Reading may involve unlearning an older skill
Jul 8th 2010
LEONARDO DA VINCI had many talents, including the ability to read (and write) mirror-writing fluently. Most adults find this extremely difficult, but new evidence suggests that recognising mirror images comes naturally to children. The 7th Forum of European Neuroscience, held in Amsterdam this week, heard that learning to read requires the brain’s visual system to undergo profound changes, including unlearning the ancient ability to recognise an object and its mirror image as identical.
Stanislas Dehaene, a cognitive neuroscientist at the French medical-research agency, INSERM, believes that skills acquired relatively recently in people’s evolutionary past must have piggybacked on regions in the brain that originally evolved for other purposes, since there has not been time for dedicated neural systems to develop from scratch..
His studies suggest that one small area of the brain’s visual system is particularly activated by the written word. Dr Dehaene calls this the visual word form area (VWFA). Researchers debate the extent to which this area is specialised for word recognition, since it also responds to pictures. But Dr Dehaene thinks the VWFA evolved for object recognition and is requisitioned for word recognition. Unfortunately, it has one property that, though valuable when recognising objects, is not helpful for reading: more than other parts of the visual system it is activated both by an object and by that object’s mirror image.
Dr Dehaene thinks that the VWFA may be responsible for the ability of some primates to recognise themselves in a mirror, or to recognise a tiger even if it is seen only in reflection—thus conferring an important survival benefit. That it is also crucial for reading might explain why children make a type of error he calls “early mirror reading”. It was thought that only dyslexic children were prone to confusing “b” and “d”, and “p” and “q”, and occasionally writing their names back-to-front, but Dr Dehaene has found that all children make this error.
He suggests the error happens because when learning to read children first have to unlearn that older survival skill. If he is right, then in adults the VWFA should be insensitive to which of two mirror images it is viewing when it comes to pictures, but sensitive to that distinction when viewing words and letters. This is indeed the case. Dr Dehaene has used functional magnetic resonance imaging to show that the brains of literate adults respond to mirror images of the same object as if they were identical, but to mirror images of the same word as if they were different words.
Some writing systems, like the ancient Greeks’ boustrophedon, in which alternate lines are read in opposite directions, appear to actually support these pre-literay inclinations. In fact, so do most alphabets. Other researchers have shown that the brain region that corresponds to the VWFA in monkeys is particularly sensitive to certain shapes, such as Y, T and L. The line junctions in these letters, when found in nature, provide valuable spatial information, such as whether an object is in front of or behind another. Dr Dehaene thinks that our visual system became sensitised to them early on, and that letters were later selected because they exploited the sensitivities of the human brain to such shapes. That is why such shapes are common to all alphabets, he says.
In his latest work, Dr Dehaene has shown that literacy may change the brain in other ways too. With a group of colleagues, he compared the brain responses of illiterate and literate adults to words and other visual stimuli, including faces. They found that the patterns of activity elicited by faces, in particular, were different in literate and illiterate brains.
Dr Dehaene believes that reading probably results in an enhancement of visual perception, but that these preliminary findings indicate there might also be a mild form of competition at work, whereby readers pay for their literacy with a slight reduction in their ability to perceive faces. He speculates that illiterate people may be better at the kind of holistic pattern recognition that is important in recognising faces, whereas readers may adopt a more piecemeal approach. Happily, the brains of people who learned to read only as adults responded in a very similar way to those who had read since childhood, suggesting that it’s never too late to learn
Jul 8th 2010
LEONARDO DA VINCI had many talents, including the ability to read (and write) mirror-writing fluently. Most adults find this extremely difficult, but new evidence suggests that recognising mirror images comes naturally to children. The 7th Forum of European Neuroscience, held in Amsterdam this week, heard that learning to read requires the brain’s visual system to undergo profound changes, including unlearning the ancient ability to recognise an object and its mirror image as identical.
Stanislas Dehaene, a cognitive neuroscientist at the French medical-research agency, INSERM, believes that skills acquired relatively recently in people’s evolutionary past must have piggybacked on regions in the brain that originally evolved for other purposes, since there has not been time for dedicated neural systems to develop from scratch..
His studies suggest that one small area of the brain’s visual system is particularly activated by the written word. Dr Dehaene calls this the visual word form area (VWFA). Researchers debate the extent to which this area is specialised for word recognition, since it also responds to pictures. But Dr Dehaene thinks the VWFA evolved for object recognition and is requisitioned for word recognition. Unfortunately, it has one property that, though valuable when recognising objects, is not helpful for reading: more than other parts of the visual system it is activated both by an object and by that object’s mirror image.
Dr Dehaene thinks that the VWFA may be responsible for the ability of some primates to recognise themselves in a mirror, or to recognise a tiger even if it is seen only in reflection—thus conferring an important survival benefit. That it is also crucial for reading might explain why children make a type of error he calls “early mirror reading”. It was thought that only dyslexic children were prone to confusing “b” and “d”, and “p” and “q”, and occasionally writing their names back-to-front, but Dr Dehaene has found that all children make this error.
He suggests the error happens because when learning to read children first have to unlearn that older survival skill. If he is right, then in adults the VWFA should be insensitive to which of two mirror images it is viewing when it comes to pictures, but sensitive to that distinction when viewing words and letters. This is indeed the case. Dr Dehaene has used functional magnetic resonance imaging to show that the brains of literate adults respond to mirror images of the same object as if they were identical, but to mirror images of the same word as if they were different words.
Some writing systems, like the ancient Greeks’ boustrophedon, in which alternate lines are read in opposite directions, appear to actually support these pre-literay inclinations. In fact, so do most alphabets. Other researchers have shown that the brain region that corresponds to the VWFA in monkeys is particularly sensitive to certain shapes, such as Y, T and L. The line junctions in these letters, when found in nature, provide valuable spatial information, such as whether an object is in front of or behind another. Dr Dehaene thinks that our visual system became sensitised to them early on, and that letters were later selected because they exploited the sensitivities of the human brain to such shapes. That is why such shapes are common to all alphabets, he says.
In his latest work, Dr Dehaene has shown that literacy may change the brain in other ways too. With a group of colleagues, he compared the brain responses of illiterate and literate adults to words and other visual stimuli, including faces. They found that the patterns of activity elicited by faces, in particular, were different in literate and illiterate brains.
Dr Dehaene believes that reading probably results in an enhancement of visual perception, but that these preliminary findings indicate there might also be a mild form of competition at work, whereby readers pay for their literacy with a slight reduction in their ability to perceive faces. He speculates that illiterate people may be better at the kind of holistic pattern recognition that is important in recognising faces, whereas readers may adopt a more piecemeal approach. Happily, the brains of people who learned to read only as adults responded in a very similar way to those who had read since childhood, suggesting that it’s never too late to learn
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