While some may not notice any big difference if they close one eye, we stereophiles are sharply aware of a great change, as our world suddenly loses its spaciousness and depth and becomes as flat as a playing card. Perhaps our stereoscopy is more acute; perhaps we live, subjectively, in a deeper world; or perhaps we are simply more aware of it, as others may be more attuned to color or shape. We want to understand how stereoscopy works. The problem is not a trivial one, for if one can understand stereoscopy, one can understand not only a simple and brilliant visual stratagem but something of the nature of visual awareness, and of consciousness itself. — Oliver Sacks, The Mind’s Eye
A faint breeze on your nose. A slight, blurred object in your vision. You cross your eyes, straining to focus, and see it—a gnat—in your personal space. You quickly swat it away before it flies into your nostril. Did you ever wonder, “How could I tell it was so close to me?”
We innately perceive depth with our binocular system of two eyes, spaced slightly apart so as to have two slightly different views of the world. Our brain assembles its sense of depth (stereopsis) primarily from the differences between the 2D images each eye presents. That sense informs how we understand our surroundings—how close a fly is to our nose or the how deep the rocky face of a mountain is to a pilot. It influences how and where we see ourselves in the world.
Ironically (or perhaps prophetically), perfect vision doesn’t necessarily equate with better perspective. Rembrandt van Rijn, regarded by many as one of the greatest European painters, was probably stereoblind, which is to say that he had a vision disorder that would have perceived his world as flatter than most. Neuroscientists Margaret Livingstone and Bevil Conway noticed that Rembrandt, prolific in self-portraiture, often painted his eyes slightly off. One eye usually appears to look directly at the viewer while the other looks to the side. When normal eyes focus on an object, they automatically point at it. For a person with stereoblindness, that doesn’t happen as easily. Many suffer from cross- or lazy-eyes. With such conditions, the brain suppresses the input from the weak eye and relies on the strong eye.
Livingstone and Conway measured Rembrandt’s gaze in 36 paintings and found that he most likely struggled to see depth. If Rembrandt had stereoblindness, he belonged to an exclusive club: About three percent of people globally experience it. But each of us generally has a dominant eye. Here’s how to find yours:
Look at something, across the room—an object small enough that you can make a triangle around, palms outward, thumbs forming the base.
Close each eye individually. From one eye, inside the triangle, you will see your object, and from the other eye, inside the triangle, you will see something else.
Now focus on your chosen object and cover it with your thumb, both eyes open. You can’t do it, right?
Change your focus between the object and your thumb. You’ll find yourself seeing double.
That is convergence. Other objects in the depth field are doubled due to binocular disparity, much in the same way they fall out of focus. Eyes focus automatically, and our brain converges the images. We don’t even have to think about it.
People with stereoblindness can use size, context, shadows, movement, and other signals to perceive depth. For centuries, painters like Rembrandt have used those same signals to communicating depth in their two-dimensional art. And for the last century, it’s how filmmakers have been depicting moving images. It seems, then, that beauty doesn’t solely belong to those with “perfect” vision, and that a slight imperfection could have aided Rembrandt in becoming one of the most famous painters of all time.
Livingstone and Conway extended their study beyond Rembrandt and found that art students tend to have poorer stereo vision than non-art majors. Stereoblindness was worst among the more established artists.
“One possible explanation for the correlation between stereopsis and artistic talent is that poor binocular vision interferes with reading skills and therefore encourages the pursuit of nonacademic activities, such as art,” the researchers wrote in Psychological Science. “However, poor stereopsis might also be an asset to the artist because it makes monocular depth cues more salient. … At a minimum, if poor stereopsis does not contribute to artistic talent, it certainly does not detract from it.”
Not a Toy
Rembrandt may have known that the images seen by each eye were slightly different; Leonardo da Vinci observed as much, for example. But it wasn’t until the 1830s that Charles Wheatstone studied the brain’s ability to fuse these two disparate images together to give cues about the third dimension.
Within months of his influential 1838 paper on binocular vision, Wheatstone invented the stereoscope. Wheatstone’s device was like the View-Masters children have loved since the 1950s, but it was no more a toy or a gimmick than the photograph, which arrived at the same time. Where we remember View-Master discs, stereoscopes used rectangular cards with twin images to create a 3D scene. When one peered into the viewer, rudimentary lenses reduced the size of the card so close to the face, allowing the eyes to break the relationship between focus and convergence.
“The first effect of looking at a good photograph through the stereoscope is a surprise such as no painting ever produced,” Oliver Wendell Holmes Sr. raved about the stereoscope in an 1859 Atlantic article: “The mind feels its way into the very depths of the picture. The scraggy branches of a tree in the foreground run out at us as if they would scratch our eyes out. The elbow of a figure stands forth so as to make us almost uncomfortable. Then there is such a frightful amount of detail, that we have the same sense of infinite complexity which Nature gives us.”
Early use was as broad as the photograph. William Henry Jackson took stereoscopic photos as he documented what would become Yellowstone National Park for the railroads and the federal government in 1871. Professional and amateur photographers captured the battles and aftermath of the Civil War. Families sought three-dimensional portraiture of loved ones. And it wasn’t long before inventors began doggedly pursuing the creation of 3D films. The pioneering Lumière brothers devised a 3D system and reshot their famous Arrival of a Train at La Ciotat (1896). Though accounts of the date of production differ, the men exhibited the film in 1935.
Through Rose-Colored Glasses
Stereoscopy improved in jolts as technology advanced, but various problems have always presented in mimicking human vision. While acquisition of left- and right-eye views was fairly straightforward, movie exhibition proved to be a challenge. Exhibitions in the early 20th century relied primarily on anaglyph projection, which used filtered glasses of different colors (most commonly red and blue). Two strips of film (black and white) were colored red and blue respectively and projected simultaneously on one screen. Paper glasses were cheap and easy to make and the simple color filters did not muddy the black and white images too much. But in full-color film, the technology is imperfect.
Polarized 3D systems invented in the 1950s (Kiss Me, Kate; Dial M for Murder) have a way of filtering light that led to unprecedented color and clarity, but they require a different kind of glasses. But early color 3D systems required two projectors and the light transmission could cause viewers to see both left and right images in both eyes (called “ghosting”). It makes watching a long film exhausting. Eventually, an adapter squeezed both left and right images onto a single film strip, reducing the strain for many viewers.
Polarized 3D had a resurgence in the 1980s when IMAX brought mathematical precision in stereoscopic production to its giant screens. Theme parks also took interest in producing 3D films, with Disney’s Captain EO (1986) and Universal’s T2 3-D: Battle Across Time (1996). Avatar (2009) led another 3D film craze of the late 2000s as it became as easy to render digital effects and backgrounds in three dimensions as in two.
Can 3D Videos Cure?
For anyone with stereo blindness, however, all these films will appear just as flat as a typical film. The films do not lack the magic of the art form, but they lack the depth the brain grasps through two properly functioning eyes.
Ironically, stereoscopy could actually help those with stereoblindness gain the perception of depth. Current therapies for stereoblindness involve patching the strong eye. Virtual reality videogames offer a more enjoyable—and perhaps more effective—solution. The design of virtual reality systems like Google Cardboard and Oculus Rift harkens back to the early days of stereoscopy and the Wheatstone stereoscope—presenting images directly to each eye. Google Cardboard uses a smartphone much like the stereo cards of old. But now the images are alive with video. Meanwhile, smartphones and the Rift have accelerometers that detect user movement, accounting for head tilt and making the stereo images agree with the body’s awareness of its own position.
Eric Gillet saw in 3D for the first time during a trial at the University of California at Berkeley. Gizmodo reports, “Gillet was walking through the towering redwood, pine, and eucalyptus trees that provide the unique atmosphere of the campus, on his way to meet a friend for lunch. Glancing up at an oak tree, he realized something had changed. ‘Suddenly I could see the space between its branches and the sky. They were no longer flat and stuck together. It was just a few seconds, but it was very powerful.’ ” Though his vision still isn’t perfect, his improvement continued.
Could virtual reality systems someday lead to eliminating stereo blindness for most? Maybe. Some experts say the treatment won’t work for many stereoblind people. But imagine if Rembrandt lived today and tried to correct his vision. Would we want him to?
It is wondrous to understand the miracle of human eyes, through which we see the world, and a brain, which translates two images received from each eye into the depth important for navigating the world. Despite humanity’s massive technological prowess, our attempts to simulate human vision still pale in comparison to real thing.
We communicate our truths and experience with art. Stereography enables us to perceive the depth seen by the eyes of another, but Rembrandt proved that perhaps never quite seeing something the same way as someone else is part of the beauty.
Mason Morris is a videographer in Eugene, Oregon. Rebecca Randall is The Behemoth’s science editor.
The Behemoth is a small magazine about a big God and his big world. From the editors of Christianity Today, these articles aim to help people behold the glory of God all around them, in the worlds of science, history, theology, medicine, sociology, Bible, and personal narrative.
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- Editor’s Note
Issue 51: Our Special 3D Issue. /
- If Jesus Came to Flatland
How to think about dimensions beyond our own. /
- An Object Can Be Worth 10,000 Photos
Why I pursued 3D printing for Dallas Theological Seminary. /
- The Old West in 3D
Photos that shaped a nation’s view of its expanding horizon.
- Wonder on the Web
Issue 51: Links to amazing stuff in 3D.
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