Perceived Quality in Game Audio - Game Sound Technology and Player Interaction: Concepts and Developments - page 160

• range (the number of possibilities for ac-
tion at any given time)
• mapping (the ability of a system to map
its controls to changes in the mediated
environment in a natural and predictable
manner).

Fitts' Law target acquisition task in which they
had to move the mouse from a starting point to a
target, with a latency of between 25ms and 225ms
from moving the mouse to actually seeing the cur-
sor move on the screen. The authors report that
the threshold at which latency started to affect the
performance was approximately 75ms. This effect
was also dependent on the difficulty of the task:
the harder the task, the greater was the adverse
effect caused by increased latency.
Wenzel (1998, 1999, 2001) has published a
number of reports about the impact of system
latency on dynamic performance in virtual acous-
tic environments with a focus on localization of
sound sources. The bottom line is that depending
on the source velocity of the audio signal itself,
localization of sound sources might be impaired
when total system latency (end-to-end latency)
is higher than around 60ms for audio-only pre-
sentations (Wenzel, 1998). On the other hand,
error rates in an active localization task, tested
on an HRTF-based reproduction system, showed
comparable error rates for both low and very high
latencies suggesting that subjects were largely
able to ignore latency altogether (Wenzel, 2001).
Nordahl (2005) examined the impact of self-
induced footstep sounds on the perception of pres-
ence and latency. Interestingly, for audio-visual
feedback in a VE, the maximum sound delay that
was possible without latency being perceived as
such was around 50% higher than for the audio-
only feedback case (mean values of 60.9ms against
41.7ms). Nordahl explains this as attention being
focused mainly on the visual, rather than the audi-
tory feedback in the audio-visual case.
Looking at these experimental results, it is
difficult to draw a general conclusion on the maxi-
mum allowed latency for computer games. Appar-
ently, the perception of latency as such depends
on the system setup itself (screen, loudspeakers/
headphones, for example), on the task, and on
the content that is displayed. At the same time,
measuring total system latency correctly is not a
trivial task. Therefore, a general recommendation

These factors are related to technological con-
straints that come into play when an application is
supposed to provide interactivity to the user, as is
the case for computer games. These technological
constraints are briefly discussed in the following
subsections.

Latency

Latency is one of the main concerns in computer
games. Latency in the context of interactivity can
be defined as the time that elapses between a user
input and the apparent reaction of the system to that
input. It is closely related to Steuer's speed factor.
Latencies are introduced by individual com-
ponents of the system. These components may
include input devices, signal processing algo-
rithms, device drivers, communication lines and
so on. Although these components may interact in
more than one way on a game platform, a system's
end-to-end latency should not vary over time to
make it predictable.
Meehan, Razzaque, Whitton, and Brooks
(2003) report a study in which they tested the
perceived sense of presence (see below) for two
different end-to-end latencies in a Virtual Environ-
ment (VE). The low latency was 50ms, the high
latency was 90ms. Test subjects were presented
with a relaxing environment that was switched to
a threatening one and their response was observed.
Meehan et al. report that subjects in the low-
latency group had a higher self-reported sense of
presence and a statistically higher change in heart
rate between presentations of the two situations.
MacKenzie and Ware (1993) conducted the
first quantitative experiments with respect to ef-
fects of visual latency. Participants completed a