Scientific Legend of Mona Lisa's Famous Gaze Debunked

It's called the Mona Lisa effect: that eerie feeling that the eyes of painting are following us. But, according to researchers, the peepers of Leonardo da Vinci's masterpiece don't actually do this at all.

The phenomenon happens when the subject of an image directs his or her gaze into the camera or is painted as doing so. This causes viewers to feel as if they are being watched no matter their position in relation to the image, the authors explained in their paper, published by the journal i-Perception.

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"The effect itself is undeniable and demonstrable," study co-author Sebastian Loth explained in a statement. "But with the Mona Lisa, of all paintings, we didn't get this impression."

The researchers at Bielefeld University, Germany, zoomed in on the 16th-century painting, also known as La Gioconda, from 30 percent to 70 percent, in 10 percent increments, until only her eyes and nose were visible. A total of 15 cropped images was the result. The team showed 24 participants the images three times at random on a computer. The volunteers were asked to say where they thought she was looking.

On average, the participants said the Mona Lisa was looking to their right-hand side at a 15.4-degree angle.

"Thus, it is clear that the term 'Mona Lisa Effect' is nothing but a misnomer. It illustrates the strong desire to be looked at and to be someone else's center of attention—to be relevant to someone, even if you don't know the person at all," said study co-author Gernot Horstmann from Bielefeld University's Department of Psychology, an expert in eye movement and attention.

He explained viewers may still perceive they're being looked at if the subject of the image has a "slightly sideward glance."

"This was perceived as if the portrayed person were looking at your ear and corresponds to about 5 degrees from a normal viewing distance. But as the angle increases, you would not have the impression of being looked at," Horstmann said.

Other than clearing up the inaccuracies of the commonly used phrase "Mona Lisa effect," the research has potential significance for designers in industries including gaming, the authors suggested.

"When communicating with an avatar, for example in a virtual environment, gaze improves our understanding of the avatar," Loth said. "Using their eye gaze, the virtual agent can express its attention, and it can point at objects that are or will become relevant to the task—just like a human."

Professor Christopher Tyler, a visual neuroscientist at City, University of London, U.K., who was not involved in the study, told Newsweek: "It seems very obvious that Mona Lisa is looking to your right, so it does not surprise me that the researchers were able to show that this is how people perceive it.

"What nobody seems to have explained, despite reams of text written on it, is why it works for some front-facing images and not others. My own view is that the key variable is the perceived depth, or 3D impression, of the face.

"When the face seems flat, the eyes following effect should be much less than when it has a lot of depth. I am not aware of any specific test of this hypothesis, however."

The study is the latest deep dive into how our brains process optical illusions. Last year, researchers debunked the myth that eating off a small plate tricks our brains into believing we have eaten more food than we have.

The paper, published in the International Journal of Obesity, concluded that harnessing the Delboeuf illusion, where the brain changes how it perceives an object depending on its context, does not help us feel more satiated.

This article has been updated with comment from Professor Christopher Tyler​.