\u3ci\u3eMedicine Meets Virtual Reality 21\u3c/i\u3e

Editors: James D. Westwood, Susan W. Westwood, Li Felländer-Tsai, Cali M. Fidopiastis, Randy S. Haluck, Richard A. Robb, Steven Senger, Kirby G. Vosburgh. Chapter, Varying the Speed of Perceived Self-Motion Affects Postural Control During Locomotion, co-authored by Joshua Pickhinke, Jung Hung Chien, Mukul Mukherjee, UNO faculty and staff members. Virtual reality environments have been used to show the importance of perception of self-motion in controlling posture and gait. In this study, the authors used a virtual reality environment to investigate whether varying optical flow speed had any effect on postural control during locomotion. Healthy young adult participants walked under two conditions, with optical flow matching their preferred walking speed, and with a randomly varying optic flow speed compared to their preferred walking speed. Exposure to the varying optic flow increased the variability in their postural control as measured by area of COP when compared with the matched speed condition. If perception of self-motion becomes less predictable, postural control during locomotion becomes more variable and possibly riskier.https://digitalcommons.unomaha.edu/facultybooks/1261/thumbnail.jp

Changes in the Dynamics of Postural and Locomotor Control as a Result of Varying Task Demands

The aim of this study was to examine changes in postural and locomotor control under varying task demands. Three experiments were designed to address the impact that fast walking had on standing posture over time, slow walking had on gait dynamics over time, and the extent to which gait speed interacts with the ability to walk randomly. For experiment I, the aim was to identify the time course in which postural adaptation occurred while walking at faster than preferred speeds. Postural motion was assessed at specific intervals over a 35-min walking trial. Findings revealed that walking at a faster speed increased the amount, variability, and structure (Approximate Entropy-ApEn) of postural motion compared to baseline assessments. Subsequent trials following baseline assessments revealed a leveling-off for specific center of pressure (COP) variables and decline in path length, although heart rate (HR) and rate of perceived exertion (RPE) increased over the entire walking trial. In experiment II, the aim was to examine changes in stride-to-stride variability over time while walking at slower than preferred speeds. The results revealed an increased stride-to-stride variability and signal regularity (lower ApEn) during walking at 80% preferred walking speed (PWS) compared to PWS. After 10-15 mins a decrease stride-to-stride variability and increase in signal irregularity was seen. Changes leveled-off for the remainder of the session. Experiment III was designed to examine the effect that intentionally increasing variability (random) had on gait dynamics. Participants were asked to vary their gait while walking on a treadmill at three different speeds. The results revealed gait speed was a significant factor in the amount of variability (CV, range), with higher levels produced during the slower speed than at PWS and the faster speed. Higher levels of complexity (higher SampEn) were seen in stride time and knee joint motion during the random condition irrespective of gait speed. Overall, young adults are able to walk at speeds faster or slower than preferred as well as increase gait variability when instructed. These changes in postural and locomotor dynamics reveal that a healthy motor control system can quickly adapt to the task demands imposed upon it

The Role of Optic Flow and Gaze Direction on Postural Control

Objective: The observers use the optic flow to control self-motion. However, the current state of knowledge indicates that it is difficult to understand how optic flow is used by the visual system without a direct measurement of the changes in the flow patterns caused by eye movements during natural behaviour. The purpose of this literature review is to highlight the importance of the integration between optic flow and eye movements for postural control. Methods: A literature review of the electronic papers through July 2022 was independently performed by three investigators. The selection of the studies was made by a search on PubMed, Scopus, and Google Scholar with two groups of selected keywords. We excluded papers performed on subjects with pathologies, children, and the elderly. Results: The results of this literature analysis highlight that eye movements are required to drive visual motion processing and heading perception in both static and dynamic contexts. Conclusion: Although we now know many neural mechanisms that process heading direction from the optic flow field, a consideration of optic flow patterns relative to gaze direction provides more detailed information on how the retinal flow field is used to control body balance. Doi: 10.28991/ESJ-2022-06-06-020 Full Text: PD

Locomotor Sensory Organization Test: How Sensory Conflict Affects the Temporal Structure of Sway Variability During Gait

When maintaining postural stability temporally under increased sensory conflict, a more rigid response is used where the available degrees of freedom are essentially frozen. The current study investigated if such a strategy is also utilized during more dynamic situations of postural control as is the case with walking. This study attempted to answer this question by using the Locomotor Sensory Organization Test (LSOT). This apparatus incorporates SOT inspired perturbations of the visual and the somatosensory system. Ten healthy young adults performed the six conditions of the traditional SOT and the corresponding six conditions on the LSOT. The temporal structure of sway variability was evaluated from all conditions. The results showed that in the anterior posterior direction somatosensory input is crucial for postural control for both walking and standing; visual input also had an effect but was not as prominent as the somatosensory input. In the medial lateral direction and with respect to walking, visual input has a much larger effect than somatosensory input. This is possibly due to the added contributions by peripheral vision during walking; in standing such contributions may not be as significant for postural control. In sum, as sensory conflict increases more rigid and regular sway patterns are found during standing confirming the previous results presented in the literature, however the opposite was the case with walking where more exploratory and adaptive movement patterns are present

Larger Head Displacement to Optic Flow Presented in the Lower Visual Field

Optic flow that simulates self-motion often produces postural adjustment. Although literature has suggested that human postural control depends largely on visual inputs from the lower field in the environment, effects of the vertical location of optic flow on postural responses are not well investigated. Here, we examined whether optic flow presented in the lower visual field produces stronger responses than optic flow in the upper visual field. Either expanding or contracting optic flow was presented in upper, lower, or full visual fields through an Oculus Rift head-mounted display. Head displacement and vection strength were measured. Results showed larger head displacement under the optic flow presentation in the full visual field and the lower visual field than the upper visual field, during early period of presentation of the contracting optic flow. Vection was strongest in the full visual field and weakest in the upper visual field. Our findings of lower field superiority in head displacement and vection support the notion that ecologically relevant information has a particularly important role in human postural control and self-motion perception

HEAD STABILIZATION AND CORTICAL ACTIVATION IN CONTACT SPORT ATHLETES DURING WALKING UNDER DIFFERENT VISUAL TASK CONSTRAINTS

Contact sport participation exposes athletes to repetitive sub-concussive head impacts, which have been shown to elicit cortical neurophysiologic, cognitive, and motor performance alterations that have the potential to disrupt visual perception. Despite the growing concern regarding sub-concussive impacts, our understanding of their implications on motor performance and risk for further injury is limited. A stable head provides a consistent perceptual platform for the visual and vestibular sensory systems, but the effects of contact sport participation on head stability and visual perception remain poorly understood. The goal of this dissertation was to understand whether contact sport participation modifies athletes’ ability to stabilize their head in space and the cortical mechanisms associated with these modifications. To address this goal, we asked the following questions: 1) how does contact sport exposure impact an athlete’s perception-action capabilities during visually demanding locomotor tasks; and 2) whether changes in cortical activity would relate to these motor performance changes. To address our questions, a stepwise approach was taken in three studies to understand how repetitive head impact exposure affects movement control, and how this xi is related to changes in visual perception and cortical activity. First, athletes completed a series of treadmill walking tasks with varying levels of visual task constraints; these constraints increased walking task difficulty to gain insights into how contact sport exposure disrupts the underlying dynamics associated with locomotor tasks and visual perception. By examining coordination, coordination variability, local dynamic stability, and dynamic visual acuity, a more complete understanding of the effects of cumulative sub-concussive impact exposure on locomotor dynamics, and how they relate to perceptual awareness was achieved. Next, to establish whether cortical alterations were associated with changes in motor performance, cortical neurophysiology was assessed while athletes completed a series of two postural and two locomotor tasks, some of which (one postural and one locomotor) included a visually demanding cognitive challenge. We aimed to assess cortical activity in athletes during cognitive and motor challenges to further our understanding of the cortical mechanisms associated with behavioral performance in ecologically relevant environments; this was done through lab-based protocols that attempted to mimic real world environments. Results from the first study indicated contact sport exposure modifies head control. Contact athletes reduced mediolateral head displacement while increasing vertical head and trunk displacement during locomotor tasks. This may be reflective of the reduced independent head control in the transverse plane, revealed through a coordination assessment. The findings from study two highlighted group differences during more demanding fast baseline walking, as indicated by reduced vertical head local dynamic stability in contact sport athletes compared to noncontact athletes during walking at higher speed than preferred. In addition, contact athletes significantly reduced xii both upper and lower body coordination variability during locomotor tasks. This lower variability in the contact group for trunk-head coordination was observed while performing the visual Landolt-C task was imposed, while group differences in lower body variability were present across all conditions. Also, contact athletes exhibited more frequent reductions in lower body variability during visual tasks compared to noncontact athletes. While the beneficial aspects of variability may be task dependent, in the context of sport performance and visual perception, higher variability may be indicative of exploiting abundant degrees of freedom, while reductions in variability are suggestive of sub-optimal performance and/or potential for injury. These findings highlight consistent reductions in movement flexibility and adaptability that may result from contact sport participation. In study three, no statistically significant changes in dorsolateral prefrontal cortex activity were present between groups, but moderate differences were observed during postural tasks, where on average, noncontact athletes increased cortical activity in response to a visual working memory task while contact athletes did not show a response. Similarly, while no statistically significant differences in motor performance were observed, moderate effects were observed for both postural and locomotor motor performance. Specifically, contact athletes displayed greater average mediolateral Center of Mass velocities during postural tasks, and reduced mediolateral head and trunk local dynamic stability during baseline gait compared to noncontact athletes. Collectively across all three studies, no differences in dynamic visual acuity or visual working memory performance were observed. The present studies utilized treadmill walking tasks with varying levels of visual task constraints to assess the consequences of contact sport participation on visual xiii perception, motor performance and cortical neurophysiology. Contact sport athletes exhibited distinct movement dynamics compared to noncontact athletes, including changes in whole-body coordination, variability, and local dynamic stability. Contact athletes reduced independent head control and whole-body coordination variability, which may suggest a modified ability to control joint and segmental degrees of freedom independently. Similarly, while limited within task differences were observed, how athletes responded to the changing constraints differed based on speculated repetitive sub-concussive head impact exposure. Despite prior reports, which identify cortical neurophysiologic alterations associated with increased head impact exposure, we observed no statistically significant group differences in dorsolateral prefrontal cortex oxyhemoglobin concentration changes in response to visual working memory and locomotor tasks imposed in the present study. These findings collectively underscore the intricate nature of the effects of subconcussive head impact exposure on cortical neurophysiology, motor performance, cognition, and visual perception. While visual task performance did not differ, contact athletes demonstrated reductions in independent segment control and movement adaptability during visually demanding motor tasks, which could potentially heighten the risk of injury during sport-specific tasks, though further study is needed

QUANTIFYING GAIT ADAPTABILITY: FRACTALITY, COMPLEXITY, AND STABILITY DURING ASYMMETRIC WALKING

Successful walking necessitates modifying locomotor patterns when encountering organism, task, or environmental constraints. The structure of stride-to-stride variance (fractal dynamics) may represent the adaptive capacity of the locomotor system. To date, however, fractal dynamics have been assessed during unperturbed walking. Quantifying gait adaptability requires tasks that compel locomotor patterns to adapt. The purpose of this dissertation was to determine the potential relationship between fractal dynamics and gait adaptability. The studies presented herein represent a necessary endeavor to incorporate both an analysis of gait fractal dynamics and a task requiring adaptation of locomotor patterns. The adaptation task involved walking asymmetrically on a split-belt treadmill, whereby individuals adapted the relative phasing between legs. This experimental design provided a better understanding of the prospective relationship between fractal dynamics and adaptive capacity. Results from the first study indicated there was no association between unperturbed walking fractal dynamics and gait adaptability in young, healthy adults. However, there was an emergent relationship between asymmetric walking fractal dynamics and gait adaptability. Moreover, fractal dynamics increased during asymmetric walking. The second study investigated fractal dynamics and gait adaptability in healthy, active young and older adults. The findings from study 2 showed no differences between young and older adults regarding unperturbed or asymmetric walking fractal dynamics, or gait adaptability performance. The second study provided further evidence for the lack of association between unperturbed fractal dynamics and gait adaptability. Furthermore, study 2 delivered additional support that asymmetric walking not only yields increased fractal scaling values, but also associates with adaptive gait performance in older adults. Finally, while the first two studies explored stride time monofractality during various walking tasks, the third study aimed to understand the potential multifractality, i.e. temporal evolution of fractal dynamics, of unperturbed and asymmetric walking. The results suggest that unperturbed walking is monofractal in nature, while more challenging asymmetric walking reveals multifractal characteristics, and that multifractality does not associate with adaptive gait performance. This dissertation provides preliminary evidence for the lack of relationship between gait adaptability and unperturbed fractal dynamics, and the emergent association between adaptive gait and asymmetric walking fractality

Math Modeling of Interlimb Coordination in Cat Locomotion

Locomotion is an evolutionary adaptation that allows animals to move in 3-D space. The way that mammalian locomotion is controlled has been studied for generations. It remains unclear how the neuronal network that controls locomotion is structured and how the mammalian locomotor network keeps balance in the face of a changing environment. In this body of research, we build mathematical models of locomotion and fit our models to experimental data of walking cats to gain understanding of network connectivity and of balance control. Specifically, we test the biological plausibility of a particular connectivity of the mammalian locomotor network by matching network activity to phases of walking in different experimental conditions. We gain understanding of balance control with an inverted pendulum model that fits the center of mass oscillations during walking in different experimental conditions

The effects of expectancy and control on the perception of ego-motion in space: a combined postural and electrophysiological study

In the beginning of this work was the scientific question: does the amount of control over visual self-motion cues influence their processing and/or perception? In Experiment 1, we tried to explore the possibility to use optic flow as a visual motion cue and see whether we can observe a sensory attenuation or modulation on the behavioural level in trials in which the optic flow was self-initiated using putative different levels of control by instructed or uninstructed button-presses compared to passive flow. This experiment, while not able to demonstrate a sensory modulation and with several important limitations (see below), was however an important basis for the planning of Experiment 2 and a proof-of-concept that this method has the potential to address our research question and is feasible given our facilities. In Experiment 2, we tried to overcome some of the limitations, further improved the re-producibility (e.g. stimuli and instructions) and extended our methodology to the measurement of neurophysiological and postural data to enquire about not only the behavioural level but also the processing on the physiological level. This experiment presented evidence that self-motion cues with the same physical properties are somehow processed differently at the cortical level depending on whether they are self-initiated or not. In addition to overcoming certain limitations in Experiment 3 (e.g. having a no optic flow control condition and using the standard EEG setup besides the mobile setup from Experiment 2), we were able to reproduce our findings in different subjects, a larger population and under a different posture. We were also able to show that our results are highly robust (e.g. removal of half the participants from the analysis did not change the pattern). Further outcomes from our study are that the scientific community can put more trust into mobile EEG setups given robust effects and diligent artifact removal. Additionally, we contributed findings on the relationship of vection and VIMS and tried to bridge the gap between the highly relevant fields of research on visual motion perception and sense of agency. This might act as an exploratory foundation for further research which will be essential for the economical and medical applicability of VR devices and for a deeper understanding of locomotion and navigation per se. The ability to perceive self-motion cues and dissociate them from cues for motion in the environment is fundamental for being able to take actions in the complex, dynamic environments which are our daily lives. In fact, it could be seen as a classical example of the dynamic coupling of action and perception to reach goals which is one of the most fundamental abilities not only for humans, but throughout the animal kingdom which may have lain the evolutionary basis for the later development of the human brain with its complexity as we see it nowadays (Godfrey-Smith 2016).Den Grundstein für diese Arbeit legte die Frage: spielt es für die Wahrnehmung und Verarbeitung von visuellem Feedback, das in Folge von Eigenbewegung im Raum entsteht, eine Rolle wie viel Kontrolle wir über die Bewegung haben? Wird das Feedback von aktiven Bewegungen anders verarbeitet als das von passiven? Im ersten Experiment explorierten wir die Möglichkeit uns dieser Fragestellung mit optic flow als visuellem Stimulus zu nähern. Wir haben dazu ein Experiment entwickelt bei dem gesunde Proband:innen unterschiedlich viel Kontrolle über den optic flow haben und sie anschließend zu ihrem Bewegungsempfinden (Vection) befragt. Während dieses Experiment keine relevante Modulation nachweisen konnte, so stellte es doch eine wichtige methodologische Grundlage für die Entwicklung der weiteren Experimente dar. Die wichtigsten Änderungen in Experiment 2 umfassten zum einen Modifikationen an den Stimuli und eine ausgeprägtere Formalisierung der Instruktionen, zum anderen die zusätzliche Erhebung von neurophysiologischen und posturalen Daten. Diese Änderungen erlaubten uns nicht nur explizite Unterschiede in der Intensität der Wahrnehmung von Vection zu erfassen, sondern auch eventuelle Modifikationen in der Verarbeitung der Stimuli messbar zu machen. Dieses Experiment lieferte Hinweise darauf, dass Stimuli mit denselben physikalischen Eigenschaften auf kortikaler Ebene anders verarbeitet werden, je nachdem ob sie selbst initiiert oder Computer-generiert sind. In Experiment 3 führten wir klassische Kontrollbedingungen wie zum Beispiel Versuche mit statischen Stimuli ein. Wir veränderten weiterhin die Körperposition, so dass Proband:innen nun saßen und die Hälfte der Versuche mit einer Kinnstütze stattfand. Damit konnten wir das Risiko, das unsere neurophysiologischen Effekte Bewegungsartefakte sind, minimieren. Insgesamt waren wir dazu in der Lage die Haupteffekte von Experiment 2 (agency-abhängige Modulation der evozierten Desynchronisation und der Amplitude der evozierten Potentiale) in Experiment 3 zu reproduzieren, obwohl wir hier eine deutlich größere Kohorte sowie andere Pro-band:innen in einer anderen Körperhaltung testeten. Diese Resultate sind sehr robust, so dass sie weiterhin deutlich erkennbar sind, auch nachdem wir ver-suchsweise die Hälfte der Proband:innen aus der Analyse ausgeschlossen hatten. Zusätzlich zu unserer ursprünglichen Fragestellung zeigten unsere Experimente, dass die wissenschaftliche Community mehr auf die Ergebnisse von Studien, die ein mobiles EEG-Setup verwenden, vertrauen kann, solange es sich um robuste Effekte handelt und ausreichend auf die Identifikation und Entfernung von Bewegungsartefakten geachtet wird. Außerdem konnten wir mit unseren Daten dazu beitragen die Zusammenhänge zwischen Vection und visuell-induzierter Bewegungskrankheit besser zu verstehen. Unsere Experimente versuchen die Brücke zu schlagen zwischen den jeweils für sich gesehen hoch relevanten Forschungsfeldern rund um die visuelle Bewegung-swahrnehmung und den Sense of Agency. Diese Felder zusammenzubringen wird eine essenzielle Rolle spielen, sowohl um das volle Potential von VR-Applikationen zu entfalten als auch um Lokomotion und Navigation umfassender zu begreifen. Die Fähigkeit Eigenbewegung von Bewegungen in der Umgebung anhand von visuellen Informationen zu unterscheiden, ist entscheidend um in der komplexen, dynamischen Umwelt unseres täglichen Lebens erfolgreich agieren und navigieren zu können. Diese Fähigkeit ist ein schönes Beispiel für die dynamische Koppelung von Handlung und Wahrnehmung zum Erreichen unserer Ziele und vermutlich eine der fundamentalsten Fähigkeiten nicht nur für Menschen, sondern auch im übrigen Tierreich. Möglicherweise so fundamental, dass sie die evolutionäre Basis für die spätere Entwicklung des menschlichen Gehirns in all seiner Komplexität und Schönheit, gelegt haben könnte (Godfrey-Smith 2016)

Effects of footwear cushioning on walking performance in females with multiple sclerosis, The

2018 Fall.Includes bibliographical references.Multiple sclerosis is a chronic and progressive neurodegenerative disease which incurs a multitude of walking impairments. Protective strategies targeted at maintaining postural stability during walking include increasing stance and double support time with reciprocal decreases in swing and single support time, however these adaptions inadvertently increase fall risk. The midsole construct of footwear has demonstrated the ability to mediate these deficits in running but has not been explored in a neurologic population with known fall risk. The purpose of this study was to investigate the effects of two different midsole conditions on the spatiotemporal parameters of gait in females with multiple sclerosis (MS). Gait testing was conducted while 18 females with MS performed two-minute walk tests in 1) a high-cushion and 2) a standard-cushion midsole shoe. Spatiotemporal gait parameters were assessed using wireless inertial sensors. Participants spent less time in double support and stance phase with concomitantly more time in single support and swing phase in the high-cushion midsole shoe as compared to the standard-cushion. The high-cushion shoe may decrease fall risk by improving gait parameters associated with increased risk of falls