You're playing your favorite shooter or sneaker game. Stealthily, you inch along a narrow and foreboding corridor. It's dark - so dark that it's a good thing you have your flashlight handy. The surround sound coming from your speaker set supplies the fittingly sinister soundscape for the gloomy scene, and you are completely immersed in the game's world. You go around the next corner and a lurking monster lunges out and attacks, hurling globes of fire at you. The screen shakes and turns dark red.

This kind of experience may make you jump, frightening you a little - or even a lot, as the case may be - but in the end, it still doesn't feel real. Something is missing to make the experience more believable, more true to real life: three-dimensional, spatial perception.

On the computer, we look at a 2D flat screen that, by its very nature, only displays an equally flat rendering of a scene. The effect is that of being a spectator, like looking at a photograph. You get the impression of what it would be like, but you're not really there.

The reason is that all the polygons that your fast 3D graphics card throws at the monitor will still end up on a 2D display - just like a snapshot or a portrait. Reality is different, obviously - it is three-dimensional. Case in point: watching a video of a roller coaster ride will never bring on the same sense of vertigo as the real deal - it's just not the same. Just as you won't get woozy from looking at snapshot taken from the roof of a skyscraper. It is stereoscopic vision, or depth perception, that helps produce the giddiness - or vertigo, depending on the situation.

What makes a roller coaster ride so exciting? Aside from the centrifugal force and the high speed, it is the visual impression, the depth, that makes it such a (pleasantly) terrifying experience.

Although much effort has been expended over the years to enable real 3D presentation on the computer, 3D displays were never able to establish themselves on the home PC. Towards the end of the 1990s, 3D shutter glasses marked one of the early attempts to bring real 3D perception to the gaming community, but quickly disappeared from the market place with the arrival of modern TFT flat panel displays. The technology simply put too great a strain on the CRT monitors, and extended sessions using 3D glasses tended to cause headaches and dry eyes - not the most pleasant experience. Nonetheless the effect was quite stunning; it is nothing short of fascinating when objects suddenly seem to come towards you, protruding from the monitor.

Since then, 3D stereo technology has continued to move forward. In this article, we take a closer look at the technology behind current 3D stereo displays, and present possible applications.