Patients with damage to the primary visual cortex have severely impaired vision - they typically have a difficult or impossible time reading, driving, or getting out to do ordinary chores like grocery shopping. Patients may walk into walls, oftentimes cannot navigate stores without bumping into goods or other people, and they may be completely unaware of cars on the road coming toward them from the left or right.
Depending on where in the brain the stroke occurred, most patients will be blind in one-quarter to one-half of their normal field of view. Everything right or left of center, depending on the side of the stroke, might be gray or dark, for instance.
Building on blindsight
Despite the stroke, the patients' eyes are taking in visual information. It's just that the damaged brain cannot make sense of it to create vision.
Huxlin's team sought to build on this "blindsight" - visual information, of which the patient is unaware, that still reaches the brain. A few past studies have shown promise for the idea of building on blindsight to improve a person's vision.
"The question is whether we can we recruit other, healthy regions of the brain to benefit the person's vision. Can we train those brain regions so hard and stimulate the brain to such a degree that this visual information is brought to consciousness, so the person is aware of what they're seeing?" said Huxlin.
Huxlin began the study with seven people, four women and three men, ranging from their 30s to their 80s, who had had a stroke anywhere from eight to 40 months before the experiment began. All had suffered substantial damage to the primary visual cortex. The funding to support the work came from Research to Prevent Blindness, the Pfeiffer Foundation, the Schmitt Foundation, and the National E
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