Not just standing there: the use of postural coordination to aid visual tasks

Postural control is an integral part of all physical behavior. Recent research has indicated that postural control functions in a manner that facilitates other higher order (suprapostural) tasks. These studies, while showing that postural sway is modulated in a task specific manner, have not examined the form of postural coordination that allows for the achievement of these higher behavioral goals. The current study examined the relation between visual task constraints (viewing distance), environmental constraints (changes in the surface of support), and the postural coordination employed to complete the task. Thirty-one participants were asked to perform a reading task while standing on various surfaces. Postural motion was recorded from the head, cervico-thoracic spine, sacrum (hip), and ankle. It was found that body segment coordination changed as a function of surface characteristics and task constraints. Additionally, the overall pattern of postural sway (head motion) replicated that which was found by Stoffregen et al. [J. Exp. Psychol. Human Percep. Perform. 25 (6) (1999) 1641]. These findings suggest that postural adaptation involves more than basic reduction or increase of motion; it involves the functional coordination of body segments to achieve a particular goal. The data further suggest that there is a need to examine postural control in the absence of external perturbations.     

Effects of Visual Tasks and Conversational Partner on Personal and Interpersonal Postural Activity

The control of stance is influenced by activities that are engaged in during stance. We investigated simultaneous constraints imposed by individual-specific factors (such as the distance of visual targets) and of interpersonal factors arising from dyadic conversation. Each member of participant pairs looked at targets (drawings) that were similar to, but differed from, that of a conversational partner. Conversational partners conversed to identify the differing elements. In Experiments 1 and 2, members of each dyad conversed with each other or separately conversed with a confederate (an experimenter). We varied the distance of targets (Experiment 1) and their size (Experiment 2). In Experiment 3, target size could be the same for both members of a dyad (i.e., small-small, large-large) or could differ (i.e., small-large, large-small). Interpersonal postural coordination was stronger when members of dyads conversed with each other, replicating earlier studies, but this manipulation also influenced parameters of individual sway. In Experiment 3, interpersonal postural coordination also was influenced by variation in the size of the partner's target. Analysis of the sway of individuals revealed influences of target distance and size, replicating previous effects; however, these manipulations also influenced interpersonal postural coordination. Overall, the results indicate that postural activity was modulated simultaneously with respect to individual and dyadic parameters of the task situation. We argue that it may be useful, both theoretically and empirically, to interpret the effects of conversation on postural activity within the broader context of relations between postural control and the performance of suprapostural tasks.     

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

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

Interstimulus Intervals and Sensory Modality Modulate the Impact of a Cognitive Task on Postural Control

The present literature not only reveals the use of a wide variety of cognitive tasks but variability in their interaction with postural control. The question then arises, as to, whether postural control is sensitive to specific features of a cognitive task. The present experiment assessed the impact of cognitive tasks with interstimulus intervals (ISI) of varied duration and sensory modality on postural control in young adults. Seventeen participants (23.71 ± 1.99 years old) were instructed to stand on a force platform while concurrently performing cognitive tasks with ISIs of two and 5 s. The tasks were presented both, auditorily and visually. The visual tasks consisted of counting the total occurrence of a single digit. The auditory tasks consisted of counting the total occurrence of a single letter. Performing the cognitive tasks with an ISI of 2 s resulted only in an increase in the anteroposterior mean power frequency. Presenting the tasks visually also significantly reduced area of 95% confidence ellipse and AP and mediolateral sway variability. These results may suggest that ISIs can modify postural performance by altering the allocation of attentional focus. Also, presenting tasks using a visual sensory modality appears to yield lower postural sway.     

Specificity of Postural Control: Comparing Expert and Intermediate Dancers

The expert–novice approach is inappropriate for studying postural control in sport and dance when novices are completely unable to perform relevant postural tasks and experts cannot demonstrate specific skills on everyday postural tasks. We tested expertise-specific differences on 6 static everyday and 5 dynamic dance-like postural tasks of varying difficulty in 13 professional and 12 intermediate nonprofessional dancers. Results showed a clear expert advantage on sway area for dance-like postural tasks, but not for static everyday tasks. This effect was also found for the control parameter of root mean square (RMS) velocity and partly for RMS amplitude of the difference signal between CoP and CoG line location. Results indicate that the expert advantage is task-specific and deliver new insights into the specificity of experts' postural performance.     

The control of posture in newly standing infants is task dependent

The postural sway patterns of newly standing infants were compared under two conditions: standing while holding a toy and standing while not holding a toy. Infants exhibited a lower magnitude of postural sway and more complex sway patterns when holding the toy. These changes suggest that infants adapt postural sway in a manner that facilitates visually fixating on and stabilizing the toy in their hand. When simply standing, infants exhibited postural sway patterns that appeared to be more exploratory in nature. Exploratory sway patterns may allow infants to learn the affordances of their new standing posture. These results demonstrate that newly standing infants are capable of task-dependent postural control.     

Measures of postural control and mobility during dual-tasking as candidate markers of instability in Huntington's disease

BackgroundIndividuals with Huntington's disease (HD) have impairments in performing dual-tasks, however, there is limited information about the effects of changing postural and cognitive demands as well as which measures are best suited as markers of underlying motor-cognitive interference.MethodsForty-three individuals with HD and 15 healthy controls (HC) completed single tasks of walking (Timed Up & Go (TUG), 7 m walk), standing (feet together, feet apart and foam surface) and seated cognitive performance (Stroop, Symbol Digit Modalities Test (SDMT), Delis-Kaplan Executive Function System (DKEFS) Sorting test) and dual cognitive-motor tasks while standing (+ Stroop) and walking (+ DKEFS, TUG cognitive). APDM Opal sensors recorded measures of postural sway and time to complete motor tasks.ResultsIndividuals with HD had a greater increase in standing postural sway compared to HC from single to dual-tasks and with changes to support surface. Both groups demonstrated a decrease in gait performance during the TUG cognitive, however, this difference was greater in people with HD compared to HC. While those with HD showed a greater dual-task motor cost compared to HC, both groups behaved similarly as condition complexity increased.ConclusionsStanding postural sway is a more sensitive marker of instability than change in standard gait speed, particularly under dual-task conditions. The more complex TUG cognitive is a sensitive measure of walking dual-task performance. The results of this study provide insights about the nature of motor-cognitive impairments in HD and provide support for a distinction between static and dynamic postural control mechanisms during performance of dual-tasks.     

Interacting Constraints and the Emergence of Postural Behavior in ACL-Deficient Subjects

In this study, the authors examined how task, informational, and sensorimotor system constraints influence postural control. Postural behavior of subjects with (n = 15) and without (n = 15) a key sensorimotor system constraint, anterior cruciate ligaments (ACLs) in 1 knee, was examined during 1- and 2-legged stance with and without vision. Postural control was assessed on a commonly used postural sway meter and on a dynamic stabilometer. Data on postural sway characteristics were obtained for 30 s under 6 different conditions: standing, with eyes open and closed, on both legs, on the injured leg, and on the noninjured leg. The interaction of task, informational, and sensorimotor constraints was observed only on the dynamic stabilometer and not the postural sway meter. Vision was the most important informational constraint on postural control for subjects on the dynamic stabilometer, particularly for the ACL-deficient group standing on the injured leg. Under more static task constraints, ACL deficiency did not prove a significant disadvantage, because vision was confirmed as a significant source of exproprioceptive information. The results support the functionality of using dynamic tasks such as a stabilometer in assessing postural behavior of subjects with sensorimotor system constraints.     

Age Changes in Interlimb Coupling and the Development of Bimanual Coordination

Changes in interlimb coupling, and their role in the development of bimanual coordination, were studied longitudinally in 6- to 12-month-old infants (N = 6). Infants were observed while they were reaching for simple objects of 2 different sizes. Their use of a uni-versus bimanual strategy for reaching as well as the coupling of their bimanual movements were compared; progress in bimanual coordination of complementary movements was evaluated on 8 different bimanual tasks. The bimanual tasks involved an asymmetrical cooperation between the 2 hands. Although spatiotemporal coupling of bimanual reaching movements did not decrease during the age period studied, infants around 7 months of age used their 2 hands infrequently for reaching. Occurrences of bimanual reaching were particularly low at the session preceding the first bimanual success at a bimanual task. This suggests that the temporal coincidence between greater independence of the 2 hands and progress in bimanual coordination of complementary movements acts in 2 directions: Infants may be more at ease when using their 2 hands in differentiated patterns as the hands move less in synchrony, but, in turn, they may be less likely to move their hands in synchrony as the anticipate mirror manipulations of the object less. The frequency of bimanual reaches increased toward the end of the 1st year. This might have been caused by an increase in the repertoire of bimanual asymmetrical object manipulations and by the fact that the development of bimanual coordination allows infants to manipulate objects with complementary movements even after a bimanual approach toward the object.     

Interacting Constraints and the Emergence of Postural Behavior in ACL-Deficient Subjects

In this study, the authors examined how task, informational, and sensorimotor system constraints influence postural control. Postural behavior of subjects with (n = 15) and without (n = 15) a key sensorimotor system constraint, anterior cruciate ligaments (ACLs) in 1 knee, was examined during 1 - and 2-legged stance with and without vision. Postural control was assessed on a commonly used postural sway meter and on a dynamic stabilometer. Data on postural sway characteristics were obtained for 30 s under 6 different conditions: standing, with eyes open and closed, on both legs, on the injured leg, and on the noninjured leg. The interaction of task, informational, and sensorimotor constraints was observed only on the dynamic stabilometer and not the postural sway meter. Vision was the most important informational constraint on postural control for subjects on the dynamic stabilometer, particularly for the ACL-deficient group standing on the injured leg. Under more static task constraints, ACL deficiency did not prove a significant disadvantage, because vision was confirmed as a significant source of exproprioceptive information. The results support the functionality of using dynamic tasks such as a stabilometer in assessing postural behavior of subjects with sensorimotor system constraints.     

Optimization of postural control in precise gaze shifts and laser pointing

Young adults are known to reduce their postural sway to perform precise visual search and laser pointing tasks. We tested if young adults could reduce even more postural and/or center of pressure sway to succeed in both tasks simultaneously. The methodology is novel because published pointing tasks usually require continuously looking at the pointed target and not exploring an image while pointing elsewhere at the same time. Twenty-five healthy young adults (23.2 ± 2.5 years) performed six visual tasks. In the free-viewing task, participants randomly explored images with no goal. In two visual search tasks, participants searched to locate objects (easy search task) or graphical details (hard search task). Participants additionally pointed a laser beam into a central circle (2°) or pointed the laser turned off. Postural sway and center of pressure sway were reduced complementarily – in various variables – to perform the visual search and pointing tasks. Unexpectedly, the pointing task influenced more strongly postural sway and center of pressure sway than the search tasks. Overall, the participants adopted a functional strategy in stabilizing their posture to succeed in the pointing task and also to fully explore images. Therefore, it is possible to inverse the strength of effects found in the literature (usually stronger for the search task) in modulating the experimental methodology. In search tasks more than in free-viewing tasks, participants mostly rotated their eyes and head, and not their full body, to stabilize their posture. These results could have implications for shooting activities, video console games and rehabilitation most particularly.     

Effects of visual and auditory short-term memory tasks on the spatiotemporal dynamics and variability of postural sway

The authors measured postural sway while participants (N = 20 in each experiment) stood on a rigid or a compliant surface, with their eyes open or closed, and while they did or did not perform a short-term memory (STM) task. In Experiment 1, the STM stimuli were presented visually; in Experiment 2, the stimuli were presented auditorily. In both experiments, fine-scaled, mediolateral postural-sway variability decreased as the cognitive load imposed by the STM task increased. That effect was independent of support surface and vision manipulations. The spatiotemporal profile of postural sway was affected by both visual and auditory STM tasks, but to a greater degree by the auditory task. The authors discuss implications of the results for theories and models of postural control.     

Hierarchical control in redundant and non-redundant postural tasks

Prior studies of postural coordination have shown inconsistencies between hip-ankle coordination in redundant and non-redundant coordination tasks as well as predictions of the HKB model. These inconsistencies were investigated by testing the hypothesis that there are different hierarchical control structures for redundant (multiple potential task solutions) and non-redundant (a single task solution) coordination tasks (Bernstein, 1996). The transfer between a non-redundant postural tracking task and a redundant scanning task consisting of 16 hip-ankle relative phase patterns from 0° to 337.5° was investigated. The results showed that the transfer between the tasks was transitory, negative and occurred only from the non-redundant to the redundant task. This finding supports the hypothesis that inconsistencies between redundant and non-redundant coordination dynamics may be due to a hierarchical relation between control structures for the performance of these types of tasks.     

Postural stabilization of perceptual but not cognitive performance

In 2 experiments, the authors independently varied the degree of cognitive and perceptual difficulty of suprapostural tasks. Participants were 23 students in Experiment 1 and 15 in Experiment 2. Increases in perceptual difficulty tended to be correlated with decreases in the variability of postural sway, consistent with the hypothesized functional integration of postural control with suprapostural tasks. Sway variability was not influenced by changes in the cognitive difficulty of tasks when perceptual difficulty was held constant, contrary to predictions derived from the perspective that postural and suprapostural activities compete for a limited pool of central processing resources. The results underscore the need for researchers to differentiate between suprapostural tasks that require perceptual contact with the environment and those that do not.     

Absence of Ankle Stiffening While Standing in Focus and Cognitive Task Conditions in Older Adults

Abstract

Research suggests that an external focus or cognitive task may improve postural control. Removing attention from movement production may promote automaticity, or the tasks may promote ankle stiffening. To investigate these two theories, twenty older adults stood while performing baseline standing, internal focus, external focus, and two cognitive tasks. Changes in postural control occurred in external focus and cognitive task conditions compared to baseline and internal focus, while no change occurred in cocontraction indices. This suggests that an external focus and cognitive task can improve postural control in older adults. Since no change occurred in cocontraction indices across conditions, this suggests that stiffening cannot explain these changes. Instead, changes could be due to automaticity of sway.     

Dual-task training reduces impact of cognitive task on postural sway

Postural sway increases when a cognitive task is performed concurrently with a postural task. The author examined the hypothesis that following dual-task training, a concurrent cognitive task would not amplify postural sway. Participants (N = 18) were assigned to no-training, single-task training, or dual-task training groups. Single-task training consisted of 3 sessions in which the postural task, quiet standing on a compliant surface, and the cognitive task, counting backward by 3s, were practiced separately. Dual-task training consisted of 3 sessions of concurrent practice of the cognitive and postural tasks. After training, performance of a concurrent cognitive task increased postural sway in the no-training and single-task training groups but not in the dual-task training group. Results suggest that dual-task practice improves dual-task performance.     

Task demand effects on postural control in older adults

The literature shows conflicting results regarding older adults' (OA) postural control performance. Differing task demands amongst scientific studies may contribute to such ambiguous results. Therefore, the purpose of this study was to examine the performance of postural control in older adults and the relationship between visual information and body sway as a function of task demands. Old and young adults (YA) maintained an upright stance on different bases of support (normal, tandem and reduced), both with and without vision, and both with and without room movement. In the more demanding tasks, the older adults displayed greater body sway than the younger adults and older adults were more influenced by the manipulation of the visual information due to the room movement. However, in the normal support condition, the influence of the moving room was similar for the two groups. These results suggest that task demand is an important aspect to consider when examining postural control in older adults.     

Effects of passive interpersonal light touch during walking on postural control responses: An exploratory study

The effects of passive interpersonal light touch (PILT) on postural stability can be observed through improved postural coordination through haptic feedback from the contact provider to the contact receiver while walking. It is unclear, however, whether PILT affects the contact receiver's detailed physical responses, such as muscle activity, body sway, and joint movements. In this study, surface electromyography and an inertial measurement unit were used simultaneously to explore changes in walking speed and control responses induced by PILT. We evaluated fourteen healthy participants for their walking speed and physical responses under two walking conditions: no-touch (NT) and PILT. As a physical response during walking, we measured muscle activity (rectus femoris, semitendinosus, tibialis anterior, and soleus muscles), body sway (pelvis and neck), and joint angles (direction of hip, knee, and ankle joint movements). In PILT condition, fingertip contact force was measured while the contact provider touched the third level of the recipient's lumbar spine. In comparison with the NT condition, PILT condition increased walking speed and decreased body sway on neck position. There were significant correlations between walking speed and neck sway regarding NT and PILT change values. Passive haptic information to the contact receiver may assist in the smooth shift of the center of gravity position during gait through interpersonal postural coordination. These findings suggest that PILT may provide an efficient and stable gait.     

Noninvasive Brain Stimulation over the M1 Enhances Bimanual Force Control Ability: A Randomized Double-Blind Sham-Controlled Study

Well-coordinated bimanual force control is common in daily life. We investigated the effects of anodal transcranial direct current stimulation (tDCS) over the primary motor cortex on bimanual force control. Under a cross-over study, young adults (n = 19; female = 6, male = 13) completed three bimanual force control tasks at 5%, 25%, and 50% of bimanual maximum voluntary force (BMVF) before and after real or sham tDCS. Real tDCS enhanced accuracy at all BMVF, reduced variability at 5% BMVF, and increased coordination at 5% BMVF. Real tDCS improved force control at 5% and 25% BMVF, and especially increased bimanual coordination at 5% BMVF. These findings might have implications for establishing interventions for patients with hand force control deficits.     

Impact of Handedness Consistency on Bimanual and Unimanual Continuous Movements

Bimanual coordination is an essential human function requiring efficient interhemispheric communication to produce coordinated movements. Previous research suggests a “bimanual advantage” phenomenon, where completing synchronized bimanual tasks results in less variability than unimanual tasks. Additionally, of hand dominance has been shown to influence coordinated performance. The present study examined the bimanual advantage in individuals with consistent and inconsistent handedness. It was predicted that participants with consistent handedness would not display a bimanual advantage unlike those with inconsistent handedness. Fifty-six young adults completed a finger-tapping paradigm in five conditions: unimanual tapping with either left or right hand, in-phase bimanual tapping, and out-of phase bimanual tapping led by either left or right hand. Results were not consistent with the hypothesis that participants with consistent handedness displayed the “bimanual advantage”. However, the “bimanual advantage” was not evident for the inconsistent handers when the temporal consistency was measured with either the left or right hand only. Overall, the “bimanual advantage” may be dependent upon consistency of hand preference, as well as the direction of hand dominance.