IEEE Spectrum March, 2013 - 46

"PINHOLE"
AREMAC

TRANSPARENT
FLUID

BARRIER
WITH
PINHOLE

CAMERA
DOUBLE-SIDED
MIRROR

LASER POINT
SOURCE
SPATIAL LIGHT
MODULATOR

CONDENSING
LENSES

MIRROR, MIRROR: Aligning the camera with the wearer's eye
requires an angled, double-sided mirror. Light from the scene
reflects off the front of the mirror, sending it to the side and into a
camera mounted near the wearer's nose. The images captured by
the camera are computer-processed and then sent to a special
display called an aremac ("camera" spelled backward). The
aremac shown here uses a point source of light and a spatial light
modulator to project images off the back side of the mirror and
into the wearer's eye. The use of a pinhole aremac ensures that
the images remain sharp, no matter how the eye's lens is focused.

these systems. Worse, poorly configured
products might even damage some people's
eyesight and set the movement back years.
My concern comes from direct experience.
The very first wearable computer system I
put together showed me real-time video
on a helmet-mounted display. The camera
was situated close to one eye, but it didn't
have quite the same viewpoint. The slight
misalignment seemed unimportant at the
time, but it produced some strange and
unpleasant results. And those troubling
effects persisted long after I took the gear
off. That's because my brain had adjusted
to an unnatural view, so it took a while to
readjust to normal vision.
Research dating back more than a century helps explain this. In the 1890s, the
renowned psychologist George Stratton
constructed special glasses that caused
him to see the world upside down. The remarkable thing was that after a few days,
Stratton's brain adapted to his topsy-turvy
worldview, and he no longer saw the world
upside down. You might guess that when
46

MAR 2013

NORTH AMERICAN

EYE

he took the inverting glasses off, he would
start seeing things upside down again. He
didn't. But his vision had what he called,
with Victorian charm, "a bewildering air."
Through experimentation, I've found that
the required readjustment period is, strangely,
shorter when my brain has adapted to a dramatic distortion, say, reversing things from
left to right or turning them upside down.
When the distortion is subtle-a slightly offset viewpoint, for example-it takes less time
to adapt but longer to recover.
The current prototypes of Google Glass
position the camera well to the right side of
the wearer's right eye. Were that system to
overlay live video imagery from the camera
on top of the user's view, the very same problems would surely crop up. Perhaps Google
is aware of this issue and purposely doesn't
feed live video back to the user on the display. But who knows how Google Glass will
evolve or what apps others will create for it?
They might try to display live video to
the wearer so that the device can serve as
a viewfinder for taking pictures or video,

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for example. But viewing unaligned live video through one
eye for an extended time could
very well mess up the wearer's
neural circuitry. Virtual-reality
researchers have long struggled
to eliminate effects that distort
the brain's normal processing
of visual information, and when
these effects arise in equipment
that augments or mediates the
real world, they can be that
much more disturbing. Prolonged exposure might even do
permanent damage, particularly
to youngsters, whose brains and
eye muscles are still developing.
Google Glass and several similarly configured systems now
in development suffer from another problem I learned about 30 years ago that arises
from the basic asymmetry of their designs, in
which the wearer views the display through
only one eye. These systems all contain lenses
that make the display appear to hover in
space, farther away than it really is. That's
because the human eye can't focus on something that's only a couple of centimeters away,
so an optical correction is needed. But what
Google and other companies are doing-using
fixed-focus lenses to make the display appear
farther away-is not good.
Using lenses in this way forces one eye to
remain focused at some set distance while
the focus of the other eye shifts according to
whatever the wearer is looking at, near or far.
Doing this leads to severe eyestrain, which
again can be harmful, especially to children.
I HAVE CONSTRUCTED four generations of Digital Eye Glass in the course of figuring out how
to solve this and other problems. While my
latest hardware is quite complicated, the basic
principles behind it are pretty straightforward.

ILLUSTRATION BY

Emily Cooper

http://SPECTRUM.IEEE.ORG

Table of Contents for the Digital Edition of IEEE Spectrum March, 2013