Straight black hair, flirtatious gaze, hands crossed in anticipation. Thewoman that is constantly staring at you. Is she the woman every mandreams to have?

Only if that man is into going out with a 500 year-old lady who goes by the name Mona Lisa. Yes, Mona Lisa, the famous Renaissance painting by Leonardo Da Vinci, painted between 1503 and 1505.

But is it her looks or her smile that brought the fame? Whichever it is, one thing is certain: something mysterious is going on with Mona Lisa and her famous smile.

On Mona Lisa’s 500 th birthday, we found out at last what it is. We know why her smile appears and disappears while our eyes concentrate on different parts of the painting.

Dr. Margaret S. Livingstone, Professor of Neurobiology at the Harvard Medical School explains the phenomenon like this: when you first look at the portrait, you see a broad flirtatious smile. On closer inspection of the mouth, however, the broad smile just disappears.

Livingstone’s curiosity about Mona Lisa’s mystery smile arose while she was preparing her book called Vision and Art: the Biology of Seeing. One day while riding her bike home, an idea popped into her mind. “I just realized the answer and how to test it,” she said. “The degree of her smile varies depending on where you are looking.” In other words, the answer to the mystery rests lies, not in the eyes of Mona Lisa, but in how our own eyes work.

In their book, Psychology, Lester Sdorow and Cheryl Rickabaugh explain that our eyes contain two types of cells, the cones and the rods. The rods are important to night vision and help us see shadows and motion. The cones, on the other hand, are excellent at picking up colors, reading fine print and picking out details. “The rods are more prevalent in the periphery of the retina and the cones are more prevalent in the center”, the authors explain.

Basically, we see clearly only what we are directly looking at. All peripheral things are a big blur. Livingstone says that because Mona’s smile is blurry, it is more visible when we are not directly looking at her mouth. In other words, when we see her mouth through our peripheral vision.

Look at her eyes. Can you see that broad smile of hers? Now look at her mouth. Our cones in the center of our eyes don’t properly process the shadows and we can’t see her broad smile anymore. Look again at her eyes and, voila, she’s smiling broadly again.

But why we see like this in the first place? “It’s a matter of economy of processing. We don’t have enough neurons to see the whole visual field at such a high resolution,” Livingstone explains. “It would take too much processing power”.

You might expect her answer to the 500-year mystery of the smile to raise eyebrows, but when Livingstone presented the theory at the American Association for the Advancement of Science’s (AAAS) annual meeting in Denver, Colorado, a year ago, it received a positive response. “People like the idea” she said. “Most people said it was very clear.”

And when she publicized her theory she says that she personally received no negative comments or responses.

Livingstone believes that Da Vinci did not know of the appear-disappear effect when he was painting Mona Lisa 500 years ago. “He wrote about other ‘tricks’ he used in his artwork, but nothing about Mona’s smile,” she said. Livingstone does not believe that Da Vinci used this technique, even unconsciously, in any of his other paintings.

So do we have to fly all the way to the Louvre museum in Paris to see Mona’s mysterious smile? “The same effect can be seen in any reasonably good reproduction. Even in some bad ones,” Livinstone reassured me. With one caveat: “The one in the Louvre is uncannily lifelike in the degree to which her expression changes”.

So, you can just buy a copy of Mona Lisa. Dr. Livingstone has not seen her up close either.

REFERENCES

All quotes from Dr. Livingstone are taken from the interview with her via e-mail.

Livingstone, Dr. Margaret S. Personal Interview. 21 May 2004.

Sdorow, Lester M. and Cheryl A. Rickabaugh “Psychology: Fifth Edition” New York: McGraw-Hill Higher Education, 2002.

“Mona Lisa’s Smile Secrets Revealed” BBC News UK Edition Online 18 Feb. 2004. 15 Mar. 2004. < http://news.bbc.co.uk>

Kleiner, Fred S., Christin J. Mamiya and Richard G. Tansey “Art through the ages” 11 th ed. Fort Worth: Harcourt College Publishers, 2001.