Nature and nurture of language development Flashcards
What is the difference between language development and language ability?
language development - the process of acquiring language
language ability- can be assessed with specific tests
Language ability:
- when does it appear?
- across?
- without?
- what ability?
- Appears in the first three years of life
- Across different languages and cultures- it’s universal
- Without need of explicit instructions
- Innate ability- genetic factors
Language development:
What are early language skills important for?
- children’s readiness for school
- qualifications gained at school
- earnings, literacy skills and mental health in adulthood
- for health and wellbeing
Language ability and disability:
- what is the most widely used test?
- what does it show?
- what is the distribution of scores?
- high vs low performers?
The most widely used test by all speech pathologists is the Clinical Evaluation of Language Fundamentals (CELF): child’s understanding and use of language (receptive and expressive language skills) and compares this to their peers of the same age (percentile rank).
Shows high variation in the population
Distribution of the scores will follow the normal distribution- majority of children will be in the middle of the distribution.
High performers: Some children will perform much better than their peers at the same age.
Low performers: much lower level of development in comparison to peers of the same age.
Nature vs nurture
Nature = genetic factors
Nurture = environmental factors
What is the evidence for the role of genetic factors?
- Twin studies
- KE family with members with language disability
- Comparative genomic studies
- Genetic association studies
Twin design: MZ and DZ twins
Monozygotic (MZ): share ~100% of genes
Single egg fertilised by single sperm then splits into two
Dizygotic (DZ): share ~50% of genes
Separate eggs fertilised by separate sperm
How can you compare resemblance (similarity) of MZ and DZ twins on specific traits (eg. language ability)?
By looking at correlations
Definitions of heritability, common environment and unique environment
A = heritability = genetic influence = the proportion of variance in a population attributable to genetic differences between people
C = common environment = shared environmental influence = the degree to which siblings in a family are similar to one another, once their genetic similarity has been accounted for
E = unique environment = non-shared environmental influence = the degree to which siblings in a family are different from one another, once their genetic differences have been accounted for
How do you calculate heritability?
2(rMZ - rDZ)
(We expect the similarity of MZ twins to be higher-
twice as high)
Twin studies results
These bars show the % of individual diffs that can be explained by genetic factors
- height and weight- around 80% therefore genetic factors substantially and significantly contribute to the development of height and weight
- math, language - the contribution of genetic factors is low in comparison to height and weight. eg. language- 40% explained by genetic so 60% by environmental
- none of these traits show 100% heritability- this shows all these traits are also influenced by environmental factors
Twin studies of language ability
- what is language ability?
- age 2
- age 4
- what was obtained at age 16
- what can we conclude about language abiloty
Language ability is a heritable trait
- At age 2 years, heritability for vocabulary = 26%, and for grammar = 52% (in boys) & 43% (for girls)
- At age 4, the heritability estimates were even higher (45%-68%) and further increased by age 6 (44%-92%)
- Convergent evidence for moderate-to-high heritability was obtained at age 16 in a different sample (TEDS)
- Language ability is not 100% heritable; environmental influences also play an important role
Contribution of genetic factors and heritability
- the contribution of genetic factors will change across development
- heritability increases as children develop
- co-heritability is significant, it may change across the lifespan
Twin studies of language ability
Limitations
(a) Large sample sizes are required- we need one of MZ and one of DZ twins
(b) Population-based samples are preferred, to avoid overrepresentation of MZ pairs
(c) It can be difficult to identify twins
when measuring specific traits language effect for example is harder to measure?
(d) Language phenotypes are often limited and lacking in metrics interpretable for comparisons to singleton age peers
(e) Possible twinning effect (twins are more likely to have delayed speech and language skills than singletons)
Behavioural phenotype and neural phenotype
Behavioural phenotype: for every test of speech and language that was administered, the group of affected family members was, on average, significantly impaired relative to the unaffected group.
Neural phenotype: Bilateral voxel-based morphometry (VBM) analyses showing some of the regions in which affected KE members have significantly reduces grey matter