Blind spot (vision)
As to why the blind spot is normally not seen, there are two theories. One, less favoured, is that it is simply ignored by the brain. The other is that they are 'filled in' by the brain with information from surrounding areas. Perception theorists have generally favoured this second hypothesis. The filling-in works with quite complex and unusual visual patterns, suggesting an active brain process works to mimic patterns surrounding the blind spot.