Correlation of presence with locomotion Presented by Xiang Lin Liu & Philippe Vervoort Virtual Environments University College London November

Sense of presence & locomotion ► Sense of being in the virtual place rather than in the real physical place ► used as qualitative property for good virtual environments ► locomotion: self-propelled movement

Background & objectives ► Problem: Development of natural and effective virtual surrogates for user interactions with physical spaces and objects ► E.g. touching objects while actually feeling them ► In general: Having your own body actively involved in the actions you take in virtual world ► Locomotion through virtual spaces is most primitive and important special case

Background & objectives ► Active usage of participant’s body with real sensations matched by synthetic visual and aural data STRONGLY affects virtual presence. ► 2 streams:  Wide-area trackers  Body-active surrogates for walking ► Common mode of locomotion: local walking limited by tracker range, combined with button- controlled flying

Virtual walking ► Walk-in-place technique ► Uses neural net to analyze the tracked head motion to detect steps ► Reproduce physical head motions generated during actual walking but without physically locomoting ► Indications that this technique significantly enhances subjective rating of presence, for subjects who subjectively associated with their avatars. (Study by Slater et al.)

Virtual walking ► Changes in head position fed to a neural network ► Network recognizes when participants are walking in place ► When virtual walking detected: moved in virtual space in direction of head-facing ► This technique is intuitive

Slater study [1995] ► Slater study: naive subjects in an immersive virtual environment experience a higher subjective sense of presence when they locomote by walking in place than when they push-button-fly along the floor

Replicated study ► 2 streams brought together in replicated study:  Wide-area ceiling tracker  Replicating Slater study of virtual walking  Real walking as a third condition ► Objectives:  See if earlier conclusions still hold true (more recent technology)  Compare flying, virtual walking and real walking with respect to ease of locomotion and subjective presence

Expectations of replicated study? ► If virtual walking indeed better than flying:  Very economical, future substitute for applications that use flying for locomotion ► If virtual walking essentially equivalent to real walking:  Wide area tracking only used for applications where physical motion is very essential

Enhancements to the original study ► Real walking:  Walk around in same manner as in a real environment  Tracked user’s head and one hand  Tracker range ~10m by 4m (mm precision)  Updates at ~1.5kHz  Reports fed to application at 70Hz  Total latency 100ms  Allowing participants to walk freely around a large area: danger is to snag/trip cables, collisions => Experimenter walks behind participant to prevent this

Enhancements to the original study ► Virtual Walking:  As with 1995 Slater study a neural network trained for standard virtual walking was used  This standard net derived from gait of principal author  Effective in recognizing walking-in-place motion  Casual visitors were able to replicate the movements (no need to train network again)

Enhancements to the original study ► Flying:  In original experiment: flying was in direction of pointing hand  Decoupled head and hand  To make the flyer and virtual walker groups match locomotion along head direction was chosen ► More modern graphics engine: 40 times as many polygons, radiosity lighting and texturing for almost half the polygons ► 1995 study showed importance of user association with virtual body => over polygons invested in detailed avatar ► Subject able to see:  tracked virtual right hand  Virtual feet when looking down ► Virtual body oriented in head direction: looking at virtual feet while changing head direction: virtual body shifts correspondinlgy

The virtual world

Visual cliff ► Ways in which infants perceive the world ► Infants generally respond to cues for depthby time they are able to crawl ► Sheet of plexiglass covers cloth ► One side cloth dropped about 4 feet ► Majority of infants refused to go onto the seemingly unsupported surface

The virtual world

Measures and data collection ► Subjective reporting using questionnaires is the most common method ► problem: subject’s experiences AFTER event are reported ► Should be DURING event (break in presence) ► Recent approach: gestalt psychology to record presence levels without interfering with the VE experience

The experiment ► Subjects practise locomotion and picking up blue box in training room ► Task is to grasp the green box and carry it to the chair in the virtual pit room ► Free to choose path to chair:  Go along ledge, left or right  Move directly towards chair over the pit (indicates lower sense of presence)

Results: Overall conclusions ► Experiment confirms 1995 result that presence correlates highly with degree of association with virtual body This suggests that: This suggests that:  Presence is higher for virtual walkers than for flyers;  Presence is higher for real walkers than for virtual walkers; Effect of oculomotor discomfort Effect of oculomotor discomfort  It reduces the presence for the virtual walkers and flyers.  No effect on real walkers: greater match in real walking overcoming the discomfort ► Ease of locomotion  Real walking is better option than other techniques if one wants locomotion to be considered natural, easy and uncomplicated.

Results User Reports ► Sense of “being there”  innate responses: ”I was afraid to experience the falling sensation I might have had if I’d walked straight over the virtual pit” ► Other factors that broke the simulation  Incorrect behavior of environment and avatar  Background Noise  Interference by the Hardware

Results ► Locomotion

Results Behavioral Presence ► This means the extent to which the actual behaviors or internal states and perception indicated the sense of being in the situation depicted by the VE simulation rather than being in the real world of the laboratory. The score was constructed from 5 components.

Results ► 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 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 falling when looking down over the virtual pit. when looking down over the virtual pit. ► The willingness to walk out over the pit. ► The path they actually took to the chair at the other side of the pit. pit.

Results ► Subjective presence using enhanced questionnaires:  Females generally have higher sense of presence than males (less of game playing)  The higher the association with the virtual body, the greater sense of presence. the greater sense of presence.  Major difference between first group and second two: virtual and real walkers much higher sense of presence

Unexpected result A compelling virtual environment experience: Real walking and to a lesser extent virtual walking through enhanced version of Slater’s virtual environment yields a 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 pit A few people even refuse to go through the door into the pit room. Others don’t care to come back from the chair to the room. Others don’t care to come back from the chair to the door,… door,…

Unexpected result

Why is this such a good experiment? ► The compelling nature is due to the confluence of many factors   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

Lessons  Real Walking  Virtual Walking  Substantially improved virtual walking  Avatar realism  Clothing identification  Investigator location incongruity  Ambiguous and erroneous interpretations

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