A woman in Florida who was ‘fully blind’ for more than 20 years has regained her sight after she fell and hit her head. The doctor who treated Mary Ann Franco called it a ‘miracle’ and thinks the knock may have caused blood flow to return to a crucial part of the brain.
Although this was probably not the case for Franco, it is possible to see without knowing you can see. Different neural pathways in the brain are responsible for our perception of what something is, and our sense of where something is.
Sometimes if only one of these pathways is damaged, a rare phenomenon known as blindsight can occur. If you give someone with blindsight a letter and ask them to post it, they won’t be able to see the postbox or describe it in any way. But if they try anyway, they can do it - even if the postbox slot is at an unusual angle.
This is because while the conscious sensation of seeing has been cut off, the pathway that controls interaction with what we see is still in use. Franco’s case shows us how much we still don’t know about the visual system, even in our own heads.
Dr Daniel Glaser is director of Science Gallery at King’s College London
