Let us assume, for simplicity, that an image has been created in the occipital lobes with good clarity and colour, and no visual field loss (this is often not the case, and the effects of combined visual field loss from both the occipital lobes and posterior parietal lobes, and with other CVIs will be explained).
The image is dinner.
Lucy is a schoolgirl who loves her dinner. Lucy has visual neglect affecting the left-hand side of her vision. Lucy's occipital lobes have sent a good image of her dinner (above) through her visual brain, but when the image reaches her right posterior parietal lobe, it is unable (due to a brain injury) to award any attention to the left hand side.
Lucy can't see half of her dinner because the picture isn't there - although we know that a complete picture has been delivered.
Lucy does not know the other half of her dinner is on the left side of the plate, because she can only be aware of something if her brain gives it attention. Without attention, the left-side of Lucy's table could have a dancing goldfish performing a limbo and she wouldn't see it.
Imagine there is a coffee-table in your lounge, with a sharp protruding corner, that you keep knocking your shin on in the same place, over and over again. You would, over time, remember that the sharp corner was there, and give the table a wider berth as you walk past it.
No one is challenging your ability of form useful memories, especially when you are subject to repeated physical injury. But for that memory to be useful, and protect your shin from another bruise, whilst you are walking through the room past that table you have to be aware that it is there at that moment.
That awareness comes from your brain awarding the table attention.
It doesn't matter how many times you have walked into the table, if at the time you are walking past it, you are not aware of it, it might as well have been invisible - because it is not visible to you when there is no attention.
Another form of inattention that is rare, but interesting:
Amy is an 8 year old girl who was born prematurely and developed hydrocephalus which was treated. She panics in long straight corridors.
Her visual fields were assessed by the eye doctor holding up extended forefingers of both hands in first the upper and lower quadrants of her visual field.
When one finger was moved by each hand in turn, it was seen on each side.
But when both fingers were moved on both sides with mirror image symmetry, only the one to her left was seen in both the upper and lower visual field.
Amy has a mild form of visual inattention in which movement is seen on each side, but not on the left side when the right side of her vision is being equally and symmetrically stimulated.
This is called inattention hemianopia. It shows that the two sides of the brain compete for attention and if one side does not work so well then the better functioning side wins.
What must it be like walking down a symmetrical corridor? The left half must look very odd or disappear.
Pictures were hung along both sides of the corridor in random places to decrease the symmetry, and Amy was no longer scared.
Inattention is a lesser form of neglect. With inattention, something may draw your visual attention to the table if the pop-out effect was significant enough.
A pop-out effect, as briefly described in the Understand section, is a heightened visual stimulus that may draw your attention, for example something moving, or brightly lit, or flashing, maybe a lit candle, or a moving toy.
Connor has visual neglect in his lower peripheral vision.
There was a raised (black tiled) hearth around the family fireplace, and Connor ALWAYS tripped over it.
Connor's family knew he had a good memory, and thought he would eventually learn to avoid the hearth, but he never did.
To avoid tripping over the hearth, Connor would need to be aware that it was there. The hearth was in Connor's lower visual field where he has NO ATTENTION (visual neglect), thus he cannot learn to avoid tripping over it.
Eventually, Connor's parents had a wooden shelf built, to help Connor stop tripping over the hearth.
Connor saw the shelf and learnt to walk around it within three seconds.
The new shelf was now visible in Connor's upper visual field, where he was aware of it, so could see it.
Back to Lucy's dinner. It may seem easier to understand how Connor can trip over a hearth when it is in his lower visual field, as opposed to Lucy, who can't see half her dinner. Although we know that it is isn't the case that Lucy can't see her dinner, Lucy is not aware of the left half of her dinner. These are two quite separate / different things. But Lucy's dinner is right in front of her, and she is eating the other half - surely that's a big enough clue?
There's no question about half a plate magically disappearing, or gravy pouring over a side.
What Lucy sees is her full visual world.
Nothing is 'missing', but Lucy does need to learn techniques to explore her left side where she has no awareness, or she will bump into things, and go hungry if she leaves half her dinner.
For Lucy to see the left side of her dinner she needs to move her body.
The image, produced from the information received by the eyes and sent to the occipital lobes, has been created, it is there, right in front of her. Lucy does not need to move her eyes or head, she needs to give attention to the left side.
When Lucy turns her body to the left she both extends her field of vision slightly, and is able to see (now she has moved her attention) the left side of her dinner place.
To move her attention Lucy needs to turn her body to the left, as this diagram demonstrates.
In the same way, for Connor to give attention to his lower visual field he has to bend over, not just look down.
This type of lack of attention, given to what Lucy and Connor are looking at is called allocentric. Allocentric visual neglect or inattention relate to not being able to see something you are looking at due to the area not having attention.
Visual neglect and inattention are often also egocentric, meaning there is no attention to that part of your physical body too. When Connor walks he behaves as if he is not aware that he has feet on the bottom of his legs. Other people with lower visual field neglect have described the experience as 'walking on clouds', or as never having known they had feet. Calum, whom we met in the previous section, never understood the point of hockey, he could never see a ball. Lucy might pick something up, and still be holding onto it hours later, completely unaware that it is in her left hand, for which she has no attention.
Egocentric visual neglect or inattention may not sound like a visual impairment, but it is completely intertwined with the persons allocentric neglect and inattention, thus they cannot be understood in isolation from each other.
Think of Calum playing hockey with lower visual neglect - he can't see the ball (allocentric neglect) and is not aware of his feet (egocentric neglect). Not surprisingly Calum chose to give up hockey at the first opportunity!
If the two papers below, (marked L and R for left and right) with a story were placed in front of Lucy:
From this image, how is Lucy supposed to know that there is another page she is missing?
The first page is missing so the story won't make sense. This might be a prompt to turn her body to her left, or it might make Lucy feel foolish because she can't understand
Lucy uses her blindsight, however relies heavily on support from other people.
To lead a full and independent life, to access information like reading, and to make friends, Lucy needs to learn techniques and strategies to access her left side where there is no attention, herself.
Lucy's mother writes:
As with all our kids, their CVI profiles are multi faceted. With Lucy, blindsight is just part of her CVI profile - the image of the dinner would not be as clear as the photo of the roast dinner shows. She would use touch to determine what is in front of her. Lucy would intellectually know there is more than half a dinner there due to custom and experience. She is able to "see" the known but not able to "see" the unknown or "un-remembered". In a known and well mapped environment she can appear to be a sighted child. In fact sometimes people forget or overlook her CVI by pointing to things or saying things like "it's over there".
Lucy scans a lot. Both to register her general environment and to look for an object she wants. She seems to be really good at mapping places and knows the layout of places she hasn't visited for a while. She also surprises us frequently with her ability to "see" and pick up objects. At her last visual clinic she was great at the Rice Krispie test. Clear desk top with 4 Rice Krispies placed randomly. Lucy was able to scan the desk and find them all very quickly. She was just as good with the half-rice Krispies test.
Lucy also uses a white cane and can move independently around school - the teacher will send her off ahead to the art room or music for example.
At the same time she does need constant support and direction as she can easily come a cropper. Her visual acuity is very poor and she's registered blind.
Activities with lots of movement are favourites. Football, riding, skiing, swimming. Reading is perhaps equal with football. Books are absolutely her favourite objects and she knows many of them off by heart.
Lucy has developed a way of creating memories using a combination of repeated experiences with other senses. This can over-ride her lack of visual attention and is called haptic memory.
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