The Secret Of Mona Lisa’s Smile

For hundreds of years, art critics have mused over why the Mona Lisa‘s smile seems so mysterious. Now the Harvard neurobiologist Margaret Livingstone has a fascinating answer: It’s because Da Vinci painted her face in colors that play tricks on the eye.

Livingstone’s work has long examined the way that different cells in the visual system process different types of information, such as form, color, depth and movement. When she analyzed the Mona Lisa, she found that Da Vinci painted her smile almost completely in low spatial frequencies, and these are best picked up in your peripheral vision. The result, as she notes on her web site, is a nifty illusion:

These three images — [pictured above!] — show her face filtered to show selectively lowest (left) low (middle) and high (right) spatial frequencies.

So when you look at her eyes or the background, you see a smile like the one on the left, or in the middle, and you think she is smiling. But when you look directly at her mouth, it looks more like the panel on the right, and her smile seems to vanish. The fact that the degree of her smile varies so much with gaze angle makes her expression dynamic, and the fact that her smile vanishes when you look directly at it, makes it seem elusive.

Interesting, yes?