The role of executive functions in typical and atypical preschoolers' speech sound development

For most children, the acquisition of adult-like speech production is a seamless process. Yet for children with cognitive-linguistic speech sound disorder (SSD), in the absence of any obvious etiology such as hearing-related or motor processing deficits, the rules that govern their native phonology or speech sound system must be explicitly taught in speech therapy. A fundamental question asks why children with SSD are often unable to transition to adult-like production without direct therapy. One plausible, yet relatively unexplored explanation for this difficult transition is that there are differences in executive function abilities (EFs) in children with SSD as compared to typically-developing (TD) children. The core EFs (inhibitory control, cognitive flexibility, and working memory) are the cognitive functions needed to control initial or habituated impulses, shift flexibly between rule sets, and store and manipulate information; these could logically be involved in the process of replacing early, inaccurate production patterns with adult phonology. For this study, 4- to 5-year-old children, 20 with SSD and 45 with TD speech, participated in a battery of EF, speech production, and speech perception tasks. In addition, children were assessed using a modified version of the Syllable-Repetition Task (SRT; Shriberg et al., 2009), which is a variant of non-word repetition for children with SSD. Performance accuracy was compared across groups and also correlated with speech sound accuracy from a single-word naming task. It was found that children with SSD performed more poorly than the TD speech group on the forward digit span, SRT, and Flexible Item Selection (FIST; Jacques & Zelazo, 2001) tasks. Only forward digit span and SRT performances were positively correlated with speech production accuracy. Factor and regression analyses suggested that phonological memory capacity, but not inhibitory control, cognitive flexibility or mental manipulation is likely impaired in this population. Results from the SRT suggest that an additional cognitive component, such as phonological encoding or quality of underlying representations, may also be implicated. Interpretations for these and other results as well as their clinical implications are discussed