For the first time, researchers have shown that people can navigate an obstacle course even after brain damage leaves them with no awareness of sight and no activity in the visual cortex.
Visual cortex is a region of the brain's cortex that is primarily responsible for processing visual inputs.
The study has revealed the importance of alternative routes in the brain, which are active in those who have suffered severe brain damage to the visual cortex and in all of our everyday lives.
Already, some previous studies have shown a similar ability in monkeys with comparable brain lesions.
But, the new study could only be possible because of the participation of an unusual patient known as TN, who was left blind after selective damage to the visual cortex in both hemispheres of his brain following consecutive strokes.
"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 these evolutionarily ancient visual paths. They contribute more than we think they do for us to function in the real world," said Beatrice de Gelder of Tilburg University, The Netherlands and of the Martinos Center for Biomedical Imaging and Harvard Medical School.
Earlier TN was known to have blindsight, which is the ability to detect things in the environment without being aware of seeing them. For example, he responds to the facial expressions of others, as indicated by activity in brain regions consistent with emotional expressions of fear, anger, and joy. And he does that despite being totally blind.
He walks like a blind person, using a stick to track obstacles and requiring guidance by another person when walking around buildings.
In the current study, which aimed at testing his navigational ability, the researchers constructed an obstacle course with randomly arranged boxes and chairs and asked him to cross it without the help of his cane or another person.
To their surprise, TN negotiated the course perfectly, without even once colliding with any obstacle.
The demonstration is an indication that alternative visual paths available in the brain allow people to orient themselves, and rapidly detect obstacles in the environment without any conscious attention or experience of seeing them.
"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 and doing things we think we are unable to do," she said.
That's an important message for patients with brain damage in particular, said the researchers.
"There is much that patients can do outside the grip of their being too aware of what they cannot do," said de Gelder.
The study has been published in the latest issue of Current Biology, a Cell Press publication.