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Brain Story - 3/6

The Mind's Eye

Vision is one of the most complex areas of brain activity and one that is still far from fully understood. It is the brain that manages to sort out a sense of meaning from the jumbled pattern of light hitting the retina. Movement, size, shape and colour all have to be pieced together by the brain in a matter of milliseconds. For the last 20 years, Gisela Liebold has been unable to see moving images, even though her other senses will tell her that the object is in motion. 'I find it terribly disturbing when a fast train approaches ' in general, when something comes towards me that's even worse ' it's better when it's far away.' Gisela can see things only as a series of freeze frames. This is because the human eye can only capture static images ' it is the brain which incorporates them to create the sensation of seeing movement.

Susan looks at other ways in which the brain is clearly able to 'fill in the gaps' from the limited information coming from the eyes, and she also explores how hard the brain works to make sense of the most subtle differences in this information. She examines how, for example, the brain enables the viewer to differentiate between thousands of different faces even though their physical differences are actually minute, and she finds out what happens when the part of the brain which analyses this information is damaged leaving the victim 'face-blind'.