So you want to make a game but before you complete it you want to test it out with people who haven't played it yet to see their reactions. How can you rate the test player's reaction to playing a game? Via a survey? Watching them play. For Valve, those methods are old hat. In a chat with PC Gamer, Valve's head man Gabe Newell talks about another method of play testing.

Specifically, Newell says that Valve has been experimenting with biometrics as a way to gage how a player reacts while playing a game. He says using techniques like "gaze tracking, skin galvanic response, pulse rate, and so on" can give Valve " a much more accurate indication of player state." He adds that giving that info to players can actually have benefits, saying " .. you're in a competitive situation, and you see somebody's heart rate go up, it's way more rewarding than we would have thought."

In fact Valve has bought a $50,000 gaze tracking machine to see what players are looking at on the screen. Newell says they have learned a lot with the use of the machine, saying, "A huge percentage of the stuff we draw on the screen people never even look at. And so what you want to do is use that and redesign it."