Riddoch Syndrome (also called the Riddoch Phenomenon) is where, quite simply, people who should not be able to see, due to occipital lobe damage, can see to a degree, when there is movement. This is the case for The Blind Woman Who Saw Rain, who harnessed this skill to be able to do many things using this vision, including moving around independently, avoiding obstacles.
Riddoch Syndrome is connected to blindsight.
To understand blindsight we have to look at the many elements that come together to create our visual world.
First, in the occipital lobe we have the picture, a bit like a high quality photograph, clear, with high contrast well defined colour and detail.
Separately, in the middle temporal (MT) lobe, movement, to match the movement you are looking at, is added to the picture.
Also, depth is added separately, as is visual attention, and the whole process of recognition. Many different elements, all working together like a perfectly synchronised orchestra, to create the visual world you are aware of (your conscious visual world).
To understand blindsight, we need to look at the relationship between the picture (created in the occipital lobe) and movement, but non-conscious movement.
With blindsight, the information from your eyes goes deep into the brain to an area in the thalamus called the pulvinar.
This area, whilst processing visual information received from the eyes, does not create a picture as such.
If something moves very fast from the side, maybe an animal running in front of your car, or a flicking tree branch, needing you to blink, the visual information sends a signal to essentially override all of your systems of attention, to alert you, to do something, quickly! This process is non-conscious, so you are not aware it is happening, thus not something you can control. The reaction is very fast. Faster than your conscious vision.
So blindsight, whilst a visual response, does not create an image, but it does bring about a reflex response.
Once you understand blindsight, it becomes relatively easy to pick up when it happens.
Have you ever been driving and someone suddenly pulls out from a side road? It is likely that you had slammed your foot on the brakes (reacted) before you consciously saw them. That's your blindsight. Clever huh? It is there to protect us - visual information that triggers a reaction. Probably left over from our hunter gatherer days - to protect us from wild animal attacks, still protecting us today.
So that is blindsight - it comes from vision (from our eyes) but does not create a picture, only a reaction to act - like turn quickly or slam on the brakes or blink in time, for example.
So how does something that is just a reaction create a picture? Pictures are created in the occipital lobe, however with the Riddoch Phenomenon, people who are unable to create a picture due to an occipital lobe injury, unquestionably can see things. In the film of The Blind Woman Who Saw Rain, not only could she see thing without the use of her occipital lobes, but she could see small detail, like raindrops running down a window and the swish of her daughter's pony tail.
We know the picture wasn't coming from her occipital lobe. We know she wasn't making it up. We know these weren't visual memories from before her brain injury. So where was this vision coming from?
The first thing with the Riddoch Phenomenon is to understand that there are pictures and there are pictures. The occipital lobes create the high definition photograph quality like pictures. This is not the picture created by the Riddoch Phenomenon, that picture has gone due the brain injury.
With the Riddoch Phenomenon, movement is key. Movement is key to blindsight too.
Try to think of movement without the image - it is difficult, this moving image of biological motion may help.
Movement and the image come together but are created in separate parts of the brain, from information received through the eyes. So, what happens when the eyes are working well, sending the visual information to the different parts of the brain to create the visual world, but the picture bit is missing (due to occipital lobe injury)?
There seems to be growing evidence, that through movement (that can be created simply by rocking in a rocking-chair) the brain is not only able to produce an image of the movement, a bit like an outline (very well illustrated in the Blind Woman Who Saw Rain film), but possibly it could be harnessed and controlled. So the unconscious reaction that is blindsight, evolves into the conscious controlled vision that those with Riddoch Syndrome enjoy.
The potential impact on the person's life is enormous.
So blindsight may be seen as a spectrum, and Riddoch Syndrome is on the blindsight spectrum.
This case is the first we are aware of involving a child. It is interesting because the brain is at its most plastic during childhood, so in theory, there should be the greatest opportunity for development.
This paper is an easy to read single case study, about a boy, referred to as B.I.
Only two weeks old, B.I. suffered a brain injury as a result of a condition called medium-chain acyl-Co-A dehydrogenase deficiency. This condition stops some fats being converted into energy, and can cause many difficulties, including for B.I. seizures and hypoglycaemia (very low blood sugar level) which lead to brain injury. B.I. suffered bilateral (both sides) occipital lobe damage. This should have left B.I. with no conscious vision.
When aged 6 and 7, B.I. undertook many different tests, and rather than being blind, as would be expected, he had 'extensive conscious visual abilities". B.I. (quoting from the paper)
This paper looks to see "what secondary pathways are responsible for this extraordinary capacity?"
What secondary pathways are responsible for this extraordinary capacity?
These skills go beyond blindsight at its most basic (reactive) level, as described above. Using tests and state of the art imaging technology to view brain activity, this team attempted to identify the pathway B.I. was using, possibly linking blindsight to the Riddoch Phenomenon.
This paper mentions the following areas of the brain:
So, there are two separate areas, both processing vision and movement, but differently. PI gives the super-fast automatic reactions, as described in our explanation of blindsight (above). MT "organises our perceptions of our moving worlds, with a seamless synchronicity, to match our perceptions to real-world events we are looking at" (from our introduction to Blindsight Newspaper Feature).
There are three relevant points on the brain (MT, P1 & LGN), and quite simply, the team are looking to see if they can find the pathway. It's a little like the main road from one town to another being blocked, but still some seem to be able to get through - but how? If not using the main road, then what are the other options - are there unknown tracks that are passable maybe?
The paper notes that in trying to understand the Riddoch Phenomenon, it has previously been shown that the area MT has been active in people who cannot see due to occipital lobe injury. This means that whilst the picture is not created, the other parts of the visual brain are still active, and doing their job.
The researchers subjected B.I. to many tests, showing he was above average when it came to intelligence, but his contrast sensitivity was poor and to tell shapes apart they needed to be big. B.I. could also correctly recognise facial expressions like smiles, this has been attributed in others to an emotional reflex called affective blindsight, as explained in our Blindsight section. B.I's tests show two fascinating results:
Thinking of B.I's brain as roads, the MRI showed that on both sides, the roads from V1 to LGN were severely compromised, making them almost impassable. Looking at other possible roads, they made an interesting discovery. Not only was B.I.'s road between LGN and MT on the left side completely clear, but there was almost twice as much traffic on it as other children that were tested (the control group, who had typical brains).
The control group had little use for the LGN to MT back-street, because their main roads between LGN and V1 were clear.
This fascinating paper raises many questions, which may lead to a completely new approach to rehabilitation for people who have sight loss due to occipital lobe injury. This is relatively rare in children, but is much more common in adults, particularly stroke survivors.
It is extraordinary. B.I. has created an alternative visual world, without the primary visual cortex, but this isn't really Riddoch Phenomenon, it would seem to be a type of blindsight, but more! B.I. can also see colour without the picture created in V1, but is able to add it to a different picture created possibly in MT.
Can this skill be transferred? Can motivating dynamic visual games be designed to help others with occipital lobe injury, regain conscious vision? Can motivating programmes of progressive exploration be developed (remembering that as we start to move, the scenery starts to move in the opposite direction)?
This paper is behind a paywall, although the abstract can be read for free, and it may be available through certain academic or medical institutions.
Paper: More than blindsight: Case report of a child with extraordinary visual capacity following perinatal bilateral occipital lobe injury Mundinana, I.-C., Neuropsychologia (2017)
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