The effects of actuator selection on non-volitional postural responses to torso-based vibrotactile stimulation

Abstract Background Torso-based vibrotactile feedback may significantly reduce postural sway in balance-compromised adults during quiet standing or in response to perturbations. However, natural non-volitional postural responses to vibrotactile stimulation applied to the torso remain unknown. Methods The primary goal of this study was to determine, for two types of actuators (tactors) and in the absence of instruction, whether vibrotactile stimulation induces a directional postural shift as a function of stimulation location. Eleven healthy young adults (20 – 29 years old) were asked to maintain an upright erect posture with feet hip-width apart and eyes closed. Two types of tactors, Tactaid and C2, which differ in design and stimulation strength, were placed on the skin over the right and left external oblique, internal oblique, and erector spinae muscles in a horizontal plane corresponding approximately to the L4/L5 level. Each tactor of the same type was activated twice randomly for each individual location and twice simultaneously for all locations at a frequency of 250 Hz for a period of 5 s. Results Vibration applied over the internal oblique and erector spinae muscle locations induced a postural shift in the direction of the stimulation regardless of the tactor type. For the aforementioned four locations, the root-mean-square (RMS) and power spectral density (PSD) of the body sway in both the A/P and M/L directions were also significantly greater during the vibration than before or after, and were greater for the C2 tactors than for the Tactaid tactors. However, simultaneous activation of all tactors or those over the external oblique muscle locations did not produce significant postural responses regardless of the tactor type. Conclusion The results suggest that the use of a torso-based vibrotactile sensory augmentation display should carefully consider the tactor type as well as the instruction of corrective movements. Attractive instructional cues (“move in the direction of the vibration”) are compatible with the observed non-volitional response to stimulation and may facilitate postural adjustments during vibrotactile biofeedback balance applications.http://deepblue.lib.umich.edu/bitstream/2027.42/112652/1/12984_2012_Article_451.pd

Design and Assessment of Vibrotactile Biofeedback and Instructional Systems for Balance Rehabilitation Applications.

Sensory augmentation, a type of biofeedback, is a technique for supplementing or reinforcing native sensory inputs. In the context of balance-related applications, it provides users with additional information about body motion, usually with respect to the gravito-inertial environment. Multiple studies have demonstrated that biofeedback, regardless of the feedback modality (i.e., vibrotactile, electrotactile, auditory), decreases body sway during real-time use within a laboratory setting. However, in their current laboratory-based form, existing vibrotactile biofeedback devices are not appropriate for use in clinical and/or home-based rehabilitation settings due to the expense, size, and operating complexity of the instrumentation required. This dissertation describes the design, development, and preliminary assessment of two technologies that support clinical and home-based balance rehabilitation training. The first system provides vibrotactile-based instructional motion cues to a trainee based on the measured difference between the expert’s and trainee’s motions. The design of the vibrotactile display is supported by a study that characterizes the non-volitional postural responses to vibrotactile stimulation applied to the torso. This study shows that vibration applied individually by tactors over the internal oblique and erector spinae muscles induces a postural shift of the order of one degree oriented in the direction of the stimulation. Furthermore, human performance is characterized both experimentally and theoretically when the expert–trainee error thresholds and nature of the control signal are varied. The results suggest that expert–subject cross-correlation values were maximized and position errors and time delays were minimized when the controller uses a 0.5 error threshold and proportional plus derivative feedback control signal, and that subject performance decreases as motion speed and complexity increase. The second system provides vibrotactile biofeedback about body motion using a cell phone. The system is capable of providing real-time vibrotactile cues that inform corrective trunk tilt responses. When feedback is available, both healthy subjects and those with vestibular involvement significantly reduce their anterior-posterior or medial-lateral root-mean-square body sway, have significantly smaller elliptical area fits to their sway trajectory, spend a significantly greater mean percentage time within the no feedback zone, and show a significantly greater A/P or M/L mean power frequency.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91546/1/channy_1.pd

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

Potential Mechanisms of Sensory Augmentation Systems on Human Balance Control

Numerous studies have demonstrated the real-time use of visual, vibrotactile, auditory, and multimodal sensory augmentation technologies for reducing postural sway during static tasks and improving balance during dynamic tasks. The mechanism by which sensory augmentation information is processed and used by the CNS is not well understood. The dominant hypothesis, which has not been supported by rigorous experimental evidence, posits that observed reductions in postural sway are due to sensory reweighting: feedback of body motion provides the CNS with a correlate to the inputs from its intact sensory channels (e.g., vision, proprioception), so individuals receiving sensory augmentation learn to increasingly depend on these intact systems. Other possible mechanisms for observed postural sway reductions include: cognition (processing of sensory augmentation information is solely cognitive with no selective adjustment of sensory weights by the CNS), “sixth” sense (CNS interprets sensory augmentation information as a new and distinct sensory channel), context-specific adaptation (new sensorimotor program is developed through repeated interaction with the device and accessible only when the device is used), and combined volitional and non-volitional responses. This critical review summarizes the reported sensory augmentation findings spanning postural control models, clinical rehabilitation, laboratory-based real-time usage, and neuroimaging to critically evaluate each of the aforementioned mechanistic theories. Cognition and sensory re-weighting are identified as two mechanisms supported by the existing literature

Spatial and temporal influences on discrimination of vibrotactile stimuli on the arm

Body\u2013machine interfaces (BMIs) provide a non-invasive way to control devices. Vibrotactile stimulation has been used by BMIs to provide performance feedback to the user, thereby reducing visual demands. To advance the goal of developing a compact, multivariate vibrotactile display for BMIs, we performed two psychophysical experiments to determine the acuity of vibrotactile perception across the arm. The first experiment assessed vibration intensity discrimination of sequentially presented stimuli within four dermatomes of the arm (C5, C7, C8, and T1) and on the ulnar head. The second experiment compared vibration intensity discrimination when pairs of vibrotactile stimuli were presented simultaneously vs. sequentially within and across dermatomes. The first experiment found a small but statistically significant difference between dermatomes C7 and T1, but discrimination thresholds at the other three locations did not differ. Thus, while all tested dermatomes of the arm and hand could serve as viable sites of vibrotactile stimulation for a practical BMI, ideal implementations should account for small differences in perceptual acuity across dermatomes. The second experiment found that sequential delivery of vibrotactile stimuli resulted in better intensity discrimination than simultaneous delivery, independent of whether the pairs were located within the same dermatome or across dermatomes. Taken together, our results suggest that the arm may be a viable site to transfer multivariate information via vibrotactile feedback for body\u2013machine interfaces. However, user training may be needed to overcome the perceptual disadvantage of simultaneous vs. sequentially presented stimuli

An experimental setup to test dual-joystick directional responses to vibrotactile stimuli

In this paper we investigate the influence of the location of vibrotactile stimulation in triggering the response made using two handheld joysticks. In particular, we compare performance with stimuli delivered either using tactors placed on the palm or on the back of the hand and with attractive (move toward the vibration) or repulsive prompts (move away from the vibration). The experimental set-up comprised two joysticks and two gloves, each equipped with four pager motors along the cardinal directions. In different blocks, fifty-three volunteers were asked to move the joysticks as fast as possible either towards or away with respect to the direction specified by a set of vibrating motors. Results indicate that participants performed better with attractive prompts (i.e. responses were faster and with fewer errors in conditions where participants were asked to move the joysticks in the direction of the felt vibration) and that the stimulation delivered on the back of the hand from the gloves gives better results than the stimulation on the palm delivered by the joysticks. Finally, we analyse the laterality, the relation between correct responses and reaction times, the direction patterns for wrong responses and we perform an analysis on the Stimulus-Response Compatibility and on the training effect

An experimental setup to test dual-joystick directional responses to vibrotactile stimuli

In this paper we investigate the influence of the location of vibrotactile stimulation in triggering the response made using two handheld joysticks. In particular, we compare performance with stimuli delivered either using tactors placed on the palm or on the back of the hand and with attractive (move toward the vibration) or repulsive prompts (move away from the vibration). The experimental set-up comprised two joysticks and two gloves, each equipped with four pager motors along the cardinal directions. In different blocks, fifty-three volunteers were asked to move the joysticks as fast as possible either towards or away with respect to the direction specified by a set of vibrating motors. Results indicate that participants performed better with attractive prompts (i.e. responses were faster and with fewer errors in conditions where participants were asked to move the joysticks in the direction of the felt vibration) and that the stimulation delivered on the back of the hand from the gloves gives better results than the stimulation on the palm delivered by the joysticks. Finally, we analyse the laterality, the relation between correct responses and reaction times, the direction patterns for wrong responses and we perform an analysis on the Stimulus-Response Compatibility and on the training effect

Cell phone based balance trainer

<p>Abstract</p> <p>Background</p> <p>In their current laboratory-based form, existing vibrotactile sensory augmentation technologies that provide cues of body motion are impractical for home-based rehabilitation use due to their size, weight, complexity, calibration procedures, cost, and fragility.</p> <p>Methods</p> <p>We have designed and developed a cell phone based vibrotactile feedback system for potential use in balance rehabilitation training in clinical and home environments. It comprises an iPhone with an embedded tri-axial linear accelerometer, custom software to estimate body tilt, a "tactor bud" accessory that plugs into the headphone jack to provide vibrotactile cues of body tilt, and a battery. Five young healthy subjects (24 ± 2.8 yrs, 3 females and 2 males) and four subjects with vestibular deficits (42.25 ± 13.5 yrs, 2 females and 2 males) participated in a proof-of-concept study to evaluate the effectiveness of the system. Healthy subjects used the system with eyes closed during Romberg, semi-tandem Romberg, and tandem Romberg stances. Subjects with vestibular deficits used the system with both eyes-open and eyes-closed conditions during semi-tandem Romberg stance. Vibrotactile feedback was provided when the subject exceeded either an anterior-posterior (A/P) or a medial-lateral (M/L) body tilt threshold. Subjects were instructed to move away from the vibration.</p> <p>Results</p> <p>The system was capable of providing real-time vibrotactile cues that informed corrective postural responses. When feedback was available, both healthy subjects and those with vestibular deficits significantly reduced their A/P or M/L RMS sway (depending on the direction of feedback), had significantly smaller elliptical area fits to their sway trajectory, spent a significantly greater mean percentage time within the no feedback zone, and showed a significantly greater A/P or M/L mean power frequency.</p> <p>Conclusion</p> <p>The results suggest that the real-time feedback provided by this system can be used to reduce body sway. Its advantages over more complex laboratory-based and commercial balance training systems in terms of cost, size, weight, functionality, flexibility, and accessibility make it a good candidate for further home-based balance training evaluation.</p

Reaching Performance in Heathy Individuals and Stroke Survivors Improves after Practice with Vibrotactile State Feedback

Stroke causes deficits of cognition, motor, and/or somatosensory functions. These deficits degrade the capability to perform activities of daily living (ADLs). Many research investigations have focused on mitigating the motor deficits of stroke through motor rehabilitation. However, somatosensory deficits are common and may contribute importantly to impairments in the control of functional arm movement. This dissertation advances the goal of promoting functional motor recovery after stroke by investigating the use of a vibrotactile feedback (VTF) body-machine interface (BMI). The VTF BMI is intended to improve control of the contralesional arm of stroke survivors by delivering supplemental limb-state feedback to the ipsilesional arm, where somatosensory feedback remains intact. To develop and utilize a VTF BMI, we first investigated how vibrotactile stimuli delivered on the arm are perceived and discriminated. We determined that stimuli are better perceived sequentially than those delivered simultaneously. Such stimuli can propagate up to 8 cm from the delivery site, so future applications should consider adequate spacing between stimulation sites. We applied these findings to create a multi-channel VTF interface to guide the arm in the absence of vision. In healthy people, we found that short-term practice, less than 2.5 hrs, allows for small improvements in the accuracy of horizontal planar reaching. Long-term practice, about 10 hrs, engages motor learning such that the accuracy and efficiency of reaching is improved and cognitive loading of VTF-guided reaching is reduced. During practice, participants adopted a movement strategy whereby BMI feedback changed in just one channel at a time. From this observation, we sought to develop a practice paradigm that might improve stroke survivors’ learning of VTF-guided reaching without vision. We investigated the effects of practice methods (whole practice vs part practice) in stroke survivors’ capability to make VTF-guided arm movements. Stroke survivors were able to improve the accuracy of VTF-guided reaching with practice, however there was no inherent differences between practice methods. In conclusion, practice on VTF-guided 2D reaching can be used by healthy people and stroke survivors. Future studies should investigate long-term practice in stroke survivors and their capability to use VTF BMIs to improve performance of unconstrained actions, including ADLs

Étude sur l'effet de l'augmentation sensorielle sur le contrôle de l'équilibre

Pour maintenir notre équilibre debout, notre cerveau utilise des informations sensorielles. Lorsque ces signaux sont détériorés, le control postural est perturbé et peut être amélioré grâce à l'augmentation sensorielle (AS). Il n'est pas cependant établi si les rétroactions devraient être fournies à chaque déséquilibre. L'objectif était de comparer l'effet de différentes quantités d'AS de type vibrotactile sur le contrôle postural debout et d'évaluer si les effets persistent dans le temps, alors que la qualité des informations somatosensorielles et visuelles sera altérée. Méthode : 24 jeunes adultes en santé aléatoirement divisés en deux groupes (rétroaction 100 % et 33 %) étaient debout les yeux fermés sur un tapis de mousse. Ils recevaient d'abord des rétroactions synchronisées avec la direction des oscillations posturale puis aucune rétroaction. Ensuite, les rétroactions n'étaient plus congruentes avec la direction des oscillations posturales. Afin d'évaluer le contrôle postural, la valeur moyenne quadratique selon les axes médio-latéral et antéro-postérieur et 85 % de l'aire totale couverte en utilisant un ajustement en ellipse ont été calculées à partir de la cinématique du tronc (angle et vitesse angulaire) et des forces au sol (effort neuromusculaire). Résultats : L'AS vibrotactile congruente diminue l'angle du tronc et augmente la vitesse angulaire du tronc et les forces au sol de façon similaire pour les deux groupes. Cette réduction de l'angle du tronc perdure dans l'axe médio-latéral, à la suite de l'arrêt de l'AS, alors que la vitesse angulaire du tronc et les forces au sol diminuent. L'AS vibrotactile non congruente accentuent tous les paramètres suggérant une détérioration de l'équilibre. Conclusion : Les participants ont intégré les rétroactions vibrotactiles pour contrôler leurs oscillations posturales. Les deux quantités d'AS sont aussi efficaces pour améliorer le contrôle postural. L'AS vibrotactile fournie une fois sur trois pourrait être priorisée afin de limiter la charge cognitive.During upright standing, the brain uses sensory cues to estimate body sways amplitude and direction. These sensory information helps in controlling upright balance. For individuals with balance control impairment, sensory information is altered and vibrotactile feedback improves their balance. It is unclear, however, if feedback must be provided each time balance is compromised. The goal of this study was to compare two quantities of trunk vibrotactile feedback while visual and somatosensory information were altered and to evaluate if the results on upright balance control were maintained afterward. Method: Twenty-four healthy young adults randomly assigned to two groups (feedback 33% and 100%) stood upright on the foam surface with their eyes closed. They first received vibrotactile feedback provided according to body sway angle amplitude and direction and then without feedback. Thereafter, vibrotactile feedback was unrelated to body sway angle and direction. To assess balance control, we measured the ground reaction forces, body sway angle and angular velocity along the anteroposterior and mediolateral axes. We calculated the root mean square values and an ellipse covering 85% all these measures. Results: Balance control of both groups was similar. When vibrotactile feedback was provided, body sway angle amplitude decreased while body sway angular velocity and the ground reaction forces increased. Immediately following vibrotactile feedback, the reduction in body sway angle was maintained while the body sway velocity and the ground forces decreased. When vibrotactile feedback was unrelated to body sway angle, all balance control parameter increased. Conclusion: Participants processed vibrotactile feedback to control their balance. Vibrotactile feedback was effective in improving balance control despite the quantity of vibrotactile feedback provided. We argue that providing vibrotactile feedback one-third of the time that balance control is compromised could be the best choice as it enhances balance control, and it likely implies less cognitive load