Functionalmagnetic resonance imaging, here being performed on graduate student Melissa Sáenz, tracks blood flow in the brain. UCSD researchers usedthis same technique at Stanford University, in collaboration with theSalk Institute, to chart Mike May's visua processing after his sightwas restored.
MacLeod's laboratory at theuniversity is a labyrinth of filing cabinets, optical equipment, andoddly placed desks. "It's well booby-trapped," he says, steering Maytoward the first of many tests one afternoon. "But May has an uncannyability to navigate complicated arrangements." Tall and athletic, withfeatures that look boyishly handsome despite his graying black hair,May would make a good James Bond if not for a few side effects of hisblindness. Unlike the rest of his body, his eyelids haven't had alifelong workout. Perpetually half closed, they lend a stoic blanknessto his face that's relieved only by the occasional smile. He has yet tolearn facial expressions.
Sitting obligingly in front of anancient computer monitor, May watches as thick black-and-orange barsappear on the screen. MacLeod and Fine are testing his ability to seedetail. His job is to adjust the contrast with a trackball until he canjust see the bars. A click on a mouse brings up another set of bars,thinner than the last, and he plays around with those until he can seethem too. Although his right eye ought to provide 20/20 vision, inreality it's closer to 20/500. Instead of discerning the letter Eon an eye chart from 25 feet, May can see it only from two. In the pastthe blurred vision of people with restored sight was blamed on scartissue from surgery. But stem-cell surgery leaves no scars. The signalsare reaching May's brain, but they are not being interpreted very well.
More than 300 years ago, in a famous letter to the philosopherJohn Locke, the Irish thinker William Molyneux anticipated what Maysees. A blind man who is suddenly given vision, Molyneux suggested,wouldn't be able to tell the difference between a cube and a sphere.Sight is one kind of perception and touch another; they can be linkedonly through experience.
