Blind Spot and "Filling In" Illusions
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Select "black bar" or "yellow disk." Close your left eye and fix your right eye on the cross on the left. If your eye is about 12 inches (30 cm) away from the monitor, it should appear that the black dot and the red cross disappear. Why? Because in each eye, the optic nerve displaces the photoreceptors in a particular area.[more]
Now to explore the "filling-in" phenomenon, which works by "filling in" the most probable stimulus in a "blind spot" area. Thus, for the first illusion, the most probable stimulus would be blank space; for the second, a black bar; and for the third, a yellow disk.[less]
Contributed by: Nathan Lian (February 2016)
Open content licensed under CC BY-NC-SA
 Colorcube. "Blind Spot and the 'Filling-in' Phenomenon." (Feb 8, 2016) www.colorcube.com/illusions/blndspot.htm.