representing people in virtual environments · 2009-01-26 · representing people in virtual...

Representing People

in Virtual Environments

Will Steptoe

11th December 2008

What’s in this lecture?

•! Part 1: An overview of Virtual Characters

–!Uncanny Valley, Behavioural and Representational

Fidelity.

•! Part 2: Virtual Characters in VEs

–!Games, Online Social Worlds, Immersive VR,

Avatars, Agents.

•! Part 3: 3D Studio Max Demo

•! Part 4: Technical Aspects of Virtual Characters

–!Graphics, Animation, Behaviour

What is in this lecture?

•! Virtual characters and realism

–! Graphics, Animation and Behaviour

•! Virtual characters in Virtual Environments

–! Avatars, agents, interaction and AI

•! Character rigging and Animation

–! 3DS Max Demo

Highly realistic characters

Highly realistic characters

•! Highly realistic characters can cause more

problems

•! Realistic characters existing in stills (beginning to

in games and VEs) but less so in movies.

–! Not just a computing power issue

•! There are a lot of complex issues to deal with

when you have more realistic characters

Uncanny Valley

•! As the behaviour and representation of robots

(and other facsimiles) of humans approaches that

of actual humans, it causes a response of

revulsion among human observers.

•! Theory from 70s by roboticist Masahiro Mori

–! Controversial, its not very rigorous or scientific, many

people don’t believe it

–! There are problems but it maybe captures something

The Uncanny Valley

The Uncanny Valley

•! Dreamworks reduced realism

of Princes Fiona (Shrek):

–! “she was beginning to look too

real, and the effect was getting distinctly unpleasant”

•! Final Fantasy

–! “it begins to get grotesque. You start to feel like you're puppeteering a corpse”

Uncanny Valley

•! At low levels of realism, the more realistic a

character the more people like it (even this is

dubious)

•! But when you get almost real then characters start

to get disturbing

•! This is very strong, the uncanny means very

disturbing, corpses are used a lot as metaphors

•! Interestingly, there are 2 graphs, movement and

appearance, movement is more important

Different Levels of Realism

•! Graphical Realism –!What it looks like (pictures, games, VE, film)

•! Animation Realism –! How it moves, animation (film, games, VE)

•! Behavioural Realism –! How it responds and interacts (games/VE)

Mismatch in Realism

•! Maybe the problem is that levels of movement

and behavioural realism do not match

graphical realism

•! This mismatch disturbs us, something that

looks human but does not act like a human

•! Consistency

Appearance vs. Behaviour

Vinayagamoorthy, V., Garau, M., Steed, A., and Slater, M. (2004b). An eye gaze model for dyadic interaction in

an immersive virtual environment: Practice and experience. Computer Graphics Forum, 23(1):1–11.

Realistic responses in VE ?

•! Individuals' self-rated performance was positively correlated with the perceived good mood of the agents

•! Evidence of a negative response especially strong with the negatively inclined audience –! Sweating and stammering

–! Vocal protests at the agent behaviours

•! Virtual humans with minimal behavioural-visual fidelity can elicit significant user responses

•! Holy grail: Virtual humans with high visual fidelity that mimic real-life context-appropriate behaviours


App.

Beh.

Cartoon

– Form

Higher –

Fidelity

Random

gaze

3 ! pairs 3 " pairs

3 ! pairs 3 " pairs

Inferred*

gaze

3 ! pairs

3 " pairs

3 ! pairs

3 " pairs

Garau, M., Slater, M., Vinayagamoorthy, V., Brogni, A., Steed, A., and Sasse, A. M. (2003). The impact of avatar

realism and eye gaze control on the perceived quality of communication in a shared immersive virtual environment. In Proceedings of SIGCHI, pages 529–536.


App.

Beh.

Cartoon

– Form

Higher –

Fidelity

Random

gaze

3 ! pairs 3 " pairs

3 ! pairs 3 " pairs

Inferred*

gaze

3 ! pairs

3 " pairs

3 ! pairs

3 " pairs

Garau, M., Slater, M., Vinayagamoorthy, V., Brogni, A., Steed, A., and Sasse, A. M. (2003). The impact of avatar

realism and eye gaze control on the perceived quality of communication in a shared immersive virtual environment. In Proceedings of SIGCHI, pages 529–536.

App.

Beh.

Cartoon

– Form

Higher –

Fidelity

Random

gaze High Low

Inferred*

gaze

Low High


•! In each of the responses, the higher fidelity avatar had a higher response with the inferred-gaze model

•! And a low response with the random-gaze model –! Important to note that the differences between both the gaze models were very subtle

•! Saccadic velocity and inter-saccadic intervals (means)

•! Analysis demonstrated a very strong interaction effect between the type of avatar and the fidelity of the gaze model –! The higher-fidelity avatar did not outperform the cartoon-form avatar

–! Similar hypothesis in the fields of robotics


•! Sparse environment – abandoned building –!Minimise visual distraction

–! One genderless cartoon form character

–! Two gender-matched higher fidelity characters

•! Behaviour –! Common limb animations and condition-dependent gaze animations

–! Individuals listening in a conversation look at their conversational partner for longer periods of time and more often than when they are talking

•! Negotiation task to avoid a scandal - 10 minutes

What responses do you get?

•! David

•! Not very comfortable with

public speaking

•! Asked to speak about his

favourite subject: cables

•! Behaviours triggered at

appropriate intervals

•! Look at the virtual humans

Pertaub, D.-P., Slater, M., and Barker, C. (2002). An experiment on public speaking anxiety in response to

three different types of virtual audience. Presence: Teleoperators and Virtual Environments, 11(1): 68-78

The Fear of public speaking

•! The user was asked to give a presentation thrice

–! Positive, Negative and Mixed

•! Positive - agents smiled, leaned forward, faced the user,

maintained gaze, clapped hands, etc.

•! Negative - agents yawned, slumped forward, put feet on

the table, avoided eye contact, and finally walked out

•! Mixed - agents started off with largely negative

responses and gradually turned positive

Realism vs Believability

•! The lesson is that we need to be careful with

realism for virtual humans

•! Often we prefer to use the term “Believability”

–! Not how much a character is objectively like a human

–! How much we feel it is/respond to it as if it is

–! Bugs Bunny is very Belivable

•! Photorealism is only one element of believability

–! But don’t turn into an anti-realism zealot!

Part 2: Characters in Virtual Environments

•! So far we haven’t talked about characters in virtual

environments

•! Characters are often key to an environment, the

primary content

•! We are interested in people so populated

environments are interesting

Games

•! Some characters are just there to be shot at

Games

•! Some games like the Sims have more complex

interactions

•! Supposedly, they have important social

interactions

•! (To me it seems more about going to the toilet)

Games

•! Mario is interesting, he is your representation in

the game

•! An avatar

•! Can be compared to a cursor, marking your

position, but is clearly something more

•! A strong personality, you take on some of his

personality, rather than him just representing you

Multi-user worlds

Multi-user worlds

•! Avatars become much more important in multi-

user worlds (the most important feature?)

•! They also represent you to other people

•! They affect how people perceive you

Immersive VR

Immersive VR

•! In immersive systems you can interact with life

size, real time character

•! This changes the experience again

Avatars and Agents

•! Characters in virtual environments fulfill many

roles but there are two primary types

•! Avatars

–! Representations of you, or other people

–! User controlled (tracked)

•! Agents

–! Others, that you interact with

–! Computer Controlled

•! Hybrid

–! Part tracked, part simulated

Interactive Behaviour

•! Key to both roles is the interaction with a character

•! Composed of two elements, UI and AI

•! “User interface”

–! In what ways do we interact with a character?

•! “Artificial (Augmented) Intelligence”

–! How does the character respond?

–! How is it controlled?

Agents

•! Many different style of interaction for agents

•! Cannon fodder, Non-player Characters, Crowds,

Complex conversational agents

•! Many interactions, shooting, moving, conversation

(from dialogue trees to spoken interaction)

Agents - Game NPC

•! UI:

–!Moving, shooting

–! Simple conversation

•! AI:

–! Finite state machines

–! Scripts

–! Path Planning

Agents - Embodied Conversational Agents

•! UI:

–! Speech conversation

–! Gestures etc.

–! Tracking data

•! AI:

–! Complex conversational

–! AI methods

Agents - Embodied Conversational Agents

Virtual Humans - Agents

http://www.miralab.unige.ch!

Agents are entirely "

program controlled rather"

than representing an on-line"

human.!

These are examples from"

virtual fashion shows.!

Avatars

•! Your representation in the VE

•! A vital part of multi-user worlds

•! A very complex relationship

•! A separate identity that to take on (e.g. Mario)

•! A new identity that you create for yourself (e.g.

Second Life)

Avatars Outline

•! Why Virtual Human Representations?

•! Avatars and Agents

•! Representing a Person in a VE

•! Designing Virtual Humans

•! Emotion, Personality and Social Intelligence

•! Believable behaviour

•! Conclusions

Virtual Human Representations

•! Useful and interesting applications are with

other people

–! Simulation of real events

–! Training

–! Entertainment

–! Shared VEs

•! The Others are entirely ‘virtual’

•! The Others are entirely ‘real’

–! As in shared (networked VEs)

Networked VEs

•! Need some representation of the other people in the shared VE

•! Typically called ‘avatars’

•! Avatars represent the real tracked person –! Spatial representation

•! Where they are, what they are looking at

–! Behavioural representation •! What they are doing

Avatars in Shared VE

Avatar Representations

•! Spatial

•! Behavioural

Avatars and Identity

•! Most users of virtual worlds use avatars as a

means of identity creation

•! Customization is vital

–! Appearance, clothes, hair, sometimes animation

•! The relationship to real identity is complex

–! Have a different appearance, personality, gender

–! Explore hidden sides of yourself

–! Some people feel their avatar is “More Me” than their

physical self

Avatars as social tools

•! Ideally avatars is social VEs should support social

interaction

•! Display the bodily functions of communication

(body language)

•! However, most avatars in most virtual worlds don’t

•! The body movements often exist, but most users

use them unrealistically or often not at all

•! Primarily a problem of control

Avatar Mediated Communication

Controlling avatars •! Typed Text, Emoticons, Traditional GUI, Speech, Full body tracking

Problems with Controlling Avatars

•! Two modes of control: at any moment the user must choose between either selecting a gesture from a menu or typing in a piece of text for the character to say. This means the subtle connections and synchronisations between speech and gestures are lost.

•! Explicit control of behaviour: the user must consciously choose which gesture to perform at a given moment. As much of our expressive behaviour is subconscious the user will simply not know what the appropriate behaviour to perform at a give time is

[BodyChat, Vilhjalmsson, H. and Cassell, J., 1998]

Problems with Controlling Avatars

•! Emotional displays: current systems mostly concentrate on displays of emotion whereas Thórisson and Cassell (1998) have shown that envelope displays – subtle gestures and actions that regulate the flow of a dialog and establish mutual focus and attention – are more important in conversation.

•! User tracking: direct tracking of a user’s face or body does not help as the user resides in a different space from that of the avatar and so features such as direction of gaze will not map over appropriately.


Solutions

•! Always ensure that any control is done through a

single interface (e.g. through text chat)

•! BUT….

•! The body language of an avatar should be largely

autonomous, and indirectly controlled by users

•! Minimize the level of control needed


Solutions: Spark

•! Text Chat based

environment

•! Parse users text

input for interactional

information

•! Use this information

to generate

behaviour

Solutions: Spark

Solutions: PIAVCA

User Interaction

Script Database

Motion Queue

Operator

Speech

Generation

Final Animation

Gaze Posture Shifts Proxemics

Concurrent

Behaviours

Speech

Movements

Multi-model

utterances

Part 3: 3DSMax Demo

Part 4: Technical Aspects of Virtual

Characters

•! Graphics

–! Polygon meshes, rendering

•! Animation

–! Skeletal animation, mesh morphing, physical simulation

•! Behaviour

Graphics

•! Techniques: Meshes, texture mapping, standard

graphics stuff

•! Hand modelling: can be cartoony or highly realistic

•! 3D Scanning/phototextures: can have very high

realism

•! Rendering Opacity: Subsurface scattering

Modelling

Scanned body results in huge mesh

which can be rendered at different

resolutions (numbers of polygons)!

Body Animation

•! Can Hand animate the

skeleton

•! Often use motion capture

•! Real data = Realism (?)

Skeletal Animation

•! The fundamental aspect of human body motion is

the motion of the skeleton

•! The motion of rigid bones linked by rotational

joints (first approximation)

•! I will discuss other elements of body motion such

as muscle and fat briefly later

Typical Skeleton

•! Circles are rotational joints lines are rigid links (bones)

•! The red circle is the root (position and rotation offset from the origin)

•! The character is animated by rotating joints and moving and rotating the root

Forward Kinematics (FK)

•! The position of a link is calculated by

concatenating rotations and offsets

O0

R0

O1

O2

R1

P2


•! First you choose a position on a link (the end point)

•! This position is rotated by the rotation of the joint

above the link

•! Translate by the length (offset) of the parent link and

then rotate by its joint. Go up it its parent and iterate

until you get to the root

•! Rotate and translate by the root position


•! Simple and efficient

•! Come for free in a scene graph architecture

•! Difficult to animate with,

–! often we want to specify the positions of a characters

hands not the rotations of its joints

•! The Inverse Kinematics problem:

–! Calculating the required rotations of joints needed to put

a hand (or other body part) in a given position.

Inverse Kinematics

•! An number of ways of doing it

•! Matrix methods (hard)

•! Cyclic Coordinate Descent (CCD)

–! A geometric method (secretly matrices underneath)

R1

Pt

R0

O1

O2

Inverse Kinematics

•! Start with the final link

Inverse Kinematics

•! Rotate it towards the target

Inverse Kinematics

•! Then go to the next link up

Inverse Kinematics

•! Rotate it so that the end effector points towards the target

Inverse Kinematics

•! And the next…

Inverse Kinematics

•! And iterate until you reach the target

Inverse Kinematics

•! IK is a very powerful tool

•! However, it’s computationally intensive

•! IK is generally used in animation tools and for

applying specific constraints

•! FK is used for the majority of real time animation

systems

Minimal Tracking for IK in VR

•! Badler et al showed a minimal

configuration for IK representing

the movements of a human in VR

–! www.cis.upenn.edu/

~hollick/presence/presence.html

•! It was shown that 4 sensors are

sufficient to reasonably

reconstruct the approximate body configuration in real-time.

Representation

•! Layered representation

–! Skeleton structure forms a

scene graph

–! Scene graph embodies a set of joints

–! A mesh overlays the scene

graph

–! As the skeletal structure

moves the mesh must

deform appropriately

(otherwise there are holes)

MPEG4 example!http://ligwww.epfl.ch/~maurel/Thesis98.html!

Facial Animation

•! Don’t have a common

underlying structure like a

skeleton

•! Faces are generally

animated as meshes of

vertices

•! Animate by moving

individual vertices

Morph Targets

•! Have a number of facial expressions, each

represented by a separate mesh

•! Each of these meshes must have the same

number of vertices as the original mesh but with

different positions

•! Build new facial expressions out of these base

expressions (called Morph Targets)

Morph Targets

Morph Targets

•! Smoothly blend between targets

•! Give each target a weight between 0 and 1

•! Do a weighted sum of the vertices in all the targets

to get the output mesh

Using Morph Targets

•! Morph targets are a good low level animation

technique

•! Also need ways of choosing morph targets

•! Could let the animator choose (nothing wrong with

that)

•! But there are also more principled ways

Summary

•! Virtual human avatars are necessary to represent people to themselves and in shared VEs.

•! Virtual human agents are necessary to represent social situations.

•! VHs are represented typically as ‘skinned’ skeletal scene graphs, representing sets of joints.

•! Forward kinematics determines overall configuration given joint angles and Inverse kinematics determines joint angles from requirements for end-effectors

•! Representations typically need to be a mixture based on tracking data and inferred state.

•! Morph targets are a method of mesh deformation often used for facial animation

•! Later will go on to consider more sophisticated models of behaviour determination, and also social intelligence.

Believable Behaviour

•! For agents the behaviour is completely programmed.

•! For avatars the behaviour is ideally completely determined by the behaviour of the real tracked human.

•! In practice the human cannot be fully tracked –typically in VR only head and one hand movements are tracked!

Controlling/Inferring Behaviour

•! In practice some elements of avatar behaviour are programmed not tracked

•! E.g., breathing and eye blinking at the least

•! Ideally can use information about ‘mood’ to determine aspects of avatar behaviour.

•! Impossible to track every aspect of the human’s behaviour so much must be inferred and programmed.

•! Real avatars are mixed.

Avatar!

Agent!

Tracking!

Programming!

Mixture of both!

Behaviour

•! Autonomously deciding what action to take at a

given time

•! Not necessary for film but vital for real time

interaction

•! At the interface between Graphics, AI and A-Life

•! The subject of the rest of this talk

Behaviour Outline

•! An overview of early (land mark) behavioural

simulation techniques

•! An overview of social behaviour simulation taking

in

–! Control algorithms

–! Psychological theories

–! How social behaviour is expressed in animation

Social Intelligence

•! These techniques work well as far as they go but

do not model the complexities of human social

interaction

•! Vital if we are to have interesting interactions with

autonomous characters

•! Also useful for making our interactions via avatars

closer to real interactions

Designing virtual humans

•! GOAL: Represent the Person in VE consistently

–!With perceived realism, believability …

•! Induce responses to the virtual human

–! Inducing realistic/lifelike responses

•! Enhancing collaborative experience

•! Facilitate social communication and interpersonal

relationships

Designing behaviour

•! Creating apparent social intelligence is challenging

•! Have to present behavioural cues to depict a perceived (and plausible) psychological state –! Or the near-truth internal state of the Person being represented

•! Human behaviour is a very intricate phenomenon –! Dependent on many factors

•! Extremely difficult to replicate especially if the design process is approached in an ad-hoc manner –! For instance: In social interactions within VE, the more visually realistic the virtual human, the more naturalistic users expect it to act

Inferring Behaviour: Animation imitating life

•! Emotional models –! Controllers of behaviour in accordance to internal states

•! Personality models –! Creating unique identities

•! Conversation-feedback models –! Controlling behaviour

•! Social models –! Interpersonal relationships and attitudes

•! ???

Lasseter, J. (1987). Principles of traditional animation applied to 3d computer animation. ACM

SIGGRAPH Computer Graphics, 21(4):35–44.

Categories of behavioural cues

•! Vocal properties –! Tone, Pitch, Loudness…

•! Facial expressions –! The most studied behavioural cue due to it’s role in communication

•! Gaze behaviour –! Probably the most intense social signallers

•! Kinesics: Posture and Motion –! Numerous gestures depending on culture for instance

•! Proxemics –! Culture and gender dependent

Argyle, M. (1998). Bodily Communication. Methuen & Co Ltd, second edition.

Facial expression

•! In reality, 20000 facial expressions exist

•! Normally animated by blending “Morph Targets”

•! Different granularities of facial expression

–! Facial action parameters (most basic units)

•! Basic emotions

–! Phonemes (mouth shapes for lip-sync)

–! Principal component analysis

Gesture

•! Normally animated by choosing from a library of

gestures

•! Very closely associated with speech

–! Also back channel gestures by listeners (e.g. head nod)

•! Different types of gesture

–! E.g. beat, iconic

•! Again see Cassell’s work referenced earlier

Posture

•! Over 1000 stable postures have been observed

•! Normally animated by choosing from (or blending between) a library of gestures

•! Associated with attitude and emotion

•! Associated also with interpersonal attitude

Coulson, M. (2004). Attributing emotion to static body postures: Recognition accuracy, confusions, and

viewpoint dependence. Journal of Nonverbal Behavior, 28(2):117–139.

Measuring Success

•! So the careful design of behaviour is important but there are caveats

•! Success of a VE is measured in terms of the extent to which sensory data projected within a virtual environment replaces the sensory data from the physical world –! quantified by rating the individuals’ sense of presence during the experience

•! For Virtual Humans: Success is taken as the extent to which participants act and respond to the agents as if they were real –! Subjective: Questionnaires, Interviews

–! Objective: Physiological, Behavioural

Subjective means

•! Traditional methods: Questionnaires and interviews –! Various questionnaires exist

–! http://www.presence-research.org

•! Criticised due to its various dependencies –! the individual’s accurate post-hoc recall,

–! processing and rationalisations of their experience in the VE and

–! Varying interpretations of the word ‘presence’

Objective: Responses to stimuli

•! Numerous possible objective measures –! Subconscious responses

•! Threat-related facial cues provokes individuals to use different viewing strategies

–! Neural responses •! Different areas of the brain are activated during +ve, -ve and neutral situations

–! Psychological responses •! Stress and Anxiety in response to threat

–! Physiological responses •! Galvanic Skin Responses, Heart Rate Variability, electrocardiograms, electromyography, Respiratory activity

–! Behavioural responses •! Flight or Fight (based on cognitive appraisal)

•! Vary based on cognitive factors, personality, emotional state, gender etc. –! How do we interpret the data and results?

Conclusion

•! Virtual human agents are necessary to represent social

situations

•! Social intelligence is rather difficult to capture

•! Emotional, personality and interpersonal models

•! The design of behaviours should be implemented with

consideration to many other factors

•! Current Research focus on quantifying the successful

creation of Virtual Humans using objective measures

representing people in virtual environments · 2009-01-26 · representing people in virtual...

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