Blindsight
Where vision is absent due to occipital lobe damage causing hemianopia, quadrantanopia or complete occipital blindness, sometimes movement in the blind part of the visual field can be fairly accurately detected by guesswork more often than not, hence the term blindsight. If it can be harnessed, blindsight can be very useful, to learn how to avoid obstacles, and in some affected people it can be given useful conscious awareness. Ability to see things that move in an otherwise blind area of vision is called the Riddoch phenomenon. Further reading, Lesson 6b Blindsight.