Why did the grumpy face disappear?
The ‘Blind spot’
Close your left eye.
Stare at the happy face
Move the picture away from and towards your right eye
You are aware of the grumpy face is in your peripheral vision, don’t look directly at it.
Did the grumpy face disappear?
Yes? Then the light from the grumpy face image hit the ‘blind spot’ on the back of the eye.
What is the blind spot?
The blind spot is a patch on the back of the eye where there are no cells that can recognise light (rods) or colour (cones). Any part of the image hitting this spot won’t be seen.
Does it have another name?
Yes. It’s called the Scotoma, originally from a Greek word, skotos, which means darkness.
Why is there a blind spot?
It is because there are no image recognising cells on this part of the retina. No cells, no image.There are no image recognising cells(photoreceptors), because this patch on the retina, on the back of the eye, is where the nerve fibres which have come from all the other cells come together as a bundle. Like hairs being collected into a pony tail. The hairs are the nerve fibres, the pony tail is the nerve. It goes from the eye to the brain and is called the optic nerve.
What is the optic nerve?
The optic nerve carries all the information collected by the retina and taking the information to the brain. Here, all this data is sorted and we are then able to ‘see’ the object.
Isn’t having a blind spot a design fault?
It could have been a problem, but the brain is clever because it knows about this gap and tries to fill it with what we expect to see. We don’t know it is there normally, but you can look for it.