Correlation of Correlation of presence with presence with

locomotionlocomotionPresented byPresented by

Xiang Lin Liu & Philippe VervoortXiang Lin Liu & Philippe Vervoort

Virtual EnvironmentsVirtual EnvironmentsUniversity College LondonUniversity College London

November 2004-2005November 2004-2005

Sense of presence & Sense of presence & locomotionlocomotion

►Sense of being in the virtual place Sense of being in the virtual place rather than in the real physical placerather than in the real physical place

►used as qualitative property for good used as qualitative property for good virtual environmentsvirtual environments

► locomotion: self-propelled movementlocomotion: self-propelled movement

Background & objectivesBackground & objectives► Problem: Development of natural and effective virtual Problem: Development of natural and effective virtual

surrogates for user interactions with physical spaces and surrogates for user interactions with physical spaces and objectsobjects

► E.g. touching objects while actually feeling themE.g. touching objects while actually feeling them

► In general: Having your own body actively involved in the In general: Having your own body actively involved in the actions you take in virtual world actions you take in virtual world

► Locomotion through virtual spaces is most primitive and Locomotion through virtual spaces is most primitive and important special caseimportant special case

Background & objectivesBackground & objectives

► Active usage of participant’s bodyActive usage of participant’s body

with real sensations matched by synthetic with real sensations matched by synthetic visual and aural data STRONGLY affects visual and aural data STRONGLY affects virtual presence.virtual presence.

► 2 streams:2 streams: Wide-area trackersWide-area trackers Body-active surrogates for walkingBody-active surrogates for walking

► Common mode of locomotion: local walking Common mode of locomotion: local walking limited by tracker range, combined with limited by tracker range, combined with button-controlled flyingbutton-controlled flying

Virtual walkingVirtual walking

► Walk-in-place techniqueWalk-in-place technique► Uses neural net to analyze the tracked Uses neural net to analyze the tracked

head motion to detect stepshead motion to detect steps► Reproduce physical head motions Reproduce physical head motions

generated during actual walking but generated during actual walking but without physically locomotingwithout physically locomoting

► Indications that this technique Indications that this technique significantly enhances subjective rating significantly enhances subjective rating of presence, for subjects who of presence, for subjects who subjectively associated with their subjectively associated with their avatars. (Study by Slater et al.)avatars. (Study by Slater et al.)

Virtual walkingVirtual walking

►Changes in head position fed to a Changes in head position fed to a neural networkneural network

►Network recognizes when participants Network recognizes when participants are walking in placeare walking in place

►When virtual walking detected: moved When virtual walking detected: moved in virtual space in direction of head-in virtual space in direction of head-facingfacing

►This technique is intuitiveThis technique is intuitive

Slater study [1995]Slater study [1995]

►Slater study: naive subjects in an Slater study: naive subjects in an immersive virtual environment immersive virtual environment experience a higher subjective sense experience a higher subjective sense of presence when they locomote by of presence when they locomote by walking in place than when they push-walking in place than when they push-button-fly along the floorbutton-fly along the floor

Replicated studyReplicated study

► 2 streams brought together in replicated 2 streams brought together in replicated study:study: Wide-area ceiling trackerWide-area ceiling tracker Replicating Slater study of virtual walkingReplicating Slater study of virtual walking Real walking as a third conditionReal walking as a third condition

► Objectives:Objectives: See if earlier conclusions still hold true (more See if earlier conclusions still hold true (more

recent technology)recent technology) Compare flying, virtual walking and real walking Compare flying, virtual walking and real walking

with respect to ease of locomotion and subjective with respect to ease of locomotion and subjective presencepresence

Expectations of replicated Expectations of replicated study?study?

► If virtual walking indeed better than If virtual walking indeed better than flying:flying: Very economical, future substitute for Very economical, future substitute for

applications that use flying for locomotionapplications that use flying for locomotion

► If virtual walking essentially equivalent If virtual walking essentially equivalent to real walking:to real walking: Wide area tracking only used for Wide area tracking only used for

applications where physical motion is very applications where physical motion is very essentialessential

Enhancements to the original Enhancements to the original studystudy

► Real walking:Real walking: Walk around in same manner as in a real Walk around in same manner as in a real

environmentenvironment Tracked user’s head and one handTracked user’s head and one hand Tracker range ~10m by 4m (mm precision)Tracker range ~10m by 4m (mm precision) Updates at ~1.5kHzUpdates at ~1.5kHz Reports fed to application at 70HzReports fed to application at 70Hz Total latency 100msTotal latency 100ms Allowing participants to walk freely around a large Allowing participants to walk freely around a large

area: danger is to snag/trip cables, collisionsarea: danger is to snag/trip cables, collisions=> Experimenter walks behind participant to prevent this=> Experimenter walks behind participant to prevent this

Enhancements to the original Enhancements to the original studystudy

►Virtual Walking:Virtual Walking: As with 1995 Slater study a neural network As with 1995 Slater study a neural network

trained for standard virtual walking was usedtrained for standard virtual walking was used This standard net derived from gait of This standard net derived from gait of

principal authorprincipal author Effective in recognizing walking-in-place Effective in recognizing walking-in-place

motionmotion Casual visitors were able to replicate the Casual visitors were able to replicate the

movements (no need to train network again)movements (no need to train network again)

Enhancements to the original Enhancements to the original studystudy

► Flying:Flying: In original experiment: flying was in direction of pointing handIn original experiment: flying was in direction of pointing hand Decoupled head and handDecoupled head and hand To make the flyer and virtual walker groups match locomotion To make the flyer and virtual walker groups match locomotion

along head direction was chosenalong head direction was chosen

► More modern graphics engine: 40 times as many polygons, radiosity More modern graphics engine: 40 times as many polygons, radiosity lighting and texturing for almost half the polygonslighting and texturing for almost half the polygons

► 1995 study showed importance of user association with virtual body 1995 study showed importance of user association with virtual body => over 11000 polygons invested in detailed avatar => over 11000 polygons invested in detailed avatar

► Subject able to see:Subject able to see: tracked virtual right handtracked virtual right hand Virtual feet when looking downVirtual feet when looking down

► Virtual body oriented in head direction: looking at virtual feet while Virtual body oriented in head direction: looking at virtual feet while changing head direction: virtual body shifts correspondinlgychanging head direction: virtual body shifts correspondinlgy

The virtual worldThe virtual world

The virtual worldThe virtual world

The virtual worldThe virtual world

Visual cliffVisual cliff

►Ways in which infants perceive the Ways in which infants perceive the worldworld

► Infants generally respond to cues for Infants generally respond to cues for depthby time they are able to crawldepthby time they are able to crawl

►Sheet of plexiglass covers clothSheet of plexiglass covers cloth►One side cloth dropped about 4 feetOne side cloth dropped about 4 feet►Majority of infants refused to go onto Majority of infants refused to go onto

the seemingly unsupported surfacethe seemingly unsupported surface

The virtual worldThe virtual world

Measures and data collectionMeasures and data collection

►Subjective reporting using Subjective reporting using questionnaires is the most common questionnaires is the most common methodmethod

►problem: subject’s experiences AFTER problem: subject’s experiences AFTER event are reportedevent are reported

►Should be DURING event (break in Should be DURING event (break in presence)presence)

►Recent approach: gestalt psychology to Recent approach: gestalt psychology to record presence levels without record presence levels without interfering with the VE experienceinterfering with the VE experience

The experimentThe experiment

►Subjects practise locomotion and Subjects practise locomotion and picking up blue box in training roompicking up blue box in training room

►Task is to grasp the green box and Task is to grasp the green box and carry it to the chair in the virtual pit carry it to the chair in the virtual pit roomroom

►Free to choose path to chair:Free to choose path to chair: Go along ledge, left or rightGo along ledge, left or right Move directly towards chair over the pit Move directly towards chair over the pit

(indicates lower sense of presence)(indicates lower sense of presence)

Results:Results:

Overall conclusionsOverall conclusions

► Experiment confirms 1995 result that presence Experiment confirms 1995 result that presence correlates highly with degree of association with correlates highly with degree of association with virtual bodyvirtual body

This suggests that:This suggests that: Presence is higher for virtual walkers than for flyers;Presence is higher for virtual walkers than for flyers; Presence is higher for real walkers than for virtual walkers;Presence is higher for real walkers than for virtual walkers;

Effect of oculomotor discomfortEffect of oculomotor discomfort It reduces the presence for the virtual walkers and flyers.It reduces the presence for the virtual walkers and flyers. No effect on real walkers: greater match in real walking overcoming the No effect on real walkers: greater match in real walking overcoming the

discomfortdiscomfort

► Ease of locomotionEase of locomotion Real walking is better option than other techniques if one wants Real walking is better option than other techniques if one wants

locomotion to be considered natural, easy and uncomplicated.locomotion to be considered natural, easy and uncomplicated.

ResultsResults

User ReportsUser Reports► Sense of “being there”Sense of “being there”

innate responses: ”I was afraid to innate responses: ”I was afraid to experience the falling sensation I might experience the falling sensation I might have had if I’d walked straight over the have had if I’d walked straight over the virtual pit”virtual pit”

► Other factors that broke the simulationOther factors that broke the simulation Incorrect behavior of environment and Incorrect behavior of environment and

avataravatar Background NoiseBackground Noise Interference by the HardwareInterference by the Hardware

ResultsResults

► LocomotionLocomotion

ResultsResults

Behavioral Presence Behavioral Presence ► This means the extent to which the actual This means the extent to which the actual

behaviors or internal states and perception behaviors or internal states and perception indicated the sense of being in the situation indicated the sense of being in the situation depicted by the VE simulation rather than depicted by the VE simulation rather than being in the real world of the laboratory. The being in the real world of the laboratory. The score was constructed from 5 components.score was constructed from 5 components.

ResultsResults► The extent to which the subject was aware of background The extent to which the subject was aware of background sounds in the real laboratory;sounds in the real laboratory; ► The extent to which their reaction when looking down over the The extent to which their reaction when looking down over the pit was self-assessed as being similar to what it would have pit was self-assessed as being similar to what it would have been in a similar situation in real life.been in a similar situation in real life.

► The extent to which they had any vertigo or fear of fallingThe extent to which they had any vertigo or fear of falling when looking down over the virtual pit.when looking down over the virtual pit.

► The willingness to walk out over the pit.The willingness to walk out over the pit.

► The path they actually took to the chair at the other side of the The path they actually took to the chair at the other side of the pit.pit.

ResultsResults

►Subjective presence using enhanced Subjective presence using enhanced questionnaires:questionnaires: Females generally have higher sense of Females generally have higher sense of

presence than males (less of game playing)presence than males (less of game playing) The higher the association with the virtual The higher the association with the virtual

body,body,

the greater sense of presence.the greater sense of presence. Major difference between first group and Major difference between first group and

second two: virtual and real walkers much second two: virtual and real walkers much higher sense of presencehigher sense of presence

Unexpected resultUnexpected result

A compelling virtual environment experience:A compelling virtual environment experience:

Real walking and to a lesser extent virtual walking throughReal walking and to a lesser extent virtual walking throughenhanced version of Slater’s virtual environment yields aenhanced version of Slater’s virtual environment yields astrikingly compelling virtual environment:strikingly compelling virtual environment: “ “Wow! Whoa! Uh-Oh!” are typical reactions of participants Wow! Whoa! Uh-Oh!” are typical reactions of participants when finding themselves above the pit.when finding themselves above the pit. A few people even refuse to go through the door into the pitA few people even refuse to go through the door into the pit room. Others don’t care to come back from the chair to theroom. Others don’t care to come back from the chair to the door,…door,…

Unexpected resultUnexpected result

Why is this such a good Why is this such a good experiment?experiment?

► The compelling nature is due to the confluence of many The compelling nature is due to the confluence of many factorsfactors

The visual cliff environment itself, the depth and narrowness of the ledge

Almost imperceptible end-to-end system lag, 100 ms Real walking about in a significant space The reasonably realistic avatar The visual fidelity of the detailed, textured, scene The excellent resolution and color saturation The precision and crispness of the tracker

LessonsLessons

Real WalkingReal Walking Virtual WalkingVirtual Walking Substantially improved virtual walkingSubstantially improved virtual walking Avatar realismAvatar realism Clothing identificationClothing identification Investigator location incongruityInvestigator location incongruity Ambiguous and erroneous Ambiguous and erroneous

interpretationsinterpretations

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