Redirected Walking in Mixed Reality Training Applications - Human Walking in Virtual Environments - page 312

14.1 Locomotion in Virtual Environments
To create effective immersive training experiences, it is important to engage users in
simulated environments that convincingly replicate the mental, physical, and emo-
tional aspects of a real world situation. Such applications seek to invoke a sense
of presence—the feeling of “being there” in the virtual world, despite the fact that
the user is aware that the environment is a simulation. For users to respond realis-
tically in a virtual environment, the system must support the sensorimotor actions
that allow them to walk around and perceive the simulated content as if it were real
[ 18 ]. Indeed, experiments have demonstrated that walking yields benefits over less
natural forms of locomotion such as joystick travel. When walking naturally, users
experience a greater sense of presence [ 28 ] and less cognitive demand on working
memory and attention [ 23 , 30 ]. Additionally, studies have also shown that walking
results in superior performance on travel and search tasks [ 16 , 24 ].
The military has long been interested in providing immersive training experiences
that attempt to replicate the energy and motions of natural locomotion. For example,
the U.S. Naval Research Laboratory developed Gaiter, an immersive system that
uses a harness and full-body tracking to allow users to locomote by walking-in-place
[ 27 ]. Other examples include omni-directional treadmills (e.g. [ 4 , 17 ]) and mechan-
ical human-sized “hamster balls” (e.g. [ 9 ]). While recent research has shown that
walking on an omnidirectional treadmill can be very close to real walking [ 19 ], these
devices introduce translational vestibular conflicts when users alter their walking
speed. Furthermore, omnidirectional treadmills are generally expensive, mechani-
cally complicated, and only usable by a single person at a time. Thus, many immersive
systems continue to rely on handheld devices to simulate walking through the virtual
environment. For example, the U.S. Army recently awarded a $57 million contract to
develop the Dismounted Soldier Training System, a multi-person immersive virtual
reality training simulator using head-mounted displays and joysticks mounted on
each soldier's weapon for locomotion [ 13 ].
In the past few years, advances in wide-area motion tracking technology have
made it possible to realize natural walking through larger physical workspaces than
were previously possible with traditional electromagnetic trackers. Additionally,
portable rendering devices have made it possible to provide untethered movement
through large-scale immersive spaces, such as the HIVE system developed at Miami
University [ 29 ], and even outdoor environments with the integration of GPS track-
ing. Although it is now feasible to design virtual environments that can be explored
entirely through natural walking, the finite dimensions of the physical tracking space
will ultimately limit the size of the virtual environment that can be represented.
To address this limitation, researchers developed redirected walking , a technique
that subtly manipulates the mapping between physical and virtual motions, thereby
enabling real walking through potentially expansive virtual worlds in comparably
limited physical workspaces. In this chapter, we present design considerations for
employing redirected walking techniques in immersive training applications. We
also demonstrate an alternative redirection technique designed for mixed reality