Virtual Petz: A Hybrid Approach to Creating Autonomous, Lifelike Dogz and Catz

Video Paper for the 1998 Autonomous Agents Conference

Andrew Stern, Adam Frank, Ben Resner

PF.Magic

501 2nd St, Suite 400

San Francisco, CA 94107

+1 415 495 0400

1. ABSTRACT

We have developed a series of lifelike computer characters called Virtual Petz. These are autonomous agents with real-time layered 3D animation and sound. Using a mouse the user moves a hand-shaped cursor to directly touch, pet, and pick up the characters, as well as use toys and objects. Virtual Petz grow up over time on the user's PC computer desktop, and strive to be the user's friends and companions. They have evolving social relationships with the user and each other. To implement these agents we have invented hybrid techniques that draw from cartoons, improvisational drama, AI and video games.

1.1 Keywords: lifelike, believability, storytelling, interactive drama

2. INTRODUCTION

Traditional digital interactive entertainment has centered around characters for years. Most entertainment products contain computer characters that represent the user, and the user puppeteers the character in its environment. In Petz products, the characters are completely autonomous, the user is represented as a hand cursor, and the pets perceive the user as just another socially intelligent autonomous character. In this way the Petz and the user are on essentially equal footing.

The virtual Petz concept has been a good way for us to explore the complicated issues in creating interactive, real-time autonomous characters. Choosing dogs and cats as our agents helps us in a few ways. People understand what pets are and essentially know how to interact with them. This is critical for producing believable characters. Pets are also a good choice because they are expected to behave in ways that we can successfully implement. They have relatively simple gestures, language and cognitive abilities. Also, animated dogs and cats have well established cartoon archetypes, upon which we base their look and behavior.

The virtual Petz experience is non-goal oriented. We allow users to explore the characters and their toys in any order they like. This freedom allows users to socialize with the Petz in their own way and at their own pace. This also encourages users to come up with their own interpretation of their pet's feelings and thoughts. Often the scope of their interpretations exceeds what we originally planned for.

3. DEVELOPING RELATIONSHIPS

The goal of the Petz is to build an intimate relationship with the user. Therefore the pet's primary motivation is to receive attention and affection. They feed off of this interaction. Without it they become lethargic, depressed, and if ignored long enough, they will run away.

The most direct way the user shows affection is through petting. Using the left mouse button users can pet, scratch and stroke. The pet immediately reacts in a variety of ways depending on what spot on its body is being petted, how fast, and how the pet feels at the time. We call this direct interaction. The fact that you can touch the character is a very effective way of building an intimate relationship and creating an illusion of life.

We've tried to make the Petz have equal footing in their relationship with the user. The toys and objects in the pet's environment have direct object-like interaction for both the user and the Petz. Petz have full access to the toy shelf, and if they really want something, they will just go and get it themselves. This helps express the unpredictability and autonomous nature of the Petz. It also requires users to share control of the environment, further strengthening the owner-pet relationship.

By picking up and using a toy, the user can initiate play. For example, throwing a ball may initiate a game of fetch, or holding a tugtoy in front of a pet may initiate a game of tug-of-war. Similarly a pet can get its own toy and bring it to the user to initiate play. This cooperative decision-making helps build the relationship.

We have created a variety of personalities - playful terriers, grumpy bulldogs, hyper Chihuahuas, finicky Siamese cats, lazy Persian cats, aggressive hunter cats, timid scaredy cats and so on. Additionally each pet has its own individual likes and dislikes, spots and body coloration, and personality quirks. Users get to play with a pet and see if they like them before deciding to adopt. Once adopted, the user gives them a name. This individual variation allows the user to develop a unique relationship with a particular pet. Every owner-pet relationship is different.

4. COMMUNICATING WITH PETZ

Petz communicate with the user in a variety of ways. Emotion can be expressed through different facial expressions (eyebrows, mouth, ears), styles of movement and body language (sad walks, happy trots, various postures, a variety of tail motions), and sounds (excited playful barks and meows, sad whines and whimpers, yelps of pain, etc.). They get fat when they eat too much and get skinny when hungry.

Petz communicate their intentions and desires through their actions. We have created a broad base of behavior for the Petz -- they can eat, sleep, play, attack, groom, hiss, explore and so on. When a pet wants attention they may start barking or meowing. If hungry they may go searching for food, hunt mice, or start begging. When they are upset or scared they may run and hide, act aggressively, or cower and shiver.

It is important to note that the only way the user can understand what the Petz are feeling is to interpret their actions and physical cues, in the same way an audience interprets an actor's performance. We do not display bar graphs or text messages describing the pet's internal variables, biorhythms or emotional state. By forcing a natural interpretation of the pet's behavior, we don't break the illusion of a relationship with something alive.

The user is given a few specific hand gestures that pets may respond to. By double-clicking in an empty space on the screen the hand cursor animates a "come here" motion and plays a whistling sound. Petz tend to stop what they're doing and come to the user's cursor. Users can pick up and wiggle food treats in different directions to train their Petz to jump, sit, rollover, somersault, and so on. Additionally, users can reward or discipline any behavior. Methods of rewarding include giving treats, feeding and petting, while discipline is achieved by squirting a pet with a water spray bottle. In this way users can modify a pet's overall behavior through positive and negative reinforcement. Additionally the personalities of each pet can change under extreme circumstances. For instance if any pet is underfed it will begin hunting and acting aggressively. If a pet is overfed it will become fat and lazy. So depending on how their user treats them, their behavior can slide along a broad spectrum of personalities.

5. RELATIONSHIPS BETWEEN PETZ

When two Petz first meet each other, typically as puppies or kittens, they cautiously investigate each other. As they wrestle and play they form relationships and attitudes towards one another. Some will become best friends, and others may become enemies. Adults tend to nurture and protect younger Petz, who follow the adults around and attempt to copy their behavior. However once adolescent, a pet will form an adult relationship with the other adults.

We have found that the interplay between a variety of personalities gives rise to many dramatic situations. Small "stories" seem to emerge as these complex agents act out their innate characters. For example, a tired old dog won't be able to go to sleep when a young playful kitten is bouncing around him. The dog may try to take a nap after distracting the kitten with a bowl of food, but the kitten's short attention span defeats this strategy. In another scenario, even a loving relationship between two buddies can be upset when the user pays more attention to one pet than the other. The jealous pet will become angry and upset and may even act aggressively to the user or the other pet. However the two Petz will eventually make up and return to their friendly relationship. None of these "stories" were pre-programmed into the system.

6. CONCLUSION

The Petz products are an experiment that turned out to be successful. The product is equally popular among girls and boys, kids and adults. We receive many letters from users describing feelings and complex behavior that we never put in the product. It seems that through combining a direct interaction interface, strong and recognizable personalities, and some fundamental social intelligence, an intimate owner-pet relationship can arise.

We've found that developing these agents requires people with interdisciplinary skills from both technology and the arts. Until recently, building lifelike artificially intelligent characters has been treated as a computer science problem. Character development, in any medium, is fundamentally an artistic process which combines elements of drama, storytelling and expressive action. Lifelike computer characters are ultimately perceived through the filter of human interpretation. No computer character can be perceived as truly alive and intelligent unless its builders always keep in mind what the final user will perceive.