Development of coronal tongue shape in voiceless sibilants: An ultrasound study

Articulation of English voiceless sibilants requires precise constriction locations (i.e., alveolar for /s/ and postalveolar for /ʃ/) and a midline tongue groove, which necessitates investigation of both the sagittal (i.e., anterior-to-posterior) and coronal (i.e., left-to-right) tongue shapes. In particular, the midline groove requires both sides of the tongue to be raised along the edges while the midline remains lowered. This configuration creates a narrow channel that funnels airflow to generate high-frequency turbulence for /s/, whereas the /ʃ/ production requires a shallower groove that results in lower frequency frication noise than /s/. Despite the importance of coronal tongue shape in sibilant articulation, previous studies have focused primarily on sagittal plane investigation. To address this gap, the present study examined sagittal and coronal tongue shapes of voiceless sibilants from typically developing English-speaking children aged 3–11, alongside the acoustic and perceptual analysis. Ultrasound tongue images were extracted from the temporal midpoint of frication noise and contoured for analysis. Preliminary findings revealed that articulatory differentiation between /s/ and /ʃ/ emerged earlier in the sagittal plan than in the coronal plane. Younger children showed greater variability and less distinct midline groove patterns compared to older children. Additionally, positive correlation was found between articulatory precision and perceptual accuracy.