The man made his way down the hallway, maneuvering with ease around the boxes, chairs, and other obstacles. For most people, this act would be routine, one performed countless times each day. This man’s journey, however, was anything but ordinary. He circumnavigated the clutter without a misstep—while seeing none of it.
Damage from two strokes had left lesions in both of the man’s visual cortices, rendering him blind. Identified only by his initials, TN required a cane and his wife’s assistance to walk down the street. His performance in the obstacle course, part of an experiment to assess visual capacities in the blind, stunned investigators.
“We were absolutely shocked by his ability to navigate the corridor,” says the study’s lead researcher, Beatrice de Gelder, a cognitive neuroscientist at both HMS and Tilburg University in the Netherlands. TN was surprised, too. “He hadn’t made any conscious effort to hear or feel his way around,” de Gelder explains. “This was all automatic behavior.”
De Gelder’s study was the first to show in humans what had been reported previously in monkeys: that we may be able to detect aspects of our environment, even if we aren’t aware of seeing them—a concept known as blindsight. The result, says de Gelder, “illustrates in a fairly dramatic way that the brain has a number of alternate routes that can be mobilized when the main avenues to vision are blocked.”
That’s because retinal cells appear to project images not only to the visual cortex, but also to other parts of the brain related to vision and emotion. For TN and others whose other cognitive functions and eyes remain intact, these areas may still respond to visual cues, allowing them to react to such stimuli, if not actually “see” them.
Blindsight isn’t limited to navigational skills. Other research by de Gelder and her colleagues suggests that blind people may be able interpret facial expressions as well. Experiments with TN and other visually impaired people have shown that certain facial expressions—fearfulness, for example—can cause study subjects to cringe or otherwise react, even though they cannot consciously view those expressions.
For de Gelder, who is planning further studies involving TN this year, such findings demonstrate the importance of looking beyond the obvious. “We tend to concentrate on the major visual systems in the brain,” she says. “But we may have hidden resources.”