The role of processing in children and adolescents with language impairment

In this chapter we have reviewed the evidence for processing limitations in children and adolescents with SLI and NLI who participated in the Iowa Project. Both speed of processing and working memory measures have been considered. At a group level, it is clear that children and adolescents with SLI and NLI process information more slowly than same- age typically developing peers, and their working memory, likewise, is more limited. Processing limitations are not confned to linguistic tasks; they are seen as well when non-linguistic processing is evaluated. Tese limitations are seen at both younger and older ages, and are related to language ability, though they are not necessarily the direct cause of language impairment. Although speed of processing appears to be related to language ability, verbal working memory, especially, seems important in this relationship.

Te sentence processing abilities of adolescents with SLI and NLI are clearly not at the level of their peers, whether assessed by RT or by electrophysiological measures. Processing of grammatical details seems quite vulnerable, especially when sensitivity to grammatical agreement is the focus.

Children and adolescents with NLI ofen process information more slowly and less accurately than their counterparts carrying the designation of SLI, but evidence for a diagnostic distinction between these two groups is not compelling. Even though the low language test scores of individuals with NLI are (by defnition) accompanied by relatively low scores on nonverbal IQ tests, their performance profle across linguistic and nonlinguistic processing tasks do not diverge greatly from the profles seen for individuals with SLI.

Over the years of the Iowa Project, we have employed a wide variety of processing tasks with the participants, and have endeavored to determine how performance on these tasks might explain a piece of the larger puzzle of language impairment. We are not certain that the processing limitations observed in SLI and NLI are the direct source of the language impairment. However, we are quite frm in our belief that, whatever the original source of the language impairment, these processing limitations render more difcult the children’s intake and interpretation of linguistic material. For this reason, the processing limitations of children with SLI and NLI must remain an important focus of future investigations and should be considered in any clinical assessment and treatment plan for these children.