The concept of believability is a key design goal for many synthetic character research projects. Andrew Stern and his team at PF.Magic realized that developing lifelike, believable characters requires people with interdisciplinary skills from both technology and the arts, drawing experience from cartoons, improvisational drama, AI and video games. When people talk about wanting really intelligent characters on their desktops, what they really want is the experience of interacting with something that feels truly alive. The best way to define what is truly alive means is to study real living beings. So they ended up with creatures that are very reactive, expressive and interactive. They are also able to communicate and learn, adapt and change over time - everything you would expect from a real living creature. At the end, PF.Magic - Mindscape sold several million copies of virtual Petz around the world.

After playing for only a few days with my virtual petz, it became obvious why the game is such big success. In the newest version of the software, Petz can breed and give birth to offspring that inherit traits of their parents, they can live and play in colorful virtual environments, and you can even use a Web publisher that helps owners design and post their own Petz sites for free. But the key feature is believability. These creatures really know how to emote and express feelings. Compare this to the "Tamagotchi-style", demanding and annoying approach with no real reward for your love and affection.

There are other interesting ideas used in Petz series. The characters are completely autonomous, and the user is represented only as a hand cursor, so the pets perceive the user as just another socially intelligent autonomous character. The whole concept has been a good way to explore the complicated issues in creating interactive, real-time autonomous characters. People understand what pets are and essentially know how to interact with them. On the other hand, pets have relatively simple gestures, language and cognitive abilities which were relatively easy to implement. The goal of the game (although it can be interpreted anyway you like) is to build an intimate relationship with 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 technology behind Petz looks equally impressive as the end result. New display techniques has to be developed to create this kind of socially intelligent agents on a personal computer. Drastic optimizations on the display level are required to achieve such level of interactivity and lifelikeness. The Petz products use a network of basic 3D body animation which has a high resolution of branch points, so each character can easily change poses. As the pet's general body animation moves across this network, additional animation is layered on top. This allows the pet to look in all directions no matter what its body doing, and to layer other general and character specific postures. The look of the each breed and their ages are in fact layers, but the subsequent number of permutations is enormous and therefore passes a critical threshold in human perception, creating an illusion of life.

There are small mechanisms to control blinking and breathing and a variety of cognitive mechanisms to keep track of multiple goals, different plans to execute each goal, multiple emotions towards other characters and objects and attitudes towards other characters and objects. Constrained randomness was used to achieve a real, unpredictable, non-repetitive quality in these mechanisms. This means that there is always some randomness in each decision, which enhances the user's perception of the character. The links listed below will give you much more information on the implementation details of this and other related projects.

Announced for later this year, Petz 4 will use voice recognition technology to allow owners to talk to their Dogz and Catz and train them to respond to voice commands just like a real dog or cat. The newest version will also include a playscene editor and several new environments for Petz to explore. It will be Mindscapes second virtual life product to feature voice recognition technology. The company recently announced plans for Babyz, the worlds first virtual baby (!), which will also ship this fall with voice recognition. The Learning Companys Mindscape Entertainment Division also publishes the Creatures and Aquazone virtual life product lines.

   Site(s) of interest:

• Petz.com
  Virtual home for Dogz, Catz, Babyz, and other virtual characters with funny "*z" names.
• Artificial Emotion
  Ian Wilson maintains a great site discussing the role of emotion in developing rich, believable artificial characters. Don't miss his great collection of papers on this topic.
• Andrew Stern
  One of the creators of this line of virtual characters has a great home page with plenty of articles, papers and links to related sites.
• Babyz
  The world's first virtual babies - the newest product from Mindscape Entertainment, with its beta testing program.
• Steve Grand
  Director of Technology at CyberLife Technology Ltd., an Artificial Life company in Cambridge, UK. Includes links to some of the best papers and articles on this topic.
• Bruce M. Blumberg
  Leader of the "Synthetic Characters" group at MIT which focuses on the problem of building interactive animated characters.
• Improv
  The IMPROV Project at NYU's Media Research Lab is building technologies to produce distributed responsive virtual environments in which human-directed avatars and computer-controlled agents interact with each other in real-time, through a combination of Procedural Animation and Behavioral Scripting techniques.
• Extempo
  Extempo develops interactive characters to staff ecommerce Web sites.
• Oz Project
  The Oz Project at CMU is developing technology and art to help artists create high quality interactive drama, based in part on AI technologies. This especially means building believable agents in dramatically interesting micro-worlds.
• Hamlet on the Holodeck
  Janet H. Murray's resource page for her great new book.