Consider the flightless fluffs of brown otherwise known as herring gull chicks. Since they're entirely dependent on their mothers for food, they're born with a powerful instinct. Whenever they see a bird beak, they frantically peck at it, begging for their favorite food: a regurgitated meal.

But this reflex can be manipulated. Expose the chicks to a fake beak—say, a wooden stick with a red dot that looks like the one on the end of an adult herring gull's beak—and they peck vigorously at that, too. Should the chicks see a wood stick with three red dots, they peck even faster. Abstracting and exaggerating the salient characteristics of a mother gull's beak strengthens the response. The phenomenon is known as the "peak-shift effect," since a peak pecking response comes from a shifted stimulus. In it lies one of the core principles of visual art.

The Truth in the Lie

In 1906, Pablo Picasso was determined to reinvent the portrait and push the boundaries of realism, and one of his early subjects was Gertrude Stein. After months in his Paris studio, carefully reworking the paint on the canvas, Picasso still wasn't satisfied. He didn't finish the painting until after a trip to Spain.

What Picasso saw there that affected him so deeply has been debated—the ancient Iberian art, the weathered faces of Spanish peasants—but his style changed forever. When he returned to Paris, he gave Stein the head of a primitive mask. The perspective was flattened and her face became a series of dramatic angles. Picasso had intentionally misrepresented various aspects of her appearance, turning the portrait into an early work of cubist caricature.

Despite the artistic license, the painting is still recognizable as Stein. Picasso took her most distinctive features—those heavy, lidded eyes and long, aquiline nose—and exaggerated them. Through careful distortion, he found a way to intensify reality. As Picasso put it, "Art is the lie that reveals the truth."

What's surprising is that such distortions often make it easier for us to decipher what we're looking at, particularly when they're executed by a master. Studies show we're able to recognize visual parodies of people—like a cartoon portrait of Richard Nixon—faster than an actual photograph. The fusiform gyrus, an area of the brain involved in facial recognition, responds more eagerly to caricatures than to real faces, since the cartoons emphasize the very features that we use to distinguish one face from another. In other words, the abstractions are like a peak-shift effect, turning the work of art or the political cartoon into a "super-stimulus."

The sly connection between the instincts of baby gulls and abstract art is the work of V.S. Ramachandran, and director of the Center for Brain and at the University of California at San Diego. Ramachandran believes the peak-shift effect explains a wide variety of art, from abstract expressionist paintings to ancient religious sculptures like a 12th-century Indian sculpture of the goddess Parvathi with exaggerated feminine features. These creations are all examples of the "deliberate hyperbole" that defines the artistic process, says Ramachandran.

In this sense, the job of an artist is to take mundane forms of reality—whether a facial expression or a bowl of fruit—and make those forms irresistible to the human brain. As Ramachandran puts it, "If herring gulls had an art gallery, they would hang a long stick with three red strips on the wall; they would worship it, pay millions of dollars for it, call it a Picasso, but not understand why they are mesmerized by it. That's all any art lover is doing when buying contemporary art: behaving exactly like those gull chicks."

Ramachandran is a in neuroaesthetics, a new scientific field that uses the tools of modern neuroscience, like brain imaging, to unravel the mysteries of art. While much of this research focuses on modern art—it's easier to study visual "hyperbole" in a Picasso than a Vermeer—the scientists believe their findings apply to all artists, even so-called realists. "A Martian who came to earth would be very curious about why all these people go to museums and look at 2D representations," Ramachandran says. "Why does art work? That's the question we're trying to answer."

Reverse-Engineering the Mind

At first glance, the premise of neuroaesthetics seems bizarre: Scientists are using artists to learn about the mind. They're looking for objective facts in the most subjective of places, using paintings and sculptures as sources of experimental data. Sometimes, it seems as if the scientists are simply trying to catch up with insights long ago "discovered" by artists.

"The artist is, in a sense, a neuroscientist, exploring the potentials and capacities of the brain, though with different tools," observes Semir Zeki, a neurobiologist at University College London and director of the Institute of Neuroesthetics. Picasso had an intuitive understanding of the mechanics of vision—which he expressed in his paintings. Likewise, the power of a Rembrandt self-portrait is not an accident: The Old Masters knew how to captivate the eye and the mind, which is why we still gaze at their canvases in museums. Scientists can learn about the mind by reverse-engineering art.

But neuroaesthetics is also trying to bring precision to the study of art. Unlike traditional approaches, which treat the artwork as a product of historical and cultural forces, neuroaesthetics looks at art through the lens of neuroscience. Neuroaesthetics researchers want to decipher the power of a Picasso or a Rembrandt, to explain the sublime in terms of the visual cortex. All the adjectives we use to describe art—vague words like "beauty" and "elegance"—should, in theory, have neural correlates. According to these scientists, there is nothing inherently mysterious about art. Its visual tricks can be decoded. Neuroaestheticians hope to reveal "the universal laws" of painting and sculpture, to find the underlying principles shared by every great work of visual art.

Blame it all on an astonishing set of experiments conducted by David Hubel and Torsten Wiesel in the 1950s. Scientists long assumed the eye was like a camera, and that our visual reality was composed of dots of light, neatly arranged in time and space. Just as a photograph is made up of a quilt of pixels, so must our eyes create a two-dimensional representation of reflected light, which scientists thought was then seamlessly transmitted to the brain.

But Hubel and Wiesel demonstrated that the brain is much stranger than that. Instead of responding to pixels, cells in the visual cortex respond to straight lines and angles of light. The neurons prefer contrast over brightness, straight edges over curves; contrasts allow us to more efficiently pick out objects. Hubel and Wiesel became the first scientists to describe what reality looks like before it has been perceived, when our mind is still creating our sense of sight.

The findings wowed the scientific community and won Hubel and Wiesel the Nobel Prize. It turns out that the raw material of vision is incomprehensibly bizarre, that all of our visual perceptions begin as a jigsaw puzzle of lines, edges, and angles. The experimental results help explain the aesthetic appeal of abstract paintings.

Giving the Mind a Break

When Hubel and Wiesel were still in diapers, Dutch artist Piet Mondrian was painting works in an attempt to show, as he put it, that every visual form is ultimately reducible to "the plurality of straight lines in rectangular opposition." Hoping to reveal the "constant truths regarding forms," Mondrian turned his paintings into minimalist arrangements of rectangles and primary colors. As Zeki, author of Splendors and Miseries of the Brain, notes, the geometrical art of painters like Mondrian and Kazimir Malevich is remarkably similar to the geometry of lines sensed by the visual cortex—as if these painters broke apart the brain and saw how seeing itself occurs.

Mondrian wasn't consciously trying to imitate the receptive fields of our brain cells. He was just trying to create a visually arresting image. But it was precisely that aesthetic impulse, that desire to captivate the eye, that led Mondrian to create such neurologically "accurate" art.

We may enjoy such paintings because the mind is naturally drawn to the kind of visual stimuli that are easier for it to interpret, suggests Ramachandran. It prefers pictures that accommodate its peculiar way of seeing. "It may not be coincidental," write Ramachandran and philosopher William Hirstein, "that what the cells find interesting is also what the organism as a whole finds interesting. And perhaps, in some circumstances, 'interesting' translates into 'pleasing.'"

In other words, the strange beauty of a Mondrian is rooted in the strange habits of visual neurons, obsessed as they are with straight lines. Abstract art seems so bizarre—so unrepresentative of anything at all—but it takes advantage of the innate properties of the brain. The geometric brushstrokes are a nod to the quirks of our visual neurons, which prefer straight lines. As Zeki notes, "If cells in the brain did not respond to this kind of stimulus, then this kind of art would not exist."

Teasing the Brain's Limits

Artists have learned to exploit other features of the visual system, too. The brain is an evolved machine, subject to all sorts of biological constraints. All of our color perception, for example, is wrangled from the responses of three different photoreceptors in the eye. Great art manages to translate these "limitations" into riveting creations.

When Mark Rothko painted an entire canvas in three shades of maroon, or Josef Albers painted his intensely colorful Homage to the Square in five slightly different shades of yellow, these abstract artists were tickling the parts of our visual cortex concerned with the processing of color. The visual cortex excels at perceiving contrasts between different colors, such as blue and yellow, but these paintings deliberately avoided sharp contrasts of color. The result is that the subtly distinct shades seem to shimmer and shift before our very eyes. We are riveted by these stimuli we can't understand.

The strategy of taking advantage of the brain's imperfections isn't confined to modern art. Consider Leonardo da Vinci's portrait of the Mona Lisa, perhaps the most famous painting in the world. The smile is notoriously enigmatic, a precise summary of an ambiguous emotion. But what is it about those slyly upturned lips that make the portrait so intriguing?

Margaret Livingstone, a neuroscientist at Harvard and author of Vision and Art, argues that da Vinci exploits the peculiar structure of the retina. The facial expression of the Mona Lisa fluctuates depending on which part of our retina we are using to look at her mouth, she explains. When we first look at the painting, our eyes are automatically drawn to her eyes, which means our peripheral vision perceives her smile. This part of the retina naturally focuses on the shadows cast by her cheekbones, which serve to exaggerate the curvature of her lips. As a result, our peripheral vision concludes that the Mona Lisa is smiling. Livingstone demonstrated this by blurring the entire painting with Adobe Photoshop to replicate what we would see if we were relying solely on peripheral vision. The end result: a much happier Mona Lisa.

But when we focus on her mouth, the retina ignores the shadows—the blurriness disappears. Instead, we fixate on the lips of the Mona Lisa, which are virtually expressionless. All of a sudden, she is no longer happy: The painting has literally changed before our eyes. This ambiguity is intriguing, Livingstone argues, as we keep staring at the painting to figure out what she's actually feeling. "I do not mean to take away the mystery of Leonardo," Livingstone told the New York Times. "It took the rest of us 500 years to figure out what he was up to."

Bare Spots and the Peekaboo Principle

While much of neuroaesthetics focuses on the most elemental aspects of vision—the sensations detected by the retina and visual cortex—the field is also trying to explain art that engages higher levels of cognition. Look, for example, at a late Cézanne painting. As Cézanne aged, his landscapes became filled by more and more naked canvas. No one had ever done this before. The painting is clearly incomplete, complained critics; how could it be art? Cézanne was unfazed. He knew his paintings were only literally blank.

The incompleteness effect is most apparent in Cézanne's watercolors of Mont Sainte-Victoire and the surrounding Provencal landscape. In these pieces, Cézanne wanted to paint only the essential elements, the necessary skeleton of form. He summarized the river in the foreground as a single swerve of blue. The groves of chestnut trees are little more than dabs of dull green, interrupted occasionally by a subtle stroke of umber. And then there is the mountain. Cézanne often condensed the foreboding mass of Mont Sainte-Victoire into a thin line of dilute paint, just a jagged silhouette. The painting is defined by its voids.

And yet when you look at the painting, the mountain is there, an implacable presence. Our mind easily invents the form that Cézanne's paint barely insinuates. Although the mountain is literally invisible—Cézanne has only implied its presence—its looming gravity anchors the painting. The brain has seamlessly filled in the empty spaces of the canvas.

According to Ramachandran, "Mont Sainte-Victoire" is pleasurable precisely because it is so spare. Cézanne's blank spots force the brain to engage in perceptual problem-solving, as it struggles to find meaning in the brushstrokes. "A puzzle picture (or one in which meaning is implied rather than explicit) may paradoxically be more alluring than one in which the message is obvious," observe Ramachandran and Hirstein. "There appears to be an element of 'peekaboo' in some types of art—thereby ensuring that the visual system 'struggles' for a solution and does not give up too easily." In other words, the search for meaning is itself rewarding: The brain likes to solve problems. We actually enjoy looking for Cézanne's missing mountain.

The "peekaboo" principle explains why subtle erotica (a supermodel shrouded in lingerie) is not only more alluring than hardcore but also has much in common with the fractured forms of cubism. Both compel the mind to assemble reality out of its shards. In both cases, the effectiveness of the pictures depends on their ability to inspire our imagination, to create a sensory problem that our brain wants to solve.

Unweaving the Rainbow

If Playboy and Picasso can be explained by the same principle, is neuroaesthetics really dealing with art? Or is it just revealing the perceptual machinery activated by any complex visual stimulus? After all, it's easy to make the mind engage in problem-solving: Just look at the haphazard lines drawn by a 3-year-old. Are they equivalent to a Cézanne watercolor?

Attempts to define art are nothing new. But Ramachandran is seeking to define it from the perspective of the brain, and he's in the midst of a brain-imaging experiment he believes will help. Subjects lie in an fMRI machine and view examples of kitsch—art objects ridiculed for their shallowness or sentimentality—as well as fine art, like the canvases that hang in museums. A Christmas lawn ornament of Santa Claus might be juxtaposed with a Michelangelo sculpture; an image from a Hallmark card might be compared to a Rembrandt painting. By measuring brain activity, Ramachandran hopes to find out why visual stimuli that seem so superficially similar can generate such different aesthetic reactions.

"The interesting thing about kitsch is that it often looks like art," explains Ramachandran. "But it's not art, because it doesn't trigger the same intensity of feeling." He suggests that while kitsch often relies on the same tricks as great art—universal principles such as the peak-shift effect and the peekaboo principle—these tricks aren't as well executed. "Anybody can learn these visual rules," he says. "But you still need talent and training in order to turn them into fine art."

There will always be something mysterious about the visceral power of a Picasso or the perplexing smile of the Mona Lisa—but that doesn't mean the mystery can't be probed. By articulating the universals of painting and sculpture, the neuroaestheticians allow us to better understand what transforms a mass of brushstrokes into a masterpiece.

And if the brain scanner can't detect any reliable differences between kitsch and art, well, sometimes the failed experiments are the most instructive. It's possible, after all, that art has no universal definition: Perhaps each work of art activates the brain in its own peculiar way. Perhaps there is no lowest common denominator of aesthetic experience that can be detected in an fMRI machine.

The poet John Keats worried that Newton's investigations into color had "unwoven the rainbow," that scientist had destroyed the beauty of light by investigating it. But beauty is not so fragile. Neuroaesthetics doesn't diminish the impact of art or puncture the power of the imagination. Instead, it leaves us with an even more profound appreciation for the intuitive of great artists. These are the geniuses who captivate us with nothing but a flat surface and some pigment.

"I've always loved art, but now I'm in awe of it," Ramachandran says. "These guys understood the mind in a very deep way. All I'm trying to do is figure out what artists figured out a long time ago."

10 Perceptual Principles of Great Art

PEAK SHIFT: We find deliberate distortions of a stimulus even more exciting than the stimulus itself—which is why cartoon caricatures grab our .

GROUPING: It feels nice when the distinct parts of a picture can be grouped into a pattern or form. The brain likes to find the signal amid the noise.

BALANCE: Successful art makes use of its entire representational space, and spreads its information across the entire canvas.

CONTRAST: Because of how the visual cortex works, it's particularly pleasing for the brain to gaze at images rich in contrast, like thick black outlines or sharp angles—or, as in the geometric art of Mondrian, both at once.

ISOLATION: Sometimes less is more. By reducing reality to its most essential features—think a Matisse that's all bright color and sharp silhouettes—artists amplify the sensory signals we normally have to search for.

PERCEPTUAL PROBLEM SOLVING: Just as we love solving crossword puzzles, we love to "solve" abstract paintings such as cubist still lifes or Cézanne landscapes.

SYMMETRY: Symmetrical things, from human faces to Roman arches, are more attractive than asymmetrical ones.

REPETITION, RHYTHM, ORDERLINESS: Beauty is inseparable from the appearance of order. Consider the garden paintings of Monet. Pictures filled with patterns, be it subtle color repetitions or formal rhythms, appear more elegant and composed.

GENERIC PERSPECTIVE: We prefer things that can be observed from multiple viewpoints, such as still lifes and pastoral landscapes, to the fragmentary perspective of a single person. They contain more information, making it easier for the brain to deduce what's going on.

METAPHOR: Metaphor encourages us to see the world in a new way: Two unrelated objects are directly compared, giving birth to a new idea. Picasso did this all the time—he portrayed the bombing of Guernica, for example, with the imagery of a bull, a horse, and a lightbulb.