A few years ago I took part in a couple of fascinating experiments.
The first experiment involved being asked to hold my hand straight out without moving it, then to close my eyes. Next a vibrating pad was placed on the tendon of my biceps muscle.
I was then asked to open my eyes. To my surprise, my forearm was flexed and my hand was pointing upwards.
The experimenter explained that vibrations deceive the mechanism that tells our brain where are limbs are. This is called proprioception.
For the second experiment I sat down in a room without windows. The room light was turned off. The only thing I could see was a point of light straight ahead of me projected onto the wall opposite. The same vibrating pad was then applied to the back of my neck on the right side. To my surprise, the light instantly jumped to the right. As soon as it was switched off, the light jumped back to its original position.
This is how I learned why, when we turn our heads from left to right, our surroundings stay steady. This is one of the many remarkable ways we constantly know where we are located within our world. Another way, is that our eye muscles send the same sort of messages to our brains. These amazing automatic mechanisms, for example ensure that our surroundings do not appear to move to the right when we turn our head and eyes to the left!
What other brain mechanisms do we have, to know where we are?
Our balance system keeps us vertical and lets us know when we are spinning.
We can locate where sound is coming from.
Then there is touch. When walking we have our feet on the ground, so we know where the ground is. With our eyes closed we can reach out and feel what is around us and work out where each item is.
Then of course there is vision, which also provides an amazing constantly up-to-date map of our surroundings as we move around.
Next there is memory. We can remember where things are in relation to ourselves.
From moment-to-moment, our brains put all this information together to let us know where we are within our surroundings.
Can we use this knowledge to help those with cerebral visual impairment?
Indeed we can.
One day I was teaching in Belgium. My hosts showed me two short movie clips of the same young boy placing a peg into a peg board.
In the first he couldn't manage it. He kept missing the hole. Yet in the second, he did it perfectly. They asked "Why the difference?".
I was able to point out that in the second clip, his knee was touching the peg-board.
It was clear that he had impaired visual guidance of movement, or Optic Ataxia. It was only when he had to use his vision alone to guide his movements, without being able add in touch and proprioception into the mix, that he had difficulties.
Another day I saw a young man who had no vision down below. He played the piano with his thumbs rubbing along the front of the piano. Remembering the Belgian movies, we raised the piano stool until his knees touched the underneath of the key board. From then on, he used his thumbs as well to play the piano keys, because the touch information previously given by his thumbs telling him where the keyboard was, was now given by his knees, releasing his thumbs to play.
So the bottom line is...
...we need always to think about the skills that the other senses give us, and how these can be best made use of to substitute for the wide range of possible visual difficulties that those with CVI know to be their normality.
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