From da Vinci to Monet: Understanding How Artists
Can Manipulate the Human Visual System

Put away those sunglasses, because the heat and brightness depicted in the fiery Impressionist sun is nothing but an illusion, a well-kept secret of knowing artists, from Monet to da Vinci. And, by the way, yes, Mona Lisa is hiding something underneath her smile.

While the world celebrates the 500th anniversary of Mona Lisa by Leonardo da Vinci and continues to wonder whether she is smiling or frowning, neuroscientist Margaret Livingstone of Harvard University Medical School today revealed some of the science behind human visual perception of art at the 2003 American Association for the Advancement of Science (AAAS) Annual Meeting.

What makes objects appear in certain ways, in certain situations? Livingstone used artworks as examples to explain the difference between the luminance and flat-reflecting mediums, as well as between central and peripheral vision. For example, in a recent trip to Paris, Livingstone measured the luminance of the sunrise seen in Monet's Impression: Sunrise, and found that, contrary to what we perceive, the yellow sun is actually no brighter than the dark blue sky containing it.

"The reason is that in the color version the sun is interpreted as a type of brilliance; it's so striking because there is a disconnect in our visual system between the color and luminance pathways," Livingstone said.

Luminance refers to the quality of how light something appears, independent of color. It is equivalent of what appears in black and white photos (grayscales), so in a picture, if two objects are different colors, but the same luminance, they will both appear the same shade of gray.

That is exactly what happened when Livingstone took a black and white photo of the painting: the sun disappeared altogether and melted into the same gray as the sky. To the naked eye, in Impression: Sunrise, an orange sun deceives the senses and appears to shift and flicker in the middle of a dark blue sky. The sun is really, in fact, just as bright (or dull, depending on your perspective) as its surrounding sky. Although it certainly stands out as the focal point of the piece, the sun is exactly the same brightness, or "equiluminent" as the rest of the sky.

Part of the human visual system consists of the "colorblind" mammalian visual system (the same system found in cats and dogs). The mammalian visual system can see three dimensions, and recognize things that move (this is what we use to navigate our environment). As primates, humans also have an object recognition system that sees in color, recognizes faces and evaluates the environment. We use both systems simultaneously.

Artists like Monet understood this dichotomy in our visual processes and used it empirically to give the illusion of color and space. The two parts are sometimes called the "where" and "what" system. The "where" system is the "colorblind" part that allows us to orient objects spatially, whereas the "what" system lets us recognize and evaluate them.

Livingstone also readdresses the visual perception behind the Mona Lisa's unique and mysterious smile in honor of the painting's 500th anniversary.

Livingstone's previous study of Mona Lisa appeared in Science (17 November 2000) and explained the brain's processes in how and why we interpret the Mona Lisa's smile as so elusive and mysterious.

"The elusive quality of the Mona Lisa's smile can be explained by the fact that her smile is almost entirely in low spatial frequencies, and so is seen best by your peripheral vision," according to Livingstone.

Da Vinci used the shadows from her cheekbones to accentuate the Mona Lisa's mouth, so her smile appears more pronounced when one looks at her eyes or the background; however, if you look directly at her mouth, the smile seems to fade.

"I'm demystifying the procedures that some artists have known about for years, but not debunking their art in any way," she said. "These artists — the Impressionists, Da Vinci, Chuck Close, and Robert Silvers, for example — discovered fundamental truths that scientists are only now unraveling."

15 February 2003