Biomedical Engineering Reference
In-Depth Information
Fig. 11.8 a
As the person
looks directly along the head-
ing vector, optic flow radiates
outward from the center of
vision.
b
A prism is placed in
front of the eye, which shifts
the visual location of the goal
and the location of the radial
optic flow. The optic flow on
the retina is the same pattern
as on the left but shifted due
to the prism. (Adapted from
Rushton et al. [
31
])
(a)
(b)
Gibson's theories [
10
] suggest that heading is determined from the center of expan-
sion of optic flow. When people walk toward a target, they adjust their movements to
align heading direction with the intended goal. Warren et al. [
39
] further investigated
whether the egocentric direction hypothesis or the optic flow hypothesis dominates.
They had people walk through virtual scenes with different textures to create differ-
ent amounts of optic flow to see if the amount of optic flow affected participants'
heading direction as they moved to a target. Their results show that with no optic
flow participants followed the egocentric direction hypothesis, however when optic
flow was added to the ground plane, participants initially followed the egocentric
direction hypothesis, and then after traveling a few meters participants adjusted their
heading and used optic flow to aid their guidance.
The results of Warren et al. demonstrated that humans rely on both optic flow and
egocentric direction to guide locomotion. These results suggest that manipulations
of the visual representation of the scene can guide the user so she walks a straight
path in the virtual scene concurrently with walking a curved path in the laboratory.
Slight manipulation of optic flow may go unnoticed by a user; however, extreme
changes will be detectable. Studies from aircraft simulation provide further under-
standing of ways that IVE system and scene designers can manipulate rendered vi-
suals without the user noticing. Research by Hosman and van der Vaart determined
the sensitivity of the visual and vestibular senses to different rotation frequencies
or speeds, i.e., the frequency response of the two senses [
12
]. The results suggest
