StormTroopers has posted an interview with Deus Ex programmer Scott Martin, talking to him about his work on the AI in the game. It's interesting stuff, as he talks about how the NPCs in the game will function, but also about his "process" for developing the AI for each class of character. Here's an excerpt where he discusses how the NPCs will function:

I wanted NPCs to react to the world in roughly the same way that real people do. The key to this was to make the AI recognize things based on sight and sound. The Unreal engine has a decent pathfinding system built into it (written by Epic's Steve Polge), so thankfully I didn't have to build one from scratch. But because the original Unreal was a single-player shooter, its A/V event handling didn't consist of much more than "I see the player, so I attack" and "I hear the player, so I attack." I built an audio/visual event manager into the Unreal engine so NPCs could detect things like footsteps, gunshots, smashed windows, objects hitting the ground, drawn weapons, screams, distress, etc. -- and more importantly, it could distinguish between them. I also wrote behaviors for the NPCs so they could react appropriately to these events.