Lecture 8: N&N of language development

Question 1

When does language ability typically emerge?

Answer 1

Language ability emerges within the first three years of life across different languages and cultures without the need for explicit instruction.

Question 2

Why are early language skills important?

Answer 2

Early language skills influence:
* School readiness (Roulstone et al., 2011; Snowling et al., 2011).
* Academic qualifications (Parsons & Schoon, 2011).
* Adult outcomes: literacy, earnings, and mental health (Parsons & Schoon, 2011; Schoon et al., 2010).

Question 3

What are the two main factors influencing language development?

Answer 3

• Nature (Genetic factors): Includes evidence from twin studies, the KE family, and genetic association studies.
• Nurture (Environmental factors): Includes environmental exposure and upbringing.

Question 4

What is the heritability of vocabulary and grammar at age 2 according to twin studies?

Answer 4

• Vocabulary: 26% heritability.
• Grammar: 52% (boys) and 43% (girls) heritability.

Question 5

How does heritability of language ability change with age?

Answer 5

Heritability increases with age:

• Age 4: 45%-68%.
• Age 6: 44%-92%.
• Moderate-to-high heritability at age 16 (TEDS study).

Question 6

What are the limitations of twin studies in understanding language development?

Answer 6

1. Require large sample sizes.
2. Need population-based samples to avoid overrepresentation of monozygotic twins.
3. Language phenotypes often lack robust comparison metrics.
4. Possible twinning effects: delayed language skills compared to singletons.

Question 7

What is developmental verbal dyspraxia in the KE family?

Answer 7

Affected KE family members show significant impairments in speech and language due to a mutation in the FOXP2 gene

Question 8

What is the role of the FOXP2 gene in language development?

Answer 8

• A mutation in FOXP2 causes speech and language disorders due to haploinsufficiency (insufficient brain development).
• Identified as a monogenic trait—caused by a single gene mutation (Lai et al., 2001).

Question 9

What is the evolutionary significance of the FOXP2 gene?

Answer 9

FOXP2 is among the most highly conserved 5% of proteins, indicating its fundamental role in mammals (Enard et al., 2002).

Question 10

What are genetic association studies, and what do they reveal about language development?

Answer 10

Genetic association studies, such as those by Reader et al. (2014) and Eising et al. (2022), identify multiple genetic factors influencing language development, suggesting it is a multifactorial trait.

Question 11

How do nature and nurture interact in language development?

Answer 11

Genetic and environmental factors co-act to influence language development dynamically, with heritability increasing as children grow.

Question 12

What is the Clinical Evaluation of Language Fundamentals (CELF)?

Answer 12

It is a widely used test by speech pathologists to assess a child’s understanding and use of language (receptive and expressive skills) and compare these abilities to peers of the same age.

Question 13

What does the twin design method involve in language development studies?

Answer 13

It compares the resemblance (correlation) of monozygotic (MZ, share ~100% of genes) and dizygotic (DZ, share ~50% of genes) twins on a specific trait, such as language ability.

Question 14

How is heritability estimated in twin studies?

Answer 14

Heritability is calculated as:
* Heritability = 2 × (rMZ – rDZ)
Where rMZ and rDZ are the correlations for monozygotic and dizygotic twins, respectively

Question 15

What neural phenotype was identified in the KE family?

Answer 15

Affected family members showed significantly reduced grey matter in specific brain regions, identified through voxel-based morphometry (Belton et al., 2003).

Question 16

What is the significance of the KE family’s speech and language disorder findings?

Answer 16

The discovery of the FOXP2 gene mutation in this family provided key evidence that genetic mutations can significantly impact language development.

Question 17

Why is FOXP2 considered a monogenic trait?

Answer 17

The speech and language disorder in the KE family is caused by a mutation in a single gene (FOXP2), demonstrating that some traits can be linked directly to one genetic factor.

Question 18

What are some environmental factors that could influence language development?

Answer 18

Environmental factors may include:

• Quality of linguistic exposure in early life.
• Socioeconomic status of the family.
• Educational resources and support.
• Parent-child interactions and communication.

Question 19

What does it mean that genetic influences on language are “not static”?

Answer 19

The heritability of language ability increases with age, showing that genetic factors have a growing impact as children develop.

Question 20

How does the FOXP2 gene relate to other species?

Answer 20

Comparative studies show that FOXP2 is highly conserved across mammals, highlighting its fundamental role in brain and speech development (Enard et al., 2002).

Question 21

What does “multifactorial trait” mean in the context of language development?

Answer 21

It means language ability is influenced by multiple genetic and environmental factors acting together, rather than being determined by a single cause.

Question 22

What is the “twinning effect” in language development?

Answer 22

Twins are more likely to experience delayed speech and language skills compared to singletons, potentially due to shared developmental and environmental factors.

Question 23

What practical applications arise from understanding the nature and nurture of language development?

Answer 23

Insights can guide interventions such as:
* Early identification of language delays.
* Development of targeted educational programs.
* Genetic counseling for families with known language disorders.

Question 24

How do population-based samples improve the reliability of twin studies?

Answer 24

They reduce bias and ensure findings are more representative of the general population, avoiding overrepresentation of monozygotic twins.