Title

Assessment of Postural Responses to Challenging Virtual Reality Environments in Healthy Adults

Date of Award

1-1-2020

Degree Name

M.S. in Mechanical Engineering

Department

Department of Mechanical and Aerospace Engineering and Renewable and Clean Energy

Advisor/Chair

Advisor: Megan Reissman

Abstract

Balance is a common term that is usually represented as the center of pressure (COP) for standing balance. With increasing age, adults begin to show more postural sway, which can be a marker for higher risk of falls. Among those with balance issues, challenging environments can increase this risk. Challenges can occur because of difficult terrain, dynamic perturbations, and visual stimuli. As challenging environments are difficult to replicate experimentally, this study investigates balance response to different environments using Virtual Reality (VR). This study seeks to characterize differences in standing balance response between age groups, determine which VR environments (VRE) elicit the greatest postural responses, and justify the safety of VR. The VREs used were selected for the variety of individual postural responses that they could elicit. The study uses force plate data to assess center of pressure metrics of standard deviation, range, and frequency power. This study uses motion capture data to assess segment and marker-based measures of standard deviation, range, and total path length. Healthy adult participants were grouped into age brackets of Young (n=15, 19.8▒0.7), Middle (n=14, 47.3▒9.9), and Older (n=8, 68▒5.8). The participants performed a standing balance task for seven randomized VREs, each a duration of sixty seconds, and baseline Eyes Open and Eyes Closed before and after VR exposure. The VREs used were a mix of dynamic/static virtual platforms and dynamic/static visuals. Body segment motion was recorded with motion capture markers and accelerometers. Two different marker approaches for the motion capture was used (single marker and segment) to accurately track the body segments. The Fast Fourier Transform (FFT) was used to determine the power of frequency contributions to postural sway response in different frequency bands associated with different sensory systems (0-0.3 Hz for visual system, 0.3-1 Hz for vestibular system, and 1-3 Hz for proprioceptive system).When comparing baseline Eyes Open to VRE, age group was a significant factor in the frequency power in the medial-lateral plane Middle band and COP path length assessments. Generally, Middle group had the least amount of sway, then Young group, followed by Older group. Frequency power in the Low and Middle bands and segment path length demonstrated increased postural sway responses for environments with dynamic visuals and platforms. Both marker approaches were consistent but with the Power value just over 0.7 suggests more subjects are needed. Exposure to dynamic environments in VR, specifically Train or Boat Day, may benefit individuals with balance impairments by providing safe conditions under which to practice balance responses. Overall, frequency power results suggest underlying reweighting of sensory inputs under dynamic VRE conditions with increased weighting of the vestibular system and decreased weighting of the visual system. This study has also confirmed that short exposure to a headset-based VR is safe and can be an effective tool to evaluate standing balance. The results from this study can be used as age-matched healthy data for other populations. For these impaired populations, exposure to VRE may serve as a therapeutic tool to quantify and practice balance and to improve overall quality of life.

Keywords

Mechanical Engineering, Biomechanics, Biomedical Engineering, Biomedical Research, Engineering, Standing Balance, Virtual Reality, Posture, Challenging Environments, Sensory Integration

Rights Statement

Copyright 2020, author

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