TOM PIANTANIDA had entered another dimension, and it was not pleasant. It was 1993, and the research institute he was working for had been asked to test a pair of goggles for players of video games.
Developed by Sega, the goggles contained tiny screens that projected three-dimensional images in front of the eyes. By turning their heads, gamers could peer around a virtual world with rich depth. The 3D technology seemed destined to be the next big thing - until wearers said they felt like vomiting.
The goggles had fallen into what Piantanida calls the "barfogenic zone". The main cause? The intense 3D images were not changing fast enough to keep up with the motion of the player's heads as they looked around. That created a sensory conflict between what the eyes saw and actual movement sensed by the inner ear. Motion sickness soon followed. "It turned your stomach very quickly," recalls Piantanida. The goggles were shelved.
We may now be heading back to the barfogenic zone, but via the 3D displays of cinema screens and televisions. The visual lag that exacerbated nausea with Sega's prototype goggles may not be a problem, but barf-inducing sensory conflicts still exist with all 3D screens, so too much exposure to poorly made or overly intense 3D could soon have you reaching for the sick bag.
3D entertainment is in revival. The 3D movie boom shows no sign of abating, and now all the major electronics manufacturers are rushing out high-end 3D televisions.
The technology behind it has improved in recent years, but the basic concept has not changed. A pair of specs feeds each eye with the same image from a slightly different viewpoint, which tricks us into gauging depth (see "Seeing in 3D").
The trouble with such trickery is that it can cause an affliction called cybersickness, says Judy Barrett of the Australian Defence Science and Technology Organisation, who wrote a report on the issue in 2004. It starts with eye strain, disorientation and a headache, and can lead to nausea. The reason is a sensory conflict between the movement of your eyeballs and lenses. When your pupils are directed at, say, this page, the eyes turn slightly inwards as you bring the page closer to your face so that your gaze can converge on a word. Meanwhile, the lenses in your eyes change shape to focus the incoming light from the moving page surface onto the retina. Your brain is used to these two movements working in tandem.
Yet when a 3D object rushes towards you from the screen, something unnatural happens. Your eyeball angle changes, but your lens shape doesn't. To keep the film from blurring, the lens has to continue focusing the light from the stationary 2D plane of the screen (see diagram) .
Cybersickness tends to increase with proximity to the screen. That means 3D cinema is likely to score lower on the spew scale than 3D goggles, says Paul DiZio of Brandeis University in Waltham, Massachusetts. Television is a different matter, because viewers regularly sit closer. In a study by the Japan Broadcasting Corporation (NHK), volunteers who watched 3D TV for an hour from a distance of 1.2 metres experienced visual fatigue and discomfort - both symptoms known to lead to nausea (Displays, DOI: 10.1016/j.displa.2004.07.001). People are also likely to watch 3D TV for longer periods than a single movie, which puts the visual system under more strain, and so makes a lunch reappearance more likely.
Some TV manufacturers had evidently anticipated this: earlier this year, electronics giant Samsung published a document online with a list of warnings for 3D TV viewers about possible motion sickness, visual fatigue and disorientation. It also warned people not to watch when pregnant, elderly, sick, sleep-deprived or drunk. Samsung did not respond to New Scientist's request for further explanation.
So who will be most affected? You could be forgiven for thinking it would be the people who struggle to see 3D. Visual perception researchers reckon between 5 and 10 per cent of people cannot successfully combine the two images that make up 3D projections - but it's not these people who should be most concerned about the barfogenic zone. According to Marc Lambooij of the Eindhoven University of Technology in the Netherlands, a further 10 to 20 per cent of the population may have a problem with 3D and not be aware of it.
He and colleagues ran an experiment with 39 people who were perfectly capable of seeing 3D. He asked them to read 3D text projected on a screen 3 metres away. During the task, seven of the group experienced symptoms known to lead to nausea, including double vision and eye strain (Journal of the Society for Information Display, vol 18, p 931). These people "do not experience visual complaints in everyday life, but under more stressful circumstances, such as 3D displays, they might," says Lambooij.
However, anybody will feel queasy when exposed to certain kinds of 3D imagery. For example, the more that 3D effects zoom to and fro from the screen, the harder the eyes will have to work, says Marty Banks at the University of California, Berkeley. In a pair of studies, as yet unpublished, Banks asked volunteers to watch a 3D display on which dots would appear randomly at various depths. All 39 participants in the studies reported eye strain after 20 minutes, though it wasn't permanent.
Animated 3D tends to have the lowest chance of unintentional ill effects, says Juan Reyes of BluFocus, a consultancy to the TV industry in Toluca, California, because directors have total control over the images. Conversely, live-action 3D is full of potential problems. 3D filming requires two cameras to point at a scene from different angles, which means distracting effects can creep in, such as reflections in only one channel. What's more, visual techniques that work for directors in two dimensions can be nauseating in three, such as quickly cutting between shots at different depths, says John Merritt of the Merritt Group, a 3D entertainment consultancy. Sports coverage is particularly prone to uncomfortable effects, because the action can't be choreographed at all. In addition, spectators close to the camera may suddenly pop into a shot, appearing in the viewer's lap in a flash.
