Sometimes called the Floating Finger Illusion, this trick shows you what the world might look
like if you only had one eyed in the center of your forehead like a Cyclops. The illusion happens
in a special region of our visual field where the product of each eye overlaps. The following
technique will let you examine this special region and allow your mind's eye form what is called
a "cyclopean image."
Stand or sit still and extend your arms out in front, with your index fingers pointed at
each other in front of your face at eye-level. Finger tips should be about 1-inch apart.
Now focus your attention beyond your fingers into the distance. Between your fingers you
will see a floating finger form in the overlapping region, as illustrated by the image below.
Move your fingers closer or farther apart to adjust the length of the cyclopean "sausage."
Close one eye or the other and the illusion will disappear. If you focus your attention back
to your finger tips the illusion will also disappear