Children with language-learning disabilities (hereafter termed LD children) experience a wide range of academic difficulties, many of which are based on their spoken language skills. As a group, LD children have more difficulty with spoken phonology and morpho-syntax than with semantics. One major theoretical perspective, is that relative to children with typical language, LD children have limited resources for processing language. When processing limitations are exceeded, language performance is impaired. The long-term objective of the proposed research is to test the hypothesis that phonology and syntax present greater processing demands for LD children than semantics. Acquisition of derivational morphology (e.g., deriving lightness, lighten, and lightly from light) involves processing a complex intersection of phonological, syntactic, and semantic constraints. Thus, it provides a very rich avenue for exploring the processing of these language domains and the relative contribution of each domain to overall skill in language. Specifically, it is hypothesized that LD children are better able to process semantic aspects of derivational morphology than phonological and syntactic aspects. This hypothesis is tested in a series of experiments that investigate production and comprehension of each language domain in isolation and each domain as it interacts with each of the other two domains. The experiments provide converging evidence for the hypothesis from lexical decision, sentence completion, and word analysis tasks. In order to accurately interpret the LD children's performance, their performance is compared with language-normal (LN) children of the same age and also with LN children with the same language skills.
