Emergent Narrative, Social Immersion and "Storification"
Centre for Virtual Environments
Business House, University of Salford
Salford M5 4WT, UK
In this paper we consider the clash between the pre-scripted character of much narrative and the freedom afforded by a Virtual Environment. We discuss the concept of emergent narrative as a possible way of avoiding this clash. We examine the role of a VE user in a narrative and consider the concept of social presence as a means of reconciling the freedom of the user with the constraints of an emergent narrative. The idea of Storification is discussed as a way of charaterising the realtionship of a human user to an interactive narrative environment
This discussion paper looks at ideas which originally emerged from a recent project Virtual Teletubbies [Aylett et al 99]. In this project, childrens TV characters - Teletubbies - were incorporated into a virtual environment (VE), by which we mean a 3D graphically rendered world in which both they and the user have a joint spatial existence. In this case, the user was not required to use special immersive hardware, such as a head-mounted display, but was represented by an invisible camera position attached to spatial controls which allowed him or her to move within the VE.
The Teletubbies were implemented using a behavioural robot architecture, in which emergent behaviour at a given moment is determined by the synthesis of responses from currently active behaviour patterns [Barnes 96]. These behaviour patterns are in turn driven by simple virtual sensors while groups of behaviour patterns (packets) are activated or deactivated according to the level of the Teletubbies internal drives, such as hunger, fatigue and curiosity.
As with robots, the initial behaviours implemented were those allowing physical movement in the environment, in this case taking into account the sloping nature of the outdoor terrain being modelled. A simple form of gravity was also modelled so that neither Teletubbies nor user were able to fly within the VE. Virtual sensors were implemented as bounding boxes and as a forward sweeping sensor for obstacle avoidance; information about objects in a Teletubby line-of-sight was transferred directly as symbolic information rather than through a virtual retina.
While this project was successful in examining some basic architectural issues, a number of issues of narrative arose, many of which are common to virtual environments of other types. We consider the problem of narrative as it arose in this particular project, examine alternative ways of dealing with the issues, and sketch out a way forward which is being used as the basis for a new project: the "Holodeck".
A Narrative Problem
In moving characters from television to VE, the difficulty in retaining the original narrative approach was immediately evident. On television, the narrative is normally wholly pre-scripted (very tightly) and is viewed passively by the audience from camera positions determined by the creators of the narrative. While digital TV is moving towards some form of user interaction, this is currently limited to choosing between a number of pre-determined camera positions. Translating the conventional TV approach directly into a VE removes all the characteristics that differentiate a VE from television. The ability of the user to interact individually with the VE and even their ability to select their spatial viewpoint is denied. The well-known narrative paradox of VEs is how to reconcile the needs of the user who is now potentially a participant rather than a spectator with the idea of narrative coherence that for an experience to count as a story it must have some kind of satisfying structure.
One way of dealing with this issue is to move the focus from the user-as-participant to the user-as-director. Through the provision of an appropriate toolkit, characters in a VE can be treated as virtual actors and the user can construct narratives involving the virtual actors and sometimes themselves too via an avator. This approach has been investigated by a number of groups, in 2D multi-media environments as well as in VEs, as for example the Virtual Theater project of Barbara Hayes-Roth [Hayes-Roth & Brownston 95] and the IMPROV virtual actors system [Goldberg 97] as well as work at MIT [Umaschi Bers & Cassell, 00]. There is a parallel with the creative play of children in which they may switch back and forwards between the role of director and participant and there are clear educational applications . As well as empowering users who would normally be excluded from the creation of 3D spatially located narrative, this approach is also of professional interest to the film industry. Film directors are beginning to exploit the power of 3D graphic environments explicitly in films such as Toy Story and Antz and implicitly via special effects in films such as Titanic and Gladiator. Nevertheless, the extension of freedom in the process of narrative construction does not in our view remove the need to examine how the narrative experience might be extended to take advantage of the specific characteristics of a VE.
Two issues are of interest here. The first is how far the pre-determined nature of much narrative can be relaxed. The second is how far the user of a VE can freely participate in a narrative rather than acting as a spectator. Clearly these issues are related - a wholly pre-determined narrative also pre-determines the role, if any, of the user within it. Thus relaxing this constraint allows more freedom for user involvement. However it does not of itself settle the issue of exactly how the user can be incorporated into a narrative.
One way of examining narrative approaches is to divide the narrative process that is, the activity producing the story - into a number of levels, and to consider them top-down. The use of a framewrk of levels of abstraction of activity is a not uncommon technique in robotic and agent architectures and fits closely with an Aristotlean view of drama in which plot is dominant. Without making any claim for a definitive hierarchy here, one can produce something like this:
Character-level abstract action sequences
Physical behaviour - cognitively determined
- reactively determined
Thus a narrative may have a plot in which boy meets girl, boy loses girl, boy performs heroic feat, boy regains girl. This plot can be achieved by a number of different abstract action sequences. For example the first element could be implemented as: come into the room, walk up and say hello; creep up behind the character and say boo; stand close to the character near others and join in an existing conversation; and so on. In turn each such action can be embodied in different physical behaviour. This physical behaviour can be thought of as more cognitively determined by the character: exactly what words to say, for example; or more reactively determined: as in stumbling or laughing involuntarily.
At one extreme, a narrative may be wholly scripted down to the most detailed level. For example, a film director often goes to great lengths and many takes to achieve exactly the desired effect with dialogue, body language and facial expression, not to mention every physical item in the setting. Deviations from this scheme can be excluded from the finished film. From this perspective, virtual actors who never tire of retakes and do exactly what they are programmed to do may be an improvement over the real thing. A somewhat looser position can be seen in live theatre, where for example a classic text may be reinterpreted via variation in the speaking of the text and in the setting.
Further along the spectrum, both in filmed and live media, improvisation may be used. Here elements of the narrative are created dynamically, though often within overall constraints. As these constraints are set at higher levels of the hierarchy above, the improvisational element becomes greater. The abstract action sequences characters carry out may be fixed, but physical behaviour may be wholly improvised, so that the words used are dynamically generated. Alternatively, the overall narrative structure may be fixed at a general level but the exact actions characters carry out as well as the exact words they speak may be improvised. However the least-constrained form of improvisation occurs when actors are given a basic situation and some roles but no overall plot at all. For example one actor may be a mother and the other a teenage girl and the improvisation concerns the girls attempt to tell the mother that she is pregnant and the mothers reactions to it. This form of improvisation seems outside the hierarchy sugegsted above and we will return to it below.
Improvisation is investigated in VEs, but mainly at very low levels in the hierarchy above. A number of systems allow sensor-driven reactive behaviour by virtual agents. For example, training environments have been created in battlefield medical first-aid [Stansfield et al 98] in which a virtual patients physical state changes according to the first-aid administered by the user, and in hostage release [Shawver 97] in which virtual hostages dive to the floor if the user, acting as rescuer, fires a shot. Improvisation at the level of cognitive behaviour is less developed, probably because it is mostly expressed via natural language and thus poses difficult problems. Virtual agent improvisation at the level of action sequences is also infrequent as this requires some form of planning, whether through a generative approach or plan selection from libraries, as can be seen in the Steve system (Johnson et al 99) which is, however, task-oriented rather than concerned with narrative.
Could one speak of improvisation at the topmost level of the hierarchy above, that of overall plot? This may appear to require formidable creative abilities, which are difficult for humans (storytellers, playwrights, novelists, film directors) and wishful thinking in the current state-of-the-art of intelligent agents. Moreover at this level in the hierarchy, the actions of several characters are bound together, which means that no single character in character can improvise the plot: they have to be able to direct other characters (including potentially the user) , that is have out of narrative powers and abilities. One could have course have an invisible director (God), or one could allow out-of-narrative negotiation between the characters (see Pirandello Nine characters in search of an author) or one could adopt the story format in which a number of characters take it in turns to have control of the plot. However, the ideas behind the behavioural approach used in the Teletubbies project suggested an alternative view. The principle followed by behavioural architectures is that of emergence: the creation of complexity bottom up via interaction between essentially simple components. Rather than seeing the hierarchy above as a top-down structure, one may view it as a bottom-up structure, in which each level is created by interaction below it. This is essentially a character-based approach rather than a plot-based approach and rather foreign to the Aristotlean view of drama, but corresponds to the least-constrained dramatic improvisation just mentioned.
Emergent narrative may seem paradoxical since the underlying structure provided by a definite plot (or equivalent - a plot in the classic sense may not be the only type of high-level narrative structure) seems needed to make a narrative hang together. Yet in an obvious sense, narrative is emergent, since it has emerged from human life experience. If life seems too grandiose a concept to fit into a VE, there are smaller-scale examples in which explicit narrative structure is absent but narrative frequently emerges through interaction.
Team games form a particularly obvious example, as in the case of football (for any US readers, we mean soccer here). At the level of physical behaviour, football is indeed a group of people (usually men) kicking a ball about. However the addition of conflicting aims and some constraints on allowable physical behaviour together with a limited time often - though by no means invariably - produces recognisable narrative structure. For example, the late substitution producing the winning goal; the new young player scoring on his debut; the player committing a reprehensible foul who injures himself seriously in the process; the talented but petulant player who retaliates when fouled, gets sent off, and loses his team a crucial match. Arguably it is this emergent narrative structure that gives football and other multi-player games an appeal different from say gymnastics.
In order to experiment with the concept of emergent narrative in a VE, for example with the Virtual Teletubbies, a number of issues must be investigated. What structures are needed to produce narrative often enough and with enough complexity to satisfy the user? There are a lot of very boring football matches too. In the 1980s, UK television carried a live broadcast of an embassy siege being broken up by commandos. This consisted of nothing visible happening for some time and then a series of fairly mysterious events happening very quickly indeed. The narrative reconstructed after the event with suitably edited material had far greater coherence and power in this viewers estimation. One of the problems was that the camera itself was in that case excluded from participation: it could only view the scene from an arbitrary global perspective, it had no ability to follow any of the SAS commandos, and could not witness the planning meeting in which roles were allocated , contingencies discussed and actions decided which would have made sense of the events it later captured.
A useful area for investigation is that of the free improvisation in drama cited above. Arguably the basis for a free improvisation is also the basis for an emergent narrative, since actors will normally try to produce some kind of emergent narrative framework in order to hold the attention of an audience. This type of improvisation seems to require actors to have established characters and some kind of relationship between these characters. An overall goal or precipitating event is often specified, usually involving some kind of conflict between the characters. Thus: two teenage girls clash because one of them has snogged the others boyfriend; a woman tells her partner she is leaving him.
Comparing this with a football match we see that there too character is specified (being life, each footballer plays themselves) and relationships are also specified: both between teams and within teams. There is also an overall goal in both senses of the word. The hostage release incident, on the other hand, had no characterisation of the individuals involved, and no close relationship between them, at least from the television camera position (it may or may not have formed a more satisfactory narrative from the perspective of a hostage).
Two important ideas emerge from these examples. The first is that emergent narrative is essentially physically and temporally contingent: it happens in a specified place and time frame. This makes it small-scale compared to most literary, film or TV narrative but gives it something in common with theatre. This is no problem in a Teletubby context since their narratives are brief and located in one place, but it raises issues that must be considered for more extensive narratives, such as those envisaged for the Holodeck project discussed below.
The second issue is that what constitues the narrative, depends on your point of view. In the football example, the narrative for spectators may depend on which team they support; the narrative for a player may depend on what position they play and what events they directly participate in. An emergent narrative is essentially supplying the raw material for a storification process which is subjective and related to individuals [Dautenhahn 99] so that from a more global perspective there may be a number of different narratives depending on whose storifaction process we consider. This issue was well-considered in Tom Stoppards play Rosencrantz and Guilderstern are dead in which the events in Shakespeares Hamlet are seen from the point-of-view of two minor characters : some of the same events occur but their weight in the narrative experienced by spectators is quite different from the Hamlet-centred view of Shakespeares play. Thus the user cannot be considered an optional addition to an emergent narrative since the objective is to produce events that can be storified by the user from their perspective within the VE.
As already commented, the narrative structure of the Teletubbies is usually rather simple, since the television programme is aimed at children aged two or even younger. So, for example, a small pink cloud invades the Teletubby world, and the Noo-noo (a vacuum cleaner on wheels that acts as an autonomous character) tries to clean it up. However as the Noo-noo is not designed to have clouds inside it, this produces some anomalous behaviour s it tries to clean up things which are not rubbish, like the Teletubby toast machine. Eventually it expels the cloud and returns to normal. A second example involves the appearance of a pair of wellington boots one of the Teletubbies tries them on and goes stamping around in the, another Teletubby comes up, is opffered the boots, putsd them on, but being smaller,.falls over. This is the cue for a falling over game.
Thus disturbance of the environment is a common source of narrative for the Teletubbies, and it is therefore easy to imagine how a bottom-up approach might produce them. In particular, the use of language is minimal, and there is little forward-planning again, the target audience is very yound children who may not have these capabilities to any great extent. The first example seems a very plausible emergent narrative assuming a sufficiently rich set of Noo-noo behaviours - in this case both internal and external. The precipitating event would be the arrival of the cloud near the Noo-noo. This suggests that in general a suitable number of dynamic events outside the control of the characters are needed in order to produce interesting behavioural reactions. For example, the Teletubby curiosity drive is more likely to form the basis for emergent narrative if unfamiliar objects appear in their environment. Thus character-driven emergent narrative is not the only way of tackling the issue in simple cases event-driven narrative can be produced assuming that the agents have a suitable repertoire of behaviours.
We have commented that a sufficiently rich or suitableset of behaviours is required for the characters in an emergent narrative without defining what this is. Experiment is one way of exploring this issue. However it seems likely that one avenue that should be incorporated in the Teletubbies is a more sophisticated emotional system than the basic drives that Teletubbies currently possess. These drives are already used to produce sequences of Teletubby action: a hungry Teletubby will head for the dome to get some food; curiosity, as just commented, will lead a Teletubby to investigate novel objects. A wider range of emotions connected into the architecture in a more principled manner would support more interesting interaction between Teletubbies and other elements of the environment.
One of the risks of emergent narrative is that it may not emerge of course - the unpredictability that makes it interesting also makes it in some sense fragile. We have seen that it is also inherently small-scale: like free improvisation it runs in continuous time, there is no leaving out the boring bits as would be the case in a written narrative. Theatrical drama deals with this problem by breaking its narrative into scenes, so that activity the dramatist does not want to present to the audience can occur in between off-stage. One could of course implement this in a VE - flipping the environment onto the next day for example. However since episodic drama often requires that characters to behave as if they have experienced the between scenes activity, one might have to compute this for the virtual agents. This idea is one that is being investigated for the Holodeck project outlined below.
The role of the user
A second set of issues to be confronted in experimenting with emergent narrative surrounds the role of the user, not so far considered. We have argued above that the freedom of the user to interact with the VE and in particular to move freely within it are essential features - indeed it is this which contributes so greatly to the feeling of presence for which many VEs aim. However it does pose problems in establishing a user role within a narrative structure. At a simple level, the freedom of the user to be in any location they choose within the VE might just mean that when interesting interactions occur, the user misses them. The comments on the hostage release example above underline that a narrative may only emerge from a particular perspective and may fail entirely if the user is in the wrong position. We should note that even the role of spectator in a pre-scripted narrative becomes problematic in a VE, since the user may not be visually present in the position that was assumed when the narrative was constructed.
This issue has been confronted in the domain of computer games, but the solutions adopted there seem of limited applicability since they rely on the user constructing their own abstract action sequence in the hierarchy discussed above - as the central active character. In adventure games, such as Myst, there is often an enveloping narrative, but in reality there is little organic connection between this and the action sequence created by the user. The abstract action sequence is often sketchily - if at all - realised in physical behaviour. Other characters appear rarely and do not construct any developing relationship with the user that would help to anchor the users actions to the overall narrative. There are few paths often only one through the game which bring success, and the satisfaction for users lies in solving sequencing problems, not in participating in a narrative.
On the other hand, in arcade-type games, physical behaviour is dominant with little sense of abstract action sequence or overall plot other than kill the monsters and/or collect the treasure. In both types of game, the ability of the user to undo any amount of behaviour without consequences undermines the concept of narrative coherence. The user may have as little idea by the end of the game of his or her narrative path as a film actor who has appeared in dozens of takes of scenes in various orders but has not seen the final film. The imposition of a linear path through the game produces a situation in which divergence is frequent and disastrous, and restarts therefore essential.
The concept of emergent narrative suggests a different approach to the users role. Enough interaction between virtual characters must exist, independently of the users role, to produce narrative in this way. By analogy with emergent behaviour at lower levels, narrative will only emerge through the right type of components interacting in the right type of way. If the user is to contribute, they have to provide the appropriate behaviour. However, it may be difficult even for a co-operative user to be sure what behaviour is appropriate in this sense as we have argued, it is the high chance of getting it wrong which lies behind the undo facilities in games. Thus we require mechanisms which will encourage the user to do the right thing without making them feel that they have been coerced and an environment which is forgiving of a user who doesnt get it quite right. If anything, this means that the user should, initially at least, be a peripheral character in the virtual environment, extended the same sort of latitude that a child has in human societies.
A simple mechanism for helping the user to partipate sensibly in a VE is the kind of pre-briefing favoured both in adventure game booklets and in role-playing games used in training. This is a straightforward way of postulating a shared history between the user and the environment and a set of role-specific behaviours. We argue though that unless it is reinforced within the VE via interaction, the idea of staying in role, which is second nature to an actor, will not appear to the ordinary user to be particularly important. In human society, approriate behaviour is produced by teaching it, or demonstrating it, but also be rewarding it and by penalising deviations from it. It is this idea of maintaining desirable user behaviour within the VE that we refer to as the creation of social presence.
Presence in its classical sense is very much physical presence - the illusion of being physically located in a VE. In the real world, appropriate behaviour is very much socially determined. At a simple level, if a football player violates the physical constraints of a game, he is sent off the pitch by the referee. Moreover, the crowd may well express strong and noisy disapproval.An academic giving a lecture does not spit on the floor at intervals, though this is acceptable in a football match. Social presence is therefore an extension of physical presence - the illusion not only of physical location but also of social location. Thus if the VE has a social reality for the user they accept the other agents as social beings - then the behaviour required for emergent narrative could be communicated through social convention or social pressure. The large-scale MUDs and MOOs suggest that social presence can be produced with very limited amounts of physical presence, though it is worth remembering that these environments are almost entirely populated by human users with a full range of natural language and sophisticated social and cultural assumptions.
It seems clear that a prerequisite for social presence is that the user has a defined social role within the VE. Again this is either absent, or sketched in advance but never reinforced in most computer games, with the exception of some role-playing dungeon games. The other agents in the VE must reinforce role-specific behaviour and penalise role-deviant behaviour, not only second-to-second, but also in terms of a biographical memory of the users character [Dautenhahn 98]. Thus a restart facility cannot exist not only would narrative coherence be lost, but the role-coherence in terms of the perceptions of other agents would also be destroyed. This works in the opposite direction too: the users perception of the characters of the other agents would also be undermined since their social relationship would be disrupted. The absence of a restart means also that the user in character has to live with the consequences of their actions as in role playing games one could allow the user to retire their character and start again with another if they had completely messed things up, but the former character would still be remembered by other agents within the VE.
One can see therefore that the creation of social presence has substantial ramifications on the design of a VE and of the agents within it. It demands a persistent VE in which state changes are permanent and can only be unwound in role and not by an extra-narrative magic wand. It also demands persistent agents who remember what has happened and are therefore autobiographical agents in the sense discussed by Dauhtenhan [Dautenhahn 98].
The thinking in this paper is now being applied to the early stages of a new project, the Holodeck. For those readers who are not fans of the long-running TV series Star Trek in its various forms, the Holodeck was an area in a large space ship in which people would be immersed in a virtual world. This world would engage all the senses as if it were the real world and allowed personnel to experience life outside the confines of their work and immediate environment, whether for rest and recreation or learning or just for adventure.
In the Holdeck project [Cavazza et al 00] , for which we here present some initial ideas, we envisage a user entering an immersive environment such as a CAVE, wearing stereoglasses, and participating in an on-going narrative. In this environment, the user would be able to interact with a cast of virtual actors (VAs) sharing the same environment and addressing them in natural language, a difference from the Virtual Teletubbies environment. An essential feature is that the user involvement should not be a permanent one after all, they have their own lives to live. Instead, the user should be allowed to participate in the action, helping to create the story and leave the stage to watch the story unfold as a consequence of his or her intervention. Another essential aspect is that the user would still be able to get back into the story at some suitable time, or even to influence it from the spectator position, for instance by influencing the emotional state or the behaviour of VAs. This new form of entertainment would implement in its own way the convergence of VR, cinema and computer games.
We have already commented on the contingent nature of emergent narrative. The Holodeck is seen as rather like a TV Soap, with a large number of entwining narratives being generated episodically. The virtual world would be divided into on-stage and off-stage areas: the user would only be able to participate and directly view on-stage action, but other activity might well occur concurrently off-stage, in order to support the rich web of interactions required for social immersion. There are several reasons for suggesting an episodic environment: one is that the user is only present in the narrative (or even as an observer) some of the time. Another is that if activity is to take place in different physical locations, a change of scene must be produced without the kind of non-narrative effort involved in getting onto a virtual bus. This is a specific case of the general consideration that not all activity is intrinsically interesting, in which case it should happen off-stage.
A user who is not permanently present, must have an "in-character" method of joining and leaving the world (an analogy with the group-controlled skipping rope of childhood suggests itself - the user must jump in and out neatly without getting tangled in the rope!). This has implications for the role that the user is allocated in the first place - if they play character K, there should always be an in-character answer to any VA who asks where is K?, and, more strongly, an in-character answer from K if asked directly where were you yesterday?.
Next, K must only be able to leave the world in a justifiable fashion. For example, not in mid-sentence; not just as some bad action meets its just deserts from a VA. It may be necessary to incorporate some exit mechanism such as a special door leading off-stage for a VA and out of the world altogether for the user. The same applies to entering the world - K should not suddenly appear in the middle of a group of VAs as if by magic unless the scenario supports magic appearances and the VAs can also make use of it. The guiding point here is that the world must possess a guiding logic, which applies as much to the user as to the VAs.
The introduction of off-stage action requires a mechanism for communicating significant events back to the user. Both in-world and global mechanisms can be considered: the former could be embodied in a VA who gossips about what has happened or in a newspaper or virtual radio/TV (or a virtual website?). The latter could take the form of a voice-over summary of the type used at the start of TV episodes (or in written adverts for TV soaps) which would update the user if they had been absent from the world for some time. This would allow K to reappear in an appropriate place in relation to his or her view of the continuing narrative.
In observer mode, the user might be allowed to follow a VA from scene to scene. Here the issue is of guiding the user towards the interesting pieces of off-stage activity (by definition, potentially on-stage if the stage moves) and away from characters sitting eating their dinner on their own and reading a newspaper. Forcing the user to adopt a specific observation position is all too much like current non-interactive media, while letting the user wander around at will risks narrative coherence - some intermediate position in which appropriate guidance and choices are offered is probably the way forward.
While the Virtual Teletubbies had no requirement for planning, the more sophisticated inter-agent interaction supposed here clearly does. It is hoped that the interleaving of planning and execution will allow agents to remain responsive to their environment and not develop the tunnel vision typical of some classical planning approaches. This would also allow the Virtual teletubby arcghitecture to be reused as the lower level of the extended architecture needed here.
In this paper we have discussed ideas of emergent narrative and social immersion that originally arose from considering the issues raised by the Virtual Teletubbies project. We have outlined how these ideas migth be taken forward in a more complex environment of continuing narrative generation, the Holodeck.
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