language-relevant systems within that modality only. Finally, the abnormal pattern of hemispheric asymmetries in ERPs associated with semantic priming is difficult to interpret because very few studies have reported variation in the pattern. However, the results as a whole suggest age of acquisition of a language within a modality may be important.
Nonetheless, these patterns of results suggest that alterations in early sensory processing can impact the organization and operation of cognitive systems. The hypersensitivity of the auditory system in Williams subjects may in part underlie the sparing of and the precocious and hyperfluent nature of the Williams subjects' language, and the fact that this development occurs following abnormal delays in the acquisition of auditory language. The normal or hypernormal auditory priming effects contrast with the results for the visual modality. They also differ from the results for hemispheric differentiation, which appears to require language acquisition to occur at specific times for the normal pattern to occur.
This pattern of results taken as whole suggests that sensory development, age at testing, age of exposure, and skill level each have significant and distinct effects on different and specific aspects of the development of cerebral organization. When these variables are identified and controlled, studies on populations with specific neurocognitive deficits can inform hypotheses about brain function. The Williams population is particularly valuable in this endeavor by virtue of the several distinct sensory and cognitive functions that are affected in them. Moreover, they are one of a very few populations that provides an important testing ground for issues concerning the extent of interdependence of sensory and cognitive skills and the acquisition of language.
This research was supported by grants DC00128, DC00481, NS22343, DC01289, and HD26022.
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