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Gordon Dutton’ Blog 20

How does vision protect us?

A small stone in a shoe is something we tend to notice and remove. The discomfort draws the offending stone to our attention and removing it spares the foot from being injured. In his book 'The Gift of Pain', the surgeon Paul Brand explains how important pain is to protect us in this way.

The same can be said for vision.

When I was at school, I had a friend with a white scar on one eye. He hadn't managed to blink in time when a tree branch had flicked into this eye. Normally though, a rapid reflex blink protects our eyes, if and when we climb through undergrowth.

We blink even before we're aware of the danger, because our subconscious reflex visual attention is processed faster than our conscious vision.

If a child steps onto the road in front of your car, you'll swerve, or if a stone is thrown at you, you'll dodge.

Again, rapid subconscious reflex visual attention kicks in and protects you.

Subconscious visual attention?

Surely that's a contradiction in terms?

Doesn't attention need to be a conscious process?

It does when a child has to 'pay attention' to a school teacher, but not when it comes to protective reflexes. We wouldn't be able to cope with all the information we'd have to process if we always had to be on the lookout for hazards. We're really lucky to have subconscious protective visual surveillance that works automatically without our even having to think about it.

What has this got to do with cerebral visual impairment?

For the child with marked CVI the blink reflex can protect the eyes even if vision is low. If blink is absent though, the eyes need to be carefully looked after.

A child with CVI may dodge and even fear a distant event. This phenomenon (which has yet to be researched) has been called Looming on this website. The attentional reflex to avoid a perceived hazard appears to be too sensitive, but the threat feels real to the child hence what looks like an unnecessary overreaction. We think it likely that the child's less accurate 3D mapping of the visual scene will be found to be the cause.

When it comes to giving conscious attention, this can be limited by low vision, or by visual field impairment (for example down below, or to one side), or lack of perception of movement, or a reduced capacity to parallel process the whole visual scene (see blog 18).

When these difficulties are identified and explained, many affected young people are over the moon, because no longer are they criticised for not paying attention, but their difficulties are understood and catered for. They too may become able to understand what they know to be their 'normal vision', and learn to use it better.

So all in all, visual attention, whether subconscious or conscious, can be impaired in children with CVI, either by appearing overactive, or by proving less effective than for others.

But when everyone comes to understand how and why, and takes appropriate action, it can make all the difference.

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At CVI Scotland we are devoted to helping people understand cerebral visual impairments, and together working towards developing the understanding of this complex condition.