Biomedical Engineering Reference
In-Depth Information
16.4.3 Understand Your Design Tradeoffs and Users
Design tradeoffs, i.e. making changes to one part of an interface so the interface as
a whole improves, are especially important for full-body interaction as limitations
will be encountered in what you can sense of the user and recognize in the data.
You will have to know what is key to your interface and what can be changed.
The best way to understand this is to perform a requirement and task analysis (a full
discussion of this is beyond this chapter's scope). Knowing this required functionality
informs the design process when problems are encountered so a designer can make
informed decisions between: (1) spending time on specific algorithmic recognition
improvements, (2) adding new hardware, or (3) making changes to the user interface
based on which action is more important (i.e. differentiation between similar gestures
is problematic so swap in a new gesture).
In our experience, a few general assumptions can be made about how users will
want, or expect, to move in your interface, based upon naturalness ,the“ weight” and
fatigue of gestures. Expect players will start with natural movements; movements
directly matched to real-world counterparts, and then they change their actions as
these natural movements fail due to your design, real-world constraints or even your
recognition algorithms. For example, they walk a few feet forward but then realize,
when they hit a wall, they need to run in place for longer distance travel. Next,
consider the weight of a user's motion (i.e. howmuch cognitive and physical effort is
required), as users will tend to match task and motion energy. Consider a user staring
at a fixed large screen display, who needs to both look around and turn: “lighter” head
glances can be used for quickly looks and the “heavier” torso rotations can change
their in-world orientation. Lastly, expect fatigue to play a role in the long-term use
of an interface. While a simple running in place gesture might satisfy some design
considerations, it quickly tires a user. Even low fatigue motions become fatiguing
over time, especially if it requires odd motions that can lead to repetitive stress. In
these cases, create non-realistic gestures to compensate. One alternative is to use
fatiguing gestures for actions that give extra rewards, such as running in place for
sprinting, coupled with a light-weight gesture for typical walking speeds. Keep in
mind too that sometimes fatigue is wanted, such as exertion games [ 12 ] or military
trainers where fatigue is a part of the simulation.
Full body locomotion and interaction design is difficult and if the first design
is potentially not possible, know what design tradeoffs can be made. For example,
if people do not need to move their arms, then map leg movements to the arms.
People are going to fatigue quickly so know if it is important to be realistic or if
less fatiguing “magic” gestures can replace fatiguing real gestures. For instance,
leaning forward could replace running in place. Or, remove the need for the user
to move vast distances by moving them automatically or provide a game pad. Even
small error rates result in problems for the user so make sure that there is a real
reason to use full-body interaction. In these situations, keep it novel and reserve
full-body interaction for only those cases where there is a real benefit or purpose to
 
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