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View Masters
The remarkable triumphs of masters in the artist’s studio—and even one in the batter’s box—have realigned perceptions of vision.
by Margaret S. Livingstone and Bevil R. Conway


Legendary Red Sox hitter Ted Williams refused to drive in the left lane of multi-lane highways at night, to prevent oncoming headlights from damaging his vision. Another fabled slugger, Rogers Hornsby, avoided watching movies and reading newsprint for the same reason. And, more recently, when Orlando Cabrera played shortstop for the Red Sox in the seventh game of the 2004 American League Championship series against the Yankees, a pair of goggles bulged in his back pocket during the bottom of the ninth, ready to protect his eyes from the imminent champagne celebration.

For baseball players, acuity of vision is essential, as it is for most artists. Yet a surprising number of prominent painters have had abnormal depth perception, leading us to wonder whether this anomaly might actually have proved an asset in the studio.

Part of our ability to see three-dimensionally is known as stereopsis, or binocular depth perception, and it exists because our eyes register the world from two slightly different perspectives. As Leonardo da Vinci noted centuries ago, these viewpoints produce two distinct retinal images.

Try this: hold your index fingers up, with one about ten inches from your nose and the other a dozen inches away, directly behind the first. Now look at your fingers out of one eye at a time and you will notice that the two “scenes” vary significantly; through your right eye, the finger farther away is to the right of your closer finger, while through your left eye, the far finger is to the left of the near finger. The greater the separation of your fingers, the greater the discrepancy between the two retinal images. The brain uses the discrepancies between the retinal images—in addition to other monocular depth cues, such as shading, perspective, and occlusion—to estimate distance and generate a rich perception of depth.

The stereoviewers of the Victorian era and the View-Master toys dating from the 1930s both produce vivid impressions of depth by superimposing two photographs taken from slightly variant positions. Autostereograms—developed in the 1990s under the brand name Magic Eye—are based on the same principle. The Magic Eye images feature a horizontally repeating pattern, which differs slightly with each repetition. When each eye looks at a different part of the pattern, the viewer experiences an illusion of depth and thus can see three-dimensional images appearing to pop out of two-dimensional patterns. If you have normal stereopsis and view an autostereogram with uncrossed eyes, you should perceive an image floating eerily in front of the plane of the paper. Yet some viewers will fail to detect the image, either because they can’t voluntarily uncross their eyes and still focus on something, or because their lack of stereopsis prevents them from registering depth.

Stereopsis is just one important cue for depth perception; others include perspective, shading, occlusion, haze, and relative motion. In real life our visual systems integrate all these cues seamlessly, enabling us to interact accurately with our environment. In two-dimensional works of art, such as paintings, though, only the monocular static cues can contribute to the illusion of depth; stereopsis and relative motion reveal the flatness of the canvas. So the next time you find yourself looking at a painting rich in depth cues, stand at arm’s length and try closing one eye; you may experience the illusion of entering the painting.

The ability of painters to translate the three-dimensional world into two dimensions is remarkable. Perhaps more astonishing, however, is the curious feat our visual systems perform in enabling us to perceive the visual world as three-dimensional in the first place. The brain’s only visual input comes from a pair of two-dimensional images; the retinal images are, after all, flat. Our brains then convert these flat images into a vividly three-dimensional experience by using the same cues a painter employs, combined with stereopsis and relative motion.

Optical Collusion

Just as stereopsis hampers the viewer from seeing all the depth a painter places onto a canvas, it can also hinder the artist trying to depict three-dimensional scenes on flat surfaces; art teachers often instruct students to close one eye when viewing a scene in order to flatten it. In fact, we suggest that stereoblindness might prove an asset rather than a disadvantage to an artist. A person lacking stereopsis might become more sensitive to other, monocular depth cues, such as shading, perspective, and occlusion—precisely those cues artists can render in paintings.

Only about 10 percent of the population is stereoblind. The most common cause of this condition is an imbalance during infancy in the fine motor control of the six muscles that position the eyes; this produces a misalignment, or strabismus, which can be obvious—as in cross-eyed or “walleyed” people—or so subtle only experts can detect it. When the eyes are misaligned, the brain cannot interpret the differences in the two retinal images, and stereopsis cannot develop. Sometimes the misalignment produces double vision.

In such cases the brain’s solution is to suppress the input from one eye. Eventually this input will wither, and the vision from that eye will become permanently poor—a condition called amblyopia, or “lazy eye.”

Because stereopsis requires precise alignment of the eyes, people with misaligned eyes usually have weak stereopsis or lack it altogether. Poor stereopsis can be diagnosed from a photograph if the image reveals a misalignment of the eyes. (Of course, people with normal stereopsis who can voluntarily cross their eyes can mimic a misalignment.) In fact, eye alignment in photographs is the basis for the clinical test of strabismus—the Hirschberg test—in which ophthalmologists compare the relative positions of the light reflections in the eyes. For this test to be reliable, the light source and the camera cannot be too close to the subject, and the subject must be gazing into the distance.

Although the Hirschberg test can reveal ocular misalignment—and thus poor or no stereopsis—it cannot prove that a subject possesses normal stereopsis. First, the poor eye of someone with amblyopia can wander, causing the eyes to align sometimes and misalign at other times—yet at all times the person lacks stereopsis. And second, for unknown reasons stereoblindness can occur even with normal or close-to-normal eye alignment. The best way to evaluate someone’s stereo-acuity is to test it directly, but when this is impossible—as in the case of people who have died—then photographs can allow us to assess the likelihood of poor stereopsis.

Photographs of Mickey Mantle and Roger Maris show aligned eyes—the light reflex registers in precisely the same place on both eyes. Yet a photograph of Babe Ruth reveals misaligned eyes. Ruth’s ophthalmologist reported that the Babe was amblyopic; almost blind in his left eye, he likely had poor or no stereopsis.

How could the Bambino have been such a successful slugger without stereoscopic depth perception? Two explanations are possible. One is that he was not amblyopic but rather lost some vision in one eye late in life; his ophthalmologist examined him just before he died. The second is that the Sultan of Swat used other cues to gauge his famous swing. The latter seems likely because photographs often show his eyes as misaligned, even early in his career.

So is stereopsis important in hitting a baseball? Major-league pitches travel so fast that the ball reaches homeplate in less than half a second, so the batter must decide whether—and then how—to swing at a pitch early in its trajectory, within the first tenth of a second of the ball’s leaving the pitcher’s grip. Therefore the batter’s most important cues are likely to be the pitcher’s wind-up and release—and the differences between the two eyes’ images at that distance are so small that the information carried by stereopsis is probably negligible. Hitters likely base their swings on such monocular cues as the pitcher’s arm speed and the release point.

Most major league baseball players have excellent stereopsis, probably because every bit of visual information, even hints of stereo depth, can be important in hitting a ball traveling up to a hundred miles an hour. And Babe Ruth did strike out frequently. We have even wondered whether he might have developed superior vision in his good eye simply because more visual cortex was wired up to it—and this hyperacuity might have made him better at judging the monocular cues about the ball’s trajectory. If that’s true, we will never have another Babe Ruth because these days you can’t make it to the major leagues without excellent vision in both eyes.

Sleight of Sight

It seems logical that artists, like baseball players, would find any visual defect detrimental to their work. Yet, when we looked at photographic portraits and compared the position of the light reflex in the eyes of 53 famous artists, we found a surprising proportion—28 percent—with misaligned eyes, which would suggest stereoblindness. The artists with ocular misalignment included Marc Chagall, Edward Hopper, Gustav Klimt, Jasper Johns, Frank Stella, Man Ray, Chuck Close, Thomas Moran, Willem de Kooning, Roy Lichtenstein, Alexander Calder, Robert Rauschenberg, N. C. Wyeth, Andrew Wyeth, and perhaps even Pablo Picasso.

Again, because our small survey uncovered so many talented artists with enough ocular misalignment to suggest stereoblindness, we suspect that poor depth perception might actually enhance the work of artists who want to “flatten” a three-dimensional scene onto a two-dimensional surface. That is, someone who cannot perceive depth from stereopsis may be more aware of—and therefore better able to capture—the other, monocular, cues to depth and distance, such as perspective, shading, and occlusion. Picasso, Hopper, and Wyeth are recognized masters of generating depth-filled canvases based on exactly those cues. At the same time, artists lacking stereoscopic depth perception might tend to accentuate and capitalize on the flatness and surface of a painting, as Klimt, de Kooning, and Stella did.

The Master’s Pupil

While diagnosing eye misalignment from a photographic portrait is clinically acceptable, a diagnosis on the basis of a painting ordinarily wouldn’t make sense because the artist would have captured the subject’s eyes at different times, and the gaze direction could have changed during that interval. Many of Rembrandt’s self-portraits, though, show his eyes as consistently exotropic, or turned outward—more so than one would expect simply from one eye being painted at a time, and even from the fact that he probably used a mirror and therefore looked slightly rightward when painting his right eye and slightly leftward when painting the left. We wondered whether the relative gaze angle of the eyes in his self-portraits was random, or whether the deviation from alignment was systematic, as it would have been if he were accurately portraying a feature of his physiognomy.

We examined high-resolution images of a collection of Rembrandt’s self-portraits spanning his entire career. Many of these paintings and etchings show one eye gazing directly at the viewer and the other eye deviating laterally. We quantified this pattern in self-portraits in which Rembrandt had articulated both eyes well enough to allow us to gauge the position of the pupil within the opening between the eyelids. Rembrandt portrays his eyes as exotropic in 35 of 36 self-portraits. In 23 of 24 paintings the eye on the right side of the painting looks straight ahead while the other eye deviates outward; in 12 of 12 etchings, this symmetry is reversed.

Because artists make etchings by scratching lines onto a metal plate and then reversing that plate to print an image, what you see on paper is the mirror image of what the artist drew on the plate. The fact that the eye deviating outward in his etchings tends to be opposite from the one deviating outward in his paintings suggests that Rembrandt did have a unilateral strabismus; otherwise the deviating eye should be random. Moreover, Rembrandt was not in the habit of painting his subjects with a strabismus: most of his portraits of other people show aligned eyes. The degree of ocular misalignment in Rembrandt’s self-portraits is on average ten degrees of visual angle, which would be incompatible with normal stereopsis, and was likely accompanied by poor vision in the deviated eye.

The Tell-Tale Art

Stereopsis is not a prerequisite for artistic talent. Yet the notion that stereoblindness might prove an asset for painters demonstrates the broader possibility that other aspects of brain organization considered detrimental under some conditions might offer advantages under other circumstances. For example, many talented artists, musicians, mathematicians, and engineers are dyslexic. Some observers have posited that the over-representation of dyslectics among artists and musicians represents a compensation for failure in conventional academic fields. Growing evidence suggests, however, that this pattern may be based, in part, on a positive correlation between dyslexia and extraordinary talent.

Our observation that stereoblindness is associated with artistic talent is consistent with the correlation of artistic ability with dyslexia because dyslexia is often associated with poor depth perception and problems with binocular fusion. And of the artists whose eyes we believe were misaligned, at least three—Pablo Picasso, Chuck Close, and Robert Rauschenberg—had severe difficulty learning to read.

Of course, it takes more than visual acuity—or the lack of it—to make an artist or a baseball player great. Such biological factors play out in a cultural arena, inextricably tied to history, motivation, desire, and drive. But understanding the role these factors play can heighten our enjoyment of such wonders as paint daubed on canvas, lines scratched onto metal plates, and baseballs soaring through the air, high above the Green Monster.

Margaret S. Livingstone, PhD, is a professor in the Department of Neurobiology at Harvard Medical School and Bevil R. Conway, PhD, is a junior fellow in the Harvard Society of Fellows. They are now collaborating on a study that compares the stereoacuity of art students with that of students majoring in business and other nonartistic fields. Interestingly, Conway has stereoblindness and is, perhaps not coincidentally, an artist.

This article appeared in the Spring 2005 issue of the Harvard Medical Alumni Bulletin.

Photo: Kris Snibbe/Harvard News Office