Labial opacity and roundness harmony in Nawuri

Recently, a number of linguists (cf. Clements, 1991; Odden, 1991; Hume, 1992; Clements and Hume 1992) have proposed models of segment structure in which the place features of consonants and vowels are arrayed on different planes. As a consequence of this arrangement, these models predict that vowel-to-vowel place feature assimilation processes should not be blocked by intervening plain consonants (i.e., consonants with no distinctive secondary articulation).In this paper, I discuss the implications for these theories of a process of roundness harmony that occurs in Nawuri, a Kwa language of Ghana. Of crucial interest is the fact that the process may be blocked, though not triggered, by the presence of an intervening plain labial consonant. I show that while the treatment of this blocking effect is straightforward in a framework such as that of Sagey (1986), in which labial consonants and round vowels are specified for a [labial] articulator node on the same plane, it is problematic for the more recent theories in which consonantal and vocalic place features are segregated.