The mysteries of Leonardo da Vinci’s Mona Lisa, arguably one of the most famous paintings in the world, are never-ending. Who was this woman? Is she smiling? Did she once have eyebrows? The latest theory on the 16th-century masterpiece purports that da Vinci–a prolific inventor, scientist, and artist–was even more ahead of his time than we thought. According to a pair of experimental psychologists in Germany, Mona Lisa could be the world’s first 3-D image.
The Mona Lisa that attracts huge crowds at the Louvre is part of a pair. The other Mona Lisa, produced by his studio, is housed in the Prado Museum in Madrid. University of Bamberg psychologists Claus-Christian Carbon and Vera Hesslinger argue, in a paper published last year in the journal Perception and in a forthcoming article in Leonardo, that the ever-so-slight variation in perspective between the two images creates a 3-D effect when they’re combined. (Either break out your 3-D glasses to look at the image above, or try looking at it a little cross-eyed.)
Though the researchers note that whether or not da Vinci intended this is uncertain, they write that ” the Prado version and the Louvre version, generated in Leonardo’s studio about 330 years before Wheatstone invented the stereoscope, can be combined to an image of Mona Lisa that has obvious stereoscopic qualities.”
By looking at the difference in perspective between the two paintings, like the position of Mona Lisa’s nose, they recreated the setup Leonardo and the copy’s painter (likely his student) might have used in the studio with, of all things, Playmobile minifigures. The student likely stood to the left and a little bit ahead of da Vinci as they both faced their subject. This would create a 69-millimeter difference in perspective between the two resulting paintings, approximately the distance between the typical Italian man’s eyes.
ScienceNews explains how it works:
The horizontal distance between the perspectives worked out to 69 millimeters, pretty close to the average distance between an Italian man’s eyes, or interocular distance, of 64 millimeters.
And this, it turns out, is exactly how 3-D images are made. Our brains perceive depth by combining the images from each of our eyes, which each see a scene from a slightly different perspective. (This is why covering one eye hampers depth perception.) So looking at two pictures that differ in perspective by the interocular difference can create a stereoscopic, or 3-D, image.
Was Leonardo da Vinci trying to present the world with a ground-breaking optical illusion with the Mona Lisa and her twin? Still up for debate. We’ll be awaiting the day the Louvre starts handing out red and blue 3-D glasses nonetheless.