- Agnosia is an inability to recognise and identify objects or people’s faces
- It is caused by a deficit in the brain that means it can’t interpret the senses
- A study finds this same condition could be why people are ‘motion blind’
- Most people tested could not detect motion in one part of their vision field
Abigail Beall For Mailonline
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For anyone thinking of getting in a car this week, it is a scary thought – up to half the people on the road with you may suffer from a condition called motion blindness.
New research has found that the problem – which makes people unable to see movement in parts of their field of vision – is more common than previously thought.
Scientists have discovered that a condition called agnosia – which happens when the brain cannot properly interpret information from our senses – may be the underlying cause of motion blindness.
New research has shown agnosia can cause ‘motion blindness’, which makes people unable to see movement in particular parts of their field of vision. Motion blindness is caused by a failure of the brain, and has nothing to do with our eyes, a new study says
WHAT IS AGNOSIA?
Agnosia is a rare disorder characterised by an inability to recognize and identify objects or persons.
People with agnosia may have difficulty recognising the geometric features of an object or face.
They may be able to perceive the geometric features but not know what the object is used for or whether a face is familiar or not.
Agnosia can be limited to one sensory modality such as vision or hearing.
For example, a person may have difficulty in recognizing an object as a cup or identifying a sound as a cough.
Source: National Institute of Neurological Disorders and Stroke
Tests by researchers at the University of Wisconsin-Madison found that up to half the people who took part in studies suffered from this to some degree or another.
Professor Bas Rokers from the University of Wisconsin-Madison who led a study found motion blindness is caused by a failure of the brain and has nothing to do with our eyes.
‘We were surprised when we saw how many people had trouble correctly detecting motion, and put people through thousands of trials,’ said Professor Rokers.
Most people with motion agnosia will not be aware of it, as it seemed to only affect one part of the field of vision.
Face blindness is another example of agnosia.
‘It’s not that they can’t tell something is a face. They can look right at it and tell you where the nose and the mouth are,’ said Professor Rokers.
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‘They just can’t integrate that information to figure out identity, because identity depends on the relationship between those elements.’
The same problem occurs in motion blindness, except the brain cannot integrate two different visual clues.
‘If something close to you comes even closer to you, it looks bigger,’ said Professor Rokers.
‘Or you can move your head a bit—like a cat does before it jumps toward something—back and forth to get more than one vantage point.’
Most people with motion agnosia will not be aware of it, as it seemed to only affect one part of the field of vision. This means people who do have the deficit can still see moving objects, or make up for a lack of one cue by using the other
Our brains compare the difference in location of an object at different points in town using ‘changing disparity clues’.
Because we have two eyes at slightly different angles, we can use ‘inter-ocular’ differences to work out the speed of objects.
MISSING BODY PARTS
If you have trouble catching balls or determining the direction of an oncoming vehicle, you may have a condition called agnosia – which happens when the brain cannot properly interpret information from our senses.
But agnosia can also make people believe they are missing body parts.
In an experiment last year, researchers asked participants to close their eyes while they prodded each toe individually.
The participants were asked to state which toe was being touched.
Although the volunteers correctly guessed when their big or little toe was being touched more than 90 per cent of the time, they struggled with the three middle toes
They often thought their third toe was being prodded when it was their second, and believed their fourth toe to be tickled when it was their third.
The two cues are similar, but handled by different parts of the brain.
Professor Rokers and his team tested people’s use of these cues by isolating the other kind of cue.
‘In the real world, these cues happen at the same time,’ he said.
‘It’s just that the detectors in our brain can only pick up one cue or the other. You have detectors that are sensitive to disparity, and separate detectors that are sensitive to velocity.’
More than half of people tested had difficulty when relying on just one of the cues.
This means people who do have the deficit can still see moving objects, or make up for a lack of one cue by using the other.
‘But they’re implicitly aware of how good they are at using the cues,’ Professor Rokers says.
‘People combine them according to their own judged reliability. If they’re very good at using one cue, they will incorporate that information more.
‘There’s no way to predict before they are tested whether they have an agnosia for motion,’ he says. ‘It is an issue with the wiring in their brains.’
His next work will be to determine if the issues with wiring in the brain can be detected.
If so, it could help find and treat similar problems such as amblyopia, also known as a ‘lazy eye’, and the damage done by a stroke.
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