The dorsal differentiation of velar from alveolar stops in typically developing children and children with persistent velar fronting

Purpose: This study has two key aims: Firstly to provide developmental articulatory norms for the alveolar–velar distinction in 30 English-speaking typically developing children. Secondly to illustrate the utility of the reported measures for classifying and quantifying the speech of children with a history of persistent velar fronting as they develop the contrast longitudinally. Method: This study involved secondary data analysis of the Ultrasuite corpus comprising ultrasound tongue imaging recordings of speech materials from 30 typical children and longitudinal data from five children with persistent velar fronting undergoing ultrasound visual biofeedback intervention. We present two new measures of coronal dorsal differentiation: KTMax and KT crescent area. These measures distinguish /k/ and /t/ by quantifying the magnitude of this distinction in absolute spatial terms (mm of linear dorsal difference). For the typical children, we report these measures in corner vowel contexts. We then compare these to dorsal productions by the children with speech disorders, before, during, and after intervention. Results: Both measures reliably distinguished /k/ and /t/ in typically developing children. There was an effect of vowel, with larger KTmax and KT crescent area in /a/ and /o/ vowel contexts than in an /i/ context. The children with persistent velar fronting showed KTmax values near zero before intervention, showing a complete merger between /k/ and /t/. During intervention they showed variable KTmax values. Post intervention they showed values within the range of typical children. Conclusions: This study provides articulatory norms derived from ultrasound tongue imaging for the dorsal differentiation in alveolar and velar stops in typically developing children. By applying these norms to children with persistent velar fronting as they acquire this contrast, we see that /k/ is acquired in an articulatorily gradient manner.