The distribution of advanced tongue root harmony and interior vowels in the Macro-Sudan Belt

<jats:p>In this paper we investigate the distribution of vowel systems in the Macro-Sudan Belt, an area of Western and Central Africa proposed in recent areal work (Güldemann 2008, 2011; Clements & Rialland 2008). We report on a survey of 615 language varieties with entries coded for two phonological features: advanced tongue root (ATR) harmony and the presence of interior vowels (i.e. non-peripheral vowels, such as [ɨ ɯ ɜ ə ʌ …]). Our results show that the presence of ATR harmony in the Macro-Sudan Belt is limited to three separated zones: an Atlantic ATR Zone, a West African ATR Zone, and an East African ATR Zone, all geographically unconnected to one another. We additionally show that between the West and East African ATR Zones is a geographically extensive, genetically heterogeneous region of Central Africa where ATR harmony is systematically absent which we term the Central African ATR-less Zone. Our results also show a large region where phonemic and allophonic interior vowels are disproportionately prevalent, which we term the Central African Interior Vowel Zone. This zone noticeably overlaps with the Central African ATR-less Zone, suggesting that ATR and interiority have an antagonistic relationship. Chi-squared tests support the presence of a strong relationship between the two types of vowel contrasts.</jats:p>