Cosc 6326/Psych6750X

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Cosc 6326/Psych6750X

• Movement, Tracking

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Moving about virtual and real environments
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• Simulating motion through the environment
• visual (vection)
• vestibular stimulation
• auditory surround motion/vibration
• tactile surround motion/vibration
• cues associate with active and passive limb
  motion (proprioception and efference)

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Motion Perception

• Human beings are highly sensitive to retinal
  motion
• hyperacuity
• relative motion more salient than absolute
• need to account for eye movements and distance to
  obtain linear from angular speed
• autokinetic effect
• induced motion
• motion can define form

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• apparent motion
• sense of motion from sequential presentation of
  discrete images
• 15 frames per second normally considered
  marginally acceptable
• want for 30 to 60 frames per second, ideally at
  refresh rate
• patterns of motion give information about depth
  and 3D motion

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Depth from motion
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Figure ground segregation

• Motion can define form
• Boundaries of foreground image defined by
  accretion deletion regions

Motion in depth

• Various cues looming, changing disparity
• Time to contact/passage can be judged independent
  of speed
• Direction of motion in depth is also important

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Motion Parallax

• translation of observer w.r.t. to scene (or of
  scene w.r.t. observer)
• angular speed of objects across optic array
  varies with distance

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Motion Parallax

• if eye fixates
• objects nearer than fixation point move with
  observer, further objects move against observer
• retinal speed varies with distance from point of
  fixation

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• motion parallax provides information about
  spatial layout of the environment and relative
  motion relative to the environment
• many similarities to depth from stereopsis

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Self motion
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Optic flow

• Flow patterns in velocity field can be analysed
• could provide direction of heading (e.g. from
  focus of expansion)
• perception of self-motion/motion in depth
  (vection)

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• layout and depth of environment
• traditionally optic flow has been considered to
  be essential for control of locomotion
• note
• optic flow refers to velocity patterns in optic
  arrays not the retina
• need to account for eye movements to extract
  optic flow from retinal flow
• real flow fields are complex

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• Optic flow is a key component in
• perception of self-motion
• postural reflexes/body sway
• eye movements
• cybersickness

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Visual direction based locomotion

• Recently the idea that locomotion relies directly
  on the processing of optic flow has been
  challenged
• Alternative is locomotion is based upon
  egocentric direction (see seminar)

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Vection

• Normally world is stable and stationary
• A sense of self-motion can be elicited by visual
  motion (optic flow)
• Circular vection illusory rotation from optic
  flow
• Linear vection illusory translation from optic
  flow

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• vection has a latency
• depends on stimulus
• reported as 5-30 s
• believed to be due to conflict with vestibular
  system, may benefit from vestibular priming
• may be partial or saturated, can drop out

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• vection is
• strengthened by large FOV
• increased with increased optical
  velocity/spatio-temporal frequency
• sensitive to foreground background relationships
  (driven by background)
• integrated with vestibular and motor copy
  (efferent) signals centrally

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• Vection
• can provide compelling self motion cues
• enhances presence and realism
• but
• is linked to cyber sickness and other negative
  aftereffects
• main issue is mismatch between visual and other
  self motion cues (to be discussed later).

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• as well as vection, vision can provide important
  static cues to orientation (as well see in the
  tumbling room demo)

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Vestibular Inputs

• organs of balance and equilibrium in inner ear
• two distinct sub-systems
• semicircular canals angular acceleration
• otolithslinear acceleration
• self-motion perception, eye movements, postural
  control, orientation wrt gravity

http//www.medicine.mcgill.ca/physio/cullenlab/img
/ear.gif
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• canal response
• inertial sensors detect angular acceleration
  (three degrees of freedom)
• high-pass frequency response
• insensitive to low-frequency signals
• codes head velocity over relevant frequency range
• vision and other senses contribute as well but
  vestibular system most reliable at high frequency
• drives very low latency compensatory eye
  movements (vestibulo-ocular reflex VOR)

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• otolith response
• sensitive to three-dimensional linear
  acceleration
• also sensitive to gravity (head tilt or pitch)
• linear acceleration due to gravity can be
  confused with linear acceleration due to motion
• possible to trade tilt for acceleration

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Other non-visual cues to motion

• proprioceptive and somato-sensory cues can
  contribute to effective perception of self
  motion, e.g.
• wind on face or body
• weight on limbs, soles of feet, seat etc. can
  indicate direction of gravity/accelerations
• active and passive limb motions associated with
  motion, efference copy
• visceral receptors

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Motion Displays
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Actual Motion Displays
mozu.mes.titech.ac.jp/research/
walk/PW/gif/Stewart.gif
NASA space shuttle simulator
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Spaceball
Flogiston chair
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Other issues

• active motion?
• range of possible motion limited
• requirement to stay centered in range of motion

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Washout filter

• Vestibular system is most sensitive to changes in
  velocity (accelerometer)
• provides an onset cue for self motion
• extended motion simulated with vision and other
  cues
• some problems with a motion base
• simulating extended motion with limited travel
  (isomorphism)?
• need to stay near centre of range to prepare for
  future motion

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• After onset cue, desirable to home to a neutral
  position.
• Do this gradually and ideally imperceptibly
  washout
• Washout filters are based on highpass filters to
  give washout and a fast transient response

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• Wearable computers allow long range natural
  (physical) motion
• Many devices have been proposed to introduce
  somatosensory and proprioceptive cues
• treadmills
• bicycles
• hang gliders (skis, motorcycles, )
• importance of feel for vehicle controls (haptic
  feedback)

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Treadmills

• Simulating locomotion may require displays for
• forward motion
• turning
• slope
• terrain roughness, solidity
• other postures (e.g. crawling)

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• http//intron.kz.tsukuba.ac.jp/vrlab_web/gaitmaste
  r/gaitmaster_2.mpg

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movie
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Tracking
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• critical component for immersive displays
• supports
• structure from motion perception
• maneuvering
• locomotion
• active perception
• situational awareness

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• Field of Regard
• amount of space (in terms of visual angle) filled
  by the virtual world
• an effective increased effective FOV beyond the
  instantaneous FOV that is provided by tracking
  head motion

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• Tracker issues
• resolution, smoothness, degrees of freedom
• display lag is a major problem in head-slaved
  displays (more in sensory conflict lecture)
• sensor transduction, data transmission, input
  handling, simulation, rendering, wait for frame
  refresh
• when head moves or vibrates display is not
  updated immediately
• prediction can help

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• Consequences
• fatigue, nausea (simulator sickness), poor
  performance
• poor fidelity and distortions of virtual space
• image slip, blur or instability
• See Foxlin handout to be discussed

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Navigation
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• Two components to navigating
• way finding
• travel

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Wayfinding

• Refers to determination of current location and
  path to desired location
• Need to maneuver through environment and avoid
  obstacles when wayfinding (or wandering)
• need to provide cognitive information to support
  location determination and wayfinding behaviour
  (navigational awareness)

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• people believed to form cognitive maps or models
  of the environment
• In VR we need to be able to navigate about the
  VE.
• A typical goal of wearable computers is to
  provide navigational awareness.

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• Aids to wayfinding
• landmarks (natural or artificial)
• path following/leaving trails
• maps
• memorable place names
• compass/instruments
• exocentric views
• coordinate display, grid structure
• constrained travel

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Travel

• Current VR systems allow small tracked work
  spaces
• To move to other places in the virtual
  environment (or in the real world) need to
  support travel
• Physical travel fits real world
• Locomotion on foot is natural form of travel
• Vehicular travel is also familiar
• direct or indirect control and locomotion

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• Travel through computer based worlds using mice
  and joystick is familiar to many (computer games
  etc)
• Travel through time is also useful

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Travel Methods and Metaphors

• Real locomotion
• modest distances, limited by tracking
  capabilities
• some tricks possible (seminar later)
• typically some real locomotion supported in
  addition to other techniques
• Ride along a preplanned route

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• Tow rope or river metaphor

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• Fly mode
• most common, lots of freedom
• walk through is fly mode constrained to follow
  the terrain
• direction and speed control
• pointer (gaze, torso, gesture, wand/joystick, )
• can drive vehicles using virtual or physical
  controls, often with increased control over
  speed, acceleration

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• moving /scaling the world
• often used in visualization
• put me there method
• jump to a defined location
• ask to go to named location
• define location in a exocentric, map or
  world-in-miniature display
• stepping into a picture or aperture into a
  different world

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• all methods except real locomotion dissociate
  real from virtual travel
• Problems with this dissociation
• conflict between real and physical motion
• unnatural, may interfere with wayfinding
• not suitable for AR or wearable applications
• Real motion is most natural but not always
  desirable in virtual environments (for example
  travelling large distances or through outer space
  etc)

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• Interest in extending the range of real physical
  motion
• Hi-ball and other long range trackers
• vision based AR trackers wearable systems
• GPS, landmark based
• York Trike project