Interactive Storytelling - lecture slides 2012
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Transcript of Interactive Storytelling - lecture slides 2012
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Course syllabus
• objective: ‣ to present the key concepts behind interactive
storytelling
‣ to review the proposed and existing interactive storytelling systems
• credits: 5 cp.
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Lectures
• lecture times
‣ Tuesdays 10–12 a.m., lecture room λ (C1027)
‣Wednesdays 10–12 a.m., lecture room β (B1032)
• October 30 – December 5, 2012‣ no lectures: November 6, November 7,
November 27, November 28
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Assessment
• assessment is based on both‣ writing an essay and
‣ taking an examination
• you cannot pass the course without both!
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Examinations
• electronic examination‣ opens December 10, 2012
‣ closes March 31, 2013
• you can take the examination at most three (3) times
• for instructions and examination time reservations, see https://tenttis.utu.fi/
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Essay
• an essay of 10–15 pages on a chosen topic (in English or in Finnish)‣ topics and material are available in the course’s
moodle page
‣ the essay has to follow the given style standard
• the essay is returned as a PDF file‣ deadline: December 13, 2012 (Thursday) 2 p.m.
‣ papers returned after the deadline will not be graded!
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Essay (cont’d)
• grades and possible teacher’s comments are announced privately through the course’s moodle page
• all returned essays will be published in the course’s moodle page in December 2012‣ grades or teacher’s comments are not made
public
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Quick walkthrough
1. Pick topics that interest you from the list of topics.
2. Write the essay.
3. Return the PDF version of the essay before December 13, 2012, 2 p.m. using the essay return page.
4. Check your essay grade in the course’s moodle page.
5. Schedule and take an electronic examination.
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Grading
• grading is based on 20 points‣ the examination gives at maximum 10 points
‣ the essay gives at maximum 10 points
• to pass the course you need more than 10 points ‣ you cannot pass the course without both taking
the examination and writing an essay!
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Grading (cont’d)
• final grade:‣ points: (10, 12] ⇒ grade: 1
‣ points: (12, 14] ⇒ grade: 2
‣ points: (14, 16] ⇒ grade: 3
‣ points: (16, 18] ⇒ grade: 4
‣ points: (18, 20] ⇒ grade: 5
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Course homepage
http://bit.ly/intstory2012
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Contents
1. Introduction to interactive storytelling
2. Analysis of storytelling
3. Strategies for interactive storytelling
4. Characters
5. End-user
6. Author
7. Systems
8. Discussion and conclusion
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Introduction to interactive storytelling
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Interaction
• “Reciprocal action; action or influence of persons or things on each other.” (Oxford English Dictionary)
• “a cyclic process between two or more active agents in which each agent alternately listens, thinks and speaks” (Crawford, 2005)
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Storytelling is about…
• the reasons for actions (not actions)
• people
(Spierling, 2002)
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Linear psychological narrative
• psychological buy-in by the audience
• willing suspension of disbelief
(Perlin, 2005)
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Typical features of storytelling
• contingency: story time/space vs. real time/space
• narrative representation: the way of presentation
• presence: viewer sharing story time/space
• interactivity: participation in story generation process
(Aylett & Louchart, 2003)
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Comparison of different narrative forms
Cinema Theatre Literature Virtual reality
Contingency
Narrative representation
Presence
Interactivity
low medium low strong
visual visual mental visual
not physical physical not physical not physical but immersive
no no/yes no yes
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Models of user engagement
Degree of interactivity Examples
none conventional audience
non-participant control conventional authoring; film
non-participant influence Forum Theatre; The Sims
participant control points branching narrative
freely participating characters LARP, emergent narrative
• actual roles that users play in relation to the narrative experience (Aylett & Louchart, 2007)
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Examples of interactive storytelling
• inventing and telling a story to an audience (e.g. children)
• (live action) role-playing games
• improvisational theatre (e.g. Forum Theatre)
• tour guiding
• teaching
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Interactive digital storytelling
• interactive digital storytelling application is “designed for users (interactors) to take part in a concrete interactive experience, structured as a story represented in a computer” (Peinado & Gervás, 2007)
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Three partakers
Interactive storytelling
system
Author
End-userCharacters
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Forms of interactive entertainment
• computer games
• interactive fiction
• hypertext fiction
• digital storytelling
• scriptwriting software
• role-playing games (RPGs)
• simulators
• narrative intelligence (Crawford, 2005)
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Uses for interactive storytelling systems
• art
• entertainment‣ computer games
• education‣ children
• guidance‣ information kiosks
‣ tour guides
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Narrative thinking
• fundamental structuring of the human experience
• autobiographical memory holds stories about the self
(Aylett & Louchart, 2007)
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Narrative immersion
• spatial: a sense of place and pleasure taken in exploring the story-world
• temporal: a desire to know what will happen next (curiosity, surprise, suspense)
• emotional: affective reactions to the story and to the characters
(Ryan, 2008)
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Conventional narrative
constructed story
presented story
experienced story
author
spectator
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Interactive narrative
experienced storyuser
generated story
characters external events
author
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Narrative loop
Affectivechanges
Worldstate
changes
causecause
cause cause
EVENTS
ACTIONS
(Aylett et al., 2011)
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Degree of interactivity
1. speed‣ fast turnaround
2. depth‣ human-likeness
3. choice‣ functional significance
‣ perceived completeness
(Crawford, 2005)
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How to interact with stories?
1. what would change?
2. what would stay the same?
3. how do we make such a thing?
4. where is the artist/author located wrt. the observer/reader
(Perlin, 2005)
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Problems for interactive drama
1. temporal management of actions: interesting narrative from the choices?
2. multimodal representation of character’s actions in a real-time 3D environment
3. interpreting player’s actions
4. authorability: artists should be able to express themselves
(Szilas et al., 2007)
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Challenges for story generation
1. themes ‣ betrayal, yearning, love, revenge etc.
2. story control ‣ the story must remain dramatically compelling
3. strong, autonomous characters
4. personalization ‣ characters’ reasonable reactions and beliefs
(Bringsjord, 2001)
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R&D challenges
1. agency ‣ primary feature offered to the players
‣ player has to be able to affect the plot directly
2. generation ‣ real-time generation of content
‣ building blocks
3. interface ‣ expressive, multi-modal interface
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R&D challenges (cont’d)
4. connecting generation and interface ‣ planning and drama management
5. terminology ‣ young field still lacks proper terms
‣ e.g., ‘storytelling’ or ‘storymaking’
(Stern, 2008)
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Narrative paradox
• “pre-authored plot structure conflicts with the freedom of action and interaction characteristics of the medium of real-time interactive graphical environment”
(Aylett & Louchart, 2007)
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Analysis of storytelling
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Sources
• Aristotle: Poetics (ca. 335 BCE)
• Russian formalism (1916–1930s)
• Vladimir Propp: Morphology of the Folktale (1928)
• Joseph Campbell: The Hero with a Thousand Faces (1949)
• A.J. Greimas
• Roland Barthes
• Claude Bremond
• Brenda Laurel: Computers as Theatre (1991)
• Janet Murray: Hamlet on the Holodeck (1997)
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Aristotle: Poetics
Action
Character
Thought
Language
Pattern
Enactment
Inferred formal cause
Mat
eria
l cau
se
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Aristotle: Narrative forms
• epic
‣ events represented through verbal narration (diegesis)
‣ focus on the exploits of a solitary hero
‣ story can be endlessly expanded
‣ motivations of the hero remain fairly simple
• dramatic
‣ events represented through the imitation of action (mimesis)
‣ focus on the evolving networks of human relations
‣ action is mental rather than physical
‣ the dramatic arc
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The dramatic arc
a) exposition
b) inciting incident
c) rising action
d) crisis
e) climax
f) falling action
g) dénouementa bc
d
e
f
g
time
com
plic
atio
n
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Third narrative form: Epistemic narrative
• emerged in the 19th century
• superposition of two stories‣ events that took place in the past
‣ an investigation that leads to their discovery
• driven by the desire to know (e.g. mystery story)
(Ryan, 2008)
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Interactivity and narrative forms
• epic
‣ accomplishement of a mission
‣ used in many games
• epistemic
‣ player as a detective
‣ author-defined story – variable story
‣ elucidation of the mystery until the solution is found
• dramatic
‣ most difficult to implement
‣ goals of characters evolve together with their relations
‣ requires constant redefinition
‣ simulation of human reasoning
(Ryan, 2008)
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Russian formalism: Model of narrative
1. Fabula‣ logically and chronologically related series of events
caused/experienced by the characters in the storyworld
2. Sjužet‣ the finished arrangement (i.e. the plot, сюжет) of the
narrated events as they are presented to the reader
3. Media/text‣ the surface of the story expressed in language signs
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Vladimir Propp: Morphology of the Folktale
• analysis of Russian folktales
• 31 narrative units (i.e. narratemes)
• character function‣ “act of a character defined from the point-of-
view of its significance for the course of action”
‣ independent from the character who performs it
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Narratemes and spheres
• introduction
‣ βγδεζηθ
• the body of the story
‣ ABC↑
• the donor sequence ‣ DEFGHJIK
• the hero’s return
‣ ↓PrRsoLMNQExTUW
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α – initial situation
β – absentation
γ – interdiction
δ – violation
ε – reconnaissance
ζ – delivery
η – trickery
θ – complicity
A – villainy
B – mediation, the connective incident
C – beginning counteraction
↑ – departure
D – the first function of the donor
E – hero’s reaction
F – provision or receipt of a magical agent
G – spatial transference between two kingdoms, guidance
H – struggle
J – branding, marking
I – victory
K – resolution
↓ – return
Pr – pursuit, chase
Rs – rescue
o – unrecognized arrival
L – unfounded claims
M – difficult task
N – solution
Q – recognition
Ex – exposure
T – transfiguration
U – punishment
W – wedding
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Example sequences
‣ δηθ – the villain succeeds in deceiving the victim
‣ DE – the hero is tested to get a magical agent
‣ HJ – the hero fights and gets injured
‣ ↓oMNQ – the hero returns but is not recognized until he passes a test
‣ ↓oLQEx – the hero returns but a false hero has taken his place; the hero is recognized and the false hero is exposed
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Example tale
• A tsar, three daughters (α). The daughters go walking (β), overstay in the garden (δ). A dragon kidnaps them (A). A call for aid (B). Quest of three heroes (C↑). Three battles with the dragon (H-I), rescue of the maidens (K). Return (↓), reward (W)
• αβδABC↑H-IK↓W
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Character roles
• Villain
• Donor
• Helper
• Princess (and her father)
• Dispatcher
• Hero
• False hero
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Moves
• list of functions that make a subsection of the story (usually ending on F, K, Rs or W)‣ one move follows directly another
‣ new move begins before the end of old move
‣ second move is interrupted by a third move
‣ two villainies occur at once
‣ two moves have a common ending
‣ two protagonists part at a road marker with an exchange of signalling objects
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Joseph Campbell: The Hero with a Thousand Faces
• monomyth (i.e. the hero’s journey)‣ common pattern with strong reference symbols
• symbolic representation of the passage from childhood to adulthood‣ departure
‣ initiation
‣ return
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Innocent world of childhood
Separation
Call to adventure
Refusal of call
Supernatural aid
Crossing thefirst threshold
Belly of the whale
Initiation
Road of trials
Tests and ordealsDragon battle Nadir
CrucifixionSymbolic death/dismemberment
Sparagmos
Meeting withthe Goddess
Atonement torecognition by
Father
Apotheosis
The ultimate boon
Return
Refusal of return
Magic flight
Rescue
Master of two worlds
Freedom to live
The Hero’sJourney
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A.J. Greimas: Actant model
• first role-based analysis of narrative‣ background: semantics and structuralist stance
• formalization of Propp’s roles‣ not for what they are but for what they do
• the actant model can be instantiated by a specific semantic field
(Cavazza & Pizzi, 2006)
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Generic actant model
Object
Subject
Dispatcher
Helper
Sought-for person
Antagonist
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Roland Barthes: Interpretative codes
• ACT (action)‣ generalization of narrative function
‣ action sequences
• REF (reference)‣ background knowledge required for
interpretation
‣ contextual knowledge
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Interpretative codes (cont’d)
• SYM (symbolic)‣ major cultural objects that symbolic (e.g., money)
• SEM (semantic)‣ choice of words to narrative events
• HER (hermeneutic)‣ items that should trigger interpretation
‣ cues for future events
‣ elements of mystery relevant to the story
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Claude Bremond: Agent and patient
• agent is responsible for the changes in the narrative universe
‣ voluntary or unintended
‣ types: influencer, improver, protector, frustrator
• patient is influenced by the narrative actions‣ awareness of the situation
‣ the situation itself
• transient status: characters can alternate between the roles
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Brenda Laurel: Computers as Theatre
• “When we look toward what is known about the nature of interaction, why not turn to those who manage it best – to those from the world of drama, of the stage, of the theatre?” (Laurel, 1991)
• invisibility of the computer‣ designing an interface is the real problem
‣ creating a representational world that leaves the feeling of the interface behind
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Neo-Aristotelian theory of interactive drama
Action
Character
Thought
Language
Pattern
Enactment
User interaction
Mat
eria
l for
act
ion
Mat
eria
l cau
seInferred form
al cause
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The flying wedge of possibilities
Possible Probable
Potential
Potential
Necessary
t
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Janet Murray: Hamlet on the Holodeck
• can a computer provide the basis for an expressive narrative form?
• Star Trek’s holodeck as an ideal model of interactive narrative
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Representational strategies
• navigable space
• encyclopedic capacity
• participation
• procedurality
(Murray, 1997)
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Phenomenal categories
• immersion
• agency
• transformation
(Murray, 1997)
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Lessons from the holodeck: goals to pursue
• natural interface
• integration of user actions within the story
• frequent interaction
• dynamic creation of the story
• ability to create narrative immersion
(Ryan, 2008)
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Mapping and recapping the theoretical background 1(4)
Aristotle’s Poetics
Laurel: Computers as Theatre
Carnagie Mellon: OZ project
Mateas & Stern: Façade
(Koenitz, 2010)
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Mapping and recapping the theoretical background 2(4)
Derrida, Foucault, Barthes, Eco, Baudilard
Storyspace platform
hyperfiction
Joyce: AfternoonJackson: Patchwork Girl
(Koenitz, 2010)
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Mapping and recapping the theoretical background 3(4)
non-literary, non-western tradition (e.g., oral narratives)
Jennings: the book of ruins and desireHarrell: Griot system
(Koenitz, 2010)
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Mapping and recapping the theoretical background 4(4)
Barthes, Bremond, Prince, Genette, Chapman
narratology
interactive fiction (IF)
(Koenitz, 2010)
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Strategies for interactive storytelling
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Strategies
• author-centric‣ explicit authoring
• character-centric‣ emergent narrative
‣ implicit creation
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Measures
• plot coherence‣ the perception that the main events of a story
are causally relevant to the outcome of the story
• character believability‣ the perception that the events of a story are
reasonably motivated by the beliefs, desires, and goals of the characters
(Riedl, 2004)
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Author-centric
• models the creative process of a human author
• explicit authoring: predefined template to follow runtime
• strong plot coherence
• not so strong character believability
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Example: The Oz Project’s Interactive Drama Engine
Player
Presentation Drama manager
World
Character
Character
Character
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Drama manager techniques
• branching narrative
• universal plan‣ beats (i.e. action–reaction pairs)
‣ interactive plan trees (e.g. HTN)
• problems‣ anticipation of every possible action
‣ combinatorial explosion
(Louchart & Aylett, 2005)
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Drama managers ways to influence
• environmental manipulation
• goal injection
• shifting personality
• ticking clock of doom
• dropping the fourth wall
(Crawford, 2005)
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Character-centric strategy
• autonomous characters: models the mental factors that affect how characters act
• the story emerges from the characters’ decisions and interaction
• implicit creation: narrative planted beforehand
• strong character believability
• not so strong plot coherence
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Emergent narrative
• term introduced by Aylett (1999)
• story emerges bottom up based on characters described top down by the author
• exhibits perpetual novelty
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Example: Reality TV
• emergent narrative as a source for a story
• participant ‣ motivated by money, fame etc.
‣ subjected to entertain the spectators
• spectator‣ gets entertainment
‣ lacks influence on the narrative
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Example: Reality TV (cont’d)
• programme production team‣ pre-production selections
- choice and definition of the main protagonists- designing the world environment to foster emotions
‣ performance time control- tasks, eliminations etc.- compiling a broadcast to the spectators
(Louchart & Aylett, 2005)
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Storyworldrecepient designer
Narrative interpretation Emergent system
storyworld = mental model storyworld = model, rules
world state → mental state world state → world state
reconstruct storyworld by inference
generating from the rules
states, actions, events states, actions, events
(Spierling, 2007)
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Gardening metaphor
• author-centric‣ explicit authoring is like creating a paper flower
• character-centric‣ implicit creation is like planting a flower
(Spierling, 2007)
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Characters
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Features of believable agents
• personality‣ unique and specific, not general
• emotion‣ exhibit and respond personally-specifically
• self-motivation‣ internal drives and desires
• change‣ growth and change with time (wrt. personality)
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Features of believable agents (cont’d)
• social relationship‣ interaction with others changes the relationships
• illusion of life‣ multiple goals
‣ broad capabilities
‣ quick reactions
(Mateas, 2002)
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Character behaviour
1. low level (e.g. collision detection)
2. social interaction (e.g. introducing oneself)
3. idle behaviour
4. targeted behaviour (i.e. go for the goal!)
(Fairclough & Cunningham, 2002)
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Expressiveness
• independent from visual realism
• origins of expressive behaviour:‣ agent itself
‣ human creator
(Szilas, 2007)
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Flashback: Crawford on interaction…
• “a cyclic process between two or more active agents in which each agent alternately listens, thinks and speaks”
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Character’s interaction
• listen‣ perception of the world
• think‣ coloured by the character’s personality
‣ associated with and stored to the character’s memory
• speak‣ acting in the world
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The perception system in VIBES
1. acquisition sensors: abstract description of the world
2. perception filters: simulation of the physical sensors
3. cognitive filters: support for the decision-making
(Sanchez et al., 2004)
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Crawford’s personality model 1(2)
Intrinsic Accordance Relationship
Integrity “gullibility” “trust”
Virtue “willingness to see good” “virtue perceived”
Power “timidity” “fear of power”
Intelligence “judging others wise” “respect”
Attractiveness “vanity” “attractiveness perceived”
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Crawford’s personality model 2(2)
Mood Volatility
Anger/Fear Adrenaline
Joy/Sadness Manic/Depressive
Arousal/Disgust Sensuality
(Crawford, 2005)
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Event-appraisal theory
• OCC-model (Ortony, Clore and Collins)
• emotional state‣ positive/negative
‣ intensity
• agents reaction to events, actions and objects varies according to their emotional state
(Theune et al., 2004)
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OCC-model
Directed to agent itself Directed to other agents
hope – fear admiration – reproach
joy – distress hope – fear
pride – shame love – hate
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Autobiographical memory types
• type 0: agent is always telling the same story
• type I: agent has a variety of stories but not within the conversational context
• type II: agent selects a story that fits the context best
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Autobiographical memory types (cont’d)
• type III: agent tells and listens stories (i.e. interprets the meaning and has a response)
• type IV: a living, autonomous agent (i.e. personality)
(Ibanez et al., 2003)
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Memory in VIBES
• stores information (i.e. percept objects) acquired about the world‣ actor’s representation of the world
‣ knowledge the actor has acquired
• records consecutive internal states of the actor (e.g. wants, emotions)
(Sanchez et al., 2004)
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Memory in SAGA
• narrative memory stores a temporal sequence of episodes‣ cause-and-effect links between episodes
• episode comprises‣ crisis
‣ climax
‣ resolution
(Machado et al., 2004)
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Episodic memory
• personal history of an entity‣ places and moments
‣ subjective feelings and goals
• requires: persistent world and multiple actors
• autobiographic memory: longer, lifetime scope
(Brom et al., 2007)
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Requirements for a full episodic memory
1. storing complex hierarchical tasks
2. storing and reconstructing personal situations‣ what, with which and why?
‣ who saw and what did he do?
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Full episodic memory (cont’d)
3. all available information is not stored‣ perceivability
‣ importance
‣ attractiveness (or salience)
4. large time scale: the importance of forgetting (details reduced, events merged)
5. coherence: trust in the stored data
(Brom et al., 2007)
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Late commitment
• character agent’s decisions‣ in-character (IC)
‣ out-of-character (OOC)
• improvisational theatre: no agreed upon storyworld but framing as the actors go along‣ implicit OOC communication (e.g. “Hello,
daughter.”)
(Swartjes et al., 2008)
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Late commitment (cont’d)
• explicit OOC communication‣ framing operators
• late commitment‣ goal management: goals from OOC if no other
goals exist
‣ action selection: agents can create OOC plans for their goals
(Swartjes et al., 2008)
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Late commitment: observations
• IC actions should not be selected to satisfy the preconditions of framing operators
• an action contradicting a framing operator has to be ordered after the framing operator
• all characters must unconditionally accept all framing operators
(Swartjes et al., 2008)
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Problem of believability: The uncanny valley
• Masahiro Mori (1970):‣ the more human-like the robot, the more
positive the emotional response
‣ at some point the response becomes quickly a strong repulsion
‣ as the appearance and motion improve, emotional response becomes positive again
• the uncanny valley: the area of repulsion between “barely human” and “fully human”
The uncanny valley: Movement and appearance
100%0%
resp
onse
+
–human-likeness
healthyperson
bunrakupuppet
prosthetichand
corpse/zombie
android/gynoid
industrialrobot
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End-user
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Affordance
• interface design: opportunities for action made available by an object or interface
• interface “cries out” for the action to be taken
(Mateas, 2002)
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Choice problem
• how to choose from a large amount of possible actions?
(Szilas, 2004)
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Interface mapping function
• P: physically possible actions‣ perceived affordances
• L: logically (in the story) possible actions‣ real affordances
P Lf
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Interface mapping function (cont’d)
• total‣ non-surjective: filtering
interface
‣ non-injective: redundant interface
‣ bijective: direct interface
• partial‣ free interface: free
interface
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Anticipation of an action
• author’s activity: plan the user’s inferences
• stability: P and L should remain stable
• surprise: counters stability‣ new possibility should remain in the selection
‣ addition in slow pace
• duration of interaction‣ freeze or fill in the time
‣ semi-autonomy
‣ ellipsis
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User-centred actions
• ethical consistency
• motivational consistency
• relevance (history)
• cognitive load (opens/closes narrative processes)
• conflict (exhibits or pushes towards a conflict)
(Szilas et al., 2007)
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Inferring player states
• inferring player’s knowledge
• inferring player’s preferences
• inferring player’s goals
(Thue et al., 2008)
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The role of the end-user?
• users probably do not want to be tragic or comic heroes
• many users do not even want to be actors but marginally involved observers or confidantes‣ a peripheral character affecting the world and
observing the outcome (i.e. agent and spectator)
(Ryan, 2008)
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Robin Laws: Seven player types
1. power gamer: new abilities and equipment
2. butt-kicker: fight!
3. tactician: thinking ahead
4. specialist: sticks with his favourite character
5. method actor: want to test his personal traits
6. storyteller: plot threads
7. casual gamer: in the background
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Author
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Author
• authoring = delivering content for somebody else’s experience
• author defines‣ actions
‣ states
‣ events
(Spierling, 2009; Spierling & Szilas, 2009)
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A contract with the author
• there is a reason why the author is leading you through the story
• how does that work in an interactive story?
(Perlin, 2005)
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Narrative paradox and authoring
• the author cannot expect the user to make the right decision at the right moment or in the right place
• author’s role is to write interesting characters and rely on their ability to interact with one another
• author must be extremely attentive to the user’s inner state
(Louchart & Aylett, 2005)
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Second person insight
• the ability to think in terms how the expression will be perceived by the audience
(Crawford, 2005)
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Authoring challenges
• authored content depends on the run-time system architecture
• the increase in the amount of content
• not a single author task
(Aylett et al., 2011)
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Problems
• finding IS authors‣ reluctance to reduce human affairs into logical
models
• abstraction‣ writing must be at the level of story-related
abstract structures
• formatted and constrained writing‣ e.g., XML, Excel
• algorithm-centered story design
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Problems (cont’d)
• the potential of engines underused‣ reduction to linear or branching structure
‣ no inspiring examples, lack of prototypes
• authoring and programming intersecting‣ storyworld and engine have a blurry line
‣ immaturity of the medium
(Spierling, 2009; Spierling & Szilas, 2009)
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Boundaries of authoring
interaction
storyworld
runtime engine
end-user
author
developer
ISartefact
ISexperience
(Spierling & Szilas, 2009)
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Principles of design
• main characters‣ limit the number
‣ give clear relationships to one another within a dramatic situation
• character definitions‣ along the spectrum based on the value system
central to the story
• parallel characters‣ draw clear contrasts (e.g., rivals, friends, enemies)
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Principles of design (cont’d)
• characters as foils for one another‣ emphasize similarities and differences
• narrative events‣ combine functions of an overarching frame story
‣ create coherent nested sequences
(Murray, 2011)
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Potential influence
(Spierling, 2009)
abstractstoryworld
narrative discourse / sequence of events
staging /shape ofevents
(representation)
action selection
action andbehaviourmodels
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Models of actions, states and events
• Bremond: elementary sequence1.possibility for action2.actualization3.result of the action
• von Wright: logic of action1.intial state2.end state after action
3.state without the action
• AI planning1.pre-condition2.action3.post-condition
(Spierling, 2009)
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Creative process of the author
• debugging‣ altering and adapting the story content to match
the authorial intent
• co-creation‣ embracing the possible stories and letting it
change the original authorial intent
(Swartjes & Theune, 2009)
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Authoring types
• content authoring‣ which instances of story elements are in the
domain?
‣ which actions, goals etc. may occur?
• process authoring‣ how do the element connect causally?
‣ when do the elements occur?
(Swartjes & Theune, 2009)
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Iterative authoring
(Swartjes & Theune, 2009)
1. idea generation‣ get inspired
‣ find flaws
2. implementation‣ add new content
and processes
‣ constrain the domain
3. simulation‣ feel out the
storyscape
‣ detect surprising behaviour
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Principles of delayed authoring
• AI in an IDS system is a decision-making proxy for the interactive story’s authors
• delay story decisions made online: maximize the chance of new player information
• a story decision arising during the authoring process: it is better informed by inferred player information?
(Thue et al., 2008)
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Authoring in emergent narrative
• interactive story‣ who tells?
‣ to whom?
‣ what is the story?
• sender, receiver, message
(Louchart et al., 2008)
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Sender and message
• sender‣ narratorship shared between the system and the
interactor
• message‣ the interactor can construct their own message
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Receiver
• the notion of agency
• not necessary to predict the consequences of an action
• interactor can make choices they would not do in real life (even if they know the consequences)
• willingness to play within the role and its constraints
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Landscape of possible stories
• point: possible state
• climbing hill: moving towards dramatic necessity (i.e., flying wedge)
• valley: offers potential mountains
(Louchart et al., 2008)
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Design suggestions (1)3
• justify the existing boundaries‣ spatial
‣ contextual
‣ interaction
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Design suggestions (2)3
• critical mass for emergence‣ density: how well the authored content serves to
create different paths
‣ added content- new possibilities- widens the boundaries and reduces density
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Design suggestions (3)3
• dead ends‣ narrative end = lack of content
‣ continuing process involving finding dead ends and resolving by adding new content
(Louchart et al., 2008)
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Process of authoring
• modelling a dramatic abstraction of reality‣ how the characters behave (not how people are
behaving in reality)
• modelling implies complexity reduction‣ too much generalization can lead to
uninteresting stories
• author should not think in the terms of plot
(Louchart et al., 2008)
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Authoring tools and methods
• Improv: scripts
• Hap/ABL: hierarchy of goals
• FSMs/hierarchical FSMs
• Motion Factory: graphical editors
• Softimage
• Virtools: flow charts
• BEcool: oriented graphs
(Szilas, 2007)
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What does an author want?
• testing‣ debugging
‣ parameter tweaking
‣ replaying
• feedback from the users
• artistic control‣ but what is actually the author’s role in
interactive storytelling?
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Systems
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General scheme of an IS software
1. reasoning (decision-making, planning)
2. behaviour
3. animation (triggered by behaviour)
(Szilas, 2007)
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Four-level story engine
1. story engine (flow of the story)‣ narrative function the next scene should fulfil;
gets story acts
2. scene action engine (play scene using a narrative function)
3. character conversation engine (sends stage directions)
4. actor avatar engine (Spierling et al., 2002)
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Four-level story engine (cont’d)
• axis: predefined – autonomous1. strict – dynamically chosen scene
2. predefined scripts – generated scripts
3. dialogue – intelligent agent
4. stored animations – adapted animations
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Reviewed systems
• CrossTalk
• Façade
• Interactive Drama Engine
• Makebelieve
• SAGA
• Storytron
• Virtual Storyteller
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CrossTalk
• interaction triangle: three screens‣ virtual exhibition hostess
‣ changeable virtual exhibition visitors
‣ touch screen for the user’s choices
(Klesen et al., 2003)
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Narrative structure vs. story content
1. scene flow definition
2. scene content creation‣ author’s scripts
‣ automatic dialogue generation
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SceneManager
• scene‣ pieces of user-edited dialogue
‣ coherent and closed unit wrt. message, agent characterization or punchline
• compound scene = linked atomic scenes
• scene group = set of equivalent atomic scenes
• scene flow: narrative structure linking the scenes
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SceneManager (cont’d)
• scene node‣ prescribed
‣ customically created
• scene transition‣ interrupt
‣ conditional
‣ probabilistic
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SceneManager (cont’d)
• user input‣ request and wait
‣ time-out events
‣ interrupt (seamless interaction)
‣ concurrent event handling (affect long-term behaviour)
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Dialogue strategies: plan operators
• context: goal and precondition
• dialogue content
• characters: role & personality
• role & meta-role (trick for immersion)
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Façade
• story set-up‣ player takes the role of a close friend of Trip and
Grace, a couple whose relationship is in trouble
‣ events takes place at Trip’s and Grace’s home where the player is invited to have a cocktail
• player’s control‣ moving and interacting in a 3D environment
‣ typing in utterances
(Mateas, 2002; Mateas & Stern, 2004)
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System structure
• story comprises dozen carefully scripted interactive narrative scenelets
• time is discretized into beats‣ the smallest unit of a value change (i.e. an action–
reaction pair)
• techniques to steer the narrative towards the relatively linear set pieces
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Broad-and-shallow approach
• idea inherited from the Oz project‣ broad: all necessary features have an
implementation
‣ shallow: some features could have been performed better
• characters can act believably, but not necessary intelligently, in a wide range of situations
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Surface-text processing
1. map surface text into discourse acts
2. map discourse acts into character responses
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Discourse acts• agree/disagree
• positive/negative exclamation
• express of emotion
• unsure or indecisive
• thank
• greet
• ally/oppose character
• don’t understand
• apologise
• praise/criticize
• flirt
• pacify
• explain
• advice
• refer to
• ask to share intimate thoughts
• say goodbye
• miscellaneous discourse act
• can’t understand
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Interactive Drama Engine
• prototype system‣ non-linear narrative
‣ 3D characters
‣ graphical user-interface
(Szilas et al., 2007)
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IDE architecture
Narrativestructure
Actiongeneration
Actionselection
Text generation
NarrativeGUI
Behavioural engine
Game engine
Player
Narrative engine
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Makebelieve
• virtual guide system, which uses‣ Jess/CLIPS reasoning system
‣ OpenMind common sense data
‣ Unreal Tournament engine
(Ibanez et al., 2003)
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Story element
• name
• type of event
• location
• attributes (nature of the element)
• basic concepts (defined in knowledge base)
• date
• special environment condition
• granularity: ‘size’
• effects: caused by this
• subject: of the fact
• object: of the fact
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Method
1. initial situation; input
2. select a story element
3. add related story elements (causation)
4. translate according to the guide’s attitude
5. consider common sense rules
6. extend story with common sense
7. generate storyboard
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SAGA
• no predefined story
• users interacting with autonomous character collaboratively play the role of the author
• director: guide the accomplishment of a meaningful story
(Machado et al., 2004)
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SAGA system
• based on Propp’s narrative morphology
• story definition‣ initial story situation
‣ variable story schema
• function → plot point → set of generic goals → plan → hierarchy of goals and actions
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Director agent
1. update situation
2. conflict? → select a new episode
3. current plot point achieved? → select the next plot point
4. reflection event needed?
5. new story element introduction needed?
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Storytron
• components‣ authoring tool SWAT
‣ storyworld library
• launched 2006; discontinued 2011
• originally developed under the name Erasmatron
(Crawford, 2005)
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Virtual Storyteller
• multi-agent framework ‣ plot generation
‣ natural language generation
‣ presentation by an embodied agent
(Theune et al., 2004; Swartjes & Theune, 2006)
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Plot generation
• select “episodic script” from a database‣ setting: location, characters,objects
‣ goals
‣ constraints
• character asks the director’s permission before carrying out a plan
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Plot generation (cont’d)
• within episode characters are free to choose action
‣ subjected to probabilistic emotions (OCC-model)
‣ example: 90% fear means 0.9 probability of choosing a cowardly action
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General transition model (GTN)
• elements
‣G – goal
‣ A – action
‣O – outcome
‣ E – event
‣ P – perception
‣ IE – internal event
• causal relationships
‣φ – physical causality
‣m – motivation
‣ψ – psychological causality
‣ e – enablement
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GTN (cont’d)
IE
E P G A Omφ/eφ
ψψ
ψ
ψ
ψm/e
m
ψφ/e
φ
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Decision-making in interactive storytelling• six general properties of story events‣ idea: what is the occurring action
‣ actors: who or what is acting or being acted upon
‣ time: when does the action occur
‣ place: where does the action occur
‣ actions: what changes
‣ reasons: why does the action occur
• cf. the six questions in journalism‣ who? what? when? where? why? how?
(Thue et al., 2008)
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Story decisions and design decisions
property story decision property design decision
idea what should happen? result what was decided?
actors who should be involved? chooser who made the decision?
time when should it happen time when was the decision made?
place where should it happen? — —
actions how should it happen? method how was the decision made?
reasons why should the actors act? justificationwhy was the decision made in
that way?
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Story decision properties for Façade
chooser time method justification
idea
actors
time
place
actions
reasons
author offline imagination no restrictions
author offline imagination no restrictions
player & author online & offlinetension arc /
player interest
follow dramatic principle / respond to
player
author offline imagination no restrictions
player & author online & offlineinterruptible
scriptsallow player interactions
author offline imagination no restrictions
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Discussion and conclusion
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Adaptation for interactive stories
• translation between media
• adaptation types
‣ scissors adaptation
‣ distilled adaptation
‣ expanded adaptation
‣ straight adaptation
‣ wild adaptation
• adaptation in interactive storytelling: expanded or wild
‣ formalize the story into an abstract form
‣ make a creative interpretation and adaptation
(Spierling & Hoffmann, 2010)
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Multiuser interactive storytelling
• multiple users in application means handling conflicts‣ intervowen stories that consistent, responsive
and compelling
• challenges‣ solving the too-many-heroes problem
‣ maintaining persistency
‣ preventing cheating
(Smed, 2011)
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Too many heroes
• how to guarantee dramatically compelling story to everyone?
• each human-controlled character needs a group of computer-controlled characters to support them‣ each new brings along extras
‣ limit the number of human-controlled characters
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Persistency
• how do we handle players entering and leaving at any time?
• when the user leaves the storyworld‣ user’s character vanishes from the storyworld
‣ user’s character becomes a computer-controlled character
‣ user can give tactical level instruction to character to follow during the absence
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Cheating
• every action within the storyworld should be valid
• limitations exist‣ e.g. zombie attack and “I’ve been shot” in Façade
• how about multiple users?‣ is collusion cheating in an interactive story?
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Motivations for rereading interactive stories 1(3)• making sense of things‣ new fragments to be reconciled into the overall
understanding of the story
• finding out more‣ there is more to the story than can be seen on
the surface
• trying out “what-if” scenarios‣ different choices can lead to different outcomes
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Motivations for rereading interactive stories 2(3)
• seeing things from a different perspective‣ radical revision of
- player’s model of the storyworld- character’s personality and motivation- causal connections
• looking for a deeper meaning‣ process of looking for an interpretation of the
text
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Motivations for rereading interactive stories 3(3)
• reflecting on the techniques used‣ appreciating or critiquing the ways in which the
text achieves its effects
• figuring out how the system works‣ what is the underlying role system
(Mitchell, 2010)
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Dramatis Personæ 1986–2002
Brenda Laurel
Joseph Bates Chris Crawford
Janet MurrayMichael Mateas
Andrew Stern
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Dramatis Personæ2003–
Ruth Aylett
Marc Cavazza
Ana Paiva
Stefan Göbel
Ulrike Spierling
Nicolas SzilasSandy Louchart
Ivo Swartjes
Mariët Theune
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Ruth Aylett, "Narrative in virtual environments: Towards emergent narrative" in Papers from the 1999 AAAI Fall Symposium, Technical report FS-99-01, AAAAI Press, pp. 83–86, 1999.
Ruth Aylett & Sandy Louchart, "Towards a narrative theory of virtual reality", Virtual Reality 7(1):2–9, 2003.
Ruth Aylett & Sandy Louchart, "Being there: Participants and spectator in interactive narrative", in Cavazza & Donikian (eds.) Virtual Storytelling. Using Virtual Reality Technologies for Storytelling. Proceedings of the Fourth International Conference, ICVS 2007, Lecture Notes in Computer Science vol. 4871, pp. 117–128, 2007.
Ruth Aylett, Marco Vala, Pedro Sequeira & Ana Paiva, "FearNot! – An emergent narrative approach to virtual dramas for anti-bullying education", in Cavazza & Donikian (eds.) Virtual Storytelling. Using Virtual Reality Technologies for Storytelling. Proceedings of the Fourth International Conference, ICVS 2007, Lecture Notes in Computer Science vol. 4871, pp. 202–205, 2007.
Ruth Aylett, Sandy Louchart & Allan Weallans, “Research in interactive drama environments, role-play and story-telling”, in Si, Thue, André, Lester, Tanenbaum & Zammitto (eds.) Interactive Storytelling: 4th International Conference on Interactive Digital Storytelling, ICIDS 2011, Lecture Notes in Computer Science vol. 7069, pp. 1–12, 2011.
Selmer Bringsjord, "Is it possible to build dramatically compelling interactive digital entertainment?", Game Studies 1(1), 2001.
Cyril Brom, Klára Pešková & Jiří Lukavský, "What does your actor remember? Towards characters with a full episodic memory", in Cavazza & Donikian (eds.) Virtual Storytelling. Using Virtual Reality Technologies for Storytelling. Proceedings of the Fourth International Conference, ICVS 2007, Lecture Notes in Computer Science vol. 4871, pp. 89–101, 2007.
References
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Marc Cavazza & David Pizzi, "Narratology for interactive storytelling: A critical introduction", in Göbel, Malkewitz and Iurgel (eds.) Technologies for Interactive Digital Storytelling and Entertainment. Proceedings of the Third International Conference, TIDSE 2006, Lecture Notes in Computer Science vol. 4326, pp. 72–83, 2006.
Chris Crawford, On Interactive Storytelling, New Riders, Berkeley, CA, USA, 2005.
Chris Fairclough, Story Games and the OPIATE System, PhD thesis, University of Dublin, Trinity College, Dublin, Ireland, 2004.
Chris Fairclough & Pádraig Cunningham, "An interactive story engine", in O'Neill, Sutcliffe, Ryan, Eaton & Griffith (eds.) Proceedings of the 13th Irish International Conference on Artificial Intelligence and Cognitive Science, Lecture Notes in Artificial Intelligence vol 2464, pp. 171–176, 2002.
Jesus Ibanez, Ruth Aylett & Rocio Ruiz-Rodarte,"Storytelling in virtual environments from a virtual guide perspective", Virtual Reality 7(1):30–42, 2003.
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