Vowel spaces in two Kwa languages

The acoustic spaces of two languages with seven vowel systems were compared. The languages were Yoruba and Ewe, both of the Kwa group of Niger—Congo languages. The vowels were /ieεaɔou/. The formant spaces were based on the production of several token of each vowel by four speakers of each language. While the seven vowels of Ewe are distributed in a highly regular fashion around the vowel space, this is not found in Yoruba, where the upper mid /e/ and /o/ are very close to the high /i/ and /u/, respectively. The phonetic differences between the two languages cannot be accounted for by any current theory of the utilization of the vowel space. The results indicate that the historical development of vowel systems is not only influenced by principles of maximal perceptual distance, or “base of articulation,” but may also be related to different phonological processes in different languages.