Developmental Neurolinguistics Lab

Specific Language Impairment (SLI)

SLI is a developmental language disorder in the absence of frank neurological, sensori-motor, non-verbal cognitive or social emotional deficits (see Watkins, 1994).

Children with SLI lag behind their peers in language production and language comprehension, which contributes to learning and reading disabilities in school.

One of the hallmarks of SLI is a delay or deficit in the use of function morphemes (e.g., the, a, is) and other grammatical morphology (e.g., plural -s, past tense -ed). They omit function morphemes from their speech long after age-matched children with typical language development show consistent production of these elements.

Some researchers claim that SLI children's difficulty with grammatical morphology is due to delays or difficulty in acquiring a specific underlying linguistic mechanism. For example, Mabel Rice and Ken Wexler suggest that children with SLI have difficulty acquiring the rule that verbs must be marked for tense and number ("he walks", not "he walk"; Rice, 1994).

A second hypothesis is that these children have a deficit in processing brief and/or rapidly- changing auditory information, and/or in remembering the temporal order of auditory information. For example, Paula Tallal has found that some children with SLI have difficulty reported the order of two sounds when these sounds are brief in duration and presented rapidly (Tallal, et al., 1985). Laurence Leonard suggests that these deficit may underlie difficulties in perceiving grammatical forms (e.g., "the", "is"), which are generally brief in duration (Leonard et al., 1997).

A third hypothesis is that children have poor short-term memory for speech sounds (e.g., Gathercole, 1998). Children with SLI perform worse than children with typical language skills on repeating nonsense words (for example, "zapanthakis"). In a number of recent studies short-term memory for speech sounds has been shown to correlate highly with vocabulary acquisition and speech production . This has led to the hypothesis that a primary function of this memory is to facilitate language learning.

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