Validation of the Nonsense Syllable Repetition Test for Differential Diagnosis of Underlying Deficits in Children with Speech Sound Disorders

Objectives: This study aimed to categorize the underlying deficits related to speech processing in the speech sound disorder group into three categories: phonological encoding deficit, phonological memory deficit, and articulation transition deficit. By developing analytical methods corresponding to each factor using a non-word repetition task, we aimed to establish a system capable of quantitatively differentiating these underlying deficits. Methods: We developed the Nonsense Syllable Repetition Test (nSRT) as a non-word repetition task and established its scoring systzem. It was administered to 63 typically developing (TD) children, 49 children with pure speech sound disorder (SSD), and 12 SSD children with language disorder (SSD+LD). Concurrent validity was verified, and performance differences by age and group were analyzed. Results: Positive concurrent validity was established for all three underlying deficit scores. Age comparison showed improved performance with age, while group comparison revealed that the pure SSD group demonstrated weakness in phonological encoding and articulatory transition, and the SSD+LD group showed the most severe deficits in phonological memory. Conclusion: These findings suggest that the proposed nSRT analysis complements the limitations of conventional surface error analysis in existing assessment tools and indicates that it can sensitively differentiate developmental changes and clinical heterogeneity in underlying speech processing abilities.