Left 4 Dead will live or die by its artificial intelligence. But it won’t be the AI driving the undead that make or break the game, it will be the computer intelligence driving the game’s direction.

Talking to a gathering of journalists last week, Valve’s Gabe Newell talked up the company’s upcoming co-op survival horror shooter.

The game is based on four movies each of which gamers play through as survivors trying to escape an army of the undead. The game will also support an infected versus survivor mode and a split-screen cooperative mode.

In Left 4 Dead gamers live out a horror movie, but to do that the game has to be able to react to the situation, Newell said. The developers managed to do that by having the game procedurally generate character performance, pacing, lighting and music.