The word you are looking for is "HCI." Or, maybe that's not the word unless you work for MIT, NASA or the CIA.

Still, the term "human computer interface" is one that every videogame player should know. This technical-sounding acronym gathers into one place all the ideas about how people communicate with computers. The keypad on the ATM? HCI. Your new wireless mouse? HCI. PlayStation 2 EyeToy camera? Very cool HCI.

Originally released as a gimmick, or maybe even some sort of mass-market gag, the EyeToy combines a small, low-resolution camera that plugs into the PS2 with a set of simple games that work by showing the player on the screen and using that image to manipulate the in-game action. So, karate chops in the living room can snap the necks of flying ninjas, a well-placed poke can burst a ghost, and a lot of flailing around keeps a digital soccer ball bounding around the TV.

Gamers loved the EyeToy, and Sony rediscovered that people care deeply about HCI. Game players, both causal and hardcore, love their light guns and dance pads. People have a deep-down need to find new ways to get in touch with their machines.

Now, two new EyeToy games, "Operation Spy" and "Kinetic," continue to explore what you can do with a gaming system and camera.

If you've ever witnessed someone groaning along on a treadmill while watching "Oprah," then you understand "Kinetic." It turns out that losing weight and getting in shape is easy to do. The hard part is that it's very, very boring. Training for a triathlon turns out to be a lot easier than figuring out what to do with your brain during the endless hours of exercise it takes to reach race-worth conditioning. Richard Simmons became a rich man by distracting people from the dull reality that they were exercising.

"Kinetic" prompts the player, or exerciser, to stand in front of the TV and commence stretching, balancing and sweating. The game keeps things lively by dishing out interactive glowing balls, stacks of electronic boards to smash, and annoying cartoon personal trainers. The net result is a fairly sophisticated workout that feels more like "Pac-Man" than pumping iron.

"Operation Spy" sets its sights a bit lower. Instead of healthy living, it just funnels all that body waggling into the fantasy of working as a secret agent: jumping out of airplanes, cracking codes, and exploring maps. Or, when the heart rate gets too high, you can use the game to booby-trap your room with a camera-based motion detector that snaps a digital picture of any intruders.

Whether or not camera-based HCI becomes the wave of the future depends a lot on how many people think HAL 9000 was a cool computer. Somehow, keyboards and joypads give us a nice distance from our digital pals. But once they can see us, well, that just seems a little creepy.

For now, though, as they peer out, all we see is ourselves having fun on the living-room screen.