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For nearly 500 years, people have been gazing at Leonardo da Vinci’s portrait of the Mona Lisa with a sense of bafflement. Artists, historians and tourists have been fascinated by Mona Lisa’s enigmatic smile. Now it seems that the secret is being uncovered. Scientists analyzed the portrait of the Mona Lisa, a woman with famously mixed emotions, hoping to unlock her smile. They applied emotion recognition software that measures a person’s mood by examining features such as the curve of the lips and the crinkles around the eyes. Curious what they discovered?

The computer software, developed by Nicu Sebe at the University of Amsterdam and researchers at the University of Illinois, examines key facial features, the journal reports. What did this computer find? Mona Lisa was 83 percent happy, 9 percent disgusted, 6 percent fearful, and 2 percent angry, according to the British weekly “New Scientist.”

Dr. Margaret Livingstone, a Harvard neuroscientist, gives a more concrete explanation to this mystery. Mona Lisa’s smile comes and goes, she says, because of how the human visual system is designed, not because the expression is ambiguous. The human eye has two distinct regions for seeing the world, Livingstone said. A central area, called the fovea, is where people see colors, read fine print, pick out details.

The peripheral area, surrounding the fovea, is where people see black and white, motion and shadows. Then people look at a face, their eyes spend most of the time focused on the other person’s eyes, Livingstone said. Thus when a person’s center of gaze is on Mona Lisa’s eyes, his less accurate peripheral vision is on her mouth. And because peripheral vision is not interested in detail, it readily picks up shadows from Mona Lisa’s cheekbones.

Christopher Tyler and Leonid Kontsevich at the Smith-Kettlewell Eye Research Institute in San Francisco manipulated a digital image of the painting by introducing random visual noise - the equivalent of the snow seen on a badly tuned TV set - and asked 12 observers how they rated the resulting expression on a four-point scale from sad to happy.

As would be expected, noise that lifted the edges of her mouth made Mona Lisa seem happier, and those that flattened her lips made her seem sadder. More surprising though, was how readily the visual noise changed people’s perception of the Mona Lisa’s expression.

Filed under: Documentary