Theories & Diversity of Language Development - L5 HDS

Original GENETIC theory for Language development- case study example

FOXP2 gene was discovered to be a language gene by looking at the KE family who were effected by verbal dyspraxia = had mutation to this gene

What else did the FOXP2 effect? (in humans, birds and mice)

Humans: KE family also had deficits in fine motor control, non-linguistic articulation and perception of simple rhythms = NOT specific to language only.

Birds: linked to song learning and production

Mice: linked to motor control

This suggests FOXP2 is NOT domain-specific but domain-relevant to human speech = it contributes to most complex skill (using coordination + rapid movement) which in humans is speech!

How is the Brain specific to language development?

Brain is like a swiss-army knife - has become more complex throughout evolution, adding different tools. However these selectively added parts can also be impaired.

Case Study of Postnatal Hydrocephalus

44 year old man had normal development, verbal IQ of 85. However started to experience weakness in left leg. When his brain was scanned there was build-up of cerebral spinal fluid on the brain. - this had occured at such a young age the brain adapted to this issue and therefore developed normally

What is William Syndrome?

Deletion of genes of chromosome 7 - leads to deficits in visuo-spatial ability but spares language ability = language slightly lower than typical language ability but relatively higher compared to their other ability.

= this suggests their brains develop differently from birth (they are structurally different but fairly similar in language ability)

What are Cascading effects?

Other skills we have which assist in language learning:

e.g. joint attention (caregiver-infant interaction), memory development, motor development, empathy etc…

Study looking at effects of socio-economic status on language learning:

Found 30-million-word gap = suggests that children from low-income families may hear 30 million fewer words than children from higher-income families by the time they turn four.

By the age of 3, high-income children have double the vocabulary of low income children

Study of Second Language Learners (Johnson & Newport)

Found age of arrival in the US effected language proficiency in future = implies a sensitive period (biological) and environmental effect

Mean Length of Utterance for Children with Down Syndrome

Rebecca was a child with down syndrome = much later aquisition of language demonstrated by later age for the same mean length of utterance

Study of Interaction between environment and down syndrome development (D’Souza et al, 2020)

Found slower language development in children with Down syndrome with depressed parent compared to DS child without depressed parent