Interlimb coordination in prosthetic walking: effects of asymmetry and walking velocity

The present study focuses on interlimb coordination in walking with an above-knee prosthesis using concepts and tools of dynamical systems theory (DST). Prosthetic walkers are an interesting group to investigate from this theory because their locomotory system is inherently asymmetric, while, according to DST, coordinative stability may be expected to be reduced as a function of the asymmetry of the oscillating components. Furthermore, previous work on locomotion motivated from DST has shown that the stability of interlimb coordination increases with walking velocity, leading to the additional expectation that the anticipated destabilizing effect of the prosthesis-induced asymmetry may be diminished at higher walking velocities. To examine these expectations, an experiment was conducted aimed at comparing interlimb coordination during treadmill walking between seven participants with an above-knee prosthesis and seven controls across a range of walking velocities. The observed gait patterns were analyzed in terms of standard gait measures (i.e., absolute and relative swing, stance and step times) and interlimb coordination measures (i.e., relative phase and frequency locking). As expected, the asymmetry brought about by the prosthesis led to a decrease in the stability of the coordination between the legs as compared to the control group, while coordinative stability increased with increasing walking velocity in both groups in the absence of a significant interaction. In addition, the 2:1 frequency coordination between arm and leg movements that is generally observed in healthy walkers at low walking velocities was absent in the prosthetic walkers. Collectively, these results suggest that both stability and adaptability of coordination are reduced in prosthetic walkers but may be enhanced by training them to walk at higher velocities.     

Coordination deficits on the ipsilesional side after unilateral stroke: the effect of practice on nonisodirectional ipsilateral coordination

Previous studies have identified motor deficits on the ipsilesional side of patients recovering from a cerebro-vascular accident (CVA), including deficits in interlimb coordination. In the present study, unilateral stroke patients and a control group of healthy age-matched controls performed nonisodirectional coordination of the ipsilateral limbs across two days of practice with feedback. Findings revealed that control subjects were already quite successful at initiation of practice but further improved the coordination pattern across both days. The group of CVA patients also showed some improvement but problems with coordination of the ipsilateral limb segments persisted across practice. Variability in both timing and amplitude of both limb segments did improve with practice in both groups but these measures remained significantly higher in the CVA patients. Even though isodirectional and nonisodirectional coordination of the ipsilateral limb segments are normally considered to be part of the intrinsic motor repertoire, the present study suggests that nonisodirectional ipsilesional limb coordination poses considerable difficulties for CVA patients that are not easily overcome with feedback-assisted practice.     

Relational processing following stroke

The research examined relational processing following stroke. Stroke patients (14 with frontal, 30 with non-frontal lesions) and 41 matched controls completed four relational processing tasks: sentence comprehension, Latin square matrix completion, modified Dimensional Change Card Sorting, and n-back. Each task included items at two or three levels of relational complexity. Relational processing was impaired in the stroke groups. This was due mainly to items at the intermediate ternary-relational level of complexity. Less complex binary-relational items and more complex quaternary-relational items (the latter are difficult for adults generally) were less sensitive to stroke status. Impairment was greater in frontal than non-frontal stroke patients. Positive inter-correlations among measures supported the domain-general nature of relational processing. Implications for assessment and intervention are discussed.     

Bimanual circle drawing in children with spastic hemiparesis: effect of coupling modes on the performance of the impaired and unimpaired arms

The present study examined the effect of interlimb coupling on the performance of the impaired and unimpaired arm in children with spastic hemiparesis during bimanual circle drawing. The following questions were addressed: (1) does coupling positively influence the performance of the impaired arm compared to single-hand performance and (2) is such an effect dependent on mode of coordination (i.e., symmetric versus asymmetric). Twelve children with spastic hemiparesis produced circle drawings on a digitizer under different task conditions. Spatiotemporal characteristics and quality of movement of pen trajectories of the individual limbs as well as interlimb relative phase were analysed. Coupling in a symmetric coordination mode resulted in a decrease of temporal variability and an increase of smoothness of circle drawing movements in the impaired arm compared to single-handed performance. Coupling in an asymmetric coordination mode resulted in an increase of spatial and temporal variability in the unimpaired arm. It is concluded that coupling may enhance the performance of the impaired arm in children with spastic hemiparesis, but only during symmetric bimanual coordination. A possible underlying neural mechanism that might explain these findings is discussed.     

Interlimb coordination: Learning and transfer under different feedback conditions

The role of intrinsic and extrinsic information feedback in learning a new bimanual coordination pattern was investigated. The pattern required continuous flexion-extension movements of the upper limbs with a 90 ° phase offset. Separate groups practiced the task under one of the following visual feedback conditions: (a) blindfolded (reduced FB group), (b) with normal vision (normal FB group), or (c) with concurrent relative motion information (enhanced FB group). All groups were subjected to three different transfer test conditions at regular intervals during practice. These tests included reduced, normal vision, and enhanced vision conditions. Experiment 1 showed that the group receiving augmented information feedback about its relative motions in real-time produced the required coordination pattern more successfully than the remaining two groups, irrespective of the transfer conditions under which performance was evaluated. Experiment 2 replicated and extended the superiority of the enhanced feedback group during acquisition and retention. Experiment 3 demonstrated that successful transfer to various transfer test conditions was not a result of test-trial effects. Overall, the data suggest that the conditions that optimized performance of the coordination pattern during acquisition also optimized transfer performance.     

Language and syntactic impairment following stroke in late bilingual aphasics

Purpose

Bilingual aphasia generally affects both languages. However, the age of acquisition of the second language (L2) seems to play a role in the anatomo-functional correlation of the syntactical/grammatical processes, thus potentially influencing the L2 syntactic impairment following a stroke. The present study aims to analyze the influence of late age of acquisition of the L2 on syntactic impairment in bilingual aphasic patients.

Methods

Twelve late bilingual participants (speaking French as L2 and either English, German, Italian or Spanish as L1) with stroke-induced aphasia participated in the study. The MAST or BAT aphasia batteries were used to evaluate overall aphasia score. An auditory syntactic judgement task was developed and used to test participants syntactic performance.

Results

The overall aphasia scores did not differ between L1 and L2. In a multiple case analysis, only one patient had lower scores in L2. However, four patients presented significantly lower performances in syntactic processing in the late L2 than in their native language (L1). In these four patients the infarct was localized, either exclusively or at least partially, in the pre-rolandic region.

Conclusion

This pilot study suggests that, in late bilingual aphasics, syntactic judgment abilities may be more severely impaired in L2, and that this syntactic deficit is most likely to occur following anterior lesions.     

Working memory outcomes following unilateral arterial ischemic stroke in childhood

There is a dearth of research examining working memory (WM) following pediatric arterial ischemic stroke (AIS). This study assesses the WM patterns of 32 children, aged 6 to 14 years, with a history of unilateral AIS and 32 controls using a paradigm based on Baddeley and Hitch’s multi-component WM model. The results indicate compromised WM in children with AIS relative to controls and parent reports confirm higher rates of dysfunction. Supplementary analyses of impairment confirm higher rates in children with AIS, ranging from 31.25% to 38.70% on performance-based measures and 50.00% on parent reports, compared to 0.00% to 21.88% on performance-based measures in controls and 15.63% on parent reports. Continual follow-up is recommended given that a subset of children with stroke appear to be at risk for WM impairment. Moreover, the subtle nature of WM challenges experienced by many children who have experienced a stroke increases the likelihood that WM impairment could go undetected. The long-term trajectories of WM in the pediatric stroke population remains unknown and future studies are needed to track changes in WM functioning over time.     

Limb and gender differences in the development of coordination in early infancy

Young infants produce a variety of spontaneous arm and leg movements in the first few months of life. Coordination of leg joints has been extensively investigated, whereas arm joint coordination has mainly been investigated in the sitting position in the context of early reaching and grasping. The current study investigated arm and leg joint coordination of movements produced in the supine position in 10 fullterm infants aged 6, 12 and 18 weeks. Longitudinal comparisons within limbs (intralimb) as well as between limbs (interlimb, ipsilateral and contralateral) were made as well as an exploration of differences in the development for boys and girls. The relationship between the joint angles was examined by measuring pair-wise cross-correlation functions for the angular displacement curves of the leg (hip, knee and ankle) and arm (shoulder, elbow and wrist) joints of both the right and left side. Both the arms and legs were found to follow a similar pattern of intralimb coordination, although the leg joints were more tightly coupled than the arm joints, particularly the proximal with the middle joint. In support of earlier findings, differences in the development of the right and left side were identified. In addition, gender differences in joint coordination were found for both intralimb and interlimb coordination. This contrasts with the view that gender differences in motor development may be primarily a result of environmental influences.     

Concurrent cognitive task modulates coordination dynamics

Does a concurrent cognitive task affect the dynamics of bimanual rhythmic coordination? In‐phase coordination was performed under manipulations of phase detuning and movement frequency and either singly or in combination with an arithmetic task. Predicted direction‐specific shifts in stable relative phase from 0° due to detuning and movement frequency were amplified by the cognitive task. Nonlinear cross‐recurrence analysis suggested that this cognitive influence on the locations of the stable points or attractors of coordination entailed a magnification of attractor noise without a reduction in attractor strength. An approximation to these findings was achieved through parameter changes in a motion equation in relative phase. Results are discussed in terms of dual‐task performance as limited resources, dynamics rather than chronometrics, and reparameterization rather than degradation.     

Cross-sectional and prospective associations between cognitive appraisals and posttraumatic stress disorder symptoms following stroke

This study examined cross-sectional and prospective associations between cognitive appraisals and posttraumatic stress disorder (PTSD) symptoms following stroke. While in hospital, stroke patients (n=81) completed questionnaires assessing cognitive appraisals (i.e., negative cognitions about the self, negative cognitions about the world, and self-blame) and PTSD symptoms. PTSD symptoms were assessed again 3 months later when all patients had been discharged from hospital (n=70). Significant correlations were found between the time 1 measures of negative cognitions about the self and the world, but not self-blame, and the severity of PTSD symptoms measured at time 1 and at time 2. Regression analyses revealed that cognitive appraisals explained a significant amount of variance in the severity of PTSD symptoms at time 1, with negative cognitions about the self-emerging as a significant predictor. In contrast, time 1 cognitive appraisals were unable to explain additional variance in time 2 PTSD severity over and above that explained by time 1 PTSD severity. The findings therefore provide only weak support for Ehlers and Clark's cognitive model of PTSD.     

Neuropsychological sequelae following pediatric stroke: A nonlinear model of age at lesion effects

Aim: The distribution and quality of brain recovery following pediatric arterial ischemic stroke remains controversial. The literature suggests that age at stroke may be an important modulator of neuropsychological outcome, with reports inferring either greater vulnerability or plasticity in the nascent brain. Our aim was to investigate neuropsychological outcomes following pediatric stroke in a clinical sample with reference to age at lesion, lesion laterality, elapsed time from stroke to assessment, and persistent neurological sequelae.

Methods: Using comprehensive neuropsychological assessment batteries, we investigated retrospectively a large (n?=?44) and evenly distributed group of children who had ischemic stroke during “infancy” (1 month to 1 year), “early childhood” (1 to 6 years), and “late childhood” (6 to 16 years).

Results: Children who suffered a stroke performed significantly worse on a range of neuropsychological measures when compared to a normative sample. However, children who suffered a stroke between 1 and 6 years old demonstrated better preserved neuropsychological profiles than either the earlier (before age 1) or later (after age 6) age groups. In addition, those children suffering a left hemisphere lesion performed more poorly on a range of neuropsychological measures than did children with right hemisphere lesions.

Interpretation: Age at stroke is an important determinant of recovery following insult and may modulate neuropsychological and cognitive outcome.     

Learning and transfer in motor-respiratory coordination

Motor-respiratory coordination occurs naturally during exercise, but the number of coordination patterns performed between movement and breathing is limited. We investigated whether participants could acquire novel ratios (either 5:2 or 5:3). To examine complex temporal relationships between movement and breathing, we used lagged return plots that were produced by graphing relative phase against relative phase after a time delay. By the end of practice, participants performed 5:2 consistently and performed 5:3 using more stable ratios (3:2 and 2:1). Lagged return plots revealed that 5:3 learners harnessed the stable inphase and antiphase patterns to stabilize the required ratio. That strategy resulted in the performance of smaller-integer ratios in the production of 5:3 but not 5:2. Despite those differences, there was positive transfer to unpracticed ratios that was similar in both learning conditions. The time series analysis of lagged return plots revealed differences in ratio performance at transfer. Ratios whose component frequencies were farther apart, like 7:2, were performed consistently, while ratios whose component frequencies were more similar, like 5:4, elicited attraction to inphase and antiphase. The implication is that participants can combine more stable chunks of rhythmic behavior to produce more complex ratios.     

Effects of motor-cognitive coordination training and cardiovascular training on motor coordination and cognitive functions

ObjectivesNumerous recent studies showed that physical training can enhance cognitive abilities, such as attention, spatial ability, memory performance, and executive functions. However, most of these studies focused on the efficiency of cardiovascular training, whereas evidence for combined motor-cognitive training emphasizing coordination abilities is scarce. Therefore, the aim of the present study was to investigate the effects of motor-cognitive coordination training and moderate cardiovascular training on cognitive functions and to test whether these effects were related to participant's fitness level.Design and methodWe tested 50 physically active (mean age = 23.5 years, SD = 3.2) and 56 sedentary participants (mean age = 23.4 years, SD = 3.2) in a pretest-training-posttest design with 12 sessions of moderate cardiovascular training (≈60% HRmax) or motor-cognitive coordination training. The training groups were compared to a passive control group. At pretest and posttest, participants performed an untrained motor-cognitive coordination task, measures of executive control (cognitive flexibility, inhibition, working memory), spatial ability, and fluid intelligence.Results and conclusionsWe found improved coordination abilities in the coordination training group, but no transfer of training to cognitive measures in physically active participants. However, sedentary participants showed larger improvements in terms of inhibition in the coordination training group compared to the remaining groups, while the cardiovascular training group improved in cognitive flexibility compared to the remaining groups. In sum, there are positive but differential effects of cardiovascular training and coordination training on cognitive performance in sedentary young participants, suggesting that coordination training may be a useful intervention especially for individuals that cannot perform cardiovascular training.     

Temporal coordination during bimanual reach-to-grasp movements: The role of vision

The performance of bimanual movements involving separate objects presents an obvious challenge to the visuo-motor system: Visual feedback can only be obtained from one target at a time. To overcome this challenge overt shifts in visual attention may occur so that visual feedback from both movements may be used directly (Bingham, Hughes, & Mon-Williams, 2008; Riek, Tresilian, Mon-Williams, Coppard, & Carson, 2003). Alternatively, visual feedback from both movements may be obtained in the absence of eye movements, presumably by covert shifts in attention (Diedrichsen, Nambisan, Kennerley, & Ivry, 2004). Given that the quality of information falls with increasing distance from the fixated point, can we obtain the level of information required to accurately guide each hand for precision grasping of separate objects without moving our eyes to fixate each target separately? The purpose of the current study was to examine how the temporal coordination between the upper limbs is affected by the quality of visual information available during the performance of a bimanual task. A total of 11 participants performed congruent and incongruent movements towards near and/or far objects. Movements were performed in natural, fixate-centre, fixate-left, and fixate-right vision conditions. Analyses revealed that the transport phase of incongruent movements was similar across vision conditions for the temporal aspects of both the transport and grasp, whereas the spatial aspects of grasp formation were influenced by the quality of visual feedback. We suggest that bimanual coordination of the temporal aspects of reach-to-grasp movements are not influenced solely by overt shifts in visual attention but instead are influenced by a combination of factors in a task-constrained way.     

Different coordination and flexibility of the spine and pelvis during lateral bending between young and older adults

This study examined coordination of the spine and pelvis during lateral bending of the trunk in older adults. Thirty-four healthy subjects (17 young and 17 older adults) demonstrated lateral bending at a controlled speed while holding a bar at approximately 180 degrees of shoulder flexion. Kinematic data collection was completed on the thoracic spine, lumbar spine, and pelvis. The coupling angle was calculated to examine the thorax–lumbar, lumbar–pelvis, and thorax–pelvis coordination patterns. The older adults demonstrated a reduced range of motion (ROM) of the lumbar spine, while both groups revealed similar ROM in the thorax and in the pelvis. The coupling angle between the straightening and bending phases was different only for the older adults in the thorax–lumbar (23.4 ± 8.0 vs. −1.6 ± 4.4, p = 0.004) and the lumbar–pelvis (65.4 ± 7.2 vs. 86.1 ± 7.8, p = 0.001) coordination. However, there was no group difference in the thorax–pelvis coordination. These findings indicate that age-related changes in the lumbar region affect coordination patterns only during the bending phase. The older adults preserved a similar pattern of movement to the young adults during the straightening phase, but the coordination variability of the coupling angles was greater for the older adults than for the young adults. This movement pattern suggests that the older adults lacked consistent trunk control in an attempt to optimize lateral bending coordination.     

Cognitive outcomes of pediatric stroke

A limited number of longitudinal studies have investigated long-term neuropsychological development in the pediatric stroke population. This study retrospectively examines cognitive outcomes in 41 children with a history of stroke, with reference to age at stroke, laterality, region and mechanism of stroke. In the course of recovery, neuropsychological measures of intellectual functioning and memory were administered at two time points, whilst executive functioning, attention and academic skills were administered at one time point. As predicted, children with stroke performed significantly worse compared to normative expectations on all neuropsychological measures. Up to two thirds of children scored in the borderline impaired and impaired ranges on at least one domain of cognition. Performance on intellectual and memory assessment remained relatively stable over time. Younger age at stroke was found to be associated with poorer intellectual functioning. No effects of laterality of stroke on neuropsychological performance over time were found. Children with subcortical stroke demonstrated a greater improvement in immediate memory over time than children with cortical stroke. These findings reveal that children with stroke display long-term cognitive difficulties that typically remain stable over time. Attention and academic skills are particularly vulnerable to impairment. Further evidence that age at stroke is a significant factor in terms of cognitive outcome is provided, in support of the “early vulnerability” position.     

Grip Force-Load Force Coupling Is Influenced by Altered Visual Feedback about Object Kinematics

Abstract

Recent evidence suggests that visual feedback influences the adjustment of grip force to the changing load force exerted by a grasped object as it is manipulated. The current project investigated how visual feedback of object kinematics affects the coupling of grip force to load force by scaling the apparent displacements of the object viewed in virtual reality. Participants moved the object to manually track a moving virtual target. The predictability of the changing load force exerted by the object was also manipulated by altering the nature of target trajectories (and therefore the nature of object motions). When apparent object displacements increased in magnitude, grip force became more tightly coupled to load force over time. Furthermore, when load force variations were less predictable, the magnitude of apparent object displacements affected the relative degree of continuous versus intermittent coupling of grip force to load force. These findings show that visual feedback of object motion affects the ongoing dynamical coupling between grip force control and load force experienced during manipulation of a grasped object.     

Development of infant leg coordination: Exploiting passive torques

Leg joint coordination systematically changes over the first months of life, yet there is minimal data on the underlying change in muscle torques that might account for this change in coordination. The purpose of this study is to investigate the contribution of torque changes to early changes in leg joint coordination. Kicking actions were analyzed of 10 full-term infants between 6 and 15-weeks of age using three-dimensional kinematics and kinetics. We found 11 of 15 joint angle pairs demonstrated a change from more in-phase intralimb coordination at 6-weeks to less in-phase coordination at 15-weeks. Although the magnitude of joint torques normalized to the mass of the leg remained relatively consistent, we noted more complex patterns of torque component contribution across ages. By focusing on the change in torques associated with hip–knee joint coordination, we found that less in-phase hip–knee joint coordination at 15-weeks was associated with decreased influence of knee muscle torque and increased influence of knee gravitational and motion-dependent torques, supporting that infants coordinate hip muscle torque with passive knee gravitational and motion-dependent torques to generate kicks with reduced active knee muscle torque. We propose that between 6 and 15-weeks of age less in-phase hip–knee coordination emerges as infants exploit passive dynamics in the coordination of hip and knee motions.     

The acquisition of bimanual coordination is mediated by anisotropic coupling between the hands

The present study was designed to test two predictions from the coupled oscillator model of multifrequency coordination. First, it was predicted that multifrequency tasks that match the inherent manual asymmetry (i.e., the preferred hand assigned to the faster tempo) would be easier to learn than tasks that do not match the inherent dynamics (i.e., the non-preferred hand assigned to the faster tempo). Second, in the latter case acquisition of the multifrequency coordination would involve a reorganisation of the coupling dynamics such that the faster hand would exert a greater influence on the slower hand than vice versa. Sixteen right-handed volunteers received extensive training on a 2:1 coordination pattern involving a bimanual forearm pronation-supination task. Participants were randomly assigned to one of two groups: 1L:2R in which the preferred right hand performed the higher frequency, or 2L:1R in which the non-preferred left hand performed the higher frequency. The dynamic stability of the patterns was assessed by the ability of participants to maintain the coordination pattern as movement frequency was increased. Changes in the directional coupling between the hands was assessed by transition pathways and lead-lag relationship evident in a 1:1 anti-phase frequency-scaled coordination task performed prior to and following three practice sessions of the 2:1 task. The predicted differential stability between the multifrequency patterns was evident in the initial acquisition sessions but by the end of training the two patterns evidenced equivalent stability. Unexpectedly, for both groups the fast hand displayed greater variability in amplitude and movement frequency than the slow hand perhaps reflecting anchoring afforded to the slow hand by synchronising movement endpoints with the auditory pacing metronome. Analysis of pre- to post-training changes to the coupling dynamics in the 1:1 anti-phase task support the hypothesis that acquisition of the 2L:1R pattern involved reorganisation of the inherent dynamics.     

Sentence comprehension affects the dynamics of bimanual coordination: Implications for embodied cognition

Recent work in embodied cognition has demonstrated that language comprehension involves the motor system (e.g., Glenberg & Kaschak, 2002). Such findings are often attributed to mechanisms involving simulations of linguistically described events (Barsalou, 1999; Fischer & Zwaan, 2008). We propose that research paradigms in which simulation is the central focus need to be augmented with paradigms that probe the organization of the motor system during language comprehension. The use of well-studied motor tasks may be appropriate to this endeavour. To this end, we present a study in which participants perform a bimanual rhythmic task (Kugler & Turvey, 1987) while judging the plausibility of sentences. We show that the dynamics of the bimanual task differ when participants judge sentences describing performable actions as opposed to sentences describing events that are not performable. We discuss the general implications of our results for accounts of embodied cognition.