Larynx height in Kwa

The vertical positions of the larynx in various vowels in Akan, Igbo, and Ijo were measured from radiographic data. These languages have a vowel harmony such that one set of vowels [i, e, u, o] is produced with an expanded pharynx, and another set [ι, ɛ, o, ɔ] with a constricted pharynx. The major function of vertical larynx displacement is to contribute to the variation in pharyngal size for categorizing vowels into harmonizing sets. The larger pharynx is produced as a combined effect of advancing the tongue root and lowering the larynx, and the smaller pharynx is produced by retracting the root and raising the larynx. The vertical position of the larynx is reasonably well correlated with the position of the tongue root. But within each harmony set there is no consistent relationship between larynx height and vowel height or between larynx height and backness. Sometimes phonologically high vowels have a higher larynx than nonhigh vowels, sometimes not. The only possible exception is the vowel [a]. In those languages where [a] occurs, there is a strong tendency for it to have the highest larynx position of all the vowels.