A man who was left completely blind by a series of strokes has delighted scientists by negotiating a maze of obstacles without using his cane.
The man, known only as TN, walked around chairs and boxes without knocking into them in an extraordinary demonstration of "blindsight", a strange ability some blind people have to detect objects they cannot see.
Scans of the man's brain revealed that a succession of strokes had left him unable to see, while brain regions known to process visual information were completely inactive.
Nevertheless, the man is able to react to facial expressions, registering emotions such as joy and anger.
Scientists at the University of Tilburg in the Netherlands believe people with blindsight are unwittingly tapping into alternative brain circuitry that lets them process information their eyes are receiving.
In the experiment, scientists created an obstacle course from boxes and chairs and asked the man to negotiate it without his stick or help from another person. When he completed the course without bumping into anything, onlookers applauded in amazement.
"This is absolutely the first study of this ability in humans," said Beatrice de Gelder, who led the study, which appears in the journal Current Biology. "We see what humans can do, even with no awareness of seeing or any intentional avoidance of obstacles. It shows us the importance of these evolutionarily ancient visual paths. They contribute more than we think they do for us to funciuton in the real world."
Scientists have seen blindsight in monkeys with similar brain damage.
The study reveals that untapped neural pathways exist in the brain that allow people to orient themselves and quickly detect obstacles, even if they are not conscious of seeing them. "All the time, we are using hidden resources of our brain and doing things we think we are unable to do," said de Gelder. "There is much that patients can do outside the grip of their being too aware of what they cannot do," she added.