Biomedical Engineering Reference
In-Depth Information
be made taller, shorter, leaner, or stockier; one's arms or legs could be stretched or
compressed; one could be made faster, slower, stronger, or weaker. Before the user has
a chance to adapt, he or she may attempt actions that have no chance of success, pass
up opportunities to perform actions that would lead to beneficial outcomes, follow
suboptimal routes, or inadvertently collide with objects in the virtual environment.
Such behavior can be observed in real environments as well. Infants, upon first
learning to walk, have difficulty gauging their actions to their new movement capabil-
ities [ 1 ]. As such, they often attempt to descend sloped surfaces that are impossibly
steep or cross gaps that are impossibly wide. Similarly, when older children ride
bicycles, they have difficulty taking into account how long it takes to initiate move-
ment [ 27 ]. This puts them at greater risk when crossing busy streets because it leaves
them less time to reach the other side before approaching cars arrive. In both cases,
one's ability to select appropriate actions is impaired by changes that affect one's
action capabilities.
In most situations, however, people are remarkably good at choosing actions that
are appropriate given their body dimensions and movement capabilities (see [ 9 ]for
a review). They know whether an aperture between two stationary obstacles is wide
enough to permit safe passage [ 35 ], whether a gap in the ground surface is small
enough to jump [ 22 ], and whether to pass in front of or behind a moving obstacle [ 6 ].
The primary aim of this chapter is to consider how people take their body dimen-
sions and movement capabilities into account when interacting with real and virtual
environments. The specific focus will be on attempts, motivated largely by the eco-
logical approach to perception and action [ 14 ], to explain how people take their body
dimensions and dynamics into account without appealing to internal models of the
body. I will begin by reviewing some classic work on the perception of affordances
(i.e., possibilities for action), their specification by eyeheight-scaled visual informa-
tion, and why affordance perception offers a starting point for addressing this prob-
lem. I will then present more recent research aimed at generalizing the affordance-
based approach to account for behavior in a wider variety of circumstances.
The second aim of this chapter is to show how VEs have been used to study
affordance perception and the visual control of locomotion. Much of the research
presented in this chapter takes advantage of VEs and could not be conducted in the real
world. In short, VEs have created new and exciting opportunities to investigate the
way in which people perceive affordances, guide locomotion, and adapt to changes
in their body dimensions and locomotor capabilities.
4.2 Taking Body Dimensions and Movement
Capabilities into Account
4.2.1 Theoretical Approach
How do people choose actions and guide locomotion in a way that takes their
body dimensions and locomotor capabilities into account? By some accounts, the
 
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