Department of Linguistics
PHONETICS AND PHONOLOGY
Vowel Lip Postures
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Approximate lip postures for four vowels
This diagram displays the two extreme lip postures and two intermediate lip postures. The high front cardinal vowel [i] has a very spread lip posture. The high back cardinal vowel [u] has a very tightly rounded lip posture. The low front cardinal vowel [a] has a spread lip posture but this is a more neutral posture than for [i] because the lower jaw position for this vowel causes the lips to be more open. The half-open back cardinal vowel [ɔ] has a rounded lip posture but the lips are more open then for [u] because of the lower jaw position.
The actual lip posture for vowels in any particular language may be similar to that of the closest cardinal vowel with the same lip posture feature, but often speakers of many languages adopt a more neutral posture than would be indicated by these cardinal vowels. Languages that have lip posture contrasts are more likely to adopt the more extreme lip posture to emphasise those contrasts. For example, a language with the vowel phonemes /i/ and /y/ (such as French) tend to have a strongly spread /i/ and a strongly rounded /y/ to maximise their difference perceptually. Languages without rounding contrasts, such as English, may relax the degree of rounding of rounded vowels and the degree of spreading of spread vowels. In English the extent to which this is true varies from dialect to dialect. For example, Australian English is often described as having rounded vowels which are spoken by many speakers with less rounding than similar vowels in some other dialects of English. This impression may be due, however, to the observation that /ʉː/ in Australian English is less rounded than /uː/ in American English. This difference in degree of rounding may simply be due to the fact that the American phoneme is a high back vowel and the Australian phoneme is a high central vowel. There is a tendency for front vowels to be less rounded than back vowels in the absence of a rounding contrast (although there are exceptions to this tendency).
Also read the sub-topic on vowel tongue articulation.