ABSTRACT
The heterogeneity of specific language impairment (SLI) in children is a major issue in current research on the etiology of the disorder. Are these studies looking at one or many disorders? And, what are the relations between co-occurring deficits found in some children with SLI? Determining whether differences between various forms of SLI are qualitative or quantitative would considerably advance understanding of the disorder and could have direct clinical implications. For instance, if there are definable subgroups, with different etiologies, then distinctive theories as well as therapeutic approaches may be called for. Furthermore, such knowledge would provide valuable insight into the development of cognitive function and structure—a focal area of ongoing debate in cognitive science. This chapter first discusses the theoretical and methodological issues raised by the heterogeneity of SLI. Second, it argues for the detailed study of SLI subgroups to complement those of nondifferentiated SLI groups. Third, to illustrate the subgroup approach, consideration is given to the characteristics of the grammatical-SLI (G-SLI) subgroup and the representational deficit for dependent relations (RDDR) hypothesis, which has been advanced to account for the grammatical deficits found in G-SLI.
