Characters that display emotion are critical to a rich and believable simulated environment. Emotion is the essential ingredient that creates the difference between Robotic behavior Lifelike engaging behavior
Characters that display emotion are critical to a rich and believable simulated environment.
Emotion is the essential ingredient that creates the difference between
Lifelike engaging behavior
Traditionally, animators painstakingly created these behaviors for pre-rendered animations
But, truly interactive characters must generate their behavior autonomously through techniques based upon artificial emotions
Must possess their own personalities and moods
Engine simulates personality, age, gender and the low level emotional behavior that drives most of our actions.
From this simulation gestures and low level actions are generated.
Behaviors can be mapped to application specific elements, i.e. characters, robots, cell phone agents, etc
Behavior of real users can be simulated to predict
what type of action that user might take
how a unique individuals mood changes while using your product
how to adjust that behavior to ideally reward each individual
» Simulates millions of unique personalitites » Simulates ages from 5 to 105 » Simulates gender from very femenine to very masculine » Simulates core brain systems responsible for emotion level processing » Generates facial gestures using muscle simulation, MPEG4 FAPs and FACS action units » Generates eye saccade, eye movement speed/range/frequency control, blink » Generates head position movement, pitch and yaw » Generates upper body gestures (spine, shoulders, neck) with walk cycle due to follow soon » Generates low level actions such as movement speed / range / frequency, search patterns, approach, avoid » Input can be as simple as a single integer to drive the whole system » Output is a continuous stream of integer values » Output is not tied to a specific application for maximum flexibility
Ekman, P., Friesen, W.V., & Hager, J.C. (2002).
An anatomically oriented coding system, based on the definition of "action units" (AUs) of a face that cause facial movements.
Each AU may correspond to several muscles that together generate a certain facial action.
As some muscles give rise to more than one action unit, correspondence between action units and muscle units is only approximate.
46 AUs were considered responsible for expression control and 12 for gaze direction and orientation.
The FACS model has been used to synthesize images of facial expressions; exploration of its use in analysis problems has been a topic of continuous research.
MPEG-4 is the latest compression standard developed by the Moving Picture Experts Group (MPEG) of the ISO, the same group that brought us MPEG-1 and MPEG-2. MPEG-4 builds on the proven success of three fields:
Interactive graphics applications (synthetic content);
Interactive multimedia (World Wide Web, distribution of and access to content)
Inspired by FACS
Facial Definition Parameter set (FDP) and the Facial Animation Parameter set (FAP) were designed to allow the definition of a facial shape and texture, as well as the animation of faces reproducing expressions, emotions and speech pronunciation.
The FAPs are based on the study of minimal facial actions and are closely related to muscle actions.
They represent a complete set of basic facial actions, such as squeeze or raise eyebrows, open or close eyelids, and therefore allow the representation of most natural facial expressions.
All FAPs involving translational movement are expressed in terms of the Facial Animation Parameter Units (FAPU).
FAPUs aim at allowing interpretation of FAPs on any facial model in a consistent way, producing reasonable results in terms of expression and speech pronunciation.
open_jaw (F3), lower_t_midlip (F4), raise_b_midlip (F5), stretch_l_cornerlip (F6),
stretch_r_cornerlip (F7), raise_l_cornerlip (F12), raise_r_cornerlip (F13), close_t_l_eyelid (F19),
close_t_r_eyelid (F20) , close_b_l_eyelid (F21), close_b_r_eyelid (F22), raise_l_m_eyebrow (F33),
raise_r_m_eyebrow (F34), lift_l_cheek (F41), lift_r_cheek (F42), stretch_l_cornerlip_o (F53),
FDPs on the other hand are used to customise a given face model to a particular face.
The FDP set contains a 3D mesh (with texture coordinates if texture is used), 3D feature points, and optionally texture and other characteristics such as hair, glasses, age, gender.
IBM Java Toolkit for MPEG-4 (currently active)
Facial Animation Engine (FAE) (University of Genova, Digital and Signal Processing Lab.)
Miraface: MPEG-4 FAP Player (MIRALab, University of Geneva)
XFace (Cognitive and Communicative Technologies, Instituto Trentino di Cultura)
Open source project, currently active.
Visage Technologies (currently active)
Free academic license for most of their products.
C++ Software Development Kit “visage|SDK”
Emotions comprise three layers of behavior
Top level: momentary emotions
Behaviors that we display briefly in reaction to events
Next level: moods
Prolonged emotional states caused by the cumulative effect of momentary emotions
Underlying level: personality
Behavior that we generally display when no momentary emotion or mood overrides
Levels have an order of priority
Momentary emotions over mood
Mood over personality
Momentary emotions are brief reactions to events that assume the highest priority when we select out behavior
Behaviors are short lived and decay quickly
Moods are produced by momentary emotions
Usually by the cumulative affects of a series of momentary emotions
Can gradually increase in prominence
Even after the momentary emotions have subsided
Development depends on whether momentary emotions are positive or negative
If a character were to receive a stream of negative momentary emotions, then the mood would obviously be bad and would decay slowly
Personality level is always present and has a consistent level of prominence
The behavior that a character displays depends upon each emotional layer’s prominence
The more prominent the layer, the higher the probability of that behavior being selected
Autonomous AE of any depth is rarely seen in commercial interactive entertainment
Some exceptions are P.F. Magic’s Catz and Dogz series, Fujitsu’s fin fin, and Cyberlife’s Creatures series
IE is currently dominated by genres that require the user to either conquer and/or kill everything in his or her path
Little emotion is required
Emotion primarily serves a social function in IE.
Emotional responses are used to make characters believable and engaging
If we walk into a virtual bar and the characters had distinct personalities, the scene would be an immersive and believable simulation
If characters show no emotion
Our suspension of disbelief would be immediately broken
We would be immediately reminded that we were in a computer generated simulation
Using human characters necessarily implies that their behavior is deep and complex
Unfortunately, we are most attuned to recognizing human emotion
And therefore recognizing flawed human emotion.
Which could easily break the illusion of an otherwise well constructed simulated environment
One way to attack this problem is to use nonhuman characters
Cats, dogs, and Norns all show engaging levels of interactive emotional behavior that maintains the illusion of life
Without having or needing the complexity of human emotional response.
AE produces two fundamental components as output
General category dependent on the context of the situation in which the character exists
A simulation’s movement system uses AE to select and/or modify an action
AE indicates what actions are appropriate to the character’s personality and current mood
A timid character is unlikely to do anything aggressive
An outgoing, extroverted character might perform an action enthusiastically
which would probably not be the case for an extreme introvert
Hand, body and facial
Way to communicate our emotions to the outside world
AE-driven gestures are tied directly to our characters’ personalities and moods and follow definite patterns.
E.g., a sad looking fellow, shoulders hunched over, arms hanging limply and walking slowly as he makes his way through our environment
Might compel a player to ask “Why does he look so sad. What is his story? Should I go and ask him?
The kinds of questions that occur to the viewer of a truly interactive experience would be irrelevant without AE.
The genetic and environmental differences in the brain structures of individuals.
As a species, our brains are almost identical
This gives rise to our common sets of behaviors.
But, we are all genetically and environmentally unique.
It is the differences that give us our unique behavioral variations of common behavior patterns
i.e., our personality
An area in a 3-D space.
The axes of the space are Extroversion, Fear and Agression (EFA Space)
Personality traits are represented by points within this space
Positioned according to the amount with which they are correlated with the each axis.
E.g., the trait of anxiety is positioned at
(E -30, F +70, A -10)
Associated -30% with Extroversion, 70% with Fear, and -10% with Aggression
The position of the center of the personality area (P) represents by how much each of those axes (central traits) define the overall personality
P is the center of a sphere
Contains the set of personality traits that make up the aggregate personality
The set of traits available to the character
Based on the idea that the brain might have 3 central systems that mediate behavior
Associated with Extroversion
Behavioral Inhibition System
Associated with Fear
Associated with Aggression
The behavior that we display at any time is controlled by these 3 systems
And the genetic prominence of each system
E.g., for an anxious personality
Behavioral Inhibition System is very prominent
Personality would have a very high Fear component
Person generally fearful and cautious
Determined by perceived signal of punishments and rewards
Inputs for most elements of the system
Modulated by the character’s personality
The position of the personality in EFA space affects the
Range of positive moods
Maximum level of positive moods increases with E
Range of negative moods
Maximum level of negative moods increases with F
Rate of change of moods
Speed at which moods build up and decay increases with A
Personality with high E, high F and high A
Moods would have large negative and large positive values
Moods would build up and decay rapidly
Character would be very moody with large mood swings
Six of these represent conceptual neural systems
Punishment and reward
Two of these are the engine interfaces (API)
The Self State module is the central data repository for the engine
Represents the characters general emotional state at any time
Basic types of input
Takes incoming signals of raw, sensed punishment and reward (p/r) and translates into perceived signals of p/r
Perceived p/r depends on
Characters previous history of received p/r
Use of habituation
The more the character receives, in succession, a signal of one type
The lower effect the signal has
Use of novelty
The longer the character goes without receiving one type of signal
The greater the effect of that signal when it is received
Character’s personality determines how susceptible it is to punishment or reward
E.g., a psychopath is
Highly susceptible to reward
Highly unsusceptible to punishment
Makes them go after thrills without regard for the consequences
Arranged into a 4-layer hierarchy of needs
Physiological layer is always bottom
Relative positions of the remaining 3 layers in the hierarchy are determined by personality
E.g., for the psychopath, Esteem is prioritized higher than Affiliation (friendship and kinship)
Used to facilitate non-cognitive social processing
Used in conjunction with the affiliation and esteem needs to provide enhanced social behavior
Keeps track of how much a particular character is liked based on several factors
Including social preferences of our family and friends
Used by the reactive emotion module
Innate emotional reactions that have not involved any deep cognitive processing
Represent stimulus response reactions of the kind hard wired into our neural circuits
Reactions are modulated by personality
Our psychopath would show very little fear in his reactions
But may show a great deal of anger
Triggered by p/r signals when they exceed thresholds derived from levels of motivational needs
All input is in the form of integer streams
p/r signals for each of the physiological and safety needs (8 in total)
Input representing signals received by the five senses for emotional reactions
Some needs remain constant if not changed
Assume we are sheltered unless we are informed otherwise
Some needs change unless information is received to the contrary
Hunger will increase unless we receive a reward signal for the hunger need
The engine is updated with input at each developer-determined time step
Positional information required to produce emotional body and facial gestures
For a character whose body joints are being driven by an inverse kenmatics system
Output is the joint deviations from a plain ”vanilla” movement to make the movement emotional
For a timid character, the spine might be curved backwards, the shoulders hunched forwards, and the head down
Determines characters movement speed, style, and smoothness
A neurotic character would move quickly in short bursts and in a very ”staccato”, jerky fashion
Semantic action plan
Determined by the characters motivational needs
Determines both what to do and how to do it
How is taken from current mood and selected personality trait
Character has been out in the cold rain a while
Warmth need receiving a constant stream of punishment
Results in making the mood level highly negative and the warmth need a high priority
For a character with a timid personality the resulting semantic output would be
Increase warmth very anxiously
”increase warmth” comes from motivational need for warmth
”very” comes from importance of need and mood level
”anxiously” is a trait that this particular character possesses and is appropriate to a negative mood
Raw emotional state
Gives the developer the flexibility to use the emotional state in ways not handled by the first two modes
Jane is a 38-year old mother of two playing an office simulation
She is the boss and she has to manage the well being of her office co-workers
In this game, the tasks that the team has to perform are secondary to their interactions.
Different team members respond differently to the same situation
She has to make them all work well together and keep them happy (goal of the game)
Jane begins by taking a personality test and passes the result to the Engine
Engine displays behaviors similar to hers
She then decides the personalities of her 5 coworkers
A character with a personality similar to hers
Day One: Jane’s alter ego arrives at work
Her character is greeted warmly by the extrovert
The introvert sits at his desk, continues typing hardly acknowledging her presence
The neurotic looks mildly panicked, she does not like change, her shoulders slump forward, she curls up looking submissive
The psychopath sticks out his chest, shoulders back and fixes Jane’s character with a steely gaze as he marches, quickly and firmly, over to her to make his presence known
The character similar to Janes’s looks unsure. He is unable to decide if the new boss is good or bad for him. Jane, knowing his personality, can empathize with him so she makes the first move to smile and greet him.