3-D TV disparities said to cause physical, mental strain

Banks recommends two solutions to minimize eye fatigue and other symptoms: Viewers should sit very far from a 3-D TV screen as they would in a theater. The farther from the screen, the smaller the difference between the convergence and the accommodation distances, Banks said.

The second is to shoot 3-D videos so that action is located at the front of the screen, not off one side or projecting out of the screen into a crowd. By minimizing the vergence-accommodation disparity, the possibility of fatigue and other symptoms will recede in most people, according to Banks.

"The better 3-D movies, like Avatar and Pixar's 'Up' are clearly trying to minimize this conflict with the way they do the cinematography," said Banks.

Even if the theater experience is duplicated in the home, not all of the potential problems associated with 3-D TV will be resolved, according to University of Washington professor Robert Patterson. Patterson and Silzars presented their results at the 2009 Society of Information Display. According to the researchers, three other cognitive disparities can cause fatigue in addition to vergence-accommodation: binocular disparity, linear-perspective disparity and texture perspective disparity.

For instance, if a 3-D scene depicts a football player running the length of the field, depth has to be compressed into a few yards by the cinematographer to prevent too much parallax, causing viewers to see double-image ghosting. Linear perspective (geometric angles) and the texture perspective (distant objects that are less detailed) signal the brain that the distance traveled was 100 yards, thereby creating cognitive disparities.

"The reason why high-level cue conflict leads to discomfort in immersive stereo displays is that the intuitive reasoning system is attempting to make reasoned sense out of this incoming, conflicted perceptual information," Patterson and Silzars wrote.

These higher-level cues create conflicts in the brain that causes mental strain in addition to the physical eye strain of the vergence-accommodation disparity, they added, which becomes intolerable over time, resulting in a confused state of mind akin to vertigo.

"When you take away cues, you create in the brain what is called the 'doll house' effect. The scene can be very precisely constructed, but it does not look real--it looks like a doll house--because your brain is saying that its missing cues that are always present when viewing real scenes," said Silzars. "It creates a vision-to-brain conflict that can make you feel nauseous and dizzy or worse."

Worse still, according to Patterson and Silzars, is that the closer a set of cues comes to matching reality, the more discomfort viewers experience. That means the problem could get worse as cinematographers attempt to make 3-D experiences even more realistic. One solution, according to Silzars, would be to confine 3-D content to animations since the brain does not expect cartoons to contain the same realism as normal video or film.

"In Avatar for instance, the scenes that were shot with real backgrounds were less convincing than the animated scenes because the brain has lower expectations for animations," said Silzars.