A blind spot that helps visualise artwork

Looking at the world through one eye at a time automatically flattens the scene,said Margaret S. Livingstone,an expert on vision and the brain at Harvard Medical School who helped carry out a study on stereo vision. That appears to give people with stereo blindness a natural advantage in translating the richly 3-D world onto a flat 2-D canvas,she said. They use monocular depth cues like motion,relative size,shadows and overlapping figures to stimulate a 3-D world.

For one experiment in the study,published in the journal Psychological Science,the researchers measured stereoscopic ability in 403 students from two art schools known for an emphasis on representational rendering and in 190 non-art majors at a university with similar tuition. All students donned red and green glasses,the kind used to view 3-D movies,and stared at a background of coloured dots that were manipulated by a computer to flicker randomly. Those with stereo vision were able to focus their eyes to see a square floating in front of or behind the computer screen,just as they might see the blade of a sword pop out of a 3-D screen. Those who were stereo blind just saw noise on the screen. The artists as a group performed more poorly than the controls.

In a second experiment,the researchers obtained portraits of 121 famous artists and 127 members of Congress from the National Gallery of Art and the photographic archives of the Smithsonian American Art Museum. The subjects eyes were cropped from the photos and shown to observers who measured eye alignment using reflected light,not knowing anyones identity.

The eyes of the established artists were more often misaligned,Livingstone said. Livingstone and her colleagues first suspected a connection between artistic talent and stereo blindness when they examined 36 self-portraits by Rembrandt and found that his right eye was noticeably deviated in 35 of them. (That finding was published in The New England Journal of Medicine in 2004.) They wondered how widespread the phenomenon might be.

An expert not involved in the new research,Susan R. Barry,a professor of neuroscience at Mount Holyoke College,said she thought the authors were on to something. Barry is the author of Fixing My Gaze,an account of how she regained stereo vision at age 50 using vision therapy. Ten per cent of people develop various degrees of stereo blindness in early childhood because of visual defects that do not allow both eyes to line up,Barry said.

Some have weak stereo that comes and goes with fatigue,while others completely lack what she calls the palpable volumes of space that come with stereo. Stereo-blind people learn to navigate by using monocular cues and never know what they are missing.

Most artists eyes are aligned,of course,so stereo blindness is not a condition for artistic success. And many people with no stereo vision show no artistic talent.