University at Buffalo
Buffalo, NY 14260 USA
Buffalo, NY 14222 USA
In this paper, we describe a CAVE VR application, The Thing Growing, which is designed to engage the user in an emotional relationship with a computer-controlled character in the context of a fictional narrative. We discuss the process of building an interactor-centered virtual drama and assess The Thing Growing.
VR, interactive drama, intelligent agents
This paper reflects on the process and problems of building interactive drama with reference to The Thing Growing a virtual reality application created for a CAVE® VR system at the Electronic Visualization Laboratory (EVL), University of Illinois at Chicago, between 1997 - 2000. The Thing Growing is an art project, whose goal is the creation of a fictional experience in a new media; a story that involves the user in an emotional journey; a drama in which the user is the protagonist . Story telling is a modeling process (of our world, our experiences, our selves), created and experienced for a variety of often mixed purposes such as escapism, titillation, experimentation, questioning, reassurance, incitement. This process may present a protagonist with condensed dilemmas of a political, social, ethical, and/or emotional nature . Readers/listeners/viewers identify with the protagonist and in so doing rehearse and explore their own reactions to the dilemma. Computer-based fiction should be able to remove the middleman, make the interactor the protagonist, and allow that exploration to be direct. Although some find this conflation of third and first person problematic, we believe it is one of the most powerful promises and fantasies of interactive story . At the SIGGRAPH 99 panel, Fiction 2000, Jesse Schell argued that one element that keeps the interactor interested in a story is psychological proximity . By psychological proximity he means that our interest in an event - such as a stone hitting someone - varies incrementally if it happens to a stranger, if it happens to a friend, or if it happens to me. We want our fiction to be something that happens to the interactor; we don't want the application to simply tell her a story, we want it to implicate her in a chain of events.
Our general goal is to discover if, and how, interactive media can become as compelling a forum for story-telling as traditional media. Our particular challenge was to develop effective methods for exploiting the unique characteristics of our VR system for this drama. As we discuss how we approached this challenge, we will briefly argue against one common approach to interactive fiction which stresses non-linear narrative, and multi-form plots. Then we will expand upon Janet Murray's useful concept of "scripting the interactor" . An interactive story has to include a "script" for users to follow so that they are fully engaged in the story that is presented. Clearly we do not mean a script in the traditional sense in which each line of dialog and movement is assigned. Instead this "script" means creating an application in which the user will act and react in ways that we have stimulated, anticipated, and made provision for. We will present the three main areas where this scripting takes place in our work; the technical and narrative context which provides possibilities and reasons for responses and emotions; our model of the user; and the virtual actors/agents used to stimulate the user and drive the story forward by their actions.
The Thing Growing is a cultural production. Our goal was to create an involving, challenging, subjective experience for an audience that would encounter the application in an exhibition or museum context. We did not devise any scientific method for assessing the work. However, the building process included user-testing and feedback. When the work was finished we collected video-taped recordings and interviews with interactors, and we gathered statistics from a log during a month long show at the InterCommunications Center (ICC) in Tokyo in 2001. This qualitative assessment was a vitally important part of refining the dramatic impact of this work, and informs our process as we approach new projects. We will discuss it briefly in conclusion.
One much hyped strength of computer-mediated fiction is the possibility of non-linear narrative and multi-form plots. Janet Murray suggests digital techniques could present kaleidoscopic stories revealed from multiple points of view which, coupled with the encyclopedic capacity of computers, would offer the possibility of the creation of almost infinitely rich and detailed narrative epics . Brenda Laurel's describes an Interactive Fantasy System, in which she proposes using intelligent agents to develop and change the plot on the fly . However, it has proved very hard to create such ambitious works in practice.
On the other hand Andrew Glassner suggests that the interactive author needs to keep control of pacing and plot-twists, in order to create compelling drama . This in effect means taking advantage of a good linear plot, with a beginning, middle and end, serving up twists and reversals, building an exciting, emotional rhythm of high and low points, and leading to a logically self-consistent and emotionally satisfying close. Anstey's experiments with narrative in video-art also led her to respect the effectiveness of a linear narrative. She wrote the very linear short story that served as the basis for the video Let's Play Prisoners which explores a difficult relationship between two little girls . The essence of the story survived a bricolage-like reassembly by the video's director Julie Zando which completely altered the sequence of events but retained and indeed intensified the dramatic force. We therefore decided to base our drama around a straightforward narrative, and let the interactive aspects devolve from it. Murray calls digital narrative and drama an "incunabular" medium, and we agree. We believe we need to start small. The Thing Growing has a simple plot with two scene changes and minimalist graphics; two main protagonists, the user and a computer-controlled virtual actor; and lasts less than 15 minutes. All our attention went into making the interactive exchanges between our two protagonists intense.
The drama of The Thing Growing emerges from the context in which the users find themselves - a context which has both a technical and narrative aspect. The VR system establishes the possible responses the interactor can make, the narrative establishes reasons for the responses and a context for interpreting them. The arc of the narrative was one of our main tools for scripting the interactor - by providing an unraveling context in which she had to act.
The Thing Growing was built for a CAVE or CAVE-like, VR display system . The CAVE is a room-sized, virtual reality theater. Computer generated images are rear-projected onto the walls and front-projected onto the floor. In a CAVE system, the position of the interactor relative to the VR world is tracked by a number of sensors. A sensor on the head allows the system to correctly calculate the 3D perspective of the real-time graphics as the user looks about and moves through the virtual environment. To create the stereo effect the user wears active or passive 3D glasses and the graphics system projects an image for each eye. The user carries a wand with a joystick for navigation and buttons which can be programmed for interaction. This wand is also tracked so that the system knows where the user's hand is. For The Thing Growing, we added a tracker on the other hand. Therefore the information that our application knows about the interactor is the position of her head and two hands, and whether she is using the joystick or buttons. In the CAVE, interactors can see their own bodies in the virtual world, and therefore immediately and automatically assess their own size relative to virtual objects. Such an immersive and responsive VR system can lead people to feel very present in a virtual environment
As Anstey was learning to program the CAVE, she thought she saw in this medium the solutions to telling a story she had found difficult to write in a traditional prose form. The essence of the story was to communicate the feeling of being in a dysfunctional relationship; the emotional twists as the "other" is by turns loved and hated, experienced now as separate and interesting, now as unbearably intrusive; a bad relationship which is none the less compelling and hard to escape. Our goal was to make users one of the two main protagonists of our story, so they would live out this relationship (albeit phantasmagorically) flavoring it with their own emotional patterns. The CAVE creates the first conditions for such an experiment by making possible not only first person perspective, but first person experience.
Figure 1. Interactor dancing with the Thing in the CAVE.
The Thing Growing makes use of a most traditional, three act, plot structure. In act one the interactor finds a box in a shed. She opens the box. The box and shed explode outwards as rocks pour out of it. Then the Thing emerges from the bottom of the box, ecstatic to be free. It looks at the interactor and falls in love with her. In act two the Thing insists on teaching the interactor a dance that will express (in its eyes) the relationship between them. It becomes disenchanted with the interactor's attempts to dance and goes of in a huff. The rocks stalk and trap the user. The Thing frees her. The dancing begins anew - but now the Thing seductively mimics the interactor's movements. In act three, the Thing's four cousins interrupt the courtship, disgusted with the relationship they perceive between Thing and interactor. They imprison the two and threaten to kill them. The Thing passes a hidden gun to the interactor and implores her to shoot the cousins. When all the cousins are dead or have escaped, the Thing suddenly fears the interactor will shoot it. The interactor is presented with this final choice.
Robert McGee teaches a famous script-writing seminar which stresses the role of structure in creating a rising and falling curve of interest and maximizing the viewers emotional engagement . The Thing Growing's story arc is very similar to that of the paradigmatic film-script he describes. Act one introduces the characters and provides the plot with an inciting incident. Act two harries the interactor into responsiveness and ends with a plot twist. Act three leads to the denouement. Each act is also subdivided into a beginning, middle and end of its own. This structure provides the user with constantly changing clues and suggestions on how to act and incidents to act against, and imparts a forward thrust to the experience which is essential to maintaining interest. Each scene in each act also has an underlying goal to stimulate an emotion or sequence of emotions in the user. Surprises (the Thing jumping out the box); reversals of fortune (the Thing's fawning love turning to annoyance); and events with unanticipated results (killing cousins too efficiently leads the Thing to chastise the user); are all designed to elicit the current emotional goal.
Interactivity has always implied choice. However, there is nothing inherently dramatic about choosing between several options. Andrew Glassner decries interactive fictional work that offer the user a plethora of choices none of which he cares about . In The Thing Growing there are two main points at which the interactor's actions may radically change the sequence of events, or determine which of two branches he will continue down. But at a finer level of granularity there are multiple ways in which the computer controlled character can respond to the interactor's behavioral choices within each of these scenes. We considered it a plus rather than a minus that the linear plot tends to constrain the interactor's choice of actions. Brenda Laurel was the first to suggest that, "A system in which people are encouraged to do whatever they want will probably not produce pleasant experiences." And to introduce the idea of constraints that can be built invisibly into the activity or experience, so that the user chooses the things scripted for them. Our narrative serves as such a constraint. The narrative context of the scripted choice also allow us to interpret the choice more meaningfully. Thus if the user chooses to run away from the Thing instead of dancing, we interpret this as uncooperative behavior and the Thing's mood changes accordingly. Within this framework the interactor has a certain amount of agency but as in life he has nothing like total power or absolute free will.
The task of scripting the interactor clearly has a psychological component. Our model of the user assumes that the self is constructed with relationship to a specific social environment, that it is mutable, and potentially multiple depending on the environment it finds itself in. Rosanne Stone tells the story of a male psychiatrist who developed an alternate on-line female personality and suggests that cyber-space makes the exploration of typically repressed parts of our one self, or of our multiple selves, a possibility . Our goal is to make a scripted space for the interactor in our application, but we are not creating a role for them to play. We do not give them information as in a role playing game about their character, motivations and goals, rather they simply enter our story space as themselves. However, that doesn't mean they can't play with what they consider their "self" to be -- and it doesn't mean that we can't construct the space with a view to stimulating that interactive self in a specific way. We believe the signifying work the interactor does during our VR fiction experience is very similar to the process described by Judith Williamson in Decoding Advertisements with respect to commercials, "...we create the meaning of a product in an advertisement; ... we take meaning in from the product; ... we are created by the advertisement; ... we create ourselves in the advertisement." 
Our model includes assumptions about how the interactor can be psychologically manipulated, which appear to be vindicated by watching interactors using the application. We assume that users' will be emotionally stimulated by a virtual actor who is simulating emotion, (more details of this in the agent section). We assume that an interactor's sense of personal space will carry over into the virtual world, and that they will experience an emotional reaction when the virtual character invades that space. We take advantage of the fact that people learn by mimicking, and also express empathy and willingness to cooperate with mutually similar body language. Dancing together is part of the language of courtship, and we use this physical communication in the dancing section of the application to delineate the changing relationship between the interactor and the Thing.
We started showing The Thing Growing as a work in process in 1998. Early observations of people in the system and feedback from them were integral parts of a reiterative programming process which was an essential part of refining our model of the user. We could not write code for every possible action an interactor might make, but observation could show us the patterns of behavior interactors' fell into. Then we adjusted and added to the narrative and to the virtual actor's functionality, to provide responses that could fold the interactors' different reactions back into the ups and downs of our emotional script. For example, the culmination of the story is to bring the interactor to a point where she can destroy the Thing if she chooses. A major problem was creating enough ambivalence at this moment. In early versions virtually everyone shot the Thing. We adjusted the program to try and make the Thing more likable, by adding a section where the interactor moves and the Thing mimics her and by substantially reworking the dialog the Thing uses in act three. After these changes were made about half the interactors elected to let the Thing live.
Figure 2. The Thing
The prime mover of The Thing Growing is the main computer controlled character, The Thing. Several research teams have focused on using intelligent agents for interactive, narrative experiences, for example the Oz Project , the Alive Project , Virtual Theater for Children . The simulation of behavior in such systems is impressive but they have limited dramatic potential . In these projects the interactor takes a very god-like role with respect to the agents, but in our case we wanted the agent to be the interactor's peer, and even to have more power than the interactor over the course of events. We did not need an agent that behaved autonomously but one whose goals and behavior furthered our narrative. Our interactor would be confronted with a computer controlled "other," simulating half of the relationship we were setting up by behaving in emotionally demanding and erratic ways. We assumed that people, who routinely anthropomorphize inanimate objects and become enraged and frustrated by them, would react emotionally to such a computer agent - in effect allowing it to script them. Our task was to make the agent believable and effective.
Graphically the Thing and its environment are very simple and non-photorealistic. We rely on three physical characteristics to make the agent believable, movement, voice, perception. The Thing's gestures are motion captured. The Thing is a collection of unconnected pyramidal models - a head, body, arms and tail - we used the CAVE's tracking sensors to collect position and orientation data that was fed to these models - the result is a strong illusion of a humanoid being with life-like gestures. We also gave it a human voice: we recorded about 500 short phrases that encompass the narrative possibilities of our story. The voice has four basic moods, sad, mad, happy and manic, and where necessary similar phrases were recorded in different moods. The motions were captured in relation to the phrases so that the Thing's body language also reflects its mood and the meaning of the phrase. In the immersive VR environment the Thing is as big as the user and is experienced in 3D. Therefore we can also play with the interactor's sense of personal space. When the Thing is mad it can get right up in the person's face. By remaining too close and dogging the interactor's footsteps it can appear intrusive and clinging, which feeds into our narrative goals.
The Thing perceives the interactor through the tracking system. The dancing trope maximizes the meaning of the information that we receive from this system and is also a crucial element in building the emotional relationship between interactor and agent. The interactor is taught dance steps by the creature, as he dances we take information from the tracking sensors and joystick, interpret them and program the Thing with a logical response in the context of the story. The Thing praises or criticizes dance steps appropriately; knows when to teach a new step and when to go over one that the interactor is doing poorly; runs after an interactor that is trying to escape the interminable dancing; remonstrates with an interactor who refuses to move. That the Thing knows what they are doing makes it easier for users to believe that it is sentient.
Although the Thing speaks to the user, it does not hear him or respond to his utterances. The simple graphics and fact the Thing was not human in form, did not encourage the expectation that it could hear. The Thing's high-handed personality also helped to cover this technical limitation. Nevertheless, many people did talk back to it and serendipitously logical conversations occurred. We recorded the following dialog between the Thing and an interactor during the shooting section. The Thing retains its intrusive and bossy profile at this point, running along just behind the interactor as he tries to eliminate the cousins, cajoling and ordering him to shoot if he is reluctant, bewailing his blood-thirstiness if he kills too fast and easily. This interactor was failing to kill the cousins.
Janet Murray mentions three computer-based character's that have operated successfully within limited contexts, Eliza, the chatterbot Julia, and Parry's neurotic woman . In each case the limitations of the character in the Turing sense are masked by its personality traits and establishing context, and interactors' tend to explain inconsistencies by forming a complex, human-mind-based model of the character's interior processes. The Thing has a very distinctive and somewhat psychotic personality which, within the narrative context, makes it respond to the user if not logically then self consistently. Its goals are simple, determined by the exigencies of the story line and how we want the interactor to feel. At the beginning of act two, it has fallen in love with the interactor and wants the interactor to love it back. It interprets the interactor's compliance with its demands as love. It demands that the interactor learns dance steps that it is teaching. It is happy and manic when the interactor tries to dance, chiding playfully if the interactor doesn't move, dances badly or gets too far away. If the interactor is persistently disobedient, the Thing becomes upset. It shouts angrily at a interactor who uses the joystick to run off. Because the story is driving towards a plot reversal - a moment when the loving Thing turns on the user and then goes off in a huff - even if the interactor dances well, the Thing's mood worsens over time.
We expect the user to respond emotionally to the mood shifts of the virtual character. In the section described above we are attempting to induce several changes in the interactor's moods - interest, delight and affection when she first encounters the Thing; irritation or anger if it becomes domineering; bewilderment if the Thing is mean even though she is trying to please it; abandonment when it runs off. The kinds of feelings stimulated and their intensity, will depend on the individual. Our observations suggest that people do respond emotionally as they try to cope with the virtual creature and that they internalize a psychological model of it. One interactor who believed she was dancing well, suggested the Thing was just trying to tease her when it criticized; another described the creature getting in "my face, making me mad;" another said the character was very manipulative .
The Thing Growing is made up of narrative fragments. Some are pre-scripted and others are assembled on the fly in response to the user. The Thing, as a coherent actor, is created by a passage through these fragments, where each fragment is an action made up of a short spoken phrase and an accompanying motion. The effectiveness of the character depends on seamless and appropriate transitions from action to action. Visually this is done by interpolating between one motion captured sequence and the next. To make the character flexible and able to respond in a timely manner, each of its actions lasts from one to five seconds, and it also is possible for the Thing to interrupt an action abruptly when necessary. Logically and conceptually, a finite state machine architecture, based on the narrative arc, is used to trigger events in the world, and the Thing's actions. The selection of the appropriate action is informed and determined by the passing of time, the user's location and interactions, and the Thing's internal logic and moods.
The application was built using XP, a VR authoring toolkit based on C++ and IRIS Performer, which was designed to facilitate the construction of art applications in the CAVE . The toolkit handles a number of activities common to VR environments, such as assembling objects into a world, collision detection, navigation, detecting events and passing messages in response to them. It provides a text file system to rapidly assemble virtual scenes: all the models, objects, their locations and behaviors are described in the text file along with messages to be passed between objects. The Thing Growing's narrative structure was created with the text files; scripted sequences were intercut with interactive episodes; the narrative flow as a whole was produced using triggers based on time, user proximity, or the completion of specific events. The text file served as production manager for the story and could easily be edited and changed. Multiple triggers were sometimes used to avoid situations where the user could get stuck at a point in the narrative unless she performed a specific action, an important consideration when building a basically linear piece . XP also provides a framework for extension; application-specific classes can be added to define behaviors for objects or characters. In this case the basic system was extended to build classes encapsulating the virtual actors' behavior and intelligence, and a simpler set of rules for the behavior of the rocks.
In March of 2000 the finished piece showed at EVL on two ImmersaDesks and in two CAVES. Over the course of two days approximately 200 people saw the application and about forty people took the role of interactor. We video-taped a variety of different run-throughs and interviewed a number of the interactors. Comments made by interactors during the application indicated that they were engaged with the Thing and following
the story. One man told the cousins to "Let my girl go," referring to the Thing. When the Thing said to him that the cousins were going to kill them he replied, "It's your fault." Near the end of her experience of the Thing, one woman said, "I want out of this relationship." At the very end of the application, if the interactor chooses not to kill the Thing, it assumes that she loves it and wants to dance with it forever. One woman realized this as the Thing gleefully said, "Come to poppa and dance our dance." She replied, "Oh no!" 
In 2001 with the support of the ICC museum in Tokyo we built a Japanese language version of The Thing Growing. We added a log to this version that has given us some harder statistics about how interactors responded. The log time-stamped events in the story, so that we had a record of how long it took interactors on average to negotiate the various scenes or story segments. Objects could also send events to the log - the gun recorded every-time it was fired, the Thing sent every change of its state. We have not analyzed the Thing's mood changes in relation to interactor activity as yet.
Figure 3. Shows interactive and non-interactive story segments over time and plots the points in the story where 25% of the interactors left the VR environment.
The Thing Growing showed at the ICC 252 times. The average time it took to complete the whole application was just under 12 minutes. The application ran in English 29 times and the rest of the time in Japanese. We know that there were 252 interactors, but we do not know how many additional people were watching, or if a different person took the interactor position in the middle of the story. In the museum setting people tended to wander in and out of the exhibits as they felt moved to, but Figure 3 shows that 75% of the time the entire application ran, 25% of the time the museum staff reset the application before it finished. We like this setting in which the interactor's choose how much time they will allow the application.
Figure 3 also shows the point in the narrative where people dropped out and differentiates between segments where the interactor could interact and navigate freely, and where the ability to navigate was drastically slowed or disabled completely. This happened when the Thing was explaining various rules to the interactor, when she was trapped by a rock, and again when she was trapped by the cousins (the longest inactive segment.) In video-games these moments of inactivity would be referred to as cut-scenes, often these scenes are little explanatory videos with a very different graphic look than the rest of the game and can be jarring and annoying. These inactive scenes served the same explanatory function in The Thing Growing, however they are a visually seamless part of the whole, and the interactor, although watching passively as events unfold, may be spoken or referred to during the scene. We do not notice any heightened drop-out rate at these points of the narrative.
Figure 4. Number of users who killed the Thing.
Figure 4, plots the number of times the interactor shoots the gun, and the number of interactors who killed the Thing, againstthe number of cousins killed. Our aim was that the interactor should feel ambivalent about the Thing: it is annoying and dominating but also a friend. So we consider it to be a good result that about half of the people who completed the story killed the Thing and half let it live. Of course we cannot infer too much about the interactor's emotions towards the computer controlled character from this raw data. However, the numbers do indicate that interactors make a distinction between the Thing and the four cousins. Those that successfully kill all or most of the cousins do not then automatically continue and kill the Thing, in fact they are more likely to let it live. We do not know if this is because they have had a longer relationship with the Thing than the cousins, or because of the Thing's attitude and remarks. If the interactor succeeds in killing all the cousins, the Thing bewails the fact that she has "gone mad with that gun," and begs her not to kill it as well. Contrariwise, if the interactor cannot or will not kill the cousins, the Thing berates her for being a "pacifist idiot," then it suggests that she might as well kill it too, since she has not protected it.
Clearly ability to navigate the virtual space, shooting accurately, relates to the user's familiarity with interactive systems. Those who shot all four cousins, fired more often and killed all four in an average of 74 seconds. Those that killed only one cousin did so in 64 seconds. We assume this ability plays into the interactor's state of mind at this point. It is a moment of empowerment and agency for the skilled interactor, who might therefore feel more magnanimous towards the Thing at the end. We note that those that killed one cousin, killed the Thing in far greater numbers - and surmise that these people are bad at shooting and reach a point when they want revenge on the Thing for its critical carping attitude. There is a period of about 15-20 seconds in which the interactor has to make up their minds to kill or not, and the interactor's pulled the trigger across whole time period, so to kill or not, was not always a snap decision.
Our general observation is that we have been successful in scripting the interactor and making her engage with the story we have designed. Interactors have specifically said that the Thing feels like a being who is present and alert to them. They say it reminds them of their spouse or a whiny child, which indicate it is effectively stirring "relationship" responses. In show situations people usually experience the application with a group watching them interact. Some people have indicated that this makes them embarrassed; worried that they are not doing the right thing and providing an enjoyable experience for all. Groups of people tend to laugh at the more abusive and outrageous criticisms leveled at the interactor by the Thing. A small number of people have been through the experience on their own, and have tended to be more deeply effected by the character's wiles.
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