A man who completely lost his sight after brain damage has astonished scientists by negotiating an obstacle course without his cane, in a powerful demonstration of an eerie phenomenon known as “blindsight”.

The man, known only as TN, was blinded by strokes on both sides of his brain which left him unable to see and devoid of any activity in the brain regions that control vision. He uses a stick to detect obstacles, and has to be guided around buildings. However, TN was known to exhibit blindsight, a strange ability some blind people have to detect things that they cannot see.

He reacts to the facial expressions of other people, for example, and scans of his brain have confirmed that it registers facial emotions such as joy, anger and fear.

He has now shown evidence of an even more remarkable skill – the ability to navigate without being able to see. In an experiment, scientists arranged a series of boxes and chairs in an obstacle course and asked TN to move through it from one side of the room to the other without using his cane. To their amazement, he completed the course without hitting anything, earning applause from on-lookers.

Professor Beatrice de Gelder, of the University of Tilburg in the Netherlands, who led the study, said: “This is absolutely the first study of this ability in humans. We see what humans can do, even with no awareness of seeing or any intentional avoidance of obstacles. It shows us the importance of evolutionarily ancient visual paths. They contribute more than we think they do for us to function in the real world.”

TN’s blindsight is likely to be explained by these alternative visual paths in the brain, which allow him to process information received through his eyes, which are still functional. He can then use this information to navigate even though he is unaware that he has the ability to see.

Professor de Gelder said: “It’s a part of our vision that’s for orienting and doing in the world rather than for understanding. All the time, we are using hidden resources of our brain, doing things we think we are unable to do.” The research could have implications for treating patients with brain damage.

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