Transcript cummingsWalkingVR

The Perception of Walking
Speed in a Virtual
Environment
By T. Banton, J. Stefanucci, F. Durgin, A. Fass, and D. Proffitt
Presentation by Ben Cummings
For Animation (CS551-4), Fall 2003, with Dave Brogan
Perception of speed
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Important for simulation of motion in virtual
environments (driving or flight sims, for
example)
Influenced by many cues, though we'll deal
primarilly with visual and proprioceptual
(physical sensation of body movement)
Radial Optical Flow
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Results from looking
down the axis of
movement
Things expand from
the vanishing point
faster when they're
closer to the viewer
Lamellar Optical Flow
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Results from looking
closer to
perpendicular to the
axis of motion
Objects' speed in
image space stay
constant when
perpendicular
Optical Flow
●
When looking forward and moving, radial
optical flow occurs towards the center of the
view and lamellar flow occurs towards the
periphery
Perception of movement speed
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In reality, under normal conditions, people
are usually good at judging their speed of
movement
In virtual environments, there is markedly
different performance
–
Particularly, in situations on treadmills with
simulated correct optical flow, subjects perceive
the speed of the visuals to be slower than their
own speed
Perception of movement speed
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The claim: The difference in actual motion
and perceived motion is due to decreased
lamellar flow in virtual environments
–
Display technology often cuts off the peripheral
vision where lamellar flow is seen
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Head mounted displays (HMDs) are usually about
one third of the natural field of vision
Wall-mounted screens also usually occupy a small
fraction of the natural field of vision
Experiment One
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Participants walk on a treadmill wearing a
HMD with simulated optical flow and try to
match the speed of walking to the speed of
flow
–
–
Participants looked straight ahead
Treadmill ran at 3 mph ( a fast walk )
Experiment One: Results
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Subjects chose an optical flow corresponding
to 4.6 mph to match the speed of walking
Straight-ahead optical flow in the HMD is
perceived to be too slow for the actual
movement speed
Experiment Two
●
This experiment is the same setup as
experiment one, but instead of the subjects
looking straight ahead, they look
perpendicularly to the direction of motion
–
–
●
Both looking down at the ground
And looking over to a point on the horizon
This maximizes lamellar flow
Experiment Two: Results
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When looking both down and over,
participants chose the optical flow speed that
corresponded with the walking speed
–
the error of their guesses increased with walking
speed, but without general over or
underestimation
Experiment Three
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Does the walking simulation cause the
misperception of speed?
–
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Subjects walk at normal speed and in “baby
steps”
Although perception differs, subjects
perceived the optical flow to be closer to
correct when using baby steps, so stridelength cannot be used to account for the
error in estimation from experiment one
Experiment Four
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Is misperception caused by image latency or
jitter?
Experiment with perception when the eye
point is tracked to head movement (which
introduces latency) vs. when it is constant.
Result: speed is similarly misperceived with
or without jitter and latency.
Discussion
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Hypothesis is consistent with the effects of
different fields of view in speed estimation
–
–
–
Cycling speed underestimated with FOV < 73
degrees, and overestimated with FOV > 103
(Van Veen, et al. 1998; Osaka 1988)
What does this mean for perception of speed in
games with variable FOV?
Other functions such as estimation of time to
contact and simulated flight accuracy get better
with larger FOV (to a point)
More Discussion
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Some applications are not conducive to
turning to the side (e.g. driving sims)
–
They suggest “adjusting the gain of optical flow”
when facing forward. How would this work while
maintaining geometric consistency?
Questions?