Paper: Expressive AI

Expressive AI: Games and Artificial Intelligence

Michael Mateas [2003]

In this paper, the author explains that the use of AI in games should be considered an interdisciplinary practice instead of just a "purely technical", concept that he calls "expressive AI".

Michael says that game AI should create a sense of aliveness, that there is an entity living within the computer that cares about the player's actions. For example, in a first person shooter, the player can easily interpret that the enemies want to kill him while avoiding being killed. In 'The Sims', each sim responds to new objects placed in the house, altering its behavior accordingly.

An interesting example that is given in this paper is Pac-Man, where the behavior of the ghosts is critical to understanding the game because they define the primary action of the game. The ghosts have the perfect combination of behaviors to make the game enjoyable and to make them feel alive. If all four ghosts were always trailing behind you, the game would be extremely easy. If they were always setting up traps and cornering you, the game would be extremely difficult. To solve this, the creator of the game decided to give each ghost different action patterns: the red ghost chases Pacman all the time, the pink ghost is fast and moves a little bit randomly, the blue one escapes from Pacman until he approaches the ghost enough for it to start chasing him, and the orange ghost is slow and moves randomly.

The simple algorithms of the ghost AI create a rich and unpredictable behavior that can even make the player believe that sometimes, the ghosts are actually setting up traps.

With this example, the author clarifies that AI is essential when discussing the design of the game.

Based on this premise, he continues to explain the game he has been working on: Façade (a first-person interactive drama). This game incorporates a great amount of game AI in it's game design, including natural language understanding to provide a moment-by-moment interaction while developing the story's arc (complication, crisis, climax and resolution).

Finally, the author concludes that the concept of traditional AI is good but not enough for a game, whatever the specific task of the AI, the important thing to remember is that it is always performing: entertaining, frightening, and amazing the player, that's why game AI should be carefully analyzed, it is of interest not only to the AI programmer, but also to the artists and game designers involved.

Download the paper from CiteSeer.

Mateas, M. "Expressive AI: Games and Artificial Intelligence", in Proceedings of International DiGRA Conference, 2003.