dyslexia Flashcards
what is dyslexia
Dyslexia is a developmental condition associated with poor reading
Continuous rather than categorical
Heritable bases but pathway from genes → brain → behaviour not clear
Characterised by phonological weaknesses
A continuous trait and multiple risk factors likely to be implicated.
how can we explain dyslexia at the biological level
Genetic basis of dyslexia
Higher concordance between MZ than DZ twins (olson et al., 2004)
Gene markers for dyslexia identified on number of chromosomes e.g., 6, 15 and 18 (Scerri, et al., 2011)
Large number of genes, each of very small effect
Dyslexia and the Brain
Sometimes structural atypicalities e.g perisylvian regions (Broca’s and Wrnicke’s)
Many experiments observed functional differences during processing
how can we explain dyslexia at the cognitive level
the phonological deficit hypothesis
Dysleciv children have difficulty processing the sound structure of spoken language (phonology)
Particularly important in reading in alphabetic systems
Therefore they will have difficult on any task that depends on phonological skills including reading and spelling
Remains the strongest cognitive-level hypothesis
Good evidence for phonological deficits across the lifespan from at-risk babies through to ‘resolved’ adults; reciprocal influences
What exactly is ‘a phonological deficit’ and what causes it? And is it necessary and sufficient as a cause?
Can’t be seen in a vacuum: from single deficit to multiple risk models
what evidence do Dyslexia Marshall, et al. 2001 provide for reduced phonological awareness in dyslexics
Ability to reflect on (metacognition) and manipulate sounds in spoken words
Asked dyslexic children and age matched controls to participate in a odd-one-out rhyme task (spoken), phoneme deletion task (e.g say bass without the b sound)
Dyslexic children perform worse than controls on both tasks, particularly on the phonemic task
what do meta-analyses of phonological awareness with dyslexics and control show Melby-Lerväg, et al., 2012
Age matched controls and reading level matched controls
Lower phonological awareness than both age and reading level controls
Difficulty with phonological awareness not a simple consequence of lack of reading
what were the resuklts of Nation et al.’s 2001 picture naming study
dyslexic children were slower and more error prone particularly under the stress of low frequency, phonologically complex words
what did Snowling et al.’s word and nonword repeition study highlight
dyslexic children make more errors than controls and are particulalry poor at repeating non words
what is an impaired phonological representation theorised to affect in dyselxia
verbal STM nonword repetion phonological awareness phonological learning nam retrieval
what does Paulesu et al.’s 1996 PET study show
irst PET study comparing dyslexics and controls on phonological processing tasks Adult participants (undergraduates at UCL - so reading developed ‘well enough’ to support such learning) Differences in brain signatures indicating verbal STM and rhyming tasks may be passed by recruiting different brain areas (more effortful processing?)
how does the phonological hypothesis link to the alphabetic principal and triangle model
he Alphabetic Principle
Learning to read is paved by sound
Learning to decode
Learning to read requires connections between orthography and phonology
Once an ‘expert’ we jump from orthography to semantics
Phonological ability influences how easy it is to map between O and P
Given dyslexics have poor P; learning O→ P is difficult
Non-word readings are a good test of this ability as it requires the ability to apply alphabetical principle
what did Snowling et al., 1980 reveal about decoding in dyslexia
Longitudinal study following dyslexics and controls over time, measuring non-word reading
Most direct assessment of decoding is nonword
Standard finding is that dyslexics worse at reading nonwords than RA controls
Nonword deficits often persist into adulthood - don’t show improvement with development
what were the nature of spelling errors in JM
don’t capture sound
16% phonetic
18% semi-phonetic
66% dysphonetic
how do Harm & Seidenberg (1999) model dyslexia
Dyslexic children come to the task of learning to read with poorly specified phonological representations
This impacts on the quality of mappings between orthography and phonology
Degrading phonological representation in the network models dyslexic reading (nonword deficits)
what do Gallagher et al.’s 2000 family at risk study show about the direction of causality of phonological deficits
63 at-risk children recruited at 45 months, plus controls
At age 6 years, 57% of at-risk children were delayed in literacy development
At 45 months
Unimpaired group equivalent to controls on most measures
but less good at nursery rhyme knowledge, letter knowledge and digit span (verbal STM); mild phonological deficits
Impaired group showed a range of verbal deficits
Phonological skills and alphabet knowledge, but also vocabulary and expressive syntax
Phonological deficit pre-dates reading problem development and evidence for a broader phenotype (language beyond phonology)
what environmental factors explain the deficits seen in dyslexia
Environmental effects: language differences
Alphabetic languages differ in their regularity
Shallow orthographies have consistent letter-sound mappings e.g italian, german, greek
Deep orthographies have inconsistent letter-sound correspondences e.g english, danish, french
English is difficult to learn, it takes longer and the manifestations of dyslexia are more obvious
e.g Case AS bilingual japanese-english; monolingual dyslexic (Wydell et al., 1999)
