This study was designed to investigate the articulatory movements of lateral articulation. Ultrasonography was used to examine the tongue at rest and tongue movement patterns in patients with lateral articulation and to compare with those of normal subjects.
The subjects included 17 patients with lateral articulation (LA, 7-37 years old, 8 males and 9 females) and 12 normal speakers (NS, 21-48 years old, 6 males and 6 females). Symmetry of the tongue muscle echo area at rest was examined in coronal section, and tongue shape and movement patterns during vowel production were examined in coronal and sagittal sections. The vowel /i/ which is susceptible to lateral articulation and the vowel /a/ which is not susceptible were examined.
The results were as follows.
1. All LA showed an asymmetrical echo area in coronal section, while NS showed a symmetrical echo area. Anatomical asymmetry in the tongue muscle was suggested as one of the causes of lateral articulation.
2. In coronal section, most subjects in both groups showed a flat or groove shape; a convex shape was seen only in LA. The movements of the tongue edge were asymmetrical in LA but not in NS.
3. In sagittal section, LA showed different movement patterns from those of NS, suggesting that observation from sagittal section is needed.
4. Compared to NS, LA showed different tongue movement patterns not only during production of susceptible /i/ but also not susceptible /a/, suggesting the need to investigate tongue movement patterns for other vowels as well.
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