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Modeling Emotions in Game Characters: Theoretical Foundations

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Title: Modeling Emotions in Game Characters: Theoretical Foundations


1
Modeling Emotions in Game CharactersTheoretical
Foundations Practical Guidelines
Eva Hudlicka
Joost Broekens
SEP 10, 2009 ACII 2009 Amsterdam
2
Outline
  • Emotions Games Affective Gaming
  • Theoretical Foundations
  • Practical Guidelines
  • Conclusions

3
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4
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5
Where We Are Now
  • Tremendous advances in gaming technologies
  • From dots to cinematic characters
  • From single screen to virtual world
  • Focused primarily on
  • Physical realism of game characters
    environments
  • Complexity performance of simulations
    networking
  • Rich gameplay/interaction
  • Todays games still limited in
  • Affective realism for game character (NPC)
  • Social complexity realism of interactions
    between and with NPC
  • Ability to adapt to players state
    personalization of the experience (see Georgios
    talk)

6
In terms of the full potential of gaming..
We are about here
7
To achieve the next big leap
  • ..in engagement effectiveness
  • Games would benefit from
  • Adapting to players affective states
  • Enhancing social affective complexity realism
    of
  • Game characters
  • Their interaction with each other the players
  • Game narrative as a whole (interactive
    storytelling)

8
AC Methods Techniques Relevant for Affective
Gaming
  • Sensing recognition of players emotions
  • Adaptive gaming
  • Game control
  • Expression of emotions by game characters
  • More realistic visuals
  • Models of emotion in game characters
  • To support complex, autonomous behavior
  • To support adaptive behavior
  • Models of players emotions
  • Affective user models to support game
    personalization (Yannakakis)
  • Affective game evaluation
  • Use affective feedback to develop games with
    desired affective profiles

9
Emotion Models in Affective Gaming
  • Game characters emotions
  • To generate
  • realistic affectively-complex character
    behavior believable affective expressions
  • You need
  • Emotion generation emotion effects on cognition
    behavior
  • responsive to dynamically-evolving game
    scenario player behavior
  • in real-time (practical issues such as
    scalability and performance)
  • Players emotions
  • Help recognize player emotions in real-time
  • Develop gameplay adaptations
  • Generate more realistic player avatar behavior

10
Outline
  • Emotions Games Affective Gaming
  • Theoretical Foundations
  • Practical Guidelines
  • Conclusions

11
Emotion and affect in human behavior
  • Basic emotions fear, anger, happiness, sadness,
    surprise, disgust
  • Short episode of multimodal activity triggered by
    event
  • subjective feelings (the emotion we normally
    refer to),
  • tendency to do something (action preparation),
  • facial expressions,
  • evaluation of the situation (cognitive
    evaluation, thinking),
  • physiological arousal (heartbeat, alertness).
  • Affect related to emotion, mood and attitudes
  • emotion object directed, short term, high
    intensity, action oriented, differentiated.
  • mood usually unattributed and undifferentiated,
    longer term, low intensity.
  • attitude affect permanently associated with an
    object/person
  • affect abstraction of emotion/mood in terms of,
    positiveness/negativeness and activation/deactivat
    ion (e.g., Russell, Rolls).

12
Emotion and affect in human behavior
  • Situational evaluation (intrapsychic)
    andcommunication (interpersonal).
  • Heuristic relating events to actions through an
    evaluation of personal relevance (e.g., goals,
    needs, drives, motivations)
  • Evaluation of personal relevance of event
  • Speeds-up decision-making
  • fast reactions and action preparation
  • influence information processing
  • Learning adaptation, attention, mental
    search/planning, creativity, etc..
  • Communication medium
  • communicate internal state and intention
  • alert others
  • show empathy (understanding of situation of
    others)

13
Emotion dimensions
  • Set of underlying common factors of emotion
  • E.g. Russell, Mehrabian, Wundt

(Breazeal, 2003) adapted from Russell (1997)
14
Emotion categories
  • A small number of hardwired basic emotions exist
  • E.g. Tomkins, Izard, Ekman, Panskepp
  • Category is a typical emotion syndrome
  • A complex of physiology, expression, behavior,
    and feeling
  • Sadness
  • Low arousal
  • Face sad
  • Avoid
  • Bad feeling
  • Anger
  • High arousal
  • Face angry
  • Approach
  • Bad feeling
  • Joy
  • High arousal
  • Face happy
  • Play
  • Good feeling

15
Emotion components
  • Parallel evaluation in terms of appraisal
    dimensions
  • (E.g. Scherer stimulus checks)

16
Emotion summary
17
Outline
  • Emotions Games Affective Gaming
  • Theoretical Foundations
  • Practical Guidelines
  • Conclusions

18
Main questions
  • I want to build an emotional agent, now
  • Where do I start?
  • Where do I end?
  • When did I succeed?
  • A tree has no emotions
  • A mosquito has emotional behavior in the eye of
    the emotional beholder (fear, frustration).
  • A lizard has emotions, although probably only a
    couple of them (fight, flight, satisfaction)
  • A grown buffalo has emotions, and probably quite
    a lot of them (fear, excitement, joy, attraction,
    satisfaction).
  • Agent?
  • Emotion?
  • Lets dive into the details

19
Agent related issues
  • Really understand the environment agent / NPC /
    Virtual Character / etc.
  • What is the observable behavior of my agent?
  • What are its potential actions?
  • What is the environment of the agent?
  • What are the observable events for that agent?
  • What are the beliefs and motivations for the
    agent?
  • What does the agent want, like, dislike etc
  • Do emotions make sense, what are they supposed to
    add?
  • HCI aspects Believability and effectiveness
    (serious games), fun (games), interaction
  • Agent autonomy aspects intelligence, planning,
    learning and adaptation, etc.?

20
Emotion related issues
  • How do I select an emotion theory that best
    matches the
  • Internal workings of my agent (motivations,
    beliefs, etc.)
  • Observable behavior of my agent (actions)
  • Environment (events)
  • How do I value events in relation to the emotion
    theory?
  • Direct versus indirect mapping.
  • How do I represent emotion internally?
  • States, traits, moods, attitudes
  • Factors, categories, components
  • Level of complexity of the emotion object
    (level of detail)
  • How do I represent emotion dynamics?
  • Onset, decay, mixed emotions (similar versus
    opposing), etc.
  • How do I link emotion to emotion effects,
    expression and behavior?
  • Direct vs Indirect, feature vs expression
  • Facial expression, body posture, movement,
    behavior.
  • Effects on problem solving, planning, decision
    making, learning, etc.

21
Emotion architecture for an NPC
  • Guideline to make your choices
  • Not everything is needed in your model!

22
Outline
  • Emotions Games Affective Gaming
  • Theoretical Foundations
  • Practical Guidelines example integrating
    generation and effects
  • Conclusions

23
First Person Shooter NPC
  • The agent
  • Monster (zombie)
  • Needs
  • Health (hit-points)
  • Hunger (eat flesh, drink)
  • Potential events
  • see_human, see_animal, see_water,
  • health_high, health_low
  • energy_high, energy_low
  • Hunger_high, hunger_low
  • attacked
  • Potential behaviors
  • wander, chase_human, chase_animal, move_to_water,
    search_X, flee
  • eat_human, eat_animal, drink, sleep

Source resident evil
24
First Person Shooter NPC
  • The emotions
  • Why?
  • Add realism
  • Influence action choice
  • Influence attention
  • Expression
  • Fear, aggression, happiness, panic.
  • Behavior
  • Trigger search, chase and flee
  • Attention
  • Field of view (broad-narrow)
  • Object fixation
  • Self, other oriented

Source resident evil
25
First Person Shooter NPC Select theory
26
Homeostasis why?
  • Drives needs
  • Drive motivator for particular behavioral
    programs
  • Needs biological drives
  • Sleep
  • Hunger
  • Thirst
  • Etc.
  • When drives not met (or met too much) this
    influences
  • Emotion, behavior and attention to regulate
    drives
  • Process is called homeostasis
  • Behavior is aimed at satisfying needs and
    regulates emotion
  • Emotion is a signal that biases organisms towards
    interaction that satisfies current needs.

27
First Person Shooter NPC Select affect types
28
First Person Shooter NPC expression
29
First Person Shooter NPC
  • Architecture

Environment
Interpretation
Behavior
Affect Type
Effects
attention
Emotion (categories) Fear Aggression Happiness Pa
nic
Health_low Health_high Hunger_low Hunger_high
Fear Anger Happiness Panic
Biological Needs Health Hunger
See_human See_animal See_water
Search_X chase_X Flee, etc.
Emotion elicitation
Emotion representation
Emotion effects
30
First Person Shooter NPC
  • Instrumentation
  • Direct mapping based on drives/needs and
    anticipated effect.

31
First Person Shooter NPC
  • Affect dynamics
  • FeltDrivedrive1/2anticipation
  • Expression
  • Based on mapping of FeltDrive combination to
    emotion category

32
Emotion effects
  • Fewer theories exist than for emotion generation
  • Specific mechanisms of emotion effects not as
    well developed
  • Some available theories
  • Distinct modes of processing associated with
    different emotions (Oatley Johnson-Laird,
    1987)
  • Spreading activation priming (Bower, 1984
    Derryberry, 1988)
  • Emotions as patterns of parameters modulating
    processing (Fellous, Matthews, Ortony et al.,
    Hudlicka, Ritter)
  • Componential model of effects (Scherer et al.,
    Lerner Tiedens)

33
Emotion effects
  • Many relationships between affect and cognition
  • Mood influences information processing style
  • Top-down (positive) versus bottom-up (negative)
  • Heuristic/generic/assuming/creative processing
    (positive) versus detail/feature/critical/procedur
    al processing (negative)
  • Mood influences learning
  • Flow, boredom, frustration , etc.
  • Emotion influences information processing, e.g.,
  • anxiety ? threat bias (Mineka et al., 2003)
  • aggression ? higher risk tolerance (Lerner
    Tiedens, 2006)
  • arousal is related to attention capacity

34
Emotion Effects in NPC Context
  • Zombie tasks
  • Maintain health
  • Maintain energy
  • Stay fed
  • NPC behavior changes depending on emotion
  • homeostatic interpretation specific emotions
    favor specific behaviors to satisfy needs.
  • Happiness increase tendency towander, sleep.
  • Panic increase tendency tosearch_animal,
    chase_animal, flee_human
  • Aggression increase tendency to search_X,
    chase_X, eat_X
  • Fear increase tendency to wander, flee_X.

35
Emotion Effects in NPC Context (2)
  • Zombie attention
  • Nr of humans/animals tracked (parameter for field
    of view detail vs. global)
  • Object fixation (parameter for stability
    capacity working memory)
  • Focus on self-related needs vs. other (parameter
    for self-other directedness)
  • Effects (provided as example!)
  • Pos. valence global attention, distractible
    (e.g., Dreisbach Goshke, 2004)
  • Neg. valence focus on details, tunnel vision
    (e.g., Clore, Isen)
  • Anger Attribution of hostility in others
    (Lerner Tiedens, 2006)
  • Fear Threat-directed attention (Mineka et
    al., 2003)
  • Emotion influences attention parameters
    (parameter-based effect)
  • Happy Large field of view, weak object
    fixation, balanced needs
  • Panic Small field of view, weak object
    fixation, balanced needs
  • Aggression Small field of view, strong object
    fixation, hunger
  • Fear Small field of view., strong object
    fixation, health

36
Outline
  • Emotions Games Affective Gaming
  • Theoretical Foundations
  • Practical Guidelines
  • Conclusions

37
Conclusions
  • Affect-focused game design
  • emotion plays a central role in
  • Gameplay design - adapt to player emotions
  • Game character design - more affective realism
  • Assist Me, Challenge Me, Emote Me (Gilleade,
    Dix Allanson 2005)
  • Affective game engines (Hudlicka, 2009)
  • Game development tools that support
  • Sensing recognition of player emotions
  • Gameplay adaptation to player affect
  • Design of affective game characters

38
Modeling Emotions in Game Characters
Theoretical Perspectives
  • Affective gaming
  • Emotion recognition for adaptive game control
  • Emotion in NPC for adaptation, realistic behavior
    expression
  • Models of players emotions for game
    personalization
  • Affective feedback for game evaluation and
    development
  • NPC emotionsGenerate realistic affective
    character behavior expressions
  • Emotion effects on cognition behavior
  • responsive to dynamic scenario
    player behavior
  • in real-time

Affect Type Alternatives
What does my NPC need? Agent issues observable
events, actions, architecture complexity,
motivation Game issues Computational complexity
available for emotion,Intended player
experience Emotion issues Theory selection,
Emotion representation and dynamics, Emotion
effects on cognition, expression, behavior
Implementation Alternatives
Emotion Architecture Overview
  • Requirements for Affective NPCs
  • Affect-focused game design perspective
  • Tools for analysis of affective requirements
    within game
  • Tools for design and development of affective
    NPCs - Affective Game Engines
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