An operation that left a patient half-blind revealed a “second sight,” an elusive mode of consciousness in which decisions are made outside of our awareness.
When Daniel first walked into London’s National Hospital, ophthalmologist Michael Sanders could have had little idea that he would permanently alter our view of human consciousness.
Daniel turned up saying that he was half blind. Although he had healthy eyes, a brain operation to cure headaches seemed to have destroyed a region that was crucial for vision. The result was that almost everything to the left of his nose was invisible to him. It was as if he were looking out of a window, with the curtains drawn across half of his world.
And yet, as Sanders began testing him, he noticed something very strange: Daniel could reach out and grab Sanders’ hand, even when it must have fallen right behind his blind spot. It was as if some kind of “second sight” was guiding his behaviour, beyond his conscious awareness.
Intrigued, Sanders referred Daniel to the psychologists Elizabeth Warrington and Lawrence Weiskrantz, who confirmed the hunch with a series of clever tests. They placed a screen in front of Daniel’s blind spot, for instance, and asked him to point at a circle, when it appeared in different places. Daniel was adamant that he could not see a thing, but Weiskrantz persuaded him to just “take a guess”. Surprisingly, he was almost always right. Or Weiskrantz and Warrington would present a single line on the screen, and Daniel had to decide whether it was horizontal or vertical. Again, Daniel was adamant that nothing had appeared before his eyes, yet his accuracy was around 80%, much more than if he had been guessing randomly.