Page 28 - Fall2013

Front Vowels (Model A). The models shown in parts (a) and (b) of Fig. 4 are based on the bent-type model A for front vowels. A block (shown in yellow) inserted from the floor of the oral cavity controls tongue height for the front vowels /i/ and /e/. On the top surface of the block there is a groove run- ning along the vocal-tract length. The cross sectional dimen- sion of the groove is 9 mm x 9 mm (the location of the groove is indicated by the red dashed line). When the surface of the block reaches the roof of the oral cavity, the area of the con- striction becomes minimal and it simulates the vowel /i/ (Fig. 4a). When the block shifts 6-8 mm downwards, it simulates the vowel /e/ (Fig. 4b); in this case, the downward shift is 8 mm. From Figs. 4 (a) and (b) one can observe that the tongue constriction for /i/ and /e/ is in the same position, but the area of the constriction is wider for /e/ than for /i/.
Back Vowels (Model B). The models shown in Figs. 4 (c)- (e) are based on the bent-type model B for back vowels. In Figs. 4 (c) and (d), the block shown in yellow was placed inside the pharyngeal cavity to control tongue height for the back vowels /a/ and /o/. There is a groove on the surface of the block facing the pharyngeal wall, the cross-sectional dimension of which is 9 mm x 9 mm, running along the
length of the vocal tract. When the block is placed 5 mm above the bottom, as in Fig we. 4 (c), we can produce /a/. When the block is shifted up to 11 mm, one uses an addi- tional block for lip rounding (leftmost yellow block), then one can produce the vowel /o/, as shown in Fig. 4 (d). The block for lip rounding has a square hole, of which the dimen- sion is 18 mm x 18 mm (the location of the hole is also indi- cated by the red dashed line). By replacing the straight slid- ing block for /o/ with a right-angle shaped block and posi- tioning it at the corner of the vocal tract as shown in Fig. 4 (e) (rightmost yellow block), one can produce the vowel /u/. In this case, there is also a groove, 9 mm x 9 mm, on the surface of the block facing the pharyngeal wall and the palate. The block for lip rounding is also used in Fig. 4 (e), just as it was for /o/ in Fig. 4 (d).
A Single Bent-type Model with Sliding Blocks. The final design was that of a single bent-type model with sliding blocks that could simulate all five vowels (Model C). The design was achieved by combining the former two bent-type models into one model. In this latter design, the following four points were taken into consideration:
1) Front vowels have a block for tongue constriction
Figure 4. Bent-type modes A (a,b) and B (c-e): (a) vowel /i/, (b) vowel /e/, (c) vowel /a/, (d) vowel /o/ , and (e) /vowel/u
Mechanical Models of Vocal Tract 27