Biomedical Engineering Reference
In-Depth Information
support and traction supplied by the ground, they cannot reproduce the feeling of
walking on different materials.
Lower-cost methods for walking in virtual environments have been widely pur-
sued in the VR research community. Passive sensing interfaces have been used to
allow for the control of position via locomotion-like movements without force feed-
back [
94
]. Walking in place is another simple technique, in which movements of the
body are sensed, and used to infer an intended movement trajectory [
96
]. For virtual
environments that are experienced via an audiovisual head mounted display, a user's
locomotion can be directly mapped to movements in a virtual environment. The real
walkable workspace is typically much smaller than the virtual environment, and this
has led to the development of techniques, such as redirected walking [
81
], that can
engender the perceptual illusion that one is walking in a large virtual space.
The auditory and tactile experience of walking on virtual materials can be simu-
lated by augmenting foot-ground interactions with appropriate sounds or vibrations.
Although vibrotactile interfaces are simpler and lower in cost to implement than
haptic force feedback devices [
62
], they have only recently been used in relation to
walking in virtual environments. Auditory displays have been more widely investi-
gated, and walking sounds are commonly used to accompany first-person movements
in immersive games, although they are rarely accompanied by real foot movements.
Cook developed a floor interface (the Pholiemat), for controlling synthesized walking
sounds via the feet, inspired by foley practice in film [
14
,
15
], and other researchers
have experimented with acoustically augmented shoes [
77
]. Research on the use
of vibrotactile displays for simulating virtual walking experiences via instrumented
shoes [
89
] or floor surfaces [
107
] is still in its infancy.
Although tactile displays have, to date, been integrated in very few foot-based
interfaces for human-computer interaction, several researchers have investigated
the use of simple forms of tactile feedback for passive information conveyance to
the feet. Actuated shoe soles used to provide tactile indicators related to meaningful
computing events [
85
,
105
], and rhythmic cues supplied to the feet via a stair climber
have been found to be effective at maintaining a user's activity level when exercising.
In automotive settings, tactile warning cues delivered via the accelerator pedal have
been studied for many years [
67
], and eventually appeared in production vehicles.
Tactile stimulation to the feet has also been explored as an additional feedback
modality in computer music performance [
84
].
12.3.1.2 Haptic and Acoustic Signals Generated by Walking Interactions
During walking interactions, several touch interactions are involved with the virtual
ground. Stepping onto a natural or man-made surface produces rich multimodal
information, including mechanical vibrations that are indicative of the actions and
types of materials involved. Stepping on solid floors in hard-soled shoes is typified
by transient signals associated with the strike of the heel or toe against the floor,
while sliding can produce signals such as high-pitched squeaking (when surfaces
are clean) or textured noise. In indoor environments, the operation of common foot
