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itself), is often considered second-rank. Instead,
the (acoustic) similarity between the simulation
and the real situation is considered most important.
In games, this situation is reversed: the available
computational power is critical, and rendering
has to be performed in real-time. Therefore, the
concept of plausibility is applied: as long as there
is no obvious contradiction between the visual and
the acoustic representation of a virtual scene, the
human senses merge auditory and visual impres-
sions. Hence, it is usually possible to replace a
cost-intensive geometry-based room acoustic
simulation with a generic reverberation algorithm,
for example, with combinations of all pass filters
and delays according to Schroeder (1962, 1970),
with nested all pass filters according to Gardner
(1992), or with feedback delay line structures ac-
cording to Jot and Chaigne (1991). This way, the
auditory part of the presentation provides a rough
sketch of the room's characteristics, whereas the
visual part complements the overall impression
with an increased level of detail. As long as the
information provided in the two modalities is
not contradictory, there is a high chance that the
player's perceptual apparatus merges the stimuli
and blends them to form a single, multi-modal
representation of the scene.
In general, it might be arguable whether a
“perfect” reproduction of the properties of a
real life experience will ever be possible in a
computer game at all (with the assumption that
a simulation is good enough as long as there is
no perceptual difference to reality detectable by
the human senses in the given situation). A lesser
interpretation of this applies to scenes which have
no counterpart in reality: their appearance needs
to be plausible in every aspect and also in a sense
of perfect agreement between the cues offered by
the system in the different perceptual domains.
In the context of games, this requirement can be
further reduced. Because the visual representation
of the scene is limited to a region in the frontal
area and is not supposed to fill the field of view
entirely, it suffices to require that the one part of
the virtual scene that is displayed (audio-visually)
is perceived as plausible. It is thus accepted that
stimuli coming from the surrounding real world
(which cannot be entirely excluded in a typical
computer game playing environment) might in-
terfere with those from the virtual scene.
Furthermore, the time and investment neces-
sary to develop completely accurate auditory and
visual models is as much of a limiting factor for
how much detail will be rendered, as is the com-
putational power alone. It is therefore reasonable
to focus only on the most important stimuli and
leave out those that would go unnoticed in a real
world situation. In order to do so, it is necessary to
predict what the most important stimuli or objects
in the overall audio-visual percept are.
INtErActIVItY IssUEs
AND PrEsENcE
The concept of interactivity has been defined by
Lee, Jin, Park, and Kang (2005) and Lee, Jeong,
Park, and Ryu (2007) based on three major
viewpoints: technology-oriented, communication-
setting oriented, and individual-oriented views.
Here, the technology-oriented view of interac-
tivity is adopted, which “defines interactivity as
a characteristic of new technologies that makes
an individual's participation in a communication
setting possible and efficient” (Lee et al., 2007).
Steuer (1992) holds that interactivity is a
stimulus-driven variable which is determined by
the technological structure of the medium. Accord-
ing to Steuer, interactivity is “the extent to which
users can participate in modifying the form and
content of a mediated environment in real time”
(p. 14) —in other words, the degree to which users
can influence a target environment. He identifies
three factors that contribute to interactivity:
•
speed
(the rate at which input can be as-
similated into the mediated environment)
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