nyborg causes2
DESCRIPTION
What causes language impairment in children?Talk given atTRANSCRIPT
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What causes language disorders
in children?
Dorothy Bishop
University of Oxford
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Specific language impairment (SLI)
Diagnosed in children when language does not follow normal developmental course
Problems with language structure (phonology and syntax) common
Not due to hearing loss, physical abnormality, acquired brain damage
Normal development in other areas
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What causes SLI?
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Theory 1: inadequate input
x
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http://news.bbc.co.uk/1/hi/education/2638889.stm
Thursday, 9 January, 2003, 11:15 GMT
Daily grunt parents hold children back
Not enough talking going on
Parents who do little more than grunt at their children every day are
damaging their language development, a literacy expert has said.
Alan Wells, director of the Basic Skills Agency, says parents no
longer talk to their children and instead just let them sit in front of
the television or computer for hours.
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How plausible is poor language
environment as cause of SLI?
• All agree that to learn a language must hear that language – Danish children learn Danish, English children learn English!
• “Motherese” seen in many (?all) cultures – special way of talking to infants
• Correlations between maternal language and children’s language development
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Correlation ≠ Causation
Mother’s talk Child’s talk Direct causation
Child’s talk Mother’s talk Evocation
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Evidence for evocative effect
• Huttenlocher et al (2007) • Study of 50 families, diverse SES
• Measured quantity, complexity, diversity of parental language to child
• Quantity did not change with child’s age
• Complexity and diversity increased with child’s age
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Correlation ≠ Causation
Mother’s talk Child’s talk
Child’s talk Mother’s talk
Factor X Mother’s talk
Child’s talk
Direct causation
Evocation
Non-causal association
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Evidence for non-causal
association
• Twins growing up together • MZ, genetically identical
• DZ, non-identical
• If parental language input was important, would expect twins to be similar, regardless of whether MZ or DZ
• For many measures, DZ less similar than MZ
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0 0.2 0.4 0.6 0.8
Bus story info*
Action picture
grammar
BAS
Comprehension
Word
Knowledge*
Verbal fluency*
Verbal memory*
Phon
awareness*
GF articulation
Nonword
repetition*
MZ DZTwin-twin
correlations
* Indicates no
evidence of
environmental
influence
Kovas Y, et al. (2005) Genetic influences in different aspects of language development: The etiology of
language skills in 4.5 year-old twins. Child Dev 73: 632-651.
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Hearing children of deaf parents
• Schiff-Myers (1988) • Either hear no oral
language from parents, or hear limited syntax, abnormal articulation/prosody
• Some learn sign as first language
• Variable outcomes, but many have no problems with speech and language
• About 5-10 hr per week exposure to normal speakers seems sufficient
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Theory 2: inadequate speech
perception
x x
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Otitis media with effusion
• Middle ear fills with fluid
• Very common in young children
• Causes fluctuating conductive hearing loss
Healthy
tympanic
membrane
Chronic
otitis media
Otitis media
treatment -
tympanic
membrane hole
or perforation
with a ventilator
tube in place
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Otitis media with effusion (OME)
• Early studies found more language problems in children with OME
• But problem of ascertainment bias • Parent more likely to go to doctor if
child has language problems
• Doctor more likely to recommend treatment if child has language problems
• Children treated for OME not a typical sample
• Epidemiological studies: look at whole population – less evidence of language problems
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Theory 3: early brain damage
x
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Is brain damage implicated?
• Early idea of “continuum of reproductive casualty” - i.e. brain damage incurred around time of birth might lead to learning disabilities
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Evidence against brain damage as
cause of SLI
• Children with very low birthweight do have increase in all neurodevelopmental disorders, including language
• But, no obvious signs of neurological impairment in most cases of SLI
• And no excess of perinatal problems in SLI
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1000 children
10 LBW 990 OK
45
SLI
945
OK
5
SLI
5
OK
1% low birthweight 5%
have SLI
50%
SLI
SLI
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Evidence against brain damage as
cause of SLI
• Children who do have focal lesions affecting the language areas don’t develop SLI - see Basser 1962!
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Theory 4: abnormal neurodevelopment
x x x x
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Clark & Plante, 1998
• 20 biological parents of language impaired children 15 had evidence of residual language
difficulties
• 21 unrelated adult controls 4 had evidence of residual language
difficulties
• MRI scan of inferior frontal gyrus
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IFS: inferior frontal sulcus
AAR: anterior ascending ramus
AHR: anterior horizontal ramus
PCS: precentral sulcus
from Clark and Plante. 1998 Brain and Language 61, 288-303
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Clark & Plante, 1998
N with extra sulcus (either side):
• With +ve family history Parent has typical language: 5/10 = 50%
Parent has language problems: 20/30 = 67%
• With no family history Parent has typical language: 13/34 = 38%
Parent has language problems: 6/8 = 75%
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Clark & Plante, 1998
Conclusions
• Suggests prenatal event has systemic effect on developing brain
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Study of SLI using brain scanning
Kate Watkins
• Oxford study of children with SLI and
their families
• No gross differences seen in the brain
• Subtle differences in language areas in
distribution of grey matter
• Less activation of language areas
when doing a language task
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VBM Grey Matter
SLI vs. Typical
Left
IFG
Left
IFG
STS STS
Caudate
Nucleus
More grey matter in left inferior frontal gyrus in SLI
Badcock et al, 2012
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Covert Naming Task
Speech Backwards
Speech Silence
“bees make it” Hears
Thinks “honey”
8 children with SLI; 6 unaffected siblings; 13 control children;
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Activation to Covert Naming
During covert auditory naming, SLI group show reduced activity in left IFG
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Genetics
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SLI: Family aggregation
Rates of language/learning difficulties higher in relatives of those with SLI, compared with controls
0
10
20
30
40
50
Neils,
1986
Bishop,
1986
Tallal,
1989
Tomblin,
1989
% affected
relatives
SLI control
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SLI: Family aggregation
Rates of language/learning difficulties higher in relatives of those with SLI, compared with controls
0
10
20
30
40
50
Neils,
1986
Bishop,
1986
Tallal,
1989
Tomblin,
1989
% affected
relatives
SLI control
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DZ twins: share 50% of polymorphic
genes
Question:
Is concordance for disorder higher
in MZ than in DZ twins?
Twin Study Method
MZ twins: genetically identical
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Twin studies of SLI
Probandwise
concordance:
same-sex twins
MZ DZ
Lewis & Thompson, 1992 .86 .48
Bishop et al, 1995 .70 .46
Tomblin & Buckwalter, 1998 .96 .69
Hayiou-Thomas et al, 2005 .36 .33
Bishop & Hayiou-Thomas, 2008 .87 .40
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conclude……..
• Evidence for substantial genetic influence on SLI
• But lots of questions remain:
• Which types of SLI are heritable, or not?
• Can SLI be caused by a single gene?
• Should we treat SLI as a single condition?
• Is there genetic overlap between SLI and dyslexia and/or autism
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Single gene disorder: KE family
Hurst et al, 1990; Gopnik, 1990;
Vargha-Khadem et al, 1995
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KE family – a distinct type of SLI
• Distinctive clinical picture • Severe oromotor dyspraxia
• Facial dysmorphology
• Impairments of syntax
• Poor at repeating nonsense words
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Nature, October 4th 2001
A forkhead-domain gene is mutated
in a severe speech and language disorder
Lai, C. S., Fisher, S. E., Hurst, J. A.,
Vargha-Khadem,F., & Monaco, A.
• FOXP2: gene on chromosome 7q31
• Single base mutation in affected individuals
• No allelic variation in people with normal language
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Nature, August 22nd 2002
Molecular evolution of FOXP2, a gene
involved in speech and language
Enard, W., Przeworski, M., Fisher, S. E., Lai, C. S. L.
Wiebe, V., Kitano, T., Monaco, A. P., Paabo, S.
• FOXP2 differs in man and mouse in only 3 amino
acid positions
• FoxP2 differs in man vs. chimp, gorilla, rhesus
macaque in 2 amino acid positions
• i. e. 2/3 differences between human/mouse occurred
on human lineage after separation from chimpanzee
•
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Is FOXP2 a 'grammar gene'?
No!
• FOXP2 is a transcription factor: regulates expression of many other genes, and expressed in multiple organs
• Affected members of KE family have problems beyond grammar
• Abnormality of subcortical regions involved in motor control
(Watkins et al, 2002)
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The elephant pushing the boy is big
Nevertheless,affected members poor at syntactic tasks, even
when no speech is required, e.g.
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How to characterise FOXP2
• A transcription factor that affects expression of many other genes, and is expressed in multiple organs
• Human version of gene may be important for building brain areas involved in extracting hierarchical structure from linear input
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Beyond FOXP2 - other cases of SLI
• No abnormality of FOXP2 seen in most cases of SLI
• Pedigree analysis does not show straightforward pattern suggestive of single gene disorder
• Different severity in MZ twins indicates role of environmental factors
• Finding genes will be harder: gene-disorder associations probabilistic
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low
high
several genes
influence
language level
across the whole
range
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How will we discover the genes?
• “Splitting” approach: look for genes related to component language skills that are affected in SLI
• “Lumping” approach: look for genes that might affect more than one disorder
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Splitting
Move away from studying SLI to look at component skills
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Some promising component skills
• Auditory processing skills (e.g., Tallal)
• Phonological short-term memory (e.g., Gathercole & Baddeley)
• Morphosyntax (e.g., Rice & Wexler)
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“Here the boy is raking; now he is done.
Tell me what he did”.
Rice-Wexler task
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Here’s a farmer.
Tell me what a
farmer does.
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Conclusions from twin studies
Auditory deficit
phonological
STM deficit
Environmental
factors Genetic risk 2
Morphosyntax
deficit
phonological
STM deficit
Genetic risk 1
Phonological
STM deficit
twins resemble
each other
regardless of
whether MZ
or DZ
MZ twins more
similar to each
other than DZ
MZ twins more
similar to each
other than DZ, but
only within-trait
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auditory
deficit
phonological
STM deficit morphosyntax
deficit
children with co-occurring
deficits are most likely
to be identified with SLI
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Implications
• Different deficits may have different causes, but impact on language only severe when they co-occur
• Search for single cause explanations of SLI may be doomed - language is resilient enough to survive one deficit
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Genetics: common misconceptions
• Genes are the only thing that matter
• No point in treating genetic disorders
NO! even in MZ twins, find different severity
NO! genetic analysis says nothing about effects of novel environmental experience
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Genetic conditions that can be
modified
• Hair colour!
• Diabetes
• Huntington’s disease
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Dorothy Bishop
Oxford Study of Children’s Communication Impairments,
Department of Experimental Psychology,
South Parks Road,
Oxford,
OX1 3UD,
England.
http://psyweb.psy.ox.ac.uk/oscci/