Emma Iva Nielsen’s MSc Thesis Defence

Title: “Characterizing Visually Evoked Postural Responses with a Virtual Reality Head-Mounted Display in Young and Older Adults”

Thesis Supervisor: Dr. Mark Carpenter
Committee members: Dr. Romeo Chua, Dr. Tim Inglis
Chair: Dr. Bill Sheel

Abstract: Balance control requires the continuous integration of sensory information to maintain
postural stability. Widely accessible virtual reality (VR) head-mounted display (HMD) systems
can be used to directly manipulate stimuli presented to the visual system, and subsequent
postural responses can then be characterized. This manipulation is of particular importance for
older adults, who tend to have greater reliance on vision for balance control. However, at present
visual cues in VR are substantially different to those in the real world. As such, previous realworld
research investigating vision and postural stability cannot be assumed as directly
transferrable to applications in VR using HMDs. Therefore, the general purpose of this thesis
was to characterize visually evoked postural responses (VEPRs) in VR using an HMD and
examine how they varied across environmental conditions and populations of interest.
In the first study of this thesis, a pseudorandom visual stimulus was presented to young
adults in VR, with and without the postural threat of a virtually elevated surface height. Findings
of evoked sway across experimental conditions demonstrated that young adults were visually
sensitive to the stimulus. Despite pronounced psychological effects of the elevated surface
height, postural threat did not influence VEPRs. The second study compared the presentation of
real and virtual visual perturbations on VEPRs in young and older adults. Results indicated that
within a given age group, comparable levels of sway were evoked in the two environments. In
both real and virtual paradigms, older adults were more sensitive to visual stimuli than young
adults. Evidence of sensory reweighting was observed as both groups were able to proportionally
integrate balance-relevant visual cues based on the amplitude of the stimulus.
Overall, this thesis provides an evidentiary basis for the utility of VR HMDs in future
investigations of vision and balance, in young and older adults.