Beatrice de Gelder couldn't believe her eyes. How could "TN," a patient who had been blinded by two strokes that destroyed his visual cortex, be weaving his way so masterfully through the obstacle course that she and her colleagues had erected? Though unable to see in the literal sense of the word--he had consistently failed all the vision tests that de Gelder had given him--he somehow "saw" the office supplies scattered in front of him and avoided them.

The researchers concluded that TN possessed a rare form of "blindsight" wherein a brain-damaged person with normal eyes can't process visual information but can still subconsciously react to it. They reason that previously suppressed neural pathways located below TN's destroyed cortex may be stepping in to fill its role, albeit on a subconscious level.

Though it may not be possible to fully restore their sight, blindsight patients can recover some of their vision by exercising other regions of the brain involved in motor perception. In a separate study, researchers from the University of Rochester found that stroke patients who "honed" their blindsight through a series of eye exercises over several months were able to recoup some of their former abilities.