Embodied Agents in Games

Alex J. Champandard on June 18, 2007

rudy asks “I have read your article about embodied agents. Could you tell me a bit more about recent embodied agents in games?”

Starting with a quick definition: an agent is embodied if it is subject to biological constraints in its environment. For most games, this means actors are placed inside a body, and can only access information from the world via senses in a realistic way (e.g. using line of sight, in field of view, with potential hearing models).

Embodiment in Games

Game developers have always approached embodiment very pragmatically. Embodiment is useful for two main reasons:

  1. The player is expecting a certain level of realism from actors, and that includes them having limited information about the world.

  2. It’s too computationally expensive to provide actors with access to all the information in the world.

From that perspective, embodiment is a requirement. You can’t make good AI without it. Most games use it already. What’s changed within the last few years, however, is that embodiment is used more as a design guideline to provide a better experience for the player.

Embodiment Animat

Photo 1: The body is a key factor of human behavior.

Making Embodiment Fun

So instead of limiting the behaviors of actors using embodiment, these biological constraints are used as an extra parameter to enhance the AI decision making. For example, a player creeps up on an actor in a stealth game, being very careful not to be seen. A fully embodied actor would just keep doing his idle behavior, but an actor that is aware of the rules of embodiment can instead fake a talkie-walkie communication with another actor, toggling into suspicious mode to investigate the player’s location. It’s much more entertaining!

By having the AI aware of biological limitations, you gain the ability to use embodiment as another tool for enhancing the experience of the player. Game developers seem to be doing this increasingly for in-game actors:

  • Access any information in the world if it’s necessary to provide an entertaining experience.

  • Be aware of what information is not attainable in a biologically plausible way.

  • Have the actors fake extra steps to “acquire” this information a second time in an embodied way.

  • Take extra measures to act this out according to the player’s expectations.

So in effect, the AI agents in the game become digital actors that are always a step ahead of the player. Doing this right isn’t always straightforward, but taking into account embodiment during the design is a great start!

If you also have questions about artificial intelligence in computer games, then feel free to ask them on this page.

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