Estimation of Distances in Virtual Environments Using Size Constancy
Résumé
It is reported in the literature that distances from
the observer are underestimated more in virtual environments
(VEs) than in physical world conditions. On the other hand
estimation of size in VEs is quite accurate and follows a
size-constancy law when rich cues are present. This study
investigates how estimation of distance in a CAVETM
environment is affected by poor and rich cue conditions, subject
experience, and environmental learning when the position of the
objects is estimated using an experimental paradigm that
exploits size constancy.
A group of 18 healthy participants was asked to move a
virtual sphere controlled using the wand joystick to the position
where they thought a previously-displayed virtual cube
(stimulus) had appeared. Real-size physical models of the virtual
objects were also presented to the participants as a reference of
real physical distance during the trials. An accurate estimation
of distance implied that the participants assessed the relative size
of sphere and cube correctly. The cube appeared at depths
between 0.6 m and 3 m, measured along the depth direction of
the CAVE. The task was carried out in two environments: a
poor cue one with limited background cues, and a rich cue one
with textured background surfaces.
It was found that distances were underestimated in both poor
and rich cue conditions, with greater underestimation in the
poor cue environment. The analysis also indicated that factors
such as subject experience and environmental learning were not
influential. However, least square fitting of Stevens’ power law
indicated a high degree of accuracy during the estimation of
object locations. This accuracy was higher than in other studies
which were not based on a size-estimation paradigm. Thus as
indirect result, this study appears to show that accuracy when
estimating egocentric distances may be increased using an
experimental method that provides information on the relative
size of the objects used.