How many different reasons can you come up with as to why it might be difficult to recognise people by their faces due to CVI? Let's go on a journey through the visual brain....
Due to reduced visual acuity, because the features are not seen clearly enough.
Due to reduced contrast sensitivity - look at your face in a mirror, the vast majority of which is the same subtle shades of your skin tone, even mild reduced contrast sensitivity is going to remove some of the shades that define the contours of your unique face, that make you recognisable as... well... you.
Due to visual field impairment. Where there is less of a face to see, it becomes harder to recognise people, whether one side is missing, or the lower part or any other area that is absent due to the many different types of visual field impairment.
Due to not processing movement typically - ummm? We understand how this can impair detection of brief facial expressions - look in the mirror and smile - the change in facial expression is a movement. Can the same difficulty, on its own, affect facially recognising people? Not obviously as far as we can see.
Ok, moving up the dorsal stream to the map of what is being looked at. So, we have a good picture, but maybe the map hasn't placed everything quite as accurately as it could, so if you went to touch the tip of someone's nose with your outstretched index finger, you might be slightly out (called optic ataxia or inaccurate guidance of reach). Optic ataxia can be a menace, but on its own (which is quite rare), would it affect facial recognition? No, we don't think so.
Due to simultanagnostic vision, the one CVI we go on and on about! Where only a part of the face may be visible, it can make facial recognition extremely difficult, even impossible. Remember, recognising someone from a photograph is a very different process, in brain terms, from recognising them in person, where the brain isn't just matching an image, but is processing a whole moving environment including talking, listening, understanding etc. So, unquestionably YES! Simultanagnostic vision can and does affect a person's ability to recognise people by their faces. We know this from our own experiences and from the many people who have contacted us.
What about if you are in a town centre shopping and your companion says 'look, there's Mark'. Assuming Mark is actually there, and reasonably visible (so not in a crowd of hundreds) but you couldn't see Mark. It might be that you can only visually attend to one or two things at a time, and so are unable to make the purposeful eye movements required to find Mark. This is called apraxia of gaze. With apraxia of gaze, you might struggle to find people to recognise them, but if you were with Mark, and looking at him, would apraxia of gaze mean you couldn't recognise him? Probably not, but it might look like it, as undoubtedly you would have missed and ignored Mark repeatedly - not unrecognised, just unseen - but to poor Mark who is constantly ignored, they feel the same.
Then across to the ventral stream... to the right temporal lobe where there is a store, your store of face pictures, just for all the faces you know, but this store is only as good as the information it is fed. Any of the above CVIs affecting facial recognition will mean that the quality of faces in your store of faces may be reduced, making recognition of people facially more difficult. It doesn't mean there's a problem with your faces store, the problem was further back in the process, although...
...what about where all of the above are fine, but there is a problem with the faces store, that has nothing to do with the rest of the brain, maybe just affecting that store and possibly other stores nearby in the same part of the brain. This can happen for many reasons, at any age, including in children, but also as a part of degenerative conditions like dementia. If your memory store of faces is reduced or not there, then you could meet someone you have known all of your life yet not recognise them, even though you can see them perfectly clearly - in brain terms, facially, they are a stranger.
Due to prosopagnosia or face blindness, where everything already mentioned is working fine, but the matching part of the process is faulty. So you have the memory in the faces store, and can see the person clearly, but your brain does not put the two together to form a match, so you don't know who you are looking at. The writer Oliver Sacks was affected by this and we love his quote...
My problem with recognizing faces extends not only to my nearest and dearest, but also to myself. Thus on several occasions I have apologized for almost bumping into a large bearded man, only to realise the large bearded man was myself in a mirror.
That's just a few reasons why cerebral visual impairments can impair facial recognition, each quite different. We haven't even started on the combinations of CVI which are common in many, especially children. Think of simultanagnostic vision, optic ataxia and apraxia of gaze combined - how might they together affect facial recognition?
The approach to help someone can be very similar for all, for example for a parent to stand in the same place on a playground, as we explained in our Case Study, Katherine's Playground (links below). Katherine had a combination of CVIs and amblyopia, so the same approach of standing in the same spot on a playground might be effective for a child with other CVIs including right temporal (faces store) difficulties, or someone with reduced visual acuity or prosopagnosia.
So, does the cause of the difficulty, in this case recognising people by their faces, matter if the approach is the same?
The answer is it does.
Difficulty recognising faces is a visual behaviour, not a visual impairment. It is a clue as to what is going on, but there are many different possibilities, so we need to put on our detective hat and think why this is happening for that specific individual. From what we learn when the individual or combination of CVIs is understood, we can continue our detective work and think - well how might this affect other areas of their lives, like learning, or being independent, like finding the right clothes or safely crossing a road. And that is the path to understanding, and optimally helping the individual with CVIs.
We have been little quiet recently because we are busy writing the next blocks of CVI lessons, including those about facial recognition, and the many different causes of difficulties.
The CVI Scotland Team
PS Everything new can be found in our Updates section, and via Twitter @scotlandcvi and our Facebook page.
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