They studied Mirror's Edge and Battlefield for "body awareness" in Thief. Central and peripheral vision are in, and the AI will "look more believable" when they spot you.
Essentially the AI is as limited in awareness and detection as a human player, meaning they can't immediately spot and identify you without some investigation.
Roy was giving an interview on the "You can use it to adjust your aiming with the bow and the level of accuracy we get with it is really impressive," he said.talking about DualShock 4. He's very impressed with the new controller's greater precision when it comes to movement through analog.
He also touched on AI sensory perception: "We also model the sensors of the AI as realistically as possible. We distinguish between central vision and peripheral vision," he said.
"This also is put forward by the way we use head tracking to make the AI look more believable when they react to something and look at the player. And there is also the sound that will attract and alert AI. Players can control the sound they emit by controlling their movement speed, but it's also influenced by the surface they walk on."
Thief releases on PC, Xbox 360, PS3, Xbox One and PS4 February 25th in the US, 28th in EU.