January 2021


How to See the Illusion: Close your left eye and stare at the X, then move your head forward and backward from the computer screen. You'll find a point where the mouse disappears leaving an empty cage.

How the Illusion Works: When the eye is just the right distance from the computer screen, the image of the mouse lands over the optic nerve in the back of the retina. The rest of the retina is filled with over 100 million light sensing cells called photoreceptors, however there are no photoreceptors at the optic nerve, making it the blind spot of the eye. Therefore, when the mouse is focused on the optic nerve, it’s image doesn’t get sent to the brain. When both eyes are open, the mouse image from the left eye fills in the missing spot from the right eye. With the left eye closed, the brain uses information surrounding the right eye’s blind spot to “guess” what it might be missing, filling in the cage but leaving out the mouse.