physiological disconnect that can lead to headaches and even nausea. To address this issue, Akeley has been experimenting with an approach related to light-field theory, which he says has the potential to lead to new strategies for dealing with this disparity. The idea is to replace the display with a volumetric light source so light comes directly from the simulated distance, essentially eliminating the gap between vergence distance and focus distance.

Despite the promise of using light-
field theory to make stereoscopic 3D
more comfortable for viewers, the idea
has proven to be difficult to implement
in practical applications outside the
lab. The prototype systems are mainly
used to help understand human per-
ception and the effects of forcing users
to focus at one distance while looking
at an object at a different, simulated
distance. Still, Akeley remains optimis-
tic about such research. “I’m hopeful
that this virtuous cycle of researchers
using industry-created equipment to
probe human visual mechanisms and
create useful feedback for industry will
accelerate as stereoscopic viewing be-
comes the standard,” he says.

 

understanding Depth cues Another researcher focused on depth cues in stereoscopic 3D is Martin Banks, a professor of vision science at the University of California, Berkeley. Banks has conducted widely cited studies showing how this conflict between fixed display depth and vergence distance causes visual discomfort.

“We think this is potentially a serious
problem with the distribution of ste-
reoscopic media, particularly when the
viewer’s distance is likely to be short, as
with small TV screens viewed at a short
distance,” he says. “We still have lots to
learn about how stereoscopic signals
affect how people perceive things.”
Banks is currently working on how
the presentation of information over
time affects the perception of motion
and depth cues. In stereoscopic 3D
cinema, images are presented to the
left and right eye at 72 cycles per sec-
ond. While the images are presented
in counter-phase to the two eyes, each
image is shown three times before it
is updated. The update rate is only 24
cycles per second, a coarse approxima-
tion of what it would be in the natural

figure 1a and 1b. a pair of custom-designed dynamic lenses constructed with birefringent material. The lenses are used to create a volumetric stereoscopic 3D display with four apparent image depths. Rendering illuminates pixels in inverse proportion to their distance from the simulated distance, creating a seamless sense of depth.

Far

1a

Far-Mid

1b

Mid-Near
Far
Far
Far-Mid
Mid-Near
Lens Power = 6. 29 D
Focal Demand = 1. 3 D
Lens Power = 6. 89 D
Focal Demand = 0.7 D
Far
Far-Mid
Far-Mid
Mid-Near
Lens Power = 5.09 D
Focal Demand = 2. 5 D
Mid-Near
Lens Power = 5. 69 D
Focal Demand = 1. 9 D
AUgUST2010 | VOl. 53 | NO. 8 | communicaTionS of The acm 15