Positional Neutralization - Linguistics - University of California ...

Crosswhite notes, importantly, that it is not always possible to tell a prominence-
reducing UVR system from a contrast-enhancing system on the surface. Many of their
effects can be the same; for instance, both systems disfavor, and have a tendency to
eliminate, mid vowels. Contrast enhancement does so because they are non-peripheral,
and hence less perceptually robust, and prominence reduction does so because they are
fairly sonorous. As noted, in a comparison of Belorussian and Bulgarian, the only
diagnostic for the underlying formal nature and phonetic motivation for the vowel
reduction pattern instantiated in each is the presence or absence of schwa. This for
Crosswhite is a shibboleth. Schwa is extremely low in sonority, making it good for
prominence reduction. That Bulgarian UVR produces a schwa means that it is
prominence-reducing. Schwa, on the other hand, is no good for contrast enhancement,
which favors peripheral vowels. The fact that Belorussian has [a] in unstressed syllables
therefore means that it is contrast-enhancing.
That the one system raises mid vowels and the other lowers them is irrelevant,
since in both UVR types either pattern can be generated by simple reranking of
Faithfulness constraints. A system with raising of mid vowels and no raising of the low
vowel, however, would be completely ambiguous, since reduction of /a/ to schwa can
actually be blocked in a prominence-reducing system by ranking the relevant Faithfulness
constraints (Max [+low]) above even *Unstressed/a. The possibility of such cases in
82