complexity matching effect supposes that synchronization between complex systems could emerge from multiple interactions across multiple scales and has been hypothesized to underlie a number of daily-life situations. Complexity matching suggests that coupled systems tend to share similar scaling properties, and this phenomenon is revealed by a statistical matching between the scaling exponents that characterize the respective behaviors of both systems. However, some recent papers suggested that this statistical matching could originate from local adjustments or corrections, rather than from a genuine complexity matching between systems. In the present paper, we propose an analysis method based on correlation between multifractal spectra, considering different ranges of time scales. We analyze several datasets collected in various situations (bimanual coordination, interpersonal coordination, and walking in synchrony with a fractal metronome). Our results show that this method is able to distinguish between situations underlain by genuine statistical matching and situations where statistical matching results from local adjustments. [ABSTRACT FROM AUTHOR]

The principal goal of our study is to gain an insight into the coordinative structure of a complex body movement. As a first step, this paper describes the activity of multiple skeletal muscles associated with the drawing-like movements that resemble the Jeté, performed by skilled ballet dancers. The EMG activity of 18 muscles of the trunk, pelvis, and both legs was recorded when dancers standing on the left leg moved the toe of the right leg forward and backward along a straight line. A major finding is that the EMG activity of all right muscles, despite their functional and anatomical diversity, was minimised not only at the initial, vertical position but also in the reversal phase of movement when the moving leg was maximally deviated from the vertical position. In other words, the activity was minimal when torques of the weights of limb segments were minimal as well as when these torques were maximal. In contrast, in the static task when the maximally deviated leg position was maintained, there was substantial tonic activation of leg muscles, an activity that was necessary to balance these torques. The result is consistent with the hypothesis that movements of the body result from centrally induced changes in the muscle recruitment thresholds influencing the referent configuration of the body. The existence of minima in the overall EMG activity of skeletal muscles is not the only prediction of the referent configuration hypothesis. An immediate consequence of the hypothesis is that, in movements of the limb, the EMG patterns should be a direction-dependent phenomenon known as “directional tuning” of muscles. In combination with the principle of minimal interaction of neuromuscular system, the referent configuration hypothesis offers a dynamic approach to the problems of how control levels may guide multi-muscle and multi-joint systems without redundancy problems. [ABSTRACT FROM AUTHOR]

In this paper we consider whether the behaviour of the neural circuitry that controls lower limb movements in humans is shaped primarily by the spatiotemporal characteristics of bipedal gait patterns, or by selective pressures that are sensitive to considerations of balance and energetics. During the course of normal locomotion, the full dynamics of the neural circuitry are masked by the inertial properties of the limbs. In the present study, participants executed bipedal movements in conditions in which their feet were either unloaded or subject to additional inertial loads. Two patterns of rhythmic coordination were examined. In the in-phase mode, participants were required to flex their ankles and extend their ankles in synchrony. In the out-of-phase mode, the participants flexed one ankle while extending the other and vice versa. The frequency of movement was increased systematically throughout each experimental trial. All participants were able to maintain both the in-phase and the out-of-phase mode of coordination, to the point at which they could no longer increase their frequency of movement. Transitions between the two modes were not observed, and the stability of the out-of-phase and in-phase modes of coordination was equivalent at all movement frequencies. These findings indicate that, in humans, the behaviour of the neural circuitry underlying coordinated movements of the lower limbs is not constrained strongly by the spatiotemporal symmetries of bipedal gait patterns. [ABSTRACT FROM AUTHOR]

An exoskeletal device can assist walking in those with gait deficits. A passive exoskeleton can be a favorable choice for local or home rehabilitation settings because it is affordable, light weight, and less complex to utilize. While there is research that investigates the effects of exoskeleton on gait research examining the effects of such devices on gait adaptation, is rare. This is important because in diseases like stroke, the ability to flexibly adapt is affected, such that functional recovery becomes difficult. The purpose of this study was to characterize gait adaptation patterns that result from exoskeleton usage during a split-belt adaptation task. Healthy young participants were randomly assigned to a unilateral exoskeleton or a no-exoskeleton group. Each participant performed the specific split-belt adaptation tasks on the treadmill, where the speed of each belt could be controlled independently. Symmetry indices of spatiotemporal variables were calculated to quantify gait adaptation. To analyze the adaptation, trials were divided into early and late adaptation. We also analyzed degree of adaptation, and transfer effects. We also measured the symmetry of the positive power generated by the individual legs during the split-belt task to determine if using exoskeleton assistance reduced power in the exoskeleton group versus the no-exoskeleton group. Use of a passive exoskeleton device altered gait adaptation during a split-belt treadmill task in comparison to the control group. Such adaptation was found to be largely restricted to the temporal domain. Changes in the gait coordination patterns consisted of both early and late adaptive changes, especially in intra-limb patterns like stance time rather than inter-limb patterns like step time. Although the symmetry of the positive power generated during the split-belt task was found to be reduced for the exoskeleton-assistance group, it was shown that this was primarily the result of increased positive power generated by the side not receiving exoskeletal assistance. An unpowered assistive device can provide a unique solution for coordinating the lower limbs during different gait tasks. Such a solution could reduce the neural burden of adaptation consequently resulting in a reduction of the mechanical burden of walking during the bilateral gait coordination task. This may be useful for accelerating gait rehabilitation in different patient populations. However, balance control is important to consider during unilateral exoskeletal assistance. [ABSTRACT FROM AUTHOR]

Motor flexibility, the ability to employ multiple motor strategies to meet task demands, may facilitate ambulation in complex environments that constrain movements; loss of motor flexibility may impair mobility. The purpose of this study was to determine the effects of obesity (a specific model of mobility impairment) and advanced age on motor flexibility during a task that constrained foot placement while walking. Twenty-one community-dwelling obese (OB) and 25 normal weight (NW) older adults (46 total older adults—OA) and 10 younger adults (YA) walked normally on a treadmill (baseline) then walked while stepping on lighted cues projected onto the treadmill at locations corresponding to average foot placement during normal walking (cued). The uncontrolled manifold (UCM) analysis was used to partition total variance in a set of seven lower-limb segment angles into components that did ("bad" variance) and did not ("good" variance) affect step-to-step variance in the trajectory of the swing foot. Motor flexibility was operationalized as an increase (baseline to cued) in total variance with an increase in good variance that exceeded the change in bad variance. There was no significant group × walking task interaction for total and good variance for OB vs NW, but there was a strong and significant interaction effect for OA vs YA (p < 0.01; Cohen's d > 1.0). Whereas YA reduced both good and bad variance, OA increased good variance beyond the change in bad variance. In OA, these changes were associated with several functional measures of mobility. Cued walking may place greater demands on OA requiring greater reliance on motor flexibility, although otherwise healthy older obese adults may be able to compensate for functional and cognitive declines associated with obesity by increasing motor flexibility under such tasks. The extent to which motor flexibility is employed during novel or constrained tasks may be a biomarker of healthy aging and a target for (re)habilitation. [ABSTRACT FROM AUTHOR]

Coordination is often observed as body parts moving together. However, when producing force with multiple fingers, the optimal coordination is not to produce similar forces with each finger, but rather for each finger to correct mistakes of other fingers. In this study, we aim to determine whether and how this skill develops in children aged 4-12 years. We measured this sort of coordination using the uncontrolled manifold hypothesis (UCM). We recorded finger forces produced by 60 typically developing children aged between 4 and 12 years in a finger-pressing task. The children controlled the height of an object on a screen by the total amount of force they produced on force sensors. We found that the synergy index, a measure of the relationship between 'good' and 'bad' variance, increased linearly as a function of age. This improvement was achieved by a selective reduction in 'bad' variance rather than an increase in 'good' variance. We did not observe differences between males and females, and the synergy index was not able to predict outcomes of upper limb behavioral tests after controlling for age. As children develop between the ages of 4 and 12 years, their ability to produce negative covariation between their finger forces improves, likely related to their improved ability to perform dexterous tasks. [ABSTRACT FROM AUTHOR]

This small clinical trial utilized a novel rehabilitation strategy, rapid-resisted elliptical training, in an effort to increase motor, and thereby cognitive, processing speed in ambulatory individuals with traumatic brain injury (TBI). As an initial step, multimodal functional abilities were quantified and compared in 12 ambulatory adults with and 12 without TBI. After the baseline assessment, the group with TBI participated in an intensive 8-week daily exercise program using an elliptical trainer and was reassessed after completion and at an 8-week follow-up. The focus of training was on achieving a fast movement speed, and once the target was reached, resistance to motion was increased in small increments to increase intensity of muscle activation. Primary outcomes were: High-Level Mobility Assessment Tool (HiMAT), instrumented balance tests, dual-task (DT) performance and neurobehavioral questionnaires. The group with TBI had poorer movement excursion during balance tests and poorer dual-task (DT) performance. After training, balance reaction times improved and were correlated with gains in the HiMAT and DT. Sleep quality also improved and was correlated with improved depression and learning. This study illustrates how brain injury can affect multiple linked aspects of functioning and provides preliminary evidence that intensive rapid-resisted training has specific positive effects on dynamic balance and more generalized effects on sleep quality in TBI. [ABSTRACT FROM AUTHOR]

The performance of many everyday activities requires the coordination of the two upper limbs to achieve the goal of the task. Although bimanual performance has been studied in detail in adults, few studies have examined how children coordinate the movements of the two hands during symmetric and asymmetric bimanual prehension. With the current study, we asked younger (4-6 years, n = 14) and older (7-10 years, n = 16) children to complete a discrete bimanual task. Specifically, they reached to grasp cylinders located at near and far positions in either unimanual or bimanual condition. During bimanual symmetric conditions, participants performed movements with both hands toward two objects located at the same distance (both near or both far), while in the bimanual asymmetric conditions, they reached for objects at different distances. Results of the kinematic analyses indicated that the young children consistently experienced the 'two target' effect, whereby bimanual movements were executed more slowly than unimanual movements to the same distance. Older children employed a hybrid strategy, exhibiting slower movements in bimanual congruent conditions, but larger non-dominant apertures in bimanual incongruent conditions. This hybrid strategy was hypothesized to stem from developmental changes occurring in the integration of sensory information around 8 years of age. While older children exhibited temporal and spatial coordination patterns that were similar to patterns reported in adults, large relative timing differences at the start and end of bimanual movements and considerably weaker spatial coupling were seen in the younger children. [ABSTRACT FROM AUTHOR]

This experiment was setup to investigate the deterministic and stochastic properties of the recurrent dynamics of the center of pressure trajectories of each leg (COP and COP) and whole-body (COP) as a function of different foot positions in postural stance (side-by-side, staggered, and tandem standing) and the availability of visual information. The foot position of postural stance can induce degrees of asymmetry of postural instabilities as well as load on each leg that it was hypothesized would influence the deterministic and stochastic properties of COP fluctuations of each leg and of COP. Young adults performed two 60 s trials of quiet standing at each posture-vision condition. The availability of visual information increased COP path length, but had no effect on the recurrent dynamics of COP trajectories. Recurrence quantification analysis showed that recurrence, determinism, and entropy were dependent on the direction (AP/ML) of COP motion and foot position during postural stances. The degree of asymmetry between the left and right leg COP dynamics differed across all postural stances and COP dynamics were more similar to those of the more loaded leg. The cross-recurrence quantification analysis also revealed asymmetries in the coordination coupling of AP/ML under each leg; although, these differences were markedly reduced in tandem postures. The findings support the postulation that the asymmetry generated through mechanical constraints (foot position and load) is related to asymmetrical recurrent dynamics of the individual leg and COP based on the degree of postural instability. [ABSTRACT FROM AUTHOR]

Following many studies showing that the coupling in bimanual coordination can be perceptual, Bingham (Ecol Psychol in 16:45-53, ; , ) proposed a dynamical model of such movements. The model contains three key hypotheses: (1) Being able to produce stable coordinative movements is a function of the ability to perceive relative phase, (2) the information to perceive relative phase is relative direction of motion, and (3) the ability to resolve this information is conditioned by relative speed. The first two hypotheses have been well supported (Wilson and Bingham in Percept Psychophys 70:465-476, ; Wilson et al. in J Exp Psychol Hum 36:1508-1514, ), but the third was not supported when tested by de Rugy et al. (Exp Brain Res 184:269-273, ) using a visual coordination task that required simultaneous control of both the amplitude and relative phase of movement. The purposes of the current study were to replicate this task with additional measures and to modify the original model to apply it to the new task. To do this, we conducted two experiments. First, we tested the ability to produce 180° visual coordination at different frequencies to determine frequencies suitable for testing in the de Rugy et al. task. Second, we tested the de Rugy et al. task but included additional measures that yielded results different from those reported by de Rugy et al. These results were used to elaborate the original model. First, one of the phase-driven oscillators was replaced with a harmonic oscillator, so the resulting coupling was unidirectional. This change resulted in the model producing less stable 180° coordination behavior beyond 1.5 Hz consistent with the results obtained in Experiment 1. Next, amplitude control and phase correction elements were added to the model. With these changes, the model reproduced behaviors observed in Experiment 2. The central finding was that the stability of rhythmic movement coordination does depend on relative speed and, thus, all three of the hypotheses contained in the original Bingham model are supported. [ABSTRACT FROM AUTHOR]

Intra- and interpersonal coordination was investigated using a bimanual Fitts' law task. Participants tapped rhythmically between pairs of targets. Tapping was performed with one hand (unimanual), two hands (intrapersonal coordination), and one hand together with another participant (interpersonal coordination). The sizes and distances of targets in a pair were manipulated independently for each hand. When target difficulty was unequal across hands, movement times were similar in the coordination conditions, in violation of Fitts' law. Processing speed (measured by index of performance) increased for more difficult tasks, suggesting increased attention, even for dyads. These findings suggest that similar processes, not captured by centralized control, guide coordination for both individuals and dyads. Measures of coordination, though, still showed stronger coordination tendencies for intrapersonal coordination, indicating a possible role for centralized mechanisms. [ABSTRACT FROM AUTHOR]

Repetitive movements are common to many daily activities but often lead to the development of fatigue. We have previously shown that fatigue leads to changes in tridimensional spatial characteristics of the whole body. However, temporal aspects of these posture and movement adaptations have yet to be investigated. Healthy subjects ( N = 14) performed a continuous reaching task by pointing between two targets placed at shoulder height, at 100 and 30% arm's length, anterior to the subject's midline until fatigue (assessed using the Borg CR-10 scale). Whole body kinematics and upper Trapezius EMG were recorded and analyzed at 1-min intervals to document the progression of fatigue on outcome variables. For all upper limb and postural variables analyzed, changes began to occur approximately midway to fatigue and were followed by an increase in Trapezius activity from baseline. Reach-to-reach variability of joint average positions and range of motion (ROM) increased in multiple directions for shoulder and elbow parameters. Reach-to-reach variability of the center-of-mass ROM also increased in several directions. Changes were also observed in within-movement inter-segmental timing. The peak velocities of elbow and endpoint occurred closer together in time during fatigue while the shoulder peak velocity occurrence showed a greater reach-to-reach variability. Our results suggest that the effects of fatigue on repetitive movement kinematics can be observed across three temporal dimensions of the task: (1) within individual movements, (2) from one movement to the next, and (3) as fatigue develops. Each observed change is discussed as a potential contributor to task-specific control strategies to prolong task performance. [ABSTRACT FROM AUTHOR]

Shifting the direction of the line of sight in everyday life often involves rotations not only of the eyes and head but also of the trunk. Here, we investigated covariation patterns of eye-in-orbit, head-on-trunk and trunk-in-space angular horizontal displacements during whole-body rotations to targets of up to 180° eccentricity performed by standing healthy human subjects. The spatial covariation was quantified statistically across various behavioral task conditions (unpredictable, memory driven predictable, visual feedback) and constraints (accuracy) by principal components (PC) analysis. Overall, the combined movement was stereotyped such that the first two PCs accounted for essentially the whole data variance of combined gaze transfers up to about 400 ms , suggesting that the three mechanical degrees of freedom under consideration are reduced to two kinematic degrees of freedom. Moreover, quantification of segment velocity variability across repetitions showed that velocities of eye-in-space and head-in-space (i.e. ‘end-point’ velocity) were less variable than those of the elemental variables composing them. In contrast, three statistically significant PCs accounted for the covariation of the three segments during presumably vestibularly mediated nystagmic transfers, suggesting control by a separate driving circuit. We conclude that progression of the line of sight is initially stereotypic and fulfills criteria defining a motor synergy. [ABSTRACT FROM AUTHOR]

Anticipatory locomotor adjustments (ALAs) are used during locomotion to perform tasks, such as obstacle clearance, although not much is known as to how these ALAs are implemented by the central nervous system (CNS). The current study applied the planar law of intersegmental coordination to both leading and trailing limbs in a paradigm in which obstacle height and depth were manipulated to propose how ALAs are controlled. Ten healthy young adults stepped over nine obstacle conditions. Full-body 3D kinematic data were collected and elevation angles of the foot, shank, and thigh in the sagittal plane were calculated. For each limb within each trial, a principal component analysis was applied to limb segment trajectories. As well, a Fourier harmonic series was used to represent segment elevation angle trajectories, and phase differences between adjacent segments were determined. Planarity was consistently high in both limbs for all obstacle conditions, although significant differences between obstacle heights were observed. Increases in covariance loop width and rotation of the covariance plane accompanied changes in planarity. As observed in previous studies, fundamental harmonic phase differences between adjacent segments were highly correlated to plane characteristics and these phase differences changed systematically with increases in obstacle height. From the results, it is proposed that if a given environment requires a change in locomotion, the CNS adjusts a basic locomotor pattern if needed through the manipulation of the phase differences in the fundamental harmonics of the elevation angles between adjacent segments and elevation angle amplitude (with a constraint being intersegmenal elevation angle planarity). [ABSTRACT FROM AUTHOR]

An experiment was designed to investigate the temporal and spatial couplings of the transport and grasp components for bimanual movements performed by children. Thirty-one participants aged 4–6 (younger) and 7–10 (older) performed the unimanual task of reaching for, grasping, and lifting a small or large cylinder with the right or left hands or the bimanual task of reaching for, grasping and lifting two small cylinders, two large cylinders, or one small and one large cylinder with the right and left hands. Kinematic measures, relative timing differences between the hands, spatial plots and cluster analysis were used to quantify both temporal and spatial couplings of the limbs. While average kinematic results indicated that children in the 4–6 and 7–10 age range performed bimanual movements similarly to each other, spatio-temporal coupling measures indicated that the younger children performed the bimanual movements in a more sequential (serial) fashion. Kinematic results also indicated that the cost of the increase in task complexity normally seen in adults when grasping two targets bimanually compared to a single target unimanually are not consistently present for children. Instead, the cost associated with increases in task complexity appear to be mediated by whether the bimanual task imposes significantly greater demands on attentional processes. These results indicate that attention demands of the task as well as the intrinsic dynamics of the individual determine the degree of interlimb coupling of children during bimanual reach-to-grasp of different-sized objects. [ABSTRACT FROM AUTHOR]

This study aimed to apply an uncontrolled manifold (UCM) approach to investigate how children utilize the variability of multiple body segment movement to facilitate the center of mass (COM) control during quiet stance. Three groups of participants were included in this study: younger children (YC, mean age 6.3 years), older children (OC, mean age 10.3 years), and young adults (YA, mean age 20.5 years). Participants stood on a force platform with their hands on the iliac crests for 40 s in each trial. Two visual conditions were examined including eyes-open and eyes-closed and three trials were collected for each condition. Results showed that all three groups partitioned more variability of multi-segment movement into the UCM subspace (maintaining the mean COM position) than into the ORT subspace (a subspace orthogonal to the UCM subspace, causing the deviation of the COM from its mean position) in both eyes-open and eyes-closed conditions. Furthermore, both the YC and OC groups partitioned a significantly higher percentage of variability into the UCM subspace than the YA group regardless of visual condition. In addition, results of conventional COM variables indicated that only the YC group produced significantly faster sway velocity and greater standard deviation than the YA group. All the results together suggest that children at 6–10 years of age use a similar variability-partitioning strategy (a greater VUCM and a smaller VORT) like young adults in quiet stance to facilitate the COM control, but it takes more than 10 years for children to refine this strategy and achieve an adult-like variability-partitioning capability (i.e., UCM ratio). It also suggests that postural development may include two phases in which children learn to regulate the position and movement of multiple body segments and the COM first and gain an adult-like variability-partitioning capability later. [ABSTRACT FROM AUTHOR]

During multi-digit grasping both local and non-local digit force responses occur in response to changes in texture at selected digits depending on the grasp configuration. However, the extent to which the specific patterns of force distribution depend on the requirement to hold the object against gravity remains to be determined. In the present study, we examined whether grasp force sharing patterns are invariant when the constraint of maintaining the object orientation vertical against gravity is removed. We used changes in object texture to elicit force changes at single digits during two grasping tasks with different behavioral contexts. One task entailed holding an object against gravity (object hold [OH]). A second (force production [FP]) task consisted of generating lifting forces on an object clamped to the tabletop that were matched to those used during OH. Unlike OH, the FP task lacks the behavioral consequences associated with erroneous sharing of normal and tangential digit forces, e.g., object tilt. Ten subjects lifted and simulated lifting an instrumented object measuring grasping normal and vertical tangential forces at all five digits when the textures were uniformly high-friction sandpaper or low-friction rayon and when one digit contacted a different frictional texture than the other four digits. We found that in both tasks texture changes at individual digits elicited force changes at that digit as well as other digits. However, the specific pattern of force distribution changes differed during OH compared to FP. While subjects modulate the normal and tangential digit forces to different degrees depending on object texture and the grasping task, they ignore the requirement of moment equilibrium when this has no consequences on object orientation (FP task). These findings indicate that multi-digit force responses to texture revealed by previous studies are not obligatory and suggest that the behavioral context of a task should be considered when inferring general principles of multi-digit force coordination. [ABSTRACT FROM AUTHOR]

Some rats spinally transected as neonates (ST rats) achieve weight-supporting independent locomotion. The mechanisms of coordinated hind-limb weight support in such rats are not well understood. To examine these we compared ST rats (with better than 60% of weight supported steps) and normal rats that were trained to cross an instrumented runway. Ground reaction forces, coordination of hind-limb and forelimb forces and the motions of the center of pressure (CoP) were assessed. Normal rats crossed the runway with a diagonal trot. On average hind-limbs bore about 80% of the vertical load carried by forelimbs (45% body weight on hind-limbs 55% on forelimbs), although this varied. Forelimbs and hind-limbs acted synergistically to generate decelerative and propulsive rostrocaudal forces, which averaged 15% of body weight with maximums of 50%. Lateral forces were very small (<8% of body weight). Center of pressure progressed in jumps along a straight line with mean lateral deviations <1 cm. ST rats hind-limbs bore about 60% of the vertical load of forelimbs (37% body weight on hind-limbs, 63% on forelimbs), significantly less compared to intact rats ( P < 0.05). ST rats showed similar mean rostrocaudal forces, but with significantly larger maximum fluctuations of up to 80% of body weight ( P < 0.05). Joint force-plate recordings showed forelimbs and hind-limb rostrocaudal forces in ST rats were opposing and significantly different from intact rats ( P < 0.05). Lateral forces were ~20% of body weight and significantly larger than in normal rats ( P < 0.05). Center of pressure zig-zagged, with mean lateral deviations of ~2 cm and a significantly larger range ( P < 0.05). The haunches were also observed to roll more than normal rats. The locomotor strategy of injured rats using limbs in opposition was presumably less efficient but their complex gait was statically stable. Because forelimbs and hind-limbs acted in opposition, the trunk was held compressed. Force coordination was likely managed largely by the voluntary control in forelimbs and trunk. [ABSTRACT FROM AUTHOR]

It has been found in our previous studies that the initiation of aperture closure during reach-to-grasp movements occurs when the hand distance to target crosses a threshold that is a function of peak aperture amplitude, hand velocity, and hand acceleration. Thus, a stable relationship between those four movement parameters is observed at the moment of aperture closure initiation. Based on the concept of optimal control of movements (Naslin ) and its application for reach-to-grasp movement regulation (Hoff and Arbib ), it was hypothesized that the mathematical equation expressing that relationship can be generalized to describe coordination between hand transport and finger aperture during the entire reach-to-grasp movement by adding aperture velocity and acceleration to the above four movement parameters. The present study examines whether this hypothesis is supported by the data obtained in experiments in which young adults performed reach-to-grasp movements in eight combinations of two reach-amplitude conditions and four movement-speed conditions. It was found that linear approximation of the mathematical model described the relationship among the six movement parameters for the entire aperture-closure phase with very high precision for each condition, thus supporting the hypothesis for that phase. Testing whether one mathematical model could approximate the data across all the experimental conditions revealed that it was possible to achieve the same high level of data-fitting precision only by including in the model two additional, condition-encoding parameters and using a nonlinear, artificial neural network-based approximator with two hidden layers comprising three and two neurons, respectively. This result indicates that transport-aperture coordination, as a specific relationship between the parameters of hand transport and finger aperture, significantly depends on the condition-encoding variables. The data from the aperture-opening phase also fit a linear model, whose coefficients were substantially different from those identified for the aperture-closure phase. This result supports the above hypothesis for the aperture-opening phase, and consequently, for the entire reach-to-grasp movement. However, the fitting precision was considerably lower than that for the aperture-closure phase, indicating significant trial-to-trial variability of transport-aperture coordination during the aperture-opening phase. Implications for understanding the neural mechanisms employed by the CNS for controlling reach-to-grasp movements and utilization of the mathematical model of transport-aperture coordination for data analysis are discussed. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to investigate the coordination of the two effectors when one or both targets were displaced in a bimanual prehension task. Sixteen right-handed volunteers were asked to reach 20 cm to grasp and lift two cubic objects with the right and left hands. Upon initiation of the reach: (1) both objects could remain at the initial position (NN); (2) the right object could be displaced toward the subject (NJ); (3) the left object could be displaced (JN); or (4) both objects could be displaced (JJ). Generally, the results indicated that the hand moving to the perturbed object was reorganized to reach the target efficiently, but hovered to somewhat couple object lift for the two hands. In contrast, adjustments were seen in the velocity profiles of the hand moving to the non-perturbed target, including a premature deceleration phase and corrective movements to reach the target location. Together, these results indicate that when the perturbation of one object occurs during the performance of a bimanual prehension task, visual information is used to independently update the control process for the limb moving to the perturbed object. Additionally, interference causes the limb moving to the non-perturbed target to be inappropriately adjusted in response to the perturbation. Our results also indicated that perceptual and motor factors such as time allotted for the use of feedback and the direction of movement may play a role in the independence/dependence relationship between the hands during bimanual tasks. Furthermore, subjects’ expectations about the performance and goal of the task could have a further influence on the level of interference seen during bimanual movements. Finally, despite interference effects which caused multiple accelerations and decelerations, the hand moving to the non-perturbed target still achieved the target location in the same movement time as during control conditions. This final result indicates the efficiency with which subjects can reorganize both limbs in the face of altered task requirements. [ABSTRACT FROM AUTHOR]

Here we report a study of joint-action coordination in transferring objects. Fourteen dyads were asked to repeatedly reposition a cylinder in a shared workspace without using dialogue. Variations in task constraints concerned the size of the two target regions in which the cylinder had to be (re)positioned and the size and weight of the transferred cylinder. Movements of the wrist, index finger and thumb of both actors were recorded by means of a 3D motion-tracking system. Data analyses focused on the interpersonal transfer of lifting-height and movement-speed variations. Whereas the analyses of variance did not reveal any interpersonal transfer effects targeted data comparisons demonstrated that the actor who fetched the cylinder from where the other actor had put it was systematically less surprised by cylinder-weight changes than the actor who was first confronted with such changes. In addition, a moderate, accuracy-constraint independent adaptation to each other’s movement speed was found. The current findings suggest that motor resonance plays only a moderate role in collaborative motor control and confirm the independency between sensorimotor and cognitive processing of action-related information. [ABSTRACT FROM AUTHOR]

This study examined age-related differences in the coordinative mechanism of the reach-to-grasp movement in three groups of children aged 6, 8, and 11 year, and in healthy adults. Three prehension conditions were manipulated: an unimanual and a bimanual self-driven tasks in which the reaching and grasping of the object were performed by participants, and a bimanual externally-driven task, in which the experimenter brought the object into the vicinity of the participant which grasped it. Classical kinematics data—peak velocities of the reaching and the grasping, the time to onset grip opening, maximum grip opening and grip closure—were calculated. Moreover, to obtain equivalent kinematics variables for all age groups, relative time to peak velocity (% of reaching duration), relative maximum grip opening (% of object size), and percentage of the four types of phase plans between reaching velocity and grip size have been calculated for each group of age. Our main results showed (1) a high variability at age 6, (2) an age-related change between the 6- and 8-year old for almost all of the dependent variables, and (3) a significant difference between the 11-year olds and adults. In summary, at 6 years, the interdependence between the reaching and grasping programs was unstable. A transitory feedback-based coordination between reaching and grasping appeared at 8 years of age. Finally, the adults’ relationship between reaching and grasping was not attained at the age of 11. [ABSTRACT FROM AUTHOR]

To investigate the strategies developed by the central nervous system to compensate for fatigue in muscles, we studied the changes in the relative mechanical contribution of the joint torques in a multi-joint movement following an isometric exhaustion test. Eighteen male subjects performed throws, moving the arm in the horizontal plane, before and after two fatigue protocols. Muscular fatigue was induced either in the distal (extensor digitorum communis) or in the proximal (triceps brachii) agonist muscle of the arm. The kinematic, kinetic and electromyographic parameters of the movement were analysed. The subjects produced two different coordinations following the fatigue protocols. In the distal fatigue condition, the wrist angular velocity was maintained by decreasing elbow active torque. In the proximal fatigue condition, the compensatory strategy involved increasing the contribution of the wrist. In fact, the control of elbow and wrist was modified in order to compensate for the different mechanical effects. [ABSTRACT FROM AUTHOR]

Coordination between the eyes and the hand is likely to be based on a process of motor learning, so that the interactions between the two systems can be accurately controlled. By using an unusual tracking task we measured the change in brain activation levels, as recorded with 3T functional magnetic resonance imaging (fMRI), between naïve human subjects and the same subjects after a period of extended training. Initially the performance of the two groups was similar. One subject group was then trained in a synchronous, coordinated, eye–hand task; the other group trained with a 304 ms temporal offset between hand and eye tracking movements. After training, different patterns of performance were observed for the groups, and different functional activation profiles. Significant change in the relationship between functional activation levels and eye–hand task conditions was predominantly restricted to visuo-motor areas of the lateral and vermal cerebellum. In an additional test with one of the subject groups, we show that there was increased cerebellar activation after learning, irrespective of change in performance error. These results suggest that two factors contribute to the measured blood oxygen level-dependent (BOLD) signal. One declined with training and may be directly related to performance error. The other increased after training, in the test conditions nearest to the training condition, and may therefore be related to acquisition of experience in the task. The loci of activity changes suggest that improved performance is because of selective modified processing of ocular and manual control signals within the cerebellum. These results support the suggestion that coordination between eye and hand movement is based on an internal model acquired by the cerebellum that provides predictive signals linking the control of the two effectors. [ABSTRACT FROM AUTHOR]

Previous experiments by our group in normal gravity (1 G) have revealed spatial relationships between postural and focal components of whole-body reaching and pointing movements. We suggested that these relationships could be explained partly through the use of gravity to displace the CoM and attain the object or target position. In this study we compared human whole-body reaching in 1 G and microgravity (0 G) in order to more fully investigate how gravity contributes to strategies adopted for task execution and to determine possible invariant temporal relationships between multiple segments. Whole-body reaching movements made from the standing position in two experimental conditions of execution speed (naturally paced and as fast as possible) were recorded during periods of 1 G and 0 G in parabolic flight. Overall, at each speed of reaching, movement times were significantly slower when performed in 0 G than in 1 G for two of the three subjects, but all subjects were able to produce significantly faster movements in 0 G than in 1 G. Despite similar general trends across subjects observed in 1 G, angular displacements of reaching movements performed in 0 G differed greatly between subjects. There were changes at all joints, but above all at the shoulder and the ankle. However, despite a high intersubject and intratrial variability in 0 G, in both gravity conditions all subjects demonstrated times to peak curvilinear velocity for the finger (end effector) and the whole-body centre of mass (CoM) that coincided, regardless of the speed of execution. Moreover, cross-correlations between multiple segment curvilinear velocities and those of the CoM revealed tight, highly correlated temporal relationships between segments proximal to the CoM (which was expected). However, for more distal segments, the correlations were weaker, and the movements lagged behind movements of the CoM. The major and most interesting finding of this study was that although the finger was the most distal within the segment chain, with respect to the CoM, it was highly correlated with the CoM (0.99–0.98, all conditions) and with no time lag. Despite the large intersubject and interenvironmental variability recorded in this study, temporal relationships between postural task components (CoM displacements) and those of the focal movement (end-effector trajectory) were consistently conserved. [ABSTRACT FROM AUTHOR]

It has recently been reported that the spatial orientation of two moving limbs has a determining influence on the relative accuracy and stability of coordination patterns. The purpose of the present experiments was to test perceptual and neuromuscular explanations of these spatial orientation effects. Experiment 1 was an initial test of the hypotheses and an extension of a previous study [Lee et al. (2002) Exp Brain Res 146:205-212] that required participants to coordinate inphase and antiphase movement patterns in four spatial orientations: two symmetric orientations (90° and 180° separation between the limbs) and two asymmetric orientations (90° and 135° separation between the limbs). Results of Experiment 1 suggest that the symmetry of movement may be a key factor influencing spatial orientation effects observed during interlimb coordination. In Experiment 2, participants again performed inphase and antiphase movement patterns in symmetric and asymmetric spatial orientations. However, one-half of the participants in Experiment 2 were provided with mechanical constraints during the performance of the desired coordination patterns. The mechanical constraints provided postural support but did not influence the visual experience. Results showed that the addition of the postural support improved performance. These findings suggest that neuromuscular, and perhaps biomechanical, constraints contribute more to the influence of spatial orientation than visual-perceptual constraints. [ABSTRACT FROM AUTHOR]

The moment production by several fingers on a mechanically fixed vertically oriented handle was studied under the systematic variations of task parameters such as (a) moment magnitude (1.0 Nm and 2.0 Nm) and (b) direction of moment production (into pronation and supination), as well as (c) vertical position of the handle from the moment axis, P (0, 2.0, 4.0, and 6.0 cm in both directions). The purpose of this study was twofold: to investigate the dependences between the task parameters and the performance variables and to test the mechanical advantage hypothesis. The performance variables changed symmetrically with P. In particular, magnitudes of the net horizontal and vertical forces both showed an S-shape change. The position of the point of zero free moment (PZFM) was determined. In the intermediate grasp locations (when 0

free (moment produced mainly by pronational or supinational effort) and the moment of the resultant force (moment generated mainly by pushing) into the total moment production scaled linearly with the P. The magnitudes of both agonist and antagonist moments (those acting in and against the direction of the required moment, respectively) of normal forces increased with P magnitudes while the magnitude of agonist moments of tangential forces decreased. For individual fingers, the ratio of finger force to its moment arm was not constant. The mechanical advantage hypothesis was successful in explaining some of the data but could not cope with other findings. We assume, therefore, that this hypothesis is limited in its applicability and may be task and effector specific. [ABSTRACT FROM AUTHOR]

The coordination of movement is governed by a coalition of constraints. The expression of these constraints ranges from the concrete—the restricted range of motion offered by the mechanical configuration of our muscles and joints; to the abstract—the difficulty that we experience in combining simple movements into complex rhythms. We seek to illustrate that the various constraints on coordination are complementary and inclusive, and the means by which their expression and interaction are mediated systematically by the integrative action of the central nervous system (CNS). Beyond identifying the general principles at the behavioural level that govern the mutual interplay of constraints, we attempt to demonstrate that these principles have as their foundation specific functional properties of the cortical motor systems. We propose that regions of the brain upstream of the motor cortex may play a significant role in mediating interactions between the functional representations of muscles engaged in sensorimotor coordination tasks. We also argue that activity in these “supramotor” regions may mediate the stabilising role of augmented sensory feedback. [ABSTRACT FROM AUTHOR]

The study addresses an issue of possible relations between the apparent "clumsiness" of persons with Down syndrome (DS) and changes in indices of finger coordination. We hypothesized that persons with DS would prefer less challenging, safer motor strategies reflected in finger coordination patterns. Maximal single- and multi-finger force production (MVC) tasks and multi-finger tasks that required the production of a controlled time pattern (ramp) of total force were studied. As compared to typical persons, persons with DS showed lower peak forces, lower force deficit (loss of finger force in multi-finger tasks as compared to single-finger tasks), and higher enslaving (involuntary force production by fingers that are not required to produce force). They showed higher variance of total force computed across several trials for ramp tasks. Their total force variance was higher than the sum of the variances of individual finger forces over the ramp duration, while in control participants the relation was opposite during the middle and late thirds of the ramp. Persons with DS practiced force production tasks over 3 days, one group practicing only one of the tasks (the ramp task with all four fingers acting together) while the other group practiced MVC and ramp tasks (variable practice). Practice led to an increase in MVC, force deficit, and enslaving. The relation between the total force variance and the sum of the variances of individual finger forces became closer to the one observed in typical persons. The effects of practice were more pronounced in the variable practice group. We conclude that persons with DS have a deficit in control of both single fingers and multi-finger groups. They use a less challenging, suboptimal strategy of multi-finger coordination which does not take advantage of the possibility of error compensation among the fingers. Practice is an effective way of improving finger coordination in DS, particularly when using variable tasks. [ABSTRACT FROM AUTHOR]

Two experiments are reported that examined the influence of spatial orientation of the upper limbs in bimanual coordination. In both experiments, the upper limbs were oriented in either parallel, orthogonal, or obtuse spatial configurations and participants were asked to move their limbs continuously in temporal (1:1) synchrony, prepared in either in-phase or anti-phase modes of coordination. Bimanual coordination trials in Experiment 1 were paced by a metronome at one of four frequencies (1.0, 1.5, 2.0 or 2.5 Hz). Measures of relative phase accuracy and stability both revealed that, as metronome frequency increased, in-phase coordination dominated for the parallel spatial orientation, anti-phase coordination dominated for the orthogonal spatial orientation, and neither pattern dominated for the obtuse spatial orientations. In Experiment 2, an intentional switch method replicated and extended these influences of spatial orientation. The time to voluntarily switch from an anti-phase pattern to an in-phase pattern was faster than an in-phase to anti-phase switch (confirming support for the dominance of the in-phase pattern), but this was true only for the parallel spatial orientation. The reverse was true for the orthogonal spatial orientation (i.e., faster from in-phase to anti-phase), and no difference in switch times was observed for an obtuse spatial orientation. These findings support and extend previous research regarding the influence of spatial orientation in bimanual coordination and may be attributed to the role of, and potential interactions between, egocentric, allocentric, and mechanical constraints during action. [ABSTRACT FROM AUTHOR]