Mobilizedtv

Mark Schubin on Mobile 3D: Muscles Matter

Mark Schubin is a multiple Emmy-Award-winning SMPTE Fellow who has worked professionally in television since 1967.

Some people get seasick, and the result of a non-hiker’s first walk up a hill is likely to be sore muscles. What does that have to do with Mobilized TV?  Fans of 3-D better hope it’s a lot.

Clearly, technology issues are associated with 3D viewing on a mobile device.  Instead of just one image, two are needed–one for each eye.  The

display needs to prevent the wrong eye from seeing its partner’s image.  Are glasses needed?  That’s a bummer.

Engineers have been tackling those issues and have already come so far that glasses-free 3-D was demonstrated on a tiny mobile-phone screen at the April 2009 National Association of Broadcasters convention.  But that’s technology.  Then there is psychophysics.

Unrelated to psychics or psychobabble, psychophysics is the science of psychological responses to physical stimuli.  An example of a physical stimulus is the picture on a mobile-phone screen.  An example of a psychological response is liking the picture enough to want to pay for it.

Psychophysics has already played a role in mobile TV.  Handheld at a typical viewing distance, a mobile-phone screen creates a smaller retinal image than do other video displays.  So, when Fox delivered a mobile-TV version of the popular series 24, each “mobisode” had a very short duration (initially one minute, later increased to three), with louder sound effects, more close-ups, bigger bullet holes, and more blood.

Mobile 3-D will likely face the same issues of a small retinal image and a tired device-holding arm.  But there are two other major considerations. One is called the “vergence-accommodation disparity” or sometimes the convergence-accommodation disparity.  Convergence is the aiming of the eyes at a particular point.  In 3-D, that point can be on the plane of the screen, behind it, or in front of it. Accommodation is the focusing of the eyes’ lenses on a particular point.  There are some 3-D images, involving holography, moving mirrors, or volumetric displays, in which accommodation can be tied to convergence.  For traditional stereoscopic 3-D, however, accommodation is always at the plane of the screen.  The single accommodation distance and the varying convergence distances of stereoscopic 3-D create a perceptual disparity.  The muscles moving the eyes report one depth to the brain; those focusing the lenses report another.

At the 2009 SMPTE Digital Cinema Summit, University of California Professor Martin S. Banks described experiments he had performed concerning that perceptual disagreement.  “This is really the first evidence that a vergence-accommodation conflict can cause fatigue and discomfort.”

It’s not an entirely new discovery.  Writing in The American Journal of Physiological Optics, Leonard Troland said, “The basis for eye strain is undoubtedly to be found not in any direct effect of the stimulus upon the eye but in a demand for overexertion of the ocular musculature.”  “Studies… indicate that one of the most common causes of eye strain consists in an unconscious attempt on the part of the observer to modify the normal coordination of the ocular reflexes of accommodation and convergence.”  That was in July 1926.

DreamWorks head (and 3-D fan) Jeffrey Katzenberg, speaking at the International Broadcasting Convention in September 2008, said the last thing 3-D should do is “make your audience hurl.”  But, as seasickness shows, perceptual conflict can, indeed, lead to vomiting.

Banks suggested to the Digital Cinema Summit that the conflict might be reduced by increasing a viewer’s “zone of comfort.”  For any given viewing distance, there is a range of convergence distances that might be acceptable.  A cinema viewer 50 feet from a screen, for example, might not mind convergence distances that vary from, say, 40 feet to 60 feet. A mobile-TV viewer’s eyes, however, might be just 18 inches from a screen.  If the scene shows an image requiring convergence 30 feet away, that’s unlikely to fall into anyone’s zone of comfort.  Or is it?

In 1895, the Lumiere brothers presented the first cinema audience with motion pictures of a train arriving at a station.  They were silent, black-&-white, jittery, and showed the train moving at an angle, but that was enough, according to a contemporary report, to cause an audience member to jump up in fear until the last car had passed through the frame.

In 1919, Thomas Edison staged a “tone test” at a concert hall, defying members of the audience to tell the difference between a live opera singer and a phonograph recording of her voice.  A reporter for the Pittsburgh Post wrote that he couldn’t.

Today, we might laugh at the idea that the Lumiere and Edison audiences couldn’t tell playback from reality, but that’s only because we have been taught the difference.  Perception is learned.

Consider seasickness.  First-time sailors tend to suffer from it, but those who’ve spent long periods on boats get over it.  Muscles, too, can be trained.  First-time hill walkers get sore muscles; long-time hikers don’t.

So it’s possible that viewer training will get around the convergence-accommodation 3-D problem even on mobile screens.  A short 3-D piece, followed by a recovery period, and then another stereoscopic sequence might train eye muscles in a manner similar to that by which a marathon starts with short sprints.

Unfortunately, eye-fatigue and nausea are only one of the perceptual issues associated with 3-D mobile TV.  There’s also, for example, the infinity-interpupillary problem.  It’s best not to overexert what lies between the ears.  So that other problem will be discussed in Part II.  Which other problem?  The one that experienced 3-D sailor might call “i-i.”

Tags: DreamWorks, Jeffrey Katzenberg, mobile 3D, mobile device, mobile phone screen, mobile TV, psychophysics

This entry was posted on Wednesday, June 17th, 2009 at 9:00 am and is filed under Guest Column, Home Feature.