Click Consonant - The Back-vowel Constraint

The Back-vowel Constraint

In several languages, including Nama and Ju|’hoansi, the alveolar click types and only occur, or preferentially occur, before back vowels, while the dental and palatal clicks may occur before any vowel. The effect is most noticeable with the high front vowel . In Nama, for example, the diphthong is common but is rare after alveolar clicks, whereas the opposite is true after dental and palatal clicks. This is a common effect of uvular or uvularized consonants on vowels in both click and non-click languages. In Taa, for example, the back-vowel constraint is triggered by both alveolar clicks and uvular stops, but not by palatal clicks or velar stops: sequences such as */ǃi/ and */qi/ are rare to non-existent, whereas sequences such as /ǂi/ and /ki/ are common. It is also triggered by labial clicks, though not by labial stops. The clicks that are subject to this constraint are those which involve a sharp retraction of the tongue during their release.

Miller et al. (2003) used ultrasound imaging to show that the rear articulation of the alveolar clicks in Nama is substantially different from that of palatal and dental clicks. Specifically, the shape of the body of the tongue in palatal clicks is very similar to that of the vowel, and involves the same tongue muscles, so that sequences such as involved a simple and quick transition. The rear articulation of the alveolar clicks, however, is several centimeters further back, and involves a different set of muscles in the uvular region. The part of the tongue required to approach the palate for the vowel is deeply retracted in, as it lies at the bottom of the air pocket used to create the vacuum required for click airstream. This makes the transition required for much more complex and the timing more difficult than the shallower and more forward tongue position of the palatal clicks. Consequently, takes 50 ms longer to pronounce than, the same amount of time required to pronounce .

Languages do not all behave alike. In Nǀuu, the simple clicks /ʘ, ǃ, ǁ/ trigger the and allophones of /i/ and /e/, while /ǀ, ǂ/ do not. All of the affricated contour clicks, such as /ǂ͡χ/, do as well, as do the uvular stops /q, χ/. However, the occlusive contour clicks pattern like the simple clicks, and /ǂ͡q/ does not trigger the back-vowel constraint. This is because they involve tongue-root raising rather than tongue-root retraction in the uvular-pharyngeal region. However, in Gǀwi, which is otherwise largely similar, both /ǂ͡q/ and /ǂ͡χ/ trigger the back-vowel constraint (Miller 2009).