Evidence for a grammar-specific deficit in children.
BACKGROUND
Specific language impairment (SLI) is a disorder in which language acquisition is impaired in an otherwise normally developing child. SLI affects around 7% of children. The existence of a purely grammatical form of SLI has become extremely controversial because it points to the existence and innateness of a putative grammatical subsystem in the brain. Some researchers dispute the existence of a purely grammatical form of SLI. They hypothesise that SLI in children is caused by deficits in auditory and/or general cognitive processing, or social factors. There are also claims that the cognitive abilities of people with SLI have not yet been sufficiently characterised to substantiate the existence of SLI in a pure grammatical form.


RESULTS
We present a case study of a boy, known as AZ, with SLI. To investigate the claim for a primary grammatical impairment, we distinguish between grammatical abilities, non-grammatical language abilities and non-verbal cognitive abilities. We investigated AZ's abilities in each of these areas. AZ performed normally on auditory and cognitive tasks, yet exhibited severe grammatical impairments. This is evidence for a developmental grammatical deficit that cannot be explained as a by-product of retardation or auditory difficulties.


CONCLUSIONS
The case of AZ provides evidence supporting the existence of a genetically determined, specialised mechanism that is necessary for the normal development of human language.
van der Lely
H K
HK
Department of Psychology Birkbeck College University of London, Malet Street, London, WC1E 7HX, UK. h.vanderlely@psyc.bbk.ac.uk.
Rosen
S
S
McClelland
A
A
D000293:Adolescent; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007802:Language; D007805:Language Development Disorders / Q000235:genetics / Q000503:physiopathology; D007807:Language Tests; D008297:Male