Vowel Harmony and Coarticulation in Three Dialects of Yoruba: Phonetics Determining Phonology

This dissertation examines the phonology and acoustic phonetics of vowels in three dialects of Yoruba—Standard Yorùbá, Mòbà, and Àkùré Yorùbá—to investigate the role of coarticulation in the phonologization of vowel harmony (Ohala 1994).

The phonological vowel patterns of the three dialects are presented. Àkùré Yorùbá exhibits Advanced Tongue Root (ATR) vowel harmony in mid and high vowels, while harmony in Mòbà and Standard Yorùbá does not extend to high vowels.

In order to investigate this relationship, recordings of VCV nonsense words from speakers of each dialect were analyzed. Following Hess (1992), the first formant (F1) was determined to be the acoustic measurement best correlated to the ±ATR vowel sets. Other measurements—F2, F1 bandwidth, fundamental frequency, vowel duration, and spectral measures—were not found to correlate with ATR.

Using F1 as a measure, vowel to vowel coarticulation in high vowels in Mòbà and Standard Yorùbá was found to resemble high vowel harmony in Àkùré in the target vowels, the context, and the phonetic effect. This was particularly true for /i/; however the coarticulatory effects on /u/ were weaker and not statistically significant. As expected, the effect of vowel to vowel coarticulation in Mòbà and Standard Yorùbá was smaller and less robust than for vowel harmony in Àkùré.

A decision tree model is proposed that is able to generate the high vowel harmony pattern from the Àkùré acoustic data. More interestingly, the model succeeds at extracting—to a large degree—the high vowel harmony pattern from Mòbà and Standard Yorùbá, the dialects without high vowel harmony. The model does not require any reference to features or natural classes, suggesting that it is not necessary to posit features as a prerequisite to learning a phonological pattern, nor as an explanation for universal patterns.

The study argues that the acoustic patterns found in vowel to vowel coarticulation are sufficient to result in vowel harmony. The findings are consistent with the view that proto-Yorùbá did not have harmony in its high vowels (Fresco 1970, Oyelaran 1973, and Capo 1985), and that high vowel harmony developed in Àkùré and related dialects.