| Summary: | Impaired procedural learning has been suggested as a possible cause of developmental language disorder and dyslexia (Nicolson & Fawcett, 2007; Ullman & Pierpont, 2005). However, studies investigating this hypothesis have so far delivered inconsistent results. These studies typically use extreme group designs, frequently with small sample sizes and measures of procedural learning with unreported reliability. This thesis first used a meta-analysis to examine the existing evidence for a procedural deficit in language disorders. The experimental studies then took a different approach to previous studies, using a concurrent correlational design to test large samples of children unselected for ability on a wide range of implicit (serial reaction time, Hebb serial learning, contextual cueing and probabilistic category learning) and declarative learning tasks and literacy, language and arithmetic attainment measures. The reliability of the tasks was also carefully assessed. A final study explored the hypothesis from an extreme group design perspective, comparing a typically developing sample with a group of dyslexic children matched for reading ability. None of the studies found evidence of a relationship between procedural learning and language-related abilities. By contrast, a relationship between verbal declarative learning and attainment was found replicating earlier studies. Crucially, the first large-scale study showed that procedural learning tasks of a similar length to those typically used in earlier studies had unacceptably low reliability and correlated poorly with each other and with attainment. The second large-scale study, used extended procedural learning tasks that had proved reliable in adults, but found similar low levels of reliability in children. Additionally, the level of attention children paid during these extended tasks accounted entirely for the relationship between procedural learning and attainment. The results in this thesis highlight the importance of establishing task reliability, as well as considering the potential effects of individual differences in basic cognitive processes such as attention in all investigations of procedural learning.
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