Nasal retroflexes in North Boma (Bantu B82, Mai-Ndombe, DRC)

Abstract Retroflex consonants represent a major class of language sounds, but our understanding of their phonetic and phonological properties remains limited. From the standpoint of acoustics, recent contributions are largely lacking. Few fully fledged empirical descriptive studies have been made available to establish their presence and characteristics in the world’s languages. Within retroflex consonants, liquids and nasals are particularly rare, and very little descriptive, theoretical, or historical research has been conducted on them. Bantu languages from Africa are not included in most large-scale surveys. Recent fieldwork in the Mai-Ndombe Province of the Democratic Republic of Congo (DRC) in Central Africa confirms the existence of nasal retroflexes in North Boma (Bantu B82). This paper offers the first acoustic description of these rare nasal segments in any Bantu language. North Boma nasal retroflexes are shown to constitute a discrete class within the language’s nasal inventory. Compared to their non-retroflex counterparts, they are significantly shorter; they also display spectral energy concentrated in the lower frequencies around their centre of gravity, more peaked energy concentrations, higher values of F1 and F1 bandwidth, and lower values of F2 bandwidth. Furthermore, we reconstruct the historical development of nasal retroflexes in North Boma and show that they are the regular outcome of the merger of Proto-Bantu *n and *nd to /n/ in stem-medial position. We hypothesise that retroflexion might be a phonological substrate feature originating in extinct non-Bantu languages once spoken by Batwa communities living and foraging in the region or by Ubangi speech communities now only attested further north. This contribution showcases how detailed phonetic documentation and description are an asset for historical research.