What was dylexia first thought to be
morgan (1896) congenital word blindness
problem of vision and inability to recall how words looked
how does the prevalence of dyslexia change across language
english -4-10%
changes as difficulty in comprehension changes - differences in orthographic consistencies
ie italian prevalence half that of USA
social impact of dyslexia
prevalent in disadvantaged
60% inmates
75% unemployed
85% juiveniles (43% 2 years below reading age and 38% below grade 4 reading age)
what is dyslexia
disorder manifested in difficulty of learning to read despite conventionl instruction, adequate intelligences and socio cultural opportunity
definition primarily focuses on exlusion
what is alexia
inability to read completely
heritability of dyslexia
40% sons with dyslexic fathers
36% daughter with dyslexic mother
50% chance if either parent
at risk 4x more likely to develop dyslexia than norm
gender issues in looking into dyslexia
more boys studied than girls creates bias
olson et al 1989 twin study and heritability of dyslexia
discrimination of words from homophonic nonwords (e.g., rane, rain) compared for pairs of older children with reading disabilities (RD) and younger non-disabled readers matched on word recognition
Phonological coding was substantially lower in RD- unique developmental deficit in phonological coding rather than an equal developmental lag across all component reading skill
RD highly heritable and accounted for most of the heritable variance in their word recognition deficits
describe frith and morton theortical framework
way of assessing influence of biology, cognition and behaviour on dyslexia
biology - brain
cognition - workings of mental components
behaviour - difficulties and observed performance
basic causal model of dyslexia (frith and morton)
biological origin leads to cognitive deficit which is expressed in deficits in behaviour
impacts of remedial teaching on dyslexia (frith and morton)
dyslexia appears to be improved by better teaching but does not make changes to cognition or biology
environmental change
environmental causation of dyslexia (frith and morton)
thought that no cog or bio abnormalities then dyslexia due to environment
ie poor teaching or socioeconomic factors
dyslexia and IQ
not link to IQ but use discrepancy diagnosis so easier to identify in average/above average children as not expected (but poor correlation between the two)
some argue shouldnt base diagnosis on discrepancy BUT may neglect individuals who are good in all other areas and then struggle later on
dysexia and development
developmental disorders change with age
definition of dyslexia is dependent on the underlying problem
diagnoiss also likley to change dependent on language and how to read
main theories of dyslexia
phonological defecit hypothesis (snowling 1995)
double deficit hypothesis (wolf and bowers 1999)
phonological vs surface subtypes (castles and coltheart 1993)
visual theories of dyslexia
magnocellular deficit hyp (stein and walsh 1007) visual attention span (bosse et al 2007) visual stress (wilkins 2002)
miscellaneous theories of dyslexia
cerebellar theory (nicholson and fawcett 1998/habib 2000)
define phonoligical deficit hyp
pa thought tp correlate with reading ability (reciprocal relationship)
wide range of evidence suggests that dyslexics are impaired on variety of PA tasks
ie phoneme deletion (cat without /k/)
phoneme counting and phoneme blending
not a strong case to be made for rhyme
awareness being a significant independent predictor of reading and spelling acquisitio ie not a strong case to be made for rhyme awareness being a significant independent predictor of reading and spelling acquisition.
how might phonological awareness be assessed
controversy
rhyme: what word doesnt rhyme with …
segmentation: what is cat without the c
BUT - may be mistaken for vision ie what word looks like without c
limits of phonological deficit hypothesis
phonology being mistaken for vision (segmentation)
GPC has visual basis where map sounds to letters so not fully phonological
ignores a working memory component ie ability to produce speach and ability to hear others
if base dyslexia on phonology then may neglect children with other problems
describe dyslexia subtypes (dual route) theory of dyslexia
the system
which skilled readers use to read involves at least two separate procedures, one
often referred to as the lexical procedure and the other as the sublexical
procedure.
dyslexia subtypes (dual route) phonological deficit
cant map sounds to letters (sublexical GPC)
cant read non words but can do exception/irregular words
fast but cant learn new well
dyslexia subtypes (dual route) surface deficit
specific problem with exception but not regular words
use sub lexical so overall reading difficulty and slower
errors in phonolohy and correct pronounciation
problem with subytpe dyslexia dual route
fails to specify exactly were the problem lies in the model
dyslexia and RAN tasks
rapid automised naming task
problems in speed and accuracy performance
RAN measure verbal fluency and speed of processing visually presented information
describe the double deficit hypothesis (wolf and bowers 1999)
children show problems in phonology and not RAN tasks
some in RAN and not phonology
some both (Statistically the worst readers)
mechanisms driving RAN not yet fully specified BUT thought cognitive deficits that lead to poor RAN affect reading by interfering with the quality of orthographic representations with the forming of links between orthographic and phonological representations that are crucial for reading.
thought to be more than one cause of reading difficulties and RAN thought to measure different processes from phonology
describe the magnocellular deficit hypothesis (stein and walsh 1977)
deficit in dorsal magnocellular visual system thought to be cause of dyslexia - evidence for deficit in magno cells during post mortem
magno - large eye movements/ dorsal - where, space and motion
produces a deficit in the processing of visual
information at low luminance, low spatial frequency and
high temporal frequency
psychophysical deficits in m cells caue problems reading ie difficulty telling black from white at low spatial freq
limits of magnocellular deficit hypothesis
not all studies show support
p cell ‘what’ venral stream deficit?
mechanisms unclear - all children thought to have poor movement/eye control
how does GPC link to magnocellular pathway?
treatments for magnocellular theory
training in convergence
omega 3 - boost myelination of visual pathways?
coloured glasses - not certainhow work but argues just as effective as other methods
phonoloigcal awareness theory treatments
toe by toe - slow process of learning GPC - requires intense resourcing and supervision jolly phonics sound linkage
comorbidity of dyslexia
link to motor problems, ADHD, specific language impairemnts (SLI)
wider social issues : the rose report 2009
emphasises the role of GPCs and synthetic phonics teaching for children
teachers strusyter to identify at risk children as opposed to screening strategy
PROBLEMS: not full understanding of dyslexia, some children not respond to all treatment and need LT and trivialises the disorder
NEED SPECIALIST TEACHERS
issues of dyslexia diagnosis
only diagnose via educational psychologist
assessment no solely reading (STM, motor coordination)
discrepancy vs delay - - GVPR likley to be diagnose as dyslexic but not discrepants
what is acquired dyslexia
dyslexia via brain damage
jyvaskyla 2012 longditudinal study of dyslexia
following the early development of children born at risk for dyslexia in finland
Familial risk for dyslexia is a strong predictor of difficulties in reading and spelling developmen - 4x more likely to develop dyslexia at end of grade 2 language development has been found to be linked to maternal supportive behaviour in play situations (Lyytinen et al., 2003b), maternal activating strategy (Laakso et al., 1999a), and to the amount of parent-child shared book reading (Torppa et al., 2007)
stanovich 1986 IQ and dyslexia
31% corr between reading and iq in normal pop
the children inthese samples should have small but pervasive cognitive deficits, because on one omnibus index of cognitive functioning (an intelligence
test) they show a small deficit. They are not the
extreme statistical outliers that the definitions of
reading disability imply
define phonological awareness
conscious awareness of the ability to manipulate the sounds within words
bradley and bryant 1983 PA
experiences with rhyme before school effect later success in learning to read and write
longitudinal study and an intensive training program in sound categorization - measured before read and then related to their progress in reading, spelling, and mathematics over 4 yrs
high correlations between initial sound categorization scores and Ss’ reading and spelling over 3 yr - even when IQ and memory ability controlled for.
+ This suggests that training in sound categorization is more effective when it also involves an explicit connection with the alphabet.
Castles and Coltheart 2004 PA review findings against b&b
b&b may measure phonemic awareness in addition to rhyme awareness (MacMillan, 2002).
This is because a child can potentially obtain the correct answer on many items, not by noticing that one word does not sound the same overall (a rhyme judgement), but by noticing that one word does not end in the same final sound (a phonemic judgement).
not a strong case to be made for rhyme
awareness being a significant independent predictor of reading and spelling acquisition.
dual route lexical surface route
involves retrieving, from a mental lexicon, the phonological form appropriate to a particular orthographic stimulus.
by definition, the mental lexicon contains only representations of real words which the reader has previously encountered- unable to read nonwords
dual route sublexical phonological route
using correspondence rules which specify relationships between submorphemic orthographic and phonological segments (e.g., GPC). Pronunciations are “assembled” from smaller orthographic components.
duces incorrect responses for
irregular or exception words, like yacht, as these words disobey the correspondence
rules
holmes 1973 surface dyslexia case study
CD, was a 17-year-old girl with an IQ exceeding 100 but a reading age of only 10 years
Her reading performance closely resembled that of acquired surface dyslexics - more successful at reading aloud regular words than irregular words and made
frequent regularisation errors.
The authors attributed her performance to a selective difficulty in using the lexical procedure and so justified the use of the term developmental surface dyslexia to describe her condition.
Temple and Marshal 1982 phonological dyslexia case study
HM a 17-year-old girl of average intelligence and with a reading age of around 10 years.
She could read aloud both regular and irregular words quite well, but performed very poorly on nonwords and rare words.
Her responses to the nonwords contained word components, suggesting that she used real word analogies in attempting to pronounce them.
HM had a specific difficulty in using the sublexical procedure and that her condition was therefore analogous to acquired phonological dyslexia.
Powell et al 2007 Double Deficit
assessed RAN, phonological awareness, and reading performance in 1010 7- to 10-year-olds
RAN deficits occurred in the absence of phonological awareness deficits
Children with single
RAN deficits showed slower speed of processing than did closely matched controls performing normally
on RAN. However, regression analysis revealed that RAN made a unique contribution to reading
even after accounting for processing speed
livingstone et al 1991 magnocellular deficit
recoreded VEP in normal and dyslexic subjects
dyslexic appear to show delay/deficit of neg evoked potential
thought to relate to magnocellular system
+ post mortem show - magnocall more disorganised, smaller cells which may lead to deficit
define parvocellular deficit hypothesis
deficit at high luminance, high spatial frequency
and low temporal frequency
whitney and Cornelissen 2005
deficits of pa may be a symptom>cause, of dyslexia -dyslexia results from the failure to form normal grapheme-phoneme associations
reading acquisition itself creates a phonemic representation, via ‘graphoneme’: linkages of graphemes to groups of phonetic features - phonemic encoding depends on a linkage to orthography.
the inability of dyslexics to perform phonological-awareness tasks would indicate the
absence of graphonemic representations