Valve has said playtesting is the most vital part of its development process - so much so, that it hooks testers up to machines to measure their responses.
There are so many Portal jokes to be made here, I'm not even going to start.
"For us, playtesting is the most important part of the game development process," experimental psychologist and Valve's playtesting lead Mike Ambinder told Gamespot as part of a feature on testing.
"It's not something we save for the end of the development, or use as a quality assessment or balancing tool. It is the dominant factor that shapes our decisions about what to release and when to release it."
Describing thorough testing as "crucial", Ambinder said Valve begins testing "as soon as [Valve has] something playable" and "basically never stops".
Valve uses bio-feedback metrics as part of its testing process. As well as the usual pbserved play sessions and surveys, it track s eye-movement with monitor-mounted cameras; heart rate monitoring; and even skin conductivity tests, all of which are supposed to track a player's enjoyment of a game.
"We became interested in the use of biofeedback both as a playtesting methodology and as potential user input to gameplay because the idea of quantifying emotion or player sentiment seems to have utility," Ambinder says.
"On the playtesting side, recording more objective measurements of player sentiment is always desired. People sometimes have a hard time explaining how they felt about various things, and memories of feelings and events can become conflated.
"Conversely, if you have a more objective measurement of arousal or engagement, you can get a clearer picture for how people are emotionally consuming your game."
Valve is perhaps channeling a little too much of the spirit of Aperture here.
There's much of interest for would-be testers, designers, and those interested in psychology in the four-page feature; Valve and Epic are also discussed. Hit the link above to read the whole thing.