NEW YORK—When ancient denizens of central France painted leaping horses on the cave walls at Lascaux, they might not have had the late Renaissance understanding of how to illustrate perspective and three dimensions. But they did, with simple black lines, give the implication of depth, showing the far pair of limbs behind the closer pair.

That seemingly simple detail reveals a world of information about the human brain, concluded various scientists and artists at a World Science Festival panel held June 3 at New York University.

In the world itself, lines do not define objects. "You cannot find objects that have lines around them," rather most people make sense of their surroundings using shapes, color, shading and subtleties of depth, explained Patrick Cavanagh, of the Vision Sciences Lab at Harvard University.

By that measure, line drawings are "not something we've evolved to be able to understand," he said, but rather, people in all cultures—and even babies and monkeys—can understand a simple line drawing. The effectiveness of simple line-based representations "wasn't invented; it was discovered by artists," he noted. Cavanagh called this discovery "a backdoor to the brain," through which scientists can learn more about how the brain makes sense of the visual world: for instance, why we all understand that a straight line that ends at a square's edge and then continues on the same plane on the other side is probably "behind" the square—and why our brain has so much trouble sorting out even simple optical illusions.

As someone who has worked in pen and ink for decades, cartoonist Jules Feiffer realizes that "what we see is often quite divorced from what is actually there," he noted. He calls the two-dimensional representations metaphors, noting that "the metaphor is often more understandable than the real thing."

And research on the perception of faces reveals that the human brain and individual neurons are tuned to extreme representations, explained Margaret Livingstone, a professor of neurobiology at Harvard Medical School. Her research has shown that people are much quicker to recognize caricatures of people than documentary photographs, showing how the brain at work prizes the representative over the more factual.

After thousands of years of simple line-based drawing—and hundreds of years of more intricate perspective-based art—many researchers and artists alike are now trying to create the experience of three dimensions on a flat page or screen. Although we experience the world as three-dimensional (thanks to the separation of our two eyes, which produce two different vantage point, and the visual cortex, which reassembles the images into a cohesive landscape), recreating that world in art and film has been challenging.

The perplexing task of transforming the two-dimensional depiction into something the brain actually perceives as three-dimensional (à la Avatar) rather than just presuming it (such as prehistoric cave paintings), captured the imagination of Christopher Tyler, who is now director of the Smith Kettlewell Brain Imaging Center. He developed algorithms for patterns of dots that seem to grow off the page into three-dimensional objects even without special glasses (giving birth to the Magic Eye books and posters of the '90s). Although the pages first appear to be a random splattering of dots, they have been carefully distributed to create what he calls "the attentional shroud" that slowly appears as a three-dimensional shape. With the assistance of classic blue-and-red 3-D glasses, he demonstrated to the audience the complexity of the visual processing system by presenting progressively more difficult images and pointing out the lag time most people experienced before seeing the object—if they could at all.

Generating a moving image in three-dimensions has provided a very different set of problems, explained Buzz Hays, senior vice president of Sony 3D Technology Center. Because humans get a sense of three dimensions by gathering information from each eye and reassembling it in the brain, shooting live action films or television in three dimensions requires two very carefully placed cameras. How far apart the cameras are and where they are angled, however, affect whether an object will appear in front of the screen, on the screen's plane or behind it—and small changes can make a big difference. If the cameras are too far apart, a scene might have depth of field but objects in it will appear very tiny. And if a director goes amiss trying to create the illusion of infinity, a viewer's eyes will briefly diverge and go walleyed—a rather painful experience that often isn't noticed on smaller production monitors, Hays noted.

The advent of three-D movies and TV, however, has left many people squinting in vain. Some 10 percent of all people do not have stereopsis (depth perception), resulting from misalignment of the eyes or focusing trouble, and has trouble seeing depth in three-dimensional movies, art and even, often, physical surroundings. But that seems to come in handy for some professions, noted Harvard's Livingstone.

About three percent of the general population has misaligned eyes—a condition that can be diagnosed just by looking at photographs of a person, as she demonstrated by showing photos of famous old baseball players with normal eyes and then a picture of the lazy-eyed Babe Ruth. Ruth's condition was a rarity in professional sports, but the prevalence of lazy eyes, crossed eyes and walleyes, however, seems to be much higher in accomplished artists, her research has shown.

By examining photographs of artists, Livingstone and her fellow researchers found that Andrew Wyeth, Edward Hopper, Marc Chagall, Jasper Johns, Frank Lloyd Wright, Robert Rauschenberg, Alexander Calder and others all had misaligned eyes. (And by studying the self-portraits and etchings of Rembrandt, she found he also seems to have had a strong lazy eye.) Why this pattern? She proposed that people who have less detailed three-dimensional vision of the world might have an easier time translating what they see onto the two-dimensional page—whether it was for a painting of a diner scene, sketch for a mobile or plan for a building.

Despite the complex and still largely mysterious workings of the visual cortex—and all of the heady research that has gone into trying to understand it—many artists ignore these ideas and others about visual perception when they're at work. "I'm not thinking when I'm doing it," Feiffer noted, as he sketched a quick pen line drawing of a dancing man for the audience. "There's no thought process."

Image of Lascaux cave painting courtesy of Wikimedia Commons; image of Marc Chagall, an artist with misaligned eyes, courtesy of Wikimedia Commons