Isofrequency and Multifrequency: Coordination Patterns as a Function of the Planes of Motion

A series of studies examine the maintenance of the relative phase of simultaneous cyclic limb movements by the manipulation of the planes of motion during isofrequency and multifrequency conditions. To evaluate predictions from a dynamic pattern approach in which differences in the limbs' uncoupled frequencies give way to competitive interactions when the limbs are moved simultaneously, Experiment 1 determined the preferred frequencies of single-limb movements during sagittal and transverse planes of motions. The results revealed that the plane in which the motion was produced significantly affected the cycle frequencies. In investigating isofrequency coordination, Experiment 2 showed that homologous limbs were more accurate in attaining the relative phasing when moving in one as compared to two separate planes, whereas no such effect was observed for non-homologous limbs. Furthermore, the planes of motion significantly influenced the variability of relative phasing such thattwo-plane motionswere less stable than one-plane motions.Experiment 3 examined the effect of the planes of motion upon multifrequency coordination and demonstrated that the homologous and homolateral limbs were less successful in producing the relative phasing when the motions were produced in one as compared to two planes, whereas this effect was not observed for the heterolateral limbs. These findings indicate that frequency detuning resulting from the planes manipulation affects the quality of phase-locking during isofrequency and multifrequency conditions, even though it may be assumed that additional neural constraints are involved in the interlimb coordination process.     

Intentional switching between behavioral patterns of homologous and nonhomologous effector combinations.

Intentional switching between preferred coordination modes (Experiment 1) and between isofrequency and multifrequency conditions (Experiments 2 and 3) was compared across different effector combinations. Experiment 1 showed that homologous limbs switched faster toward the in-phase and anti-phase mode than nonhomologous limbs, supporting their distinct degree of coordinative stability during 1:1 synchronization. Experiments 2 and 3 revealed that switching time between isofrequency and multifrequency conditions depended on the attractiveness of both coordination dynamics associated with the combination of segments involved. These results are consistent with the unique prediction derived from dynamic pattern approach in which the differential stability of the coordination modes determines the switching time.     

Influence of target uncertainty on reaching movements while standing in stroke

Stroke individuals frequently have balance problems and impaired arm movements that affect their daily activities. We investigated the influence of target uncertainty and the side of the brain lesion on the performance of arm movements and postural adjustments during reaching in a standing position by stroke individuals. Participants stood on force plates and reached a target displayed on the center of a monitor screen under conditions differentiated by the prior knowledge of the target location at the beginning of the movement. Individuals who had a stroke in the right side of the brain performed the tasks with the ipsilesional, right upper limb while the individuals with a left stroke performed with the ipsilesional, left upper limb. Healthy individuals performed with right and left limbs, which data were later averaged for statistical analysis. Kinematic analysis of the arm and lower limb joints and displacements of the center of pressure of each lower limb were compared between target conditions and groups. Stroke individuals showed larger center of pressure displacements of the contralesional compared to the ipsilesional limb while these displacements were symmetrical between lower limbs for the healthy individuals, regardless of the target condition. The target uncertainty affected both the characteristics of the arm movements and postural adjustments before movement onset. Right stroke individuals used more ankle joint movements under the uncertain compared to the certain condition. The uncertainty in target location affects the arm reaching in upright standing, but the effects depend on the side of the brain lesion.     

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

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

Development of movement schema in young children

To examine the development of movement schema in young school-age children, i.e., whether principles which govern fine eye-hand coordination skill learning as suggested by Schmidt's schema theory apply to the learning of gross motor skills Exp. 1 involved 48 right-handed first-grade children. On a modification of the Fitts Reciprocal Tapping task children moved a stylus (held in the hand or attached to a special shoe worn on the foot) between two metal targets separated by different distances. Children were randomly assigned to one of eight groups: two control or no-practice groups and six experimental or transfer groups. A one-way analysis of variance followed by appropriate Scheffé post hoc tests indicated that movements of the lower limbs were not organized into a movement schema, but a pattern of schema of movement for the upper limbs developed. That no movement schema developed for lower limb movements suggests development of movement schema is intricately linked to both the existing as well as the potential for developing precise movement in those limbs. Exp. 2 involved 40 first-grade children who were randomly assigned to perform a gross-motor agility task under one of three conditions: direct practice on the criterion task, constant practice on a modification of the criterion task, or variable practice on several different modifications of the criterion task. A groups X trials analysis of variance with appropriate post hoc tests indicated that there were no significant differences among direct, constant, or variable practice groups. Data suggest that the amount of practice may be as important as the type of practice in developing movement schema involved in gross motor skills in young children.     

Impact of action planning on spatial perception: Attention matters

Previous research suggested that perception of spatial location is biased towards spatial goals of planned hand movements. In the present study I show that an analogous perceptual distortion can be observed if attention is paid to a spatial location in the absence of planning a hand movement. Participants judged the position of a target during preparation of a mouse movement, the end point of which could deviate from the target by a varying degree in Exp. 1. Judgments of target position were systematically affected by movement characteristics consistent with perceptual assimilation between the target and the planned movement goal. This effect was neither due to an impact of motor execution on judgments (Exp. 2) nor due to characteristics of the movement cues or of certain target positions (Exp. 3, Exp. 5A). When the task included deployment of attention to spatial positions (former movement goals) in preparation for a secondary perceptual task, an effect emerged that was comparable with the bias associated with movement planning (Exp. 4, Exp. 5B). These results indicate that visual distortions accompanying manipulations of variables related to action could be mediated by attentional mechanisms.     

Spatial coupling affects both homologous and non-homologous limbs

The present study examined the interaction between limb movements in space. The amount of interaction was measured by how much moving one limb affected the movement of another limb. Participants were 24 right-handed university students (19 female, mean age=19 years). The task was to draw lines with the right hand while moving another limb in lines or circles of different sizes. Significant coupling effects were found between both homologous and non-homologous limbs. Movement of the right hand was most strongly affected by the left hand, less by the right foot, and least by the left foot, consistent with the functional cerebral distance model. This effect of limb was observed only in the major dimension along which movement was not restrained. Both the limb and dimension effects were reduced when the trajectory of motion decreased in size.     

Matching of Movements Made Independently by the Two Arms in Normal Humans

Comparisons were made of voluntary movements of the right and left arms in normal human subjects. A series of movements of different amplitudes, made at the subject’s own speed, was performed with one limb. After a rest period, the same series was repeated with the contralateral limb. The relation between movement peak velocity and movement amplitude was linear and was the same for both arms. With repeated testing over periods up to two months, the slope of the peak velocity—amplitude relation decreased during the first week, thereafter remaining unchanged. In a second series of experiments, six normal subjects continuously wore a 1 lb (0.45 kg) weight strapped to their left (non-dominant) forearm for up to 1 week. This resulted in an increase in the slope of the peak-velocity/amplitude relation in this arm. A parallel change occurred in movements made independently by the right (non-loaded) arm. A similar matching of movement performance of the two limbs was seen following removal of the weight. The data is interpreted as providing support for the hypothesis that there is a single movement “command” which is applied to both limbs. The interaction of this command with the limbs which have similar second-order mechanical properties yields similar movements even when they are made independently.     

Recognition and recall in slow movements: separate memory states?

If slow positioning movements are governed only by a recognition process (e.g., Schmidt, 1975) then subject's performance should be independent of the mode or response (active versus passive). Two groups learned a criterion movement under either active or passive conditions following which KR was withdrawn. Although no differences were apparent on acquisition trials, active-group performance deteriorated dramatically during KR withdrawal while passive-group performance remained stable. These results suggest that recall and recognition are potentially separable in slow movements on the basis of the information available to the performer.     

Immersive virtual reality as a rehabilitative technology for phantom limb experience: a protocol.

This paper describes a study protocol to investigate the use of immersive virtual reality as a treatment for amputees' phantom limb pain. This work builds upon prior research using mirror box therapy to induce vivid sensations of movement originating from the muscles and joints of amputees' phantom limbs. The present project transposes movements of amputees' anatomical limbs into movements of a virtual limb presented in the phenomenal space of their phantom limb. It is anticipated that the protocol described here will help reduce phantom limb pain.     

Handedness-related asymmetry in coupling strength in bimanual coordination: furthering theory and evidence

The effects of handedness on bimanual isofrequency coordination (e.g., phase advance of the dominant limb) have been suggested to result from an asymmetry in interlimb coupling strength, with the non-dominant limb being more strongly influenced by the dominant limb than vice versa. A formalized version of this hypothesis was tested by examining the phase adjustments in both limbs in response to mechanical perturbation of the bimanual coordination pattern and during frequency-induced phase transitions, for both right- and left-handed participants. In both situations, the phase adaptations were made predominantly by the non-dominant limb in right-handers, whereas this effect failed to reach significance in left-handers. Thus, the asymmetry in coupling strength was less pronounced in the latter group. In addition, the degree of asymmetry depended on movement frequency. The observed asymmetry was discussed in relation to pertinent neurophysiological findings.     

Prechtl's assessment of general movements: a diagnostic tool for the functional assessment of the young nervous system

General movements (GMs) are part of the spontaneous movement repertoire and are present from early fetal life onwards until the end of the first half a year of life. GMs are complex, occur frequently, and last long enough to be observed properly. They involve the whole body in a variable sequence of arm, leg, neck, and trunk movements. They wax and wane in intensity, force and speed, and they have a gradual beginning and end. Rotations along the axis of the limbs and slight changes in the direction of movements make them fluent and elegant and create the impression of complexity and variability. If the nervous system is impaired, GMs loose their complex and variable character and become monotonous and poor. Two specific abnormal GM patterns reliably predict later cerebral palsy: 1) a persistent pattern of cramped-synchronized GMs. The movements appear rigid and lack the normal smooth and fluent character. Limb and trunk muscles contract and relax almost simultaneously. 2) The absence of GMs of fidgety character. So-called fidgety movements are small movements of moderate speed with variable acceleration of neck, trunk, and limbs in all directions. Normally, they are the predominant movement pattern in an awake infant at 3 to 5 months. Beside a sensitivity and specificity of 95% each, the assessment of GMs is quick, noninvasive, even nonintrusive, and cost-effective compared with other techniques, e.g., magnetic resonance imaging, brain ultrasound, and traditional neurological examination.     

Interlimb coordination following stroke

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

Self-Optimization of Walking in Nondisabled Children and Children With Spastic Hemiplegic Cerebral Palsy

Children voluntarily adopt a frequency and movement pattern for walking. The force-driven harmonic oscillator (FDHO) model was used in this study for accurate prediction of the preferred walking frequency of nondisabled children and children with spastic hemiplegic cerebral palsy. Four potential optimality criteria with which the preferred walking pattern was forced to comply were examined: minimization of physiological costs, maximization of mechanical energy conservation, minimization of asymmetry in lower limb movements and minimization of variability of interlimb and intralimb coordination. Age and gender-matched nondisabled children (n = 6) and children with spastic hemiplegic cerebral palsy (n = 6) were tested under six frequency conditions of walking at a constant speed on a treadmill. For the nondisabled children, the results indicated that their preferred walking frequency could be accurately predicted by the FDHO model. They freely adopted a walking pattern that minimized physiological costs, asymmetry, and variability of inter- and intralimb coordination. For the children with spastic hemiplegic cerebral palsy, the prediction of preferred overground walking frequency required that the FDHO model be modified to account for muscle mass and leg length discrepancies between limbs and increased stiffness. Most of the children achieved the same optimality goals as the nondisabled when walking at the preferred frequency. However, the children were found to use different mechanisms to attain these goals: for example, a steeper increase observed in physiological cost at higher frequencies; a lowered center of gravity of the body, which allowed for angular symmetry; and greater variability of between-joint coordination in the nonaffected limb and less variability in the affected limb.     

The effect of viewing the moving limb and target object during the early phase of movement on the online control of grasping

Two experiments were conducted to investigate (1) during which phase of the movement vision is most critical for control, and (2) how vision of the target object and the participant's moving limb affect the control of grasping during that movement phase. In Experiment 1, participants, wearing liquid crystal shutter goggles, reached for and grasped a cylinder with a diameter of 4 or 6 cm under a shutting paradigm (SP) and a re-opening paradigm (RP). In SP, the goggles closed (turned opaque) 0 ms, 150 ms, 350 ms, 500 ms, or 700 ms after movement onset, or remained open (transparent) during the prehension movements. In RP, the goggles closed immediately upon movement onset, and re-opened 0 ms (i.e., without initially shutting), 150 ms, 350 ms, 500 ms, or 700 ms after the initial shutting, or remained opaque throughout the prehension movements. The duration of the prehension movements was kept relatively constant across participants and trials at approximately 1100 ms, i.e., the duration of prehension movements typically observed in daily life. The location of the target object was constant during the entire experiment. The SP and RP paradigms were counter-balanced across participants, and the order of conditions within each session was randomized. The main findings were that peak grip aperture (PGA) in the 150 ms-shutting condition was significantly larger than in the 350 ms-shutting condition, and that PGA in the 350 ms-re-opening condition was significantly larger than in the 150 ms-re-opening condition. These results revealed that online vision between 150 ms and 350 ms was critical for grasp control on PGA in typical, daily-life-speeded prehension movements. Furthermore, the results obtained for the time after maximal deceleration (TAMD; movement duration-time to maximal deceleration) demonstrated that early-phase vision contributed to the temporal pattern of the later movement phases (i.e., TAMD). The results thus demonstrated that online vision in the early phase of movement is crucial for the control of grasping. In addition to the apparatus used in Experiment 1, two liquid shutter plates placed in the same horizontal plane (25 cm above the experimental table) were used in Experiment 2 to manipulate the visibility of the target and the participant's moving limb. The plate closest to the participant altered vision of the limb/hand, while the more distant plate controlled vision of the object. The conditions were as follows: (1) both plates were open during movement (full vision condition); (2) both plates were closed 0, 150, or 350 ms following onset of arm movement (front-rear condition: FR); or (3) only the near plate closed 0, 150, or 350 ms following the onset of the arm movement (front condition: F). The results showed that shutting at 0 and 150 ms in the FR condition caused a significantly larger PGA, while the timing of shutting in the F condition had little influence on the PGA. These findings indicated that online vision, especially of the target object, during the early phase of prehension movements is critical to the control of grasping.     

Effects of velocity and limb loading on the coordination between limb movements during walking

The authors investigated the effects of velocity (increasing from 0.5 to 5.0 km/hr in steps of 0.5 km/hr) and limb loading on the coordination between arm and leg movements during treadmill walking in 7 participants. Both the consistency of the individual limb movements and the stability of their coordination increased with increasing velocity; the frequency coordination between arm and leg movements was 2:1 at the lower velocities and 1:1 at the higher velocities. The mass manipulation affected the individual limb movements but not their coordination, indicating that a stable walking pattern was preserved. The results differed qualitatively from those obtained in studies on bimanual interlimb coordination, implying that the dynamical principles identified therein are not readily applicable to locomotion.     

Adaptation to visual displacement with active and passive limb movements: effect of movement frequency and predictability of movement

Three experiments were performed to evaluate the influence of active and passive limb movements on adaptation to visual displacement. Over a wide frequency range (0·5-1·25 Hz) with constant amplitude, 30°, significant adaptation was achieved with active and passive movements. When arm movement frequency was constant at 1·0 Hz but amplitude of movement was varied, less adaptation was achieved for both active and passive movements than when amplitude was held constant. Even at a frequency above that of most naturally occurring limb movements, 1·67 Hz, and with variable amplitude motion, significant adaptation was achieved with active and passive limb movements. These findings emphasize the importance of visual-proprioceptive discordances for adaptation to visual displacement when only sight of the hand is permitted. Significant differences did not appear between the active and passive movement conditions in any of the experiments.     

Attentional costs of coordinating homologous and non-homologous limbs

This study aimed to examine the attentional demands of coordinating movement patterns across limbs. Eighteen participants performed a circle drawing task involving in-phase and anti-phase coordination modes under homologous, contralateral and ipsilateral limb combinations. Results indicated that: (a) attentional focus further stabilised coordination patterns with a cost at the central level; (b) there was an inverse relationship between stability and probe reaction time (RT) for all coordination patterns, that is the stronger the coupling between the limbs the lower the central cost. Overall, the results support previous research suggesting that attention plays an important role in sustaining coordination pattern stability and that the co-variation between coordination stability and central cost can also be extended to coordination across limbs.     

The contribution of peripheral and central vision in the control of movement amplitude

Past research has revealed that central vision is more important than peripheral vision in controlling the amplitude of target-directed aiming movements. However, the extent to which central vision contributes to movement planning versus online control is unclear. Since participants usually fixate the target very early in the limb trajectory, the limb enters the central visual field during the late stages of movement. Hence, there may be insufficient time for central vision to be processed online to correct errors during movement execution. Instead, information from central vision may be processed offline and utilised as a form of knowledge of results, enhancing the programming of subsequent trials. In the present research, variability in limb trajectories was analysed to determine the extent to which peripheral and central vision is used to detect and correct errors during movement execution. Participants performed manual aiming movements of 450 ms under four different visual conditions: full vision, peripheral vision, central vision, no vision. The results revealed that participants utilised visual information from both the central and peripheral visual fields to adjust limb trajectories during movement execution. However, visual information from the central visual field was used more effectively to correct errors online compared to visual information from the peripheral visual field.     

Reaching measures of monocular distance perception: forward versus side-to-side head movements and haptic feedback

We investigated whether forward or side-to-side head movements yielded more accurate and precise monocular egocentric distance information, as shown by performance in a reaching task. Observers wore a head-mounted camera and display to isolate the optic flow generated by their head movements and had to reach to align a stylus directly under a target surface. Performance in the two head movement conditions was also tested with normal monocular vision. We tested performance in the two head movement conditions when the observers were given haptic feedback and compared performance when haptic feedback was removed. Performance was both more accurate and more precise in the forward head movement condition than in the side-to-side head movement condition. Performance in the side-to-side condition also deteriorated more after the removal of haptic feedback than did performance in the forward head movement condition. In the normal monocular condition, performance was comparable for the two head movement conditions. The implications for enucleated patients are discussed.