Sightless, but Not Walking Blindly?

"There could be training for these residual skills," de Gelder said. "One would hope it could have implications for dormant abilities in the brain that could be capitalized on, such as the ability to move around the house."

Other people previously have been shown to have "blind sight" -- the ability to sense the movement and location of objects, and even identify emotions on others' faces. This ability surfaces when parts of the brain involved in interpreting vision are damaged but the eyes and optic nerves survive, allowing unaffected areas of the brain to still get input.

But the man in the hallway, a middle-aged physician identified only as TN, marks the first time any patient with such extensive brain damage has been documented to have this ability. TN's strokes had destroyed the visual cortex, the part of the brain primarily responsible for processing vision, on both sides of his brain.

"This was a radical case with complete loss of conscious vision," de Gelder said.

After confirming the extent of TN's brain damage with a series of scans and other tests in the Netherlands, the researchers concocted and then videotaped the hallway experiment.

Someone walked behind him in case he stumbled, but he never needed help. Because TN made no sounds while walking down the hallway, the researchers were confident he was not unconsciously using his ears for guidance, and they saw no signs he was subtly feeling his way past obstacles with his feet.

"If you look at how his feet move, he doesn't do it by touching, and there's no sound location," de Gelder said.

While the researchers were thrilled, TN was baffled by their excitement.
"He was surprised," de Gelder said. "It didn't mean much to him. He didn't see what he was able to achieve."

De Gelder said he must be using more-primitive parts of the brain: parts that prompt us to, for example, move away from a door that suddenly flies open, parts that enable animals with poor vision to navigate adroitly.

"They contribute more than we think they do for us to function in the world," she said.
Held agreed.

"There is a form of relatively crude vision that survives the destruction of striate cortex," he said, using the scientific term for the primary visual cortex. "We really don't have an adequate understanding of what those other visual pathways are doing, where they are and how they are functioning."

Other researchers noted that there could be alternative explanations for the findings.
There might have been some activity remaining in TN's visual cortex that the brain scans missed. Or the person behind him may have inadvertently given him subtle cues.

"I worry a little bit that an observer followed the patient," said Jon Kaas, a Vanderbilt University psychologist. "But ... I believe these findings."

The case provides more evidence that human actions may be guided by unconscious brain activity, he said.

"We have this impression that everything is in our conscious repertoire and we are operating accordingly," Kaas said. "But that might not be the case, and a lot of our behavior may be at an unconscious level. We may not know why we do them, but we do do them."

As for TN, his wife later told de Gelder that insight from the hallway experiment had enabled him to move about somewhat more easily.

"Consciously he is like a blind man," she said. "He walks like a blind man. He talks about himself as a blind man. With this, we can say, 'We know you can do it.' We are planning to do some training with him again next year."