Presence in Virtual Environments Mel Slater Department of Computer Science UCL www.cs.ucl.ac.uk/staff/m.slater
Outline • Evaluation of VEs • Immersion and Presence in Virtual Environments • Four experiments with the ‘pit room’ • Ways of Walking • Latency • Static Visual Realism • Dynamic Visual Realism • Experiment with virtual characters • Real man meets virtual woman • Teaching by punishment • Conclusions
Evaluating VEs • Task performance is an important measure of the effectiveness of a VE • Task performance within the VE • Task performance in the transfer of learning from the VE to the real world • Task performance – specific to applications • ‘Presence’ is common across applications and has been used as an overall measure of the effectiveness of VEs.
Immersion: the technology • Inclusive – sensory experience from VE only • Extensive – more sensory modalities • Surrounding – from all directions • Vivid – high fidelity • Egocentric – first person point of view • Plot – things are happening • Proprioceptive match – between sensory data and proprioception
Applications of VR in Scientific Visualisation Obvious applications of VR in visualisation, modelling, etc • Above is collaboration with Andy Van Dam at Brown • University, Mavi Sanchez-Vives at UMH, Spain, … Visualisation of neurons obtained through confocal microscope images •
Some Presence Definitions • ‘The sense of “being there”’ (Held & Durlach, Sheridan, Zeltzer: premier issue of PRESENCE, 1992) • ‘A perceptual illusion of nonmediation’ (Lombard and Ditton, 1997) • ‘A mental state in which a user feels physically present within the computer-mediated environment’ (Draper & Kaber, 1998) • ‘The subjective experience of being in one place or environment, even when one is physically situated in another’ (Witmer & Singer, 1998)
Presence Operationally • Successful substitution of real sense data by computer generated sense data • ‘Successful’ – response is realistic, similar to what would be expected if the events were real • ‘Response’ – • Low level physiological → high level cognitive and emotional • Includes verbal responses about ‘being there’
Measurement of Presence • Questionnaires & Self Report Measures • Behavioural responses • Physiological responses • Breaks in presence
The ‘Pit Room’ Experiments
Walking in Place • Hypothesis that the correlation between proprioception and sensory data is an important factor in maintaining presence • Navigating a VE by using a ‘mouse’ breaks this match • Compared a ‘walking in place’ method with a point-and-click (‘flying’) method Slater M, Usoh M, Steed A (1995) Taking steps: the influence of a walking technique on presence in virtual reality. ACM Trans Comput-Hum Interact 2:201-219.
Experiment 16 subjects • 8 in a walking-in-place group • 8 in a point-and-click group • Task was to take an object to the chair • A between groups design • Each subject had a virtual body that • they could see when looking down HMD display with Virtual Research • Flight Helmet 360 × 240 with 75 deg. horizontal FOV Polhemus sensors for head tracking •
Some Measured Variables • Presence Questionnaire • Three questions • The sense of ‘being there’ • Whether the environment the virtual room was remembered as somewhere visited rather than only images seen • The extent to which the pit room became the dominant reality, and that the real lab was forgotten • Each measured on a 7-point scale • (1) Not at all • (7) Very much so • Final score is x = the number of ‘6’ or ‘7’ answers given (x = 0,1,2,3) • Path taken to the chair • Extent to which they ‘associated’ with their Virtual Body
Results • For the ‘walkers’ – greater their association with their VB the greater their presence score • For the ‘pointers’ – no correlation • If they associated with their VB then the ‘walkers’ reported higher presence than the ‘pointers’ • Path across the precipice associated with lower reported presence.
Walking, Walking In Place, Flying • A follow-up study compared • (RW) Really walking (UNC wide-area tracker) • (WIP) Walking in place • (PAC) Point and click (‘flying’) • Between groups experiment (11 subjects per group) • Results showed (RW,WIP) >> PAC • No sig. difference between RW and WIP Usoh M, Arthur K, Whitton MC, Bastos R, Steed A, Slater M, Brooks Jnr F.P (1999) Walking > walking-in-place > flying, in virtual environments. (SIGGRAPH ’99), 359-364
Further Studies Meehan/Insko (2002) • exposed 10, 52 and 33 subjects in 3 different studies. Heart rate increase when • Meehan M, et al (2002) in the pit room. Physiological measures of presence Static haptics further • in stressful virtual environments. significantly increased Acm Transactions on Graphics 21:645-652 heart rate. Heart rate correlated with • subjective self-report of presence level. Insko B et al (2001) Passive Haptics Significantly Enhances Virtual Environments. Department of Computer Science, p 111. UNC Chapel Hill:
Influence of Latency • Lower and Higher latency conditions in a ‘pit’ experiment. • Skin response, HR and presence questionnaire used. • HR change most sensitive. • Meehan et al VR’2003 Lower latency ∼ higher ‘presence’
Global Illumination – Who Cares? • Why spend effort and resources on ‘global illumination’ (eg, ray tracing, radiosity, photon mapping,…)? • Scientific and practical question? • What is its impact on people who are in immersive virtual environments?
Visual Realism • In a between-groups study utilising the ‘pit room’ Zimmons et al. (2003) used 5 levels of rendering: • From wire frame to radiosity (global illumination) • All subjects showed increased heart rate when approach the precipice in all conditions • No significant differences between the conditions in heart rate or reported presence. • So, from the point of view of presence is visual realism not important?
Does Ray Tracing Help? • What do we get with ray tracing? • Shadows (umbras only) • Reflections • Cost – long rendering times! • Real-time ray-tracing (parallelism + GPU) offers chance to investigate impact of dynamic changes (shadows+reflections) on presence
Experimental Design • 34 people • Displayed with V8 HMD + polhemus tracking • Pit room rendered in two ways • Real-time Ray Tracing with reflections and shadows of virtual body • OpenGL shading (no reflections/shadows) • Virtual Lightfield Project at UCL • Pankaj Khanna, Jesper Mortensen, Insu Yu
Experimental Design • Subjects divided into two groups • 17 experienced first RT and then OpenGL • 17 experienced first OpenGL and then RT • Both groups had relaxation periods for ‘baseline’ readings • This design is both between groups • Consider 1 st results only • Within groups • Consider comparisons between the two results • (with high danger of interference between the two experiences!) • (Experiment finished last week!) • VIDEO of early pilot experiment
Measured Variables • Elaborated questionnaire presence • Skin conductance • Heart rate and respiration • Demographic variables – age, gender • Background • Programming knowledge, game playing, prior experience of VR, etc
Early Results • Consider the between groups experiment only (comparing responses to the first experiences only):- • Reported presence is sig. associated with: • Ray tracing (higher than for OpenGL) • Prior VR experience (+vely related) • Programming experience (-vely related) • Age (-vely related)
Interactions with Virtual People • Most interesting VEs are • those that involve other • people • Real online people • Represented by avatars • Virtual people • Represented as humanoid
Fear of Public S peaking Does ‘ audience’ behaviour influence anxiety response? Pertaub, D-P., et al. (2002) An Experiment on Public Speaking Anxiety in Response to Three Different Types of Virtual Audience, Presence, 11(1) 68-78.
Positive Audience Behaviours � pay attention � lean forwards � encouraging noises � maintain eye contact � Enthusiastic applause � nod encouragingly � Smile frequently � standing ovation
Reactions • ‘ It was clear that the audience was really positive and interested in what I was saying and it made you feel like telling them what you know.’ • ‘ I felt great. Finally nobody was interrupting me. .. Here I felt people were there to listen to me.’ ‘ They were staring at me. They loved you • unconditionally, you could say anything, you didn’ t have to work’ .
Negative Audience Behaviours � yawn, cough, mumble � fall asleep � talk amongst themselves � put feet on table � read papers/notes � avoid eye contact � turn torso away from speaker � frown and grimace � walk out of room
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