The Triple Helix @ UChicago

Winter 2016

"Decoding Mona Lisa’s Smile: The Neuroscience Behind Art" by Natalie Petrossian

 

As Pablo Picasso once said: “art is a lie”, and it is the artist’s objective “to convince others of the truthfulness of his lies” in order to create a masterful piece. This concept could not be truer of Leonardo Da Vinci’s Mona Lisa. One moment the enigmatic woman seems to be smiling, and the next her smile fades away. How can a two dimensional expression on a 500-year old portrait continue to baffle us? 

Throughout history, artists have figured out ways to create illusions to convince us to buy into the “lie” of art. Since the human brain is wired to make sense of lines, colors, and patterns – even on a two-dimensional plane – artists have managed to exploit our visual shortcomings to portray depth and brightness that actually does not exist.  

The Italians have one word to explain this masterful manipulation: sfumato.[1] Meaning blurry and ambiguous, sfumato leaves much of the interpretation to one’s imagination. However, neuro-aestheticians like Dr. Margaret Livingston from Harvard Medical School use another term to explain this phenomenon: dynamism.[2] She, among other scientists, believes that Mona Lisa’s smile comes and goes not because her expression is enigmatic, but because of how our visual network is designed. 

The human eye has two distinct regions for viewing the world: the fovea and the peripheral area.[3] Centrally located in the back of the retina, the fovea has a high density of cones, which are the cells responsible for seeing colors, reading fine print, and picking out details. The peripheral area, which surrounds the fovea, is dense in rods. These photoreceptors are responsible for differentiating black and white, and seeing motion and shadows. Consequently, these two zones constitute the two major processing streams for our visual system, which Dr. Livingstone calls the “what” and “where” streams.[4] The “what” allows us to see in color and recognize details in faces and objects, while the “where” is less detail-oriented and color insensitive, allowing for faster processing as well as helping us navigate our environment. When these two types of cells are stimulated upon seeing an image, the activity is transmitted to the visual brain through the optic nerve where the stimuli are grouped together to give rise to our observed image.[5] This image is formed by specific neurons of the visual cortex in the brain.  

Both of these channels constantly encode data about an object’s size, clarity, brightness, and location within our visual fields. However, they can occasionally send mixed signals to the brain, explaining how Mona Lisa can be beaming one moment and somber the next. When the center of your gaze is focused on her eyes, your coarser peripheral vision registers her mouth.[6] And because peripheral vision is not responsible for detail, it readily picks up low-frequency shadows from Mona Lisa’s cheekbones and upper lip, which suggest the curvature of a smile. Conversely, when the viewer’s eyes are directly on her mouth, their central vision does not see the shadows, which makes the smile fade away. This dynamism in her expression creates a flickering quality that changes as you move your eyes around the painting, producing the presence or absence of a smile.[7] 

While the perception of Mona Lisa’s smile does depend on the location of your gaze, the visual cortex in the brain is hardwired to interpret visual information in specific ways, regardless of the focus on your gaze. Based on current neuroimaging studies, there have been over thirty visual sensory areas identified in the brain, each tasked with a specific function.[8] The principal visual area, V1/V2, has been shown to respond to vertical and horizontal lines, such as those created by the light-dark edges from the shadows on Mona Lisa’s face. Adjacent to V1/V2 in the visual cortex is V3, which is necessary for recognizing the shape, size, and form of an object. Below V3 lies V4, which is the visual center for color perception, and thus receives activation signals from retinal cone cells. While all of these areas work together in allowing us to see the world around us, the most important visual area in observing the flickering, dynamic quality of Mona Lisa’s smile is the area V5. Responsible for identifying motion in the visual field, V5 has direction-specific neurons that fire in response to oriented lines. Hence, lines drawn in different orientations on a painting, such as for the shading in Mona Lisa’s smile, are thought to stimulate V5 neurons and provoke an imaginative sensation of movement. 

In addition to the varying orientations in brush strokes, scientists believe that the painting’s dark background and light contrasts are also crucial in portraying the flickering quality in Mona Lisa’s smile.[9] Artists often play with luminance through their use of materials, shading, colors, and textures in order to give the illusion of three dimensions. But since the range of luminance in real life is far greater than what can be reproduced in a two-dimensional painting, artists have to place shadows and emphasize light in areas that wouldn’t be present in real life.[10] In the case of the Mona Lisa, Da Vinci revolutionized her appearance by adding dark shadows above her lip, near the bridge of her nose, and extending beyond her eyes, in addition to emphasizing her cheekbones and her upper neck. For every one of these dark contrasts, Da Vinci added extra light on her forehead, directly below her eyes, and on her chin in order to trick the eye into perceiving depth. By highlighting certain features and muting others, he not only created a very natural expression, but also managed to impart the illusion of movement in an otherwise static painting. 

Despite these advances in the neuroaesthetics of Mona Lisa’s smile, scientists and art historians have barely begun to scratch the surface of this iconic masterpiece. By attempting to understand Da Vinci’s techniques, they have uncovered more questions than answers. How did this man, who had little to no biological knowledge of the visual system, know how to manipulate our hard-wired visual sensibilities in order to achieve his greatest work of art? Why did he not apply these same techniques to his other paintings? And how is it that no other great artists of his or future times have figured out how to reproduce these techniques in their paintings? Additionally, Mona Lisa’s smile is not the only enigma of this great work of art: how is it that her eyes seem to follow the viewer at nearly every angle? Which techniques and visual quirks did Da Vinci exploit in order to accomplish this feat with paint and a flat canvas? 

While these logistical questions primarily aim to explain how a painting was created, the cultural questions that arise in the process are equally intriguing. Art historians are still searching for answers about the identity of “Mona Lisa” herself, and her mysterious relationship to Da Vinci. Considering its alternative title, “La Gioconda”, the portrait is thought to be of Lisa Gherardini, wife of a Florentine cloth merchant named Francesco del Gioconda.[11] However, even this promising theory raises additional questions: who commissioned the painting, how long did it take Da Vinci to complete it, how long did he keep it, and how did it end up in the French Royal collection instead of in the hands of the commissioner? Meanwhile, neuroscientists are simply using these works of art to better understand the brain. By attempting to explain our perception of art, they hope to uncover the mechanisms by which our brains see and interpret the world around us. By tracing these complex processes, scientists might one day discover the manner with which we experience our personal realities, and the factors that may influence our perception throughout our lives. 

References

[1] Sandra Blakeslee. "What Is It With Mona Lisa's Smile? It's You!" The New York Times, November 21, 2010. 
[2] Chakravarty, Ambar. "Mona Lisa’s Smile: A Hypothesis Based on a New Principle of Art Neuroscience." Medical Hypotheses 75, no. 1 (February 19, 2010): 69-72. Accessed January 1, 2016. 
[3] Kolb, Helga. "The Organization of the Retina and Visual System: Photoreceptors." NCBI. May 1, 2005. Accessed January 5, 2016. http://www.ncbi.nlm.nih.gov/books/NBK11522/. 
[4] Livingston, Margaret. "Neuroscience & Art: Margaret Livingstone Explains How Artists Take Advantage Of Human Visual Processing." Interview by Cara Santa Maria. Accessed January 5, 2016. http://www.huffingtonpost.com/2013/01/07/neuroscience-art-margaret-livingstone_n_2339429.html. 
[5] Kolb, Helga. "The Organization of the Retina and Visual System: Photoreceptors." NCBI. May 1, 2005. Accessed January 5, 2016. http://www.ncbi.nlm.nih.gov/books/NBK11522/. 
[6] Huang, Mengfei. "The Neuroscience of Art." Stanford Journal of Neuroscience, 2009, 24-26. Accessed January 5, 2016. http://web.stanford.edu/group/co-sign/Huang.pdf. 
[7] Chakravarty, Ambar. "Mona Lisa’s Smile: A Hypothesis Based on a New Principle of Art Neuroscience." Medical Hypotheses 75, no. 1 (February 19, 2010): 69-72. Accessed January 1, 2016. 
[8] Ibid. 
[9] Landau, Elizabeth. "What the Brain Draws From: Art and Neuroscience." CNN. September 15, 2012. Accessed January 5, 2016. http://www.cnn.com/2012/09/15/health/art-brain-mind/. 
[10] Ibid. 
[11] Scailliérez, Cécile. "Mona Lisa – Portrait of Lisa Gherardini, Wife of Francesco Del Giocondo." Louvre. Accessed January 5, 2016. http://www.louvre.fr/en/oeuvre-notices/mona-lisa-portrait-lisa-gherardini-wife-francesco-del-giocondo.

 
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