Differentiating phonological delay from phonological disorder: Executive function performance in preschoolers

Background The conversational speech of most children can be understood by people outside the family by the time they reach 4 years. However, for some children, speech sound disorders (SSDs) persist into their early school years, and beyond, despite adequate hearing, oromotor function, and language learning opportunities. One explanation for children's SSDs are domain-general cognitive-linguistic deficits that impair the child's ability to correctly derive rules governing how speech sounds legally combine to form words in a specific language. Aims To explore whether there are differences in performance on executive function tasks between children who make speech errors characteristic of phonological delay and those who make speech errors characteristic of phonological disorder. Methods & Procedures Twenty-six children aged from 3;6 to 5;2 (13 with phonological delay and 13 with phonological disorder), matched pairwise for age and sex (nine males), were assessed on tasks measuring cognitive flexibility (rule abstraction and cognitive shift) and phonological working memory. Outcome & Results For the cognitive flexibility tasks, the performance of children with phonological delay was significantly better than that for children with phonological disorder, but there were no group differences for the phonological working memory task. Conclusions & Implications Children with phonological disorders might benefit from intervention programmes that incorporate training in cognitive flexibility. What is already known on the subject Children with phonological delay and phonological disorder comprise the two largest SSD subgroups that present to speech-language therapy clinics. Evidence suggests domain-general cognitive processes (e.g., phonological working memory, ability to revise faulty underlying representations, rule abstraction, and cognitive shift) influence phonological development. Differences between the two subgroups in the types of speech errors, linguistic abilities, developmental trajectories, and responses to intervention have been reported, yet little is known about the underlying cognitive-linguistic deficits. What this paper adds to existing knowledge The results of this study suggest that children with phonological delay and phonological disorder have distinct patterns of performance on executive function tasks: Children with phonological disorder showed deficits in domain general rule-abstraction and cognitive shift when compared to children with phonological delay. What are the potential or actual clinical implications of this work? The findings draw attention to: (1) the importance of differential diagnosis of phonological delay and phonological disorder; (2) the role of domain-general cognitive processes in explaining why children make particular types of errors; and (3) the need to develop innovative and tailored intervention techniques that target specific underlying deficits.