c4r5 wrote:
but then i saw stuff on TV about blind people who could sense movement but could not see things in the usual way. This was put down to an extra set of nerves running from the eye to the brain, (total of 4).
This is known as blind-sight. It's when people are cortically blind, meaning that they have no awareness of sight because their occipital cortex is damaged, but other, lower-level visual-processing areas of their brain are still intact. So, although they cannot consciously "see" anything, they can still navigate unerringly through a room filled with obstacles because their brains are processing what they are seeing at a sub-conscious level. It's not because they have extra nerves, it's because the only damaged part of their visual system is the occipital lobe.
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They also had stuff about stroke victims who could sense reality on one side but not on the other.
You could be referring either to neglect or hemianopsia (blindness in one half of visual field). I'm going to guess that you are referring to neglect, which most often occurs when the stroke/brain damage occurs in the right hemisphere. What happens is that the person does not attend to information coming from one side of the body (the left side, in the case of a right hemisphere stroke), including sight, hearing, touch, etc. They may deny that their left arm even belongs to them, may run into doors on the left hand side, and will only read the right hand side of a piece of paper (not realizing that what they are reading makes no sense). Through therapy however, people can often be taught to pay attention to that neglected side.