PhD Thesis

Human Balance Behaviour in Immersive Virtual Environments

Abstract

Presence is defined as the illusion of being in a place depicted by an immersive virtual reality (IVR) system. A
consequence of this illusion is that participants respond to places and events in an IVR as if they were real. Currently,
there is no objective measure of presence that applies across all systems and applications. In this thesis we examine a
particular type of response-as-if-real, human balance behaviour (HBB), the actions that prevent the body’s centre of
gravity from moving outside the base of support, as a way to measure presence in an IVR.

Our first experiment was designed to investigate whether HBB can detect presence in IVRs. We used surface EMG to
measure muscle activations and found an increase when subjects walked on a virtual raised platform compared to a
virtual floor registered to the laboratory floor. A similar increase was found when subjects walked on a real raised
platform. This provides evidence of real HBB induced by an IVR.

In a second experiment HBB was used to compare partial-body and full-body tracking configurations. When participants
viewed a lateral lean imposed on the torso of a synchronous virtual body (SVB), their stance angle changed in a
compensatory direction. We found no significant difference in leaning between the tracking configurations, indicating that
for this application, partial-body tracking is sufficient for a SVB to influence HBB.

We carried out a case study to show the relevance of HBB for IVRs used for movement rehabilitation. Hemiparetic stroke
patients observed a SVB that was co-located with their own. When an animation caused their virtual arms to rise up, we
found evidence of counterbalancing in centre of pressure data that was not apparent when the subjects were told to simply
imagine the movement. Here HBB directly indicates the effectiveness of an IVR application.

This page last modified 15 January, 2011 by [Angus Antley]