Professor Weiskrantz has been studying Graham

"I've lost all the vision to my right. I used to walk around town and walk into lamp-posts."

However, a visit to the opticians 15 years later revealed something remarkable going on inside his head.

Although he was not actually seeing anything, the sight test revealed that his brain was still processing information from the right hand side, even if he was unaware of it.

This is a condition called "blindsight", and Graham Young, because of the very specific and localised nature of his brain damage, is one of the most perfect examples of it in the world.

As a result, scientists from other countries are prepared to fly him around the world to use him in their experiments.

Other experiments was carried out by Professor Larry Wieskrantz of Oxford University: "Larry has damage restricted to the visual cortex and not to the rest of the brain, which makes him a much more pure case."

The brain works harder to produce conscious sight

He found that when Graham was shown tiny moving lights on a screen on his right hand side, although he was not aware of them, nine out of ten times he was able to "guess" which direction the lights were moving.

"I am completely unaware of anything happening in my right field, yet I get it right 90% of the time, which is a little bit weird. I don't know how I do it."

Brain scans revealed that when this unconscious process was going on, a primitive vision pathway was being used by the brain to communicate the information.

Normally, when he was processing vision signals and fully conscious of them, much more of the brain was in use.

Professor Wieskrantz believes that these different reactions could hold the key to a mystery which has puzzled brain scientists for many years.

Somehow your brain creates an inner world of experiences, memories and emotions called consciousness - but experts have little idea how.

Graham, a man whose brain sees things, but who has no consciousness of doing so, provides an interesting way of probing this.

"Brain Story" will be shown on BBC2 on Tuesday at 2100BST/2200GMT