Title: Nasal vowel systems in West Africa: Typological, areal, and perceptual perspectives
Contrastive nasal vowels are a common feature of West African phonological systems, and have contributed significantly to previous descriptively and theoretically oriented Africanist work - e.g. Hyman (1972), Williamson (1973), Maddieson (1984, 2007), Clements (2000), Clements & Rialland (2006), and Miehe (2013). There remain, however, a number of issues which are insufficiently addressed: (1) in which precise geographic areas and genetic groups do we find nasal vowels in West Africa, (2) what are the profiles of these nasal vowel inventories and how are they geographically and genetically distributed, and (3) how can we situate these patterns within larger typological-areal and phonetic-phonological literature?
To this end, we have created a typological database of 246 languages/language clusters in West Africa, covering all major families. This survey supports previous work which identifies an expansive areal zone stretching roughly south of the Sahel from Guinea to Nigeria, within which contrastive nasal vowels are nearly categorical. We refer to this area as the West African Nasal Vowel Zone. A novel component of our survey is that we also coded for vowel inventory type, focusing on identifying gaps in the nasal vowel inventory. We found that while the overwhelming majority of West African languages contrast oral /e o/ vs. /ɛ ɔ/ (epsilon and open o), a large continuum of languages stretching from Western Nigeria into Cote D'Ivoire lack nasal /ẽ õ/, constituting the core of the Nasal Vowel Zone. In contrast, languages which show the presence of contrastive /ẽ õ/ appear at the fringes of the West African Nasal Vowel Zone. We show that both of these patterns are subject to areal effects which cut across genetic group.
We conclude our discussion by situating these patterns more broadly, noting two major findings. The first is that a robust and areal constraint against /ẽ õ/ as found in West Africa is not mirrored in other nasal vowel zones, such as South America and Mesoamerica. In the second, we note that a gap of /ẽ õ/ can be understood as phonetically natural due to oral-nasal acoustic coupling effects on F1 perception (Ohala 1975, Wright 1986, Beddor et al. 1986, Beddor 1993, Maeda 1993), referred to as the Nasal Height-Centralization Effect. We present, however, a series of arguments against a "phonetic determinism” account, and understand these patterns as the result of an interplay of acoustic and areal pressures.