How to map your blind spot

Legend has it that before an execution, King Charles II of England closed one eye and aimed his blind spot on the head of the condemned man. This allowed Charles' brain to decapitate the prisoner before the axe took its turn.

In the video above, you can take advantage of this ability by "decapitating" author and psychologist Richard Wiseman, just as Charles II did to his victims.

When Wiseman's head falls into our blind spot, our brain makes sense of the mismatch by replacing his head with the yellow background. When Wiseman raises a black bar across his body, our brain jettisons the background to avoid splitting the bar into two discontinuous halves.

Blind spots occur because of design quirk in the architecture of our eyes. Cells at the back of the eye, in a layer called the retina, gather light focused through our lens from everything that's in front of us.

However, where a bundle of nerves connects our eyes to our brain these light-sensitive cells cannot grow. Hence, light that hits this bundle is not sensed and a blind spot is the result.

Fortunately, our brain is good at filling in gaps in our field of vision, so even with one eye shut, we rarely notice our blind spot.

Map your own blind spots here
New Scientist
the big world