BRAIN HAS VISUAL SENSE FOR BLIND

MIND’S EYE: A patient whose visual lobes in the brain were destroyed, was able to navigate an obstacle course and recognize fearful faces subconsciously, researchers report

The man, a doctor left blind by two successive strokes, refused to take part in the experiment. He could not see anything, he said, and had no interest in navigating an obstacle course — a cluttered hallway — for the benefit of science. Why bother?

When he finally tried it, though, something remarkable happened. He zigzagged down the hall, sidestepping a garbage can, a tripod, a stack of paper and several boxes as if he could see everything clearly.

“You just had to see it to believe it,” said Beatrice de Gelder, a neuroscientist at Harvard and Tilburg University in the Netherlands, who with an international team of brain researchers reported on the patient in the journal Current Biology.

The study, which included extensive brain imaging, is the most dramatic demonstration to date of so-called blindsight, the native ability to sense things using the brain’s primitive, subcortical — and entirely subconscious — visual system.

Experts have previously reported cases of blindsight in people with partial damage to their visual lobes. The new report is the first to show it in a person whose visual lobes — one in each hemisphere, under the skull at the back of the head — were completely destroyed. The finding suggests that people with similar injuries may be able to recover some crude visual sense with practice.



“It’s a very rigorously done report and the first demonstration of this in someone with apparent total absence of a striate cortex, the visual processing region,” said Richard Held, an emeritus professor of cognitive and brain science at the Massachusetts Institute of Technology, who with Ernst Poppel and Douglas Frost wrote the first published account of blindsight in a person, in 1973.

Scientists have long known that the brain digests what comes through the eyes using two sets of circuits. Cells in the retina project not only to the visual cortex but also to subcortical areas.

In an earlier experiment, researchers also found that the same African doctor had emotional blindsight. When presented with images of fearful faces, he cringed subconsciously in the same way that almost everyone does, even though he could not consciously see the faces. The subcortical, primitive visual system apparently registers not only solid objects but also strong social signals.