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findings from studies of affordance perception in VEs generalize to the real world.
The answer most likely depends on what aspect of affordance perception one is inter-
ested in. For example, in the aforementioned study by Fath and Fajen [
11
], subjects
often rotated their shoulders even when the distance between virtual obstacles was
more than 1.3
shoulder width, which was the critical value above which subjects
in Warren and Whang's [
35
] real world study did not rotate their shoulders. Such
behavior could be attributed to an underestimation of exocentric distances in VEs
(although there is some evidence that exocentric distances are accurately perceived
in VEs; e.g., [
13
]). Therefore, if one is interested in the critical value for gap pass-
ability in the real world, then caution must be exercised when drawing conclusions
based on passability judgments made in VEs. On the other hand, there is no reason to
believe that the tendency to underestimate aperture size in VEs should affect subjects
differently in the three conditions used in that study (i.e., Post, Tall Post, and Wall).
Therefore, the perceptual bias does not present any problems for testing the contribu-
tions of eyeheight-scaled, head-sway-scaled, and stride-length-scaled information,
which was the primary goal of that study.
Another issue that arises in studying affordance perception in VEs is that people's
motor capabilities in VEs may differ from those in the real world. For example,
subjects are unlikely to move as quickly in VEs due to the added weight of the
HMD, greater postural instability, or fear of colliding with walls or other objects in
the laboratory. Interestingly, Fajen et al. [
6
] found that subjects' judgments of their
ability to pass through a shrinking gap between a pair of moving obstacles closely
matched their ability to actually pass through shrinking gaps. Given that subjects'
locomotor capabilities in the VE differ from those in the real world, the accuracy of
judgments may initially seem surprising. Even in the real world, however, locomotor
capabilities are not fixed. People's ability to move is continually affected by factors
such as fatigue, injury, or carrying a heavy load. Therefore, the ability to adapt to
altered locomotor capabilities in VEs may reflect a well-developed ability to adapt to
changes in the real world. To summarize, although there are differences in perception
and motor control in virtual versus real environments, experiments can be designed
in such a way as to minimize the significance of these differences, thereby allowing
researchers to take advantage of manipulations that are not possible in the real world.
Just as our understanding of affordance perception in the real world has benefited
from VEs, so might our understanding of perception and action in VEs benefit from
the study of affordance perception. The need to take one's body dimensions and
locomotor capabilities into account applies in VEs just as it does in the real world.
Attempts to understand how people cope with the many sensorimotor rearrange-
ments and disruptions that are encountered in VEs often focus on the perception
(or misperception) of conventional spatial properties. If the goal is to understand
how people move in and interact with VEs, then more research on the perception of
action-relevant properties (i.e., affordances) in VEs could be beneficial.
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Acknowledgments
Preparation of this chapter was supported by a grant from the National
Institutes of Health (1R01EY019317).
