An investigation of sentence-level abilities in children with different types of speech disorder
Recent studies have highlighted the co-occurrence of speech disorders with language disorders, yet few studies have attempted to explore the relationship between them. This thesis examines the sentence-level abilities of children with different types of speech disorders, and addresses the following questions: (i) Can children with different types of speech disorders be differentiated according to their sentence-level performance? (ii) Is there a more-than-chance co-occurrence of sentence-level difficulties in children with different types of speech disorders? (iii) What is the relationship between speech disorders and sentence production? (iv) Is sentence imitation an efficient, effective and reliable method of assessing expressive syntax in children with severe speech difficulties? The research focuses on two groups of children, each with a different type of speech disorder: one using atypical phonological processes consistently (CPD) and the other using atypical phonological processes inconsistently (IPD). Their performance was compared to children with SLI and typical development. Results of a group study assessing sentence imitation revealed that children with CPD were no more likely to have co-occurring sentence-level difficulties than typically developing children. The IPD group showed difficulties at the sentence level, with significant variation within the group. Further investigations of sentence processing-related skills found that the IPD group could be divided into those who had IPD only and obtained high sentence imitation scores, and those who had co-occurring IPD and sentence-level difficulties, reflected in their low sentence imitation scores. The performance of the low-scoring IPD children was similar to the SLI group's performance in terms of their sentence imitation accuracy scores and most sentence processing-related abilities. However, they could be differentiated by the types and proportions of their errors and their sentence imitation performance when repeating sentences containing multi-syllabic words. The theoretical and clinical implications of the research outcomes are explored.