The three lessons in this level (Level 9) have been written from many first-hand accounts shared by people who have a type of CVI where their posterior parietal lobes have been affected. This is therefore more subjective than our other lessons, but it is the subject of ongoing research. As the accounts have been so consistent, we wanted to share them, because the understanding they give us lets us make simple adjustments to help many people, especially those unable to communicate their challenges, as is the case for young children and those with limited communication skills.
Following on from the previous lesson where we asked you to spend a few days thinking about your own map, we are going to do a few more exercises. This is because this subject cannot be understood just by reading about it. You need to first understand your own map, and then try to get a sense of how it is different for those with a CVI.
We will explain using a simple sliding scale....
For this exercise we are going to imagine we are standing in front of shelves of books, close enough to reach them.
In the image above, imagine the middle row is the same height as your head.
Looking straight ahead, and keeping your body position central and still, let us mark the middle area (with a white circle, below), where your voxels are smallest.
We will call this our original position.
The area in the circle is where you can reach most accurately, so once you have chosen a book, if it is in that circle, you should be able to reach out with your arms, put your fingers on it (and not accidentally on another book) and slide it towards yourself to remove it from the shelf.
Now, we are going to create a voxel map sliding scale, it can go left or right, ours will go right....
The scale is not very long is it? But, keeping your original position (body and head and eye position), as the circle moves to the right, very quickly you will no longer be able to see a book well enough in your peripheral vision to recognise it, let alone look at it (without moving your head and eyes, explained below).
So, standing in your original position, the dashed circle in the image above is your best vision, where you have the smallest voxels. The circle to the right, where you see less, recognise less and reach much less accurately, may be the 'normal' central (original position) vision for the person with CVI, whose peripheral vision provides an even less accurate map.
You need to go out and try this, at home, at a book shop, at a library, anywhere there are books. From your original position, think about your vision to the right, and what happens in relation to the map:
All, because of bigger voxels. This is why understanding the CVI map in the brain of those affected, is so important, because those with CVI can have fewer, and so bigger voxels. What is central and best vision for them, may be similar to how yours is, slightly to the side, although they will be unaware of this.
We can't emphasise enough how important it is to understand the CVI posterior parietal map.
Please take time to practice these exercises, and get a real sense of the difficulties where voxels are fewer and bigger. Always safely.
Checklist: Before moving on to the next lesson please check you have understood.
Next lesson 9c Dorsal (2) The Dynamic Map
Your generous donations will be put to immediate use in supporting our charity...
At CVI Scotland we are devoted to helping people understand cerebral visual impairments, and together working towards developing the understanding of this complex condition.