Virtual Environments

Presence

Week 9 Seminar

\

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(/s)

Tree 1

(low)

Tree2

(high)

Task Level 1

(simple)

Task Level 2

(complex)

Pitch Mean=3.4 sd=1.4

Mean =3.3sd =1.4

Mean= 3.7, sd = 0.9

Mean = 5.1

Sd = 1.1

Yaw Mean=12.3

Sd=3.7

Mean=10.1

Sd=3.5

Mean=9.4

Sd=3.3

Mean=13.0

Sd=3.1

Roll Mean=13.5

Sd = 4.1

Mean=11.2

Sd=3.7

Mean=2.6

Sd=0.7

Mean=4.0

Sd=1.7

€

±

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

• The extent and fidelity of sensory information. • The match between sensors and displays• Content factor• User characteristics

In order to improve the sense of presence we analyze theFactors that encourage or discourage the feeling of “being there”

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