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Modeling Emotions in Game Characters:Theoretical Foundations &
Practical Guidelines
Joost Broekens
SEP 10, 2009ACII 2009
Amsterdam
Eva Hudlicka
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Outline
• Emotions & Games: Affective Gaming
• Theoretical Foundations
• Practical Guidelines
• Conclusions
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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
• Today’s games still limited in:– Affective realism for game character (NPC)– Social complexity & realism of interactions between and with NPC– Ability to adapt to player’s state: personalization of the experience (see Georgios’ talk)
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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)
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Current focus of Affective Gaming
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
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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
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Outline
• Emotions & Games: Affective Gaming
• Theoretical Foundations
• Practical Guidelines
• Conclusions
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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/deactivation (e.g., Russell, Rolls).
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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)
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Emotion: dimensions
• Set of underlying common factors of emotion– E.g. Russell, Mehrabian, Wundt
+P
+A
+D
-A
-P
-D
The following sample ratings illustrate definitions of various emotion terms when scores on each PAD scale range from -1 to +1:
angry (-.51, .59, .25) bored (-.65, -.62, -.33) curious (.22, .62, -.01) dignified (.55, .22, .61) elated (.50, .42, .23) hungry (-.44, .14, -.21) inhibited (-.54, -.04, -.41), loved (.87, .54, -.18) puzzled (-.41, .48, -.33) sleepy (.20, -.70, -.44) unconcerned (-.13, -.41, .08) violent (-.50, .62, .38).
The emotional state "angry" is a highly unpleasant, highly aroused, and moderately dominant emotional state. The "bored" state implies a highly unpleasant, highly unaroused, and moderately submissive state.
From: Albert Mehrabian’s (1980) PAD Scales.
(Breazeal, 2003) adapted from Russell (1997)
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Emotion: categories
• Sadness:– Low arousal– Face: sad– Avoid– Bad feeling
• Anger:– High arousal– Face: angry– Approach– Bad feeling
• Joy:– High arousal– Face: happy– Play– Good feeling
• 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
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Emotion: components
• Parallel evaluation in terms of appraisal dimensions– (E.g. Scherer: stimulus checks)
Novelty Pleasantness Goal/Need conduciveness
Coping potential
Sensory-Motor level
Sudden, intense stimulation
Innate preferences/ aversions
Basic needs Available energy
Schematic level
Familiarity: schema matching.
Learned preferences or aversions
Acquired needs motives
Body schema
Conceptual level
Expectations: cause/effect, probability
Recalled, anticipated, or derived positive-negative estimates
Conscious goals, plans
Problem-solving ability.
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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?
• Let’s dive into the details…
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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.?
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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.
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Emotion architecture for an NPC• Guideline to make your choices• Not everything is needed in your model!
Environment Interpretation Behavior
Internal Events
ExternalEvents
Psychological
Biological
Social
Physiological
Affect Type
Trait
Emotion
Mood
Attitude
Face
Posture
Actions
Behaviors
Emotion generation Emotion representation Emotion effects
Effects
Psychological
Biological
Social
Physiological
Thoughts
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Outline
• Emotions & Games: Affective Gaming
• Theoretical Foundations
• Practical Guidelines: example integrating generation and effects
• Conclusions
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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
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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
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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.
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First Person Shooter NPC: Select affect types
Affect type CharacteristicsEmotion Quick onset and decay, intensive, targeted, expressed, direct link to
behaviorMood Slow onset and decay, moderate, indirect link to behavior
Trait Bias to mood, emotion (propensity to be in a certain emotion or mood) and nature of affective dynamics.
Attitude Emotional counterpart of cognitive event, influence emotion and mood
Complex affect dynamics Simple
Updates to affect type values are based on changes (deltas) resulting from interpretation
Result of interpretation is an absolute value that “sets” the affect type values
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First Person Shooter NPC
• Architecture
Environment Interpretation Behavior
Health_lowHealth_highHunger_lowHunger_high
See_humanSee_animalSee_water
Biological
Needs:HealthHunger
Affect Type
Emotion(categories)
FearAggressionHappiness
Panic
FearAnger
HappinessPanic
Search_Xchase_XFlee, etc.
Emotion elicitation Emotion representation Emotion effects
Effects
attention
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First Person Shooter NPC
• Instrumentation– Direct mapping based on
drives/needs and anticipated effect.
Event/behavior Drive effect Anticipation effect
See_human Hunger -0.5Health -0.1
See_animal Hunger -0.25Energy -0.2
Chase_human Health -0.1 Health –0.3Hunger -0.5
Chase_animal Health –0.1 Hunger –0.25
attacked Health -0.3
Eat_human Hunger -0.5
Eat_animal Hunger –0.25
Wander Health -0.1
Search Health -0.2 Hunger -0.1
Sleep Health +0.2
Etc.
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First Person Shooter NPC
• Affect dynamics– FeltDrive=drive+1/2*anticipation
• Expression– Based on mapping of FeltDrive combination to emotion category
Hunger Health Emotion
Low high Happiness
High high Anger
High low Panic
Low Low Fear
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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)
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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/procedural 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
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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 to…wander, sleep. – Panic: increase tendency to…search_animal, chase_animal, flee_human– Aggression: increase tendency to… search_X, chase_X, eat_X– Fear: increase tendency to… wander, flee_X.
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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
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Outline
• Emotions & Games: Affective Gaming
• Theoretical Foundations
• Practical Guidelines
• Conclusions
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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
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Modeling Emotions in Game CharactersAffective gamingAffective 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
Affective gamingAffective 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 emotionsNPC emotionsGenerate realistic affective character behavior & expressions•Emotion effects on cognition & behavior … responsive to dynamic scenario & player behavior … in real-time
•NPC emotionsNPC emotionsGenerate realistic affective character behavior & expressions•Emotion effects on cognition & behavior … responsive to dynamic scenario & player behavior … in real-time
What does my NPC need?What does my NPC need?Agent issuesobservable events, actions, architecture complexity, motivationGame issuesComputational complexity available for emotion,Intended player experienceEmotion issuesTheory selection, Emotion representation and dynamics, Emotion effects on cognition, expression, behavior
What does my NPC need?What does my NPC need?Agent issuesobservable events, actions, architecture complexity, motivationGame issuesComputational complexity available for emotion,Intended player experienceEmotion issuesTheory selection, Emotion representation and dynamics, Emotion effects on cognition, expression, behavior
Requirements for Affective NPCsRequirements 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
Requirements for Affective NPCsRequirements 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
Emotion Architecture OverviewEmotion Architecture Overview
Affect Type AlternativesAffect Type Alternatives
Theoretical PerspectivesTheoretical Perspectives
Implementation AlternativesImplementation Alternatives