Vibrotactile Sensory Augmentation and Machine Learning Based Approaches for Balance Rehabilitation

Vestibular disorders and aging can negatively impact balance performance. Currently, the most effective approach for improving balance is exercise-based balance rehabilitation. Despite its effectiveness, balance rehabilitation does not always result in a full recovery of balance function. In this dissertation, vibrotactile sensory augmentation (SA) and machine learning (ML) were studied as approaches for further improving balance rehabilitation outcomes. Vibrotactile SA provides a form of haptic cues to complement and/or replace sensory information from the somatosensory, visual and vestibular sensory systems. Previous studies have shown that people can reduce their body sway when vibrotactile SA is provided; however, limited controlled studies have investigated the retention of balance improvements after training with SA has ceased. The primary aim of this research was to examine the effects of supervised balance rehabilitation with vibrotactile SA. Two studies were conducted among people with unilateral vestibular disorders and healthy older adults to explore the use of vibrotactile SA for therapeutic and preventative purposes, respectively. The study among people with unilateral vestibular disorders provided six weeks of supervised in-clinic balance training. The findings indicated that training with vibrotactile SA led to additional body sway reduction for balance exercises with head movements, and the improvements were retained for up to six months. Training with vibrotactile SA did not lead to significant additional improvements in the majority of the clinical outcomes except for the Activities-specific Balance Confidence scale. The study among older adults provided semi-supervised in-home balance rehabilitation training using a novel smartphone balance trainer. After completing eight weeks of balance training, participants who trained with vibrotactile SA showed significantly greater improvements in standing-related clinical outcomes, but not in gait-related clinical outcomes, compared with those who trained without SA. In addition to investigating the effects of long-term balance training with SA, we sought to study the effects of vibrotactile display design on people’s reaction times to vibrational cues. Among the various factors tested, the vibration frequency and tactor type had relatively small effects on reaction times, while stimulus location and secondary cognitive task had relatively large effects. Factors affected young and older adults’ reaction times in a similar manner, but with different magnitudes. Lastly, we explored the potential for ML to inform balance exercise progression for future applications of unsupervised balance training. We mapped body motion data measured by wearable inertial measurement units to balance assessment ratings provided by physical therapists. By training a multi-class classifier using the leave-one-participant-out cross-validation method, we found approximately 82% agreement among trained classifier and physical therapist assessments. The findings of this dissertation suggest that vibrotactile SA can be used as a rehabilitation tool to further improve a subset of clinical outcomes resulting from supervised balance rehabilitation training. Specifically, individuals who train with a SA device may have additional confidence in performing balance activities and greater postural stability, which could decrease their fear of falling and fall risk, and subsequently increase their quality of life. This research provides preliminary support for the hypothesized mechanism that SA promotes the central nervous system to reweight sensory inputs. The preliminary outcomes of this research also provide novel insights for unsupervised balance training that leverage wearable technology and ML techniques. By providing both SA and ML-based balance assessment ratings, the smart wearable device has the potential to improve individuals’ compliance and motivation for in-home balance training.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143901/1/baotian_1.pd

Measuring center of pressure signals to quantify human balance using multivariate multiscale entropy by designing a force platform

Copyright @ 2013 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).To assess the improvement of human body balance, a low cost and portable measuring device of center of pressure (COP), known as center of pressure and complexity monitoring system (CPCMS), has been developed for data logging and analysis. In order to prove that the system can estimate the different magnitude of different sways in comparison with the commercial Advanced Mechanical Technology Incorporation (AMTI) system, four sway tests have been developed (i.e., eyes open, eyes closed, eyes open with water pad, and eyes closed with water pad) to produce different sway displacements. Firstly, static and dynamic tests were conducted to investigate the feasibility of the system. Then, correlation tests of the CPCMS and AMTI systems have been compared with four sway tests. The results are within the acceptable range. Furthermore, multivariate empirical mode decomposition (MEMD) and enhanced multivariate multiscale entropy (MMSE) analysis methods have been used to analyze COP data reported by the CPCMS and compare it with the AMTI system. The improvements of the CPCMS are 35% to 70% (open eyes test) and 60% to 70% (eyes closed test) with and without water pad. The AMTI system has shown an improvement of 40% to 80% (open eyes test) and 65% to 75% (closed eyes test). The results indicate that the CPCMS system can achieve similar results to the commercial product so it can determine the balance.National Science Council (NSC) of Taiwan and the Center for Dynamical Biomarkers and Translational Medicine, National Central University, Taiwan (which is sponsored by the NSC)

A MECHANISTIC APPROACH TO POSTURAL DEVELOPMENT IN CHILDREN

Upright standing is intrinsically unstable and requires active control. The central nervous system's feedback process is the active control that integrates multi-sensory information to generate appropriate motor commands to control the plant (the body with its musculotendon actuators). Maintaining standing balance is not trivial for a developing child because the feedback and the plant are both developing and the sensory inputs used for feedback are continually changing. Knowledge gaps exist in characterizing the critical ability of adaptive multi-sensory reweighting for standing balance control in children. Furthermore, the separate contributions of the plant and feedback and their relationship are poorly understood in children, especially when considering that the body is multi-jointed and feedback is multi-sensory. The purposes of this dissertation are to use a mechanistic approach to study multi-sensory abilities of typically developing (TD) children and children with Developmental Coordination Disorder (DCD). The specific aims are: 1) to characterize postural control under different multi-sensory conditions in TD children and children with DCD; 2) to characterize the development of adaptive multi-sensory reweighting in TD children and children with DCD; and, 3) to identify the plant and feedback for postural control in TD children and how they change in response to visual reweighting. In the first experiment (Aim 1), TD children, adults, and 7-year-old children with DCD are tested under four sensory conditions (no touch/no vision, with touch/no vision, no touch/with vision, and with touch/with vision). We found that touch robustly attenuated standing sway in all age groups. Children with DCD used touch less effectively than their TD peers and they also benefited from using vision to reduce sway. In the second experiment (Aim 2), TD children (4- to 10-year-old) and children with DCD (6- to 11-year-old) were presented with simultaneous small-amplitude touch bar and visual scene movement at 0.28 and 0.2 Hz, respectively, within five conditions that independently varied the amplitude of the stimuli. We found that TD children can reweight to both touch and vision from 4 years on and the amount of reweighting increased with age. However, multi-sensory fusion (i.e., inter-modal reweighting) was only observed in the older children. Children with DCD reweight to both touch and vision at a later age (10.8 years) than their TD peers. Even older children with DCD do not show advanced multisensory fusion. Two signature deficits of multisensory reweighting are a weak vision reweighting and a general phase lag to both sensory modalities. The final aim involves closed-loop system identification of the plant and feedback using electromyography (EMG) and kinematic responses to a high- or low-amplitude visual perturbation and two mechanical perturbations in children ages six and ten years and adults. We found that the plant is different between children and adults. Children demonstrate a smaller phase difference between trunk and leg than adults at higher frequencies. Feedback in children is qualitatively similar to adults. Quantitatively, children show less phase advance at the peak of the feedback curve which may be due to a longer time delay. Under the high and low visual amplitude conditions, children show less gain change (interpreted as reweighting) than adults in the kinematic and EMG responses. The observed kinematic and EMG reweighting are mainly due to the different use of visual information by the central nervous system as measured by the open-loop mapping from visual scene angle to EMG activity. The plant and the feedback do not contribute to reweighting

ADVANCES IN BALANCE AND BIOFEEDBACK MEASUREMENT: THE CASE FOR HEALTH-BASED, POSTURAL SERIOUS GAMES

Health games are increasingly seen as a means to address issues from therapy and rehabilitation. Yet, as a transformative technology, rarely have such games been explored or exploited to assist research into pathologies. Serious games for research (SGR) to uncover pathologies would allow clinicians to develop new differential diagnostics while providing a positive experience for the subject. This paper is not about game design; nevertheless it presents an outlook to considerations that could be taken forward when developing health-based SGRs for pathomechanics, etiopathogenesis and biofeedback. This work relates to preliminary studies on balance challenges manifested in pathologies of the central nervous system. As technology advancements seek to augment human sensory contact between virtual and real worlds this may impact on how virtual environments are used and designed in future. As a consequence heightened sensory (or lack of thereof) may result in falls, for example users with vestibular disorder – because postural stability is a key aspect of motor ability that allows individuals to sustain and maintain the desired physical position of their body Here, our investigation is specific to functional correspondence of the incidental properties in human body sway between healthy subjects and subjects with dyslexia. Our early results suggest postural sway between healthy subjects and those with mild disorders can be distinguished

The effects of attractive vs. repulsive instructional cuing on balance performance

Abstract Background Torso-based vibrotactile feedback has been shown to improve postural performance during quiet and perturbed stance in healthy young and older adults and individuals with balance impairments. These systems typically include tactors distributed around the torso that are activated when body motion exceeds a predefined threshold. Users are instructed to “move away from the vibration”. However, recent studies have shown that in the absence of instructions, vibrotactile stimulation induces small (~1°) non-volitional responses in the direction of its application location. It was hypothesized that an attractive cuing strategy (i.e., “move toward the vibration”) could improve postural performance by leveraging this natural tendency. Findings Eight healthy older adults participated in two non-consecutive days of computerized dynamic posturography testing while wearing a vibrotactile feedback system comprised of an inertial measurement unit and four tactors that were activated in pairs when body motion exceeded 1° anteriorly or posteriorly. A crossover design was used. On each day participants performed 24 repetitions of Sensory Organization Test condition 5 (SOT5), three repetitions each of SOT 1–6, three repetitions of the Motor Control Test, and five repetitions of the Adaptation Test. Performance metrics included A/P RMS, Time-in-zone and 95 % CI Ellipse. Performance improved with both cuing strategies but participants performed better when using repulsive cues. However, the rate of improvement was greater for attractive versus repulsive cuing. Conclusions The results suggest that when the cutaneous signal is interpreted as an alarm, cognition overrides sensory information. Furthermore, although repulsive cues resulted in better performance, attractive cues may be as good, if not better, than repulsive cues following extended training.http://deepblue.lib.umich.edu/bitstream/2027.42/134532/1/12984_2016_Article_131.pd

Benefits of short-term training with vibrotactile biofeedback of trunk sway on balance control in multiple sclerosis

Background and Aims: Patients with multiple sclerosis (MS) suffer from diminished balance control. We examined whether 4 sessions of training with vibrotactile biofeedback (VTfb) of trunk sway could improve their balance control and provide a carry-over effect. Methods: Baseline trunk sway was first measured for 15 MS patients. Then they received head mounted VTfb of trunk sway which was directionally active when trunk sway exceeded limits set using the baseline assessments. Stance and gait tasks were trained 2 times weekly for 2 weeks with VTfb. Assessments with VTfb were performed at the end of each week. Two weeks later balance was assessed without VTfb to determine if a carry-over effect was present. Results: Assessments with VTfb showed a significant decrease in trunk sway after 1 and 2 weeks of VTfb training (p<0.02). Carry-over improvements were also present (p<0.02). The greatest effects were found for tests of standing eyes closed stance on foam which resulted in a 59% decreased pitch sway angle (p=0.002) with VTfb and a 51% reduction (p=0.03) carry-over effect. Conclusions: This study indicates that balance control in MS patients improves rapidly after one week of training with VTfb and more slowly subsequently. The carry-over effect lasted at least 2 weeks. Future studies should determine, with more weeks of VTfb training, the time course of the slower balance and carry-over improvements following the first rapid improvement in balance control. We conclude that training with VTfb of trunk sway significantly improves balance control in MS patients, and could possibly reduce falls

Age Differences in Vestibular Processing: Neural and Behavioral Evidence

The vestibular system is well known for its role in balance, but its mechanisms of action in this role are not well understood. My dissertation aims to provide a better understanding of vestibular brain function, its correlation with postural control, and its alteration with advancing age. This is an important topic considering that falls are the current leading cause of injuries in older adults in the U.S., and they have negative consequences on wellbeing and independence. In this dissertation, I first review the conventional methods for studying vestibular function in the human brain, and I evaluate a novel MRI-compatible method, which relies on a pneumatic tapper. This approach successfully induces vestibular responses, while preventing the aversive effects of stimulation that are common in other approaches. Next, I assess age differences in brain responses to pneumatic vestibular stimulation, and find that older adults demonstrate less sensitivity to stimulation. Also, those with better postural control exhibit less deactivation of cross-modal sensory regions (e.g. visual and somatosensory cortices). This greater engagement of non-vestibular sensory regions in older adults with better balance could be a mechanism to compensate for inefficient vestibular processing. Consistent with this hypothesis, the relationship between postural control and deactivation of sensory regions was only evident in tasks of low difficulty (i.e. normal stance) in which compensatory neural recruitment might be most effective. After assessing the brain responses to vestibular stimulation in terms of activation and deactivation, I examine connectivity of the vestibular cortex with other regions. This last experiment demonstrates that vestibular cortex connectivity increases in response to vestibular stimulation, and young adults exhibit greater connectivity relative to older adults. Also, connectivity predicts postural stability in high difficulty tasks for young adults, and in low difficulty tasks for older adults. Better balance in young adults is associated with less vestibular connectivity (i.e. they engaged vestibular cortex more selectively), whereas better balance in older adults is associated with higher connectivity (i.e. more recruitment of other sensory regions). These findings reinforce the conclusions from the second experiment, and provide more evidence in support of the compensation related utilization of neural circuits hypothesis (CRUNCH) of neural processing in older adults.PHDKines & Psychology PhDUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/145857/1/fnoohi_1.pd

Aging affects postural tracking of complex visual motion cues

Postural tracking of visual motion cues improves perception–action coupling in aging, yet the nature of the visual cues to be tracked is critical for the efficacy of such a paradigm. We investigated how well healthy older (72.45 ± 4.72 years) and young (22.98 ± 2.9 years) adults can follow with their gaze and posture horizontally moving visual target cues of different degree of complexity. Participants tracked continuously for 120 s the motion of a visual target (dot) that oscillated in three different patterns: a simple periodic (simulated by a sine), a more complex (simulated by the Lorenz attractor that is deterministic displaying mathematical chaos) and an ultra-complex random (simulated by surrogating the Lorenz attractor) pattern. The degree of coupling between performance (posture and gaze) and the target motion was quantified in the spectral coherence, gain, phase and cross-approximate entropy (cross-ApEn) between signals. Sway–target coherence decreased as a function of target complexity and was lower for the older compared to the young participants when tracking the chaotic target. On the other hand, gaze–target coherence was not affected by either target complexity or age. Yet, a lower cross-ApEn value when tracking the chaotic stimulus motion revealed a more synchronous gaze–target relationship for both age groups. Results suggest limitations in online visuo-motor processing of complex motion cues and a less efficient exploitation of the body sway dynamics with age. Complex visual motion cues may provide a suitable training stimulus to improve visuo-motor integration and restore sway variability in older adults

THE INFLUENCE OF DECREASED AMBIENT LIGHTING ON REACTIVE BALANCE MECHANISMS IN YOUNG ADULTS

Introduction: Balance recovery/reactive balance prevents falls by restabilizing the center of mass (COM) when instability occurs. Dim lighting is a risk factor for falling, although limited research has examined how lighting conditions affect the ability to recover from losses of balance. The purpose of this thesis was to examine the effect of lighting conditions on reactive balance mechanisms. Methods: 20 young adults (23.3(4.4) y) completed forward lean-and-release perturbations in two lighting conditions: 1) Light: ~800 Lux; 2) Dark: 0 Lux. Optical motion capture and surface electromyography were used to quantify stepping/angular kinematics, COM control, and the timing, activation, and coordination of lower-limb neuromuscular responses. Differences between lighting conditions were analyzed with paired sample t-tests (alpha=0.05). Results: In darkness, individuals showed modified stepping (increased step length, knee flexion/extension velocity, and hip flexion velocity (pDiscussion:Balance recovery in dark environments can result in modified stepping responses and decreased COM control, which could prevent successful balance recovery in real-world environments and populations. Evidence-based lighting standards could minimize fall risk in built environments and public spaces