Adaptive visual re-weighting in children's postural control

Can head sway patterns differentiate between patients with Meniere's disease vs. peripheral vestibular hypofunction?

Background

Meniere's disease (MD) is defined by episodic vertigo, unilateral sensorineural hearing loss and fluctuating aural symptoms. Due to the variable clinical presentation, objective tests of MD may have significant diagnostic utility. Head kinematics derived from a head-mounted display (HMD) have demonstrated to be sensitive to vestibular dysfunction. The purpose of this pilot study was to investigate whether head sway can differentiate between patients with MD, vestibular hypofunction (VH) and healthy controls.

Materials/methods

80 adults (30 healthy controls, 32 with VH, and 18 with MD) were recruited from a tertiary vestibular clinic. All underwent a postural control assessment using the HTC Vive Pro Eye HMD that recorded head sway in the anterior-posterior (AP), medio-lateral (ML), pitch, yaw and roll direction. Participants were tested with 2 levels of visual load: a static versus oscillating star display. Each scene lasted 60 s and was repeated twice. Sway in each direction was quantified using root mean square velocity (VRMS) for the first 20 s and full 60 s of each scene.

Results

Static visual: participants with VH showed significantly larger head VRMS than controls in the AP (60 s and 20 s) and pitch (20 s) directions. Dynamic visual: participants with VH showed significantly larger head VRMS than controls all directions for both the 60 and 20 s analysis. Participants with MD did not differ significantly from the control or the VH group.

Conclusion

While limited in numbers, Patients with MD had a high variability in head sway in all directions, and their average head sway was between controls and those with VH. A larger sample as well as patients with worse symptoms at time of testing could elucidate whether head sway via HMD could become a viable test in this population. A similar finding between 20- and 60-s scene and the full portability of the system with an in-clinic testing setup could help these future endeavors. Head sway derived from HMD is sensitive to VH and can be clinically useful as an outcome measure to evaluate sensory integration for postural control.

Multisensory and biomechanical influences on postural control in children

Children's ability to maintain balance requires effective integration of multisensory and biomechanical information. The current project examined the interaction between such sensory inputs, manipulating visual input (presence vs. absence), haptic (somatosensory) input (presence vs. absence of contact with a stable or unstable finger support surface), and biomechanical (sensorimotor) input (varying stance widths). Analyses of mean velocity of the center of pressure and the percentage stability gain highlighted the role of varying multisensory inputs in postural control. Developmentally, older children (6-11 years) showed a multisensory integration advantage compared with their younger counterparts (3-5.9 years), with the impact of varying sensory inputs more closely akin to that seen in adults. Subsequent analyses of the impact of anthropometric individual difference parameters (e.g., height, leg length, weight, areas of base of support) revealed a shifting pattern across development. For younger children, these parameters were positively related to postural stability across experimental conditions (i.e., increasing body size was related to increasing postural control). This pattern transitioned for older children, who showed a nonsignificant relation between body size and balance. Interestingly, because adults show a negative relation between anthropometric factors and stability (i.e., increasing body size is related to decreasing postural control), this shift for the older children can be seen as a developmental transition from child-like to adult-like balance control.

Weighting of visual and auditory inputs in dancers with and without previous ankle injury

Elite dance requires highly controlled balance performance in dynamic visual and auditory environments characterized by the use of stage lighting and music. Perturbing visual input is known to influence balance in dancers, but the effects of sounds have not been clearly established. Ankle inversion injuries are common in dancers and may also play a role in dancers' ability to respond to sensory perturbations. The aims of this study were to identify changes in static balance in response to visual or auditory perturbation in elite collegiate dancers with and without a history of ankle injury, and to describe coupling of measurements obtained from the waist and head during balance. Thirty-seven dancers: 22 controls and 15 with a history of ankle sprain, performed single-leg balance under static and dynamic visual and auditory conditions. Dancers demonstrated increased waist sway when viewing a dynamic visual scene and when presented with moving sounds and increased head sway with dynamic visuals. These results did not vary by history of ankle sprain. While dancers appear to dampen the impact of waist sway on head motion during single leg stance, even highly trained dancers may experience challenges controlling balance under perturbing visual and auditory conditions like those present during stage performance.

Differing postural control patterns in individuals with bilateral and unilateral hearing loss

OBJECTIVES

Hearing loss (HL) is associated with imbalance and increased fall risk. The mechanism underlying this relationship and differences across types of hearing loss remains unclear. Head mounted displays (HMD) can shed light on postural control mechanisms via an analysis of head sway.

PURPOSE

The purpose of this study was to evaluate head sway in response to sensory perturbations in individuals with bilateral (BHL) or unilateral hearing loss (UHL) and compare them to controls.

MATERIALS AND METHODS

We recruited 36 controls, 23 individuals with UHL and 14 with BHL. An HMD (HTC Vive) measured head sway while participants stood on the floor, hips-width apart. Stimuli included two levels of visuals and sound. Root Mean Square Velocity (RMSV) and Power Spectral Density (PSD) were used to quantify head sway.

RESULTS

Adjusting for age, individuals with BHL had significantly higher anterior-posterior and medio-lateral RMSV than controls and individuals with UHL. Individuals with UHL demonstrated significantly lower response to visual perturbations in RMSV AP and in all 3 frequency segments of PSD compared to controls. Individuals with UHL showed significantly lower movements at high frequencies compared to controls. Sounds or severity of HL did not impact head sway.

CONCLUSIONS

Individuals with BHL demonstrated increased sway with visual perturbations and should be clinically assessed for balance performance and fall risk. Individuals with UHL exhibited reduced responses to visual stimuli compared with controls, which may reflect conscious movement processing. Additional studies are needed to further understand the mechanistic relationship between hearing loss and imbalance.

Decrease in head sway as a measure of sensory integration following vestibular rehabilitation: A randomized controlled trial

OBJECTIVE

The purpose of this study was to determine the extent to which sensory integration strategies via head sway, derived from a Head-Mounted Display (HMD), change in people with vestibular disorders following vestibular rehabilitation.

DESIGN

Randomized Controlled TrialSetting:Vestibular Rehabilitation ClinicParticipants:Thirty participants with vestibular dysfunction and 21 age-matched controls.

MAIN OUTCOME MEASURES

Participants experienced two levels of visual surround (static or moving 'stars', front to back at 0.2 Hz, 32 mm) and white noise (none or rhythmic) while their head sway was recorded via the HTC Vive. We quantified head sway via Directional Path (DP) and Root Mean Square Velocity (RMSV) in 5 directions: anterior-posterior, medio-lateral, pitch, yaw, and roll and Power Spectral Density in low (PSD 1), medium (PSD 2) and high (PSD 3) frequencies in the anterior-posterior direction.

INTERVENTIONS

Participants performed the assessment prior to being randomized into 8-weeks of contextual sensory integration training in virtual reality or traditional vestibular rehabilitation and once again following completion of the intervention. Controls performed the assessment once. Twelve participants dropped out, half due to covid lock-down. We applied an intention to treat analysis.

RESULTS

We observed significant increases in AP DP, RMSV and all PSDs with change in visual level. Both intervention groups significantly decreased medio-lateral, pitch and roll DP and RMSV and anterior-posterior PSD 2 with no group differences. Vestibular participants were significantly higher than controls on all outcomes pre rehabilitation. Post rehabilitation they were only significantly higher on PSD 2. Sound was not a significant predictor of head sway in this protocol.

CONCLUSIONS

Head sway decreased following vestibular rehabilitation regardless of visual load or type of intervention applied. This change was measured via head kinematics derived from a portable HMD which can serve as a sensitive in-clinic assessment for tracking improvement over time.

Long-term effects of mTBIs includes a higher dependency on visual inputs to control vertical posture

This study investigated the hypothesis that individuals living with long-term effects of mild traumatic brain injury (mTBI) develop an increased dependency on visual inputs to control upright posture. To test this hypothesis, we quantified visuo-postural dependency indices (VPDIs) calculated for multiple postural behavioral markers extracted from the body's center of pressure coordinates signals. These signals were recorded during the execution of a quiet bipedal stance under Vision and No-Vision experimental conditions. VPDIs were calculated as the normalized pair-wise subtraction of recordings obtained under Vision and No-Vision. A total of one hundred and twenty-nine volunteers were organized into two groups: mTBI group (n = 50) and neurotypical control group (n = 79). Consistent with our hypothesis, the results reveal that balance behavior of participants with mTBI deteriorate more abruptly in the absence of visual inputs when compared to neurotypical controls. These impairments might increase the likelihood of recurrent injuries and falls when time-constrained reactions are needed in daily activities, sports practice, or military operations. Additionally, the methodology used in this study shows to be potentially useful to aid future investigations of neural circuitry impaired by mTBI. It also provides indices of recovery for future clinical trials testing mTBI-related clinical interventions.

Insight into postural control in unilateral sensorineural hearing loss and vestibular hypofunction

This pilot study aimed to identify postural strategies in response to sensory perturbations (visual, auditory, somatosensory) in adults with and without sensory loss. We tested people with unilateral peripheral vestibular hypofunction (N = 12, mean age 62 range 23-78), or with Unilateral Sensorineural Hearing Loss (USNHL, N = 9, 48, 22-82), or healthy controls (N = 21, 52, 28-80). Postural sway and head kinematics parameters (Directional Path in the anterior-posterior and medio-lateral directions (sway & head); pitch, yaw and roll (head) were analyzed in response to 2 levels of auditory (none, rhythmic sounds via headphones), visual (static, dynamic) and somatosensory cues (floor, foam) within a simulated, virtual 3-wall display of stars. We found no differences with the rhythmic auditory cues. The effect of foam was magnified in the vestibular group compared with controls for anterior-posterior and medio-lateral postural sway, and all head direction except for medio-lateral. The vestibular group had significantly larger anterior-posterior and medio-lateral postural sway and head movement on the static scene compared with controls. Differences in pitch, yaw and roll emerged between vestibular and controls only with sensory perturbations. The USNHL group did not increase their postural sway and head movement with the increased visual load as much as controls did, particularly when standing on the foam. They did not increase their medio-lateral sway with the foam as much as controls did. These findings suggest that individuals with USNHL employ a compensatory strategy of conscious control of balance, the functional implications of which need to be tested in future research.

Postural Control under Cognitive Load: Evidence of Increased Automaticity Revealed by Center-of-Pressure and Head Kinematics

How postural responses change with sensory perturbations while also performing a cognitive task is still debatable. This study investigated this question via comprehensive assessment of postural sway, head kinematics and their coupling. Twenty-three healthy young adults stood in tandem with eyes open or wearing the HTC Vive Head-Mounted Display (HMD) with a static or dynamic (i.e., movement in the anterior-posterior direction at 5 mm or 32 mm at 0.2 Hz) 3-wall stars display. On half of the trials, participants performed a cognitive serial subtraction task. Medio-lateral center-of-pressure (COP) path significantly increased with the cognitive task, particularly with dynamic visuals whereas medio-lateral variance decreased with the cognitive task. Head path and velocity significantly increased with the cognitive task in both directions while variance decreased. Head-COP cross-correlations ranged between 0.78 and 0.66. These findings, accompanied by frequency analysis, suggest that postural control switched to primarily relying on somatosensory input under challenging cognitive load conditions. Several differences between head and COP suggest that head kinematics contribute an important additional facet of postural control and the relationship between head and COP may depend on task and stance position. The potential of HMDs for clinical assessments of balance needs to be further explored.

The Relative Contributions of Visual and Proprioceptive Inputs on Hand Localization in Early Childhood

Forming an accurate representation of the body relies on the integration of information from multiple sensory inputs. Both vision and proprioception are important for body localization. Whilst adults have been shown to integrate these sources in an optimal fashion, few studies have investigated how children integrate visual and proprioceptive information when localizing the body. The current study used a mediated reality device called MIRAGE to explore how the brain weighs visual and proprioceptive information in a hand localization task across early childhood. Sixty-four children aged 4–11 years estimated the position of their index finger after viewing congruent or incongruent visuo-proprioceptive information regarding hand position. A developmental trajectory analysis was carried out to explore the effect of age on condition. An age effect was only found in the incongruent condition which resulted in greater mislocalization of the hand toward the visual representation as age increased. Estimates by younger children were closer to the true location of the hand compared to those by older children indicating less weighting of visual information. Regression analyses showed localizations errors in the incongruent seen condition could not be explained by proprioceptive accuracy or by general attention or social differences. This suggests that the way in which visual and proprioceptive information are integrated optimizes throughout development, with the bias toward visual information increasing with age.

Quantitative assessment of the level of instability of a single-plane balance platform

BACKGROUND

Balance training on unstable surfaces is widely used in medicine and sports. The main disadvantage of balance platforms is weakly definable assessment of the level of instability (IL) they create.

OBJECTIVE

To evaluate the mechanical characteristics of a suspended single-plane instability balance platform which determines quantitative instability characteristics.

METHODS

Three criteria influencing the IL were evaluated: 1. The displacement of the platform board by changing the position of the object on the board; 2. Amount of force required for board displacement; 3. The vibration damping of the platform.

RESULTS

1. 1IL the displacement of the object on the board affected 0.66 cm. the displacement of the board relative to the platform frame; 2IL - 0.79 cm; 3IL - 0.91 cm.; 2. A force of 2.64 is required for a board displacement of 1IL compared to 2IL and 5.76 times that of 3IL. 3. Damping factor 1IL - 0.015, 2IL - 0.006, 3IL - 0.003.

CONCLUSIONS

1. The longer the suspension, the change in the position of the object on the board affects the greater movement of the board relative to the platform. 2. Different IL can be compared with each other depending on how different the force required to cause the board to move. 3. The platform dampens vibrations weakly, but the damping between 1 and 3 IL differs about 5 times.

Variability of visually-induced center of pressure displacements is reduced while young adults perform unpredictable saccadic eye movements inside a moving room

This study investigated the modulation of center of pressure (CoP) displacements of young adults as they performed predictable and unpredictable saccadic eye movements in stationary and moving visual scenarios. We also examined whether the relationship between CoP displacements and visual stimulus, provided by the moving scenario, and gaze control itself, are affected by the demands of the saccadic tasks. Fifteen young adults (20.53 ± 2.1 years old) stood upright on a force plate, inside a moving room, wearing an eye tracker while performing three tasks: gaze fixation (fixating on a target in the center of the screen), predictable task (saccades while following a target which continuously appeared and disappeared on the right and left sides), and unpredictable task (similar to the previous task, but the participants did not know which side the target would appear on). For saccadic tasks, the target appeared at a frequency of 1.1 Hz and with eccentricity of 11.5 degrees of visual angle. Two blocks of six trials were performed: in the first block, the room remained stationary and in the second, it oscillated (0.6 cm amplitude; 0.2 Hz frequency). Mean amplitude of CoP displacements was lower in the saccadic tasks compared to the gaze fixation, in both conditions; and higher in the moving scenario than in the stationary condition. Variability of CoP displacements was lower in the unpredictable saccades than gaze fixation task. Saccade reaction time was longer in the unpredictable than predictable task. We conclude that CoP displacements are reduced to facilitate performance of the saccadic tasks regardless of conditions and task complexity. Furthermore, lower variability suggests modulation of CoP displacements to deal with the increased attentional demands associated with the performance of the unpredictable saccades, indicating the important role of visual task constraints in postural control.

Postural sway in the moving room scenario: New evidence for functional dissociation between self-motion perception and postural control

Postural control in quiet standing is often explained by a reflexive response to optical flow, the apparent motion of environmental objects in a visual scene. However, moving room experiments show that even small-amplitude body sway can evoke odd sensations or motion sickness, indicating that a consciousness factor may also be involved. Studies targeting perception of self-motion, vection, typically use rapid visual stimuli moving in a single direction to maintain a constant feeling of vection, and there are few studies of vection using low-speed sinusoidal visual stimuli similar to human pendular movement. In the present study we searched for changes in postural control during periods of vection during quiet standing. Participants (N = 19, age = 20.4 ±1.1 years) were shown dynamic visual stimuli in the form of sinusoidally expanding and contracting random dots, and the stimuli speed and visual field were manipulated. Posture was continually evaluated using Center of Pressure (CoP) measurements. Participants were also asked to report feelings of vection, both by pressing a button during the trial and through an overall rating at the end of each trial. Using repeated-measures ANOVA, we assessed changes in the CoP and vection variables between experimental conditions, as well as possible interactions between the variables. The results show that postural reaction and vection were both affected by the visual stimuli and varied with speed. The peripheral visual field was found to couple to stronger feeling of vection and better quality of postural control. However, no significant relationship between postural control and vection, nor evidence of vection interaction to the relationship between optical flow and postural control, was found. Based on our results we conclude that for postural stability during quiet standing, visual cues dominate over any potential consciousness factor arising due to vection.

Multisensory postural control in adults: Variation in visual, haptic, and proprioceptive inputs

Maintaining balance is fundamentally a multisensory process, with visual, haptic, and proprioceptive information all playing an important role in postural control. The current project examined the interaction between such sensory inputs, manipulating visual (presence versus absence), haptic (presence versus absence of contact with a stable or unstable finger support surface), and proprioceptive (varying stance widths, including shoulder width stance, Chaplin [heels together, feet splayed at approximately 60°] stance, feet together stance, and tandem stance) information. Analyses of mean velocity of the Centre of Pressure (CoP) revealed significant interactions between these factors, with stability gains observed as a function of increasing sensory information (e.g., visual, haptic, visual + haptic), although the nature of these gains was modulated by the proprioceptive information and the reliability of the haptic support surface (i.e., unstable versus stable finger supports). Subsequent analyses on individual difference parameters (e.g., height, leg length, weight, and areas of base of support) revealed that these variables were significantly related to postural measures across experimental conditions. These findings are discussed relative to their implications for multisensory postural control, and with respect to inverted pendulum models of balance. (185 words).

Sex and age influence on postural sway during sit-to-stand movement in children and adolescents: Cross-sectional study

We investigated the influence of sex and age in postural sway during sit-to-stand (STS) in children and adolescents of 5-15 years. We evaluated sway during STS in 86 typical participants. STS was divided into three phases: preparation, rising, and stabilization. We calculated for each phase: area, anterior-posterior, and medial-lateral velocity of center-of-pressure sway. We applied a stepwise multiple linear regression model to determine if age and sex might be predictors of postural sway during STS. Only age was associated with sway, accounting for between 6.5% and 14.6% of the variability in sway during STS. The age of the subject influences postural sway during STS, but in a small amount. This variable should be taken into account as a variable of control in the assessment of dynamic postural control. Moreover, postural stability during STS was not associated with the sex of the participants.

Postural and Head Control Given Different Environmental Contexts

Virtual reality allows for testing of multisensory integration for balance using portable Head Mounted Displays (HMDs). HMDs provide head kinematics data while showing a moving scene when participants are not. Are HMDs useful to investigate postural control? We used an HMD to investigate postural sway and head kinematics changes in response to auditory and visual perturbations and whether this response varies by context. We tested 25 healthy adults, and a small sample of people with diverse monaural hearing (n = 7), or unilateral vestibular dysfunction (n = 7). Participants stood naturally on a stable force-plate and looked at 2 environments via the Oculus Rift (abstract "stars;" busy "street") with 3 visual and auditory levels (static, "low," "high"). We quantified medio-lateral (ML) and anterior-posterior (AP) postural sway path from the center-of-pressure data and ML, AP, pitch, yaw and roll head path from the headset. We found no difference between the different combinations of "low" and "high" visuals and sounds. We then combined all perturbations data into "dynamic" and compared it to the static level. The increase in path between "static" and "dynamic" was significantly larger in the city environment for: Postural sway ML, Head ML, AP, pitch and roll. The majority of the vestibular group moved more than controls, particularly around the head, when the scenes, especially the city, were dynamic. Several patients with monaural hearing performed similar to controls whereas others, particularly older participants, performed worse. In conclusion, responses to sensory perturbations are magnified around the head. Significant differences in performance between environments support the importance of context in sensory integration. Future studies should further investigate the sensitivity of head kinematics to diagnose vestibular disorders and the implications of aging with hearing loss to postural control. Balance assessment and rehabilitation should be conducted in different environmental contexts.

Perceptual-motor styles

Even for a stereotyped task, sensorimotor behavior is generally variable due to noise, redundancy, adaptability, learning or plasticity. The sources and significance of different kinds of behavioral variability have attracted considerable attention in recent years. However, the idea that part of this variability depends on unique individual strategies has been explored to a lesser extent. In particular, the notion of style recurs infrequently in the literature on sensorimotor behavior. In general use, style refers to a distinctive manner or custom of behaving oneself or of doing something, especially one that is typical of a person, group of people, place, context, or period. The application of the term to the domain of perceptual and motor phenomenology opens new perspectives on the nature of behavioral variability, perspectives that are complementary to those typically considered in the studies of sensorimotor variability. In particular, the concept of style may help toward the development of personalised physiology and medicine by providing markers of individual behaviour and response to different stimuli or treatments. Here, we cover some potential applications of the concept of perceptual-motor style to different areas of neuroscience, both in the healthy and the diseased. We prefer to be as general as possible in the types of applications we consider, even at the expense of running the risk of encompassing loosely related studies, given the relative novelty of the introduction of the term perceptual-motor style in neurosciences.

Postural mechanisms in moderate-to-severe cerebral palsy

People with moderate-to-severe cerebral palsy (CP) have the greatest need for postural control research yet are usually excluded from research due to deficits in sitting ability. We use a support system that allows us to quantify and model postural mechanisms in nonambulatory children with CP. A continuous external bench tilt stimulus was used to evoke trunk postural responses in seven sitting children with CP (ages 2.5 to 13 yr) in several test sessions. Eight healthy adults were also included. Postural sway was analyzed with root mean square (RMS) sway and RMS sway velocity, along with frequency response functions (FRF, gain and phase) and coherence functions across two different stimulus amplitudes. A feedback model (including sensorimotor noise, passive, reflexive, and sensory integration mechanisms) was developed to hypothesize how postural control mechanisms are organized and function. Experimental results showed large RMS sway, FRF gains, and variability compared with adults. Modeling suggested that many subjects with CP adopted "simple" control with major contributions from a passive and reflexive mechanism and only a small contribution from active sensory integration. In contrast, mature trunk postural control includes major contributions from sensory integration and sensory reweighting. Relative to their body size, subjects with CP showed significantly lower damping, three to five times larger corrective torque, and much higher sensorimotor noise compared with the healthy mature system. Results are the first characterization of trunk postural responses and the first attempt at system identification in moderate-to-severe CP, an important step toward developing and evaluating more targeted interventions.NEW & NOTEWORTHY Cerebral palsy (CP) is the most common cause of motor disability in children. People with moderate-to-severe CP are typically nonambulatory and have major impairments in trunk postural control. We present the first systems identification study to investigate postural responses to external stimulus in this population and hypothesize at how the atypical postural control system functions with use of a feedback model. People with moderate-to-severe CP may use a simple control system with significant sensorimotor noise.

People with persistent postural-perceptual dizziness demonstrate altered postural strategies in complex visual and cognitive environments

BACKGROUND

People with PPPD report imbalance, increase in symptoms and impaired function within complex visual environments, but understanding of the mechanism for these behaviors is still lacking.

OBJECTIVE

To investigate postural control in PPPD we compared changes in center of pressure (COP) and head kinematics of people with PPPD (N = 22) and healthy controls (N = 20) in response to different combinations of visual and cognitive perturbations during a challenging balance task.

METHODS

Participants stood in a tandem position. Static or moving stars (0.2 Hz, 5 mm or 32 mm amplitude, anterior-posterior direction) were displayed through a head-mounted display (HTC Vive). On half the trials, participants performed a serial-3 subtraction task. We measured medio-lateral and anterior-posterior path and acceleration of COP and head.

RESULTS

Controls significantly increased all COP and head parameters with the cognitive task whereas PPPD increased only COP ML path and acceleration. Only controls significantly increased head anterior-posterior & medio-lateral acceleration with moving visual load. Cognitive task performance was similar between groups.

CONCLUSIONS

We observed altered postural strategies in people with PPPD, in the form of reduced movement with challenge, particularly around the head segment. The potential of this simple and portable head-mounted display setup for differential diagnosis of vestibular disorders should be further explored.

Visuo-postural dependency index (VPDI) in human postural control

Background

Computerized stabilometry has been utilized to investigate the effect of vision on the neuromechanisms of human postural control. However, this approach lacks operational methods to quantify visual dependency during upright stance. This study had three goals: (1) To introduce the concept of visuo-postural dependency indices (VPDI) representing balance sway characteristics in multiple analytical domains (spatial, temporal, frequency, and structural), (2) To investigate the age and gender effects on VPDIs, and (3) To investigate the degree of relationships between VPDI and both subjective visual vertical and horizontal perception (SVV and SVH, respectively).

Methods

102 participants (16 to 80 years old) performed bipedal stances on a force platform with eyes open and closed. Response variables included the VPDIs computed for each postural index. In addition, 29 participants also performed SVV and SVH assessments.

Results

Fifteen VPDIs showed to be robust indicators of visual input modulation, and the variation across their magnitudes of modulation revealed a non-homogeneous response to changes in visual stimuli. Gender and age were not found to be a significant factor to VPDI modulation.

Conclusions

VPDIs revealed to be potential measures capable to quantitatively assess visuo-postural dependency and aid the assessment of fall risks and balance impairments.

Association between the level of attention and dual-task costs on postural sway and cognitive yield in children, adolescents, and young adults

BACKGROUND

Postural stability requires attentional resources. Dual-task paradigms are used to investigate the attentional demand of the studied tasks. However, no studies have been conducted on the subjects' level of attention, analyzing its association with dual-task costs (DTC).

RESEARCH QUESTION

To evaluate the attentional level and DTC on postural sway and cognitive yield in children, adolescents, and young adults, investigating age-related differences, and to analyze if the participants' attention level is associated with DTC.

METHODS

Postural sway and cognitive-yield of 30 children, 24 adolescents, and 32 young adults were assessed in a dual-task paradigm. We calculated DTC on postural sway and cognitive yield. Attention level was tested using Psychological Battery for Attention Assessment. We tested the association between DTC and attention level.

RESULTS

Young adults showed higher DTC on area and velocity of postural sway than children and adolescents. No differences in DTC on cognitive yield were found between the groups. Children showed lower attention levels than adolescents and young adults. Attention level was negatively associated with DTC on cognitive yield in young adults. Focused Attention is responsible for 24.4% of the variance in DTC on cognitive yield.

CONCLUSION

Age impacts DTC on postural stability, but not on cognitive performance. The smaller changes in sway found in children/adolescents when dual-tasking, potentially reflect less developed attentional levels and postural control, which make them performing postural tasks closed to their stability boundaries, and, therefore, make them prioritize stability protection more than adults. Similar DTC on cognition between groups may reflect an equalization of the chosen cognitive task at everyone's difficulty level. The lower attention levels of children may reflect an attentional system in development, with prioritization o postural tasks when dual-tasking to maintain stability. Although attention level increases throughout age, attention only predicted DTC on cognition. Better Focused Attention's levels predicted lower DTC on cognitive yield for young adults.

Neuromuscular performance of balance and posture control in childhood and adolescence

This study examined a potential age-dependency of both posture and stability (balance) control in children and adolescents in a healthy population. Body posture with open and closed eyes was examined for a total of 456 test persons (age 6.7–17.6 years. Posture parameters (posture index, upper body tilt, trunk tilt) were assessed in the sagittal plane. Additionally, the oscillation of the center of pressure with open and closed eyes was additionally analyzed in a sub-sample of 318 subjects.

Absolute values of stability control parameters changed significantly during childhood and adolescence for both boys (p = 0.005) and girls (p = 0.01). Relative changes of stability and posture parameters when closing the eyes did not change (p > 0.05) and were independent of age, gender or sports activity in healthy children and adolescents.

The shifting of the body segments towards each other, as a result of the loss of visual information, does not seem to be primarily responsible for the increase in COP fluctuation. This is a further indication that stability control and posture control are complex interdependent mechanisms whose interaction is not yet fully understood.

Sensory Reweighting During Bipedal Quiet Standing in Adolescents

A cross-sectional, prospective, between-subjects design was used in this study to establish the differences in sensory reweighting of postural control among different ages during adolescence. A total of 153 adolescents (five age groups; 13-17 years old) performed bipedal standing in three sensory conditions (i.e., with visual restriction, vestibular disturbance, and proprioceptive disturbance). Center of pressure displacement signals were measured in mediolateral and anteroposterior directions to characterize reweighting in the sensory system in static postural control when sensory information is disturbed or restricted during adolescent growth. The results indicate a development of postural control, showing large differences between subjects of 13-14 years old and older adolescents. A critical change was found in sensory reweighting during bipedal stance with disturbance of proprioceptive information at 15 years old. Adolescents of 13-14 years old showed less postural control and performance than older adolescents during the disturbance of proprioceptive information. Moreover, the results demonstrated that the visual system achieves its development around 15-16 years old. In conclusion, this research suggests that a difference of sensory reweighting under this type of sensorial condition and sensory reweight systems would seem to achieve stabilization at the age of 15.

Dyslexic children need more robust information to resolve conflicting sensory situations

The study involved investigating dyslexic children's postural control responses when visual and somatosensory cues were separately manipulated. Twenty dyslexic and 19 nondyslexic children performed a trial by standing upright inside a moving room and another by lightly touching a moving bar. Both trials lasted 240 s with the following three different stimulus characteristics: low (pretransition), high (transition), and low amplitude (posttransition). Body sway magnitude and the relationship between the movement of the room/bar surface and body sway were examined. When compared to nondyslexic children, dyslexic children oscillated with higher magnitude in the transition and posttransition under visual and somatosensory manipulation; their sway was more influenced by visual manipulation in the transition and posttransition, and they used higher applied force levels in the somatosensory modality in all conditions. The results suggest that dyslexic children could not efficiently reweight visual cues when compared to nondyslexic children. The same was not observed in the somatosensory cues when dyslexic children reduced the influence of the somatosensory stimulus. The proper use of somatosensory information was related to stronger acquired cues and higher applied forces as observed for dyslexic children. Dyslexic children experience difficulties in dynamically reweighting sensory cues although these types of difficulties are overcome when more informative sensory cues are provided.

A virtual reality head stability test for patients with vestibular dysfunction

BACKGROUND

The contribution of visual information to standing balance in patients with vestibular dysfunction varies between patients. Sensitive tools to detect kinematic response to visual perturbation are needed to individualize treatment.

OBJECTIVE

Using the Oculus Rift headset and sensors, we developed a novel virtual reality (VR) test of head stability (HST) in response to visual perturbation. During the test, head movements were tracked in six degrees-of-freedom. The purpose of this pilot study was to test the sensitivity of the VR_HST to differences between patients with vestibular dysfunction and controls.

METHODS

Seventeen patients and 16 controls performed static balance tasks with eyes closed (feet together or tandem on floor and foam) and observing 'moving stars' (amplitude 32 mm, frequency 0.2 Hz) via the Oculus (tandem). Directional Path and Root Mean Square Velocity were calculated for postural and head oscillations.

RESULTS

Postural sway differed significantly between groups when standing on foam with feet together and on floor while observing the 'moving stars' task. Head oscillations were larger among patients, primarily in pitch, yaw, and roll rotation.

CONCLUSIONS

The VR_HST was found to be sensitive to differences between small and diverse groups. Its clinical utility should be studied in larger samples of patients with vestibular dysfunction.

Weighting and reweighting of visual input via head mounted display given unilateral peripheral vestibular dysfunction

We translated a well-established laboratory paradigm to study sensory integration into a Head-Mounted-Display (HMD). In the current study, a group of 23 individuals with unilateral vestibular dysfunction and 16 age-matched controls observed moving spheres projected from the Oculus Rift. We confirmed increased visual weighting with an unstable surface and decreased visual weighting (i.e., reweighting) with increased visual amplitude. We did not observe significant differences in gains and phases between individuals with vestibular dysfunction and age-matched controls. The vestibular group increased sway in mid and high frequencies significantly more than controls with the change in surface or visual amplitude. Mild visual perturbations within HMDs carry the potential to become a useful portable assessment of postural control in individuals with vestibular disorders.

Control Mechanisms of Static and Dynamic Balance in Adults With and Without Vestibular Dysfunction in Oculus Virtual Environments

BACKGROUND

Deficits in sensory integration and fear of falling in complex environments contribute to decreased participation of adults with vestibular disorders. With recent advances in virtual reality technology, head-mounted displays are affordable and allow manipulation of the environment to test postural responses to visual changes.

OBJECTIVES

To develop an assessment of static and dynamic balance with the Oculus Rift and (1) to assess test-retest reliability of each scene in adults with and without vestibular hypofunction; (2) to describe changes in directional path and sample entropy in response to changes in visuals and surface and compare between groups; and (3) to evaluate the relation between balance performance and self-reported disability and balance confidence.

DESIGN

Test-retest, blocked-randomized experimental design.

SETTING

Research laboratory.

PARTICIPANTS

Twenty-five adults with vestibular hypofunction and 16 age- and sex-matched adults.

METHODS

Participants stood on the floor or stability trainers while wearing the Oculus Rift. For 3 moving "stars" scenes, they stood naturally. For a "park" scene, they were asked to avoid a virtual ball. The protocol was repeated 1-4 weeks later.

OUTCOME

Anteroposterior and mediolateral center-of-pressure directional path and sample entropy were derived from a force plate.

RESULTS

We observed good to excellent reliability in the 2 groups, with most intraclass correlations above 0.8 and only 2 at approximately 0.4. The vestibular group had higher directional path for the stars scenes and lower directional path for the park scene compared with controls, with large variability in the 2 groups. Sample entropy decreased with more challenging environments. In the vestibular group, less balance confidence strongly correlated with more sway for the stars scenes and less sway for the park scene.

CONCLUSION

Virtual reality paradigms can shed light on the control mechanism of static and dynamic postural control. Clinical utility and implementation of our portable Oculus Rift assessment should be further studied.

LEVEL OF EVIDENCE

II.

Alterations of Functional Brain Connectivity After Long-Duration Spaceflight as Revealed by fMRI

The present study reports alterations of task-based functional brain connectivity in a group of 11 cosmonauts after a long-duration spaceflight, compared to a healthy control group not involved in the space program. To elicit the postural and locomotor sensorimotor mechanisms that are usually most significantly impaired when space travelers return to Earth, a plantar stimulation paradigm was used in a block design fMRI study. The motor control system activated by the plantar stimulation involved the pre-central and post-central gyri, SMA, SII/operculum, and, to a lesser degree, the insular cortex and cerebellum. While no post-flight alterations were observed in terms of activation, the network-based statistics approach revealed task-specific functional connectivity modifications within a broader set of regions involving the activation sites along with other parts of the sensorimotor neural network and the visual, proprioceptive, and vestibular systems. The most notable findings included a post-flight increase in the stimulation-specific connectivity of the right posterior supramarginal gyrus with the rest of the brain; a strengthening of connections between the left and right insulae; decreased connectivity of the vestibular nuclei, right inferior parietal cortex (BA40) and cerebellum with areas associated with motor, visual, vestibular, and proprioception functions; and decreased coupling of the cerebellum with the visual cortex and the right inferior parietal cortex. The severity of space motion sickness symptoms was found to correlate with a post- to pre-flight difference in connectivity between the right supramarginal gyrus and the left anterior insula. Due to the complex nature and rapid dynamics of adaptation to gravity alterations, the post-flight findings might be attributed to both the long-term microgravity exposure and to the readaptation to Earth's gravity that took place between the landing and post-flight MRI session. Nevertheless, the results have implications for the multisensory reweighting and gravitational motor system theories, generating hypotheses to be tested in future research.

Postural control adaptation to optic flow in children and adults with autism spectrum disorder

BACKGROUND

Sensory reweighting is important for humans to flexibly up-weigh and down-weigh sensory information in dynamic environments. There is an element of time involved in the sensory reweighting process. A longer time spent on sensory reweighting may increase the destabilizing effect of postural control. Individuals with autism spectrum disorder (ASD) are reported to have poor postural control. It is uncertain if a different sensory reweighting process underlies the postural control deficit in children and adults with ASD.

RESEARCH QUESTION

To explore the sensory reweighting capability in ASD, the present study examined whether the temporal domains of postural control differed in children and adults, with and without ASD under various optic flow conditions.

METHODS

Thirty-three children (8-12 years old) and 33 adults (18-50 years old) with and without ASD underwent quiet standing in six radial optic flow conditions. Each condition lasted for 60 s and was shown twice to all participants. For each optic flow condition, changes in postural response within-trial and between-trials were measured.

RESULTS

Under various optic flow illusions, both children with and without ASD took a longer time to restore their posture compared with adults with and without ASD. Nonetheless, all groups demonstrated comparable abilities to adjust their posture to one that is close to the baseline position after one exposure to the optic flow stimulation.

SIGNIFICANCE

The present study showed that the temporal domains of postural control under different optic flow conditions were similar between individuals with and without ASD from the same age group. The ability to down-weigh visual information efficiently comes with the developmental progression of the sensory reweighting system. These findings suggest that the sensory reweighting process does not elucidate the postural control deficits in individuals with ASD and thus alternative explanations to determine the underlying mechanism for postural instability are needed.

Assessment via the Oculus of Visual "Weighting" and "Reweighting" in Young Adults

Substantial advances in virtual reality technology open an exciting window toward better understanding of subdomains of balance control. Here, we studied whether a portable virtual reality headset can be used to test sensory integration for balance. Twenty young adults stood on a both-sides-up ball or floor. Moving spheres were projected from an Oculus Development Kit 2 at various amplitudes and frequencies. Participants' gains indicated visual "weighting" when standing on both-sides-up but not on the floor and "reweighting" with increased visual amplitude. Intraclass correlations showed acceptable to good reliability for all floor conditions and for some of the both-sides-up conditions when we repeated the protocol a week later. Future steps to further develop our paradigm into a clinical assessment of sensory integration for postural control are discussed.

Optical Flow Structure Effects in Children's Postural Control

The aim of this study was to investigate the effect of distance and optic flow structure on visual information and body sway coupling in children and young adults. Thirty children (from 4 to 12 years of age) and 10 young adults stood upright inside of a moving room oscillating at 0.2 Hz, at 0.25 and 1.5 m from the front wall, and under three optical flow conditions (global, central, and peripheral). Effect of distance and optic flow structure on the coupling of visual information and body sway is age-dependent, with 4-year-olds being more affected at 0.25 m distance than older children and adults are. No such difference was observed at 1.5 m from the front wall. Moreover, 4-year-olds' sway was larger and displayed higher variability. These results suggest that despite being able to accommodate change resulting from varying optic flow conditions, young children have difficulty in dodging stronger visual stimuli. Lastly, difference in sway performance may be due to immature inter-modality sensory reweighting.