Amazingly, people who are blind because of brain damage but whose eyes still function can often see things without any conscious awareness of doing so.
For example they may be able to point to or grasp objects. They may be able name simple shapes more accurately than can be down to random chance. They may be to recognise the emotions shown in faces (although they cannot recognise the faces themselves).
However if asked how they were able to locate the object, identify the shape or detect the emotion displayed they cannot say, or put it down to guesswork. As far as they are concerned they have not actually seen anything at all.
This startling ability is called ‘blindsight’. Although early reports of blindsight encountered scepticism there is now a great deal of experimental evidence and there can be little doubt that blindsight is real.
Many subjects of investigations into blindsight are stroke survivors who have lost some, or in unlucky cases all, of their visual field.
You can see a remarkable demonstration of blindsight on the Scientific American website here. I think this site is fairly accessible.
TN, who lost all vision following two strokes, was filmed by researchers as he navigated his way along a corridor strewn with numerous obstacles. Without even realising the obstacles existed he was able to avoid them all.
How can this be? What can can be going on? Isn’t it illogical or contradictory to say we can see something yet not see it? What does ‘seeing something’ mean?
This is where your inner bird comes in.
We have more than one visual pathway. One theory of blindsight is that as well as ‘mammalian’ vision, we retain a more primeval form of sight, similar to the visual system of birds and fishes. This second system provides visual information at a level below our consciousness (but which is still useful to us: maybe it helped our ancestors to avoid being eaten).
Hemianopic (half-blind, on one side) people have often taken part in studies of blindsight, so I am a candidate. I would love to know if I have blindsight in the parts of my visual field where I have become blind. But unless I can persuade someone to take me on as an experimental subject I shall have to look for some way of experimenting on myself.
I’ll end with a possibility that I find very exciting and very intriguing.
An article by Professor Beatrice de Gelder in the May 2010 issue of Scientific American raised the possibility of helping blind people unlock their blindsight, perhaps to the extent that it would help them with tasks such as getting around in daily life.
How wonderful if such a thing could happen!