Articulatory modeling of so-called advanced tongue root vowels

Many West African languages have two sets of vowels that are said to differ by one having an advanced tongue root [+ATR], and the other a retracted tongue root [−ATR]. The [+ATR] set may also have an enlarged pharynx and a lowered larynx. Words (roots) in these languages must contain vowels that are all of one set or the other. To test whether there is a constant articulatory difference between the two sets of vowels in Degema, a Delta Edoid language spoken in Nigeria, DAT recordings were made of 8 speakers. For 2 of the speakers, frontal and lateral videos were made of the lip aperture. The frequencies, amplitudes and bandwidths of the first 3 formants of the 5 pairs of vowels were determined from LPC analysis. These data were modeled using an articulatory synthesizer. After an appropriate set of vocal tract shapes had been determined for the [−ATR] set of 5 vowels, articulatory perturbations such as tongue root advancement, pharynx enlargement, and larynx lowering, were applied to the modeled [−ATR] vocal tract shapes to generate the [+ATR] set. A variety of articulatory gestures seem to be needed to convert vowels from one set into the other.