Friday 23 November 2012
cognitive theory
http://openlearn.open.ac.uk/mod/oucontent/view.php?id=398452§ion=2.2.1 the open university
2.2 Cognitive explanations of dyslexia
2.2.1 The phonological processing deficit
Recall Alexander Faludy's difficulties in learning to read and write, and the other behavioural characteristics associated with having dyslexia. You might have noticed that many features of dyslexia point to a difficulty with some aspects of memory. That is, people with dyslexia have difficulty with tasks that require short-term memory processing such as mental arithmetic, writing and learning new information. However, these tasks have an additional feature in common: they contain a phonological component. That is, they involve the processing of speech sounds in short-term memory. It is therefore possible to suggest that a deficit in phonological processing may provide an explanation of dyslexia. To understand why a phonological deficit would have an impact on reading and writing we need to understand how people typically learn to read (see Box 6).
Box 6: Learning to read (after Frith 1985)
It has been suggested that initially we adopt two strategies. One strategy, widely suggested to be the first to develop in beginning readers, is the whole word, or logographic strategy. This refers to the way children learn to associate a spoken word with its written form, without showing any awareness of the sounds that each of the individual letters make. This strategy is often encouraged in early years classrooms where objects are labelled with their names and teachers use ‘flashcards’ to teach children a core ‘sight vocabulary’ of common words. This technique is useful in enabling children to build a large sight vocabulary quickly, which will enable them to begin reading with some degree of fluency. However, this approach places huge demands on visual memory and does not provide children with a strategy for coping with unfamiliar words.
To address these limitations, children also need an alphabetic decoding strategy. This requires them to learn the sounds that each letter of the alphabet makes, and then learn how to blend those sounds together during reading to work out how to pronounce the word. Alphabetic decoding is also needed during spelling to analyse spoken words and break them down into their corresponding letter sounds.
A skilled reader is one who moves beyond letter by letter decoding and rapidly processes longer ‘strings’ of letters that recur across different words (an orthographic strategy).
Did you notice how these strategies reflect what we know about reading processes from the acquired dyslexias?
The alphabetic decoding strategy draws heavily on phonological processing – both in the learning of letter-sound correspondences, and in the manipulation of those sounds during reading and spelling. People with dyslexia often find it difficult to move beyond a logographic strategy and problems with spelling usually persist into adulthood.
The severity of the phonological deficit is best demonstrated by the awareness of rhyme by children with dyslexia. Recognising that two words rhyme is a skill that most children acquire at an early age. However, studies have repeatedly shown that children with reading difficulties have trouble identifying words that rhyme (e.g. Bradley and Bryant, 1978). This is just one finding from a large literature showing that children with reading difficulties find it difficult to isolate and manipulate sounds in words.
What is still not clear is whether the phonological deficit is related to the encoding or retrieval of phonological representations in memory. While there is evidence of difficulties in processing phonological information in short-term memory, there is also speculation that the way this information is represented and stored in long-term memory could further explain the poor performance of people with dyslexia on phonological tasks.
Much of the research into phonological awareness and reading disability has centred on English-speaking children. However, this presents a misleading picture, as letter-sound correspondences in English are complex. Often, the same sound can be spelt a number of different ways (e.g. /f/ can be spelt f and ph), and the same letter can make a variety of different sounds (consider the sound that ‘a’ makes in ‘bat’, ‘part’ and ‘apron ’). Furthermore, it is not a simple case of one letter per sound: mouse has five letters but only three sounds: /m/ /au/ /s/. The phonological awareness deficit that has been demonstrated with English speakers may not be a universal characteristic of reading disability, as many other European languages have much more predictable letter-sound correspondences. Research into phonological deficits in other languages is ongoing, but there does seem to be evidence of phonological deficits in people with dyslexia (and at risk of dyslexia) who learn to read in more regular languages (see Courcy, Béland and Pitchford, 2000; Müller, Saarenketo and Lyytinen, 2000). It has also been suggested that measuring the speed of performance on tests may be a more universal indicator of reading difficulties across languages.
Almost all types of reading difficulty appear to be characterised by a phonological processing deficit, not just dyslexia. However, this does not mean that because it appears to have the same underlying cognitive deficit as other reading difficulties, dyslexia is the same as other types of reading difficulty. While the phonological processing deficit may ‘explain’ the reading and writing difficulties associated with dyslexia, it cannot account for the full range of behavioural symptoms that are observed, and that make dyslexia a distinctive condition. Other cognitive accounts are needed to explain the origins of the other behavioural symptoms of dyslexia. We have already proposed in the previous section that dyslexia can be thought of as consisting of several overlapping dimensions – it seems likely that a phonological deficit may be just one of several cognitive components associated with the condition. Moreover the phonological deficit hypothesis is exactly that, a hypothesis. While it has a good deal of empirical support, it is a theoretical proposal – but not something that we know definitely exists.
Developmental Dyslexia and the Cerebellum (Cerebellar Theory)
http://www.learningbreakthrough.com/learning-breakthrough-blog/entry/developmental-dyslexia-and-the-cerebellum-cerebellar-theory The learning breakthrough programme
Developmental Dyslexia and the Cerebellum (Cerebellar Theory)
- Hits: 584
- 0 Comments
- Subscribe to updates
- Bookmark
Dyslexia is a learning disorder that manifests itself as a difficulty with reading, spelling and in some cases mathematics. It is separate and distinct from reading difficulties resulting from other causes, such as a non-neurological deficiency with vision or hearing, or from poor or inadequate reading instruction. It is estimated that dyslexia affects between 5% and 12% of the U.S. population in some degree and is thought to be the result of a neurological defect/difference, and though not an intellectual disability, a language disability, among others. It is also worth noting that most dyslexics who have Boder's Dysiedetic type, have attentional and spatial difficulties which interfere with the reading acquisition process as well.
Visuospatial Cognition and Theories of Developmental Dyslexia:
When we look at a scene we feel that we perceive the visual world in all its detail and richness. This experienced quality and effortlessness of vision masks the fact that scene perception is actually a highly complex cognitive process, which requires the explorative scanning by eye movements, the quick and accurate direction of attention, the anticipation of the consequences of actions, and the integration and comparison of current visual input with stored representations of previously viewed parts of the scene and knowledge of objects and their relationships. A number of striking visual illusions demonstrate that scene perception is in fact a rather fragile process that essentially builds upon assumptions about the visual world to optimally piece together observations from a number of fields of scientific study.
The leading theories on the topic of developmental dyslexia should not be viewed as competing, but instead be seen as a complementary set of theories trying to explain the underlying causes of a similar set of symptoms but from a variety of research perspectives and backgrounds.
When we look at a scene we feel that we perceive the visual world in all its detail and richness. This experienced quality and effortlessness of vision masks the fact that scene perception is actually a highly complex cognitive process, which requires the explorative scanning by eye movements, the quick and accurate direction of attention, the anticipation of the consequences of actions, and the integration and comparison of current visual input with stored representations of previously viewed parts of the scene and knowledge of objects and their relationships. A number of striking visual illusions demonstrate that scene perception is in fact a rather fragile process that essentially builds upon assumptions about the visual world to optimally piece together observations from a number of fields of scientific study.
The leading theories on the topic of developmental dyslexia should not be viewed as competing, but instead be seen as a complementary set of theories trying to explain the underlying causes of a similar set of symptoms but from a variety of research perspectives and backgrounds.
Here is a great link for information on the history and theories of developmental dyslexia.
Cerebellar Theory:
One such theory that has gained note in the past decade is represented by the automaticity/cerebellar theory of dyslexia. Here the biological claim is that the cerebellum of people with dyslexia is mildly dysfunctional and that a number of cognitive difficulties ensue from this dysfunction.
One such theory that has gained note in the past decade is represented by the automaticity/cerebellar theory of dyslexia. Here the biological claim is that the cerebellum of people with dyslexia is mildly dysfunctional and that a number of cognitive difficulties ensue from this dysfunction.
For many years, developmental dyslexia was thought to be a problem related to language itself. However, with the arrival of neuroimaging tools and greater research into the relationship between dyslexia and balance, among other things, opinions began to shift. It has become clear to researchers that developmental dyslexia and the cerebellum are somehow related due to the function of the cerebellum matching the deficits in function associated with developmental dyslexia.
The cerebellum, more than many other areas of the brain, is engaged in processing and deciphering a constant series of "behind the scenes" events. It is forever multitasking in the background of our conscious mind. It is responsible for the sequencing of input, the automatization of tasks and skills, as well as the production and interpretation of verbal and written language. Since developmental dyslexia is defined by problems in these three exact areas, the hypothesis that the cerebellum was responsible, especially when coupled with revelatory neuroimaging studies, has gathered strength and wide acceptance as a promising area of study.
The cerebellum plays a critical role in overall brain function but has particular importance in reading and writing tasks. “Impairments of the cerebellum cause deficits in motor control such as posture and balance, and additional difficulties in achieving ‘automaticity’ of other learned skills” including skills that are related to reading and writing. The complicated issue is deciding where and how there is a “misfire” among neural pathways—a task that can be almost impossible without the use of sophisticated imaging equipment over a long span.
Dyslexia Treatment:
While these problems seem difficult to overcome and detection of the exact location of the impairment may never be known, this does not mean there are not options for those with developmental dyslexia. In fact, cerebellar dysfunction as a theory does not imply a sentence for those with developmental dyslexia to a life of failed reading attempts. With concentrated effort on refining the neural pathways in the cerebellum, along with the sensory connections from the cerebellum to the other critical informational processing centers in the brain, the brain’s natural plasticity can be taken advantage of to establish better neuro-processing to help overcome developmental dyslexia as well as other processing-based learning difficulties.
While these problems seem difficult to overcome and detection of the exact location of the impairment may never be known, this does not mean there are not options for those with developmental dyslexia. In fact, cerebellar dysfunction as a theory does not imply a sentence for those with developmental dyslexia to a life of failed reading attempts. With concentrated effort on refining the neural pathways in the cerebellum, along with the sensory connections from the cerebellum to the other critical informational processing centers in the brain, the brain’s natural plasticity can be taken advantage of to establish better neuro-processing to help overcome developmental dyslexia as well as other processing-based learning difficulties.
Nothing about the brain is static. It is always on, always at work; sending, receiving, responding, interpreting. Accordingly, it is always handling input, although this input or the pathways it travels on may not be “optimized” for adequate processing. Neurological issues like these underlie learning challenges and indicate that specific disabilities likedevelopmental dyslexia may be addressed simply… with vestibular-based brain training exercises like those available in the Learning Breakthrough Program.
Sources
Rochelle, K., & Talcott, J. (2006). Impaired balance in developmental dyslexia? A meta-analysis of the contending evidence. Journal of Child Psychology & Psychiatry, 47(11), 1159-1166.
Rochelle, K., & Talcott, J. (2006). Impaired balance in developmental dyslexia? A meta-analysis of the contending evidence. Journal of Child Psychology & Psychiatry, 47(11), 1159-1166.
Cyril R Pernet, Jean Baptiste Poline, Jean Francois Demonet and Guillaume A Rousselet: BMC Neuroscience (in press) – Brain classification reveals the right cerebellum as the best biomarker of dyslexia. http://www.biomedcentral.com/bmcneurosci/
dore website causes
http://www.dore.co.uk/learning-difficulties/dyslexia/what-causes-dyslexia/ website
http://www.dore.co.uk/case-studies/emily-halse/ case study
http://www.dore.co.uk/case-studies/emily-halse/ case study
causes of dyslexia
It’s generally agreed that dyslexia can ‘run in the family’. It might be there in your genes, but exactly how and if it will show itself varies considerably from individual to individual.
Sometimes dyslexia can be attributed to a wide range of environmental factors, like birth trauma, problems during pregnancy, brain injuries, infections and toxins. Extensive research has identified chromosome abnormalities linked to reading and spelling. However, although considerable progress has been made, the exact mechanism that causes genes to contribute to the multi-faceted dyslexic condition is still unknown.
Over years of continuous study, numerous hypotheses have been put forward to explain the causes of dyslexia, but currently the most credible theory is to do with ‘automaticity’ and a small, but very important part of the brain called the cerebellum – your ‘skill centre’. Scientific research has identified that the cerebellum plays a major role in the process of learning and automating of skills, so that we can perform tasks ‘without thinking’.
However, the efficiency of the cerebellum varies between individuals.
When the ‘skill centre’ is not working as efficiently as it should, it does not communicate adequately with all the major centres of the brain, especially the cerebrum – your ‘thinking centre’. If the whole cerebellum is affected, then the result is problems in making a whole range of skills, like reading, writing, concentration and coordination become fully automatic. It can also affect balance, so learning to ride a bike becomes more difficult. When even the most mundane tasks become a problem, frustration and low self-esteem set in and, with it, accompanying behavioural and emotional difficulties. However the cerebellum is not always wholly affected, so a mix of different symptoms is usually the case.
When the ‘skill centre’ is not working as efficiently as it should, it does not communicate adequately with all the major centres of the brain, especially the cerebrum – your ‘thinking centre’. If the whole cerebellum is affected, then the result is problems in making a whole range of skills, like reading, writing, concentration and coordination become fully automatic. It can also affect balance, so learning to ride a bike becomes more difficult. When even the most mundane tasks become a problem, frustration and low self-esteem set in and, with it, accompanying behavioural and emotional difficulties. However the cerebellum is not always wholly affected, so a mix of different symptoms is usually the case.
Improving the efficiency of the cerebellum is fundamental to the Dore programme’s treatment of dyslexia. It’s the focus of the personalised, exercise-based programme created for each and every Dore participant, designed to achieve greater responsiveness in the skill centre and develop the links between it and other parts of the brain. It takes perseverance, dedication and a good deal of effort, but the results are worth it – Take a look at some case studies of people who says that the Dore Programme has helped change their lifes forever.
Wednesday 21 November 2012
cognitive study
2008 S Heim et al. in a paper "Cognitive
subtypes of dyslexia" describe how they compared different sub-groups of
dyslexics in comparison with a control group. This is one of the first studies
not to just compare dyslexics with a non dyslexic control, but to go further and
compared the different cognitive sub groups with a non dyslexic control group.
read book online
http://www.amazon.co.uk/Dyslexia-Theory-Practice-Angela-Fawcett/dp/1861562101/ref=sr_1_1?s=books&ie=UTF8&qid=1353534688&sr=1-1
Neurobiology of dyslexia: a reinterpretation of the data
Neurobiology of dyslexia: a reinterpretation of the data
- a Laboratoire de Sciences Cognitives et Psycholinguistique (EHESS/CNRS/ENS), 46 rue d'Ulm, 75230 Paris Cedex 5, France
- b Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK
Theories of developmental dyslexia differ on how to best interpret the great variety of symptoms (linguistic, sensory and motor) observed in dyslexic individuals. One approach views dyslexia as a specific phonological deficit, which sometimes co-occurs with a more general sensorimotor syndrome. This article on the neurobiology of dyslexia shows that neurobiological data are indeed consistent with this view, explaining both how a specific phonological deficit might arise, and why a sensorimotor syndrome should be significantly associated with it. This new conceptualisation of the aetiology ofdyslexia could generalize to other neurodevelopmental disorders, and might further explain heterogeneity within each disorder and comorbidity between disorders.
Figures and tables from this article:
- Figure 1. Three causal models of the aetiology of developmental dyslexia. Ovals represent traits at the biological, cognitive and behavioural levels of description; arrows represent causal relationships between traits. Only a subset of all possible behavioural manifestations is represented. (a) Traits and relationships postulated by the phonological theory. (b) Traits and relationships postulated by the magnocellular theory. (c) The proposed model. Solid lines are used for core traits of developmental dyslexia, dashed lines for associated traits that are not necessarily present in each affected individual. Cases of comorbidity with other developmental disorders (e.g. specific language impairment) are not represented. Abbreviations: LGN, lateral geniculate nucleus; MGN, medial geniculate nucleus.
- Figure 2. A molecular layer ectopia in a dyslexic subject. Neurons and glia have escaped into the molecular layer of the cortex, through a breach in the external glial limiting membrane, to form an ectopia (between the two arrows). Scale bar, 250 μm. Micrograph kindly provided by Glenn D. Rosen.
- Figure 3. Neurobiology of developmental dyslexia. (a) Overall distribution of cortical ectopias observed across different dyslexic subjects (kindly provided by Glenn D. Rosen). (b) Brain areas activated in oral language tasks and exhibiting structural differences between dyslexics and controls. Areas in orange are supported by one published study, areas in red by more than one. Reproduced, with permission of Sage Publications, Inc., from Ref. [15]. (c) Brain areas activated during performance of the main phonological skills impaired in dyslexia: phonological awareness (yellow), rapid serial naming (red) and verbal short-term memory (blue). Reproduced, with permission, from Ref. [39].
Subscribe to:
Posts (Atom)