While art remains subjective in philosophy and practice, recent scientific studies consider the objective ways in which the human visual system perceives art. Margaret Livingstone, a Harvard Medical School neurobiology professor, has conducted research on the parallel processing of different kinds of visual information: form, color, depth and movement. Through her research, she and her colleagues have gained a developing understanding of the human mind's response to these stimuli.

Livingstone uses impressionist artwork to explain the difference between two elements that affect visual perception: luminant versus flat-reflecting mediums, and central versus peripheral vision. Differences in luminance, for example, affect an object's apparent brightness despite its color. In a study of the sunrise pictured in Monet's Impression: Sunrise, Livingstone found that, although the yellow sun and blue sky appear as distinct colors to the human visual system, the two objects are of equal luminance. Thus, in a black-and-white version of the painting, the two objects will appear the same “lightness,” blending into one object.

According to Livingstone, the duality of the human visual system accounts for this phenomenon. Two sets of signals, both of which cover the entire visual field, travel from two major classes of ganglion cells of the retina to two distinct areas, or systems, of the cortex. The more primitive visual system, known as the "Where" system, carries information about motion, depth, and spatial organization. We, as well as dogs, cats, and other mammals, navigate our environment with this colorblind system inherited from our mammalian ancestors. Only primates have a second system, called the "What" system, that signals color but not contrast. The sharpness (image clarity or resolution) of this system is three times greater than that of the Where system. Also, while the Where system signals a moving object, such as something oscillating or bouncing, the What system signals fine details, such as size and shape.

Returning to the Sunrise example, the Where system would see only the black and white version, whereas the What system would be capable of distinguishing color as well as distinct form. The What system could see the yellow sun and the blue sky as separate objects, but the Where system would not distinguish them.

Despite these differences, the What and the Where systems work together in the human visual system and, because of their separate abilities, often create illusions from the images they perceive. Livingstone said that in certain paintings, images appear to move when the What system carries colors, while the Where system lacks color information. Additionally, Livingstone found that different messages conveyed by color and contrast can make unrealistic colors of shadows appear at a natural depth.

Livingston applied this phenomenon of mixed acuity across the visual system to the notoriously elusive smile of Leonardo da Vinci's Mona Lisa.

“I filtered images of Mona Lisa's face so that you could see what the peripheral and central vision could see," Livingstone explains. "It turns out that most of the smile is in the blurry components best seen by peripheral vision. In some sense, she's coy. She smiles until you look directly at her, then she stops."

Scientists are just beginning to explore brain activity during identification of certain objects or recognition of the emotional quality of a painted scene. According to Livingstone's colleague David Hubel, “our knowledge of visual science is rudimentary,” but understanding the different properties of the Where and What systems in the brain will lead to a more thorough comprehension of the how we perceive art, nature and each other.

 

References

1. Conway, B.R. "Spatial structure of cone inputs to color cells in alert macaque primary visual cortex (V-1)." J. Neurosci. Vol. 21 (2001): 2768-2783.

2. "From da Vinci to Monet: Understanding How Artists Can Manipulate the Human Visual System." Retrieved March 20, 2003, American Association for the Advancement of Science. <http://www.aaas.org/news/releases/2003/0215art.shtml>

3. Macknik, S.L. and Livingstone, M.S. "Neuronal correlates of visibility and invisibility in the primate visual system." Nature Neurosci. Vol. 1 (1998): 144-149.

4. "Margaret S. Livingstone, Ph.D.: Professor." Retrieved March 20, 2003, Harvard Medical School Department of Neurobiology. <http://neuro.med.harvard.edu/site/faculty/livingstone.html>

5. Morton, C. "Science Illuminates Art." Retrieved March 20, 2003, Focus: News, Harvard Medical, Dental, and Public Health Schools. <http://focus.hms.harvard.edu/2002/May17_2002/neurobiology.html>