17/02/2020
1
PA201
Virtual Environments
Lecture 1
Introduction to Virtual Reality
Fotis Liarokapis
liarokap@fi.muni.cz
17th February 2020
Fotis Liarokapis
• PhD in Computer Engineering
– University of Sussex, UK
• MSc in Computer Graphics
and Virtual Environments
– University of Hull, UK
• BSc in Computer Systems
Engineering
– University of Sussex, UK
My Research
• Research areas:
– Computer Graphics
– Virtual Reality
– Augmented Reality
– Procedural Modeling
– Interactive Environments
– Serious Games
– User studies
Contact Details
• Email:
– liarokap@fi.muni.cz
• Telephone:
– 549493948
• Office Location:
– C411
• Office Hour:
– Monday 13:00 to 14:00
Course Details
• Prerequisites
– Knowledge of computer graphics fundamentals
• Lectures
– Every Monday
– Time: 14:00 to 16:00
– Location: B411
• Lab/Seminar
– Every Monday
– Time: 16:00 to 17:00
– Location: B311
Course Objectives
• Demonstrate an understanding of the main
mathematical concepts, hardware and software
technologies used in immersive virtual
environments
• Evaluate different approaches, methodologies
and tools focused on virtual reality
• Propose virtual environments for both indoor
and outdoor environments
• Design virtual reality applications for various
application domains
17/02/2020
2
Syllabus
• Introduction to Virtual
Environments
• Head Mounted Displays
• Other Visualisation
Technologies
• Virtual reality interaction
techniques
• Design guidelines
• Tracking technologies
• Physical simulation
• Haptics
• Perception Issues for Virtual
Environments
• Psychological aspects of
Virtual Environments (i.e.
motion sickness, nausea)
• Collaborative Virtual
Environments
• Software for Virtual
Environments (i.e. VR toolkits)
• Mobile Virtual Environments
• Application Domains
• Future of Virtual Environments
Teaching Methods
• Delivery of the material will
be based on
– Expositional lectures
– Reinforced by computer
demonstrations of the
application of the material
– Video demonstrations
Assessment Methods
• An assignment about designing, implementing
and testing a virtual environment
– An essay
– Practical assignment
• 4 credits awarded
Plagiarism and Cheating
• If you use an external resource cite it clearly!
• Don’t do things that would be considered
dishonest... if in doubt ask
• Cheating earns you:
– Fail in the class
– Getting reported to the University
– No exceptions
Report Structure
• Title page
• Contents
• Abstract (or summary)
• Introduction
• Background theory
• Methodology and results
• Conclusions
• References
• Appendices
VR History
17/02/2020
3
First VR Interpretation
http://www.bradshawfoundation.com/news/cave_art_paintings.php?id=The-Spanish-Cave-of-Altamira-opens-with-politics
Stereoscopic Photos & Viewers
• In 1838 Charles Wheatstone’s demonstrated that
the brain processes the different 2D images from
each eye into a single object of three dimensions
– Viewing two side by side stereoscopic images or photos
through a stereoscope gave the user a sense of depth and
immersion
– The later development of the popular View-Master
stereoscope (patented 1939), was used for “virtual
tourism”
– The design principles of the Stereoscope is used today for
the popular Google Cardboard and low budget VR head
mounted displays for mobile phones
http://www.vrs.org.uk/virtual-reality/history.html
Stereoscopic Photos & Viewers .
• 1838 : The stereoscope (Charles Wheatstone)
http://www.vrs.org.uk/virtual-reality/history.html
Stereoscope and View-Master
• 1849: The lenticular stereoscope (David
Brewster)
• 1939: The View-Master (William Gruber)
http://www.vrs.org.uk/virtual-reality/history.html
Link Trainer
• In 1929 Edward Link created the
“Link trainer” probably the first
example of a commercial flight
simulator, which was entirely
electromechanical
– Patented 1931
• Controlled by motors
– That linked to the rudder and steering
column to modify the pitch and roll
– A small motor-driven device mimicked
turbulence and disturbances
http://www.vrs.org.uk/virtual-reality/history.html
Link Trainer .
• US military bought six of these devices for $3500
(~ $50,000 today's money)
– During World War II over 10,000 “blue box” Link
Trainers were used by over 500,000 pilots for initial
training and improving their skills
http://www.vrs.org.uk/virtual-reality/history.html
17/02/2020
4
Science Fiction Story Predicted VR
• In the 1930s, Stanley G. Weinbaum (Pygmalion’s
Spectacles) proposed a pair of goggles that let
the wearer experience a fictional world through
holographics, smell, taste and touch
http://www.vrs.org.uk/virtual-reality/history.html
Sensorama (1950)
• In mid 1950s Morton H Eilig
built a single user console called
Sensorama that included a
stereoscopic display, fans, or
emitters, stereo speakers and a
moving chair
– This enabled the user watch
television in 3D
Telesphere Mask (1960)
• In 1960, Morton Heilig invented
the Telesphere Mask (patented
1960)
– First example of a head-mounted
display (HMD), albeit for the noninteractive
film medium without
any motion tracking
– The headset provided
stereoscopic 3D and wide vision
with stereo sound
http://www.vrs.org.uk/virtual-reality/history.html
Headsight HMD (1961)
• In 1961, Philco Corporation engineers
developed the first Head-Mounted Display
(HMD)
– Known as the ‘Headsight’
• The helmet consisted of a video screen along
with a tracking system
– Also linked to a closed circuit camera system
• Similar HMD was used later for helicopter pilots
Ultimate Display (1965)
• In 1965, Ivan Sutherland
proposed the ‘Ultimate Display’
– After using this display a person
imagines the virtual world very
similar to the real world
• During 1966, he built an HMD
– Was tethered to a computer system
Ultimate Display
HMD
GROPE (1967)
• In 1967, Brooks
developed force
feedback GROPE
system
17/02/2020
5
Sayre Glove (1977)
• Sandin and Sayre invent a bendsensing
glove
– The first wired glove
• The Sayre Glove, created by
Electronic Visualization
Laboratory in 1977
– Used light based sensors with
flexible tubes with a light source
at one end and a photocell at the
other
– As the fingers were bent, the
amount of light that hit the
photocells varied, thus providing
a measure of finger flexion
https://www.evl.uic.edu/entry.php?id=2162
Polhemus FASTRAK Tracker (1979)
• FASTRAK tracks the position (X, Y, and Z
Cartesian coordinates) and orientation
(azimuth, elevation, and roll)
• Uses electro-magnetic fields to determine the
position and orientation of a remote object
https://polhemus.com/
Virtual Reality Birth (1987)
• In 1987, Jaron Lanier,
founder of the visual
programming lab (VPL),
coined the term ‘virtual
reality’ and developed a
range of VR gear
– Dataglove (along with Tom
Zimmerman)
– EyePhone head mounted
display
• A major development in the
area of virtual reality haptics
http://www.vrs.org.uk/virtual-reality/history.html
VIEW (1989)
• The first complete VR
system was developed by
NASA
– “Virtual Visual
Environmental Display”
• Became “Virtual Interface
Environment Workstation”
(VIEW) 1989
Sega VR Headset
• In 1993, Sega announced the Sega
VR headset for the Sega Genesis
console
– The wrap-around prototypeglasses
had head tracking, stereo sound and
LCD screens in the visor
• Commercial failure!
– Developed 4 games for this product
– Never made it to the market due to
technical development difficulties
http://www.vrs.org.uk/virtual-reality/history.html
Nintendo Virtual Boy
• In 1995, Nintendo Virtual Boy
(known as VR-32) was the first
ever portable console that could
display true 3D graphics
• A commercial failure
– The following year they discontinued
its production and sale
• Reasons for this failure were
– Lack of colour in graphics (games
were in red and black)
– Lack of software support
– Difficult to use the console
http://www.vrs.org.uk/virtual-reality/history.html
17/02/2020
6
The Rig (1999)
• Philip Rosedale founds Linden
Lab and focuses on developing
‘The Rig’
– A VR device users could wear on
their shoulders
• Development proves impossible
• Linden Labs starts developing
virtual worlds
– Including ‘Second Life’
https://vrroom.buzz/vr-news/lifestyle/second-life-virtual-real-relationships
VR Nowadays
Current State of VR
• Nowadays VR is moving from the research
laboratories to the working environment by
replacing ergonomically limited HMD’s with
– Projective displays
• CAVE and Responsive Workbench
– Mobile devices
• PDAs, smartphones, tablets, etc
– Interaction devices
• Wii, Kinect, many others
VR Nowadays
• $3-5 Billion VR business
– Around $150 Billion Graphics
Industry
– Visualization, simulation,
gaming, CAD/CAE, multimedia,
graphics arts
• Closely aligned with computer
games/video games and other
apps
VR Nowadays .
• A number of different expensive
devices exist
• Target to get full immersion
Forecast unit shipments of AR and VR
headsets from 2019-2023 (in millions)
https://www.statista.com/statistics/653390/worldwide-virtual-and-augmented-reality-headset-shipments/
17/02/2020
7
https://www.forbes.com/sites/solrogers/2019/06/21/2019-the-year-virtual-reality-gets-real/#40e6d63c6ba9 https://venturebeat.com/2019/10/24/superdata-facebook-sold-180000-oculus-quests-in-q3-2019/
https://nwn.blogs.com/nwn/2019/06/vr-headset-shipments-superdata-2022-forecast.html
VR Headsets
Google Cardboard
• Launched in 2014
• SDK is available for the
Android and iOS
• Over 5 million Cardboard
viewers
• Over 1,000 compatible
applications
https://vr.google.com/daydream/
Open Source Virtual Reality
• The Open Source Virtual
Reality (OSVR) introduced on
January 2015
• VR headset that claims to be
open-source hardware and
use open-source software
– Developed by Razer and
Sensics
https://www.razerzone.com/osvr
17/02/2020
8
Samsung Gear VR
• Released on November
27, 2015 in collaboration
with Oculus
• Designed to work with
Samsung’s flagship
smartphones
http://www.samsung.com/global/galaxy/gear-vr/
Google Daydream
• The Daydream View headset is made with
lightweight fabric and launched in 2016
– Discontinued 2019
• Paired with a controller equipped with smart
sensors to understand movements and gestures
https://vr.google.com/daydream/
PlayStation VR
• Project Morpheus launched
on October 13, 2016
• Designed to be fully
functional with the
PlayStation 4
• Tracks 360 degree head
movement based on nine
positional LEDs on its
surface for the PlayStation
Camera
https://www.playstation.com/en-us/explore/playstation-vr/
Oculus Rift
• Released on March 28, 2016
• The Rift has a stereoscopic OLED display,
1080×1200 resolution per eye, a 90 Hz refresh
rate, and 110° field of view
https://www.oculus.com/
HTC Vive
• Released on 5 April 2016
• Refresh rate of 90 Hz, two screens, one per eye,
each having a display resolution of 1080x1200
• Laser position sensors, 4.6 by 4.6 m tracking
space
http://store.steampowered.com/app/358040/
FOVE
• FOVE is the first virtual
reality headset that
utilizes eye tracking
– Accuracy of 1/20th of a
degree
– Will utilize SteamVR's
Lighthouse technology for
positional tracking
https://www.getfove.com/
17/02/2020
9
Oculus Go
• All-in-one headset that’s portable and easy to
use
– No need to use mobile phones
• Lacks cameras and can't track a whole room, or
even part of one
– Not as powerful as the PC version
https://www.oculus.com/go/
HTC VIVE Pro Eye
• Improves input and navigation
• Eye tracking
– Foveated Rendering
• Perfect for VR experiments
https://www.vive.com/eu/product/vive-pro-eye/
Oculus Quest
• Best mobile VR solution to date
• Quest' users have more freedom of movement
and can virtually (thus physically) walk around
with the headset on
https://www.oculus.com/quest/ https://www.reddit.com/r/OculusGo/comments/adx2vg/differences_between_oculus_go_quest_and_rift_from/
VR Definitions
Virtual Reality Definition
• “The computer-generated simulation of a 3D
image or environment that can be interacted
with in a seemingly real or physical way by a
person using special electronic equipment, such
as a helmet with a screen inside or gloves fitted
with sensors”
• Some popular related terms include:
– Virtual Environments (VE), Artificial Reality,
Telepresence and Cyberspace
http://www.oxforddictionaries.com/definition/english/virtual-reality
17/02/2020
10
Telepresence
• The use of various
technologies to
produce the effect of
placing the user in
another location
Artificial Reality
• Responsive Environment
– An environment where human
behavior is perceived by a
computer which interprets
what it observes and responds
through intelligent visual and
auditory displays
Burdea’s 3 I’s of VR
• Interactivity
– User impacts world
• Immersion
– Believing you are there
• Imagination
– User ‘buying’ into the experience
Zeltzer’s Cube
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
VR Typical Architecture
User
(programmer,
trainee, etc.)
Modern VR Systems
17/02/2020
11
Basic Components
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
VR Rendering
• The visual display transformation for VR is much
more complex than in standard computer
graphics
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
Stereoscopy
• Stereo vision relies on depth-cues based on retinal
disparity and therefore may greatly increase the feeling
of immersion
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
Stereoscopic depth-cues: (a) eye convergence, (b) retinal disparity
VR Types
Characteristic Types
• Windows on World
• Immersive
• Telepresence
• Distributed
• Mixed Reality
• Extended Reality
Windows on World (WoW)
• Also called monitorbased
VR
– Similar to games
• Using a conventional
computer monitor (or
mobile device) to
display the 3D virtual
world
17/02/2020
12
Immersive VR
• Completely immerse the
user's personal viewpoint
inside the virtual 3D world
• The user has no visual
contact with the physical
word
• Often equipped with a Head
Mounted Display (HMD) or
use of CAVE displays
Telepresence
• A variation of visualizing complete computer
generated worlds
• Links remote sensors in the real world with
the senses of a human operator
• The remote sensors might be located on a
robot
• Useful for performing operations in dangerous
environments
Teleoperating
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
Distributed VR
• A simulated world runs on several computers
which are connected over network and the
people are able to interact in real time,
sharing the same virtual world
Mixed Reality
• Milgram coined the term ‘Augmented Virtuality’
to identify systems which are mostly synthetic
with some real world imagery added such as
texture mapping video onto virtual objects
Paul Milgram and Fumio Kishino, 1994
Extended Reality (XR)
• Referring to all real-andvirtual
combined
environments and humanmachine
interactions
generated by computer
technology and wearables
– Includes augmented reality
(AR), mixed reality (MR) and
virtual reality (VR)
17/02/2020
13
VR Paramount
VR Immersion
• In a typical VR system the user’s natural
sensory information is completely replaced
with digital information
• The user’s experience of a computersimulated
environment is called immersion
• As a result, VR systems can completely
immerse a user inside a synthetic environment
by blocking all the signals of the real world
VR Paramount
• Paramount for the sensation of immersion
into virtual reality are
– High frame rate
• At least 95 fps
– Low latency
– Pixel persistence lower than 3 ms is required
• If not, users will feel sick when moving their head
around
https://en.wikipedia.org/wiki/Virtual_reality
VR Paramount Diagram
https://en.wikipedia.org/wiki/Virtual_reality
VR Technologies
VR Tracking
• Many technologies exist
– Optical and magnetic and the most dominant
• Of course it depends on the application domain
• Immersive VR requires the position and
orientation of the viewer’s head
– Needed for the proper rendering of images
• Additionally other parts of body may be tracked
– Hands: to allow interaction
– Chest or legs: to allow the graphical user
representation
17/02/2020
14
VR Tracking .
• In general there are two
kinds of trackers:
– Those that deliver absolute
data (total
position/orientation values)
– Those that deliver relative data
(i.e. a change of data from the
last state)
• More in another lecture ...
Emitter and receiver units
of Polhemus Fastrak
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
Eye Tracking
• Eye-tracking techniques may be incorporated
to determine the gaze direction
• Useful for interaction and experiments
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
NAC Eye Mark eye tracker
Complete Body Experience
• VPL Research DataSuit
developed in 1989
• Full-body outfit with
sensors for measuring
the movement of:
– Arms
– Legs
– Trunk
https://en.wikipedia.org/wiki/Virtual_reality
VR Interfaces
• Keyboard, Mouse, Joystick
– 3D Pointing Devices
– Spaceball
– CyberWand
– Ring Mouse
– EEG
– ECG
VR Interfaces .
• Whole-hand and body input
– 5th glove
– Handmaster
– ArmMaster
– TCAS Dataware
Auditory Interfaces
• Auralization
– 3D simulation of a complex
acoustic field
• Sonification
– Audible display of data
• Speech Recognition
17/02/2020
15
Haptics
• Haptic, from the Greek ἁφή (Haphe), means
pertaining to the sense of touch
• Haptic technology refers to technology which
interfaces the user via the sense of touch by
applying forces, vibrations and/or motions to
the user
360-degree VR
• An audiovisual simulation of an altered,
augmented or substituted environment that
surrounds the user, allowing them to look
around them in all directions, just as they can
in real life
https://photo360tours.com/venice-in-italy-virtual-tour/
Augmented Reality
Introduction to Augmented Reality
• Augmented Reality
– Abbreviation (AR)
• Czech Translation…
– Rozšířená realita
Some Definitions
• “A technology that superimposes a computergenerated
image on a user’s view of the real
world, thus providing a composite view.”
• “An enhanced image or environment as viewed
on a screen or other display, produced by
overlaying computer-generated images, sounds,
or other data on a real-world environment.”
http://dictionary.reference.com/browse/augmented+reality
http://www.oxforddictionaries.com/definition/english/augmented-reality
Another Definition
• “… Augmented Reality is a type of virtual reality that aims to
duplicate the world's environment in a computer. An
augmented reality system generates a composite view for the
user that is the combination of the real scene viewed by the
user and a virtual scene generated by the computer that
augments the scene with additional information. The virtual
scene generated by the computer is designed to enhance the
user's sensory perception of the virtual world they are seeing
or interacting with. The goal of Augmented Reality is to create
a system in which the user cannot tell the difference between
the real world and the virtual augmentation of it. Today
Augmented Reality is used in entertainment, military training,
engineering design, robotics, manufacturing and other
industries.”
http://www.webopedia.com/TERM/A/Augmented_Reality.html
17/02/2020
16
Invisible Interfaces
Jun Rekimoto, Sony CSL
Augmented Reality Concept
• The concept of AR is the opposite
of the closed world of virtual spaces
since users can perceive both
virtual and real information
• Most AR systems use more complex
software approaches compared to
VR systems
– So, it is harder!
Augmented Reality Concept .
• The basic theoretical principle is to
superimpose digital information directly into a
user’s sensory perception rather than
replacing it with a completely synthetic
environment as VR systems do
– In some cases we want it to be very realistic, in
some other cases not!
VR and AR Similarities
• Both technologies process and display the same
digital information and often make use of the
same dedicated hardware
• For example, both an VR and an AR system may
be equipped with a head-mounted display
(HMD) to visualize the same 3D computer
generated model
VR and AR Differences
• An AR system uses the real world instead of
trying to replace it
• On the other hand, in a VR system the whole
environment is synthetic
• The user is completely immersed within a virtual
world trying to mimic reality
• A VR simulated world does not always have to
obey all laws of nature
VR and AR Differences .
• The most common problems of VR systems are
of emotional and psychological nature including
motion sickness, nautia, and other symptoms,
which are created by the high degree of
immersiveness of the users
• Although AR systems are influenced by the same
factors the amount of influence is much less than
in VR since only a portion of the environment is
virtual
17/02/2020
17
VR and AR Technology Requirements
Billinghurst, M., Clark, A. Lee, G. A Survey of Augmented Reality, Foundations and Trends in Human-Computer Interaction, Vol. 8, No. 2-3 2014
Mann’s Mediated Reality
Billinghurst, M., Clark, A. Lee, G. A Survey of Augmented Reality, Foundations and Trends in Human-Computer Interaction, Vol. 8, No. 2-3 2014
Metaverse
• Neal Stephenson’s “SnowCrash”
• The Metaverse is the convergence of:
– virtually enhanced physical reality
– physically persistent virtual space
• Metaverse Roadmap
– http://metaverseroadmap.org/
Metaverse Dimensions
• Augmentation technologies that layer
information onto our perception of the physical
environment.
• Simulation refers to technologies that model
reality
• Intimate technologies are focused inwardly, on
the identity and actions of the individual or
object
• External technologies are focused outwardly,
towards the world at large
Metaverse Components
• Four Key Components
– Virtual Worlds
– Augmented Reality
– Mirror Worlds
– Lifelogging
Mirror Worlds
• Mirror worlds are informationally-enhanced
virtual models of the physical world
– Google Earth, MS Street View, Google Maps
17/02/2020
18
LifeLogging
• Technologies record and report the intimate
states and life histories of objects and users
– Nokia LifeBlog, Nike+, FitBits
Human Factors
Contribution of Human Senses
• The contribution of each of the five human
senses:
– Sight................. 70 %
– Hearing.............. 20 %
– Smell ..................5 %
– Touch..................4 %
– Taste ...................1 %
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
Human Factors in VR
Human
Performance
Efficiency
Health
and
Safety
Societal
Implications
Stanney et al., 1998
Human Factors in VR .
Will the user get sick in VR?
Which tasks are most suitable
for users in VR?
Which user characteristics
will influence VR performance?
Will there be negative societal
impact from user’s misuse of
the technology?
What kind of designs will
enhance user’s performance
in VR?
How much feedback from VR
can the user process?
Will the user perceive
system limitations?
How should VR technology
be improved to better meet
the user’s needs?
?
Stanney et al., 1998
Simulator Sickness
• There are potentially many sources of
simulator sickness
• Hardware imperfection may contribute to the
generation of sickness feeling, because it fails
to provide perfect stimuli to human senses
• However, there are other crucial design issues:
– System latency
– Frame rate variations
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
17/02/2020
19
Dangers of VR/Video Games
• Excessive game play can be fatal
– Can be worst with immersive VR!
• In Korea, where 30% of the population
subscribes to online multiplayer games,
one man died in 2005 after playing 50
hours (almost non-stop) StarCraft
• 3 Chinese died in 2007 after playing
more than 50 hours, and 2 died in 2005
Dangers of VR/Video Games .
• EverQuest is a 3D online game
played by more than 400,000
people
• Games can lead to isolation and
suicide
• Hudson Wooley, an epileptic who
was playing 12-hours per day,
eventually committed suicide
Advantages of VR/Games
• People regularly exposed to video-games have
improved:
– Visual and Spatial attention (C. S. Green, D. Bavelier,
Nature, 2003)
– Memory (J. Feng et al., Psychol. Sci., 2007)
– Mental rotation abilities
– Enhanced sensorimotor learning (D. G. Gozli, et al.,Hum.
Mov. Sci., 2014)
• Extensive video-game practice has also been shown
to improve the efficiency of
– Movement control brain networks
– Visuomotor skills (J. A. Granek, et al., Nerv. Syst. Behav.,
2010)
Applications
Entertainment
• In last years W-Industry has successfully brought
to the market networked multi-player game
systems
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
Virtuality 1000DS from W-Industries
Medicine
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
VR in medicine: (left) eye surgery (right) leg surgery
17/02/2020
20
Simulations
https://www.cg.tuwien.ac.at/research/publications/1996/mazuryk-1996-VRH/TR-186-2-96-06Paper.pdf
Advanced flight simulator of Boeing 777: (left) outside view, (right) inside view
Cultural Heritage
https://imareculture.eu/
And Many More !
• Military
• Manufacturing
• Geography
• Education
• Etc ...
Videos
Cyber Tennis (1997) Video
https://www.youtube.com/watch?v=Ci6gL0da4R0
Social Phobia Video
https://www.youtube.com/watch?v=-4x1t6-UNjo
17/02/2020
21
Virtual Guide Video
https://www.youtube.com/watch?v=b6MkXsGViB4
More videos
• https://www.youtube.com/watch?v=b6MkXsG
ViB4
• https://www.youtube.com/watch?v=eCvs_pk
RAl4
• https://www.youtube.com/watch?v=rDjYa5LP
n5s
Questions