See Your Amazing Nervous System In Action With This Test
Rotate your phone to landscape.
Close your left eye and stare at the cross mark in the diagram bove with your right eye. Hold the phone close to your face. You should be able to see the spot. Don’t LOOK at it: just notice it is there off to the right.
Keep your eye focused on the cross. Now slowly move your device away from you.
Keep looking at the cross mark while you move your device slowly away. At a particular point you will see the spot will disappear (it will reappear again if you move it closer again or further away
The spot disappears because it falls on the location where the optic nerve enters the eye, which is basically a hole in the photoreceptor sheet at the back of the eye.am percolator.
Simple but fascinating stuff.