[from here]

1. A man ("TN") suffers two strokes and says he's blind. Standard tests confirm it.
2. He still reacts to someone smiling at him. Researchers are thrilled to find out that his emotional processing center -the amygdala- seems to receive information.
3. Researchers build him an obstacle parcours to walk through. He is able to do it. He sees, but only subconscious parts of his brain still process the visual information.
4. They are excited because now they will be able to study how far our subconscious processing goes, in isolation. At least for vision, that is.