The brain/eye mechanism at work again

Here is an excellent video, from Quirkology author Richard Wiseman, illustrating an aspect of the blind spot in the human eye that I’d never before thought of. Go and have a look, and then come back here.

The new wrinkle isn’t that Wiseman’s head disappears when it hits the blind spot (which is the bit of the retina where there are no light-receptive cells, because that’s where all the bundled wiring makes its way out to the brain). What’s interesting is that when he raised the horizontal bar over where his head ought to be (but isn’t, because it is missing), the bar itself is visible!

What seems to be happening is that the brain, attempting to compensate for the hole, fills it in with its surroundings. The hole isn’t ’empty’. It has the orange background of the wall. And the brain must extrapolate between the bits to the left and right of the hole, since it fills in a horizontal bar.

Or, perhaps, it stretches the visual material to the left and right of the hole inwards, so as to fill it in. Either explanation would work with the content there.

Fascinating. And another illustration of the fact that human senses are not scientific instruments.

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