Valve has begun testing new biofeedback technologies based on a player's sweat levels and eye movements, as part of the company's ongoing efforts to incorporate user emotions into gameplay. As VentureBeat reports, Mike Ambinder, Valve's resident experimental psychologist, discussed the developments at last week's NeuroGaming Conference and Expo, held in San Francisco.

According to Ambinder, Valve has already begun conducting sweat-based experiments with the game Left 4 Dead, whereby researchers correlated a player's perspiration levels with his or her level of excitement. These data were then relayed to the game software, and gameplay was adjusted accordingly. If a user remained calm during a shootout sequence, for instance, the game would unfold normally. If he became nervous, however, the pace would speed up and the player would have less time to complete a given task.

"It’s still experimental, but it worked pretty well."

The company has also developed a version of Portal 2 that users can control using only their eyes. "It’s still experimental, but it worked pretty well, and we were pleased with that," he noted.

Valve has made no secret of its desire to incorporate biometrics and emotion into its gameplay experience. The company posted a job listing for a psychologist last year, and CEO Gabe Newell stressed the importance of biofeedback during an interview with The Verge at this year's CES.

It's not clear when any of these technologies will be ready for the market, but Ambinder says that deeper physiological integration could open up new frontiers in game interaction. "The more interesting side of the equation is what you can do when you incorporate physiological signals into the gameplay itself," he said last week. "If we could start tapping into that, we could tap into a whole wealth of data."