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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)

6We are about here…

In terms of the full potential of gaming..

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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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Emotion: summary

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Outline

• Emotions & Games: Affective Gaming

• Theoretical Foundations

• Practical Guidelines

• Conclusions

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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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First Person Shooter NPC: Select theory

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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: expression

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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