Differences between the production of [s] and [?] in the speech of adults, typically developing children, and children with speech sound disorders: An ultrasound study

This study describes the criteria that are used in ultrasound to measure the differences between the tongue contours that produce [s] and [?] sounds in the speech of adults, typically developing children (TDC), and children with speech sound disorder (SSD) with the phonological process of palatal fronting. Overlapping images of the tongue contours that resulted from 35 subjects producing the [s] and [?] sounds were analysed to select 11 spokes on the radial grid that were spread over the tongue contour. The difference was calculated between the mean contour of the [s] and [?] sounds for each spoke. A cluster analysis produced groups with some consistency in the pattern of articulation across subjects and differentiated adults and TDC to some extent and children with SSD with a high level of success. Children with SSD were less likely to show differentiation of the tongue contours between the articulation of [s] and [?].