Bates 2004, Language deficits across groups

Bates, E. (2004). Explaining and interpreting deficits in language development across clinical groups: Where do we go from here? Brain and Language, 88, 248-253.

This commentary by Elizabeth Bates accompanies a group of articles in a 2004 issue of the journal Brain and Language. The studies deal with clinical populations -- children with Williams syndrome, children with Downs syndrome, children with left-hemisphere damage (LHD), right-hemisphere damage (RHD), "late talkers", children with the diagnosis of specific language impairment (SLI), and others. The articles make comparisons of language development across these populations.

Bates points out three findings of the cross study work (first two from Holland):

1. Kids with a variety of impairments experience the same sequence and types of problems, although at different rates. The metaphor suggested is that the problem space, English, is like a highway. These kids are all stuck in the same slow lane.
2. Young kids who have either RHD or LHD usually move into the normal range in elementary school. They seem to "catch up" somewhere between the ages of 3 and 5.
3. Kids with Williams syndrome perform language tasks that are in keeping with their mental age. This contradicts other research that suggests that those with Williams syndrome are capable of complex grammatical constructions and sophisticated speech far beyond their levels of cognition. The claims of language savant status for Williams syndrome kids would have been used to challenge the notion of cognitive prerequisites for language.

Regarding the first finding above, Bates asks, if RHD/LHD kids catch up, why can't those with Williams or other impairments? Bates refers to Holland's supposition that, while the otherwise healthy brain of a young child who has an injury to a specific location is sufficiently plastic and adaptable to reroute language processing around the injury, other disorders are either located in "gate-keeper" systems or too

 broadly distributed to allow the brain to compensate. 

Some research implications of these findings noted by Bates:

• More research should be done using subjects with 'normal' language abilities placed under stressful processing situations in an attempt to simulate language processing disorders.
• More longitudinal studies across the language acquisition period.
• The need to recognize a new metaphor for language development. Rather than a Swiss Army knife, filled with specialized tools for specific situations, Bates compares the language-enabled brain to a giraffe's neck -- adapted to serve a new function (reaching high leaves) while retaining its older functions (turning the head, passing air and food). Bates refers to the "Functional infrastructure for language" chart to show older adaptations combining to provide the basis for language. 

To extend that implication further, it's possible that language impairment always results from the impairment of one of the subsystems. There is no language impairment; only an impairment of one or more of the systems that allow language acquisition to occur. "Non-linguistic deficits can have serious consequences for language, temporarily or on a more protracted basis." p. 252. As Bates points out, this may have major implications for diagnosis and treatment of language disorders.