You're slowly creeping along the darkened halls of a haunted mansion, waiting for the next zombie to come shambling around the corner. It's a familiar situation, and you're not afraid. Sensors convey this information to your game console, and suddenly an ear-piercing shriek fills the air behind you. Your heartbeat…

Let's get physical, or more specifically, let's get biometrical, as Valve's Gabe Newell, Erik Johnson and Doug Lombardi talk to PC Gamer about using players' intrinsic physical reactions to playing video games.

Let's clear this up - the creatures in Left 4 Dead are NOT after your brains. They aren't zombies, they are the infected. Valve Software though? They totally want to have a root around inside your gray cells. In piece written for Edge magazine, Valve's Gabe Newell spoke about how Left 4 Dead's AI Director analyses a…