Virtual Environments
Week 9 Seminar
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Presence
Presence
• Presence:
– Refers to ‘Being in an environment
– Degree of presence in one environment relative to another
• Subjective presence
– Response to questions about being there
– Verbal and conscious
– Evaluation of an experience
• Behavioural Presence
– Observable responses to stimuli
– Responses to the events in the environment in question
• May be measured by subjective means or through observation
Bodily Movement and Presence
• Main Hypothesis:
– “ The environment relative to which major body movements are made has a higher
probability of being the dominant presence environment, other things being equal”
– Examine influence of two factors
• Extent of body movement
• Complexity of task
• Major interest on body movement
– Motivated by two factors
• “aha” type of experience
• Construct interactive techniques
• Null Hypothesis
• Scores are attributed randomly and independently
• Measured with questionnaires with six questions each on scale of 1 to
7
Factorial Design
• Assess the extent to which body movement influences
presence, particularly bending and head movement
• Scenario devised that would naturally induce subjects to
use bending and head movements
– Field of unusual plants or trees with large leaves distributed at
random through the field
• Half subjects put into field where heights varied, other half
where heights were constant
• Asked to move around field and count number of diseased
plants
• More complex task also given
Design
Virtual field
Virtual lab
Design(2)
• 20 subjects in total, between factorial design used
within 5 subjects in each condition
• 15 male subjects, no subject had involvement in
research or knowledge of purpose
• 150 trees in each scene, randomly distributed in a
garden of dimension 90m-75
• Each tree had 16 leaves
– A healthy one
– One bad leaf
– 4 bad leaves
Procedure
• When initially put HMD on subjects were placed in
virtual lab
• Carried out initial training tasks “in the lab”
– Instructed to turn head, bend down, e.t.c to realise
these actions were possible
• Then went through door into field of plants and
told to carry out tasks
– 3 minutes time limit stated beforehand
• Then returned to lab, removed HMD and
questionnaires administered
Explanatory Variables
•
•
•
•
•
Background information: gender and occupation
Pitch in degrees/sec
Yaw in degrees/sec
Roll in degrees/sec
Mean and standard deviation of hand height
above ground level
Results
• Body movement
• Variation of body height (bending and standing)
• Degree of head colation
• ‘Tree height’ main source of variation for body movement,
whereas task main source of variation for head colation
• Low variation tree field - no bending down but
considerable head movement.
• Average head movement not significant between 2 tree
groups – major difference was overall body movement
• Body movement measured by hand height
Results 2
Variable( Tree 1
/s)
(low)
Tree2
(high)
Task Level 1
(simple)
Task Level 2
(complex)
Pitch
Mean=3.4
sd=1.4
Mean =3.3
sd =1.4
Mean= 3.7,
sd = 0.9
Mean = 5.1
Sd = 1.1
Yaw
Mean=12.3 Mean=10.1 Mean=9.4
Sd=3.7
Sd=3.5
Sd=3.3
Mean=13.0
Sd=3.1
Roll
Mean=13.5 Mean=11.2
Sd = 4.1
Sd=3.7
Mean=4.0
Sd=1.7

Mean=2.6
Sd=0.7
Note: The differences within each pair of Task means are significant on a t test at
5% on 18 df),
Analysis
• Task not as significant as interaction between
gender and task
• Significant relationship between presence and
body movement variables
• Positively associated with yaw
• Negatively associated with vertical variation
Conclusion
• Presence likely to be positively associated with
amount of body movement
• Results of impact of type of task inconclusive
Walking>Walking in-Place>Flying in Virtual
Environment
• Previous Study:
–
–
–
–
Slater et.al 1995
Walking-in-Place Vs push button flying
Virtual treadmill
Neural Networks to analyze the tracked head motion
• Gains:
– Virtual Walking has higher subjective sense of presence
than push button flying.
Current Project Hypothesis: Real walking results
in higher sense of presence
• Current Study:
– Add Real Walking
– Use Wide area tracker
– Enhanced Graphics & Avatar representation
• Objectives:
– Do Results of previous study hold true given more
recent technology?
– To compare Virtual walking, Real Walking & flying with
respect to ease of Locomotion & subjective presence.
Terminologies
• Flying:
– Flying is done in the direction of gaze to make the Flyer
& Virtual walker groups match.
• Virtual Walking:
– Participants reproduce the physical head motion
generated during actual walking, but without physical
locomotion
• Real Walking:
– Participants are free to walk around in the entire Virtual
scene as in real.
Real Walking Implemented
• Implementing Virtual Walking:
– Track user’s head & one hand using a custom optical
tracker
– Track over a range of 10m x 4m with millimeter
precision
– Two optical sensors view infrared LED’s on ceiling.
– Tracked Position & Orientation updated every 1.5kHz
– Tracker latency of 25ms, total latency 100mm
• Problems:
– Watch the cables!!
How does the world look like?
• The Virtual World
– Divide tracked place into a training & experimental area.
(room with the virtual pit)
– Modern Graphics Engine, 40000 polygons
– More Detailed Avatar, 11000 polygons
– Radiosity lighting & texture for almost half the polygons
– Subjects looking down can see their virtual body, feet,
untracked left hand & tracked right hand.
The task
• In the training room:
• Instructions given to
– Travel to a certain point along the corridor
– Grasp virtual objects
• In the experiment room
– Walk to the chair
How does the world look like?
The Experiment
• Technology
– Silicon, Onyx2 with 1 graphic pipeline, two raster
managers.
– Four 195Mhz R10000 processors, 2GB main memory.
– Scene Rendered using OpenGL, frame rate 30Hz
stereo
– Viewing by V8 Head Mounted Display with VGA
resolution (640x3) x 480
– Display consists of two1.3 inch active LCD
Experiment 2
• Input
– Joystick with four buttons, two were used in experiment, tracked by ceiling
tracker.
• Participants
– 33 ‘naive’ subjects, grouped into virtual walkers, real walkers, flyers. 5
women, 6 men. & 11 ‘expert ’ subjects, 10 men, 1 woman
• Questionnaires
– Simulation sickness questionnaires
– Presence questionnaires
– Oral sessions
Conclusions & Results
• Conclusions
– Confirm that presence is highly correlated with degree
of association with virtual body.
– Presence is higher for real walkers than for virtual
walkers & flyers.
• Locomotion
Results 2
• Subjective Presence
– No significance difference in all groups
– Association with virtual body, directly related to rating of
presence
– Females have higher sense of presence than males
(play less video games)
– For flyers & virtual walkers higher discomfort is created
by less sense of present but not the case for real
walkers
Improvements
• Cables are unsatisfactory, currently working on wireless
• Real walkers are best for human scale space but not
cheap
• Replace flying with virtual walking, when presence is
important, & inexpensive to implement
• Avatar realism, worth investing on
• Clothing identification very important for some
• Investigate voice location e.g. give instructions through
HMD.
The concept of Presence
“Perceptual illusion of non-mediation”
Lombard and Ditton
The extent to which the person fails to perceive or
acknowledge the existence of a medium during a
technologically mediated experience.
Presence
“when the individual fails to perceive the medium
throughout a technologically mediated experience..”
Types of Presence
The sense of presence has been studied as some
Type of Presence:
Physical: Feeling of been located somewhere (else).
Social: Feeling of been (and communicate) together.
Determinants of presence
In order to improve the sense of presence we analyze the
Factors that encourage or discourage the feeling of
“being there”
•
•
•
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The extent and fidelity of sensory information.
The match between sensors and displays
Content factor
User characteristics
The extent and fidelity of sensory information
• the ability of a technology to produce a sensorially rich
mediated environment.
• the amount of useful and salient sensory information
presented in a consistent manner to the appropriate
senses of the user.
The match between sensors and displays
Refers to the sensory-motor contingencies, i.e. the
mapping between the user’s actions and the
perceptible spatio-temporal effects of those actions.
For example, using head tracking, a turn of the user’s head should result
in a corresponding real-timeupdate of the visual and auditory display.
Content factor
Our ability to interact with the content and to modify it
•
objects, actors, and events represented by the medium
•
the user’s representation or virtual body in the VE
•
autonomy of the environment, i.e. the extent to which objects and actors (e.g.
agents) exhibit a range of autonomous behaviors
•
Social elements, such as the acknowledgement of the user through the
reactions of other actors, virtual or real, will be important for establishing a
sense of social presence15
User characteristics
• the user’s perceptual, cognitive and motor abilities (e.g.
stereoscopic acuity, susceptibility to motion sickness,
concentration)
• prior experience with and expectations towards mediated
experiences
• willingness to suspend disbelief
• various mental health conditions, like depression, anxiety,
or psychotic disorders, are also likely to affect an
individuals sense of presence
Relationship between presence factors