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A recent study in active-duty military in the Coast Guard suggested that lifetime experience with mild traumatic brain injury (mTBI) was associated with subtle deficits in postural control when exposed to multi-sensory discordance (i.e., rotating visual stimulation). The present study extended postural assessments to veterans recruited from the community. Service veterans completed the Defense Veteran Brain Injury Center TBI Screening Tool, Post-Traumatic Stress Disorder (PTSD) Checklist (PCL-5), and Neurobehavioral Symptom Inventory (NSI). Postural control was assessed using a custom-designed, virtual-reality-based device, which assessed center of pressure sway in response to six conditions designed to test sensory integration by systematically combining three visual conditions (eyes open, eyes closed, and rotating scene) with two somatosensory conditions (firm or foam surface). Veterans screening positive for lifetime experience of mTBI (mTBI

The Color Trails Test ("CTT") is among the most popular neuropsychological assessment tests of executive function, targeting sustained visual attention (Trails A), and divided attention (Trails B). During the pen-and-paper (PP) test, the participant traces 25 consecutive numbered targets marked on a page, and the completion time is recorded. In many cases, multiple assessments are performed on the same individual, either under varying experimental conditions or at several timepoints. However, repeated testing often results in learning and fatigue effects, which confound test outcomes. To mitigate these effects, we set the grounds for developing shorter versions of the CTT (25 targets), using virtual reality (VR) based CTT (VR-CTT). Our aim was to discover the minimal set of targets that is sufficient for maintaining concurrent validity with the CTT including differentiation between age groups, and the difference between Trails A and B. To this aim, healthy participants in three age groups (total

Exoskeleton devices can reduce metabolic cost, increase walking speed, and augment load-carrying capacity. However, little is known about the effects of powered assistance on the sensory information required to achieve these tasks. To learn how to use an assistive device, humans must integrate novel sensory information into their internal model, but under certain sensory conditions, this may present a challenge. We investigated the exoskeleton-induced changes in balance performance and the sensory system adaptations during quiet standing. We asked 11 unimpaired adults to perform a virtual reality-based test of sensory integration in balance (VRSIB) on two days while wearing the exoskeleton either unpowered, using proportional myoelectric control, or with regular shoes. We measured postural sway, equilibrium scores, and sensory ratios. In addition, we measured postural control strategy, joint kinematics and kinetics, and muscle activity. Results showed improvement in balance performance when wearing the exoskeleton on firm ground. The opposite occurred when standing on an unstable platform with eyes closed or when the visual information was non-veridical. The balance performance was equivalent when the exoskeleton was powered versus unpowered in all conditions except when both the support surface and the visual information were altered. We argue that in stable ground the passive stiffness of the device dominates the postural task. In contrast, when the ground becomes unstable the passive stiffness negatively affects balance performance. Furthermore, when the visual input to the user is non-veridical, exoskeleton assistance can magnify erroneous muscle inputs and negatively impact the user's postural control.

The objective of this study was to explore the correlation between preseason measures of cervical sensorimotor function and musculoskeletal injury rates across a contact sport season. The authors hypothesized that athletes with higher sensorimotor dysfunction at baseline would be more likely to suffer an injury. The authors further hypothesized that contact sport participation would lead to greater changes in cervical sensorimotor function across a sport season compared with noncontact controls. Forty-nine collegiate club athletes (26 rugby and 23 noncontact controls) participated in a cohort study. Low positive correlations between baseline sign and symptom severity (r = .383), and score (r = .344), and cervical joint position error (r = .385–.425) and time loss injury were observed. Combining sign and symptom severity score and the neck reposition error predicted musculoskeletal injury status with 80.8% accuracy (area under the curve = 0.80, p = .003). The results suggest preseason deficits in cervical sensorimotor function may be related to future musculoskeletal injury risk. Sign and symptom severity score, Neck Disability Index score, and cervical joint position error can help identify athletes requiring more comprehensive cervical spine assessment that may benefit from preventative intervention.

Objective: Identify cervical sensorimotor function differences between amateur athletes with and without a history of contact sport participation. A secondary aim of the study was to explore the as...

Background Life expectancy of the U.S. population will continue to rise, increasing the workforce demands in the treatment of musculoskeletal pathologies. With a declining primary care physician workforce, physical therapists (PT) may be in a unique situation to help absorb this demand. Objective Our primary objective was to compare physical function between two primary care groups, a "physical therapy-led pathway" versus "physician-led pathway" in the management of recent-onset musculoskeletal pain at 1-month follow-up. Our secondary objectives were to compare other patient-important outcomes between the groups at 1 month and health utilization at 1 month and 1 year. Methods A pragmatic randomized controlled trial with a 1-year follow-up was conducted, enrolling 150 university employees with recent onset musculoskeletal pain. Participants were randomized at first contact to either a PT-led pathway or physician-led pathway. The primary outcome was change in Patient-Reported Outcomes Measurement Information System (PROMIS) ShortForm v1-Physical Function 10a at 1 month; groups were compared with repeated measurement of analysis of variance and chi-square for both primary and secondary outcomes, except for satisfaction score at 1 month, which was cross-sectionally compared by independent two-sample t-test. At 1 year, healthcare utilization was assessed through medical record extraction, and healthcare utilization was converted to total episodic standard cost. Utilization was compared between groups using chi-square and Wilcoxon rank-sum tests. Results Both groups demonstrated improvement at 1-month follow-up but showed no significant between-group difference in mean PROMIS scores at 1 month (PT-led pathway vs physician-led pathway, 2.04, [95% CI -0.28 to 4.36]; P = .082). At 1 year, there was no difference in healthcare utilization or cost between groups. No harm or misdiagnosis was found, filed, or reported by participants at 1 year. Conclusion This study shows equivalence in outcomes for two low-cost musculoskeletal care pathways with no risk of harm. These results reinforce other findings in the literature that support PTs as safe and effective initial providers for individuals with musculoskeletal disorders.

Background: Postural stability depends on the integration of multisensory inputs to drive motor outputs. When visual and somatosensory input is available and reliable, this reduces the postural control system’s reliance on the vestibular system. Despite this, vestibular loss can still cause severe postural dysfunction (1,2). Training one or more of the three sensory systems can alter sensory weighting and change postural behavior. Vestibular activation exercises, including horizontal and vertical headshaking, influence vestibular-ocular and -motor responses and have been showed to be effective in vestibular rehabilitation (3–8). Purpose/Hypothesis: To assess sensory reweighting of postural control processing and vestibular-ocular and -motor responses after concurrent vestibular activation with postural training. It was hypothesized that the effect of this training would significantly alter the pattern of sensory weighting by changing the ratio of visual, somatosensory and vestibular dependence needed to maintain postural stability, and significantly decrease vestibular responses. Methods: Forty-two young healthy individuals (22 females; 23.0+3.9 years; 1.6+0.1 meters) were randomly assigned into four groups: 1) visual feedback weight shift training (WST) coupled with an active horizontal headshake (HHS), 2) same WST with vertical headshake (VHS), 3) WST with no headshake (NHS) and 4) no training/headshake control (CTL) groups. The headshake groups performed an intensive body WST together with horizontal or vertical rhythmic headshake at 80 to 120 beats/minute. The NHS group performed the WST with no headshake while the controls did not perform any training. Five 15-minute training sessions were performed on consecutive days for one week with the weight shift exercises involving upright limits of stability activities on a flat surface, foam or rocker board (Fig. 1). All groups performed baseline- and post-assessments including sensory organization test (SOT) and force platform ramp perturbations, coupled with electromyographic (EMG) recordings. A video head impulse test was also used to record horizontal vestibulo-ocular reflex (VOR) gain. A between- and within-group repeated measures ANOVA was used to analyze five COP sway variables, the equilibrium and composite scores and sensory ratios of the SOT as well as EMG signals and horizontal VOR gain. Similarly, COP variables, EMG, as well as vestibular reflex data (vertical VOR, vestibulo-collic reflex [VCR] and vestibulo-spinal [VSR] gains) during ramp perturbations were analyzed. Alpha level was set at p

To compare the scaling of the postural stability variables between older nonfallers and fallers during gait initiation (GI) while stepping over increasing obstacle distances.Cross-sectional study.University research laboratory.A sample of participants (N=24) divided into 2 groups: older nonfallers (n=12) and older fallers (n=12). Participants had no known neurologic, musculoskeletal, or cardiovascular conditions that could have affected their walking, and all were independent walkers. All the participants had an adequate cognitive function to participate as indicated by a score of more than 24 on the Mini-Mental State Examination.Not applicable.The primary dependent variables were peak anterior-posterior (AP) center of mass (CoM)-center of pressure (CoP) separation during anticipatory postural adjustments (APAs), AP CoM-CoP separation at the toe-off, and peak AP CoM-CoP separation during the swing. Secondary dependent variables were AP trunk angle during GI. Within- and between-repeated measures analysis of variance was used to compare means between groups across different task conditions for all the dependent variables.There was a main effect of group for peak AP CoM-CoP separation during APA (P=.018), an interaction effect between group and condition for AP CoM-CoP separation at toe-off (P=.009), and a main effect of condition for peak AP CoM-CoP separation during the swing (P.001). We also found a main effect of group for peak AP trunk angle during the swing (P=.028).For GI while stepping over increasing obstacle distances, older fallers adopt a more conservative strategy of AP CoM-CoP separation than nonfallers prior to toe-off and demonstrate increased peak AP trunk lean during the swing. AP CoM-CoP separation prior to toe-off during the GI task may be a critical marker to identify fallers and warrants additional investigation.

Vestibular and oculomotor testing is emerging as a valuable assessment in sport-related concussion (SRC). However, their usefulness for tracking recovery and guiding return-to-play decisions remains unclear. Therefore the purpose of this study was to evaluate their clinical usefulness for tracking SRC recovery. Vestibular and oculomotor assessments were used to measure symptom provocation in an acute group (n=21) concussed≤10 days, prolonged symptoms group (n=10) concussed ≥16 days (median=84 days), healthy group (n=58) no concussions in >6 months. Known-groups approach was used with three groups at three time points (initial, 2-week and 6-week follow-up). Provoked symptoms for Gaze-Stabilization (GST), Rapid Eye Horizontal (REH), Optokinetic Stimulation (OKS), Smooth-Pursuit Slow (SPS) and Fast (SPF) tests, total combined symptoms scores and near point convergence (NPC) distance were significantly greater at initial assessment in both injury groups compared to controls. Injury groups improved on the King-Devick test and combined symptom provocation scores across time. The acute group improved over time on REH and SPF tests, while the prolonged symptoms group improved on OKS. A regression model (REH, OKS, GST) was 90% accurate discriminating concussed from healthy. Vestibular and ocular motor tests give valuable insight during recovery. They can prove beneficial in concussion evaluation given the modest equipment, training and time requirements. The current study demonstrates that when combined, vestibular and oculomotor clinical tests aid in the detection of deficits following a SRC. Additionally, tests such as NPC, GST, REH, SPS, SPF OKS and KD provide valuable information to clinicians throughout the recovery process and may aid in return to play decisions.

Traumatic brain injury by gunshot creates a variety of unique sequelae that can be very challenging for clinicians to develop rehabilitation interventions. This case report presents an example of supplementing traditional physical therapy with virtual reality training for a patient who suffered a penetrating traumatic brain injury to the back of the head. By personalizing and modulating the virtual scenes to the patient’s deficits and tolerance for virtual reality exposure, the patient was able to progress in his rehabilitation, which had plateaued after traditional therapy alone. At the conclusion of his rehabilitation, the patient showed clinically meaningful improvements in functional mobility assessments and subjective self-reports.

Objective: To investigate whether shifts in head position, measured via an Oculus Rift head-mounted display (HMD), is a valid measure of whole-body postural stability. Background: The inverted single-link pendulum model of balance suggests shifts in whole-body center of mass can be estimated from individual body segments. However, whether head position describes postural stability such as center-of-pressure (COP) remains unclear. Method: Participants ( N = 10) performed six conditions while wearing an HMD and performing a previously validated virtual reality (VR)-based balance assessment. COP was recorded with a Wii Balance Board force plate (WBB), while an HMD recorded linear and angular head displacement. Visual input was presented in the HMD (stable scene, dark scene, or dynamic scene) and somatosensory information (with or without foam) was varied across each condition. The HMD time series data were compared with the criterion-measure WBB. Results: Significant correlations were found between COP measures (standard deviation, range, sway area, velocity) and head-centered angular and linear displacements (roll, pitch, mediolateral and anteroposterior directions). Conclusions: The Oculus Rift HMD shows promise as a measure of postural stability without additional posturography equipment. These findings support the application of VR HMD technology for assessment of postural stability across a variety of challenging conditions. Application: The human factors and ergonomic benefit of such an approach is in its portability, low cost, and widespread availability for clinic and home-based investigation of postural disturbances. Fall injury affects millions of people annually, so assessment of fall risk and treatment of the underlying causes has enormous public health benefit.

Many field sports involve equipment that restricts one or both arms from moving while running. Arm swing during running has been examined from a biomechanical and physiologic perspective but not from an injury perspective. Moreover, only bilateral arm swing suppression has been studied with respect to running. The purpose of this study was to determine the influence of running with one arm restrained on lower extremity mechanics associated with running or sport-related injury. Fifteen healthy participants ran at a self-selected speed with typical arm swing, with one arm restrained and with both arms restrained. Lower extremity kinematics and spatiotemporal measures were analysed for all arm swing conditions. Running with one arm restrained resulted in increased frontal plane knee and hip angles, decreased foot strike angle, and decreased centre of mass vertical displacement compared to typical arm swing or bilateral arm swing restriction. Stride length was decreased and step frequency increased when running with one or both arms restrained. Unilateral arm swing restriction induces changes in lower extremity kinematics that are not similar to running with bilateral arm swing restriction or typical arm swing motion. Running with one arm restrained increases frontal plane mechanics associated with risk of knee injury.

Objective: Postural control is frequently compromised after sub-concussive and concussive head trauma, and balance testing is an integral part of neuromotor assessment and management. The main objective of this paper is to develop a novel smartphone-based neuromotor assessment protocol for screening of dynamic balance decrements stemming from head trauma. Approach: Experiments 1 and 2 compared Android smartphone orientation detection algorithms to a biomechanics laboratory motion capture system using a pendulum (i.e. non-biological movement) and a human stepping task (i.e. biological movement). Experiment 3 examined the test-retest reliability of a stepping-in-place protocol in three different sensory conditions (eyes open, no-vision, head shake) using temporal and spatial variability metrics extracted from thigh orientation signal in a sample of healthy young adults. Main results: Smartphone sensors provided valid measurements of movement timing and amplitude variables. However, sensor firmware version and Android OS version significantly affected quality of measurement. High test-retest reliability was shown for the temporal and spatial variables of interest during the stepping-in-place task. Significance: Collectively, these experiments show that our smartphone application is a valid and reliable way to measure leg movement characteristics (mean stride time and its variability (CV), Peak Thigh SD, Thigh ROM, and Peak Return Velocity) during dynamic balance activity, which could provide an objective way to assess neuromotor function after head trauma and in other populations with balance dysfunction.

This study aimed to determine the acuity of head and neck position sense in a novel joint position matching paradigm using a head-mounted virtual reality display. The results show that the head-neck position sense acuity of healthy adults is generally within three degrees on matching trials and that acuity increases as the joint angle increases.

Postural control and stress reactivity were investigated in active duty coast guard personnel to determine whether they are sensitive to lifetime effects of mild traumatic brain injury (mTBI). A custom-designed and validated virtual reality-based computerized posturography device was used to assess postural stability, whereas emotional reactivity was assessed using the acoustic startle response (ASR), and neurocognitive performance was assessed using the defense-automated neurobehavioral assessment (DANA). It was hypothesized that residual and subtle postural control imbalance and deficits in cognitive and sensory reactivity would be evident in those reporting multiple lifetime mTBI. Active duty military personnel (N = 36; 7 females and 29 males) with no Deployment Limiting Medical Condition were recruited and tested on all assessments. Medical history information provided a history of head injury. Thirty-nine percent of participants reported having a previous mTBI (nine reporting one and five reporting more than one incident). No participant had experienced a head injury within the past year and all were symptom free. A significant effect of number of mTBI was found in the postural assessment (p = 0.002). Lifetime mTBI was associated with suppressed ASR magnitude (p = 0.03) but did not affect neurocognitive performance. The current findings provide new insight into ongoing controversies concerning sensitivity to functional deficits following mTBI and when the window for treatment or restoration ends.

Blast exposure is a prevalent cause of mild traumatic brain injury (mTBI) in military personnel in combat. However, it is more common for a service member to be exposed to a low-level blast (LLB) that does not result in a clinically diagnosable mTBI. Recent research suggests that repetitive LLB exposure can result in symptomology similar to symptoms observed after mTBI. This manuscript reports on the use of an Android-based smartphone application (AccWalker app) to capture changes in neuromotor functioning after blast exposure. Active duty U.S. Navy personnel (N = 59) performed a stepping-in-place task before repetitive LLB exposure (heavy weapons training), and again immediately after, 24 hours after, and 72 to 96 hours after the completion of the training. The AccWalker app revealed that there are changes in neuromotor functioning after LLB exposure (slower self-selected movement pace and increased stride time variability) in participants who experienced neurocognitive decline. These data suggest that neurocognitive and neuromotor decline can occur after repeated LLB exposure.

Introduction Progressive supranuclear palsy (PSP) is characterized by early postural instability and backward falls. The mechanisms underlying backward postural instability in PSP are not understood. The aim of this study was to test the hypothesis that postural instability in PSP is a result of dysfunction in the perception of postural verticality. Methods We gathered posturography data on 12 subjects with PSP to compare with 12 subjects with idiopathic Parkinson’s Disease (PD) and 12 healthy subjects. Objective tests of postural impairment included: dynamic sensory perception tests of gravity and of surface oscillations, postural responses to surface perturbations, the sensory organization test of postural sway under altered sensory conditions and limits of stability in stance. Results Perception of toes up (but not toes down) surface tilt was reduced in subjects with PSP compared to both control subjects (p≤0.001 standing, p≤0.007 seated) and subjects with PD (p≤0.03 standing, p≤0.04 seated). Subjects with PSP, PD and normal controls accurately perceived the direction of gravity when standing on a tilting surface. Unlike PD and control subjects, subjects with PSP exerted less postural corrective torque in response to toes up surface tilts. Discussion Difficulty perceiving backward tilt of the surface or body may account for backward falls and postural impairments in patients with PSP. These observations suggest that abnormal central integration of sensory inputs for perception of body and surface orientation contributes to the pathophysiology of postural instability in PSP.

Balance impairment is a common sensorimotor symptom in mild traumatic brain injury (mTBI). We designed an affordable, portable virtual reality (VR)-based balance screening device (Virtual Environment TBI Screen [VETS]), which will be validated relative to the Neurocom Sensory Organization Test (SOT) to determine if it can replace commonly used postural assessments.This preliminary study examines healthy adults (n = 56) and adults with mTBI (n = 11). Participants performed six upright postural tasks on the VETS and the SOT. Analysis of variance was used to determine between-group differences. Pearson's correlations were used to establish construct validity. Known-groups approach was used to establish classification accuracy.The mTBI cohort performed significantly worse than the healthy cohort on the new device (p = 0.001). The new device has 91.0% accuracy and an ROC curve with a significant area-under-the-curve (AUC = 0.865, p 0.001). Conditions with dynamic visual stimulation were the most sensitive to health status. The SOT had an 84.8% accuracy and AUC =0.703 (p = 0.034).The new VR-based device is a valid measure for detecting balance impairment following mTBI and can potentially replace more expensive and cumbersome equipment. Assessments that test visual-vestibular processing, such as VETS, increase sensitivity to mTBI-related balance deficits, which can be used to guide rehabilitation. Implications for rehabilitation Emerging technology using virtual reality can be economically integrated into the clinical setting for easy testing of postural control in neurologically impaired populations. Tailoring postural assessments to include tasks that rely on visual and vestibular integration will increase the accuracy of detecting balance impairment following mild traumatic brain injury.

Impaired arm swing is a common motor symptom of Parkinson's disease (PD), and correlates with other gait impairments and increased risk of falls. Studies suggest that arm swing is not merely a passive consequence of trunk rotation during walking, but an active component of gait. Thus, techniques to enhance arm swing may improve gait characteristics. There is currently no portable device to measure arm swing and deliver immediate cues for larger movement. Here we test report pilot testing of such a device, ArmSense (patented), using a crossover repeated-measures design. Twelve people with PD walked in a video-recorded gym space at self-selected comfortable and fast speeds. After baseline, cues were given either visually using taped targets on the floor to increase step length or through vibrations at the wrist using ArmSense to increase arm swing amplitude. Uncued walking then followed, to assess retention. Subjects successfully reached cueing targets on >95% of steps. At a comfortable pace, step length increased during both visual cueing and ArmSense cueing. However, we observed increased medial-lateral trunk sway with visual cueing, possibly suggesting decreased gait stability. In contrast, no statistically significant changes in trunk sway were observed with ArmSense cues compared to baseline walking. At a fast pace, changes in gait parameters were less systematic. Even though ArmSense cues only specified changes in arm swing amplitude, we observed changes in multiple gait parameters, reflecting the active role arm swing plays in gait and suggesting a new therapeutic path to improve mobility in people with PD.

Dynamic signals from multiple sensory channels must be integrated by the central nervous system to create a unified perception of self-motion and spatial orientation. Using immersive virtual environments, we altered the relative contribution of visual and inertial inputs and evaluated the effects on perceptuomotor outputs. Subjects seated in a tilting chair were exposed to a combined 0.25 Hz sinusoidal roll-tilt (+/-7.5 degrees) about the naso-occipital axis while viewing one of four visual conditions. One visual condition was in darkness, and the other three depicted 2 m of sinusoidal horizontal or vertical linear motion either synchronous or asynchronous with the roll-tilt. Subjects performed a perceptuomotor task of aligning a handheld object to gravitational vertical (GV) with the entire arm being free to move in six degrees of freedom. Subjects were tested with two objects, a joystick and glass of water, in counter-balanced order. Specific visual effects were as follows: (1) the phase leads of object tilt relative to chair/subject roll-tilt were affected by visual condition, (2) horizontal translation of the object was entrained with visual velocity, rather than with visual acceleration or maximum roll-tilt, and (3) when vertical visual motion was viewed during chair/subject roll-tilt, vertical object translation increased. Although the head-fixed scene meant visual vertical cues were always aligned with the subject's median sagittal plane, object tilt showed sensitivity to inertial roll-tilt (Gain0.5) which was not significantly different from the dark condition. Two object effects were found: (1) tilt deviation from GV was greater when wielding a joystick compared to a full glass of water, and (2) the phase of horizontal visual motion relative to subject roll tilt affected the joystick amplitude of horizontal translation but not the glass of water. In conclusion, an attentional shift driven by postural assumptions can account for the two object effects, however, the visual effects suggest that a process for deriving the net gravitoinertial force from visual and inertial cues is involved. Inertial signals dominated the perception of verticality, but visual linear translation affected the spatiotemporal dynamics of the manual motor responses during object wielding.

Mild traumatic brain injury (mTBI) following a head impact or blast exposure can cause diffuse injury to the brain, which can affect sensorimotor, cognitive, and emotional processes. Among the most common sensorimotor symptoms of mTBI is balance impairment. A commonly used assessments of balance following mTBI is the sensory organization test (SOT). This test has shown that postural deficits following head injury may be due to visual-vestibular processing issues, but it is less sensitive to unremitting symptoms that do not spontaneously resolve within a week. Our current project involves demonstrating validity and reliability of a novel low-cost, portable virtual reality-based balance screening device that employs established principles of sensorimotor reweighting and visual-vestibular integration. The goal is to determine if it can replace existing tools that are either prohibitively expensive or lack reliability or sensitivity. Methods: Healthy adults with no known musculoskeletal or neurological injury (n=27; 17 males, 10 females; 22.1+3.9 years) were tested to establish healthy norms. Individuals with mTBI (n=8; 4 males, 4 females; 20.0+1.7 years) were compared to the healthy norms. The new VR-based balance assessment system consists of a Wii balance board (WBB), a large screen television, and a custom-designed software user interface used to collect and process data. Subjects performed six upright postural tasks (three visual conditions either standing directly on the WBB or on foam placed on the WBB). Subjects viewed a virtual reality scene displayed on a 60" television. The three visual conditions were Static Scene, Dark Scene, and Dynamic Scene (Roll at 60 deg/s). The WBB recorded COP at 100Hz for 30 sec. Dependent variables included COP velocity, root mean square, and sway area. Subjects also performed the sensory organization test (SOT), which can be used as criterion-measures for intraclass correlations with the new device. Results: Preliminary data on healthy subjects validates effectiveness of the device to reduce postural stability as sensory input reliability and availability decreases. Additionally, ur results reveal that individuals with mTBI have significantly worse balance scores on the new VR-device (p

We evaluated the influence of moving visual scenes and knowledge of spatial and physical context on visually induced self-motion perception in an immersive virtual environment. A sinusoidal, vertically oscillating visual stimulus induced perceptions of self-motion that matched changes in visual acceleration. Subjects reported peaks of perceived self-motion in synchrony with peaks of visual acceleration and opposite in direction to visual scene motion. Spatial context was manipulated by testing subjects in the environment that matched the room in the visual scene or by testing them in a separate chamber. Physical context was manipulated by testing the subject while seated in a stable, earth-fixed desk chair or in an apparatus capable of large linear motions, however, in both conditions no actual motion occurred. The compellingness of perceived self-motion was increased significantly when the spatial context matched the visual input and actual body displacement was possible, however, the latency and amplitude of perceived self-motion were unaffected by the spatial or physical context. We propose that two dissociable processes are involved in self-motion perception: one process, primarily driven by visual input, affects vection latency and path integration, the other process, receiving cognitive input, drives the compellingness of perceived self-motion.

Postural control is commonly assessed by quantifying center of pressure (CoP) variability during quiet stance. CoP data is traditionally filtered prior to analysis. However, some researchers suggest filtering may lead to undesirable consequences. Further, sampling frequency may also affect CoP analysis, as filtering CoP signals of different sampling frequencies may influence variability metrics. This study examined the influence of sampling frequency and filtering on metrics that index the magnitude and structure of variability in CoP displacement and velocity. Healthy adults (N = 8, 27.4 ± 2.6 years) balanced on their right foot for 60 s on a force plate. CoP data recorded at 100 Hz was then downsampled and/or filtered (2nd order dual-pass 10 Hz low-pass Butterworth) to create six different CoP time series for each participant: (1) original, (2) filtered, (3) downsampled to 50 Hz, (4) downsampled to 25 Hz, (5) downsampled to 50 Hz and filtered, and (6) down-sampled to 25 Hz and filtered. Data were then analyzed using four common variability metrics (standard deviation [SD], root mean square [RMS], detrended fluctuation analysis α [DFA α], and sample entropy [SampEn]). Data processing techniques did not influence the magnitude of variability (SD and RMS), but did influence the structure of variability (DFA α and SampEn) in CoP displacement. All metrics were influenced by data processing techniques in CoP velocity. Thus, when interpreting changes in CoP variability, one must be careful to identify how much change is driven by the neuromotor system and how much is a function of data processing technique.

Spatial frameworks are a class of spatial mental model that code locations of objects relative to the body axes. Spatial frameworks predict accessibility of spatial relations from memory primarily on the basis of the relative asymmetry of the body axes, such that highly asymmetric axes lead to faster retrieval of information. The present research examined how bodily asymmetries affect retrieval. Experiment 1 contrasted two theoretical accounts. The Salience Account proposes that relative degrees of asymmetry render axes differentially salient, and hence differentially foregrounded in one's mental model. The Direction Decision Account proposes that an explicit decision process is necessary to access specific locations along body axes. The ease of the decision process presumably depends on the degree of asymmetry that exists to discriminate poles along a body axis. The spatial framework pattern of accessibility was observed both when subjects identified specific directions of objects and when subjects identified just the axis to which objects were associated, supporting the Salience Account. Experiment 2 investigated whether lateralization affects accessibility from spatial frameworks. Performance of highly lateralized individuals did not differ from that of weakly lateralized individuals.

This chapter deals with the issue of resolving ambiguity between motion of objects in the world and self-motion that reflects the interdependence between multimodal signals. A growing body of evidence suggests that visual, vestibular, nonvisual, and non-vestibular aspects of virtual world immersion play an important role in self-motion perception. In this chapter, five experts from the fields of postural and locomotor control present the work they have engaged in to understand how the brain uses multiple pathways of sensory feedback to organize movement behavior. Each will discuss their work showing how VR may help us understand or engage the mechanisms underlying sensorimotor integration.

Previous work has shown that fractal patterns in gait can be altered by entraining to a fractal stimulus. However, little is understood about how long those patterns are retained or which factors may influence stronger entrainment or retention. In experiment one, participants walked on a treadmill for 45 continuous minutes, which was separated into three phases. The first 15 minutes (pre-synchronization phase) consisted of walking without a fractal stimulus, the second 15 minutes consisted of walking while entraining to a fractal visual stimulus (synchronization phase), and the last 15 minutes (post-synchronization phase) consisted of walking without the stimulus to determine if the patterns adopted from the stimulus were retained. Fractal gait patterns were strengthened during the synchronization phase and were retained in the post-synchronization phase. In experiment two, similar methods were used to compare a continuous fractal stimulus to a discrete fractal stimulus to determine which stimulus type led to more persistent fractal gait patterns in the synchronization and post-synchronization (i.e., retention) phases. Both stimulus types led to equally persistent patterns in the synchronization phase, but only the discrete fractal stimulus led to retention of the patterns. The results add to the growing body of literature showing that fractal gait patterns can be manipulated in a predictable manner. Further, our results add to the literature by showing that the newly adopted gait patterns are retained for up to 15 minutes after entrainment and showed that a discrete visual stimulus is a better method to influence retention.

Adaptation of sensorimotor processes has been studied for over a century. However, rigorous experimental approaches require controlling as many variables as possible to study the phenomenon, which limits generalizability. Conversely testing adaptation in an unconstrained ecologically valid situation makes it difficult to identify what parameters affect this process. This study utilizes virtual environments (VE) to create complex, but controlled environments to test visual, vestibular, and sensorimotor adaptation of whole-body posture. Findings show automatic postural processes can be adapted to unusual and discordant sensory environments, suggesting its lability would be advantageous when employing the kind of sensorimotor rehabilitation therapy VE affords.

Sensorimotor coordination relies on fine calibration of the interaction among visual, vestibular, and somatosensory input. Our goal was to investigate how the spatiotemporal properties of passive inertial motion and visual input affect head stabilization. Healthy young adults (n=12) wore a head-mounted display during A/P sinusoidal horizontal translations of the whole body. Visual conditions (VIS) displayed forward (EO), sideways (SW), or backward (BW) visual motion relative to the head, plus an eyes-closed conditions (EC) which were combined with 4 inertial conditions to comprise 16 conditions in total. In SW either near or far DEPTH of field with 180° phase shift was displayed. Subjects were secured in a seat with head free to move. Frequency and amplitude of sinusoidal input included overlapping max acceleration (a max ) or max velocity (v max ). Amplitude and phase of angular velocity was collected with a 3-axis gyro. A main effect of inertial condition on amplitude for all axes of head motion (p

Visual and gravitoinertial sensory inputs are integrated by the central nervous system to provide a compelling and veridical sense of spatial orientation and motion. Although it's known that visual input alone can drive this perception, questions remain as to how vestibular/ proprioceptive (i.e. inertial) inputs integrate with visual input to affect this process. This was investigated further by combining sinusoidal vertical linear oscillation (5 amplitudes between 0m and +/-0.8m) with two different virtual visual inputs. Visual scenes were viewed in a large field-of-view head-mounted display (HMD), which depicted an enriched, hi-res, dynamic image of the actual test chamber from the perspective of a subject seated in the linear motion device. The scene either depicted horizontal (+/-0.7m) or vertical (+/-0.8m) linear 0.2Hz sinusoidal translation. Horizontal visual motion with vertical inertial motion represents a 90 degrees spatial shift. Vertical visual motion with vertical inertial motion whereby the highest physical point matches the lowest visual point and vice versa represents a 180 degrees temporal shift, i.e. opposite of what one experiences in reality. Inertial-only stimulation without visual input was identified as vertical linear oscillation with accurate reports of acceleration peaks and troughs, but a slight tendency to underestimate amplitude. Visual-only (stationary) stimulation was less compelling than combined visual+inertial conditions. In visual+inertial conditions, visual input dominated the direction of perceived self-motion, however, increasing the inertial amplitude increased how compelling this non-veridical perception was. That is, perceived vertical self-motion was most compelling when inertial stimulation was maximal, despite perceiving "up" when physically "down" and vice versa. Similarly, perceived horizontal self-motion was most compelling when vertical inertial motion was at maximum amplitude. "Cross-talk" between visual and vestibular channels was suggested by reports of small vertical components of perceived self-motion combined with a dominant horizontal component. In conclusion, direction of perceived self-motion was dominated by visual motion, however, compellingness of this illusion was strengthened by increasing discordant inertial input. Thus, spatial mapping of inertial systems may be completely labile, while amplitude coding of the input intensifies the percept.

The level of immersion that is induced in an individual can be measured by subjective report, but VE immersion can also affect automatic sensorimotor processes which function below perceptual thresholds. Such sub-threshold effects on central nervous system processing are important to understand for the purposes of shaping VE rehabilitation. This study investigates the effect of dynamic immersive VE on self-motion perception and automatic upper extremity motor response. Subjects viewed either horizontal or vertical sinusoidal linear translation ±1m at 0.25 Hz via a head-mounted display (HMD) while sitting in a stationary motion apparatus. Subjects performed a perceptuomotor task of aligning a handheld object to perceived vertical using their unconstrained arm (i.e. free to move in 6 DOF). Two objects were tested, a joystick and a full glass of water, in counter-balanced order. Results show the majority of subjects perceive self-motion that spatially and temporally agrees with the visually depicted VE motion. This occurs despite the absence of sinusoidally varying changes to gravitoinertial forces, since subjects are not exposed to actual physical motion. Despite only being instructed to orient the handheld object, handheld object kinematics also show automatic motor responses involving object translation. These manual motor responses were dependent on the direction and phase of the visual motion depicted in the VE. Specifically, vertical visual motion induced vertical translation and pitch tilt of the handheld object, while horizontal visual motion induced horizontal translation and roll tilt of the object. Motor responses were significantly greater in subjects who reported compelling self-motion perception. These findings suggest that a representation of net gravitoinertial forces can be derived from the high-fidelity, pictorial and dynamic depth cues visually presented in a VE. Automatic upper extremity manual responses which are controlled by descending central systems and tracts dissociable from lower extremities can be affected by immersion in a VE much like automatic postural behavior has been shown to be. This new evidence supports current efforts to conduct upper extremity rehabilitation in the relative safe and controllable experimental environments that VE technology affords.

The impaired balance of posture accounts for the fall with a large proportion of falls in older people occurring when walking. However, the mechanisms underlying impaired balance during both gait and passive postural state are poorly understood. The objective of the research is to examine the underlying causes of instability and then to eventually create therapeutic interventions that will improve balance and lessen the number of falls related injuries. This paper focuses on developing a laboratory to study the combined influence of motion impact and visual conditions on head stabilization during passive postural jerk impact and simple harmonic movements. Preliminary studies on one healthy subject shows that concordant and discordant visual inputs have more compensatory effect than eyes closed on head stabilization during the jerk impact.

Background. Conventional methods of rehabilitation in patients with chronic, severe motor impairments after stroke usually do not lessen paresis. Objective. A novel therapeutic approach (assisted movement with enhanced sensation [AMES]) was employed in a medical device phase I clinical trial to reduce paresis and spasticity and, thereby, to improve motor function. Methods. Twenty subjects more than 1 year poststroke with severe motor disability of the upper or lower extremity were studied. A robotic device cycled the ankle or the wrist and fingers at 5°/s through ±17.5° in flexion and extension while the subject assisted this motion. Feedback of the subject's active torque was displayed on a monitor. Simultaneously, 2 vibrators applied a 60 pps stimulus to the tendons of the lengthening muscles, alternating from flexors to extensors as the joint rotation reversed from extension to flexion, respectively. Subjects treated themselves at home for 30 min/day for 6 months. Every other day prior to treatment, the therapy device performed automated tests of strength and joint positioning. Functional testing was performed prior to enrollment, immediately after completing the protocol, and 6 months later. Functional tests included gait and weight distribution (lower extremity subjects only) and the Stroke Impact Scale. Results. Most subjects improved on most tests, and gains were sustained for 6 months in most subjects. No safety problems arose. Conclusion. The AMES strategy appears safe and possibly effective in patients with severe chronic impairments. The mechanism underlying these gains is likely to be multifactorial.