Learning Disabilities:
A Neuro-Behavioural Approach
Book: Developmental disorders of language learning and cognition
(Hulme & Snowling, 2009)
H1 – Understanding developmental cognitive disorders
Difference between:
- Specific difficulties: a deficit in one or some cognitive abilities, e.g. dyslexia
o In the UK: specific learning difficulty
o In the US: learning disorders (DSM-IV)
- General difficulties: deficits in most or all cognitive abilities, e.g. people with Down syndrome
o In the US: mental retardation
The distinction between these two disorders is often based off on IQ scores. The average IQ is 100
with a standard deviation of 15. The UK has 2 categories of learning difficulties based on IQ
(moderate and severe), and the US has 4: mild, moderate, severe and profound. A classification of a
specific learning disorder is given if a child has an IQ of > 80.
There are different levels of explanation in understanding developmental disorders: a biological,
cognitive and behavioral approach. Additionally at all these levels there is an interaction with the
environment, on the biological level this is called: gene-environment interaction. Morton and Frith
suggest that it is helpful to create diagrams of these explanations (causal modeling). Arrows in these
diagrams show potential causal relationships and can go back and forth between the different levels.
For example, genes have an influence on behavior and behavior can alter the expression of genes.
2 ways of examining the genetic basis of a disorder
- Population genetic study: investigating inheritance of disorders. This is based on the idea that
people with similar genes are expected to also show similar characteristics. These studies use
monozygotic and dizygotic twins.
- Molecular genetic study: identifying genes related to a disorder. This is done by searching for
genes of two closely related people with the same disorder, and relatives without the disorder
do not have these genes.
fMRI and PET are two techniques to study the activity of the brain. These methods detect fluctuations
in blood flow in the brain during a task or resting state (no task). The blood flow is an indication of the
amount of oxygen sent to a brain region, which is needed for brain activity. This method gives a good
indication of the location of the activity.
EEG and MEG are two other methods for measuring brain activity, they have a better temporal
resolution than fMRI and PET. This means that EEG and MEG are more precise in determining when
certain brain areas are active. However, the location of the activity is less accurate than in fMRI and
PET. EEG is a method based on measuring voltage changes due to firing of groups of neurons. MEG
measures magnetic fields generated by the electrical activity of the brain.
The human brain is considered to be a modular system which consists of several subsystems executing
different functions. This theory has been investigated in research which examined brain lesions and
the associated cognitive impairments. An example is that separate systems in the brain are responsible
for hearing and vision: blind people can hear and deaf people can see. This is called double
dissociation, and considered to be good evidence of modularity. However, establishing the presence of
cognitive subsystems trough double dissociation is controversial and complex. This is especially the
,case for higher cognitive abilities. The brain can create modules through learning, e.g. reading and
writing, because these are not innate abilities.
Most disorders discussed in this book are best classified as delays in development, at least in early
development. Children with a learning disorder are not incapable of learning, it is just that their skills
have not yet developed properly. Their capabilities are comparable to a younger child.
This may be related to critical periods in development in which children should learn certain abilities
or otherwise acquiring these skills will be very hard. However, empirical evidence for this hypothesis
is not strong. Still it seems plausible that there is a decrease in the simplicity to learn cognitive skills as
one gets older.
Cross-sectional studies investigate people at one point in time, this gives information about a certain
moment during development. Longitudinal studies investigate the same people over a longer period of
time, this provides information about how people change during development. This has an advantage
over cross-sectional studies because it gives more insight into the direction of a possible causal
relationship. Additionally, interventions/ experiments are needed to confirm a causal relationship.
However, longitudinal studies have some disadvantages: they take up a lot of time, cost a lot of money
and are hard to conduct.
Case-control study: a group of children with a disorder is compared with a group of children without
the disorder, at a given point in time. One type of control group is the chronological age (CA) group.
This group has kids of the same age (and sometimes also the same gender, school setting and IQ). It
gives information about if a clinical group has deficits on a task in relation to their age (do they
perform the same as peers?). Deficits could indicate a possible cause for the disorder/clinical
symptoms. However, a limitation of this method is that the observed deficit may be the consequence
of the disorder rather than a cause. To solve this, a younger typically developing group matched on
performance on a certain task/ability can be used. This is called an ability matched control group and it
eliminates possible influence of pre-existing ability differences between the groups on the outcome.
A correlation is the first indication of a causal relationship between two variables. However, a
correlation does not give information about the direction of the relationship and whether or not more
variables are associated to this relationship.
Distal cause: underlying factor related to the outcome variable
Proximal cause: variable which is closest to the outcome variable
When is a correlation likely to show a cause of a disorder?
- A cause needs to be an antecedent of the outcome: the cause was present before the
development of the disorder
- Universality: Does the deficit occur in most or all cases of the disorder?
- Power: Do variations in the severity of the deficit correlate with the severity of the disorder?
- Specificity: Is this deficit only found in this disorder?
- Theoretical plausibility: a theory of how a cause can lead to a disorder must be made when
there is a strong correlation
A correlation can never “prove” a causal relationship, an experiment can. This is however difficult to
implement in developmental studies due to ethical and methodological issues.
A theory about a cognitive deficit causing a disorder can lead to the development of an intervention
targeting this cognitive aspect. Then children classified with the disorder can be randomly assigned to
receive the just now developed intervention or another type of intervention. If the developed
intervention improves the cognitive ability, then this is strong evidence for a cognitive cause of the
disorder. This kind of studies come as close to determining causes of a disorder as we can.
,Comorbidity: different disorders are present in one person or child. It can be that one disorder leads to
the development of another or that impaired brain development led to different effects on cognitive
development.
H2 – Reading disorders I: Developmental Dyslexia
Different reading skills:
- Reading accuracy is measured by asking kids to read a list of words aloud
- Reading comprehension is measured by giving kids a passage to read and then asking them
questions about the text to assess what they have understood
Dyslexia defined by Lyon, Shaywitz and Shaywitz (2003): Dyslexia is a specific learning disability of
neurobiological origin. It is characterized by difficulties with accurate and/or fluent word recognition
and poor spelling. These difficulties result from a deficit of the phonological component of language.
More boys than girls are affected by dyslexia, and it persists into adulthood in different manifestations.
Dyslexia has comorbidity with language impairment, ADHD, developmental coordination disorder,
and difficulties in mathematical cognition.
Normal reading development
1. Making arbitrary associations between printed words and pronunciations (logographic stage)
2. Understanding of systematic relationships between letter sequences in printed words and
sounds which represent the letters
3. Reading becomes more rapid and effortless, depending on representations of relationships
between print, sound, and meaning
many models of reading development follow this path of development, but have different names for
the different stages, see below.
3 mostly used models of reading development (benoemd in laatste college dat we in ieder geval deze
moesten weten):
- Chall (1983):
o Stage 0: letters and book exposure
o Memory and contextual guessing
o Stage 1: decoding attending to letters and sounds
o Stage 2: fluency, consolidation
- Frith (1985)
o Logographic
o Alphabetic
o Orthographic
- Ehri (1998)
o Pre-alphabetic
o Partial alphabetic
o Full alphabetic
o Consolidated alphabetic, automaticity
There is a lot of literature showing that there is a strong relationship between phonological awareness
prior to reading instruction and later reading achievement. Additionally, phoneme awareness and letter
knowledge are critical foundations for the development of reading skills in children just entering
school.
The ease with which children learn to read in different languages varies according to the transparency
of the mappings between letters and sounds in the orthography. In transparent languages the mappings
are straightforward: regular sound-spelling correspondence. In transparent languages children learn to
read more easily than less transparent languages such as English.
, Typically seen difficulties in dyslexia
- Problems learning letter names and sounds (deficit in phonological learning)
- Difficulties with reading single words (no help from context)
- Struggles with reading aloud, but understand the passage well
- Learning to spell is more difficult than learning to read
- Difficulty with reading non words (e.g. zot or pim)
Cognitive explanations of dyslexia
Best developed theory of dyslexia is that it arises from a phonological deficit. 2 claims of this theory:
- A phonological deficit exists before children with dyslexia learn to read
- The severity of the phonological deficit will predict the severity of the reading difficulties
Evidence for phonological deficits can be split into:
- Phonological awareness: ability to make explicit judgements about the sound structure of
spoken words, e.g. kids with dyslexia have difficulty generating words to rhyme with a word
- Phonological processing: using speech without necessarily reflecting upon the structure of
spoken words, e.g. repeating a (non-)word, naming a picture or remembering a list of words
Possible alternative causes of dyslexia (not well supported by empirical evidence)
- Auditory or speech perceptual deficits effecting phonological skills
- Automatization/ Cerebellar Deficit Theory: difficulties on dual tasks involving motor skills
(e.g. balancing and counting at the same time)
- Visual perceptual/attentional deficit theory: problems in visual perceptual or attentional
processes could contribute to causing problems in learning to read
Etiology of dyslexia
Genetic level: A number of gene markers and a candidate gene are identified as associated with
dyslexia.
Environmental risk factors:
- Dyslexia is more common in kids from poorer SES households
- Exposure to printed text has an influence on development of reading skills
Neurobehavioral level: Structural and functional differences in various left hemisphere brain systems
involved in speaking and reading
Treatment
Systematic phonic teaching combined with phonological awareness training, especially sound-linkage
exercises, are helping to overcome reading difficulties in dyslexia. These interventions can also serve
as prevention of reading difficulties in kids at risk. However, overcoming, or preventing reading
problems in dyslexia requires many hours of highly skilled and intensive training.
H3 – Reading disorders II: Reading Comprehension impairment
Poor comprehenders can read accurate and fast, however they experience problems with
understanding the text. This group has been studied less than children with dyslexia. The prevalence
seems to be dependent on variation in school setting, with less poor comprehenders in schools in better
developed areas, and the type of comprehension test used (sometimes the comprehension questions
can be answered based on general knowledge without understanding the text).
2 comprehension tests:
- Neale Analysis of Reading Ability: testing knowledge about text and usage of cohesive
inferences (required to make links between various parts of the text)
o Mostly used in the UK
- Wechsler Objective Reading Dimensions (WORD): examines the skill to make elaborative
inferences (add information from outside of the text)
A Neuro-Behavioural Approach
Book: Developmental disorders of language learning and cognition
(Hulme & Snowling, 2009)
H1 – Understanding developmental cognitive disorders
Difference between:
- Specific difficulties: a deficit in one or some cognitive abilities, e.g. dyslexia
o In the UK: specific learning difficulty
o In the US: learning disorders (DSM-IV)
- General difficulties: deficits in most or all cognitive abilities, e.g. people with Down syndrome
o In the US: mental retardation
The distinction between these two disorders is often based off on IQ scores. The average IQ is 100
with a standard deviation of 15. The UK has 2 categories of learning difficulties based on IQ
(moderate and severe), and the US has 4: mild, moderate, severe and profound. A classification of a
specific learning disorder is given if a child has an IQ of > 80.
There are different levels of explanation in understanding developmental disorders: a biological,
cognitive and behavioral approach. Additionally at all these levels there is an interaction with the
environment, on the biological level this is called: gene-environment interaction. Morton and Frith
suggest that it is helpful to create diagrams of these explanations (causal modeling). Arrows in these
diagrams show potential causal relationships and can go back and forth between the different levels.
For example, genes have an influence on behavior and behavior can alter the expression of genes.
2 ways of examining the genetic basis of a disorder
- Population genetic study: investigating inheritance of disorders. This is based on the idea that
people with similar genes are expected to also show similar characteristics. These studies use
monozygotic and dizygotic twins.
- Molecular genetic study: identifying genes related to a disorder. This is done by searching for
genes of two closely related people with the same disorder, and relatives without the disorder
do not have these genes.
fMRI and PET are two techniques to study the activity of the brain. These methods detect fluctuations
in blood flow in the brain during a task or resting state (no task). The blood flow is an indication of the
amount of oxygen sent to a brain region, which is needed for brain activity. This method gives a good
indication of the location of the activity.
EEG and MEG are two other methods for measuring brain activity, they have a better temporal
resolution than fMRI and PET. This means that EEG and MEG are more precise in determining when
certain brain areas are active. However, the location of the activity is less accurate than in fMRI and
PET. EEG is a method based on measuring voltage changes due to firing of groups of neurons. MEG
measures magnetic fields generated by the electrical activity of the brain.
The human brain is considered to be a modular system which consists of several subsystems executing
different functions. This theory has been investigated in research which examined brain lesions and
the associated cognitive impairments. An example is that separate systems in the brain are responsible
for hearing and vision: blind people can hear and deaf people can see. This is called double
dissociation, and considered to be good evidence of modularity. However, establishing the presence of
cognitive subsystems trough double dissociation is controversial and complex. This is especially the
,case for higher cognitive abilities. The brain can create modules through learning, e.g. reading and
writing, because these are not innate abilities.
Most disorders discussed in this book are best classified as delays in development, at least in early
development. Children with a learning disorder are not incapable of learning, it is just that their skills
have not yet developed properly. Their capabilities are comparable to a younger child.
This may be related to critical periods in development in which children should learn certain abilities
or otherwise acquiring these skills will be very hard. However, empirical evidence for this hypothesis
is not strong. Still it seems plausible that there is a decrease in the simplicity to learn cognitive skills as
one gets older.
Cross-sectional studies investigate people at one point in time, this gives information about a certain
moment during development. Longitudinal studies investigate the same people over a longer period of
time, this provides information about how people change during development. This has an advantage
over cross-sectional studies because it gives more insight into the direction of a possible causal
relationship. Additionally, interventions/ experiments are needed to confirm a causal relationship.
However, longitudinal studies have some disadvantages: they take up a lot of time, cost a lot of money
and are hard to conduct.
Case-control study: a group of children with a disorder is compared with a group of children without
the disorder, at a given point in time. One type of control group is the chronological age (CA) group.
This group has kids of the same age (and sometimes also the same gender, school setting and IQ). It
gives information about if a clinical group has deficits on a task in relation to their age (do they
perform the same as peers?). Deficits could indicate a possible cause for the disorder/clinical
symptoms. However, a limitation of this method is that the observed deficit may be the consequence
of the disorder rather than a cause. To solve this, a younger typically developing group matched on
performance on a certain task/ability can be used. This is called an ability matched control group and it
eliminates possible influence of pre-existing ability differences between the groups on the outcome.
A correlation is the first indication of a causal relationship between two variables. However, a
correlation does not give information about the direction of the relationship and whether or not more
variables are associated to this relationship.
Distal cause: underlying factor related to the outcome variable
Proximal cause: variable which is closest to the outcome variable
When is a correlation likely to show a cause of a disorder?
- A cause needs to be an antecedent of the outcome: the cause was present before the
development of the disorder
- Universality: Does the deficit occur in most or all cases of the disorder?
- Power: Do variations in the severity of the deficit correlate with the severity of the disorder?
- Specificity: Is this deficit only found in this disorder?
- Theoretical plausibility: a theory of how a cause can lead to a disorder must be made when
there is a strong correlation
A correlation can never “prove” a causal relationship, an experiment can. This is however difficult to
implement in developmental studies due to ethical and methodological issues.
A theory about a cognitive deficit causing a disorder can lead to the development of an intervention
targeting this cognitive aspect. Then children classified with the disorder can be randomly assigned to
receive the just now developed intervention or another type of intervention. If the developed
intervention improves the cognitive ability, then this is strong evidence for a cognitive cause of the
disorder. This kind of studies come as close to determining causes of a disorder as we can.
,Comorbidity: different disorders are present in one person or child. It can be that one disorder leads to
the development of another or that impaired brain development led to different effects on cognitive
development.
H2 – Reading disorders I: Developmental Dyslexia
Different reading skills:
- Reading accuracy is measured by asking kids to read a list of words aloud
- Reading comprehension is measured by giving kids a passage to read and then asking them
questions about the text to assess what they have understood
Dyslexia defined by Lyon, Shaywitz and Shaywitz (2003): Dyslexia is a specific learning disability of
neurobiological origin. It is characterized by difficulties with accurate and/or fluent word recognition
and poor spelling. These difficulties result from a deficit of the phonological component of language.
More boys than girls are affected by dyslexia, and it persists into adulthood in different manifestations.
Dyslexia has comorbidity with language impairment, ADHD, developmental coordination disorder,
and difficulties in mathematical cognition.
Normal reading development
1. Making arbitrary associations between printed words and pronunciations (logographic stage)
2. Understanding of systematic relationships between letter sequences in printed words and
sounds which represent the letters
3. Reading becomes more rapid and effortless, depending on representations of relationships
between print, sound, and meaning
many models of reading development follow this path of development, but have different names for
the different stages, see below.
3 mostly used models of reading development (benoemd in laatste college dat we in ieder geval deze
moesten weten):
- Chall (1983):
o Stage 0: letters and book exposure
o Memory and contextual guessing
o Stage 1: decoding attending to letters and sounds
o Stage 2: fluency, consolidation
- Frith (1985)
o Logographic
o Alphabetic
o Orthographic
- Ehri (1998)
o Pre-alphabetic
o Partial alphabetic
o Full alphabetic
o Consolidated alphabetic, automaticity
There is a lot of literature showing that there is a strong relationship between phonological awareness
prior to reading instruction and later reading achievement. Additionally, phoneme awareness and letter
knowledge are critical foundations for the development of reading skills in children just entering
school.
The ease with which children learn to read in different languages varies according to the transparency
of the mappings between letters and sounds in the orthography. In transparent languages the mappings
are straightforward: regular sound-spelling correspondence. In transparent languages children learn to
read more easily than less transparent languages such as English.
, Typically seen difficulties in dyslexia
- Problems learning letter names and sounds (deficit in phonological learning)
- Difficulties with reading single words (no help from context)
- Struggles with reading aloud, but understand the passage well
- Learning to spell is more difficult than learning to read
- Difficulty with reading non words (e.g. zot or pim)
Cognitive explanations of dyslexia
Best developed theory of dyslexia is that it arises from a phonological deficit. 2 claims of this theory:
- A phonological deficit exists before children with dyslexia learn to read
- The severity of the phonological deficit will predict the severity of the reading difficulties
Evidence for phonological deficits can be split into:
- Phonological awareness: ability to make explicit judgements about the sound structure of
spoken words, e.g. kids with dyslexia have difficulty generating words to rhyme with a word
- Phonological processing: using speech without necessarily reflecting upon the structure of
spoken words, e.g. repeating a (non-)word, naming a picture or remembering a list of words
Possible alternative causes of dyslexia (not well supported by empirical evidence)
- Auditory or speech perceptual deficits effecting phonological skills
- Automatization/ Cerebellar Deficit Theory: difficulties on dual tasks involving motor skills
(e.g. balancing and counting at the same time)
- Visual perceptual/attentional deficit theory: problems in visual perceptual or attentional
processes could contribute to causing problems in learning to read
Etiology of dyslexia
Genetic level: A number of gene markers and a candidate gene are identified as associated with
dyslexia.
Environmental risk factors:
- Dyslexia is more common in kids from poorer SES households
- Exposure to printed text has an influence on development of reading skills
Neurobehavioral level: Structural and functional differences in various left hemisphere brain systems
involved in speaking and reading
Treatment
Systematic phonic teaching combined with phonological awareness training, especially sound-linkage
exercises, are helping to overcome reading difficulties in dyslexia. These interventions can also serve
as prevention of reading difficulties in kids at risk. However, overcoming, or preventing reading
problems in dyslexia requires many hours of highly skilled and intensive training.
H3 – Reading disorders II: Reading Comprehension impairment
Poor comprehenders can read accurate and fast, however they experience problems with
understanding the text. This group has been studied less than children with dyslexia. The prevalence
seems to be dependent on variation in school setting, with less poor comprehenders in schools in better
developed areas, and the type of comprehension test used (sometimes the comprehension questions
can be answered based on general knowledge without understanding the text).
2 comprehension tests:
- Neale Analysis of Reading Ability: testing knowledge about text and usage of cohesive
inferences (required to make links between various parts of the text)
o Mostly used in the UK
- Wechsler Objective Reading Dimensions (WORD): examines the skill to make elaborative
inferences (add information from outside of the text)
